Ocean Carbon and Biogeochemistry (OCB) Summer Workshop Woods Hole Oceanographic Institution

July 25-28, 2016

POSTER ABSTRACTS Diatom community composition shifts in response to eddies in the California coastal transition zone Z. M. Abdala1, S. Einarsson1, K. Powell1, J. Fitzsimmons2, T. Coale3, C. P. Till4, P. D. Chappell1 1. Old Dominion University, zabda001@odu.edu 2. Texas A&M University 3. University of California San Diego 4. University of California Santa Cruz Diatoms are photosynthetic, unicellular, planktonic organisms that rely on nutrient availability and play a fundamental role in global ecosystems. Community structures and distributions of these important phytoplankton will fluctuate for many reasons, but in the California current upwelling regime, nutrient circulation (especially nitrate and iron) is thought to be a major determining factor in diatom abundance. Samples collected along a transect that passed through two sea surface height anomalies were analyzed for diatom community composition changes. Community composition was found to shift rapidly in response to the physical forcing manipulating nutrient availability. Communities from the offshore anomaly were found to be mostly dominated by a single Rhizosolenia species, whereas surrounding areas were comprised of a variety of different diatoms. The diatom community data is being analyzed in the context of nutrient and physical data to speculate on what factors were potentially responsible for the shifts in composition. Phytoplankton biogeography, primary productivity and nitrogen uptake in the ultra-oligotrophic Indian Ocean S. E. Baer1, S. Rauschenberg1, A. Steinberger3, A. C. Martiny2, B. S. Twining1, M. W. Lomas1

1. Bigelow Laboratory for Ocean Sciences 2. University of California, Irvine 3. Williams College Biogeochemical data from the central Indian Ocean is currently limited, but it is known that there are stark geographical gradients in the physical and chemical conditions that may lead to unique biogeochemical regimes. As participants on the IO9N GO-SHIP cruise, a transect from 28ºS to 18ºN in the Indian Ocean completed in spring of 2016, samples for nutrient uptake and phytoplankton cell counts were obtained at approximately every other degree of latitude. Stable isotopically labeled 13C-bicarbonate

was used to measure primary productivity and 15N labeled nitrate, ammonium, and urea to measure uptake of nitrogen compounds in near surface waters (~20 m). Nitrate and phosphate concentrations were below detection limits throughout the surface 50 m, while ammonium was undetectable at all stations and depths measured. Below ~50 m, nitrate and phosphate concentrations steadily increased from south to north, to a maximum of 31 and 2.2 µM respectively, with their supply ratio (N:P) always below 15. Absolute uptake rates of all N compounds were less than 1.5 nmol N L-1 h-1 south of 15°S, and steadily increased until highest observed values were reached between 1.5-6.5°N; 1.8, 5.2, and 5.1 nmol N L-1 h-1 for nitrate, ammonium, and urea respectively. In the Bay of Bengal (10-18°N), uptake rates were not variable, with a mean of 0.86, 3.2, and 3.1 nmol N L-1 h-1 for nitrate, ammonium, and urea respectively. Ammonium and urea uptake rates were consistently 3-5 times higher than concurrent nitrate uptake rates, with a mean observed f-ratio of 0.23 for the entire transect. Rates of primary production followed the same general trend of nitrogen uptake, with a maximum of 77.8 nmol C L-1 h-1. Cell counts by flow cytometry indicate that at all stations and depths, heterotrophic bacteria dominated in both numerical abundance and biomass. Prochlorococcus was the dominant phytoplankton group, but with increasing contributions of Synechococcus and small eukaryotes from south to north. This data represents the first reported direct measurements of primary production, nitrogen uptake, and phytoplankton abundance in the eastern central Indian Ocean, a large but relatively understudied region of the global ocean. Relative roles of dissolution lengthscale and uptake ratio in the global distribution of silicateR. Bernardello1, M. C. Moore2, A. P. Martin1 1. National Oceanography Centre Southampton 2. Ocean and Earth Science, University of Southampton We investigate controls on the global distribution of silicate with a coupled physical-biogeochemical model using a set of experiments designed to test the sensitivity of an idealized non-limiting nutrient (Xnu). In a fixed steady-state circulation dissolution lengthscale for Xnu and its uptake ratio by phytoplankton with respect to phosphate were varied across a wide range and over different regions. Steady state solutions for Xnu were then compared with observed climatological silicate. Both deep dissolution and high uptake ratio were able to cause the sharp meridional gradient observed for silicate at the surface of the Southern Ocean. However, only the former was able to determine the meridional gradient in concentration between the deep North Pacific and the deep Southern Ocean. Experiments with regional variations in the two parameters revealed an important role for the deep dissolution in the North Pacific, pointing to locally recycled silicate being determinant in the build-up of deep silicate. Although it's not possible to tell which of the two studied processes is the main driver in the Southern Ocean, only a deep dissolution lengthscale was able to reproduce both main characteristics of the global silicate distribution. We speculate that the high uptake ratio of silicate with respect to

other macro-nutrients observed in the Southern Ocean would then be only a consequence (rather than a driver) of the high surface silicate concentration. The local and remote influences of remineralization in setting global nutrient distributions R. Bernardello1, A. Martin1, S. Henson1, A. Yool1, S. Khatiwala2, I. Kriest3, M. Moore4, J. Blundell4, J. Dunne5, I. Allen6, I. Totterdell7. 1. National Oceanography Centre Southampton 2. University of Oxford 3. GEOMAR 4. University of Southampton 5. Geophysical Fluid Dynamic Laboratory 6. Plymouth Marine Laboratory 7. Met Office Nutrient concentrations at any depth or location are the sum of organic material that has been remineralised and unused nutrients from the surface (preformed). Even for macro-nutrients, such as phosphate, the relative roles of the biological carbon pump (BCP) and of the ocean circulation in shaping their global distribution are still unclear. The former acts mainly in the vertical dimension while the latter acts to redistribute nutrients in three dimensions. Furthermore, both components act locally and remotely. We use a three-dimensional coupled physical-biogeochemical model to investigate local and remote contributions to steady-state phosphate distribution in a biome-based framework. Remineralised phosphate produced in each biome is tagged and conserved in the interior of the ocean once outside the biome of origin. Two different representations of ocean circulation are used. We find that local remineralisation exerts a limited control on total phosphate contributing only between 2-24% below 1000m depth, depending on the model and biome considered. Even with respect to remineralised phosphate the locally produced fraction reaches only about 45% maximum. When comparing results between the two different circulations important differences are found in some biomes, highlighting the importance of considering uncertainty in circulation. We conclude that nutrient profiles provide a weak constraint on local biogeochemical processes. Carbon Hot Spot: A field program to understand bio-physical drivers of carbon sequestration in western boundary current regions S. P. Bishop1, A. J. Fassbender2, M. F. Cronin2, D. Zhang2,3, R. Inoue4, C. Osburn1, E. Oka5, B. Qiu6, X. Lin7 1. North Carolina State University, spbishop@ncsu.edu 2. NOAA/Pacific Marine Environmental Laboratory 3. Joint Institute for the Study of the Atmosphere and Ocean 4. Japan Agency for Marine Earth Science and Technology 5. University of Tokyo 6. University of Hawaii at Manoa

7. Ocean University of China Western Boundary Currents (WBC) are dynamic ocean regions characterized by large air-sea exchanges of heat, moisture, and carbon, and exhibit the highest eddy kinetic energy in the global ocean. As centers of subtropical mode water (STMW) formation, these strong carbon sink zones are thought to account for a majority of anthropogenic carbon sequestered by the ocean outside of the polar deep-water-formation regions, making WBCs hotspots for studying the carbon cycle. Many questions remain about the specific processes driving formation and long-term evolution of STMW in the presence of meso- and submesoscale eddies. Coupled climate models that include biogeochemical (BGC) properties are in their infancy and still rely on parameterizations for mesoscale eddies. In order to adequately make and understand future climate projections, it is pivotal to improve our dynamical understanding of these ocean processes, as well as the accompanying bio-physical interactions that influence marine carbon cycling. The objective of Carbon Hot Spot is to develop an interdisciplinary and international research community that will facilitate better understanding and awareness of the role that WBCs play in climate and anthropogenic carbon sequestration. We hope to achieve this by planning and conducting a field program in the Kuroshio Extension region. In order to foster new collaborations and realize scientific breakthroughs in the realm of WBCs, we encourage community participation and feedback to ensure that Carbon Hot Spot reflects the goals of the broader oceanographic community. Currently, our Scientific Committee on Oceanic Research (SCOR) Working Group proposal is under open review (http://www.scor-int.org/) and we have been encouraged by US CLIVAR to pursue funding for a Bio-Physical Interactions workshop to gain community feedback and support. Finally, we have been invited to apply for shiptime to conduct a pilot study with Japanese collaborators in winter/spring of 2018. This study will incorporate autonomous vehicles to measure physical and BGC properties of the upper kilometer of the ocean in the vicinity of the Kuroshio Extension Observatory (KEO). The goals of this study are to observe air-sea fluxes of CO2 while resolving submesoscale eddies in both space and time in order to close dynamical budgets of heat and BGC tracers during the winter/spring transition when STMW formation peaks. KEO is in the optimal location for this study as meteorological observations as well as temperature and salinity measurements throughout the surface mixed layer have been made since 2004. Additionally, observations of pCO2 in the surface ocean and atmosphere have been made since 2007, with surface ocean pH measurements added to the observing effort in 2011. Findings from this pilot study will inform future planning for an international process study near KEO. Autonomous image processing on the Carbon Flux Explorer H. Bourne1, J. Bishop1,2, I. Walker1, T. Wood2, L. Claxton1

1. University of California Berkeley, hbourne@berkeley.edu 2. Lawrence Berkeley National Laboratory

The Carbon Flux Explorer (CFE) is an autonomous, lagrangian float that images particles in three lighting modes at different depths in the water column in order to study the rate and attenuation of particle sedimentation.1 The CFE is an autonomous instrument capable of spending months at sea collecting and transmitting data. When the CFE surfaces, about once a day, it sends back data over the Iridium Satellite network. Because each image is about 10Mb, transmitting entire images back to shore is prohibitively slow and costly. Currently, image analysis is done after retrieving the instrument. Data is then processed using both Fortran software and the program ImageJ (Bishop et al., 2016).

The goal of this study is to write software capable of being executed on microcontrollers in order to remotely calculate data to quantify amount of particles, particle attenuation of light, and particle size distribution, on board the CFE. This work is necessary, as it will allow us to collect valuable information on particle sedimentation in real time. As we are not able to transmit the entire image, if we were not able to retrieve a float, this data would otherwise be lost.

Images taken under cross-polarized light illuminate particles containing calcium carbonate such as coccolith plates and foraminifera. We have worked on quantifying calcium carbonate particles in these images by manually counting forams present in each image, and then comparing that method to calculating foram numbers using Matlab and ImageJ. Our next step is to develop the polarized image analysis methods to be run on the CFE board. The software will be tested at sea this upcoming August off the coast of California. Redefining ocean biomes and identifying microbial dark matter with the Tara Oceans dataset J. Bowman1, H. Ducklow1 1. Lamont Doherty Earth Observatory, bowmanjs@ldeo.columbia.edu In the marine environment, bacterial communities are structured by a variety of physical and biogeochemical factors, including turbulence and carbon and nutrient availability. In turn, bacterial community structure has a direct impact on the ecosystem functions performed by the community, including bacterial production and nutrient remineralization. To facilitate the incorporation of community structure data in biogeochemical models we’ve developed a technique to establish “modes” of community structure with emergent self-organizing maps (ESOMs). Using a multi-year time series of 16S rRNA amplicon data, flow cytometry, and biogeochemical data from a long term study site off the West Antarctic Peninsula we’ve observed that bacterial production, a key indicator of biomass flow in the marine ecosystem, is best described by a linear model combining flow cytometry observations and community mode. Here we use 16S rRNA gene fragments recovered from the Tara global ocean expedition dataset to identify bacterial modes, equivalent to biomes, for the global ocean. For biogeochemical context we compare these biomes to data available from WOCE and JGOFS. To identify

microbial “dark matter” captured in the Tara dataset we compared the results of a metabolic inference conducted with paprica to direct observations of metabolic pathways. Poor correlations between the metabolic inference and direct observations indicate samples with poor genomic representation among the completed genomes in Genbank.

Air-sea oxygen and carbon dioxide fluxes from profiling floats in the Southern Ocean: Seasonal and spatial patterns and flux ratios

S. Bushinsky, J. Sarmiento

Princeton University

The Southern Ocean is a region of strong carbon dioxide exchange with the atmosphere, with outgassing of CO2 from deep upwelled waters and drawdown of atmospheric CO2 through the solubility and biological pumps. Harsh conditions and seasonal sea ice have historically limited observations during the winter. The recent advent of biogeochemical Argo floats has begun to provide a wealth of novel data on the Southern Ocean biogeochemical cycles. The Southern Ocean Carbon and Climate Observations and Modeling program is deploying Argo floats equipped with oxygen, nitrate, and pH sensors and a recent reanalysis by the University of Washington of older Argo oxygen data now yield an opportunity to better understand the biological and physical components of the carbon and oxygen cycles in this region. In combination with alkalinity estimates derived from a multiple linear regression to ship-board data, these pH data can be used to calculate pCO2 to ± 10 µatm. Preliminary analyses illustrate significant deviations from climatologies due to newly available wintertime data. Carbon dioxide to oxygen air-sea flux ratios indicate a positive CO2:O2 relationship north of the Subtropical Front, indicating a region dominated by seasonal solubility-driven fluxes. Conversely, in the region south of the Polar Front biological production and respiration or the upwelling of water low in oxygen and high in CO2 combine to form a negative CO2:O2 relationship. These data provide a new look at the Southern Ocean carbon cycle and point the way toward determination of the physical and biological components driving air-sea exchange.

Alkalinity and inorganic carbon export from intertidal salt marshes S. N. Chu1, Z. A. Wang1, K. D. Kroeger2, M. E. Gonneea2, N. K. Ganju2

1. Woods Hole Oceanographic Institution 2. US Geological Survey Intertidal salt marshes are highly productive coastal ecosystems that export carbon and other biogeochemical species to the coastal ocean. Recent carbon budgets for the coastal ocean suggest organic carbon, nutrient, dissolved inorganic carbon (DIC) and total alkalinity (TA) exports may be important fluxes. However, despite their importance, published literature on salt marshes contains few studies with sufficient spatial and

temporal resolution to accurately quantify these fluxes. In particular, marsh TA export flux and its effects on carbonate chemistry and carbon cycling of adjacent coastal systems is unknown. Alkalinity is produced in salt marsh sediments due to anaerobic respiration processes such as denitrification and sulfate reduction. In this study, a combination of high-resolution, in situ measurements, and bottle sampling is used to quantify high-resolution total alkalinity flux. We confirmed that during ebb tides the exported water has high concentrations of DIC and low pH due to input from sediment porewaters. However, while DIC export occurs throughout the year, most of the alkalinity export occurs in the summer, concurrent with higher rates of marsh productivity and anaerobic respiration in marsh sediments. An accurate estimate of TA export fluxes allows for a better assessment of salt marshes as sources of buffering capacity to coastal oceans. Export of high TA and low pH water from salt marshes can act simultaneously as buffering and acidifying sources to the coastal ocean and our time series data show how this delicate balance changes tidally and seasonally. These results will help reduce uncertainty in current estimates of marsh DIC and TA export and establish a baseline export flux in order to evaluate the importance of intertidal salt marshes in coastal carbon cycling. This is particularly timely as marshes continue to be destroyed by anthropogenic perturbations such as land development and nutrient enrichment. Mass conservative modeling of dissolved organic matter photochemistry and biogeochemical cycling J. B. Clark1*, W. Long2, R. R. Hood1

1. University of Maryland Center for Environmental Science, 2020 Horns Point Rd, Cambridge, MD 21613 2. Pacific Northwest National Laboratory, 1100 Dexter Ave. North, Suite 400, Seattle, WA 98109 *bclark@umces.edu The absorption of light energy alters the chemical and biological properties of chromophoric dissolved organic matter (CDOM) in estuarine and coastal waters. Non-linear interactions hypothesized to be driven by the simultaneous photochemical production and destruction of compounds are difficult to empirically quantify. Simplifying the system, however, into a numerical model that mechanistically represents photochemical interactions allows the study of CDOM photochemistry in an idealized framework. A new mechanistic model is proposed to simulate photochemical processes, optical characteristics and DOM cycling in the coastal ocean. Numerical experiments that replicate empirical photodegradation incubations offer model validation and insight into CDOM and DOM cycling in experimental and field studies. Submesoscale fronts structure phytoplankton communities and modulate net community production S. Clayton1, 2, H. Palevsky1, F. Ribalet1, J. Swalwell1, M. Lévy3, E. V. Armbrust1 1. School of Oceanography, University of Washington, Seattle, WA 98105, USA

2. eScience Institute, University of Washington, Seattle, WA 98105, USA 3. Sorbonne Université (UPMC, Paris 6)/CNRS/IRD/MNHN, Laboratoire d’Océanographie et du Climat (LOCEAN), Institut Pierre Simon Laplace (IPSL), 75252 Paris Cedex 05, France To date, the net effect of ocean fronts on phytoplankton community structure and biodiversity has been difficult to determine due to a paucity of data collected at appropriate spatial scales and taxonomic resolution. In this study, we analyze an extensive set of continuous measurements of picophytoplankton community composition and net community production to uncover how phytoplankton assemblages and biodiversity are modulated by submesoscale fronts. Our dataset is made up of highly spatially resolved (~ 1 km) sea surface measurements of O2/Ar-based net community production (~12,000 km of cruise track), and flow cytometric counts of Prochlorococcus, Synechococcus and picoeukaryotes (~35,00km of cruise track), as well as temperature, salinity and chlorophyll a fluorescence, predominantly across the North Pacific, spanning all seasons. We apply a temperature gradient criterion to identify the location of fronts and compare frontal and background conditions. We find that although the community response varies from front to front, there is an overall tendency for increased export production, biodiversity (Shannon Index) and biomass of picophytoplankton at fronts, compared to background conditions. The response of different functional groups at fronts, however, varies. Prochlorococcus abundance is consistently suppressed at fronts, whereas the abundance of Synechococcus and picoeukaryotes is generally enhanced, with some regional variations. We hypothesize that these differential responses are likely due to a combination of populations being mixed, and enhanced nutrient fluxes at fronts driving competition, with Synechococcus and picoeukaryotes outcompeting Prochlorococcus in more nutrient-rich environments. COMPASS science communication Our vision is to see more scientists engage, and engage effectively, in the public discourse about the environment. Through communication trainings, coaching and real-world connections, we empower researchers to build the communication skills, networks, and relationships they need to realize this vision. We are a non-profit, non-advocacy organization. Sediment deposition patterns on the Chukchi Shelf using radionuclide inventories

L. W. Cooper1, J. M. Grebmeier1

1. Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science

Forty sediment cores collected on the Chukchi shelf and adjacent portions of the East Siberian Sea have been assayed for the sedimentation tracers 137Cs and 210Pb. Radiocesium deposition patterns indicate that cores can be separated into two broad categories, first, cores where sedimentation influence exceeds bioturbation, and second,

those where bioturbation is the dominant redistribution process. The first category generally includes cores collected in high current areas such as Herald Canyon, and comparatively low sedimentation areas such as Hanna Shoal, as well as some portions of the northeast Chukchi shelf. In other portions of the northeast Chukchi shelf and in productive benthic “hotspots,” the influence of bioturbation exceeds sedimentation, and radiocesium is more evenly distributed within the sediments. Sedimentation rates were also calculated for 14 of the 40 cores where there was a consistent decline in excess sedimentary 210Pb with depth in the core, but sedimentation rate estimates were only consistent with estimated 137Cs sedimentation rates in 5 of the 14 cores. These data show the complexities of considering sedimentation rate estimates for productive continental shelves in comparison with cores collected at deeper depths, such as one collected from 400 m in the Bering Sea. Despite these limitations on continental shelves, distribution patterns of these radionuclides, particularly the depth where 137Cs reaches maximum activity and the activity of 137Cs at that depth provide new insights on the interplay between sedimentation and bioturbation in influencing the broader distribution of contaminants within continental shelf sediments. Development of an Agent-Based model for active organic carbon flux by vertically migrating zooplankton C. Countryman1, A. Burd1 1University of Georgia, chandler.countryman25@uga.edu The vertical flux of organic carbon in the oceans is driven by both abiotic and biotic processes. Diel vertical migration (DVM) of zooplankton is one such biotic process, where typically zooplankton feed in surface waters at night and descend to depth during the day. Vertical migrators ingest particles at the surface and metabolize it at depth, or consume particles throughout their travel, resulting in an organic carbon flux that is as much as 50% of the passive, gravitationally settling flux. Variability in zooplankton community structure and behavior can lead to spatial and temporal variability in organic carbon flux, attenuation, and sequestration. The goal of this project is to develop an agent-based model of zooplankton community structure and behavior, and use it to examine the effects of particulate organic carbon (POC) flux in the upper 500 m of the ocean. The advantage of the agent-based approach is that it allows us to explicitly examine the effects of different zooplankton community composition and animal behavior on POC flux and attenuation. Here we outline the development of the model and show preliminary results using a small number of zooplankton and behaviors. Identifying mechanisms of the biological pump through high resolution observations of surface ocean properties and sinking particles C. A. Durkin1, M. Omand2, M. Estapa3

1. Moss Landing Marine Laboratories, cdurkin@mlml.calstate.edu

2. University of Rhode Island 3. Skidmore College Recent studies have demonstrated that significant variability in export production occurs over short time- and space-scales, but the mechanisms underlying this variability remain under-observed. This variability likely derives from ecological and physical processes, down to the scale of individual particles. To resolve particle export processes at these scales, a suite of observational platforms were deployed in close vicinity, in the upper mesopelagic at the New England continental shelf break in November 2015 and June 2016. A drifting WireWalker (WW) continuously profiled the upper 100 m of the water column, measuring physical and optical properties. A sediment trap tethered beneath the base of the wire captured sinking particles from the overlying water column. In parallel, a Neutrally-Buoyant Sediment Trap (NBST) was deployed in the upper mesopelagic with attached particle collection tubes, and a vertically mounted transmissometer to continuously measure sinking particles at high temporal resolution via an optical proxy (optical sediment trap, OST). Additionally, a surface tethered sediment trap (STST) with collection tubes at 5 increasing depths was deployed to monitor the attenuation of particle flux with depth. All sediment trap platforms included collection tubes containing a polyacrylamide gel layer, enabling microscopy-based quantification of sinking particle size distributions and particle identities. Though analysis of the small-scale processes are ongoing, preliminary data is presented here which describes the substantial difference between the fall and spring observations. These preliminary data implicate a mechanistic difference between export due to diatom-influenced/aggregation versus coccolithophore-influenced/fecal pellet export pathways. A preliminary view of a metatranscriptomic time-series from sinking particles collected from 4000 m at Station ALOHA B. R. Edwards1,2, A. Romano1,2, J. M. Eppley1,2,3, J. Cardwell1,2, F. O. Aylward1,2, E. F. DeLong1,2,3

1. Daniel K. Inouye Center for Microbial Oceanography: Research and Education, University of Hawaii, Honolulu, HI, USA 2. Department of Oceanography, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI, USA 3. Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA Sediment traps that autonomously capture and preserved organic material with bi-weekly sampling resolution were deployed at Station ALOHA from March 15th to November 27th 2014. RNA and DNA were extracted from the trap material and a split was set aside for future lipidomic analysis. Here we present preliminary results from the RNA that was sequenced from this time-series, representing the first metatranscriptomic analysis of sinking particles from the deep ocean. Analysis of the rRNA transcripts revealed near equal contribution of eukaryotes and bacteria to the particulate biomass across the time-series. Eukaryotic rRNA reads were positively correlated with estimates of carbon flux which is consistent with a eukaryotic source of exported carbon. Analysis of the protein

encoding transcripts showed that bacteria were more metabolically active than eukaryotes. The most abundant bacterial taxa on sinking particles were generally the most transcriptionally active. Arcobacteria sp., Colwellia sp., Moritella sp., and Shewanella sp. were 49, 16, 9, and 6 % of the SSU rRNA reads and accounted for 25, 9, 6, and 4 % of the protein encoding transcripts. These taxa are generally psychrophilic suggesting community succession and re-colonization of sinking particles as they were transported from the surface ocean to depth. Further exploration of the metatranscriptome will be geared towards addressing what types of compounds were being accessed, which metabolic pathways were being utilized, and how this bears on ocean biogeochemistry. Diatom community composition along Oregon Coast upwelling in relation to environmental variables S. Einarsson (seina001@odu.edu)1, Z. Abdala1, K. Powell1, B. Twining2, C. P. Till3, T. Coale4, P. D. Chappell1 1. Ocean, Earth and Atmospheric Sciences Department, Old Dominion University, Norfolk, VA, USA 2. Bigelow Laboratory for Ocean Sciences, East Boothbay, Maine, USA 3. University of Santa Cruz, Santa Cruz, California, USA 4. Scripps Institution of Oceanography, San Diego, California, USA Diatoms are unicellular phytoplankton known for an ability to respond quickly to nutrient pulses, allowing them to bloom in upwelling environments. Different diatom species are more readily found in areas of low nutrients as opposed to areas of upwelling, depending on both their nutrient requirements for growth and their ability to access different nutrient sources. In this study, sampling was done along a transect following a plume of upwelling waters off the coast of Oregon to examine diatom community composition shifts in response to changing nutrient regimes. Bray Curtis dissimilarity analysis of diatom community composition showed that stations outside of the upwelling plume were related to each other but distantly related to stations located within the plume, while stations along the edge of upwelling areas were found to be closely related. The majority of the diatom community consisted of species from the genera Thalassiosira and Pseudo-nitzschia, with Thalassiosira species higher in areas of no upwelling and Pseudo-nitzschia species higher in areas of upwelling. Bio-Env analysis comparing the distance matrix from the Bray Curtis dissimilarity and environmental variables showed particulate aluminum, iron, and scandium, and copper, silicate and phosphate all having a strong influence on community composition. With sea surface temperature, salinity, copper, particulate aluminum and scandium together explaining 72.75 percent of the dissimilarity. An advective mechanism for Deep Chlorophyll Maxima formation in southern Drake Passage Z. K Erickson1, A. F. Thompson1, N. Cassar2, J. Sprintall3, M. R. Mazloff3

1. California Institute of Technology, Environmental Science and Engineering, zerickso@caltech.edu 2. Duke University, Division of Earth and Ocean Sciences 3. Scripps Institution of Oceanography A Deep Chlorophyll Maximum (DCM) layer was observed off-shelf of the Western Antarctic Peninsula in southern Drake Passage during a Seaglider deployment in austral summer 2014-15. The feature is present in fluorescence and backscatter, indicating a probable biomass maximum at depth. The DCM lies beneath the euphotic depth and the pycnocline, suggesting that neither in situ growth nor phytoplankton buoyancy regulation is primarily responsible for its formation. It is connected along isopycnals to an on-shelf surface bloom, and we consider the case for its formation through a three-dimensional subduction/advection mechanism of high chlorophyll or, alternatively, high micronutrient water sourced from the on-shelf bloom. Scaling results and model output from the Southern Ocean State Estimate (SOSE) confirm two pathways for the subduction and advection of water masses from on-shelf waters through the mean and eddy components of the residual circulation. This mechanism represents a biological term not observed by surface satellite measurements, which may contribute significantly to the strength of the biological pump in this region. Characterizing the mechanisms underlying Southern Ocean diatom community composition shifts L. Z. Filliger1, T. O. Delmont2, A.-C. Alderkamp3, A. Post1,2, B. D. Jenkins1

1. University of Rhode Island, Kingston, RI, USA (lzfilliger@my.uri.edu) 2. Marine Biology Laboratory, Woods Hole, MA, USA 3. Stanford University, Stanford, CA, USA Diatoms play an important role in Southern Ocean (SO) primary production and biogeochemical cycling. We characterized in situ diatom community composition across varying regions of the SO, including a latitudinal transect from Rothera Station to the Ross Sea (RothR), within the Ross Sea Polynya (RSP), and in a bloom observed in the Antarctic Circumpolar Current (ACC). This was accomplished via high-throughput sequencing of the variable V4 region of the 18S rDNA amplified with diatom-targeted primers. Either Pseudo-nitzschia spp. or Fragilariopsis spp. dominated most sampled areas, although community shifts were apparent. A shift from Thalassiosira sp. to Fragilariopsis sp. was detected in the RothR transect. The abundance of Fragilariopsis sp. declined in the RSP, where sequences from Pseudo-nitzschia sp. were the most prevalent and chlorophyll a concentrations were high compared to the RothR transect and the ACC bloom. In the ACC bloom, the diatom community was dominated by two Fragilariopsis spp., while the larger community was composed mainly of haptophytes. We are currently determining how the diatom distributions in these three SO regions correlate with various physicochemical parameters. To develop ecologically relevant laboratory models, we established a culture collection of >300 isolates from two austral summer and winter cruises conducted in 2013-2014. By comparing isolate and community amplicon data, we have determined our culture collection contains representatives of the major taxa identified with molecular barcoding. This will allows us

to conduct physiology experiments with relevant and recent culture representatives. With these representatives, we can begin to probe the physiological status of diatoms important in different regions of the SO.

Developing a field-deployable membrane inlet mass spectrometer for discrete samples of noble gases

E. Friedberg1, H. Pleskow1, Y. Oyenuga1, E. Van Scoy1, R. Stanley1

Wellesley College, Wellesley, USA, corresponding author: rachel.stanley@wellesley.edu

Noble gases are biologically and chemically inert, making them excellent tracers for physical processes. There are 5 stable noble gases: He, Ne, Ar, Kr, and Xe, with a range of physicochemical properties; the diffusivities of the noble gases in seawater differ by approximately a factor of 5 and the solubilities of the noble gases in seawater differ by approximately a factor of 10. This broad range in physicochemical characteristics leads to differing response to physical forcing. Thus, measurements of multiple noble gases made concurrently allow quantification of many physical processes. In seawater studies, noble gas measurements have been used to investigate air-sea gas exchange, allowing explicit separation of the bubble component from the diffusive gas exchange component, to study equilibration during deep water formation and to quantify basal melting of glaciers. Additionally, noble gases can be combined with biologically active gases, such as O2 or N2, in order to quantify rates of biological production and denitrification.

A recently developed mass spectrometer, the Gas Equilibrator Mass Spectrometer (GEMS) can measure noble gases continuously – such as from underway water in a ship, pumped in from a coastal location, or in a wind-wave tank – yielding large amounts of high-quality noble gas data. We are currently modifying the GEMS to be able to measure noble gases in discrete samples (<100 mL seawater per sample). This would be useful in environments where water flow is limited and/or where the mass spectrometer can be brought to a field-based lab but not into the field itself. The system relies on a membrane inlet, similar to that used in N2/Ar studies. Here we describe initial tests and modifications of the system.

Assessment of the impacts of ocean acidification on phytoplankton functional types from the Amazon River Plume using bio-optical data J. Goes1, H. R. Gomes1, K. McKee1, T. Galina1, T. Chen1, P. Yager2

1. Lamont Doherty Earth Observatory, Columbia University, Palisades, New York, USA, jig@ldeo.columbia.edu 2. Department of Marine Sciences, University of Georgia

As human activities continue to raise the levels of atmospheric and oceanic CO2, we require a clearer understanding of the responses of plankton to these increases and better

ways to detect the global impacts of anthropogenic change on marine ecosystems. The Amazon River plume which contains the surface ocean's largest environmental gradient of pCO2 (~100 ppm and ~1300 µmol C kg-1), provides the perfect natural laboratory for making critical progress on these challenges. Our recent ship-based bio-optical measurements along the plume’s gradient of salinity, CDOM, nutrients and pCO2, together with on-deck and laboratory - CO2 manipulation experiments, suggest that phytoplankton community structure and metabolic activity may be in large part controlled by DIC concentrations and to a lesser degree by dissolved inorganic phosphate and nitrate availability. These observations allow us to postulate that 1) coastal-estuarine phytoplankton, which are typically exposed to a wider range of pH than their truly oceanic counterparts, are as susceptible to ocean acidification as their oceanic counterparts and 2) changes in the carbonic acid system will fundamentally alter the community structure and function of tropical marine primary producers. We also discuss our findings in the context of their potential application to ocean acidification studies using satellite data. An assessment of environmental drivers responsible for the emergence of mixotrophy in the Arabian Sea H. R. Gomes1, J. I. Goes1, K. McKee1, A. Al-Azri2, K. Al-Hashmi3 1. Lamont Doherty Earth Observatory, Columbia University, Palisades, New York, USA jig@ldeo.columbia.edu

2. Ministry of Foreign Affairs, Muscat, Sultanate of Oman, 100

3. College of Agriculture and Marine Sciences, Sultan Qaboos University, Muscat, Sultanate of Oman, 123

In the last decade and a half, the northern Arabian Sea (AS) has witnessed a radical shift in the composition of winter phytoplankton blooms. Diatoms typical of the winter monsoon and favored by nutrient-enriched waters from convective mixing have been replaced by thick and widespread blooms of the large, green dinoflagellate Noctiluca scintillans (Noctiluca). Unlike the exclusively heterotrophic red Noctiluca from temperate waters, the green species of Noctiluca from the Arabian Sea is a mixotroph. It harbors hundreds of green, free-swimming cells of the symbiont Pedinomonas noctilucae in the central vacuole of its cytoplasm, and can sustain itself either through carbon fixation by its endosymbionts or via ingestion of exogenous prey. Data collected by us aboard Indian research vessels in the Arabian Sea suggest that the recent outbreaks of blooms of green Noctiluca are caused by the spread of hypoxic waters into the euphotic zone and possibly exacerbated by warming and enhanced stratification of the water column as well as greater nutrient inputs via aerosols and land runoff. Noctiluca is not a preferred food for micro- and mesozooplankton. It uses inorganic nutrients and grazes on other phytoplankton. Thus, it competes with both its prey and predators for resources, posing special challenges for ecosystem modeling studies. The emergence of this mixotroph as a major plankton player in the ecosystem will require a revision of our earlier understanding of the Arabian Sea food web dynamics and allied biogeochemistry gained from the Joint Global Flux Studies (JGOFS) expeditions of the 1990s.

Seasonal trends of the inorganic carbon system in the Gulf of Cádiz (eastern North Atlantic) R. Guerra1,2, M. G. Zuzolo2, T. O. Diaz3, J. Forja3

1. Department of Physics and Astronomy, Alma Mater Studiorum – Università di Bologna, Italy (roberta.guerra@unibo.it) 2. CIRSA, Alma Mater Studiorum – Università di Bologna, Ravenna Campus, Italy 3. Dpto. Química-Física, CACYTMAR, Universidad de Cádiz, Spain The Gulf of Gulf of Cádiz (GoC) plays an important role in the carbon cycle of the eastern North Atlantic and the Mediterranean Sea. A wide and shallow shelf, river discharges, the formation of the Atlantic inflow into the Mediterranean Sea, and the transition of the Mediterranean outflow to the North Atlantic through the Gilbraltar Strait make this region of unique interest to study the carbon cycle at small spatial and temporal resolution scale. To this end, a year-long study of the marine inorganic carbon system (pH, TA, DIC, and ΩA) has been conducted in shelf waters of the GoC in 2015. Three water masses were clearly identified according to their different thermohaline properties: the Atlantic Surface Water (SAW), the Eastern North Atlantic Central Water (ENACW) and the Mediterranean Outflow Water (MOW). The analysis of the spatial distribution of the carbon system parameters in the area covered by the GoC reflected the presence of different water masses that were characterized by distinct biogeochemical properties. The SAW and ENACW displayed TA and DIC values of >2350 µmol kg-1 and >2200 µmol kg-1, respectively, and reflected the dominating influence of riverine alkalinity inputs within the GoC. This distinctive signal can be attributed to the high concentrations of bicarbonate ion delivered by the region’s major river (Guadalquivir River). As expected, the highest TA and DIC values (> 2400 µmol kg-1 and > 2300 µmol kg-1, respectively) were found in the MOW. Data attained in the Strait of Gibraltar and the GoC by previous studies have indicated that a net export of total inorganic carbon occurs from the Mediterranean to the Atlantic Ocean. The data collected during our study showed seasonal changes of the carbon system parameters in the euphotic zone of the GoC (~ 0-50 m depth). The main DIC drawdown concomitant with a rise in pH and ΩA occurred during fall months in the GoC. High rate of inorganic carbon consumption by photosynthesis could have led to the depletion of DIC in the euphotic zone, whereas high remineralization rate could have contributed to a DIC increase detected below the euphotic zone during spring-summer months. All sampled surface and subsurface waters within the GoC were always supersaturated with respect to aragonite (saturation state ΩA > 1), ranging between 1.4 and 4.8. Our 1-year time-series showed that a large part of the seasonal carbonate chemistry variation was mainly controlled by the seasonal change, riverine inputs, and biological activity (primary production-respiration) also exerted a significant influence within the GoC. Further research is needed to understand the role of net primary production (NPP) in the carbon cycle of the GoC by combining ocean ecological, biogeochemical, physical and optical processes.

Diapycnal mixing inhibits ocean carbon storage A. Gunn1,2,3, M. Nikurashin2,3 1. Now at Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia USA. Email: andle@sas.upenn.edu. 2. Institute for Marine and Antarctic Studies, University of Tasmania, Hobart Australia. 3. ARC Centre of Excellence for Climate Systems Science, Australia. The ocean stores about 60 times more carbon than the atmosphere. Since they are free to exchange CO2, a greenhouse gas, this implies a small change in ocean carbon can have a large impact on climate. The Meridional Overturning Circulation (MOC) influences the partition of carbon between these stores, and is driven by phenomena including diapycnal mixing and Southern Hemisphere Westerlies.

Recently Schmittner et al (2015) modeled over a 70% global decrease in diapyncal mixing from the Last Glacial Maximum (LGM) to present day (PD). Many have studied how changing SHW can alter ocean carbon, but the influence of diapycnal mixing is relatively understudied.

Motivated by this predicted paleoclimate transience in mixing, here we create a novel analytical theory tying diapyncal mixing and ocean carbon together by the MOC’s regulatory role over biogeochemical action. The theory parameterizes biological uptake and remineralization of phosphate and carbon, whilst allowing exchange of CO2 between the ocean and atmosphere. The interplay of timescales of biology, gas exchange and residence time allow a steady-state solution which gives ocean carbon as a function of diapyncal mixing.

To test the validity of the theory, we employ the MITgcm. The ocean-only 2.8-degree model includes a biogeochemical package with 6 active tracers, and is forced with an annual preindustrial climatology. Experiments with different values of prescribed diapycnal mixing are run to equilibrium and DIC is diagnosed.

Both the model and theory predict with good agreement that stronger diapycnal mixing results in a smaller ocean carbon store. Stronger mixing drives quicker convection in the MOC, reducing residence time in the surface ocean. Nutrients are less available for uptake, and outgassing is reduced since oversaturated waters from depth are less available for air-sea exchange.

The change in the ocean carbon store is significant, with an implied decrease in atmospheric CO2 of 40ppmv from the LGM to PD, in opposition to the net real change. This study highlights the importance of diapyncal mixing as a driver of climate.

Biochemistry and group selectivity of nitrate and urea enrichment on coastal phytoplankton assemblages, a community approach D. P. Harrison Sydney Institute of Marine Science, Chowder Bay, Mosman NSW Australia Marine Studies Institute, University of Sydney, Australia Humankind has fundamentally altered the global nitrogen cycle, such that today as much nitrogen is fixed from the atmosphere anthropogenically, as is fixed naturally by terrestrial and aquatic systems. 70% of this alteration is in the form of nitrogenous fertilizers, and Haber-Bosh production of urea now accounts for ~30% of total global nitrogen fixation (anthropogenic and natural).

Cultural eutrophication has long been implicated in an apparent increase in the number and severity of harmful algal blooms (HAB). More recently the form of introduced nitrogen has been receiving attention, with urea in particular singled out as a potential causative agent, yet this deduction seems to largely rely on observed correlations rather than establishment of a direct link. An alternative hypothesis is that environmental factors rather than the specific form of nitrogen exert a controlling influence on the nature of phytoplankton response to nutrient enrichment.

Here I present the results of a series of eight repeated experiments conducted over an annual cycle in 2013-2014 using oligotrophic coastal phytoplankton assemblages to asses the effect of urea and nitrate enrichment on size distribution, speciation, and biochemistry. Experiments were conducted at one location offshore Sydney, Australia but had very different oceanographic starting conditions. The result of enrichment (+8 µM N & +0.5 µM P) using both nitrate and urea, was a greater abundance of diatoms than dinoflagellates in all cases. Overall species composition was not significantly different (p, 0.05) for nitrate and urea, as revealed by multidimensional scaling and permutational ANOVA. However in some cases, contrary to previously published speculation, nitrate rather than urea resulted in increased abundance of dinoflagellates. A generalized mixed modeling approach identified aspects of the water column, which appear to be associated with the influence of the East Australian Current as influential in the outcome. At the time of peak biomass DIN/DIP depleted cultures exhibited extreme carbon overconsumption, coincident with around 50% of the added nitrogen present in the DON pool, with potential implications for the understanding of carbon export resulting from boom-to-bust type phytoplankton bloom dynamics. These results imply that caution should be applied when extrapolating observed correlations and laboratory measurements of individual cultured species to predict the reaction of planktonic community assemblages to nutrient enrichment. Given that urea production is expected to double again by 2050 understanding its influence in diverse marine environments is particularly critical.

Interannual variability in global suspended particulate inorganic carbon (PIC) inventory using space-based measurements J. Hopkins1, S. A. Henson2, A. J. Poulton2, W. M. Balch1

1. Bigelow Laboratory for Ocean Sciences, East Boothbay, Maine, USA (jhopkins@bigelow.org) 2. National Oceanography Centre, Southampton, UK Coccolithophores, the single celled phytoplankton that produce an outer covering of calcium carbonate coccoliths, are considered to be the greatest contributors to the global oceanic particulate inorganic carbon (PIC) pool. The reflective coccoliths scatter light back out from the ocean surface, enabling PIC concentration to be quantitatively estimated from ocean color satellites. Here we use datasets of AQUA MODIS PIC concentration from 2003-2014 (using the recently-revised PIC algorithm), as well as statistics on coccolithophore vertical distribution derived from cruises throughout the world ocean, to estimate the average global, depth integrated PIC standing stock and its associated inter-annual variability. In addition, we divide the global ocean into Longhurst biogeochemical provinces and identify those regions that have the greatest inter-annual variability and thus those that may exert the greatest influence on global PIC standing stock and the alkalinity pump. Using noble gases in a salt marsh pond to compare common gas exchange parameterizations and constrain efflux of oxygen by ebullition E. M. Howard1, R. H. R. Stanley1,2, I. Forbrich3

1. Woods Hole Oceanographic Institution 2. Wellesley College 3. Marine Biological Laboratory Coastal environments such as estuaries and marshes have high rates of photosynthesis and respiration, and may be both large sources and sinks of greenhouse gases such as methane and carbon dioxide. Dissolved gases such as oxygen and carbon dioxide have dynamic diel cycles of influx and efflux, and measurements of these gases are often used to calculate metabolic fluxes and study carbon cycling in these settings; determination of these fluxes in turn requires an accurate estimate of air-water gas exchange fluxes. However, gas exchange fluxes are not well constrained in shallow, coastal environments. Indeed, most existing parameterizations of these fluxes based on readily measured variables may be site-specific because they often lack fundamental mechanisms of gas transfer including bubble processes, bottom turbulence, fetch dependency, etc. In particular, most parameterization of gas exchange are derived using only the efflux of bubble-insensitive gases. The noble gases are a suite of natural abundance tracers sensitive to a range of physical processes over the same timescales as oxygen and carbon dioxide. We use a unique dataset of four noble gases in a shallow, salt marsh pond to evaluate three commonly used wind speed-based gas exchange parameterizations. We find that for the most part all three do fairly well at characterizing fluxes over hourly to

daily periods, but that during oversaturated periods leading to ebullition the parameterizations may be underestimating gas fluxes, and thus photosynthesis. Ebullition of photosynthetic oxygen could account for 20% of the net oxygen efflux during one of the periods we evaluated. New field portable equilibrator inlet mass spectrometers designed for measuring noble gases could expand the utility of this approach.

Effects of sea ice on satellite-detected primary production in the Arctic Ocean M. Kahru1, Z. Lee2, B. G. Mitchell1, C. D. Nevison3

1. Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA 2. School for the Environment, University of Massachusetts Boston, Boston, MA 02125, USA 3. University of Colorado, Boulder, Boulder, CO 80309, USA The influence of decreasing Arctic sea-ice on net primary production (NPP) in the Arctic Ocean has been considered in multiple publications but is not well constrained due to the potentially large errors in satellite algorithms. In particular, the Arctic Ocean is rich in coloured dissolved organic matter (CDOM) that interferes in the detection of chlorophyll-a concentration of the standard algorithm, which is the primary input to NPP models. We used the quasi-analytic algorithm (QAA, Lee et al. 2002) that separates absorption by phytoplankton from absorption by CDOM and detrital matter. We merged satellite data from multiple satellite sensors and created a 19-year time series (1997-2015) of NPP. During this period both the estimated annual total and the summer monthly maximum pan-Arctic NPP increased by about 47%. Positive monthly anomalies in NPP are highly correlated with positive anomalies in open water area during the summer months. Following the earlier ice retreat, the start of the high-productivity season has become earlier, e.g. at a mean rate of -3.0 day/year in northern Barents Sea, and the length of the high-productivity period has increased from 15 days in 1998 to 62 days in 2015. While in some areas the termination of the productive season has been extended, due to delayed ice formation, the termination has also become earlier in other areas, likely due to limited nutrients.

Ocean color in an IPCC-class Earth System Model: How colored detrital matter affects ocean temperature, heating and biogeochemistry

G. Kim*, A. Gnanadesikan, M.-A. Pradal

Johns Hopkins University, Department of Earth and Planetary Sciences *correspondence to gracekim@jhu.edu Recent in-situ measurements of ocean optical properties have found that colored dissolved organic matter (CDOM) contributes significantly to light attenuation in the surface ocean. However, this aquatic constituent is not included in most of the current generation of Earth System Models (ESMs). In this study, model runs were conducted

with and without light attenuation by colored detrital matter (CDM), the combined optical contribution of CDOM and non-algal particles, in the fully-coupled GFDL CM2Mc ESM. A modified parameterization for shortwave attenuation was derived from concurrent in-situ measurements of the diffuse attenuation coefficient for downwelling irradiance, chlorophyll concentration and light absorption by CDM. The global spatial distribution of CDM was prescribed using the GSM ocean color satellite data product for the light absorption coefficient for CDM at 443nm. Including CDM shoaled the attenuation depth globally, trapping heat by solar radiation near the surface and shrinking the euphotic zone. Biomass decreased by 9% and particulate organic carbon flux at 200m decreased by 7% when CDM was included. The largest relative changes in ocean biomass were found in high latitude biomes. Additionally, the standard deviation of sea surface temperatures (SSTs) increased almost everywhere in the ocean. The minimum and maximum temperatures from the control run were exceeded numerous times in the model run including CDM. In the high latitude northern hemisphere, colder SSTs were associated with a 5% increase in integrated ice mass and 6% increase in total ice extent. These studies demonstrate the global and local scale impacts of including an optically important aquatic constituent on ocean biogeochemistry and circulation in a fully-coupled ESM.

Palmer LTER: Climate-biogeochemical coupling in an Antarctic coastal ecosystem H. Kim1,2, S. C. Doney4, R. A. Iannuzzi3, M. P. Meredith5, D. G. Martinson1,3, H. W. Ducklow1,2 1. Department of Earth and Environmental Sciences, Columbia University, New York, NY 10027, USA 2. Division of Biology and Paleo Environment, Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA 3. Division of Ocean and Climate Physics, Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA 4. Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA 5. British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK The regional climate and oceanic variability along the Western Antarctic Peninsula (WAP) are affected by teleconnections of the El Niño-Southern Oscillation and the Southern Annular Mode (SAM), which in turn cause high seasonal and interannual variability of biogeochemical processes, with sea ice as a mediating physical forcing. As a long-term monitoring effort, the Palmer LTER project now spans over 20 years of observations (1991-2015) of key biological variables in the WAP to better understand how ecosystem functions interplay with climate and physical factors. With interdecadal (1993-2013) and decadal (2002-2014) analyses of dissolved inorganic nutrients (nitrate, N; phosphate, P; and silicate, Si), phytoplankton (chlorophyll, Chl; primary production; PP) and heterotrophic bacteria (bacterial production, BP; bacterial biomass, BB) at Palmer Station (64.8°S, 64.1°W), we investigated how these ecological functions and biogeochemical variables are shaped by the large-scale climate variability and associated local physical forcing. The EOF-decomposed patterns of each nutrient showed a mixed

signal of impacts of wintertime wind dynamics and different phenologies of seasonal drawdown events driven by phytoplankton and were influenced by different sets of climate and physical forcing mechanisms. N and P drawdown events (i.e. N, P EOF2) during December-March were influenced by the winter and spring SAM phases, where nutrient utilization is enhanced in a stratified water column as a consequence of SAM-driven winter sea ice and spring wind dynamics. However, the springtime Si drawdown event (i.e. Si EOF2) by diatom-dominated blooms was driven by early sea ice retreat, where ice breakup may induce abrupt water column stratification and a subsequent diatom bloom or release of diatom cells from within the sea ice. BP was equivalent to ~6% of PP, consistent with low BP:PP ratios in polar oceans and better correlated to Chl implying that bacteria in the coastal WAP feed on DOC produced from a variety of trophic levels as well as phytoplankton-derived DOC. Seasonally, bacteria were always under DOC-limitations and to a lesser extent, their carbon consumption rates were also influenced by low temperature. The generalized linear models for monthly composites of BP and BB revealed that similar to physical and climate forcing mechanisms for bloom-associated nutrient drawdown, physically, high BP and large BB were shaped by a stratified water-column as it first provides a better chance for large phytoplankton accumulations and therefore DOC. Overall, our findings of climate-biogeochemical connections may improve our understanding of how coastal Antarctic ecosystem responds not only to climate variability, but also to long-term climate change which has been accelerated along the WAP over the past decades.

Temperature and oxygen effects on remineralization of organic matter C. Laufkötter, J. G. John, C. A. Stock, J. P. Dunne NOAA/Geophysical Fluid Dynamics Laboratory, Princeton University, New Jersey An accurate representation of the remineralization of sinking particles of organic matter is crucial for reliable projections of the ocean's biogeochemical cycles, particularly that of carbon. Both water temperature and oxygen concentration are thought to influence the remineralization speed, but particularly temperature effects are difficult to explicitly observe.

We develop a new parameterization of POC flux to depth which includes a Michaelis-Menten-type oxygen dependence and an exponential temperature dependence. To test the parameterization, we use a compilation of POC flux measurements from 19 different sites, covering a wide range of temperature- and oxygen conditions. Best results are achieved with a temperature coefficient that results in a Q10 between 1.65-2.1, and an oxygen half-saturation constant between 6 and 12 umol O2/L. Using those coefficients, the average logarithmic error between the normalized POC measurements and the fit improves by 30% compared to the Martin Curve. We test the new parameterization in the ecosystem model COBALT coupled to GFDL’s ESM2M Coupled Climate–Carbon Earth System Model. Under the RCP8.5 scenario, the temperature and oxygen dependance cause an additional 10% decrease in POC flux at 2000m and a decrease in oceanic carbon uptake of 0.4 PgC/year by the end of the century.

Seasonal and interannual variability in net community production in the Southern Ocean Z. Li*, N. Cassar, M. S. Lozier

Division of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Durham, North Carolina, USA *zuchuan.li@duke.edu Photosynthesis at the ocean surface is largely controlled by the availability of light and nutrients, both of which are influenced by mixed-layer dynamics. In this study, we examine the spatial pattern of net community production (NCP) in the Southern Ocean using satellite-derived NCP estimates from 1997 to 2014, and investigate the influence of mixed-layer dynamics on the seasonal and interannual variability and long-term trend of NCP. We find high annual NCP in the Antarctic Circumpolar Current in the Atlantic sector and downstream of islands; and high summer NCP in the shelf regions. We find increasing trends in annual NCP in the Atlantic sector and southeast of Australia, decreasing trends in the Pacific and Atlantic sectors, yet no statistically-significant trend for the entire Southern Ocean. We explore factors driving these variabilities using correlation and linear regression analyses. On seasonal time scales, NCP is dominated by light availability in austral spring, with micronutrient (i.e., dissolved iron) likely becoming a dominant control in the latter part of the growing season. Though recent studies have suggested that deep winter mixing may sustain summer productivity, our preliminary analyses show no statistically-significant correlation between annual NCP and winter mixed layers derived from Argo floats. On interannual time scales, NCP is at most weakly correlated to mixed layer depth, stratification, and wind kinetic energy. At this time, it remains unclear which factors drive interannual variability and long-term trends of NCP. However, Bayesian hierarchical linear regression using these parameters and their interactions can explain about 50% of the variance of NCP interannual variability, indicating that NCP is likely controlled by multiple factors on this time scale. Modeling bubble-mediated air-sea gas exchange during a winter storm J.-H. Liang1, S. Emerson2, E. D’Asaro3, C. McNeil3, R. Harcourt3

1. Department of Oceanography and Coastal Sciences & Center for Computation and Technology,

Louisiana State University, Baton Rouge, LA (jliang@lsu.edu) 2. School of Oceanography, University of Washington, Seattle, WA 3. Applied Physics Laboratory, University of Washington, Seattle, WA Oceanic bubbles play an important role in the air-sea exchange of weakly soluble gases at moderate to high wind speeds. A Lagrangian bubble model embedded in a large eddy simulation model is developed to study bubbles and their influence on dissolved gases in the upper ocean. The transient evolution of mixed-layer dissolved oxygen and nitrogen gases at ocean station Papa (145ºW, 50ºN) during a winter storm are reproduced. Among different physical processes, gas bubbles are the most important in elevating dissolved

gas concentrations during the storm, while atmospheric pressure governs the evolution of gas saturation anomaly. For the same wind speed, bubble gas fluxes are more than twice larger during rising wind than during falling wind. Wave condition is the primary cause for the bubble gas flux difference. A new floating aquatic eddy covariance platform for determining air-sea exchange M. Long, D. Nicholson Dept. of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution The air-sea exchange of biogeochemically relevant gases is fundamental to our understanding of marine primary production and its effect on the climate. Oxygen is a commonly used tracer of primary productivity in marine environments, but gas exchange across the air-sea interface has presented significant challenges to standard aquatic methods, such as Lagrangian and Eulerian techniques, that rely on wind-derived assumptions about this air-sea exchange. To better constrain this air-sea exchange and evaluate marine primary production we developed a new aquatic eddy covariance system located on a floating platform where the sensing elements are located just below the sea surface. The system employs an acoustic Doppler velocimeter for measuring turbulent transport and a fast-response oxygen sensor to determine oxygen exchange from high-frequency, direct-covariance measurements. The newly developed, moored platform includes high-frequency measurements of the float movement to correct for accelerations due to surface waves and currents that are vital for making accurate turbulence measurements. The system has the advantages of sampling under natural in-situ conditions and integrating primary production throughout the water column and, in shallow ecosystems, the benthic surface. It is expected that this new system will have a variety of applications for both coastal and pelagic ecosystems and will provide a new tool for the analysis of biogeochemical cycling and atmosphere-sea exchange.

Net removal of dissolved organic carbon in the anoxic waters of the Black Sea A. R. Margolin1, L. J. A. Gerringa2, D. A. Hansell1, M. J. A. Rijkenberg2 1. Rosenstiel School of Marine and Atmospheric Science, University of Miami, amargolin@rsmas.miami.edu 2. NIOZ Royal Netherlands Institute for Sea Research, Department of Ocean Systems (OCS), Utrecht University Dissolved organic carbon (DOC) concentrations in the deep Black Sea are ~2.5 times higher than found in the global ocean. The two major external sources of DOC are rivers and the Sea of Marmara, a transit point for waters from the Mediterranean Sea. In addition, expansive phytoplankton blooms contribute autochthonous carbon to the Black Sea’s ~800 Tg C DOC reservoir. Here, a basin-wide zonal section of DOC is explored using data from the 2013 Dutch GEOTRACES GA04-N, cruise 64PE373. DOC distributions are interpreted with respect to well-described hydrographic and

biogeochemical layers of the Black Sea. Observed DOC concentrations were >180 µmol kg-1 at the surface, decreasing to ~125 µmol kg-1 at the base of the oxic layer and reaching a minimum of ~113 µmol kg-1 in the upper anoxic layer between ~150 and 500 m. At greater depths the concentrations increased; maximum anoxic layer concentrations of 122 µmol kg-1 were found in the homogeneous benthic bottom layer (>1775 m). Concentrations are then predicted based on conservation with respect to salinity using linear end-member mixing models, and predictions are compared with observations to estimate net removal (i.e., deficits) and accumulation (i.e., surpluses). A maximum surplus of ~10 µmol kg-1 was identified at the surface, likely due to local primary production. DOC exported to depth was non-conservative: up to ~34-41 µmol kg-1 was removed from the basin's oxic layer in <5 years, and an additional 13 ± 5 µmol kg-1 was removed from the anoxic layer during its ~300 to 600-year residence time, given steady state. These deficits represent a removal of ~19% in the oxic water and a further removal of ~10% under anoxia, for a net removal of 48 µmol kg-1 (or ~29%) of allochthonous DOC, with respect to predicted concentrations. We find no evidence for DOC accumulation (i.e., net production) in the anoxic Black Sea, and suggest that concentrations are elevated relative to the ocean due to input of terrigenous DOC from rivers; we estimate that >50% of DOC in the deep Black Sea is terrigenous. The Black Sea's relatively elevated DOC pool may be analogous to a hypothesized anoxic Eocene ocean's elevated reservoir only if the Eocene ocean received a substantial amount of terrigenous DOC.

Phenology of size-partitioned phytoplankton carbon-biomass from Ocean Color Remote Sensing and CMIP5 models” I. Marinov1, A. Cabre1, D. Shields1, T. Kostadinov2 1. Dept. of Earth and Environmental Science, University of Pennsylvania 2. Earth Research Institute, University of California Santa Barbara We use a novel satellite time series of size-partitioned phytoplankton biomass to construct and analyze classical and novel seasonality metrics. Biomass and particle size distribution are computed from SeaWiFS ocean color data using the Kostadinov’15 algorithm. The phenological metrics include the peak blooming date, bloom strength, shape of the seasonal cycle, and reproducibility of the seasonal cycle. We compare the seasonal cycle of total biomass with that of three classical size classes (pico-, nano-, and micro-phytoplankton), which are correlated with phytoplankton functional types (PFTs). The spatial distribution of phenological indices is strongly correlated with bottom-up drivers such as sea surface temperature, mixed layer depth, winds, and photosynthetic available radiation.

The biomass peak date doesn't change much across PFTs, but the blooming period is more prominent for large PFTs. Small PFTs act as a more constant biomass background, with smoother (less pronounced) seasonal cycles. We find significant differences between seasonality metrics in the SeaWiFS data and the latest generation of IPCC AR5 Earth System models (CMIP5). Models in the CMIP5 archive do not capture the

pronounced mid-latitude and frontal PFT patterns found in the satellite data. In models, phytoplankton biomass peaks later at high latitudes and earlier at low latitudes. The models exhibit a higher reproducibility of the biomass seasonal cycle and larger phenological differences between PFTs than observed. Models fail to capture secondary peaks at mid and high latitudes. Continuous improvement of satellite algorithms that retrieve phytoplankton groups is necessary to advance the modeling of phytoplankton in Earth System Models. Air-sea exchange of carbon dioxide in the Southern Ocean and Antarctic marginal ice zone

S. D. Miller*, B. J. Butterworth

Atmospheric Sciences Research Center, University at Albany, State University of New York *smiller@albany.edu The Southern Ocean is an important part of the carbon cycle, responsible for roughly half of the carbon dioxide (CO2) absorbed by the global ocean. The air-sea CO2 flux (Fc) is expressed as the product of the water-air CO2 partial pressure difference (ΔpCO2) and the gas transfer velocity (k). Global climatologies of monthly surface-ocean pCO2 concentration have been developed over the past two decades using underway systems on ships. Meanwhile, the gas transfer velocity has typically been parameterized as a function of the neutral wind speed at 10-m height above the sea surface (U10n), though the lack of CO2 flux measurements in the Southern Ocean has made it difficult to constrain the functional dependence of k on U10n and increased the uncertainty in the Southern Ocean CO2 flux and the global carbon cycle. A ruggedized closed-path eddy covariance (EC) system was deployed on the Antarctic research vessel Nathaniel B. Palmer to directly measure Fc in the Southern Ocean and Antarctic sea ice zone (SIZ). The system was designed to operate (mostly) unattended, which allowed for data collection during nine cruises over 18 months (January 2013 to June 2014). The measured Fc was combined with in situ surface water pCO2 from the Lamont-Doherty underway system (Taro Takahashi) to compute k. In open water, the data showed a quadratic relationship between k (cm hr−1) and U10n (m s-1), 𝑘 =0.245 𝑈!"!! + 1.3, in close agreement with decades old tracer-based results and much lower than previous EC studies that suggested a cubic wind speed dependence. In the SIZ, k decreased in proportion to sea ice cover, validating methods typically used to calculate Fc in the SIZ and contrasting with recent measurements and models that suggest that k is enhanced in the presence of sea ice. The results of this study are used to demonstrate the sensitivity of the Southern Ocean carbon budget to parameterization of k in open water and the SIZ.

Diagnosing oceanic nutrient deficiency

M. Moore

Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, E-mail: cmm297@noc.soton.ac.uk The (re-)supply of a range of nutrient elements to surface waters is an important driver of oceanic production and the subsequent linked cycling of the nutrients and carbon. Relative deficiencies of different nutrients with respect to biological requirements, within both surface and internal water masses, can be both a key indicator and driver of the potential for these nutrients to become limiting for the production of new organic material in the upper ocean. The availability of high quality, full depth and global scale data sets on the concentrations of a wide range of both macro- and micro- nutrients produced through the international GEOTRACES programme provides the potential for estimation of multi-element deficiencies at unprecedented scales. Resultant coherent large scale patterns in diagnosed deficiency can be linked to the interacting physical-chemical-biological processes which drive upper ocean nutrient biogeochemistry. Calculations of ranked deficiencies across multiple elements further highlights important remaining uncertainties in the stoichiometric plasticity of nutrient ratios within oceanic microbial systems and caveats with regards to linkages to upper ocean nutrient limitation.

Geochemical evidence of calcification from the Drake Passage Time-series D. R. Munro1, N. S. Lovenduski1, T. Takahashi2, B. B. Stephens3, T. Newberger4,5, C. Sweeney4, 5 1. Department of Atmospheric and Oceanic Sciences and Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO, USA 2. Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA 3. National Center for Atmospheric Research, Boulder, CO, USA 4. Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA 5. Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA Satellite imagery suggests high particulate inorganic carbon (PIC) in a band that stretches across the Drake Passage north of the Antarctic Polar Front. We compare the change in total alkalinity (TA) indicated by satellite-based calcification rates to seasonal changes in surface TA observed by the Drake Passage Time-series (DPT) from 2002 to present. Additionally, we examine recent hydrographic data, including two DPT cruises where depth profiles were collected, to assess the calcium carbonate to organic carbon export ratio across the Drake Passage. The DPT dataset allows us to evaluate satellite-based PIC estimates and assess meridional gradients in calcium carbonate production across the Antarctic Circumpolar Current.

Simulated impact of high alkalinity glacial runoff on CO2 uptake in the Coastal Gulf of Alaska D. J. Pilcher1, S. A. Siedlecki2, A. J. Hermann2, K. O. Coyle3, J. T. Mathis4 1. NOAA Pacific Marine Environmental Laboratory 2. Joint Institute for the Study of the Atmosphere and Ocean, University of Washington 3. School of Fisheries and Ocean Sciences, University of Alaska Fairbanks 4. NOAA Arctic Research Program, Ocean and Atmospheric Research The Coastal Gulf of Alaska (CGOA) receives substantial freshwater inputs from nearby glaciers that are rapidly melting. This glacial runoff has a significant impact on global sea-level rise, in addition to the regional circulation and biology, yet there has been relatively little research on the direct impact on carbon chemistry. Limited observational evidence suggests that these glacial inputs are elevated in alkalinity but undersaturated in carbon, thereby generating enhanced local CO2 uptake. The CGOA is thought to be a net annual sink of CO2, with periods of significant CO2 uptake in spring-fall, but CO2 efflux during winter. This region is already highly susceptible to ocean acidification due to the naturally cold, lower carbonate ion concentration waters. Thus, additional carbon uptake due to melting glaciers may accelerate the rate of decrease in pH and aragonite saturation state. We use a regional biogeochemical model to test the quantitative impact of this process on CO2 uptake by varying the alkalinity concentration of the freshwater inputs. Increasing the alkalinity from the current estimated zero salinity end-member to values representative of different major river systems generated a net 18-27% increase in CO2 uptake. This increase is more pronounced in the nearshore region where regional shellfish aquaculture is located and is most prevalent in summer and fall. These results suggest that glacial runoff with elevated alkalinity/carbon ratios can significantly increase local carbon uptake via enhanced air-sea exchange, and identify a local carbon-climate feedback that is currently not included in global simulations.

Water-column transformation of particle organic carbon composition in the Southern Ocean Great Calcite Belt S. Z. Rosengard1,2*, P. J. Lam3, V. Galy1, A.P. McNichol1 1. Woods Hole Oceanographic Institution 2. MIT-WHOI Joint Program in Chemical Oceanography 3. University of California - Santa Cruz * srosengard@whoi.edu The euphotic and mesopelagic zones are the most dynamic depth intervals for particulate organic carbon (POC) flux in the water column. The region encompassing the Great Calcite Belt- a calcite-rich band produced by a coccolithophore bloom across the Southern Ocean - spans a wide range in primary productivity and POC transport from surface to 1000 m, offering an opportunity to explore the mechanisms that control POC transfer to depth. Bulk compositional measurements from this region show that the

efficiency of POC transfer through the euphotic and mesopelagic zones varies with phytoplankton community composition, suggesting that different assemblages generate and transport compositionally distinct POC to the deep ocean. To directly assess whether such compositional differences influence POC transport down the water column, we submitted <51 µm diameter size-fraction samples of POC from three depth profiles in the Great Calcite Belt region to ramped-oxidation from room temperature to 700°C. Plots of released CO2 concentration against temperature, or thermograms, differentiate POC by its thermal stability, providing a unique, higher-resolution perspective of organic matter composition throughout the first 1000 meters of the water column. By coupling thermal stability with stable carbon isotope measurements of CO2 generated at distinct temperature intervals during ramped oxidation, we find differences in the compositional transformation of POC transferred by diatom vs. coccolithophore-rich primary producer communities. These first three thermogram profiles of Southern Ocean POC also reveal several important caveats and advances in interpreting the biological pump via this method. Decadal decreasing of the CO2 uptake and enhanced acidification in the East China Sea P.-Y. Shen, C.-M. Tseng* Institute of Oceanography, National Taiwan University, Taipei 106, Taiwan *cmtseng99@ntu.edu.tw (presenter)

The role of the productive East China Sea (ECS) as a river-dominated marginal sea, in regulating the anthropogenic CO2 and effect of environmental changes on CO2 uptake changes are progressively being disclosed. The effects of the Changjiang river discharge (CRD) on the CO2 uptake have been discerned and changes due to the CRD fluctuation are examined through an empirical simulation by sea surface temperature (SST) and the CRD as well (Tseng et al., 2011, 2014). Here we, furthermore, report the time-series data of the CO2 fluxes and pH from 1982 to 2013 based on both observations and model calculation. The CO2 time-series with hydrography reveals apparent inter-annual variations and decadal changes. Results show subtle long-term increasing trends in the SST, pCO2air, and pCO2water with rates of 0.1°C yr-1, and 1.7 and 2.8 matm yr-1, respectively. Eventually, rates of the CO2 uptake and pH decreased gradually ~0.1 mole C m-2 yr-1 and ~3.2 x 10-3 pH yr-1, respectively. A comparison of results of the period from 2003 to 2013 to those from 1982 and 2003 was shown that the SST increased 1.3°C, CRD reduced by about 10%, pCO2 water increased ~43 µatm, CO2 flux reduced from -2.4 (i.e., sink from atmosphere to sea) to -1.6 mole C m-2 yr-1. Seasonal fluxes were moreover -3.5, -1.9, -1.1, -3.2 mole C m-2 yr-1 from spring to winter and decreased to -3.1, -0.7, -0.1, -2.3. The weak sink status during warm periods in summer-fall was significantly declined, fairly sensitive to changes in pCO2 and easily shifted from a sink to a source due to climate changes and anthropogenic forcing.

Surface Ocean-Lower Atmosphere Study: Linking ocean-atmosphere interactions with climate and people

R. H. R. Stanley1, V. Garcon2, S. Kontradowitz 3, E. Boss4

1. Wellesley College, Wellesley, USA rachel.stanley@wellesley.edu 2. LEGOS, Toulouse France, and SOLAS Chair 3. GEOMAR – Helmholtz Centre for Ocean Research, Kiel, Germany, and SOLAS IPO 4. University of Maine, Orono, USA

What are the key biogeochemical and physical interactions and feedbacks between the ocean and atmosphere? That is the central question being investigated by SOLAS, an international research initiative with over 2400 scientists in over 75 countries. Additionally, SOLAS tries to facilitate growing engagement from social scientists and stakeholders. The 5 core themes of SOLAS include (i) greenhouse gases in the ocean, (ii) air-sea fluxes of mass and energy, (iii) atmospheric deposition and ocean biogeochemistry, (iv) interactions between aerosols, clouds and ecosystems, and (v) ocean biogeochemical control on atmospheric chemistry. SOLAS currently sponsors several international workshops per year including upcoming workshops on science and society (Belgium, October, 2016), biogeochemical exchange processes at sea-ice interfaces (San Diego, April 2017), and air sea interface and fluxes of mass and energy (Cargese May, 2017) as well as a much loved summer school for graduate students and early postdocs (next one: Cargese, August 2018).

What can SOLAS USA do to be more useful to researchers? What can USA researchers to do interact more with SOLAS? These topics will be explored in this poster presentation, at the “Friends of SOLAS” table on Wednesday lunch – a table at which everyone interested in SOLAS is invited to sit – and at a plenary discussion Wednesday afternoon.

The role of subduction and gravitational sinking in particle export, carbon sequestration, and the remineralization length scale in the California Current Ecosystem M. R. Stukel1,*, H. Song2, R. Goericke3, A. J. Miller3

1. Dept. of Earth, Ocean, and Atmospheric Science, Florida State University, Tallahassee, FL 2. Massachusetts Institute of Technology, Cambridge, Massachusetts USA 3. Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA Sinking particles and aggregates created in the surface layers of the ocean are transported not only by gravity, but also by the horizontal and vertical advection of the surrounding water. Subduction, in particular, can transport organic matter out of the surface ocean in a manner that will not be detected by typical in situ carbon export measurements (sediment traps and 234Th-238U disequilibrium). To assess the importance of subduction to the biological pump, we combined in situ sediment trap, thorium, primary productivity,

and particulate organic carbon (POC) measurements, with a data-assimilative physical circulation model and a Lagrangian particle tracking model. We parameterized two alternate particle sinking rate models (fecal pellet model and aggregate model) using results from 13 extensively sampled water parcels in the California Current Ecosystem. Both models suggested that subduction was an important, though not dominant, mechanism of POC export (median 41% and 26% for aggregate and fecal pellet models). The percentage contribution of subduction was highly variable across water parcels (ranging from 7% - 90%), with subduction typically more important in offshore, oligotrophic regions. The fate of particles that are passively transported out of the surface layer by advection is distinctly different from that of particles that sink across the 100-m depth horizon. Subducted particles were predominantly remineralized shallower than 150 m, while approximately 50% of gravitationally exported POC was sequestered at depths >500 m.

Linking prokaryotic assemblages and biogeochemistry to long-term declines in chemoautotrophy in the Cariaco Basin G. T. Taylor1, E. Suter1, S. Chow1, D. Stinton1, Y. Astor2, M. I. Scranton1

1. School of Marine and Atmospheric Sciences, Stony Brook University, NY 11794-5000;

gordon.taylor@stonybrook.edu 2. Fundación La Salle de Ciencias Naturales, EDIMAR, Porlamar, Edo Nueva Esparta, Venezuela Chemoautotrophic carbon fixation has been measured semiannually in the CARIACO Ocean Time Series from November 1996 to the present. Early observed rates were inexplicably rapid, rivaling euphotic zone primary productivity. Over the last 19 years, rates integrated across the redoxcline and measured by consistent methodology have slowed by ~40 mgC m-2 d-1 y-1 on average. Coincident with this trend, the suboxic zone has narrowed while penetration of O2 to depth as well as distributions of deep water ammonium and phosphate have shoaled. Community analyses reveal that integrated inventories (250-450 m) of total prokaryotes have also declined in this layer. Time series of specific ecophysiotypes derived from fluorescent in situ hybridization (FISH) reveal a changing prokaryotic community. For example, representation of epsilon-proteobacteria appears to be declining as gamma-proteobacteria are in their ascendancy. In this talk, we examine biological responses to changing biogeochemical distributions and the environmental factors driving these changes.

Physical controls of anthropogenic carbon storage in the Arctic Ocean: Insights from an ocean carbon cycle model J. Terhaar*, J. C. Orr, L. Bopp Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France *jens.terhaar@lsce.ipsl.fr

The Arctic Ocean is one of the most vulnerable regions to ocean acidification, highlighting the importance of accurate estimation of anthropogenic carbon in that region. To estimate future carbon storage in the Arctic Ocean it is essential to understand the actual controls of the evolution of anthropogenic carbon. In this study, we explore the storage rate and boundary fluxes of total and anthropogenic carbon in the Arctic Ocean. To do so, we make use of the ocean carbon cycle model NEMO-PISCES and perform centennial simulations over 1870-2012. In line with the data-based study of Tanhua et al. (2009), we obtain an Arctic Ocean anthropogenic carbon inventory of 2.7 Pg-C in 2007, i.e., 2.4% of the global ocean Cant inventory despite representing only 1.3% of the global ocean volume. Although the storage is proportionally high, we show that the time-integrated air-sea uptake of 1.1 Pg-C until 2007 (1.0%) is disproportional small compared to the ocean surface (3.5%), highlighting the role of lateral transport of anthropogenic carbon. Indeed, from 2003 to 2012, only around one third of Arctic Ocean anthropogenic carbon is supplied by air-sea flux (20±4 TgC/y). The other two thirds enter the Arctic Ocean by lateral transport via Bering Strait (24±12 TgC/y) and the North Atlantic (40±12 TgC/y). The budget is closed by a net export of anthropogenic carbon through the Canadian Archipelago (-28±6 TgC/y). We also explore how these anthropogenic carbon trends compare to the variability in air-sea and lateral fluxes in total carbon. We show that the variability in natural fluxes is one order of magnitude larger than the anthropogenic carbon trends. Air-sea exchange and atmospheric cycling of mercury in South China Sea C. M. Tseng1*, W. C. Chen1, C. S. Liu1, C. H. Lamborg2 1. Institute of Oceanography, National Taiwan University, P.O. Box 23-13, Taipei 106, Taiwan 2. Department of Ocean Sciences, University of California, Santa Cruz, CA 95064, USA *cmtseng99@ntu.edu.tw Limited knowledge exists concerning the role of the low-latitude marginal seas in mercury (Hg) emissions on a global scale, especially tropical-subtropical and monsoon-dominated marginal seas in East Asia. To assess this potential mobilization of Hg through air-sea gas exchange, we have determined the dissolved elemental Hg (DEM) and gaseous elemental Hg (GEM) concentrations in surface seawater and atmosphere, respectively, during seasonal oceanographic cruises to the SouthEast Asian Time-series Study (SEATS) station (18 oN, 116 oE) from 2003 to 2007. The sampling and analysis of GEM and DEM were performed on board ship by using an on-line mercury analyzer (GEMA). Over the SCS, the GEM concentrations are elevated 2-3 times above global background values, with higher enhancements in the winter when the northeast monsoon draws air from China. The impact of long-range transport, as controlled by seasonal monsoons, has on the Hg atmospheric distribution and cycling in the SCS. The DEM concentration varied seasonally, with a high in summer and a low in winter and showed a positive correlation with sea surface temperature (SST). The elevated DEM concentration in summer appears mainly abiologically driven. In winter, the SCS acts as a sink of atmosphere Hg0 as a result of low SST and high wind of the year, enhanced vertical

mixing and elevated atmospheric gaseous elemental mercury. Annually, the SCS serves as a source of Hg0 to the atmosphere of 300±50 pmol m-2 d-1 (390±60 kmol Hg y-1, ~2.6% of global emission in ~1% of global ocean area), suggesting high regional Hg pollution impacts from the surrounding Mainland (mostly China). What do chloropigment tracers caught by SV sediment traps tell us about particle cycling in the ocean? W.-L. Wang1,2, C. Lee1, J. K. Cochran1, F. W. Primeau2, R. A. Armstrong1 1. School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY, 11794-5000, 2. Department of Earth System Science, University of California at Irvine, Irvine, California, 92697 To investigate particle dynamics, we constructed a “two-layer” model to describe chloropigment and organic matter (OM) cycling. The model was fit to chloropigment data sampled during the 2005 MedFlux project using Indented Rotating Sphere (IRS) sediment traps operating in Settling Velocity (SV) mode. Then, Bayesian techniques were used to estimate particle aggregation, disaggregation, and organic matter remineralization rate constants. Eleven settling velocity categories collected by SV sediment traps were grouped into two sinking velocity classes (fast-sinking and slow-sinking classes) to decrease the number of parameters that needed to be estimated, with a fast/slow cutoff SV of 49 m/d adopted from previous work. The organic matter degradation rate constant was estimated to be 3.03!!.!"!!.!" y−1, which is equivalent to a degradation half-life of 0.23 years. The rate constant of chlorophyll a degradation to pheopigments (pheophorbide, pheophytin, and pyropheophorbide) was estimated to be 2.27!!.!"!!.!" y−1. Disaggregation/aggregation rate constants were 46.79!!.!"!!.!" y−1 and 3.31× 10−9 y−1 , respectively, although the latter was not well constrained by the data. Intertidal salt marshes as an important source of inorganic carbon to the coastal ocean Z. A. Wang1*, K. D. Kroeger2, N. K. Ganju2, M. E. Gonneea2, S. N. Chu1 1. Woods Hole Oceanographic Institution, Woods Hole, MA, USA 2. United States Geological Survey, Woods Hole, MA, USA *Corresponding Author, zawang@whoi.edu

Dynamic tidal export of dissolved inorganic carbon (DIC) to the coastal ocean from highly productive intertidal marshes and its effects on seawater carbonate chemistry are thoroughly evaluated. The study uses a comprehensive approach by combining tidal water sampling of CO2 parameters across seasons, continuous in-situ measurements of biogeochemically-relevant parameters and water fluxes, with high-resolution modeling in a typical intertidal salt marsh of the U.S. northeast region. Salt marshes can acidify and alkalize tidal water by injecting CO2 (DIC) and total alkalinity (TA). DIC and TA generation may also be decoupled due to seasonal changes in marsh aerobic and

anaerobic respiration tied to the marsh life cycle. Acidification of tidal water causes buffering capacity to first decrease and then increase due to titration of carbonate ions and release of bicarbonate ions, so that ebbing tide may have even higher buffering capacity than incoming tide. Alkalization of tidal water, which mostly occurs in the summer due to anaerobic respiration, can further modify buffering capacity. Marsh exports of DIC and alkalinity may have complex implications for the future, more acidified ocean. Marsh DIC export exhibits high variability over tidal and seasonal cycles, which is modulated partially by marsh DIC generation, and more strongly by water fluxes. The marsh DIC export of 414 g C m-2 yr-1, based on high-resolution measurements and modeling, is more than twice the previous estimates. It a major term in the marsh carbon budget and translates to one of the largest carbon fluxes along the U.S. East Coast. Bacterial utilization of creatine in seawater B. Wawrik1*, D. A. Bronk2, S. E. Baer3, C. Liang4, S. Mei1, Z. Yang1

1. University of Oklahoma 2. Virginia Institute of Marine Science 3. Bigelow Laboratory for Ocean Sciences 4. University of North Carolina, Chapel Hill * First author email: bwawrik@ou.edu The dissolved organic nitrogen (DON) pool is recognized as an important component of the marine carbon (C) and nitrogen (N) cycles. However, the turnover of individual DON compounds and the role that DON plays in the broader context of marine biogeochemical processes is not well understood. Creatine, a component of the dissolved free amino acid (DFAA) pool, is a known byproduct of metazoan metabolism, and recent genetic evidence suggests that some phytoplankton may also have the ability to produce creatine. We hypothesized that creatine utilization by marine bacteria is more widespread than commonly assumed. The phylogenetic breadth of creatine-utilizing bacteria was investigated via a bioinformatics approach. Uncharacterized creatinases found in the genomes of Roseobacter denitrificans Och114 and Roseobacter litoralis Och149 were sub-cloned, 6-His tagged, and expressed in E. coli. Enzymatic activity assays indicated optima at pH 8.4 and 35˚C with Km values of 25-27 mM, consistent with previously characterized creatinases. Creatine concentrations were quantified via MS analysis in samples from the equatorial Pacific and found to range between 19-199 nM, with higher concentrations in the surface than at the deep chlorophyll maximum (DCM). Uptake rates were estimated using 15N-tracer techniques at 0.08-0.66 nmol N L-1 h-1. The presence of creatine in biomass from the diatom Thalassiosira preudonana, for which genome analysis had indicated the potential for creatine synthesis, was verified via LC-MS analysis. Overall, these data support the idea that phytoplankton may represent a source of creatine in marine systems. They further indicate that creatine utilization by marine bacteria might account for a significant component of DFAA turnover in the ocean.

Phosphonate utilization by eukaryotic phytoplankton L. P. Whitney1, C. A. Michaud2, M. W. Lomas3

1. Bigelow Laboratory for Ocean Sciences, lwhitney@bigelow.org 2. University of Rhode Island 3. Bigelow Laboratory for Ocean Sciences Phosphorus (P) is an essential macronutrient utilized by phytoplankton; it is a central component of nucleic acids, cellular membranes, and is integral to cellular energy production as well as post-translational regulation of enzymatic activity. As such, P availability is an important control on oceanic primary production. Dissolved inorganic phosphorus (Pi) is the preferred form of P as phytoplankton cells can easily transport and assimilate it; however, in ocean gyres like the oligotrophic western North Atlantic, Pi concentrations are consistently low (<10 nmol L-1) and may well restrict primary production. In these regions, dissolved organic phosphorus (DOP) is an important potential nutrient source, accounting for >80% of the total dissolved P, and supports significant fractions of primary production. The composition of the DOP pool is complex and remains largely unknown, but it can generally be divided into two major groups based upon bond class: P-esters and phosphonates. All marine organisms are capable of utilizing P esters through the activity of enzymes like alkaline phosphatase. Phosphonates, which comprise up to 25% of the high molecular weight DOP pool, have been shown to be an important source of P to marine cyanobacteria. With the exception of one study which found that dinoflagellates could not directly utilize phosphonate, the ability of eukaryotic phytoplankton to supplement their P source with phosphonates remains unexplored. We have found that several eukaryotic phytoplankon, from different taxonomic groups, contain genes encoding putative phosphonate metabolic pathways. In a preliminary growth study we have shown that initially axenic Emiliania huxleyi, Phaeodactylum tricornutum, and Micromonas commada cultures were able to grow at ecologically relevant growth rates when given phosphonate as the sole P source. We have also detected differential expression of a putative phosphonate transporter in M. commoda under P-stress growth conditions. Together, these preliminary results suggest at least some eukaryotic phytoplankton may be able to directly utilize extracellular phosphonate. This work is timely given the prediction that future oceans will become more stratified, which could increase the importance of DOP, including phosphonates, as a nutrient source. FlowCAM observations of microbial exopolymeric substances as indicators for sticky particulate matter in coastal and offshore waters K. Ziervogel University if New Hampshire, Ocean Process Analysis Laboratory, kai.ziervogel@unh.edu

Mechanisms that determine the export of organic carbon from the surface ocean to the deep sea are important with respect to the biological pump. The main vehicles for organic carbon export are sinking diatom aggregates, also known as marine snow. A major role in the formation of marine snow has often been attributed to exopolymeric substances (EPS) excreted by heterotrophic and autotrophic pelagic organisms during growth and metabolism. EPS are mainly comprised of acidic polysaccharides that can be visualized with Alcian Blue. Another type of EPS is classified as Coomassie stained particles (CSP) of proteinaceous origin. Analysis of EPS in the water usually includes filtration followed by spectrophotometrical and/or microscopical analysis. Recently published protocols allow direct observations of Alcian Blue stained particles (ASP) and CSP in whole water samples using a portable flow-through microscope (FlowCAM). This work presents results from FlowCAM observations on micro-particle abundance and ASP and CSP along a coastal-offshore transect during a recent cruise into the Mid-Atlantic Bight. ASP and CSP were only detectable in association with diatom cells and detritus at the shallowest coastal site. Smaller phytoplankton cells and detritus that were abundant in offshore waters did not appear to be coated with stainable EPS. Cell-free ASP and CSP forming micro-gels could not be distinguished from Alcian blue and Coomassie Blue precipitates that form due to interference of salts. All in all, the FlowCAM is a powerful tool to obtain vertical profiles of micro-particle abundance immediately after sampling. Information of EPS that can form the glue for marine snow can also be obtained with the FlowCAM; however care must be taken when analyzing cell-free EPS forming micro-gels.