Late Quaternary organic carbon accumulation south of Barbados: influence of the Orinoco and Amazon rivers?

Isotopic and geochemical proxies measured in bulk sediment samples of two g ravity cores south of Barbados were used to develop a model for the organic carbon accumulation during the last 250 kyr with respect to the influence of terrestrial sources (e.g. the Orinoco and Amazon rivers) as well as the marine contributions, sea-level, surface currents, and morphological featur es. Total organic carbon (TOC) content and the stable organic carbon isotop es of the organic matter (delta(13)C(org)) show no glacial to interglacial variability. TOC content is generally very low in both cores but increases between 40 and 120 kyr. A comparable pattern is detected in accumulation ra tes of the organic matter but is only hinted in the delta(13)C(org) ratios. The results suggest that during the last 250 kyr the organic carbon accumu lation south of Barbados has been controlled by glacioeustatic sea-level ch anges and the general morphologic settings. A sealevel stand of 15-80 m bel ow present day seems generally to favour the accumulation of organic matter south of Barbados. Although delta(13)C(org) ratios reveal no clear trend i n the organic matter composition, terrestrial organic carbon discharged by rivers (Orinoco or Amazon) seems not to be a major component in the sedimen ts of that area during the last 250 kyr. (C) 2000 Elsevier Science Ltd. All rights reserved.