Significant contribution of dissolved organic matter to seawater alkalinity

Abstract

The present study shows a previously undocumented role of dissolved organic matter in the marine carbonate system. During photosynthesis, phytoplankton release dissolved organic compounds containing basic functional groups that readily react with protons during seawater titration, and thereby contribute to alkalinity (a measure of buffering capacity). The magnitude of the contribution of dissolved organic compounds to seawater alkalinity is species dependent, suggesting that individual phytoplankton species exude dissolved organic compounds with unique proton accepting capacities. Our study shows that dissolved organic matter produced by marine phytoplankton during photosynthesis is a newly identified buffering component in the ocean, and indicates that the contribution of dissolved organic matter to seawater alkalinity can be significant in the biologically productive upper ocean, where to date it has been unrecognized or considered insignificant. Copyright 2009 by the American Geophysical Union.