Particulate Organic-Matter Delta-C-13 Variations across the Drake Passage

A 7 parts per thousand gradient in the delta-C-13 of suspended particulate organic matter (POM) was observed in samples taken during two transects across the Drake Passage during March 1986. This POM delta-C-13 transition from -23.2 parts per thousand at 53.3-degrees-S to values as low as -30.3 parts per thousand at > 62-degrees-S does not track previously reported abrupt changes in water chemistry and plankton species composition associated with the Polar Front Zone that resides at approximately 58-degrees-S in this region. Also, the north-south isotopic trend is not accompanied by significant changes in POM carbon or nitrogen concentrations, or in POM C/N. Differences in plankton standing crop or biochemistry (e.g., lipid content) therefore do not appear responsible for the isotopic trends observed. The latitudinal change in POM delta-C-13 is, however, highly correlated with water temperature and with the calculated concentration of CO2(aq) at equilibrium with atmospheric CO2. These observations are consistent with the hypothesis that [CO2(aq)] significantly influences POM delta-C-13 in ocean surface waters.