In order to understand the mechanisms responsible for the high productivity and biogeochemical cycling of carbon in the North Water Polynya (NOW), we determined physical properties and nutrient concentrations of the upper water column, and phytoplankton production, during spring/summer (April to July) 1998. Phytoplankton production of total organic carbon (P-TOC) was partitioned into production of dissolved and particulate organic carbon (P-DOC and P-POC, respectively), the latter being further partitioned into production of large and small phytoplankton (P-L and P-S, respectively) using 5 mum as threshold. The highest P-TOC was 6 g C m(-2) d(-1) at peak bloom. The fraction of P-DOC in P-TOC was lower in periods of high P-TOC than those of low P-TOC. Averaged over the whole polynya for the sampling period, P-DOC and P-POC accounted for 34 and 66% of the fixed carbon, respectively, and 81 and 19% of P-POC were in the P-L and P-S fractions, respectively. Variations in the integrated assimilation numbers of large and small phytoplankton were mostly explained by nutrients and irradiance. Even though P-POC was dominated by large phytoplankton, the sinking rates of the phytoplankton cells were relatively low (0 to 0.7 m d-1), hence low export of P-POC to depth (17%), and relatively high potential transfer to large pelagic organisms through the herbivorous food web. This explains why the NOW is a major feeding and spawning area for fish, mammals and birds.

As part of the first investigation of the North Water region of Baffin Bay to specifically examine carbon cycling in this unique and highly productive area, we found that the distributions of carbon within these waters were controlled by a complex system of transport and biological processes. We systematically collected samples throughout the North Water during April–July 1998 and August–September 1999 and analyzed them for total dissolved inorganic carbon (DIC), alkalinity, dissolved organic carbon, and total suspended particulate carbon. Consistent with biogenic drawdown, surface DIC concentrations dropped by as much as 250μmolkg−1 during the summer and began to increase again by the end of September. Although the surface waters were supersaturated with carbon dioxide in early spring, extensive ice cover limited CO2 outgassing at that time. As the ice cleared, decreasing surface DIC concentrations supported significant fluxes of CO2 into the ocean. In late September and early October, when ice again was beginning to cover the area, the surface waters were still undersaturated in CO2, implying that the North Water could be a net sink of atmospheric carbon, if winter air–sea fluxes are minimal. There is strong evidence that horizontal advection plays an important role in controlling DIC distributions, although we were unable to independently quantify the advective fluxes. Based on the observed changes in total carbon concentrations and estimates of air–sea fluxes, we found that carbon was lost from the surface waters between April 1998 and October 1999, probably due to both biological and advective export.

A 4-month multidisciplinary expedition, beginning at the end of winter to track the spring phytoplankton bloom to its termination in summer, was conducted from April to July 1998. The aim of the expedition was to investigate possible mechanisms responsible for the high biological productivity of the North Water, the most productive and largest polynya in the Northern Hemisphere. The aims of the present study were to investigate: (1) the effects of the physical forces, driving the formation of the polynya, on the dynamics of the phytoplankton stock in the polynya over the spring–summer period; and (2) the factors that limit the maximum biomass of phytoplankton. Contrasting physical characteristics, including ice concentration, surface mixed-layer depth (MLD), salinity and temperature in the surface mixed layer (SML), were observed between the east and west sides of the polynya. The Greenland (eastern) side of the polynya was characterized by a shallow SML, warm temperature, and high salinity relative to the Ellesmere Island, Canada (western) side. Chlorophyll a (Chl)>1 mg m−3 was observed in late April on the eastern side, and in late May on the western side. The peak phytoplankton bloom occurred in the southeastern part of the polynya, with average Chl of 15 mg m−3 (240–300 mg m−2) in the euphotic zone during the end of May and beginning of June. The increased phytoplankton biomass was associated with higher salinity and warmer temperature on the eastern side of the polynya. Low temperature in April and May decoupled the increase of Chl biomass from the shallowed SML, as predicted by Sverdrup's model. As Chl in the euphotic zone increased to 5 mg m−3, the proportion of light absorption by phytoplankton could not increase further with Chl biomass, which might have limited the increase of primary production in the water column. Although the initial nutrient inventories largely determined the maximum biomass of phytoplankton, self-shading occurred in the build-up phytoplankton biomass to ∼5 mg m−3, which retarded the timing of the peak bloom. Both sensible heat due to deep warm water entrainment into the SML and the biological heating effect via phytoplankton light absorption appear to contribute to the pattern of phytoplankton distribution 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 (EPOC) 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 EPOC were consistent with independent estimates of potential carbon export. Phytoplankton biomass and production were generally dominated by the large size fraction, whereas EPOC 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.

Temperature, salinity, and in vivo fluorescence of surface seawater in the North Water were recorded continuously, using a CTD+fluorometer, in August 1997, April–July 1998 and August–October 1999. The phytoplankton bloom started in the polynya on the Greenland side in April. In April and May, high phytoplankton biomass coincided with saline water on the Greenland side, while biomass was low on the Ellesmere Island (Canada) side where a deep mixed layer prevailed. High phytoplankton biomass extended over the whole polynya in June, when surface temperature increased due to solar heating and salinity decreased due to freshwater input. The initiation of the bloom was about 2 months earlier on the Greenland than the Canadian side. In July and August, phytoplankton biomass became low in the southern survey area, indicating that the phytoplankton bloom had ended. In September, relatively saline and warm water occurred in the southeastern part of the study area where, consistent with the change in water properties, high concentrations of chlorophyll a were observed again. These results imply that both the earlier start of the algal bloom in spring and the eventual increase in phytoplankton biomass in summer contribute to the high annual primary production along the Greenland side, thus influencing the structure and biological productivity of the entire North Water ecosystem.

Algal blooms sporadically occur in atoll lagoons of the Tuamotu Archipelago (French Polynesia). The present study was conducted in the lagoon of Takapoto Atoll to investigate the roles of N, P and Fe in controlling the biomass and production of algae. Addition of P alone had no significant effect on phytoplankton. The NP enrichments resulted in the highest increases of <3 and >3 mu m chlorophyll a (chl a), algal carbon production, algal abundance (especially the pennate diatom Proboscia alata), and protozoan carbon production. Addition of N alone also enhanced chi a and algal carbon production, but was less effective than when N was combined with P. Dinoflagellates, which were dominated by Gymnodinium spp,, showed the greatest response to the +N treatment. In one experiment, Fe addition (with EDTA) significantly enhanced chi a in the >3 mu m size fraction, and the net rates of algal and protozoan carbon production. The +Fe treatment especially enhanced the abundance of the coccolithophore Acanthoica sp. These results indicate that N followed by P Limited the biomass and production of small and large algae, and that Fe may have been at times in short supply and limited the large algae. A sudden supply of these nutrients to the lagoon, by natural phenomena, may trigger a phyloplankton outburst and change the taxonomic composition of the algal community. Production and grazing of protozoa may have been indirectly regulated by the availability of N, P and Fe, since the quantity of their algal food was controlled by these nutrients.

Sampling was conducted in the Northwater Polynya (between 70°20′ and 77°20′N), on 17 and 19 May 1991. At each of the 14 sampling stations, CTD profiles were recorded from surface to bottom and nutrients and phytoplankton were determined at four depths down to 30 m. The presence, between 220 and 400 m, of water temperatures >0°C is an indication that, in winter, the West Greenland Current enters the Northwater along the Greenland coast. The warm water is progressively mixed as it moves northward and eastward. It was thus hypothesized that sensible heat is as an important factor in keeping the Northwater open. Measured chemical and biological variables were quite homogeneous on the vertical down to 30 m and they showed longitudinal gradients. From east to west, the average concentrations of nutrients increased (phosphate from 0.5 to 1.4, nitrate from 3.7 to 10.8, and silicate from 6.8 to 34.2 mmol m−3), whereas the areal concentrations of phytoplankton decreased (from 47 to 9 x 109 cells m−2 and from 506 to 50 mg Chla m−2). Nutrient ratios indicated possible silicon deficiency in the easternmost part of the polynya. Diatoms dominated cell numbers (≥87% at all stations). Concentrations of the three nutrients were inversely correlated with both Chla and cell numbers. The Y-intercepts of regressions of Chla on nutrients provided an estimate of potential maximum biomass in the upper 30 m, which was ca. 600 mg Chla m−2, or lower if there was silicon limitation. The overall picture was that of a diatom bloom, moving westward and progressively exhausting the nutrients. Initiation of the bloom appeared to have been linked to the absence of sea ice. A source of heat for this would have been the above sensible-heat process.