Late Quaternary history of glaciations in the northern Kara Sea and Arctic Ocean iceberg drift in marine isotope stage

Abstract

We present new data from two long sediment cores obtained off the St. Anna and Voronin troughs on the northern continental margin of the Kara Sea (eastern Arctic Ocean). According to preliminary age models based on microfossil findings and grain size data, the cores cover the last ca. 150 kyr. Coarse-grained layers with common to abundant iceberg-rafted lithic grains (IRD) were deposited when ice sheets on the Kara Sea shelf had advanced close to the shelf break and ice streams developed in the deep troughs opening towards the eastern Arctic Ocean. Terrestrial data suggest that large ice sheets in the area developed in marine isotope (sub)stages (MIS) 6, 5b, and 4, while glaciation was restricted to the westernmost Kara Sea in the last glacial maximum (MIS 2) (Svendsen et al., 2004, Quat. Sci. Rev.). Our new data reveal details of the ice extent during individual glacial phases. They suggest that only in MIS 6 both troughs were filled with ice streams and that in the younger glacial phases regional differences of ice extent developed along the continental margin.In several layers, coal clasts up to 4 cm in size were found. We have obtained coal petrological and organic geochemical data of these particles and of coal grains found in other sediment cores from the deep-sea eastern Arctic Ocean and the Fram Strait area. The results reveal a certain variability of data (random vitrinite reflectance (VRr %), Rock-Eval hydrogen and oxygen indices, hydrocarbon biomarkers) even among samples from the same core, suggesting that the coal grains do not stem from one restricted area. Data clusters and comparison with published information on coals from circum-Arctic continents, however, allow a tentative discrimination of our samples. The coals from the northern Kara Sea area and the central Fram Strait show relatively high oxygen indices, in opposite to coals from the NE Greenland margin. The latter resemble coals from the Cretaceous/Tertiary basins on Svalbard and NE Greenland. Available stratigraphic data from the cores suggests that the layers with high coal particle abundances in deep-sea cores from the northern Kara Sea area, the central Fram Strait, and the NE Greenland margin were deposited in MIS 6. We conclude that during MIS 6 coal-bearing layers in the NE Greenland Wandel Sea Basin were eroded by an expanded North Greenland Ice Sheet and transported by icebergs southward along the adjacent continental margin. At the same time, icebergs breaking off from the large northern Eurasian Ice Sheet drifted from northern Siberia across the Eurasian Basin towards the central Fram Strait. Our results generally support the hypothesis of a cross-Arctic iceberg transport in MIS 6 but show that caution must be applied when conclusions are made on the sources of individual coal particles.