Description: Transparent exopolymer particles (TEP) are a class of marine gel particles and important links between surface ocean biology and atmospheric processes. Derived from marine microorganisms, these particles can facilitate the biological pumping of carbon dioxide to the deep sea, or act as cloud condensation and ice nucleation particles in the atmosphere. Yet, environmental controls on TEP abundance in the ocean are poorly known. Here, we investigated some of these controls during the first multiyear time-series on TEP abundance for the Fram Strait, the Atlantic gateway to the Central Arctic Ocean. Data collected at the Long-Term Ecological Research observatory HAUSGARTEN during 2009 to 2014 indicate a strong biological control with highest abundance co-occurring with the prymnesiophyte Phaeocystis pouchetii. Higher occurrence of P. pouchetii in the Arctic Ocean has previously been related to northward advection of warmer Atlantic waters, which is expected to increase in the future. Our study highlights the role of plankton key species in driving climate relevant processes; thus, changes in plankton distribution need to be accounted for when estimating the ocean’s biogeochemical response to global change.

Description: Freshwater and sea ice in the Arctic Ocean (AO) both respond to climate forcing but changes in their distribution may in turn also significantly affect Northern Hemisphere climate. The exact mechanisms controlling their transport are, however, still subject of ongoing research. Radiogenic neodymium (Nd) isotopes (expressed as eNd) and rare earth elements (REEs) have successfully been used to trace ocean circulation in the AO and can provide valuable information on the origin, transport and fate of Arctic freshwater and drifting sea ice. Here, we present first sea-ice data and discuss the applicability of these tracers to determine the pathways of Siberian freshwater and the source areas of Arctic sea ice within the Eurasian Basin. Freshwaters originating from various Siberian rivers are well mixed and diluted prior to their advection to the central AO and the Fram Strait, thereby inhibiting the assessment of the individual contributions of the different rivers for these regions. Recent investigations of seawater Nd isotope and REE distributions on the Siberian shelves now allow for a more detailed determination of the sources of transpolar freshwater transport, and suggest that freshwater from the Lena River can at least be qualitatively traced further away from the shelves. In addition, sea ice has the potential to preserve marine and riverine eNd and REE signatures of the Siberian shelf source waters transported across the AO to the Fram Strait thereby avoiding the effects of mixing. Here, we test this potential for the first time by comparing eNd and REE signatures determined from unfiltered but essentially sediment-free sea-ice samples recovered in the Eurasian Basin of the central AO in 2012 with corresponding signatures of surface seawater in the formation regions of the ice. The sampled sea ice is dominantly characterized by ?Nd values near -8, in agreement with the incorporation of radiogenic freshwater (eNd=-6) from the Yenisei and Ob rivers and its formation east of Vilkitsky Strait as identified by a backtracking approach based on satellite-derived ice drift and concentration data. The latter also indicates that sea ice with a less radiogenic eNd signature near -11 formed north of the Laptev Sea, in agreement with mixed contributions of radiogenic waters from the Kara Sea and northward flowing highly unradiogenic Lena River water (eNd〈=-15). Compared to the REE concentrations in Siberian shelf waters, those in the sea ice are depleted, indicating rejection of REEs together with salt during sea-ice formation. Despite potential modifications during incorporation into sea ice, its REE distribution patterns indicate a predictable relationship to those of the source waters, thus in addition supporting preservation of at least some of the marine and riverine REE characteristics during sea-ice formation and transport.

Description: We derive the chlorophyll a concentration (Chla)for three main phytoplankton functional types (PFTs)-- diatoms, coccolithophores and cyanobacteria- by combining satellite multispectral-based information, being of a high spatial and temporal resolution, with retrievals based on high resolution of PFT absorption properties derived from hyperspectral measurements. The multispectral-based PFT Chla retrievals are based on a revised version of the empirical OC-PFT algorithm (Hirata et al. 2011) applied to the Ocean Colour Climate Change Initiative (OC-CCI) total Chla product. The PhytoDOAS analytical algorithm (Bracher et al. 2009, Sadeghi et al. 2012) is used with some modifications to derive PFT Chla from SCIAMACHY hyperspectral measurements. To combine synergistically these two PFT products (OC-PFT and PhytoDOAS), an optimal interpolation is performed for each PFT in every OC-PFT sub-pixel within a PhytoDOAS pixel, given its Chla and its a priori error statistics. The synergistic product (SynSenPFT) is presented for the period of August 2002 ? March 2012 and evaluated against in situ HPLC pigment data and satellite information on phytoplankton size classes (PSC) (Brewin et al. 2010, Brewin et al. 2015) and the size fraction (Sf) by Ciotti and Bricaud (2006. The most challenging aspects of the SynSenPFT algorithm implementation are discussed. Perspectives on SynSenPFT product improvements and prolongation of the time series over the next decades by adaptation to Sentinel multi- and hyperspectral instruments are highlighted.