Elemental and carbon isotopic analyses of suspended and sea ice particulate organic matter (POC) from Antarctica show enrichments in \sp13C unrelated to atmospheric CO\sb2 variations. Phytoplankton bloom-related POC from the southwestern Ross Sea during 1992 had a range in δ\sp13C of 7\perthous. δ\sp13C\sbPOC collected from pack ice had an 11\perthous range, with highest values found in the Bellingshausen and Amundsen Seas and lower values found in Ross Sea pack ice. Organic matter δ\sp13C from phytoplankton blooms in the southwestern Ross Sea is strongly correlated with POC concentration, suggesting high rates of bloom-related CO\sb2(aqueous) drawdown that may cause disequilibrium as a result of stable stratification of the upper water column and partial isolation of the surface water CO\sb2 pool. Isotopic and organic carbon composition of surface sediments is similar to the upper water column, thus primary isotopic signals are preserved. Surface sediment δ\sp13C values are 1 to 3\perthous enriched in \sp13C relative to surface water POC δ\sp13C. Highest isotopic values were found in areas that receive large amounts of phytoplankton bloom detritus. Future downcore carbon isotopic analyses may prove useful as tracers of bloom dynamics and sea ice production.