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  • 1
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    Cross-shelf transport of warm and saline water in response to sea ice drift on the Laptev Sea shelf (2013)
    Wiley
    In:  Journal of Geophysical Research - Oceans, 118 . pp. 563-576.
    Details
    Publication Date: 2014-12-16
    Description: Oceanographic moorings and conductivity-temperature-depth (CTD) surveys from September 2009 to September 2010 are used to describe recent changes in the Laptev Sea hydrography and to highlight wind- and ice-driven surface Ekman transport as the mechanism to translate these changes from the outer- to the inner-shelf bottom waters. In February 2010, moored oceanographic instruments recorded a sudden increase in temperature (+0.8°C) and salinity (+ 〉3) near the bottom of the inner Laptev Sea shelf. Such warm and saline waters had not been previously observed on the inner shelf in winter. They likely originated from the basin and were first observed during a summer 2009 CTD survey in the northwestern shelf break region, subsequently spreading east and shoreward across the Laptev Sea shelf. The changes were introduced to the mooring site by the first of a series of bottom-intensified flow events with velocities reaching 20 cm s−1, topographically guided along a relic submarine river valley. Each of the flow events coincided with negative pressure anomalies at the mooring site and offshore-directed (upwelling-favorable) winds and ice drift. We suggest that the observations to first order resemble a simplified two-dimensional two-layered ocean, where offshore surface Ekman transport is compensated for by a barotropic shoreward response flow near the bottom. In this paper, we use one of the first comprehensive long-term Laptev Sea datasets to highlight ice-ocean-atmosphere interactions in early and late winter and discuss the role of freshwater, stratification, and ice mobility on under-ice circulation on the Laptev Sea shelf.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2011JC007731
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Correlation of river water and local sea-ice melting on the Laptev Sea shelf (Siberian Arctic) (2013)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 118 (1). pp. 550-561.
    Details
    Publication Date: 2019-09-23
    Description: Hydrographic and stable isotope (δ18O) data from 4 summer surveys in the Laptev Sea are used to derive fractions of sea-ice meltwater and river water. Sea-ice meltwater fractions are found to be correlated to river water fractions. While initial heat of river discharge is too small to melt the observed 0-158 km3 of sea-ice meltwater, arctic rivers contain suspended particles (SPM) and colored dissolved organic material (CDOM) that preferentially absorb solar radiation. Accordingly heat content in surface waters is correlated to river water fractions. But in years when river water is largely absent within the surface layer absolute heat content values increase to considerably higher values with extended exposure time to solar radiation and sensible heat. Nevertheless no net sea-ice melting is observed on the shelf in years when river water is largely absent within the surface layer. The total freshwater volume of the central-eastern Laptev Sea (72-76°N, 122-140°E) varies between ~1000-1500 km3 (34.92 reference salinity). It is dominated by varying river water volumes (~1300-1800 km3) reduced by an about constant freshwater deficit (~350-400 km3) related to sea-ice formation. Net sea-ice melt (~109-158 km3) is only present in years with high river water budgets. Intermediate to bottom layer (〉25 salinities) contain ~60% and 30% of the river budget in years with low and high river budgets, respectively. The average mean residence time of shelf waters was ~2-3 years during 2007-2009.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1002/jgrc.20076
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    The impact of Siberian coastal polynyas on shelf-derived Arctic Ocean halocline waters (2012)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 117 (C4). C00G12.
    Details
    Publication Date: 2019-09-23
    Description: Hydrographic and stable oxygen isotope (H218O/H216O) sampling was carried out within the West New Siberian (WNS) coastal polynyas in the southern Laptev Sea in late winters 2008 and 2009. The impact of sea-ice formation on the water column was quantified by a salinity/{lower case delta}18O mass balance. Several stations had vertically homogeneous physical properties in April/May 2008 and featured polynya-formed local bottom water with elevated signals of brine released during sea-ice formation and elevated fractions of river water. The polynya-formed bottom water was fresher than surrounding bottom waters. At other stations salinity/{lower case delta}18O correlation showed well defined mixing lines for bottom and surface layers. In March/April 2009 surface waters were strongly influenced by Lena River water and local polynya activity with elevated brine signals reached to intermediate depth, but did not penetrate the bottom layer in the highly stratified water column. Inventory values of sea-ice formation were comparable in both years, but freshwater distributions from the preceding summers were different. Therefore, the observed difference in the impact of polynya activity on the water column is not primarily controlled by the amount of sea-ice formed during winter but by preconditioning from the preceding summer. Only in years when the river plume is mostly absent in the polynya region stratification is weak and allows winter sea-ice formation to reach the bottom layer. Thus summer stratification controls the influence of local polynya water on the shelf's bottom hydrography and, as bottom water is exported, impacts on the source water of shelf-derived halocline waters.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1029/2011JC007282
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Interannual variability of surface and bottom sediment transport on the Laptev Sea shelf during summer (2013)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 10 . pp. 1117-1129.
    Details
    Publication Date: 2019-09-23
    Description: Sediment transport dynamics were studied during ice-free conditions under different atmospheric circulation regimes on the Laptev Sea shelf (Siberian Arctic). To study the interannual variability of suspended particulate matter (SPM) dynamics and their coupling with the variability in surface river water distribution on the Laptev Sea shelf, detailed oceanographic, optical (turbidity and Ocean Color satellite data), and hydrochemical (nutrients, SPM, stable oxygen isotopes) process studies were carried out continuously during the summers of 2007 and 2008. Thus, for the first time SPM and nutrient variations on the Laptev Sea shelf under different atmospheric forcing and the implications for the turbidity and transparency of the water column can be presented. The data indicate a clear link between different surface distributions of riverine waters and the SPM transport dynamics within the entire water column. The summer of 2007 was dominated by shoreward winds and an eastward transport of riverine surface waters. The surface SPM concentration on the southeastern inner shelf was elevated, which led to decreased transmissivity and increased light absorption. Surface SPM concentrations in the central and northern Laptev Sea were comparatively low. However, the SPM transport and concentration within the bottom nepheloid layer increased considerably on the entire eastern shelf. The summer of 2008 was dominated by offshore winds and northward transport of the river plume. The surface SPM transport was enhanced and extended onto the mid-shelf, whereas the bottom SPM transport and concentration was diminished. This study suggests that the SPM concentration and transport, in both the surface and bottom nepheloid layers, are associated with the distribution of riverine surface waters which are linked to the atmospheric circulation patterns over the Laptev Sea and the adjacent Arctic Ocean during the open water season. A continuing trend toward shoreward winds, weaker stratification and higher SPM concentration throughout the water column might have severe consequences for the ecosystem on the Laptev Sea shelf.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/bg-10-1117-2013
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Summer tracer data from the Laptev Sea shelf: coupling of local sea-ice melting and river water on the Siberian shelves (2012)
    In:  [Talk] In: 10. Workshop on Russian-German Cooperation: Laptev Sea System, Kiel, 17.12.-20.12.2012, Kiel .
    Details
    Publication Date: 2019-09-23
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 6
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    Light Induced Physical-biogeochemical Implications in the Arctic Ocean: a Coupled Sea-ice – Ocean – Ecological Modeling Study (2020)
    AGU
    In:  EPIC3Ocean Sciences Meeting 2020, San Diego, CA, USA, 2020-02-16-2020-02-21San Diego, CA, USA, AGU
    Details
    Publication Date: 2020-05-14
    Description: Currently, the most rapid increase in near-surface air temperature takes place in the Arctic, accompanied by reduced sea ice concentration. Under the resulting retreat of sea ice, the underwater shortwave radiation and, thus, the amount and types of phytoplankton may change. In this study, we use a coupled sea-ice – ocean – ecological model (Darwin-MITgcm) to simulate the variability of the ocean’s major optically active constituents, comprising six phytoplankton functional types (PFTs) and colored dissolved organic matter (CDOM), in response to Arctic amplification. We further set up the general circulation model to account for the biogeochemical processes, in terms of light attenuation, so that their feedback on Arctic Ocean’s physical and biogeochemical properties can be assessed. Here, for the first time, CDOM is included in the underwater light attenuation scheme as a prognostic model variable that interacts with the changes induced by its presence. The coupled model simulation, allowing to consider explicitly the optical constituents, is compared with a constant attenuation depth formulation corresponding to Jerlov water type I, which is the case in most ocean models. Our findings suggest that the presence of CDOM and phytoplankton, by modulating the vertical distribution of the incoming light, affects significantly the upper ocean thermal structure. The promotion of heat-trapping near the surface results in summertime warming, locally even in more than 1°C, and to sea ice reduction. These changes have implications to upper ocean stratification and are accompanied by changes in nutrients supply, as well as in total but also partial PFTs chlorophyll-a.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 7
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    Observed interannual changes beneath Filchner-Ronne Ice Shelf linked to large-scale atmospheric circulation (2021)
    Springer Nature
    In:  EPIC3Nature Communications, Springer Nature, 12(1), ISSN: 2041-1723
    Details
    Publication Date: 2021-06-16
    Description: Floating ice shelves are the Achilles’ heel of the Antarctic Ice Sheet. They limit Antarctica’s contribution to global sea level rise, yet they can be rapidly melted from beneath by a warming ocean. At Filchner-Ronne Ice Shelf, a decline in sea ice formation may increase basal melt rates and accelerate marine ice sheet mass loss within this century. However, the understanding of this tipping-point behavior largely relies on numerical models. Our new multi-annual observations from five hot-water drilled boreholes through Filchner-Ronne Ice Shelf show that since 2015 there has been an intensification of the density-driven ice shelf cavity-wide circulation in response to reinforced wind-driven sea ice formation in the Ronne polynya. Enhanced southerly winds over Ronne Ice Shelf coincide with westward displacements of the Amundsen Sea Low position, connecting the cavity circulation with changes in large-scale atmospheric circulation patterns as a new aspect of the atmosphere-ocean-ice shelf system.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
    Format: application/pdf
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  • 8
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    FRIS Revisited in 2018: On the Circulation and Water Masses at the Filchner and Ronne Ice Shelves in the Southern Weddell Sea (2021)
    In:  EPIC3Journal of Geophysical Research: Oceans, 126(6), pp. e2021JC017269
    Details
    Publication Date: 2021-06-16
    Description: The Filchner-Ronne Ice Shelf (FRIS) is characterized by moderate basal melt rates due to the near-freezing waters that dominate the wide southern Weddell Sea continental shelf. We revisited the region in austral summer 2018 with detailed hydrographic and noble gas surveys along FRIS. The FRIS front was characterized by High Salinity Shelf Water (HSSW) in Ronne Depression, Ice Shelf Water (ISW) on its eastern flank, and an inflow of modified Warm Deep Water (mWDW) entering through Central Trough. Filchner Trough was dominated by Ronne HSSW-sourced ISW, likely forced by a recently intensified circulation beneath FRIS due to enhanced sea ice production in the Ronne polynya since 2015. Glacial meltwater fractions and tracer-based water mass dating indicate two separate ISW outflow cores, one hugging the Berkner slope after a two-year travel time, and the other located in the central Filchner Trough following a ∼six year-long transit through the FRIS cavity. Historical measurements indicate the presence of two distinct modes, in which water masses in Filchner Trough were dominated by either Ronne HSSW-derived ISW (Ronne-mode) or more locally derived Berkner-HSSW (Berkner-mode). While the dominance of these modes has alternated on interannual time scales, ocean densities in Filchner Trough have remained remarkably stable since the first surveys in 1980. Indeed, geostrophic velocities indicated outflowing ISW-cores along the trough's western flank and onto Berkner Bank, which suggests that Ronne-ISW preconditions Berkner-HSSW production. The negligible density difference between Berkner- and Ronne-mode waters indicates that each contributes cold dense shelf waters to protect FRIS against inflowing mWDW.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
    Format: application/pdf
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  • 9
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    Amplified Arctic Surface Warming and Sea Ice Loss Due to Phytoplankton and Colored Dissolved Material (2021)
    Details
    Publication Date: 2021-07-05
    Description: Optically active water constituents attenuate solar radiation and hence affect the vertical distribution of energy in the upper ocean. To understand their implications, we operate an ocean biogeochemical model coupled to a general circulation model with sea ice. Incorporating the effect of phytoplankton and colored dissolved organic matter (CDOM) on light attenuation in the model increases the sea surface temperature in summer and decreases sea ice concentration in the Arctic Ocean. Locally, the sea ice season is reduced by up to one month. CDOM drives a significant part of these changes, suggesting that an increase of this material will amplify the observed Arctic surface warming through its direct thermal effect. Indirectly, changing advective processes in the Nordic Seas may further intensify this effect. Our results emphasize the phytoplankton and CDOM feedbacks on the Arctic ocean and sea ice system and underline the need to consider these effects in future modeling studies to enhance their plausibility.
    Description: Plain Language Summary: The amount of microalgae and colored dissolved organic material in the ocean determines how much light is absorbed in the surface waters and how much can reach greater depths. The vertical distribution of energy affects the upper ocean temperature and general circulation. Here, we use a numerical ocean model with biogeochemistry and sea ice, in which the individual effects of microalgae and colored dissolved organic matter can be turned on and off separately. When both effects are turned on, the summertime surface temperatures in the Arctic are larger and consequently more sea ice melts, so that the sea ice season is shorter by up to one month. We find that, to a large extent, the colored dissolved material is responsible for these changes. An increase of this material due to climate change will amplify the observed Arctic surface warming. For better projections of climate change, new models should account for the effect of these light‐absorbing water constituents.
    Description: Key Points: Colored dissolved material is responsible for a significant part of the induced surface warming and sea ice loss in the Arctic Ocean. The combined effect of optical constituents reduces the sea ice season by up to one month. Considering the properties of optical constituents and their variability will enhance the plausibility of future modeling studies.
    Description: Federal Agency for Scientific Organizations (FASO) Russia http://dx.doi.org/10.13039/501100013176
    Description: German Research Foundation (DFG) http://dx.doi.org/10.13039/501100001659
    Description: Helmholtz Climate Initiative (REKLIM)
    Keywords: 551,9 ; phytoplankton ; CDOM ; Arctic Ocean ; colored dissolved organic matter ; radiative effect ; light attenuation
    Type: article
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    CITATION GEO-LEO
  • 10
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    Semidiurnal tides on the Laptev Sea shelf with implications for shear and vertical mixing (2014)
    AMER METEOROLOGICAL SOC
    In:  EPIC3Journal of Physical Oceanography, AMER METEOROLOGICAL SOC, 44(1), pp. 202-219, ISSN: 0022-3670
    Details
    Publication Date: 2017-09-13
    Description: The Arctic continental shelf seas hold a globally significant source of freshwater that impacts Arctic Ocean stratification, circulation, and climate. This freshwater can be injected below the surface mixed layer by intense turbulent kinetic energy dissipation events, as resolved by Laptev Sea microstructure observations. The tides provide a major source of energy that can be dissipated and hence drive diapycnal mixing in the Laptev Sea. Multiyear ADCP mooring records from locations across the shelf reveal that semidiurnal tides are dominated by theM2 and S2 constituents, with the largest amplitudes on the outer shelf. Throughout most of the shelf, tides are clockwise polarized and sheared by stratification, as characteristic near theM2 critical latitude. Interannual variations of the tidal and shear structures on the inner shelf aremainly determined by the stratification-setting Lena River freshwater plume. In all locations,M2 tides are enhanced under sea ice, and therefore changes in the seasonal ice cover may lead to changes in tides and water column structure. The main conclusions of this study are that (i) tides play a comparatively greater role year-round on the outer shelf relative to the inner shelf; (ii) a sea ice reduction will overall decrease the predictability of the currents, especially on the inner shelf; and (iii) the freshwater distribution directly impacts diapycnal mixing by setting the vertical tidal structure. These combined effects imply that future sea ice loss will increase the variability and vertical mixing of freshwater, particularly on the inner shelf, where the Lena River first enters the Laptev Sea.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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