Collaborators:
Frank J. Millero
Richard A. Feely
Rik Wanninkhof
 

Degree of Saturation State of CaCO₃ in the Oceans

NOAA/DOE OACES, 2 years
 

PROJECT SUMMARY

Over the last eight years (1990-1998) a large global database of high quality total alkalinity (TA) and total inorganic carbon (TCO₂) measurements in the Atlantic, Pacific, and Indian Oceans has been obtained through a multi-national and a multi-agency effort for the global CO₂ surveys.  The measurement campaigns included parts of the NOAA/OACES, the DOE/WOCE, and the JGOFS CO₂ survey programs.  This carbon database is unprecedented in terms of quality ( 2 mol kg^-1 in TA and  1 mol kg^-1 in TCO₂) and spatial coverage.  The previous studies on the degree of saturation of CaCO₃ in the oceans (Li et al., 1969; Archer, 1996) using the historical measurements (GEOSECS) suffered from spatially insufficient data coverage, less precise and less accurate carbonate measurements, and inaccurate thermodynamic constants.  Therefore, it is worthwhile to revisit this issue with recently collected global carbon data.  Another interesting aspect of this proposed research is to examine the effect of oceanic uptake of anthropogenic CO₂ on the degree of saturation state of seawater with respect to aragonite and calcite, since the amount of anthropogenic CO₂ taken up by the oceans since the Industrial Revolution can be detectable with presently available techniques.  The rising atmospheric CO₂ concentration due to burning of fossil fuels is likely to reduce the concentration of surface water of carbonate ion (CO₃^-2) by about 30% relative to the pre-industrial level as the atmospheric CO₂ concentration doubles the pre-industrial level by the middle of 21st century.  A recent pioneering study (Langdon et al., 1998) suggests that changes in the degree of saturation-state of surface seawater with respect to CaCO₃ will reduce calcification rate of coral community proportionally as the concentration of surface carbonate ion ([CO₃^2-]) decreases.  If this provocative finding can be extrapolated to all CaCO₃ bearing organisms this would mean that global production of hard tissue would decrease with increasing pCO₂, which in turn might lead to greater oceanic uptake of CO₂.  Four tangible goals below will be pursued for the execution period of this proposal:

1. Globally consistent databases for total alkalinity and total inorganic carbon;
2. A critical evaluation of the effect of anthropogenic CO₂ on the calcite and aragonite saturation horizons in the oceans;
3. Construction of a global seawater [CO₃^2-] field;
4. Comparison of the saturation horizon with the compensation depth horizon.
 
 

Kitack Lee
NOAA/AOML
4301 Rickenbacker Causeway
Miami, FL 33149
tel: (305) 361-4389
fax: (305) 361-4392
lee@aoml.noaa.gov

Frank J. Millero
RSMAS/MAC
University of Miami
4600 Rickenbacker Causeway
Miami, FL 33149
tel: (305) 361-4707
fax: (305) 361-4144
fmillero@rsmas.miami.edu

Richard A. Feely
NOAA/PMEL
7600 Sand Point Way NE
Seattle, WA 98115
tel : (206) 526-6214
fax : (206) 526-6744
feely@pmel.noaa.gov

Rik Wanninkhof
NOAA/AOML
4301 Rickenbacker Causeway
Miami, FL 33149
tel: (305) 361-4379
fax: (305) 361-4392
wanninkhof@.aoml.noaa.gov