PARTICULATE MATTER IN PACK ICE OF THE BEAUFORT GYRE

Ice observations and sediment samples were collected in the Beaufort G yre in 1988. Fine sediment occurred in very small patches of turbid ic e, as thin spotty surface layers, in mud pellets or in old snowdrifts. The latter were widespread south of 74-degrees-N, containing an estim ated 22 tonnes of silt and clay km-2. Average particle concentration i n sea ice (40 mg l-1) was much higher than in sea water (0.8 mg l-1) o r in new snow, but the sediment load was significantly smaller and of finer texture compared to that observed in a shelfal source area after a major entrainment event. About 30% of the sediment consisted of sma ll pellets. Mud in pellets has similar texture, clay minerals and orga nic/inorganic carbon content as dispersed mud. Particle sizes <16 mum dominate, sand is less than 1%, compared to as much as 8% in four samp les obtained in 1971 and 1972. Organic carbon content is about 2%, ill ite dominates clay minerals (approximately 50%), and diatoms suggest a shelf sediment source. From the prevalence of wind-reworked surficial deposits, the spotty occurrence of only small patches of turbid ice i n old clean ice, and the virtual lack of sand-size material, we assume the sediment had drifted at least 2 years since entrainment and was d istant from its source. Assuming one-third of the load is released eac h year, the estimated deposition rate would equal the measured Holocen e rate (approximately 2 cm 1000 year-1). Therefore, modern sea-ice raf ting represents a substantial fraction of the total Arctic Ocean sedim ent budget.