Biomarker and x-ray diffraction data from Site U1313 (MIS 16 - 9)

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.

Physical properties and alpha-/gamma-HCH concentrations in sea-ice and snow samples obtained during a CCGS Amundsen cruise, eastern Beaufort Sea

The alpha- and gamma-hexachlorocyclohexanes (HCHs) are being scavenged from the atmosphere by falling snow, with the average total scavenging ratios (WT) of 3.8 x 10**4 and 9.6 x 10**3, respectively. After deposition, HCH snow concentrations can decrease by 40% because of snowpack ventilation and increase by 50% because of upward migration of brine from the ice. HCH vertical distribution in sufficiently cold winter sea ice, which maintains brine volume fractions <5%, reflects the ice growth history. Initially, the entrapment of brine (and HCHs) in ice depends on the rates of ice growth and desalination. However, after approximately the first week of ice formation, ice growth rate becomes dominant. Deviations of HCH concentrations from the values predicted by the ice bulk salinity (rate of brine entrapment) can be explained by spatial variability of HCHs in surface water. HCH burden in the majority of the ice column remains locked throughout most of the season until the early spring when snow meltwater percolates into the ice, delivering HCHs to the upper ocean via desalination by flushing. Percolation can lead to an increase in alpha- and gamma-HCH in the sea ice by up to 2%-18% and 4%-32%, respectively.