Glacial–interglacial climatically forced δ13C variations in sedimentary organic matter

Abstract

SEDIMENTARY organic geochemical properties have long been used to characterize sedimentary organic matter sources1–8, but the characterizations are often not unique. There are at least four plausible mechanisms to account for the large (∼3–6%.) glacial-to-interglacial climatic variations in the sedimentary organic-carbon isotopic composition (δ 13Corg) in the northern Gulf of Mexico. They are: temperature-dependent C isotopic fractionation by phytoplankton, mixing of C3-photosynthetic terrigenous and marine organic matter, mixing of C3- and C4-photosynthetic organic matter and diagenetic alteration of the originally sedimented material. In a 208.7-m Deep Sea Drilling Project hydraulic-piston core (DSDP 619) from the Pigmy Basin in the northern Gulf of Mexico, we find that paired analyses of δ 13Corg and N/C are consistent with the hypothesis that the sedimentary organic carbon in the Pigmy Basin is a glacial-interglacial climati-cally determined mixture of C3-photosynthetic terrigenous and marine organic matter9, confirming the model of Sackett5.