Recent carbon and nitrogen uptake rates of phytoplankton in the Bering, Chukchi, and Beaufort seas

Abstract

Ongoing changes in climate and ice conditions are expected to alter the carbon and nitrogen uptake rates of phytoplankton as primary producers in the Arctic Ocean. However, a few in situ measurements, especially on the sea ice, have been currently done in the Bering, Chukchi, and Beaufort seas. Recently, we found that carbon and nitrogen production rates of phytoplankton in the Chukchi Sea were 2 or 3 fold lower than those from previous studies. We suggest that the lower rates in this study, and consequently more unused nitrate in the water column, were caused by lower phytoplankton biomass in Bering Strait and the Chukchi Sea. However, we do not know if the lower rate of production from this study is a general decreasing trend or simply temporal variations in the Chukchi Sea, since temporal and geographical variations are substantially large and presently unpredictable. In contrast, based on in situ incubations on the sea ice in the deep Canada Basin, the mean annual carbon production rate of phytoplankton under the mean 1.5-m sea ice in 2005 was significantly higher than that of phytoplankton under the mean 2.3-m sea ice in 2002. The higher carbon uptake rate in 2005 is believed to be resulted from higher light intensity through the thinner sea ice available to phytoplankton under the sea ice. These in situ measurements in the regions during the recent periods will allow us to provide valuable data for the calibration of ocean color images and ecological models and form a backbone for any future discussion of impacts of global warming and sea ice changes on the primary productivity in the regions.