The Challenge of Reconstructing the Climate History for the Arctic Ocean
Anne deVernal, Département des sciences de la Terre et de l'atmosphère, UQAM
Climate and oceanographical changes of the Arctic Ocean are still poorly documented from geological archives. The difficulty comes from remote access and problems with dating sedimentary sequences characterized by very low sedimentation rates, gaps, discontinuous biogenic records, equivocal correlation of regional data to global stacks using paleomagnetic or marine isotope stratigraphy, etc. The generally low productivity and poor preservation of biogenic remains also make it extremely difficult to interpret unequivocally proxy records. Nonetheless, the available sedimentary, geochemical and micropaleontological data suggest that sea ice has been a resilient feature during the late Cenozoic. A major change in ocean water properties (calcium carbonate preservation) possibly related to the onset of perennial sea-ice and/or reorganization in the ocean circulation occurred during the Plio-Pleistocene, but the age of this transition remains uncertain. Data spanning the late Pleistocene-Holocene are better constrained from a chronological point of view but restricted to the central Arctic Ocean. They demonstrate extremely low sedimentation rates (≤ 1 cm/ka) due to mostly perennial sea-ice. However, closer to the shelf edge, in neritic areas of the eastern Arctic, relatively high sedimentation rates up to ~5 cm/kyr are recorded, fostered during postglacial time by ice rafting supplies through the Transpolar Drift, in relation with the development of "sea-ice factories" following the submergence of the shelf. At sites near the shelf edge of the Laptev Sea, micropaleontological data indicate early-mid Holocene seasonally open sea-ice conditions instead of perennial sea-ice. Hence, whereas highly resilient perennial sea ice on long time scales characterizes the western Arctic Ocean, seasonal sea ice in the Russian Arctic might be a recurrent feature of warm episodes.