Atmospheric forcing of coastal polynyas in the south-western Weddell Sea

AbstractThe development of coastal polynyas, areas of enhanced heat flux and sea ice production strongly depend on atmospheric conditions. In Antarctica, measurements are scarce and models are essential for the investigation of polynyas. A robust quantification of polynya exchange processes in simulations relies on a realistic representation of atmospheric conditions in the forcing dataset. The sensitivity of simulated coastal polynyas in the south-western Weddell Sea to the atmospheric forcing is investigated with the Finite-Element Sea ice-Ocean Model (FESOM) using daily NCEP/NCAR reanalysis data (NCEP), 6 hourly Global Model Europe (GME) data and two different hourly datasets from the high-resolution Consortium for Small-Scale Modelling (COSMO) model. Results are compared for April to August in 2007–09. The two coarse-scale datasets often produce the extremes of the data range, while the finer-scale forcings yield results closer to the median. The GME experiment features the strongest winds and, therefore, the greatest polynya activity, especially over the eastern continental shelf. This results in higher volume and export of High Salinity Shelf Water than in the NCEP and COSMO runs. The largest discrepancies between simulations occur for 2008, probably due to differing representations of the ENSO pattern at high southern latitudes. The results suggest that the large-scale wind field is of primary importance for polynya development.

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A recent update on the circulation and water masses around the Filchner and Ronne ice shelves in the southern Weddell Sea

10.5194/egusphere-egu2020-10194 ◽

2020 ◽

Author(s):

Markus Janout ◽

Hartmut Hellmer ◽

Tore Hattermann ◽

Svein Osterhus ◽

Lucrecia Stulic ◽

...

Keyword(s):

Sea Ice ◽

Ocean Circulation ◽

Large Scale ◽

Austral Summer ◽

Weddell Sea ◽

Shelf Water ◽

Ice Shelf ◽

Present Context ◽

The Stability ◽

Ice Production

<p>The Filchner and Ronne ice sheets (FRIS) compose the second largest contiguous ice sheet on the Antarctic continent. Unlike at several other Antarctic glaciers, basal melt rates at FRIS are comparatively low, as cold and dense waters presently dominate the wide southern Weddell Sea (WS) continental shelf and effectively block out any significant inflow of warmer ocean waters. We revisited the southern WS shelf in austral summer 2018 during Polarstern expedition PS111 with detailed hydrographic and tracer measurements along both the Ronne and Filchner ice fronts. The hydrography along FRIS was characterized by near-freezing high salinity shelf water (HSSW) in front of Ronne, and a striking dominance of ice shelf water (ISW) in Filchner Trough. The cold (-2.2&#176;C) and fresher (34.6) ISW was formed by the interaction of Ronne-sourced HSSW with the ice shelf base. The strong dominance of ISW in Filchner Trough indicates a recently enhanced circulation below FRIS, likely fueled by enhanced sea ice production in the southwestern WS. We view these recent observations in a multidecadal (1973-present) context, contrast the two dominant circulation modes below FRIS, and discuss the importance of sea ice formation and large-scale sea level pressure patterns for the stability of the ocean circulation and basal melt rates underneath FRIS.</p>

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Basin-Scale Ice Motion and Deformation in the Weddell Sea During Winter

Annals of Glaciology ◽

10.3189/s0260305500007163 ◽

1989 ◽

Vol 12 ◽

pp. 178-186 ◽

Cited By ~ 4

Author(s):

P. Wadhams ◽

C.B. Sear ◽

D.R. Crane ◽

M.A. Rowe ◽

S.J. Morrison ◽

...

Keyword(s):

Large Scale ◽

Weddell Sea ◽

Atmospheric Forcing ◽

Kinematic Parameters ◽

The South ◽

North West ◽

Basin Scale ◽

Maud Rise ◽

Pattern Of Motion

Ice motion in the Weddell Sea is examined for the period 19 August (Day 232) to 12 October (Day 286) 1986 using the tracks of four Argos buoys deployed during the Winter Weddell Sea Project 1986 (WWSP 86). Two were SPRI/BAS buoys, launched in December 1985 and March 1986 in the south-east and north-west Weddell Sea. The others were part of a mesoscale array deployed in the Maud Rise area by H. Hoeber of the Meteorologisches Institut der Universität Hamburg, during the WWSP 86 cruise of FS Polarstern. The four buoys operated together for 44 d, comprising a basin-scale quadrilateral from which the differential kinematic parameters of divergence, vorticity, shear, and stretch were extracted, as well as the large-scale pattern of motion. It is found that most deformation episodes were associated with atmospheric forcing events.

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Circulation beneath the Filchner Ice Shelf, Antarctica, and its sensitivity to changes in the oceanic environment: a case-study

Annals of Glaciology ◽

10.3189/1998aog27-1-99-104 ◽

1998 ◽

Vol 27 ◽

pp. 99-104 ◽

Cited By ~ 18

Author(s):

K. Grosfeld ◽

R. Gerdes

Keyword(s):

Sea Ice ◽

Mass Loss ◽

Ocean Circulation ◽

Large Scale ◽

Ocean Model ◽

Current Situation ◽

Weddell Sea ◽

Ice Formation ◽

Shelf Area ◽

Ice Shelf

We investigate the sensitivity of the ocean circulation in the Filchner Trough to changes in the large-scale oceanic environment and its impact on the mass balance of the Filchner Ice Shelf, Antarctica. Three experiments with a three-dimensional ocean model describe (i) the current situation, (ii) a scenario with increased ocean temperatures, and (iii) a scenario with reduced sea-ice formation rates on the adjacent continental shelf. in the final discussion brief results of a combined scenario with increased ocean temperatures and reduced sea-ice formation are presented. The changes from the current situation affect the circulation in the Filchner Trough, and melting and freezing processes beneath the ice shelf. The latter affect the amount and properties of Ice Shelf Water (ISW), a component of Antarctic Bottom Water. Net basal melt rates provide an overall measure for the changes: while the control run yields 0.35 m a−1 net melting averaged over the Filchner Ice Shelf area, the warming scenario results in a more than twofold increase in ice-shelf mass loss. Reduced production of High Salinity ShelfWater due to smaller sea-ice formation rates in the second scenario leads, on the other hand, to a decrease in basal mass loss, because the deep cavity is less well ventilated than in the control run. ISW is cooled and the ice shelf is stabilized under this scenario, which is arguably the more likely development in the southern Weddell Sea.

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Basin-Scale Ice Motion and Deformation in the Weddell Sea During Winter

Annals of Glaciology ◽

10.1017/s0260305500007163 ◽

1989 ◽

Vol 12 ◽

pp. 178-186 ◽

Cited By ~ 29

Author(s):

P. Wadhams ◽

C.B. Sear ◽

D.R. Crane ◽

M.A. Rowe ◽

S.J. Morrison ◽

...

Keyword(s):

Large Scale ◽

Weddell Sea ◽

Atmospheric Forcing ◽

Kinematic Parameters ◽

The South ◽

North West ◽

Basin Scale ◽

Maud Rise ◽

Pattern Of Motion

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Modeling the Impact of Wind Intensification on Antarctic Sea Ice Volume

Journal of Climate ◽

10.1175/jcli-d-12-00139.1 ◽

2014 ◽

Vol 27 (1) ◽

pp. 202-214 ◽

Cited By ~ 42

Author(s):

Jinlun Zhang

Keyword(s):

Southern Ocean ◽

Sea Ice ◽

Surface Wind ◽

Ocean Model ◽

Weddell Sea ◽

Ice Thickness ◽

Ice Volume ◽

Antarctic Sea Ice ◽

Ice Production ◽

The Impact

Abstract A global sea ice–ocean model is used to examine the impact of wind intensification on Antarctic sea ice volume. Based on the NCEP–NCAR reanalysis data, there are increases in surface wind speed (0.13% yr−1) and convergence (0.66% yr−1) over the ice-covered areas of the Southern Ocean during the period 1979–2010. Driven by the intensifying winds, the model simulates an increase in sea ice speed, convergence, and shear deformation rate, which produces an increase in ridge ice production in the Southern Ocean (1.1% yr−1). The increased ridged ice production is mostly in the Weddell, Bellingshausen, Amundsen, and Ross Seas where an increase in wind convergence dominates. The increase in ridging production contributes to an increase in the volume of thick ice (thickness > 2 m) in the Southern Ocean, while the volumes of thin ice (thickness ≤ 1 m) and medium thick ice (1 m < thickness ≤ 2 m) remain unchanged over the period 1979–2010. The increase in thick ice leads to an increase in ice volume in the Southern Ocean, particularly in the southern Weddell Sea where a significant increase in ice concentration is observed. The simulated increase in either the thick ice volume (0.91% yr−1) or total ice volume (0.46% yr−1) is significantly greater than other ice parameters (simulated or observed) such as ice extent (0.14–0.21% yr−1) or ice area fraction (0.24%–0.28% yr−1), suggesting that ice volume is a potentially strong measure of change.

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The Copernicus Global 1/12° Oceanic and Sea Ice GLORYS12 Reanalysis

Frontiers in Earth Science ◽

10.3389/feart.2021.698876 ◽

2021 ◽

Vol 9 ◽

Author(s):

Lellouche Jean-Michel ◽

Greiner Eric ◽

Bourdallé-Badie Romain ◽

Garric Gilles ◽

Melet Angélique ◽

...

Keyword(s):

Sea Ice ◽

Sea Level ◽

General Circulation ◽

Large Scale ◽

Observation System ◽

Small Scale ◽

Atmospheric Conditions ◽

Seasonal Forecasts ◽

Sea Ice Concentration

GLORYS12 is a global eddy-resolving physical ocean and sea ice reanalysis at 1/12° horizontal resolution covering the 1993-present altimetry period, designed and implemented in the framework of the Copernicus Marine Environment Monitoring Service (CMEMS). The model component is the NEMO platform driven at the surface by atmospheric conditions from the ECMWF ERA-Interim reanalysis. Ocean observations are assimilated by means of a reduced-order Kalman filter. Along track altimeter sea level anomaly, satellite sea surface temperature and sea ice concentration, as well as in situ temperature and salinity vertical profiles are jointly assimilated. A 3D-VAR scheme provides an additional correction for the slowly-evolving large-scale biases in temperature and salinity. The performance of the reanalysis shows a clear dependency on the time-dependent in situ observation system. The general assessment of GLORYS12 highlights a level of performance at the state-of-the-art and the capacity of the system to capture the main expected climatic interannual variability signals for ocean and sea ice, the general circulation and the inter-basins exchanges. In terms of trends, GLORYS12 shows a higher than observed warming trend together with a slightly lower than observed global mean sea level rise. Comparisons made with an experiment carried out on the same platform without assimilation show the benefit of data assimilation in controlling water mass properties and sea ice cover and their low frequency variability. Moreover, GLORYS12 represents particularly well the small-scale variability of surface dynamics and compares well with independent (non-assimilated) data. Comparisons made with a twin experiment carried out at 1/4° resolution allows characterizing and quantifying the strengthened contribution of the 1/12° resolution onto the downscaled dynamics. GLORYS12 provides a reliable physical ocean state for climate variability and supports applications such as seasonal forecasts. In addition, this reanalysis has strong assets to serve regional applications and provide relevant physical conditions for applications such as marine biogeochemistry. In the near future, GLORYS12 will be maintained to be as close as possible to real time and could therefore provide relevant and continuous reference past ocean states for many operational applications.

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Thinner Sea Ice Contribution to the Remarkable Polynya Formation North of Greenland in August 2018

Advances in Atmospheric Sciences ◽

10.1007/s00376-021-0136-9 ◽

2021 ◽

Author(s):

Xiaoyi Shen ◽

Chang-Qing Ke ◽

Bin Cheng ◽

Wentao Xia ◽

Mengmeng Li ◽

...

Keyword(s):

Sea Ice ◽

Ice Cover ◽

Reanalysis Data ◽

Mean Value ◽

Ocean Model ◽

North Coast ◽

Average Value ◽

The North ◽

Wind Sea ◽

The One

AbstractIn August 2018, a remarkable polynya was observed off the north coast of Greenland, a perennial ice zone where thick sea ice cover persists. In order to investigate the formation process of this polynya, satellite observations, a coupled ice-ocean model, ocean profiling data, and atmosphere reanalysis data were applied. We found that the thinnest sea ice cover in August since 1978 (mean value of 1.1 m, compared to the average value of 2.8 m during 1978–2017) and the modest southerly wind caused by a positive North Atlantic Oscillation (mean value of 0.82, compared to the climatological value of −0.02) were responsible for the formation and maintenance of this polynya. The opening mechanism of this polynya differs from the one formed in February 2018 in the same area caused by persistent anomalously high wind. Sea ice drift patterns have become more responsive to the atmospheric forcing due to thinning of sea ice cover in this region.

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Variational data assimilation with superparameterization

Nonlinear Processes in Geophysics Discussions ◽

10.5194/npgd-2-513-2015 ◽

2015 ◽

Vol 2 (2) ◽

pp. 513-536 ◽

Cited By ~ 1

Author(s):

I. Grooms ◽

Y. Lee

Keyword(s):

Data Assimilation ◽

Large Scale ◽

Climate Models ◽

Low Cost ◽

Ocean Model ◽

Variational Data Assimilation ◽

Scale Model ◽

Small Scale ◽

New Applications ◽

Lorenz 96

Abstract. Superparameterization (SP) is a multiscale computational approach wherein a large scale atmosphere or ocean model is coupled to an array of simulations of small scale dynamics on periodic domains embedded into the computational grid of the large scale model. SP has been successfully developed in global atmosphere and climate models, and is a promising approach for new applications. The authors develop a 3D-Var variational data assimilation framework for use with SP; the relatively low cost and simplicity of 3D-Var in comparison with ensemble approaches makes it a natural fit for relatively expensive multiscale SP models. To demonstrate the assimilation framework in a simple model, the authors develop a new system of ordinary differential equations similar to the two-scale Lorenz-'96 model. The system has one set of variables denoted {Yi}, with large and small scale parts, and the SP approximation to the system is straightforward. With the new assimilation framework the SP model approximates the large scale dynamics of the true system accurately.

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Sea-ice dynamics in the Weddell Sea in winter

Annals of Glaciology ◽

10.3189/1991aog15-1-9-16 ◽

1991 ◽

Vol 15 ◽

pp. 9-16 ◽

Cited By ~ 1

Author(s):

Heinrich Hoeber

Keyword(s):

Sea Ice ◽

Bulk Viscosity ◽

Current Data ◽

Weddell Sea ◽

Small Scale ◽

Ice Dynamics ◽

Sea Ice Dynamics ◽

Momentum Budget ◽

Ice Drift

Observations of ice drift received from an array of ARGOS buoys drifting in the Weddell Sea in winter 1986 are described. Wind and current data are also available, permitting derivation of the complete momentum budget including the internal ice stress computed as residuum. It is shown that the variability of forcing both of the atmosphere and of the ocean is large, and that internal ice stress is not negligible; monthly vector averages amount to about half of the wind and water stresses. Coefficients of shear and bulk viscosity are derived according to Hibler's model of ice rheology; they turn out to be negative occasionally, in particular when small-scale forcing of the atmosphere is large.

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Evolution of the Amundsen Sea Polynya, Antarctica, 2016–2021

10.5194/tc-2021-250 ◽

2021 ◽

Author(s):

Grant J. Macdonald ◽

Stephen F. Ackley ◽

Alberto M. Mestas-Nuñez

Keyword(s):

Sea Ice ◽

Reanalysis Data ◽

Sea Ice Concentration ◽

Amundsen Sea ◽

Annual Variations ◽

Ice Concentration ◽

Ice Conditions ◽

Sar Imagery ◽

Key Sites ◽

Ice Production

Abstract. Polynyas are key sites of ice production during the winter and are important sites of biological activity and carbon sequestration during the summer. The Amundsen Sea Polynya (ASP) is the fourth largest Antarctic polynya, has recorded the highest primary productivity and lies in an embayment of key oceanographic significance. However, knowledge of its dynamics, and of sub-annual variations in its area and ice production, is limited. In this study we primarily utilize Sentinel-1 SAR imagery, sea ice concentration products and climate reanalysis data, along with bathymetric data, to analyze the ASP over the period November 2016–March 2021. Specifically, we analyze (i) qualitative changes in the ASP's characteristics and dynamics, and quantitative changes in (ii) summer polynya area, (iii) winter polynya area and ice production. From our analysis of SAR imagery we find that ice produced by the ASP becomes stuck in the vicinity of the polynya and sometimes flows back into the polynya, contributing to its closure and limiting further ice production. The polynya forms westward off a persistent chain of grounded icebergs that are located at the site of a bathymetric high. Grounded icebergs also influence the outflow of ice and facilitate the formation of a 'secondary polynya' at times. Additionally, unlike some polynyas, ice produced by the polynya flows westward after formation, along the coast and into the neighboring sea sector. During the summer and early winter, broader regional sea ice conditions can play an important role in the polynya. The polynya opens in all summers, but record-low sea ice conditions in 2016/17 cause it to become part of the open ocean. During the winter, an average of 78 % of ice production occurs in April–May and September–October, but large polynya events often associated with high winds can cause ice production throughout the winter. While passive microwave data or daily sea ice concentration products remain key for analyzing variations in polynya area and ice production, we find that the ability to directly observe and qualitatively analyze the polynya at a high temporal and spatial resolution with Sentinel-1 imagery provides important insights about the behavior of the polynya that are not possible with those datasets.

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