The results of the investigation of organic carbon deposition in Baffin Bay provide important information about paleoenvironmental evolution in high northern latitudes during Cenozoic time. During Miocene to Quaternary time, organic carbon enrichment of up to 3% insediments sampled at Ocean Drilling Program Site 645 was controlled mainly by increased supply of terrigenous organic matter. Two distinct maxima were identified: (1) a middle Miocene maximum, possibly reflecting a dense vegetation cover and fluvial sediment supply from adjacent islands, which decreased during late Miocene and early Pliocene time because of expansion of tundra vegetation due to global climatic deterioration; (2) a late Pliocene-Pleistocene maximum probably caused by glacial erosion and meltwater outwash. Significant amounts of marine organic carbon were deposited in Baffin Bay during middle Miocene time, suggesting higher surface-water productivity triggered by the inflow of cold and nutrient- rich Arctic water masses. The decrease in average surface-water productivity to values similar to those of modern Baffin Bay occurred during the late Miocene and were probably caused by development of a seasonal sea-ice cover, reaching maximum expansion during the past 3.4 m.y.