A 7 % gradient in the delta 13C of suspended particulate organic matter (POM) was observed in samples taken during two transects across the Drake Passage during March 1986. This POM delta 13C transition from -23.2 % at 53.3 degrees S to values as low as -30.3 % 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 13C 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 13C in ocean surface waters.