Chlorophyll a distribution in water column and sea-ice during the Laptev Sea freeze-up study in autumn 1995

During the Transdrift III expedition to the Laptev Sea in October 1995, samples were taken from the water column as well as various types of newly formed sea ice and analysed for Chlorophyll a (Chi a) as indicator of algal biomass. Ice samples included grease ice, nilas and cores from young ice (≤25 cm). The phytoplankton biomass in the water column (water depth 14 m to 40 m) as expressed by integrated Chi a values ranged between 2.3 mg m-2 north of the Lena Delta and 15.9 mg m-2 in a polynya at Buor Khaya Bay southeast of Tiksi. Pigment concentrations in the ice samples varied considerably (0.3 to 2.36 mg m-3 in grease ice and 0.2 to 14.6 mg m-3 in nilas, respectively). However, the Chi a content increased as soon as ice floes were formed from grease ice or pancake ice. Greenish slush ice and overlying water flooding the ice near cracks showed low pigment concentrations, indicating that the colouring was not caused by algae.