Phytoplankton biomass, production and potential export in the North Water

The seasonal patterns of phytoplankton biomass and production were determined in the North Water, located between Greenland and Ellesmere Island (Canadian Arctic), in August 1997, April-July 1998, and August-September 1999. The patterns differed among the four defined regions of this large polynya, i.e. North (> 77.5°N), East (> 75°W), West (< 75°W), and South (<76°N). Phytoplankton biomass and production were low during April throughout the North Water. Biomass first increased in the East during April. From there, the biomass spread north- and westwards during May-June, when the bloom culminated (chlorophyll a concentrations up to 19.8 mg m^-3). The large-sized (> 5 μm) fraction dominated the biomass and production during the bloom. During July, August, and September, biomass and production decreased over the whole region, with the highest biomass, dominated by large cells, occurring in the North. The annual particulate and dissolved phytoplankton production were the highest ever reported for the high Arctic, reaching maximum values of 254 and 123 g C m ^-2 yr^-1, respectively, in the East. Rates in the North and West were considerably lower than in the East (ca. two- and three-fold, respectively). The f-ratios (i.e. ratio of new to total production), derived from the size structure of phytoplankton, were high north of 76°N (0.4-0.7). Regionally, this indicated a high potential export of particulate organic carbon (E_poc) from the phytoplankton community to other trophic compartments and/or downwards in the East (155 g C m^-2 yr^-1), with lower values in the North and West (i.e. 77 and 42 g C m^-2 yr^-1, respectively). The seasonal and spatial patterns of E_poc were consistent with independent estimates of potential carbon export. Phytoplankton biomass and production were generally dominated by the large size fraction, whereas E_poc seemed to be dominated by the large size fraction early in the season and by the small size fraction (< 5 μm) from June until the end of the growing season.