Distribution, variability and burial of organic carbon at Northern Fram Strait and Yermak Plateau

The environment of the Fram Strait, the only deepwater connection of the Arctic Ocean to the world oceans via the North Atlantic (Fig.7.8.1; see Fig.7.1.9), is influenced by the distribution of sea-ice and two opposing current systems. The northward flowing West Spitsbergen Current (WSC) transports warm, near-surface water (Manley 1995; Rudels et al. 2000) to the Northern Fram Strait. About 22% of the northward flowing Atlantic waters are re-circulated within the RAC (Return Atlantic Current) between 78 and 80°N, west of Svalbard. At 80°N the WSC splits into the Svalbard (ca. 33% of the WSC waters) and the Yermak Branch (ca. 45% of the WSC waters). On the western side of the Fram Strait, the East Greenland Current (EGC) transports cold and low-salinity water southwards along the eastern continental margin of Greenland. (Fig.7.8.1). Primary production in ice-covered areas of western Fram Strait is limited by sea-ice cover, and influenced by the predominant water mass. Productivity in the interior Arctic Ocean is generally low (0.09 gC/m²/day) (Wheeler et al. 1996; see Chapter 3). At marginal ice zones and oceanic fronts in the Fram Strait, however, primary productivity exhibits strong fluctuations and may exceed 1 gC/m²/day (Hirche et al. 1991). The accumulation of organic carbon in sediments depends not only on the supply from primary productivity, but also on selective degradation in sediments. Efficient vertical transport through the water column by formation of aggregations (ballast effect) (Ittekkot et al. 1992; Knies and Stein 1998) and increased lateral transport by strong currents enable a higher preservation of organic carbon in the sediments. In this region, the WSC is capable of transporting large amounts of suspended organic matter to the ice-covered regions in northern Fram Strait (Rutgers van der Loeff et al. 2002). Numerous studies have dealt with paleoceanography and the associated organic carbon accumulation in the sediments of Fram Strait and adjacent regions during the last glacial/interglacial cycle (e.g. Hebbeln 1992; Hebbeln et al. 1994; Elverhoi et al. 1995; Andersen et al. 1996; Hebbeln and Wefer 1997; Hebbeln et al. 1998; Notholt, 1998; Vogt et al. 2001, Taylor et al. 2002). However, in most of the sedimentary records a low temporal resolution prevents the identification of short-term climatic fluctuations, like those reconstructed from high-resolution terrestrial ice-core records. (e.g. GISP2/GRIP; Grootes et al. 1993). Occasionally, short-term events recorded as enhanced organic matter accumulation have been found in cores from the northern Fram Strait/Yermak Plateau region (Knies and Stein 1998; Vogt et al. 2001). These events are caused by a rapid incorporation of organic matter in fine-grained material followed by rapid transfer to the seafloor. Rapidly changing climatic and oceanographic conditions can be recorded exceptionally well by undisturbed deep-sea sediments, particularly in the distribution and variability of organic carbon in sediments. Rapidly changing climatic and oceanographic conditions can be recorded exceptionally well by undisturbed deep-sea sediments, particularly in the distribution and variability of organic carbon in sediments. Yet, there exists little information about the regional response during the last deglaciation and the potential influence of terrigenous material on marine sedimentation of organic carbon in northern Fram Strait. To address this problem, we studied two high-resolution cores spanning the time intervals of the last glacial, the last deglaciation and the Holocene. Here, we present data on the distribution and sources of organic carbon in surface sediments and in long sediment cores. Accumulation rates of total sediment and organic carbon for three different time intervals are calculated and an organic carbon budget for Fram Strait Yermak Plateau is presented for the Holocene