Ecological implications of decreasing sea ice thickness in the Arctic Ocean

Abstract

Ice algae under the sea ice provide an additional food source to herbivores in the Arctic Ocean as well as in the Antarctic Ocean. Currently, climate changes in the Arctic have been changing at a very rapid rate. These changes might alter the relative contributions of sea ice algae and phytoplankton. However, there have been few recent studies of ice algae ecology in the Arctic Ocean. In situ carbon and nitrogen uptakes of phytoplankton and ice algae under the ice were measured in landfast sea ice of Barrow, Alaska by using both 13C tracer and 13C-15N dual tracer techniques. The ice algal total production contributed 80 % of total primary production under nearshore land fast ice in 2003 before the phytoplankton bloom. The light and nutrient enrichment experiments showed that the production of bottom sea ice algae and phytoplankton at Barrow in 2003 was limited mainly by light which is about 0.3 % of the surface irradiance under the snow-covered sea ice. Larger amount of lipid synthesis of ice algae at higher light intensity and at the end of season might be significant to the higher trophic levels in the ecosystem. Based on the experiments at Barrow, the decreases of sea ice extent and ice thickness in the Arctic Ocean suggest changes in timing, amount, and macromolecule composition of primary production and consequently change in nutritional status of higher trophic levels.