A biomarker approach to the organic matter deposited in the North Atlantic during the last climatic cycle

The study of the composition of total organic carbon (TOC), C-37 alkenones, and C-23-C-33 n-alkanes in the North Atlantic Ocean (cores SU90/08 and SU90/39) has allowed the development of a model for the differentiation of marine and terrigenous TOC. This model gives rise to results in good agreement with inorganic markers such as magnetic susceptibility (MS) and non-carbonate content. According to this model, the terrigenous TOC accounts for most of the organic matter in the glacial sediments. Thus, the higher TOC of the glacial periods (0.1-0.45% vs. 0.05-0.15% in the interglacials) is due to the increase in terrigenous TOC. The changes in marine TOC (those associated to sea-surface productivity) are independent of the glacial-interglacial evolution. The terrigenous TOC is more important at higher latitudes, probably due to higher terrigenous detrital inputs associated with iceberg transport. In this respect, the correlation between n-alkanes and MS strongly suggests that the main source of these hydrocarbons are ice-rafted materials and that aeolian inputs only represent minor contributions. The four peaks of reworked n-alkanes in the SU90/08 core that are coincident with the Heinrich Layers (H1, H2, H4, and H5) are in agreement with this hypothesis. On the ether hand, the abrupt marine TOC peaks of SU90/08 show a 23 ka periodicity, indicating that the marine productivity at 43 degrees N in the North Atlantic Ocean was precessionally driven. The productivity maxima in this core correlate with low latitude oceanographic processes, such as periods of enhanced trade wind intensity and equatorial upwelling which are also tuned to precession and independent of the global glacial-interglacial evolution. Copyright (C) 1997 Elsevier Science Ltd.