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  • Wiley  (5)
  • INT GLACIOL SOC  (2)
  • COPERNICUS GESELLSCHAFT MBH  (1)
  • AMS (American Meteorological Society)
  • 2015-2019  (8)
  • 1
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    Decadal hindcasts initialized using observed surface wind stress: Evaluation and prediction out to 2024 (2015)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 42 (15). pp. 6454-6461.
    Details
    Publication Date: 2017-04-10
    Description: We use surface air temperature to evaluate the decadal forecast skill of the fully coupled Max Planck Institut Earth System Model (MPI-ESM) initialized using only surface wind stress applied to the ocean component of the model (Modini: Model initialization by partially coupled spin-up). Our analysis shows that the greenhouse gas forcing alone results in a significant forecast skill on the 2–5 and 6–9 year range even for uninitialized hindcasts. For the first forecast year, the forecast skill of Modini is generally comparable with previous initialization procedures applied to MPI-ESM. But only Modini is able to generate a significant skill (correlation) in the tropical Pacific for a 2–5 year (and to a lesser extent for a 6–9 year) hindcast. Modini is also better able to capture the observed hiatus in global warming in hindcast mode than the other methods. Finally, we present forecasts for 2015 and the average of years 2016–2019 and 2020–2024, predicting an end to the hiatus.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2015GL064833
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Decorrelation scales for Arctic Ocean hydrogpraphy - Part I: Amerasian Basin (2018)
    COPERNICUS GESELLSCHAFT MBH
    In:  EPIC3Ocean Science, COPERNICUS GESELLSCHAFT MBH, 14, pp. 161-185, ISSN: 1812-0784
    Details
    Publication Date: 2018-03-06
    Description: Any use of observational data for data assimilation requires adequate information of their representativeness in space and time. This is particularly important for sparse, non-synoptic data, which comprise the bulk of oceanic in situ observations in the Arctic. To quantify spatial and temporal scales of temperature and salinity variations, we estimate the autocorrelation function and associated decorrelation scales for the Amerasian Basin of the Arctic Ocean. For this purpose, we compile historical measurements from 1980 to 2015. Assuming spatial and temporal homogeneity of the decorrelation scale in the basin interior (abyssal plain area), we calculate autocorrelations as a function of spatial distance and temporal lag. The examination of the functional form of autocorrelation in each depth range reveals that the autocorrelation is well described by a Gaussian function in space and time. We derive decorrelation scales of 150–200 km in space and 100–300 days in time. These scales are directly applicable to quantify the representation error, which is essential for use of ocean in situ measurements in data assimilation. We also describe how the estimated autocorrelation function and decorrelation scale should be applied for cost function calculation in a data assimilation system.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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    PAPER (OA)
  • 3
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    Arctic pathways of Pacific Water: Arctic Ocean Model Intercomparison experiments (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Oceans, Wiley, 121(1), pp. 27-59, ISSN: 0148-0227
    Details
    Publication Date: 2016-11-23
    Description: Pacific Water (PW) enters the Arctic Ocean through Bering Strait and brings heat, fresh water and nutrients from the northern Bering Sea. The circulation of PW in the central Arctic Ocean is only partially understood due to the lack of observations. In this paper pathways of PW are investigated using simulations with six state-of-the art regional and global Ocean General Circulation Models (OGCMs). In the simulations PW is tracked by a passive tracer, released in Bering Strait. Simulated PW water spreads from the Bering Strait region in three major branches. One of them starts in the Barrow Canyon, bringing PW along continental slope of Alaska into the Canadian Straits and then into Baffin Bay. The other initiates in the vicinity of the Herald Canyon and transports PW along the continental slope of the East-Siberian Sea into the transpolar drift, and then through Fram Strait and the Greenland Sea. The third branch begins near the Herald Shoal and the central Chukchi shelf and brings PW waters into the Beaufort Gyre. Models suggest that the spread of PW through the Arctic Ocean depends on the atmospheric circulation. In the models the wind, acting via Ekman pumping, drives the seasonal and interannual variability of PW in the Canadian Basin of the Arctic Ocean. The wind effects the simulated PW pathways by changing vertical shear of the relative vorticity of the ocean flow in the Canada Basin. This article is protected by copyright. All rights reserved.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    A glimpse beneath Antarctic sea ice: platelet-layer volume from multi-frequency electromagnetic induction sounding (2016)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 43, ISSN: 0094-8276
    Details
    Publication Date: 2016-01-15
    Description: In Antarctica, ice crystals emerge from ice shelf cavities and accumulate in unconsolidated layers beneath nearby sea ice. Such sub-ice platelet layers form a unique habitat and serve as an indicator for the state of an ice shelf. However, the lack of a suitable methodology impedes an efficient quantification of this phenomenon on scales beyond point measurements. In this study, we inverted multifrequency electromagnetic (EM) induction soundings, obtained on fast ice with an underlying platelet layer along profiles of 〉100 km length in the eastern Weddell Sea. EM-derived platelet layer thickness and conductivity are consistent with other field observations. Our results suggest that platelet layer volume is higher than previously thought in this region and that platelet layer ice volume fraction is proportional to its thickness. We conclude that multifrequency EM is a suitable tool to determine platelet layer volume, with the potential to obtain crucial knowledge of associated processes in otherwise inaccessible ice shelf cavities.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 5
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    Towards an estimation of sub-sea-ice platelet-layer volume with multi-frequency electromagnetic induction sounding (2015)
    INT GLACIOL SOC
    In:  EPIC3Annals of Glaciology, INT GLACIOL SOC, 56(69), pp. 137-146, ISSN: 0260-3055
    Details
    Publication Date: 2015-01-09
    Description: Ice-platelet clusters modify the heat and mass balance of sea ice near Antarctic ice shelves and provide a unique habitat for ice-associated organisms. The amount and distribution of these ice crystals below the solid sea ice provide insight into melt rates and circulation regimes in the ice-shelf cavities, which are difficult to observe directly. However, little is known about the circum-Antarctic volume of the sub-sea-ice platelet layer, because observations have mostly been limited to point measurements. In this study, we present a new application of multi-frequency electromagnetic (EM) induction sounding to quantify platelet-layer properties. Combining in situ data with the theoretical response yields a bulk platelet-layer conductivity of 1154 +/- 271 mSm–1 and ice-volume fractions of 0.29–0.43. Calibration routines and uncertainties are discussed in detail to facilitate future studies. Our results suggest that multi-frequency EM induction sounding is a promising method to efficiently map platelet-layer volume on a larger scale than has previously been feasible.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 6
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    Ice platelets below Weddell Sea landfast sea ice (2015)
    INT GLACIOL SOC
    In:  EPIC3Annals of Glaciology, INT GLACIOL SOC, 56(69), pp. 175-190, ISSN: 0260-3055
    Details
    Publication Date: 2019-12-03
    Description: Basal melt of ice shelves may lead to an accumulation of disc-shaped ice platelets underneath nearby sea ice, to form a sub-ice platelet layer. Here we present the seasonal cycle of sea ice attached to the Ekström Ice Shelf, Antarctica, and the underlying platelet layer in 2012. Ice platelets emerged from the cavity and interacted with the fast-ice cover of Atka Bay as early as June. Episodic accumulations throughout winter and spring led to an average platelet-layer thickness of 4m by December 2012, with local maxima of up to 10 m. The additional buoyancy partly prevented surface flooding and snow-ice formation, despite a thick snow cover. Subsequent thinning of the platelet layer from December onwards was associated with an inflow of warm surface water. The combination of model studies with observed fast-ice thickness revealed an average ice-volume fraction in the platelet layer of 0.25+-0.1. We found that nearly half of the combined solid sea-ice and ice-platelet volume in this area is generated by heat transfer to the ocean rather than to the atmosphere. The total ice-platelet volume underlying Atka Bay fast ice was equivalent to more than one-fifth of the annual basal melt volume under the Ekström Ice Shelf.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 7
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    Impact of snow accumulation on CryoSat-2 range retrievals over Arctic sea ice: An observational approach with buoy data (2015)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, ISSN: 0094-8276
    Details
    Publication Date: 2019-07-17
    Description: Radar altimetry measurements of the current satellite mission CryoSat-2 show an increase of Arctic sea ice thickness in autumn 2013, compared to previous years but also related to March 2013. Such an increase over the melting season seems unlikely and needs to be investigated. Recent studies show that the influence of the snow cover is not negligible and can highly affect the CryoSat-2 range retrievals if it is assumed that the main scattering horizon is given by the snow-ice interface. Our analysis of Arctic ice mass balance buoy records and coincident CryoSat-2 data between 2012 and 2014 adds observational evidence to these findings. Linear trends of snow and ice freeboard measurements from buoys and nearby CryoSat-2 freeboard retrievals are calculated during accumulation events. We find a positive correlation between buoy snow freeboard and CryoSat-2 freeboard estimates, revealing that early snow accumulation might have caused a bias in CryoSat-2 sea ice thickness in autumn 2013.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 8
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    Impact of snow accumulation on CryoSat-2 range retrievals over Arctic sea ice: An observational approach with buoy data (2015)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 42(11), pp. 4447-4455
    Details
    Publication Date: 2016-02-08
    Description: Radar altimetry measurements of the current satellite mission CryoSat-2 show an increase of Arctic sea ice thickness in autumn 2013, compared to previous years but also related to March 2013. Such an increase over the melting season seems unlikely and needs to be investigated. Recent studies show that the influence of the snow cover is not negligible and can highly affect the CryoSat-2 range retrievals if it is assumed that the main scattering horizon is given by the snow-ice interface. Our analysis of Arctic ice mass balance buoy records and coincident CryoSat-2 data between 2012 and 2014 adds observational evidence to these findings. Linear trends of snow and ice freeboard measurements from buoys and nearby CryoSat-2 freeboard retrievals are calculated during accumulation events. We find a positive correlation between buoy snow freeboard and CryoSat-2 freeboard estimates, revealing that early snow accumulation might have caused a bias in CryoSat-2 sea ice thickness in autumn 2013.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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