PRELIMINARY EVIDENCE OF MILANKOVITCH CYCLICITY RECORDED IN SEDIMENT BRIGHTNESS (L*) RECORDS FROM CENTRAL ARCTIC OCEAN SEDIMENTS RECOVERED BY THE HOTRAX PROGRAM

Modern process studies and climate models indicate that the Arctic as a region is particularly sensitive to changes in global climate due to high latitude feedback processes related to surface albedo and sea ice changes. The inaccessibility of the region and difficulties in dating Arctic sediment, have resulted in major gaps in our understanding of the long term history of climate change in much of the Arctic basin. The Healy-Oden Trans-Arctic Expedition (HOTRAX) of 2005 seeks to enhance our understanding of Arctic climate history by providing high quality sedimentary archives to reconstruct glacial-interglacial changes during the quaternary and Late Pleistocene. During HOTRAX Leg 2 aboard the USGS Ice breaker Healy this expedition collected 21 sediment cores across the Arctic Ocean, spanning the Alpha-Mendeleev and Lomonosov ridges. These cores provide unprecedented coverage of the major Arctic basins, range in length up to 15.4 m, and encompass almost 500 m of sediment. They provide an opportunity to extend the Arctic marine sedimentary record significantly beyond most existing sediment archives. Intercomparison of shipboard lithostratigraphy with Multi-Sensor core logs enabled preliminary correlation of material from the Alpha-Mendeleev Ridges, and with less certainty, the Lomonosov Ridge. Some unique stratigraphic features such as a distinctive change in lithology and prominent IRD layers provide the basis for correlation with previously developed stratigraphies. This overall correlation is confirmed by high-resolution (1cm) post-cruise color reflectance measurements and indicates a pronounced increase in sedimentation rates from the Alpha Ridge to the southern Mendeleev and Lomonosov Ridges. To evaluate changes in sediment cyclicity using representative cores from these ridges, we detrended the sediment brightness (L*) records from three cores and conducted an evolutive wavelet analysis on the detrended records which we take as a proxy for sediment lithic content and thus glacial intensity. The global wavelet from each core displays prominent peaks in sediment depth cyclicity which we preliminarily associated with the primary Milankovitch cycles.