Background

1. Coincident Autonomous pCO2 and pH data and their Application to Carbonate Chemistry Investigation on the Coastal Margins 003-788 Christopher W. Hunt1, Doug Vandemark1, Joseph Salisbury1*, Shawn Shellito1, Sylvia Musielewicz2 1 Ocean Process Analysis Laboratory, University of New Hampshire *contact: chunt@unh.edu 2 NOAA/Joint Institute for the Study of the Atmosphere and Ocean How Well Do Parameter Combinations Close the Carbonate System? Background • 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 • 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. Kennebec- Androscoggin Rivers TAlk = S*52.5 + 476 r2=0.98 Noise=7.8 µmol kg-1 Closing the carbonate system with the pCO2+pH combination results in poor retrievals of DIC. Portland ME 44007 UNH & PMEL CO2 coastal buoy at 65 m depth 44030 Portsmouth NH • 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. IOSN3 Merrimack River Fall bloom Seasonal cooling Retrievals of omegaaragonite (OMa) with pH + pCO2 are high compared to Retrievals from pH + TAlk-salinity Or pCO2 + TAlk-salinity. Boston MA • Carbonate System Closure: • There are generally four measured carbonate system variables used as inputs: • TAlk (sometimes estimated from salinity) • DIC • pCO2 • pH. • Using any two carbonate system inputs, the other two inputs, plus the rest of the carbonate system, can be derived: • Omega-a (saturation station of aragonite) • Omega-c (saturation station of calcite) • HCO3- • CO32- • Etc. 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 stdev= ± 0.0073 • pH (TAlks+pCO2) stdev = ± 0.022 TAlk-salinity regression for discrete samples collected at the buoy during the pH-pCO2 deployment period SAMI-pH sensor 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. MAP-CO2 system