Diatom assemblages in Arctic sea ice—indicator for ice drift pathways

During R.V. Polarstern expeditions ARK IV/3 and ARK VI/1, well preserved diatom assemblages were recovered from particle-laden sea ice collected from the western Barents Shelf and the Arctic Ocean between Svalbard (81°N) and the Nansen-Gakkel Ridge (86°N). Distinct variations in the abundance pattern and species composition of diatoms were found north and south of ca 83°N. Highest diatom concentrations were encountered in multi-year sea ice in the core of the Transpolar Drift Stream between 83 and 86°N. In this area diatom assemblages are dominated by marine-?brackish benthic species. Apparently, these assemblages originate in shelf waters north and east of Siberia, where they are incorporated into the sea ice as a bottom ice assemblage. During the transport of the ice floes across the Eurasian Basin within the Transpolar Drift Stream, seasonal basal freezing and surface melting processes may have led to an accumulation of diatoms at the sea ice surface. South of ca 83°N the sea ice samples contained significantly lower numbers of diatoms, dominated by freshwater taxa. Between 83 and 81°N these assemblages are dominated by planktonic freshwater taxa, but on the Barents Sea Shelf east of Svalbard significant numbers of benthic freshwater taxa and benthic marine-?brackish species also are found. This ice may originate in the Barents Sea and/or the Kara Sea, which receive a large influx of freshwater from Siberian rivers.