Description: We investigated the effect of CO2 and primary production on the carbon isotopic fractionation of alkenones and particulate organic matter (POC) during a natural phytoplankton bloom dominated by the coccolithophore Emiliania huxleyi. In nine semi-closed mesocosms (~11 m**3 each), three different CO2 partial pressures (pCO2) in triplicate represented glacial (~180 ppmv CO2), present (380 ppmv CO2), and year 2100 (~710 ppmv CO2) CO2 conditions. The largest shift in alkenone isotopic composition (4-5 per mil) occurred during the exponential growth phase, regardless of the CO2 concentration in the respective treatment. Despite the difference of ~500 ppmv, the influence of pCO2 on isotopic fractionation was marginal (1-2 per mil). During the stationary phase, E. huxleyi continued to produce alkenones, accumulating cellular concentrations almost four times higher than those of exponentially dividing cells. Our isotope data indicate that, while alkenone production was maintained, the interaction of carbon source and cellular uptake dynamics by E. huxleyi reached a steady state. During stationary phase, we further observed a remarkable increase in the difference between d13C of bulk organic matter and of alkenones spanning 7-12 per mil. We suggest that this phenomenon is caused mainly by a combination of extracellular release of 13C-enriched polysaccharides and subsequent particle aggregation induced by the production of transparent exopolymer particles (TEP).

Description: A reconstruction of Milankovitch to millennial-scale variability of sea-surface temperature (SST) and sea-surface productivity in the Pleistocene mid-latitude North Atlantic Ocean (MIS 16-9) and its relationship to ice sheet instability was carried out on sediments from IODP Site U1313. This reconstruction is based on alkenone and n-alkane concentrations, Uk37' index, total organic carbon (TOC) and carbonate contents, X-Ray diffraction (XRD) data, magnetic susceptibility, and accumulation rates. Increased input of ice-rafted debris (IRD) occurred during MIS 16, 12, and 10, characterized by high concentrations of dolomite, quartz, and feldspars and elevated accumulation rates of terrigenous matter. Minimum input values of terrigenous matter, on the other hand, were determined for MIS 13 and 11. Peak values of dolomite, coinciding with quartz, plagioclase, and kalifeldspar peaks and maxima in long-chain n-alkanes indicative for land plants, are interpreted as Heinrich-like Events related to sudden instability of the Laurentide Ice Sheet during early and late (deglacial) phases of the glacials. The coincidence of increased TOC values with elevated absolute concentrations of alkenones suggest increased glacial productivity, probably due to a more southern position of the Polar Front. Alkenone-based SST reached absolute maxima of about 19°C during MIS 11.3 and absolute minima of 〈10°C during MIS 12 and 10. Within MIS 11, prominent cooling events (MIS 11.22 and 11.24) occurred. The absolute SST minima recorded directly before and after the glacial maxima MIS 10.2 and 12.2, are related to Heinrich-like Event meltwater pulses, as supported by the coincidence of SST minima and maxima in C37:4 alkenones and dolomite. These sudden meltwater pulses - especially during Terminations IV and V - probably caused a collapse of phytoplankton productivity as indicated by the distinct drop in alkenone concentrations. Ice-sheet disintegration and subsequent surges and outbursts of icebergs and meltwater discharge may have been triggered by increased insolation in the Northern High Latitudes.

Description: AB: Multiple cores from different locations in the North Atlantic were recovered during IODP Expeditions 303/306. We have investigated the biomarker distributions of identified Heinrich layers (HL) and ambient glacial/interglacial samples from Site U1305, located in the Labrador Sea in proximity to the former major iceberg discharge pathway derived via the Hudson Strait from the Laurentide-Ice-Shield (LIS).A unique association of a multitude of "petrogenic" compounds such as benzohopanes, D-ring monoaromatic 8,14-secohopanes, rearranged diasterenes, mono- and triaromatic steranes, isorenieratene-derivatives as well as characteristic pristane/〈i〉n〈/i〉- C〈sub〉17〈/sub〉 and pristane/phytane ratios ideally allows to distinguish organic matter from HL compared to adjacent samples. They therefore are regarded and can be used as organic-geochemical tracers not only for the occurrence of Heinrich Events of the last glacial cycle but also for older Heinrich-like events.We present a biomarker based high resolution record of such events during a time interval from about 320-460 kyr at Site U1313 (MIS 10-12) and an extended record (MIS 8-16) of Heinrich-type events from Site U1308, i.e. from positions near the Mid-Atlantic Ridge and distal to the LIS.In addition, the HL-specific biomarker association provides circumstantial evidence to derive from a relatively immature, Paleozoic marine rock deposited under occasional photic zone anoxic conditions, that is today located on the Laurentide/Canadian shield. Reinvestigation of available geologic and organic-geochemical data allowed narrowing down this assumed source to an Ordovician oil shale close to Hudson Strait, that indeed bears a striking resemblance in terms of biomarker distributions when compared to the specific association of compounds from samples of Heinrich Events.

Description: AB: During IODP Expeditions 303/306, multiple cores from different locations in the North Atlantic were recovered. One of the major objectives of these expeditions was to capture Miocene-Quaternary millenial-scale climate variability in sensitive regions at the mouth of the Labrador Sea and in the North Atlantic ice-rafted debris (IRD) belt. Site 1305 is located in the Labrador Sea close to the southwest extremity of the Eirik Drift and in proximity to the former major iceberg discharge pathway derived via the Hudson Strait from the Laurentide-Ice- Shield (LIS). The upper Pleistocene part of Site 1305 afforded discrete IRD-containing detrital carbonate sections known as Heinrich layers (HL). About 30 samples from within and in between these layers were investigated in terms of quantitative and qualitative biomarker distribution using gas chromatography-mass spectrometry to (a) extend previous knowledge of biomarker inventories from identified Heinrich layers and (b) to investigate the potential of specific compounds to trace the occurrence and first appearance of Heinrich event-like episodes. Samples from HL1, HL2 and HL4 at Site 1305 are clearly distinguishable from samples between those layers due to the abundance of characteristic biomarker groups such as benzohopanes, D-ring monoaromatic 8,14- secohopanes, mono- and triaromatic steranes, aryl isoprenoids including isorenieratene-derivatives and increased pristane/n-C17 and phytane/n-C18 ratios. Such biomarker compositions are typically observed as diagenetic products within different types of mature (including Palaeozoic) source rocks and oils found in different North American/Canadian Basins, but cannot derive from sources contemporary to the time when Heinrich events occurred. More likely, these compounds originate from LIS basal erosion of Palaeozoic sedimentary outcrops, subsequently transported as IRD through the Hudson Strait and released at Site 1305 during Heinrich events. Thus, the study of specific biomarkers has a great potential not only to trace the origin and delivery pathways of IRD in the Northern North Atlantic, but also for the detection of such events within longer stratigraphic records like those newly drilled during IODP Expeditions 303/306.