Coincident Autonomous pCO2 and pH data and their Application to Carbonate Chemistry Investigation on the Coastal Margin.
Download ReportTranscript Coincident Autonomous pCO2 and pH data and their Application to Carbonate Chemistry Investigation on the Coastal Margin.
Christopher W. 1 Hunt , Doug 1 Vandemark , Joseph 1 Ocean Process Analysis Laboratory, University of New Hampshire 2 NOAA/Joint Institute for the Study of the Atmosphere and Ocean 1* Salisbury , Shawn 1 Shellito , Sylvia 2 Musielewicz *contact: [email protected] How Well Do Parameter Combinations Close the Carbonate System? Background KennebecAndroscoggin Rivers Portland ME 44007 UNH & PMEL CO2 coastal buoy at 65 m depth 44030 Objectives: How did the pH and pCO2 sensors respond during a fall bloom? •Examine seasonal pH and pCO2 sensor •pH and pCO2 co-varied inversely responses. •Observed pH (SAMI pH) was offset from derived •Examine event-driven pH and pCO2 sensor pH (TAs+pCO2) by an average of 0.0425 responses. •Standard deviation around red line is higher for •Couple measurements to close carbonate pCO2 than pH: system and derive TAlk, DIC, and Ω. •SAMI pH stdev= ± 0.0034 •Compare carbonate system closure between •pH (TAlks+pCO2) stdev = ± 0.0089 Mean Difference Parameter (DICobs Combination DICcalc) pCO2, pH -126 TAlk, pCO2 -13 TAlk, pH 7 Talk_s, pCO2 -14 TAlk_s, pH 8 Closing the carbonate system with the pCO2+pH combination results in poor retrievals of DIC. various measurement combinations. Portsmouth NH Methodology: IOSN3 •Buoy located at approximately 43°N, Merrimack River 70°W since 2006 Fall bloom Seasonal cooling Retrievals of omegaaragonite (OMa) with pH + pCO2 are high compared to Retrievals from pH + TAlk-salinity Or pCO2 + TAlk-salinity. •Paired pH and pCO2 data collected over Boston MA four deployments from fall 2010-present. •pCO2 system: PMEL MAP-CO2 (bubble equilibration with NDIR detection) •pH system: Sunburst SAMI-pH (dyebased spectrophotometric pH measurement) Carbonate System Closure: •Periodic shipboard sampling of pCO2, There are generally four measured carbonate system variables used as inputs: 1. TAlk (sometimes estimated from salinity) 2. DIC 3. 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. HCO34. CO325. Etc. TAlk = S*52.5 + 476 r2=0.98 Noise=7.8 µmol kg-1 TAlk, DIC. and Terms Abbreviations Technique pCO2 Partial Pressure of Map-CO2 Carbon Dioxide (µatm) TAlk Total alkalinity (µmol Gran kg-1) titration TAlk_s Total alkalinity Sea-bird (derived from TSG conservative salinity relationship, µmol kg1) DIC Dissolved Inorganic acidification Carbon (µmol kg-1) and NDIR detection pH spectrophotometric SAMI pH pH OMa saturation station of derived aragonite (omega-a) OMc saturation station of derived calcite (omega-c) TAlk-salinity regression for discrete samples collected at the buoy during the pH-pCO2 deployment period pH offset (pHSAMI-pHTAs+pCO2) Deployment 1 Deployment 2 Deployment 3 Deployment 4 0.048 0.0261 0.0278 0.0318 TAlk retrieved from pH+pCO2 in Unrealistically high. Subtracting the Mean pH offset results in more realistic TAlk magnitudes. 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. 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 sensor MAP-CO2 system •SAMI pH stdev= ± 0.0073 •pH (TAlks+pCO2) stdev = ± 0.022 Acknowledgments This 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.