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  • 1. Anderson, Leif G.
    et al.
    Bjork, Goran
    Holby, Ola
    Jutterstrom, Sara
    Morth, Carl Magnus
    O’Regan, Matt
    Pearce, Christof
    Semiletov, Igor
    Stranne, Christian
    Stoven, Tim
    Tanhua, Toste
    Ulfsbo, Adam
    Jakobsson, Martin
    Shelf-Basin interaction along the East Siberian Sea2017In: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 13, no 2, p. 349-363Article in journal (Refereed)
    Abstract [en]

    Extensive biogeochemical transformation of organic matter takes place in the shallow continental shelf seas of Siberia. This, in combination with brine production from sea-ice formation, results in cold bottom waters with relatively high salinity and nutrient concentrations, as well as low oxygen and pH levels. Data from the SWERUS-C3 expedition with icebreaker Oden, from July to September 2014, show the distribution of such nutrient-rich, cold bottom waters along the continental margin from about 140 to 180 degrees E. The water with maximum nutrient concentration, classically named the upper halocline, is absent over the Lomonosov Ridge at 140 degrees E, while it appears in the Makarov Basin at 150 degrees E and intensifies further eastwards. At the intercept between the Mendeleev Ridge and the East Siberian continental shelf slope, the nutrient maximum is still intense, but distributed across a larger depth interval. The nutrient-rich water is found here at salinities of up to similar to 34.5, i.e. in the water classically named lower halocline. East of 170 degrees E transient tracers show significantly less ventilated waters below about 150 m water depth. This likely results from a local isolation of waters over the Chukchi Abyssal Plain as the boundary current from the west is steered away from this area by the bathymetry of the Mendeleev Ridge. The water with salinities of similar to 34.5 has high nutrients and low oxygen concentrations as well as low pH, typically indicating decay of organic matter. A deficit in nitrate relative to phosphate suggests that this process partly occurs under hypoxia. We conclude that the high nutrient water with salinity similar to 34.5 are formed on the shelf slope in the Mendeleev Ridge region from interior basin water that is trapped for enough time to attain its signature through interaction with the sediment.

  • 2. Gao, Q.
    et al.
    Leck, C.
    Rauschenberg, C.
    Matrai, P. A.
    On the chemical dynamics of extracellular polysaccharides in the high Arctic surface microlayer2012In: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 8, no 4, p. 401-418Article in journal (Refereed)
    Abstract [en]

    The surface microlayer (SML) represents a unique system of which the physicochemical characteristics may differ from those of the underlying subsurface seawater (SSW). Within the Arctic pack ice area, the SML has been characterized as enriched in small colloids of biological origin, resulting from extracellular polymeric secretions (EPS). During the Arctic Summer Cloud Ocean Study (ASCOS) in August 2008, particulate organic matter (POM, with size range > 0.22 μm) and dissolved organic matter (DOM, < 0.22 μm, obtained after filtration) samples were collected and chemically characterized from the SML and the corresponding SSW at an open lead centered at 87.5° N and 5° E. Total organic carbon was persistently enriched in the SML with a mean enrichment factor (EF) of 1.45 ± 0.41, whereas sporadic depletions of dissolved carbohydrates and amino acids were observed. Monosaccharide compositional analysis reveals that EPS in the Arctic lead was formed mainly of distinctive heteropolysaccharides, enriched in xylose, fucose and glucose. The mean concentrations of total hydrolysable neutral sugars in SSW were 94.9 ± 37.5 nM in high molecular weight (HMW) DOM (> 5 kDa) and 64.4 ± 14.5 nM in POM. The enrichment of polysaccharides in the SML appeared to be a common feature, with EFs ranging from 1.7 to 7.0 for particulate polysaccharides and 3.5 to 12.1 for polysaccharides in the HMW DOM fraction. A calculated monosaccharide yield suggests that polymers in the HMW DOM fraction were scavenged, without substantial degradation, into the SML. Bubble scavenging experiments showed that newly aggregated particles could be formed abiotically by coagulation of low molecular weight nanometer-sized gels. Aerosol particles, artificially generated by bubbling experiments, were enriched in polysaccharides by factors of 22–70, relative to the source seawater. We propose that bubble scavenging of surface-active polysaccharides could be one of the possible mechanisms for the enrichment of polysaccharides in the high Arctic open lead SML.

  • 3.
    Norris, S. J.
    et al.
    Univ Leeds, Sch Earth & Environm, Leeds, W Yorkshire, England..
    Brooks, I. M.
    Univ Leeds, Sch Earth & Environm, Leeds, W Yorkshire, England..
    de Leeuw, G.
    Finnish Meteorol Inst, Climate & Global Change Unit, FIN-00101 Helsinki, Finland.;Univ Helsinki, Dept Phys, Helsinki, Finland.;TNO, Utrecht, Netherlands..
    Sirevaag, A.
    Univ Bergen, Inst Geophys, N-5020 Bergen, Norway.;Bjerknes Ctr Climate Res, Bergen, Norway..
    Leck, C.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Brooks, B. J.
    Univ Leeds, Sch Earth & Environm, Leeds, W Yorkshire, England..
    Birch, C. E.
    Univ Leeds, Sch Earth & Environm, Leeds, W Yorkshire, England..
    Tjernström, M.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Measurements of bubble size spectra within leads in the Arctic summer pack ice2011In: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 7, no 1, p. 129-139Article in journal (Refereed)
    Abstract [en]

    The first measurements of bubble size spectra within the near-surface waters of open leads in the central Arctic pack ice were obtained during the Arctic Summer Cloud-Ocean Study (ASCOS) in August 2008 at 8787.6 degrees N, 1-11 degrees W. A significant number of small bubbles (30-100 mu m diameter) were present, with concentration decreasing rapidly with size from 100-560 mu m; no bubbles larger than 560 mu m were observed. The bubbles were present both during periods of low wind speed (U < 6 m s(-1)) and when ice covered the surface of the lead. The low wind and short open-water fetch precludes production of bubbles by wave breaking suggesting that the bubbles are generated by processes below the surface. When the surface water was open to the atmosphere bubble concentrations increased with increasing heat loss to the atmosphere. The presence of substantial numbers of bubbles is significant because the bursting of bubbles at the surface provides a mechanism for the generation of aerosol and the ejection of biological material from the ocean into the atmosphere. Such a transfer has previously been proposed as a potential climate feedback linking marine biology and Arctic cloud properties.

  • 4. Rudels, B.
    Arctic Ocean circulation and variability - advection and external forcing encounter constraints and local processes2012In: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 8, no 2, p. 261-286Article in journal (Refereed)
    Abstract [en]

    The first hydrographic data from the Arctic Ocean, the section from the Laptev Sea to the passage between Greenland and Svalbard obtained by Nansen on his drift with Fram 1893-1896, aptly illustrate the main features of Arctic Ocean oceanography and indicate possible processes active in transforming the water masses in the Arctic Ocean. Many, perhaps most, processes were identified already by Nansen, who put his mark on almost all subsequent research in the Arctic. Here we shall revisit some key questions and follow how our understanding has evolved from the early 20th century to present. What questions, if any, can now be regarded as solved and which remain still open? Five different but connected topics will be discussed: (1) The low salinity surface layer and the storage and export of freshwater. (2) The vertical heat transfer from the Atlantic water to sea ice and to the atmosphere. (3) The circulation and mixing of the two Atlantic inflow branches. (4) The formation and circulation of deep and bottom waters in the Arctic Ocean. (5) The exchanges through Fram Strait. Foci will be on the potential effects of increased freshwater input and reduced sea ice export on the freshwater storage and residence time in the Arctic Ocean, on the deep waters of the Makarov Basin, and on the circulation and relative importance of the two inflows, over the Barents Sea and through Fram Strait, for the distribution of heat in the intermediate layers of the Arctic Ocean.

  • 5. Rudels, B.
    et al.
    Schauer, U.
    Bjork, G.
    Korhonen, M.
    Pisarev, S.
    Rabe, B.
    Wisotzki, A.
    Observations of water masses and circulation with focus on the Eurasian Basin of the Arctic Ocean from the 1990s to the late 2000s2013In: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 9, no 1, p. 147-169Article in journal (Refereed)
    Abstract [en]

    The circulation and water mass properties in the Eurasian Basin are discussed based on a review of previous research and an examination of observations made in recent years within, or parallel to, DAMOCLES (Developing Arctic Modeling and Observational Capabilities for Long-term Environmental Studies). The discussion is strongly biased towards observations made from icebreakers and particularly from the cruise with R/V Polarstern 2007 during the International Polar Year (IPY). Focus is on the Barents Sea inflow branch and its mixing with the Fram Strait inflow branch. It is proposed that the Barents Sea branch contributes not just intermediate water but also most of the water to the Atlantic layer in the Amundsen Basin and also in the Makarov and Canada basins. Only occasionally would high temperature pulses originating from the Fram Strait branch penetrate along the Laptev Sea slope across the Gakkel Ridge into the Amundsen Basin. Interactions between the Barents Sea and the Fram Strait branches lead to formation of intrusive layers, in the Atlantic layer and in the intermediate waters. The intrusion characteristics found downstream, north of the Laptev Sea are similar to those observed in the northern Nansen Basin and over the Gakkel Ridge, suggesting a flow from the Laptev Sea towards Fram Strait. The formation mechanisms for the intrusions at the continental slope, or in the interior of the basins if they are reformed there, have not been identified. The temperature of the deep water of the Eurasian Basin has increased in the last 10 yr rather more than expected from geothermal heating. That geothermal heating does influence the deep water column was obvious from 2007 Polarstern observations made close to a hydrothermal vent in the Gakkel Ridge, where the temperature minimum usually found above the 600-800 m thick homogenous bottom layer was absent. However, heat entrained from the Atlantic water into descending, saline boundary plumes may also contribute to the warming of the deeper layers.

  • 6.
    Sirevaag, A.
    et al.
    Univ Bergen, Geophys Inst, Bergen, North Ireland..
    de la Rosa, S.
    Univ Bergen, Geophys Inst, Bergen, North Ireland..
    Fer, I.
    Univ Bergen, Geophys Inst, Bergen, North Ireland..
    Nicolaus, M.
    Alfred Wegener Inst Polar & Marine Res, Bremerhaven, Germany.;Norwegian Polar Res Inst, Tromso, Norway..
    Tjernström, M.
    Stockholm Univ, Dept Meteorol, Stockholm, Sweden..
    McPhee, M. G.
    McPhee Res Co, Naches, WA USA..
    Mixing, heat fluxes and heat content evolution of the Arctic Ocean mixed layer2011In: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 7, no 3, p. 335-349Article in journal (Refereed)
    Abstract [en]

    A comprehensive measurement program was conducted during 16 days of a 3 week long ice pack drift, from 15 August to 1 September 2008 in the central Amundsen Basin, Arctic Ocean. The data, sampled as part of the Arctic Summer Cloud Ocean Study (ASCOS), included upper ocean stratification, mixing and heat transfer as well as transmittance solar radiation through the ice. The observations give insight into the evolution of the upper layers of the Arctic Ocean in the transition period from melting to freezing. The ocean mixed layer was found to be heated from above and, for summer conditions, the net heat flux through the ice accounted for 22% of the observed change in mixed layer heat content. Heat was mixed downward within the mixed layer and a small, downward heat flux across the base of the mixed layer accounted for the accumulated heat in the upper cold halocline during the melting season. On average, the ocean mixed layer was cooled by an ocean heat flux at the ice/ocean interface (1.2 W m(-2)) and heated by solar radiation through the ice (-2.6 W m(-2)). An abrupt change in surface conditions halfway into the drift due to freezing and snowfall showed distinct signatures in the data set and allowed for inferences and comparisons to be made for cases of contrasting forcing conditions. Transmittance of solar radiation was reduced by 59% in the latter period. From hydro-graphic observations obtained earlier in the melting season, in the same region, we infer a total fresh water equivalent of 3.3 m accumulated in the upper ocean, which together with the observed saltier winter mixed layer indicates a transition towards a more seasonal ice cover in the Arctic.

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