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Fram Strait sea-ice sediment provinces based on silt and clay compositions identify Siberian Kara and Laptev seas as main source regions


Dirk Dethleff, Institute for Polar Ecology, University of Kiel, Wischhofstraße 1-3, DE-24148, Kiel, Germany. E-mail:


Fram Strait sea-ice sediments (SIS) contain on average more than 94% silt and clay. Both fractions were compared with bottom deposits of the Kara and Laptev seas to identify shelf sources of fine-grained Arctic SIS. Based on silt granulometry and clay mineral assemblages we determined Fram Strait SIS provinces. Western Fram Strait SIS has medium to fine silt compositions, whereas eastern Fram Strait SIS is enriched in fine silt. Western Fram Strait SIS clays (low smectite/high illite) were statistically grouped with eastern Laptev shelf deposits, and are similar to East Siberian and North American shelf sources. Eastern Fram Strait SIS clays (high smectite/low illite) cluster with shelf deposits of the western Laptev Sea and the Kara Sea. We conclude that western Fram Strait pack ice consisted of a mixture of floes from the Laptev Sea and sources farther to the east during the 1997 and 1999 sampling periods. Eastern Fram Strait ice originated from sources towards the Kara Sea. There was an average annual flux of ca. 158 Tg (Mt) SIS export through Fram Strait during the late 1990s. We expect no qualitative changes in the SIS entrainment process (“suspension freezing”) with decreasing Arctic ice cover, although the process may increase through larger fetch. SIS incorporation and flux will be enhanced with increasing shelf open water during winter freezing, and with the current acceleration of the Transpolar Drift, but we speculate that the transport of SIS towards Fram Strait will be seasonally truncated with the onset of ice-free summers in the Arctic Ocean.