Ice algae production processes in the coastal fast ice in the western Arctic Ocean

Abstract

To investigate ice algae production processes and its related carbon flux, is important and urgent research subject in the Arctic Ocean. Because there is very little understanding regarding to the effect of recent Arctic climate changes on the sea-ice algae production and its contribution to the ecosystem and carbon cycle in the Arctic Ocean. During the last two spring seasons in 2001-2001, time series sea-ice observations and in situ ice algae incubation experiments were conducted off Pt Barrow in the northern Alaska. There are three objectives in this study as follows ; 1) to clarify ice algae production processes in the coastal fast ice, 2) to evaluate ice algae contribution to carbon cycle in the Arctic, 3) to provide the data for the Arctic biogeochemical model related to climate change. Chl.a and POC concentrations were extremely high in the bottom layer of sea-ice with the development of brown colouration depending on light availability. The Chl. a concentration in the bottom ice algal layer (bottom 10cm) was the highest in early May in 2001-2002, showing the large annual variation which might be attributed to the development of ice thickness. The stable isotope ratio (δ13C) of POC indicates that terrestrial organic matter may be the main source of POC in the entire ice core except bottom 10cm, exhibiting comparatively lighter isotopic values. The δ13C ratios of POC were heavier in the bottom 10cm (reflecting ice algae origin) in June. POC production rate was larger in May rather than in June 2001, indicating faster POC turnover rate in May. In particular, particulate fatty acids turnover rate was remarkably faster, resulting from their large production and consumption rates. Additionally, as an indicator for ecophysiological state of marine diatoms population, C16-PUFA index (a measure of the percentage of C16 fatty acids that are polyunsaturated) suggests ice algae population was in a nutrient-limited condition. Comparing Chl. a concentrations in the bottom 10cm of ice algal biomass between 2001 and 2002, Chl. a concentration on April 3, 2002 was approximately fold higher than on April 5, 2001, and the maximum Chl. a concentration was around 2 fold larger on May 1, 2002 than on May 5, 2001. This observation result reveals that ice algal biomass have a large annual variation between 2001 and 2002. However, the variability of ice algal biomass may be affected by the environmental conditions such as ice thickness, cloudiness and nutrients supply and physical events. Therefore, more through investigation should be necessary to understand the ice algal biomass variability.