Size-fractionated chlorophyll a and primary productivity in the Chukchi Sea and its northern Chukchi Plateau

Investigations on chlorophyll a and primary productivity were carried out in the Chukchi Sea and its northern Chukchi Plateau during the 2nd Chinese National Arctic Research Expedition in the summer of 2003. The results showed that chlorophyll a concentrations were 0.009–30.390 μg/dm3 at the surveyed waters; the surface chlorophyll a concentrations were 0.050–4.644 μg/dm3 and the average value was (0.875±0.981) μg/dm3 in the surveyed area. In the Chukchi Sea Shelf, chlorophyll a concentrations at the depth from 10 m to bottom were higher than that in the surface water, and the concentrations were lower at the depth below 75 m in the Chukchi Plateau. Chlorophyll a concentrations descended in 3 sequential samplings on Transect R, with average values of (2.564±1.496) μg/dm3, (1.329±0.882) μg/dm3 and (0.965±0.623) μg/dm3, respectively. The potential primary productivity ((2.305± 1.493) mgC/(m3·h)) in the Chukchi Sea was higher than that ((0.527±0.374) mgC/(m3·h)) in the Chukchi Plateau. The results of the size-fractionated chlorophyll a and primary productivity showed that microplankton accounted for the majority of the total chlorophyll a (63.13%) and primary productivity (65.16%) at the survey stations. The contributions of the nanoplankton and picoplankton to the total chlorophyll a and primary productivity were roughly the same.