High-resolution multi-molecular stratigraphic records from North Atlantic drift sediments (ODP Sites 980, 984) reflecting Holocene climate and ocean dynamics

The North Atlantic plays an important role as the source region for northern component waters of thermohaline circulation. The hydrological system is highly sensitive to climatic changes. Underlying drift sediments record both changes in the hydrological system (lateral advection) and in `direct' material input from surface waters (primary production and eolian supply), and therefore represent excellent archives for past ocean and regional climate variability. Two sediment cores from North Atlantic drift sediments were taken during ODP Leg 162 (Site 980, Feni Drift, 55°N 15°W, water depth 2179 m, and Site 984, Bjorn Drift, 61°N 24°W, water depth 1648 m). While both sites experience similar atmospheric forcing, the present-day Bjorn Drift is bathed by Iceland-Scotland Overflow Water, while the Feni Drift is influenced by more southern sourced waters. Both sites exhibit exceptionally high sedimentation rates and thus enable reconstruction of climate-related changes within the North Atlantic with high temporal resolution. The composition of the organic matter (OM) in these sediments is closely coupled to the dynamics of the environment. Key factors that control quantity and quality of OM from marine and terrigenous sources in the drift sediments are surface water temperature and nutrient supply (marine primary productivity), wind speed (eolian supply of terrigenous OM), and strength and direction of bottom water currents (lateral redistribution of OM and export from continental margins). This study seeks evidence for rapid climate changes through development of high-resolution multi-molecular stratigraphic records of the sedimentary OM using Gas Chromatography/Time-Of-Flight Mass Spectrometry (GC-TOF-MS) analysis of total lipid extracts. We present high-resolution (< 100 yr) molecular proxy records from both ODP sites that indicate changes in heat transport, marine productivity, and terrigenous supply from the Last Glacial Maximum to the present. Alkenones, sterols, and other biomarkers characteristic for different phytoplankton groups (e.g., long-chain diols) as well as lipids derived from terrigenous plant waxes serve as the primary molecular tools. Marine biomarker fluxes document past variations in climate-controlled marine productivity. Variations in the degree of saturation of alkenones (UK37') are used to reconstruct varying sea surface temperatures (SST). Vascular plant lipids, transported and deposited over the oceans as aerosols or via bottom currents, are interpreted in terms of eolian or advective terrigenous fluxes. Each of these processes is linked to specific climate conditions. We also compare 14C AMS ages of bulk OM and selected marine (alkenones) and terrigenous (plant waxes) biomarkers to those of planktonic foraminifera in order to examine current-driven sediment redistribution and advective transport. Preliminary 14C data indicate that bulk OM tends to be generally older than foraminiferal carbonate in both cores. As the age offsets appear to be coupled to sedimentation rate changes we investigate whether they reflect changes in current-driven redistribution of marine OM or supply of pre-aged terrigenous OM.