Background

Christopher W. Hunt1, Doug Vandemark1, Joseph Salisbury1*, Shawn Shellito1, Sylvia Musielewicz2

1 Ocean Process Analysis Laboratory, University of New Hampshire *contact: chunt@unh.edu2 NOAA/Joint Institute for the Study of the Atmosphere and Ocean

AcknowledgmentsThis work was funded by National Aeronautics and Space Administration grants NNX09AU89G and NNH04AA62I. Background image courtesy of Deb Brewitt. This work was supported in part by the NOAA Coastal Services Center through an award to the UNH Center for Coastal Ocean Observation and Analysis (COOA); NOAA award NA16OC2740.

SAMI-pH sensorMAP-CO2 system

Seasonal coolingFall bloom

Parameter Combination

Mean Difference (DICobs - DICcalc)

pCO2, pH -126TAlk, pCO2 -13

TAlk, pH 7Talk_s, pCO2 -14

TAlk_s, pH 8

How Well Do Parameter Combinations Close the Carbonate System?

TAlk = S*52.5 + 476r2=0.98Noise=7.8 µmol kg-1

How did the pH and pCO2 sensors respond during a fall bloom?

•pH and pCO2 co-varied inversely

•Observed pH (SAMI pH) was offset from derived

pH (TAs+pCO2) by an average of 0.0425

•Standard deviation around red line is higher for

pCO2 than pH:

•SAMI pH stdev= ± 0.0034

•pH (TAlks+pCO2) stdev = ± 0.0089

How did the pH and pCO2 sensors respond to seasonal cooling?

•pH and pCO2 co-varied inversely during a fall phytoplankton bloom•Cooling temperatures should lead to lower pCO2; other factors are superimposed on the observed pCO2 signal•Observed pH (SAMI pH) was offset from derived pH (TAs + pCO2) by an average of 0.031

•Standard deviation around red line is higher for

pCO2 than pH:

•SAMI pH stdev= ± 0.0073

•pH (TAlks+pCO2) stdev = ± 0.022

Portsmouth NH

Boston MA

Portland ME

Merrimack River

Kennebec- Androscoggin

Rivers

44030

44007

IOSN3

UNH & PMEL CO2 coastal buoy at 65 m

depth

Objectives:

•Examine seasonal pH and pCO2 sensor

responses.

•Examine event-driven pH and pCO2 sensor

responses.

•Couple measurements to close carbonate

system and derive TAlk, DIC, and Ω.

•Compare carbonate system closure

between various measurement

combinations.

Closing the carbonate system with thepCO2+pH combination results inpoor retrievals of DIC.

Retrievals of omegaaragonite (OMa) withpH + pCO2 are high compared toRetrievals from pH + TAlk-salinityOr pCO2 + TAlk-salinity.

TAlk retrieved from pH+pCO2 inUnrealistically high. Subtracting the Mean pH offset results in more realisticTAlk magnitudes.

pH offset (pHSAMI-pHTAs+pCO2)

Deployment 1 0.048Deployment 2 0.0261Deployment 3 0.0278Deployment 4 0.0318

Conclusions:•pCO2 and pH observations are tightly correlated•There appears to be an offset between pH and pCO2 data•Retrievals of carbonate system data using pH+pCO2 are problematic. Coupling of pH and pCO2 with measurements of either DIC or TAlk appears preferable for carbonate system closure.

Methodology:•Buoy located at approximately 43°N,

70°W since 2006

•Paired pH and pCO2 data collected over

four deployments from fall 2010-present.

•pCO2 system: PMEL MAP-CO2 (bubble

equilibration with NDIR detection)

•pH system: Sunburst SAMI-pH (dye-

based spectrophotometric pH

measurement)

•Periodic shipboard sampling of pCO2,

TAlk, DIC.

Carbonate System Closure:

There are generally four measured carbonate system variables used as inputs:1.TAlk (sometimes estimated from salinity)2.DIC3.pCO2

4.pH.Using any two carbonate system inputs, the other two inputs, plus the rest of the carbonate system, can be derived:1.Omega-a (saturation station of aragonite)2.Omega-c (saturation station of calcite)3.HCO3-4.CO32-5.Etc.

Abbreviations and Terms TechniquepCO2 Partial Pressure of

Carbon Dioxide (µatm)

Map-CO2

TAlk Total alkalinity (µmol kg-1)

Gran titration

TAlk_s Total alkalinity (derived from conservative salinity relationship, µmol kg-1)

Sea-bird TSG

DIC Dissolved Inorganic Carbon (µmol kg-1)

acidification and NDIR detection

pH spectrophotometric pH

SAMI pH

OMa saturation station of aragonite (omega-a)

derived

OMc saturation station of calcite (omega-c)

derived

TAlk-salinity regression for discrete samples collected at the buoy during the pH-pCO2 deployment period