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  • 2010-2014  (91)
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  • 1
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    Evaluation of a polynya flux model by means of thermal infrared satellite estimates (2011)
    International Glaciological Society
    In:  Annals of Glaciology, 52 (57). pp. 52-60.
    Details
    Publication Date: 2014-12-05
    Description: We test the ability of a two-dimensional flux model to simulate polynya events with narrow open-water zones by comparing model results to ice-thickness and ice-production estimates derived from thermal infrared Moderate Resolution Imaging Spectroradiometer (MODIS) observations in conjunction with an atmospheric dataset. Given a polynya boundary and an atmospheric dataset, the model correctly reproduces the shape of an 11 day long event, using only a few simple conservation laws. Ice production is slightly overestimated by the model, owing to an underestimated ice thickness. We achieved best model results with the consolidation thickness parameterization developed by Biggs and others (2000). Observed regional discrepancies between model and satellite estimates might be a consequence of the missing representation of the dynamic of the thin-ice thickening (e.g. rafting). We conclude that this simplified polynya model is a valuable tool for studying polynya dynamics and estimating associated fluxes of single polynya events.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    SMOS-derived thin sea ice thickness: algorithm baseline, product specifications and initial verification (2014)
    Copernicus Publications (EGU)
    In:  The Cryosphere, 8 (3). pp. 997-1018.
    Details
    Publication Date: 2015-03-13
    Description: Following the launch of ESA's Soil Moisture and Ocean Salinity (SMOS) mission, it has been shown that brightness temperatures at a low microwave frequency of 1.4 GHz (L-band) are sensitive to sea ice properties. In the first demonstration study, sea ice thickness up to 50 cm has been derived using a semi-empirical algorithm with constant tie-points. Here, we introduce a novel iterative retrieval algorithm that is based on a thermodynamic sea ice model and a three-layer radiative transfer model, which explicitly takes variations of ice temperature and ice salinity into account. In addition, ice thickness variations within the SMOS spatial resolution are considered through a statistical thickness distribution function derived from high-resolution ice thickness measurements from NASA's Operation IceBridge campaign. This new algorithm has been used for the continuous operational production of a SMOS-based sea ice thickness data set from 2010 on. The data set is compared to and validated with estimates from assimilation systems, remote sensing data, and airborne electromagnetic sounding data. The comparisons show that the new retrieval algorithm has a considerably better agreement with the validation data and delivers a more realistic Arctic-wide ice thickness distribution than the algorithm used in the previous study (Kaleschke et al., 2012).
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/tc-8-997-2014
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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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
  • 4
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    Large-scale ice thickness distribution of first-year sea ice in spring and summer north of Svalbard (2013)
    International Glaciological Society
    In:  Annals of Glaciology, 54 (62). pp. 13-18.
    Details
    Publication Date: 2014-08-28
    Description: The large-scale thickness distribution of sea ice was measured during several campaigns in the European Arctic north of Svalbard from 2007 using an airborne electromagnetic induction device. In August 2010 and April–May 2011, this was complemented by extensive on-ice work including measurements of snow thickness and freeboard. Ice thicknesses show a clear difference between the seasons, with thicker ice during spring than in summer. In spring 2011, negative freeboard and flooding were observed as a result of the extensive snow cover. We find that the characteristics of the first-year sea ice allow combining observations from different years. The ice thickness in the marginal ice zone increases with increasing latitude and increasing distance to the ice edge; however, in the inner ice pack from ∼100 km from the ice edge the thickness remains almost constant. Modal ice thickness in spring reaches 2.4 m whereas in summer it is 1.0–1.4 m. Our study provides new insight into ice thickness distributions of a typical ice cover consisting of mainly first- and second-year ice, which may become the dominant ice type in the Arctic in the future.
    Type: Article , PeerReviewed
    DOI: 10.3189/2013AoG62A146
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Variability and trends in Laptev Sea ice outflow between 1992–2011 (2013)
    Copernicus Publications (EGU)
    In:  The Cryosphere, 7 (1). pp. 349-363.
    Details
    Publication Date: 2014-12-16
    Description: Variability and trends in seasonal and interannual ice area export out of the Laptev Sea between 1992 and 2011 are investigated using satellite-based sea ice drift and concentration data. We found an average total winter (October to May) ice area transport across the northern and eastern Laptev Sea boundaries (NB and EB) of 3.48 × 10hoch5 km2. The average transport across the NB (2.87 × 10hoch5 km2)is thereby higher than across the EB (0.61 × 10hoch5 km2), with a less pronounced seasonal cycle. The total Laptev Sea ice area flux significantly increased over the last decades (0.85 × 10hoch5 km2 decade−1, p 〉 0.95), dominated by increasing export through the EB (0.55 × 10hoch5 km2 decade−1, p 〉 0.90), while the increase in export across the NB is smaller (0.3 × 10hoch5 km2 decade−1) and statistically not significant. The strong coupling between across-boundary SLP gradient and ice drift velocity indicates that monthly variations in ice area flux are primarily controlled by changes in geostrophic wind velocities, although the Laptev Sea ice circulation shows no clear relationship with large-scale atmospheric indices. Also there is no evidence of increasing wind velocities that could explain the overall positive trends in ice export. The increased transport rates are rather the consequence of a changing ice cover such as thinning and/or a decrease in concentration. The use of a back-propagation method revealed that most of the ice that is incorporated into the Transpolar Drift is formed during freeze-up and originates from the central and western part of the Laptev Sea, while the exchange with the East Siberian Sea is dominated by ice coming from the central and southeastern Laptev Sea. Furthermore, our results imply that years of high ice export in late winter (February to May) have a thinning effect on the ice cover, which in turn preconditions the occurence of negative sea ice extent anomalies in summer.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/tc-7-349-2013
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Validating satellite derived and modelled sea-ice drift in the Laptev Sea with in situ measurements from the winter of 2007/2008 (2011)
    Norwegian Polar Institute
    In:  Polar Research, 30 . p. 7218.
    Details
    Publication Date: 2015-04-27
    Description: A correct representation of the ice movement in an Arctic sea-ice-ocean coupled model is essential for a realistic sea-ice and ocean simulation. The aim of this study is to validate the observational and simulated sea-ice drift for the Laptev Sea Shelf region with in situ measurements from the winter of 2007/08. Several satellite remote-sensing data sets are first compared to mooring measurements and afterwards to the sea-ice drift simulated by the coupled sea-ice-ocean model. The different satellite products have a correlation to the in situ data ranging from 0.56 to 0.86. The correlations of sea-ice direction or individual drift vector components between the in situ data and the observations are high, about 0.8. Similar correlations are achieved by the model simulations. The sea-ice drift speed derived from the model and from some satellite products have only moderate correlations of about 0.6 to the in situ record. The standard errors for the satellite products and model simulations drift components are similar to the errors of the satellite products in the central Arctic and are about 0.03 m/s. The fast-ice parameterization implementation in the model was also successfully tested for its influence on the sea-ice drift. In contrast to the satellite products, the model drift simulations have a full temporal and spatial coverage and results are reliable enough to use as sea-ice drift estimates on the Laptev Sea Shelf.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3402/polar.v30i0.7218
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Cross-validation of polynya monitoring methods from multi-sensor satellite and airborne data: a case study from the Laptev Sea. (2010)
    Canadian Aeronautics and Space Institute
    In:  Canadian Journal of Remote Sensing, 36 (1:Special Issue: Remote Sensing Innovations During the International Polar Year). pp. 196-210.
    Details
    Publication Date: 2014-12-22
    Description: Wind-driven coastal polynyas in the polar oceans are recognized as regions of extensive new ice formation in the cold season. Hence, they may play an increasing role in the uncertain future of the sea-ice budget in the polar oceans. The Laptev Sea polynyas in the Siberian Arctic are well recognized as being significant ice producers and might gain special attention with regards to ice volume changes in the Arctic. Long-term monitoring and characterization of these polynyas require stable methods to detect the area of open water and the growth, thickness, and evolution of thin ice. We examine different parameters and methods to observe polynya area and thin ice thickness during a prominent polynya event in the Laptev Sea in April 2008. These are derived from visible, infrared, and microwave satellite data. Airborne electromagnetic ice thickness measurements with high spatial resolution and aerial photography taken across the polynya are used to assess the feasibility of the methods for long-term and large-scale polynya monitoring within this area. Our results indicate that in the narrow flaw polynyas of the Laptev Sea the coarse resolution of commonly used microwave channel combinations provokes sources of error through mixed signals at the fast- and pack-ice edges. Polynya monitoring results can be significantly improved using enhanced resolution data products. This implies that previously suggested methods for the retrieval of polynya area, thin ice thickness, and ice production are not transferable in space and time. Data as well as method parameterizations have to be chosen carefully to avoid large errors due to regional peculiarities.
    Type: Article , PeerReviewed
    DOI: 10.5589/m10-012
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Improvement and sensitivity snalysis of thermal thin-ice thickness retrievals (2013)
    Institute of Electrical and Electronics Engineers (IEEE)
    In:  IEEE Transactions on Geoscience and Remote Sensing, 51 (6). pp. 3306-3318.
    Details
    Publication Date: 2020-07-29
    Description: Considering the sea ice decline in the Arctic during the last decades, polynyas are of high research interest since these features are core areas of new ice formation. The determination of ice formation requires accurate retrieval of polynya area and thin-ice thickness (TIT) distribution within the polynya. We use an established energy balance model to derive TITs with MODIS ice surface temperatures (Ts) and NCEP/DOE Reanalysis II in the Laptev Sea for two winter seasons. Improvements of the algorithm mainly concern the implementation of an iterative approach to calculate the atmospheric flux components taking the atmospheric stratification into account. Furthermore, a sensitivity study is performed to analyze the errors of the ice thickness. The results are the following: 1) 2-m air temperatures (Ta) and Ts have the highest impact on the retrieved ice thickness; 2) an overestimation of Ta yields smaller ice thickness errors as an underestimation of Ta; 3) NCEP Ta shows often a warm bias; and 4) the mean absolute error for ice thicknesses up to 20 cm is ±4.7 cm. Based on these results, we conclude that, despite the shortcomings of the NCEP data (coarse spatial resolution and no polynyas), this data set is appropriate in combination with MODIS Ts for the retrieval of TITs up to 20 cm in the Laptev Sea region. The TIT algorithm can be applied to other polynya regions and to past and future time periods. Our TIT product is a valuable data set for verification of other model and remote sensing ice thickness data.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1109/TGRS.2012.2219539
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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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
  • 10
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    The Laptev Sea polynya project - multi-disciplinary studies of hydrography, sea ice and sea-ice/ocean/atmosphere interactions (2012)
    In:  [Poster] In: International Polar Year (IPY) Conference "From Knowledge to Action", 22.04.-27.04.2012, Montréal, Canada .
    Details
    Publication Date: 2019-09-23
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
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