TY - JOUR
T1 - Applications of in situ pH measurements for inorganic carbon calculations
AU - Cullison Gray, Sarah E.
AU - DeGrandpre, Michael D.
AU - Moore, Tommy S.
AU - Martz, Todd R.
AU - Friederich, Gernot E.
AU - Johnson, Kenneth S.
N1 - Funding Information:
We thank Cory Beatty (University of Montana) for technical support. The detailed comments from two anonymous reviewers significantly improved the manuscript. Funding for this research was provided by NSF grants OCE-0628569 and OCE-0836807 .
PY - 2011/7/20
Y1 - 2011/7/20
N2 - This study examines the utility of combining pH measurements with other inorganic carbon parameters for autonomous mooring-based carbon cycle research. Determination of the full suite of inorganic carbon species in the oceans has previously been restricted to ship-based studies. Now with the availability of autonomous sensors for pH and the partial pressure of CO2 (pCO2), it is possible to characterize the inorganic carbon system on moorings and other unmanned platforms. The indicator-based pH instrument, SAMI-pH, was deployed with an autonomous equilibrator-infrared pCO2 system in Monterey Bay, California USA from June to August 2007. The two-month time-series show a high degree of short-term variability, with pH and pCO2 changing by as much as 0.32 pH units and 240μatm, respectively, during upwelling periods. The pH and salinity-derived alkalinity (ATsalin) were used to calculate the other inorganic carbon parameters, including pCO2, total dissolved inorganic carbon (DIC) and CaCO3 saturation states. The calculated pCO2 was within 2μatm of the measured pCO2 during the first day of the deployment and within 8μatm over the first month. The DIC calculated from pH-ATsalin and pCO2-ATsalin were within 5μmolkg-1 of each other during the first month. However, DIC calculated from pH-pCO2 differed by ~50μmolkg-1 from the other estimates over the same period, reflecting the sensitivity of the pH-pCO2 calculation to measurement error. The data continued to diverge during the final month and this difference was likely driven by extensive biofouling. Because of the relative insensitivity of CO32- concentration to these errors, aragonite saturation calculated from the pH-pCO2 pair was within 0.15 of the pH-ATsalin values over the entire deployment. These results show that in situ pH, when combined with other CO2 parameters, can provide valuable insights into both data quality and inorganic carbon cycling.
AB - This study examines the utility of combining pH measurements with other inorganic carbon parameters for autonomous mooring-based carbon cycle research. Determination of the full suite of inorganic carbon species in the oceans has previously been restricted to ship-based studies. Now with the availability of autonomous sensors for pH and the partial pressure of CO2 (pCO2), it is possible to characterize the inorganic carbon system on moorings and other unmanned platforms. The indicator-based pH instrument, SAMI-pH, was deployed with an autonomous equilibrator-infrared pCO2 system in Monterey Bay, California USA from June to August 2007. The two-month time-series show a high degree of short-term variability, with pH and pCO2 changing by as much as 0.32 pH units and 240μatm, respectively, during upwelling periods. The pH and salinity-derived alkalinity (ATsalin) were used to calculate the other inorganic carbon parameters, including pCO2, total dissolved inorganic carbon (DIC) and CaCO3 saturation states. The calculated pCO2 was within 2μatm of the measured pCO2 during the first day of the deployment and within 8μatm over the first month. The DIC calculated from pH-ATsalin and pCO2-ATsalin were within 5μmolkg-1 of each other during the first month. However, DIC calculated from pH-pCO2 differed by ~50μmolkg-1 from the other estimates over the same period, reflecting the sensitivity of the pH-pCO2 calculation to measurement error. The data continued to diverge during the final month and this difference was likely driven by extensive biofouling. Because of the relative insensitivity of CO32- concentration to these errors, aragonite saturation calculated from the pH-pCO2 pair was within 0.15 of the pH-ATsalin values over the entire deployment. These results show that in situ pH, when combined with other CO2 parameters, can provide valuable insights into both data quality and inorganic carbon cycling.
KW - Autonomous sensor
KW - CO2 system
KW - Inorganic carbon
KW - Seawater pH
UR - http://www.scopus.com/inward/record.url?scp=79955643483&partnerID=8YFLogxK
U2 - 10.1016/j.marchem.2011.02.005
DO - 10.1016/j.marchem.2011.02.005
M3 - Article
AN - SCOPUS:79955643483
SN - 0304-4203
VL - 125
SP - 82
EP - 90
JO - Marine Chemistry
JF - Marine Chemistry
IS - 1-4
ER -