Organic carbon accumulation over the last 16 kyr off Vancouver Island, Canada: evidence for increased marine productivity during the deglacial

Abstract

The organic carbon content of marine sediments is commonly used as a proxy for export production. However, in continental margin sediments a large fraction of the organic matter may be of terrestrial origin, and it is necessary to correct the total organic carbon data accordingly. Radiocarbon dating of bulk organic carbon, organic geochemistry and isotope data (δ 13C and δ 15N) are used here to characterize the type of organic matter present in Core JT96-09 collected at a water depth of 920 m on the slope off Western Canada. The quantities of marine and terrestrial organic carbon are then estimated using the δ 13C data. The 16 kyr record obtained from Core JT96-09 suggests that accumulation of total organic carbon was highest during the late glacial and deglacial, but geochemical data indicate that as much as 70% of this carbon is terrestrial in origin. When the palaeo-record is corrected for this terrigenous input it is observed that accumulation of marine organic matter, and presumably marine export production, increased at the end of the last glacial contemporaneous with the Bølling, and that it peaked during the Allerød. Data from other palaeoproductivity proxies (i.e., bio-barium, opal and alkenones) also indicate relatively high productivity during the deglacial. These results indicate a return to modern upwelling conditions and high marine export production at ∼14.3 calendar kyr BP and a period of enhanced upwelling, relative to the present, during the Allerød.