Download - Ocean Acidification
Ocean AcidificationReid Bergsund and Catherine Philbin
9.7 Billion Metric Tonnes per Year of Anthropogenic Carbon Emissions in 2012
Anthropogenic emissions are the result of human combustion of fossil fuels
Anthropogenic carbon emissions grew 2.1% since 2011
Global Greenhouse Gas Emissions by Source
Balance of carbonate species shifts right from CO2 to HCO3
- and CO3-
Ocean absorbs about 1/3 of excess atmospheric CO2
The addition of CO2 to seawater causes the formation of carbonic acid
CO32- decreases with
increasing levels of CO2
Carbonic acid then undergoes two dissociations and releases H+ ions into the ocean, causing ocean pH to decrease
CO2 (g) ⇔ CO2 (aq)
CO2 dissolves in ocean water
CO2 + H2O ⇔ H2CO3
CO2 and H2O form carbonic acid
H2CO3 ⇔ HCO3- + H+
The first dissociation
HCO3- ⇔ CO3
2- + H+
The second dissociation
pH = -log10[H+]
The pH is determined by the concentration of H+ ions
The Carbonate Buffer System Helps to Maintain Equilibrium
CO2, HCO3- and CO3
2- make a carbonate buffer system
The addition of CO2 will cause the equilibrium equation to move to the right.
An increase in CO2
decreases CO32- in
order to maintain chemical equilibrium
CO2 + CO32- + H2O ⇔ 2HCO3
-Equilibrium reaction for CO2
in seawater
An Increase in Atmospheric CO2 Causes a Decrease in the Supersaturation levels of CaCO3
Surface waters are supersaturated with CaCO3
The decrease in CO32-
caused by an increase in CO2 results in less abundant dissolved CaCO3
Corals produce CaCO3 more slowly as ocean pH and CaCO3 supersaturation levels both decrease
Ca2+ + CO3
2- ⇔ CaCO3Calcification reaction
Coral with Calcite shells
Reef after ocean acidification?
Healthy Coral Reef
Time for Discussion…
Iglesias-Rodriguez et al (2008) Argue that Rising Atmospheric CO2 Partial Pressures Won’t Reduce Marine Organism Calcification
Grew cultures of Emiliania huxleyi coccolithophores (photosynthetic plankton)
Bubbled different partial pressures of CO2 through cultures ranging from 280 ppmv (pre-industrial levels) to 750 ppmv (end of 21st century worst case scenario)
E. huxleyi coccolithophore
E. huxleyi is the Most Abundant Species of Coccolithophore Found in
temperate, subtropical, and tropical oceans; forms base of large proportion of marine food webs
E. huxleyi’s abundance and importance is the reason it’s often used for studies of this nature
Relative abundance of different species of Coccolithophore
Coccolith Volume Changed During Experiments at Different CO2 Levels
Coccolith volume and CaCO3 levels generally increase with rising CO2 partial pressures
Discovered that coccolith calcification increased under higher-CO2 conditions
Experimental Results Show Coccolith Productivity Rising with Increased pCO2
Particulate Inorganic Carbon (PIC), Particulate Organic Carbon (POC): suspended, particulate inorganic and organic carbon species produced by phytoplankton at the sea surface
PIC (graph A) levels and POC (graph B) levels double at 750 ppmv CO2
PIC production rates (graph C) and POC production rates (graph D) double at 750 ppmv CO2
CO2 ppmv
CO2 ppmv
Different colored dots represent different independent experiments
Experimental Results Show Coccolith Growth Rates Decreasing with Increased pCO2
If the range of experiments is viewed as providing error bars, the experiments are consistent with each other
Different colored dots represent different independent experiments
Field Observations Confirm Upward Trend in Coccolith Mass Witnessed in Experiments
Change in coccolith mass has accelerated over recent decades
Increase in average coccolith mass correlates with rising atmospheric CO2
Atmospheric CO2 data taken from Siple ice core and Mauna Loa
Observatory
Riebesell et al (2008) Argue that Experimental Protocol is Flawed Particulate Inorganic Carbon production
rates and Particulate Organic Carbon production rates don’t increase when normalized to Particulate Organic Carbon biomass for E. huxleyi cultures under different CO2 partial pressures
Different colored dots represent different independent experiments
PIC Production Rates
POC Production Rates
Riebesell et al (2008) describe specific procedural oversights in Iglesias-Rodriguez et al (2008) experiments
E. huxleyi precultures were grown at 5x-10x natural cell density, affecting cell carbon levels
E. huxleyi precultures may have experienced nitrogen limitation during transfer to experimental flasks
Nitrogen limitation in E. huxleyi increases cell size and carbon levels
Experimental incubations only lasted 1.5 to 3 days; only 1 to 2 cell generations
With only 2 generations, differences in carbon quota, cell growth rates could be attributed to preconditioning, not CO2
differences
E. Huxleyi cultures, magnified
Procedural errors could have driven cell growth rate
and carbon levels artificially high
Iglesias-Rodriguez et al (2008) argue that experiments accurately depicted ocean conditions Alkalinity is the capacity of
an aqueous solution to neutralize an acid
Due to the long residence time of alkalinity in the ocean, alkalinity was held constant in the experiment, contrary to what Riebesell et al (2008) suggest
CO2 bubbling mimics the ocean alkalinity and the changes in the biocarbonate ion of high CO2 seawater
ALOHA Data Shows that the Surface Ocean pH has Decreased as Atm CO2 and pCO2 has Increased
Red: atmospheric CO2 at Mauna Loa in ppmv Blue: surface ocean pH
Tan: pCO2 inμatm in the subtropical North Pacific Ocean
Oceanic uptake of CO2 is a cause for increases in DIC and decreases in CaCO3 saturation
Since preindustrial age, atmospheric CO2 and the pCO2 in the ocean have increased, whereas pH has decreased by 0.1 units
Aragonite is a More Soluble Form of CaCO3 than Calcite
The crystal structure of Aragonite
The crystal structure of Calcite
Aragonite and Calcite Saturation Levels Mirror Changes in Total CaCO3
Coral reefs are defined by the ability to produce a net surplus of CaCO3
In the last 17 years the saturation of both calcite and aragonite have both decreased
Blue: saturation of aragonite
Gray: saturation of calcite
Calcite and Aragonite Saturation Levels Have Gotten Less Deep in the Ocean since Preindustrial Times
Saturation levels of aragonite and calcite are based on temp, pressure, and pH
Above the saturation levels, calcite and aragonite tend to form crystal structure
Saturation levels at present (solid) have changed since preindustrial times (dashed)
Latitude
Saturation Levels of Aragonite and Calcite Vary Across Different Oceans
Anthropogenic CO2 penetration is highest in the N. Atlantic because of deep water formation
Saturation levels of Calcite and Aragonite change most where CO2
has penetrated
Organisms Lose Calcite Shells in More Acidic Seawater Degree of sensitivity to
ocean acidification varies between species
Chronic exposure is difficult to demonstrate in laboratories
Calcification rates decrease as ocean pH and aragonite and calcite saturation states decrease
Some corals completely lose their skeletons when grown in highly acidic water Coral grown for 12
months in: (a) pH = 8.2 and (b) pH = 7.4
Varied Responses to Acidification Across Different Species
Calcification, photosynthesis, nitrogen fixation and reproduction were studied across different species
Ocean acidification has widely varied affects on different biological processes
Columns a-d represent linear positive, linear negative, level, and parabolic responses to increasing seawater pCO2
Global Warming Causes a Change in Nutrient Availability
Species, such as phytoplankton, are dependant on nutrient rich waters
Global warming increases thermal stratification of the upper ocean, and decreases nutrient upwelling Nutrient rich water is cold and
deep, and is eventually pushed to the surface. This is the
process of upwelling.
Ocean Acidification Impacts Food Webs and Ecosystems
Calcified structures provide protection from predators
With acidification, calcifiers will need to adapt, or be adversely affected
Organic matter grown at high CO2 levels have higher carbon/nitrogen ratios, affecting food quality for microbial consumers
Acidification isn’t the only effect of a changing climate, so it is difficult to predict outcomes of ocean acidification on food webs
Phytoplankton are at the base of the oceanic
food web
There are many uncertainites in the impact of increasing CO2 levels on the global CaCO3 budget
Decreasing CaCO3 saturation states cause increasing dissolution rates
If all carbonate production stops, atmospheric CO2 would decline 10-20 ppmv
Uptake rate of anthropogenic CO2 could overwhelm the natural carbonate buffer system
Oceanic CaCO3 Budget Affects Carbon Uptake
CaCO3 flux estimates for the ocean
Chemical Speciation in Seawater Changes with Ocean pH Weak acid species will
undergo speciation changes with acidification, ex: boron, phosphorous, silicon, nitrogen
These changes can affect bioavailability
More research is needed to understand effects of ocean acidification on trace metals and organic mater Changes in phosphoric
acid speciation due to changes in pH
Ocean acidification will definitely occur, but how will the oceanic ecosystems
respond?
A descriptive title
• yellow: …
• red: …
• Black: …
caption, explaining exactly what’s shown in the figure including both axes and all lines, etc
A brief take home message. Everything on slide in 24 points or larger