New measurements of phytoplankton and ice algal production in the Arctic Ocean

Abstract

During the Canada/U.S. 1994 Arctic Ocean Section, algal biomass (Chlorophyll a) and primary production were measured in the water column, at the ice-water interface and in the bottom 2–4 cm of the sea ice along a transect from the Chukchi Sea to the Nansen Basin via the North Pole. Algal biomass and primary production were determined for 0.7–5 μm and > 5 μm size fractions. The algal release rate of DO14C during incubation was also measured. In the Chukchi Sea and in leads of the Makarov and Nansen Basins, total maximum particulate phytoplankton production rates were 2570, 73 and 521 mg C m−2 day −1, respectively. At these stations, where ice cover varied from 55 to 90%, large phytoplankton (> 5 μm) represented 61–98% of the total algal biomass. At stations with higher ice coverage (>90%), the total phytoplankton production decreased to 9–57 mg C m−2 day −1. At these stations, small phytoplankton (0.7–5 μm) accounted for 59–88% of the total biomass and more than 64% of the total production. Along the transect, the percentage of the total phytoplankton production released as extracellular carbon was generally less than 20%, except in the Canadian Basin where it ranged from 31 to 65%. Total particulate ice algal production ranged from 0.5 to 310 mg C mt-2 day−1 and showed maximum rates in the central Arctic Ocean. Large cells (> 5 μm) generally dominated the ice algal community, representing 50–100% of the total biomass and more than 50% of the total production. Ice algae released on average 34% of total carbon fixed during the 4–12 h incubation. Ice algae contributed on average 57% of the entire primary production (water column + sea ice) in the central Arctic and 3% in the surrounding regions. Total primary productivity in the central Arctic Ocean is estimated at 15 g C m−2 year−1, a value at least 10 times higher than previously reported. The difference between estimates is due in part to the previously unmeasured contribution of the particulate production by ice algae and the release of DOC by both ice and pelagic algae.