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  • 1
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    Greater role for Atlantic inflows on sea-ice loss in the Eurasian Basin of the Arctic Ocean (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-04-21
    Description: Arctic sea-ice loss is a leading indicator of climate change and can be attributed, in large part, to atmospheric forcing. Here, we show that recent ice reductions, weakening of the halocline, and shoaling of the intermediate-depth Atlantic Water layer in the eastern Eurasian Basin have increased winter ventilation in the ocean interior, making this region structurally similar to that of the western Eurasian Basin. The associated enhanced release of oceanic heat has reduced winter sea-ice formation at a rate now comparable to losses from atmospheric thermodynamic forcing, thus explaining the recent reduction in sea-ice cover in the eastern Eurasian Basin. This encroaching "atlantification" of the Eurasian Basin represents an essential step toward a new Arctic climate state, with a substantially greater role for Atlantic inflows.
    Keywords: Oceanography
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Laboratory measurements of sea ice: Connections to microwave remote sensing (1998)
    In:  IEEE Transactions on Geoscience and Remote Sensing, Basel, Elsevier Science Publishers, vol. 36, no. 5, pp. 1716-1730, pp. B03304, (ISSN: 1340-4202)
    Details
    Publication Date: 1998
    Keywords: Electromagnetic methods/phenomena ; Laboratory measurements
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    BIBLIOGRAPHY SEISMOLOGY
  • 3
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    Inverse electromagnetic scattering models for sea ice (1998)
    In:  IEEE Transactions on Geoscience and Remote Sensing, Bonn, Pergamon, vol. 36, no. 5, pp. 1675-1704, pp. 2050, (ISBN: 0534351875, 2nd edition)
    Details
    Publication Date: 1998
    Keywords: Electromagnetic methods/phenomena ; Scattering ; Inversion
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    BIBLIOGRAPHY SEISMOLOGY
  • 4
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    Contributions of growth and deformation to monthly variability in sea ice thickness north of the coasts of Greenland and the Canadian Arctic Archipelago (2016)
    Wiley
    Details
    Publication Date: 2016-07-26
    Description: Regional variability in monthly CryoSat-2 sea ice thickness is partitioned into contributions from dynamics and thermodynamics using ice deformation calculated from large-scale ice drift. For five winters (December to April, 2011-2015), over a region of persistent convergence north of the coasts of Greenland and the Canadian Arctic Archipelago, deformation explains ~34% of the overall variance (up to 69% in 2014/15) in monthly thickness changes. Approximately 42-56% (or ~ 0.6 m) of the seasonal changes in mean regional ice thickness can be attributed to divergence and shear. The estimated area-averaged growth of 0.12 ± 0.03 m/month compares favorably with measurements from ice mass balance buoys. Examination of the time-variable thickness distributions shows areas covered by ice 〈 3 m are reduced, while areas of thicker ice (〉3 m) increased. Albeit at fairly coarse resolution, this coupled analysis of thickness changes and deformation offered a first look at the character of the regional thickness redistribution process.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Arctic sea ice circulation and drift speed: Decadal trends and ocean currents (2013)
    Wiley
    Details
    Publication Date: 2013-04-10
    Description: We examine the basin-wide trends in sea ice circulation and drift speed, and highlight the changes between 1982-2009 in connection to local winds, multiyear sea ice coverage, ice export, and the thinning of the ice cover. The polarity of the Arctic Oscillation (AO) is used as a backdrop for summarizing the variance and shifts in decadal drift patterns. The 28-year circulation fields show a net strengthening of the Beaufort Gyre and the Transpolar Drift, especially during the last decade. The imprint of the Arctic Dipole Anomaly on mean summer circulation is evident (2001-2009) and enhances summer ice area export at the Fram Strait. Between 2001 and 2009, the large spatially averaged trends in drift speeds (winter: +23.6%/decade, summer: +17.7%/decade) are not explained by the much smaller trends in wind speeds (winter: 1.46%/decade, summer: -3.42%/decade). Notably, positive trends in drift speed are found in regions with reduced multiyear sea ice coverage. Over 90% of the area of the Arctic Ocean has positive trends in drift speed and negative trends in multiyear sea ice coverage. The increased responsiveness of ice drift to geostrophic wind is consistent with a thinner and weaker seasonal ice cover and suggests large-scale changes in the air-ice-ocean momentum balance. The retrieved mean ocean current field from decadal-scale average ice motion captures a steady drift from Siberia to the Fram Strait, an inflow north of the Bering Strait, and a westward drift along coastal Alaska. This mean current is comparable to the geostrophic current from satellite-derived dynamic topography.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    The Greenland Sea Jet: A mechanism for wind-driven sea ice export through Fram Strait (2011)
    Wiley
    Details
    Publication Date: 2011-06-28
    Description: We present a mechanism for wind-driven sea ice export from the Arctic Ocean through Fram Strait for the period 1979–2007, using the output of a high-resolution regional atmospheric climate model. By explicitly calculating the components of the atmospheric momentum budget, we show that not large scale synoptic forcing (LSC), but mainly thermal wind forcing (THW) causes the persistent northerly jet (the Greenland Sea Jet) over Fram Strait. The jet results from horizontal temperature gradients in the atmospheric boundary layer (ABL), set up between cold ABL-air over the sea ice covered western Greenland Sea and the relatively warmer ABL over the ice-free eastern Greenland Sea. From 1993 onwards we find a negative trend in THW, due to a stronger response to climate warming of the ABL over the sea ice covered ocean, compared to that over the ice free ocean. Although on average LSC is smaller than THW, year to year variations in LSC explain most of the interannual variability in the sea ice area flux through Fram Strait (R = 0.81). A small positive trend is found for LSC, partly compensating the decrease in THW in recent years.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Airborne surveys of snow depth over Arctic sea ice (2011)
    Wiley
    Details
    Publication Date: 2011-11-16
    Description: During the spring of 2009, an ultrawideband microwave radar was deployed as part of Operation IceBridge to provide the first cross-basin surveys of snow thickness over Arctic sea ice. In this paper, we analyze data from three ∼2000 km transects to examine detection issues, the limitations of the current instrument, and the regional variability of the retrieved snow depth. Snow depth is the vertical distance between the air-snow and snow-ice interfaces detected in the radar echograms. Under ideal conditions, the per echogram uncertainty in snow depth retrieval is ∼4–5 cm. The finite range resolution of the radar (∼5 cm) and the relative amplitude of backscatter from the two interfaces limit the direct retrieval of snow depths much below ∼8 cm. Well-defined interfaces are observed over only relatively smooth surfaces within the radar footprint of ∼6.5 m. Sampling is thus restricted to undeformed, level ice. In early April, mean snow depths are 28.5 ± 16.6 cm and 41.0 ± 22.2 cm over first-year and multiyear sea ice (MYI), respectively. Regionally, snow thickness is thinner and quite uniform over the large expanse of seasonal ice in the Beaufort Sea, and gets progressively thicker toward the MYI cover north of Ellesmere Island, Greenland, and the Fram Strait. Snow depth over MYI is comparable to that reported in the climatology by Warren et al. (1999). Ongoing improvements to the radar system and the utility of these snow depth measurements are discussed.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Dynamic topography of the ice-covered Arctic Ocean from ICESat (2011)
    Wiley
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    Publication Date: 2011-01-26
    Description: We construct the dynamic ocean topography (DOT) of the Arctic Ocean, for five ICESat campaigns (winter of 2004–2008), using sea surface height estimates in open leads. Results show that the mean winter DOT over the Arctic Ocean varies by ∼1 m and features a distinct dome of ∼40 cm over the Beaufort Sea. Standard deviation of the mean field is ∼20 cm. Spatial coherence between the five winter DOTs is consistently high (〉0.9), whereas the coherence between the DOTs and the winter (DJFM) sea-level pressure fields over the Arctic Basin is variable. This suggests persistence of the underlying hydrodynamic processes at interannual time-scales compared to seasonal atmospheric forcing. Comparison of dynamic heights (DH) from hydrographic surveys and the DOT in 2008 shows a remarkable correlation of 0.92. The geostrophic velocity fields computed from the DOT and interpolated DH fields highlight the smaller scale oceanographic features in the satellite estimates.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Observational assessment of Arctic Ocean sea ice motion, export, and thickness in CMIP3 climate simulations (2011)
    Wiley
    Details
    Publication Date: 2011-09-24
    Description: We compare the CMIP3 model fields with observations of sea ice motion, export, extent, and thickness and analyze fields of sea level pressure and geostrophic wind of the Arctic Ocean. These variables play important roles in the distribution and annual balance of sea ice volume within the basin. While it is not expected that uninitialized simulations agree completely with observations, these assessments serve to summarize ensemble behavior, as baselines for measuring improvements, and to evaluate reliability of CMIP3 simulations (and potentially CMIP5) for projection of decline rates of Arctic sea ice coverage. We find the model-data differences and intermodel scatter in summarizing statistics are large. In a majority of model fields the mean high-pressure pattern in the southern Beaufort is significantly displaced toward the central Arctic Basin, leading to difficulties in reproducing the mean spatial patterns of sea ice circulation, thickness, and ice export. Thus, even though the CMIP3 multimodel data set agrees that increased greenhouse gas concentrations will result in reductions of Arctic sea ice area and volume, these comparisons suggest considerable uncertainties in the projected rates of sea ice decline.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
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    Arctic sea ice freeboard from IceBridge acquisitions in 2009: Estimates and comparisons with ICESat (2012)
    Wiley
    Details
    Publication Date: 2012-02-09
    Description: During the spring of 2009, the Airborne Topographic Mapper (ATM) system on the IceBridge mission acquired cross-basin surveys of surface elevations of Arctic sea ice. In this paper, the total freeboard derived from four ∼2000 km transects are examined and compared with those from the 2009 ICESat campaign. Total freeboard, the sum of the snow and ice freeboards, is the elevation of the air-snow interface above the local sea surface. Prior to freeboard retrieval, signal dependent range biases are corrected. With data from a near co-incident outbound and return track on 21 April, we show that our estimates of the freeboard are repeatable to within ∼4 cm but dependent locally on the density and quality of sea surface references. Overall difference between the ATM and ICESat freeboards for the four transects is 0.7 (8.5) cm (quantity in bracket is standard deviation), with a correlation of 0.78 between the data sets of one hundred seventy-eight 50 km averages. This establishes a level of confidence in the use of ATM freeboards to provide regional samplings that are consistent with ICESat. In early April, mean freeboards are 41 cm and 55 cm over first year and multiyear sea ice (MYI), respectively. Regionally, the lowest mean ice freeboard (28 cm) is seen on 5 April where the flight track sampled the large expanse of seasonal ice in the western Arctic. The highest mean freeboard (71 cm) is seen in the multiyear ice just west of Ellesmere Island from 21 April. The relatively large unmodeled variability of the residual sea surface resolved by ATM elevations is discussed.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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