SEDIMENTS IN ARCTIC SEA-ICE - IMPLICATIONS FOR ENTRAINMENT, TRANSPORTAND RELEASE

Despite the Arctic sea ice cover's recognized sensitivity to environme ntal change, the role of sediment inclusions in lowering ice albedo an d affecting ice ablation is poorly understood. Sea ice sediment inclus ions were studied in the central Arctic Ocean during the Arctic 91 exp edition and in the Laptev Sea (East Siberian Arctic Region Expedition 1992). Results from these investigations are here combined with previo us studies performed in major areas of ice ablation and the southern c entral Arctic Ocean. This study documents the regional distribution an d composition of particle-laden ice, investigates and evaluates proces ses by which sediment is incorporated into the ice cover, and identifi es transport paths and probable depositional centers for the released sediment. In April 1992, sea ice in the Laptev Sea was relatively clea n. The sediment occasionally observed was distributed diffusely over t he entire ice column, forming turbid ice. Observations indicate that f razil and anchor ice formation occurring in a large coastal polynya pr ovide a main mechanism for sediment entrainment. In the central Arctic Ocean sediments are concentrated in layers within or at the surface o f ice floes due to melting and refreezing processes. The surface sedim ent accumulation in central Arctic multi-year sea ice exceeds by far t he amounts observed in first-year ice from the Laptev Sea in April 199 2. Sea ice sediments are generally fine grained, although coarse sedim ents and stones up to 5 cm in diameter are observed. Component analysi s indicates that quartz and clay minerals are the main terrigenous sed iment particles. The biogenous components, namely shells of pelecypods and benthic foraminiferal tests, point to a shallow, benthic, marine source area. Apparently, sediment inclusions were resuspended from she lf areas before and incorporated into the sea ice by suspension freezi ng. Clay mineralogy of ice-rafted sediments provides information on po tential source areas. A smectite maximum in sea ice sediment samples r epeatedly occurred between 81 degrees N and 83 degrees N along the Arc tic 91 transect, indicating a rather stable and narrow smectite rich i ce drift stream of the Transpolar Drift. The smectite concentrations a re comparable to those found in both Laptev Sea shelf sediments and an chor ice sediments, pointing to this sea as a potential source area fo r sea ice sediments. In the central Arctic Ocean sea ice clay mineralo gy is significantly different from deep-sea clay mineral distribution patterns. The contribution of sea ice sediments to the deep sea is app arently diluted by sedimentary material provided by other transport me chanisms.