In low and middle latitudes, the Cretaceous/Tertiary boundary is marked by a sudden and pronounced decrease in delta (super 13) C values of near- surface-water carbonates and a reduction in the surface-to-bottom delta (super 13) C gradient. These isotopic data have been interpreted as evidence of a decline in surface-water productivity that was responsible for the extinction of many planktic foraminiferal species and other marine organisms at or near the K/T boundary. We present planktic and benthic foraminiferal isotopic data from two almost biostratigraphically complete sections at Ocean Drilling Program Site 738 in the Antarctic Indian Ocean and at Nye Klov in Denmark. These data suggest that planktic carbonate delta (super 13) C values in high latitudes may not have decreased dramatically at the K/T boundary; thus, surface-water productivity may not have been reduced as much as in low and middle latitudes. Comparison of the records of Site 738 with those of ODP Sites 690 and 750 indicates a pronounced decline in delta (super 13) C values of planktic and benthic foraminifera and fine-fraction/bulk carbonate approximately 200000 yr after the K/T boundary. This reflects a regional shift in the carbon isotopic composition of oceanic total dissolved carbon (TDC) and correlates with a similar change in benthic foraminiferal delta (super 13) C values at mid- and low-latitude Deep Sea Drilling Project Sites 527 and 577. This oceanographic event was followed by the ecosystem's global recovery approximately 500000 yr after the K/T boundary. These data suggest that the environmental effects of the K/T boundary may have been less severe in the high-latitude oceans than in tropical and subtropical regions.