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Paulsen, ML, Seuthe L, Reigstad M, Larsen A, Cape MR, Vernet M.  2018.  Asynchronous accumulation of organic carbon and nitrogen in the Atlantic gateway to the Arctic Ocean. Frontiers in Marine Science. 5   10.3389/fmars.2018.00416   AbstractWebsite

Nitrogen (N) is the main limiting nutrient for biological production in the Arctic Ocean. While dissolved inorganic N (DIN) is well studied, the substantial pool of N bound in organic matter (OM) and its bioavailability in the system is rarely considered. Covering a full annual cycle, we here follow N and carbon (C) content in particulate (P) and dissolved (D) OM within the Atlantic water inflow to the Arctic Ocean. While particulate organic carbon (POC), particulate organic nitrogen (PON), and dissolved organic carbon (DOC) accumulated in the surface waters from January to May, the dissolved organic nitrogen (DON)-pool decreased substantially (Delta - 50 mu g N L-1). The DON reduction was greater than the simultaneous reduction in DIN (Delta - 30 mu g N L-1), demonstrating that DON is a valuable N-source supporting the growing biomass. While the accumulating POM had a C/N ratio close to Redfield, the asynchronous accumulation of C and N in the dissolved pool resulted in a drastic increase in the C/N ratio of dissolved organic molecules (DOM) during the spring bloom. This is likely due to a combination of the reduction in DON, and a high release of carbon-rich sugars from phytoplankton, as 32% of the spring primary production (PP) was dissolved. Our findings thus caution calculations of particulate PP from DIN drawdown. During post-bloom the DON pool increased threefold due to an enhanced microbial processing of OM and reduced phytoplankton production. The light absorption spectra of DOM revealed high absorption within the UV range during spring bloom indicating DOM with low molecular weight in this period. The absorption of DOM was generally lower in the winter months than in spring and summer. Our results demonstrate that the change in ecosystem function (i.e., phytoplankton species and activity, bacterial activity and grazing) in different seasons is associated with strong changes in the C/N ratios and optical character of DOM and underpin the essential role of DON for the production cycle in the Arctic.

Wassmann, P, Ratkova T, Andreassen I, Vernet M, Pedersen C, Rey F.  1999.  Spring bloom development in the marginal ice zone and the central Barents Sea. Marine Ecology-Pubblicazioni Della Stazione Zoologica Di Napoli I. 20:321-346.   10.1046/j.1439-0485.1999.2034081.x   AbstractWebsite

The knowledge of the relative contribution of algal groups and the environmental factors that control their abundance in the marginal ice zone of the Parents Sea is rather limited. Therefore, a field investigation to study the hydrography and the phytoplankton composition of the marginal ice zone (M1Z) in the central Parents Sea was carried out along a south-north transect in May 1993. The weakly stratified Atlantic sector of the transect appeared to be in a prebloom state and had intermittent intrusions from the meandering Polar Front and the Norwegian Coastal Current, introducing water of a more advanced bloom state. Pico- and nanoplankton flagellates and monads dominated, with a few diatoms and Phaeocystis pouchetii colonies. The average new production rate of 26 g C.m(-2) as reflected by NO, depletion in the euphotic zone, however, indicated that the vernal bloom had been in progress for some time in the Atlantic sector without leaving specific signals in the suspended fraction. The ice-edge and Polar Front area was characterized by a dominance of centric colonial diatom genera Chaetoceros and Thalassiosira with some development of P. pouchetii. In the densely ice-covered and stratified Arctic zone the vernal bloom was at its maximum and dominated by the diatom genera Fragilariopsis and Chaetoceros. Diatoms were limited by silicate concentrations <2 mu M in 32% of all samples. New production, as revealed by the C equivalent of nitrate depletion in the upper layer, ranged between 12 g C m(-2) in the north to 45 g C.m(-2) in the meandering Polar Front, with an average of about 27 +/- 28% g C.m(-2). The time development of the vernal bloom in the marginal ice zone and the central Parents Sea in late May 1993, with its complicated zonal structure, was not from south to north, but intermittently from north to south. Later during the year the general development of the vernal bloom was, as expected, from south to north.