Pan-Arctic Ocean Primary Production Constrained by Turbulent Nitrate Fluxes

Arctic Ocean primary productivity is limited by light and inorganic nutrients. With sea ice cover declining in recent decades, nitrate limitation has been speculated to become more prominent. Although much has been learned about nitrate supply from general patterns of ocean circulation and water column stability, a quantitative analysis requires dedicated turbulence measurements that have only started to accumulate in the last dozen years. Here we present new observations of the turbulent vertical nitrate flux in the Laptev Sea, Baffin Bay, and Young Sound (North-East Greenland), supplementing a compilation of 13 published estimates throughout the Arctic Ocean. Combining all flux estimates with a Pan-Arctic database of in situ measurements of nitrate concentration and density, we found the annual nitrate inventory to be largely determined by the strength of stratification and by bathymetry. Nitrate fluxes explained the observed regional patterns and magnitudes of both new primary production and particle export on annual scales. We argue that with few regional exceptions, vertical turbulent nitrate fluxes can be a reliable proxy of Arctic primary production accessible through autonomous and large-scale measurements. They may also provide a framework to assess nutrient limitation scenarios based on clear energetic and mass budget constraints resulting from turbulent mixing and freshwater flows

Bio-optical input parameters.

<p>Chlorophyll <i>a</i> (chl <i>a</i>) concentrations (mean ± S.D.), chl <i>a</i>-specific absorption coefficient (a*), ratio of absorbed quanta in PSII (a*_PSII:<i>a</i>*), spectrally weighted absorption coefficients (</p><p></p><p></p><p></p><p><mi>a</mi></p><mo>¯</mo><p></p><mi>*</mi><p></p><p></p>), and the PSII-specific weighted absorption coefficient (<p></p><p></p><p></p><p><mi>a</mi></p><mo>¯</mo><p></p><mi>*</mi><p></p><p></p>_PSII) for the incubated samples and applied incubators (i.e. the water bath incubator and internal cuvette of the PAM instrument).<p></p><p>^a High Light</p><p>^b Low Light</p><p>Bio-optical input parameters.</p

Climate change effects on Arctic fjord and coastal macrobenthic diversity-observations and predictions

Abstract The pattern of occurrence and recent changes in the distribution of macrobenthic organisms in fjordic and coastal (nearshore) Arctic waters are reviewed and future changes are hypothesized. The biodiversity patterns observed are demonstrated to be contextual, depending on the specific region of the Arctic or habitat type. Two major areas of biotic advection are indicated (the North Atlantic Current along Scandinavia to Svalbard and the Bering Strait area) where larvae and adult animals are transported from the species-rich sub-Arctic areas to species-poor Arctic areas. In those Arctic areas, increased temperature associated with increased advection in recent decades brings more boreal-subarctic species, increasing the local biodiversity when local cold-water species may be suppressed. Two other large coastal areas are little influenced by advected waters; the Siberian shores and the coasts of the Canadian Archipelago. There, local Arctic fauna are exposed to increasing ocean temperature, decreasing salinity and a reduction in ice cover with unpredictable effect for biodiversity. One the one hand, benthic species in Arctic fjords are exposed to increased siltation (from glacial meltwater) and salinity decreases, which together may lead to habitat homogenization and a subsequent decrease in biodiversity. On the other hand, the innermost basins of Arctic fjords are able to maintain pockets of very cold, dense, saline water and thus may act as refugia for coldwater species

Biological transformation of Arctic dissolved organic matter in a NE Greenland fjord

Arctic waters are often enriched with terrestrial dissolved organic matter (DOM) characterized by having elevated visible wavelength fluorescence (commonly termed humic-like). Here, we have identified the sources of fluorescent DOM (FDOM) in a high Arctic fjord (Young Sound, NE Greenland) influenced by glacial meltwater. The biological transformation of FDOM was further investigated using plankton community size-fractionation experiments. The intensity of ultraviolet fluorescence (commonly termed amino acid-like) was highly variable and positively correlated to bacterial production and mesozooplankton grazing. The overall distribution of visible FDOM in the fjord was hydrographically driven by the high-signal intrusion of Arctic terrestrial DOM from shelf waters and dilution with glacial runoff in the surface waters. However, the high-intensity visible FDOM that accumulated in subsurface waters in summer was not solely linked to allochthonous sources. Our data indicate that microbial activity, in particular, protist bacterivory, to be a source. A decrease in visible FDOM in subsurface waters was concurrent with an increase in bacterial abundance, indicating an active bacterial uptake or modification of this DOM fraction. This was confirmed by net-loss of visible FDOM in experiments during summer when bacterial activity was high. The degradation of visible FDOM appeared to be associated with bacteria belonging to the order Alteromonadales mainly the genus Glaciecola and the SAR92 clade. The findings provide new insight into the character of Arctic terrestrial DOM and the biological production and degradation of both visible and UV wavelength organic matter in the coastal Arctic

Variability in phytoplankton absorption spectra, incubator light quality and spectrally-weighted absorption.

<p>A) Chl <i>a</i>-specific in vivo absorption spectra [<i>a</i>*(λ)] at sampled stations and depths, B) spectral irradiance of the incubator light sources [E(λ)], and C) the spectrally-weighted chl <i>a</i>-specific absorption of phytoplankton at GF7 (5m), corrected for E(λ) in the water bath (green) and for the internal light source of the PhytoPAM (blue). Integrated values for <i>a</i>* and </p><p></p><p></p><p></p><p><mi>a</mi></p><mo>¯</mo><p></p><mi>*</mi><p></p><p></p> are given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133275#pone.0133275.t002" target="_blank">Table 2</a>.<p></p