Sedimentation rates in the Makarov Basin, central Arctic Ocean: A paleomagnetic and rock magnetic approach

Three long sediment cores from the Makarov Basin have been subjected to detailed paleomagnetic and rock magnetic analyses. Investigated sediments are dominated by normal polarity including short reversal excursions, indicating that most of the sediments are of Brunhes age. In general, the recovered sediments show only low to moderate variability in concentration and grain size of the remanence-carrying minerals. Estimations of relative paleointensity variations yielded a well-documented succession of pronounced lows and highs that could be correlated to published reference curves. However, together with five accelerator mass spectrometry C-14 ages and an incomplete Be-10 record, still two different interpretations of the paleomagnetic data are possible, with long-term sedimentation rates of either 1.3 or 4 cm kyr(-1) However, both models implicate highly variable sedimentation rates of up to 10 cm kyr(-1), and abrupt changes in rock magnetic parameters might even indicate several hiatuses

Paläozeanographische Untersuchungen in der Vilkitsky-Straße und östlich von Severnaya Zemlya mit sedimentologischen und geophysikalischen Methoden

During the expeditions ARK IX/4 (1993) and ARK XI/1 (1995) by RV "Polarstern" glaciomarine deposits were discovered east off Severnaya Zemlya, in the Vilkitsky Strait and Vilkitsky-Khatanga Channel using PARASOUND subbottom profiling. For reconstruction of the palaeoenvironment and glacial history of the Severnaya Zemlya archipelago the geophysical properties (magnetic susceptibility, wet bulk density, pwave velocity, porosity and water content) of gravity cores taken in this area were studied using a high resolution multi-sensor core logger (MSCL). Additional investigations included the determination of fine lithological structures and ice rafted debris (IRD) by x-ray photographs, grain-size (sand, silt, clay), grain-size distribution of silt, and clay mineral distribution by x-ray diffraction of four sediment cores in key positions. The comparison of the results with PARASOUND-profiles and AMS 14C datings allowed the identification of 5 seismic units and their stratigraphical correlation from the Vilkitsky-Khatanga Channel into the Vilkitsky Strait.The results can be summarized as follows:Morainic ridges were identified along the north eastern continental slope of Severnaya Zemlya and in the Vilkitsky Strait (seismic unit 5). They were produced by a former glaciation of the archipelago of unkown age. Large debris flow deposits (seismic unit 4) in the Vilkitsky Strait indicating ice-proximal conditions are presumably linked to the glaciation of Severnaya Zemlya and the Taymyr Peninsula during marine isotope stage 4. In the Vilkitsky Strait and Vilkitsky-Khatanga Channel, clayey sediments (seismic unit 3) reflect hemipelagic accumulation under a possibly frequently closed sea-ice cover showing no evidence of ice-proximal conditions at stage 3. Stage 2 is characterized by a global sea-Ievel lowering of approximately 120 m resulting in the formation of a sediment fan (seismic unit 2) belonging to the river Khatanga at the shelf break of the Laptev Sea close to the Vilkitsky-Khatanga Channel and possible fjord-like conditions in the Vilkitsky Strait. The appearance of a diamicton in the Schokalsky Channel suggests, that presumably during stage 2 the Schokalsky Strait was closed by a grounded ice-shield. Massive meltwater sediments occurring in the western Vilkitsky Strait could be related to an existing ice-shield in the Kara Sea during stage 2. An increased input of smectite and magnetite by the Khatanga during termination 1 a could be interpreted as deglaciation of the Putoran-Plateau which was ice-covered at stage 2. The asymmetrie accumulation of Holocene Sediments (seismic unit 1) in the Vilkitsky Strait and Vilkitsky-Khatanga Channel may have depended on the formation of dense and cold water bottom currents caused by sea-ice production on the Kara shelf. The local appearance of the Holocene at the continental slope of Severnaya Zemlya could have been produced by conturites