scholarly journals A numerical study of the Southern Ocean including a thermodynamic active ice shelf – Part 1: Weddell Sea

2012 ◽  
Vol 5 (4) ◽  
pp. 4037-4069
Author(s):  
V. Meccia ◽  
I. Wainer ◽  
M. Tonelli ◽  
E. Curchitser
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ocean Circulation ◽  
Numerical Study ◽  
Weddell Sea ◽  
Future Climate Change ◽  
Climate Change Scenarios ◽  
Ice Shelf ◽  
Model Framework ◽  
Ice Shelves

Abstract. There is a great amount of uncertainty regarding the understanding of the atmosphere-ocean-cryosphere interactions in the Southern Ocean despite the role that the region plays in our changing climate. With the aim of studying the relative importance of sea-ice and ice shelf processes in the Southern Ocean, a coupled ocean circulation sea-ice/ice shelf cavity model based on the Regional Ocean Model System (ROMS) is used in a periodic circumpolar domain with enhanced resolution in the Weddell Sea. A hierarchy of numerical experiments is performed where first a sea-ice model is used and then an ice shelf thermodynamic parameterization is included in order to evaluate the improvements resulting from each component. Results show that it is necessary to consider the formation and melting of sea-ice in order to adequately reproduce the observed hydrography and circulation. Inclusion of ice shelves cavities in the model only improves results if the ice shelf-ocean thermodynamic fluxes are active. Ice shelves and ocean interactions are an important process to be considered in order to obtain realistic hydrographic values under the ice shelf. The model framework presented in this work is a promising tool for analyzing the Southern Ocean response to future climate change scenarios.

Productivity and carbon export potential in the Weddell Sea, with a focus on the waters near Larsen C Ice Shelf

2020 ◽  
Author(s):  
Raquel Flynn ◽  
Jessica Burger ◽  
Shantelle Smith ◽  
Kurt Spence ◽  
Thomas Bornman ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Phytoplankton Community ◽  
Late Summer ◽  
Weddell Sea ◽  
Global Ocean ◽  
Ice Shelf ◽  
Carbon Export ◽  
Study Region ◽  
Ice Shelves

<p>Net primary production (NPP) is indicative of the energy available to an ecosystem, which is central to ecological functioning and biological carbon cycling. The Southern Ocean’s Weddell Sea (WS) represents a point of origin where water masses form and exchange with the atmosphere, thereby setting the physical and chemical conditions of much of the global ocean. The WS is particularly understudied near Larsen C Ice Shelf (LCIS) where harsh sea-ice conditions persist year-round. We measured size-fractionated rates of NPP, nitrogen (N; as nitrate, ammonium, and urea) uptake, and nitrification, and characterized the phytoplankton community at 19 stations in summer 2018/2019, mainly near LCIS, with a few stations in the open Weddell Gyre (WG) and at Fimbul Ice Shelf (FIS). Throughout the study region, NPP and N uptake were dominated by nanophytoplankton (3-20 μm), with microphytoplankton (>20 μm) becoming more abundant later in the season, particularly at FIS. Here, we observed high phytoplankton biomass and diversity, and the community was dominated by diatoms known to enhance carbon export (e.g., <em>Thalassiosira spp</em>.). At LCIS, by contrast, the community comprised mainly <em>Phaeocystis Antarctica</em>. In the open WG, a population of small and weakly-silicified diatoms of the genus <em>Corethron</em> dominated the phytoplankton community. Here, euphotic zone-integrated uptake rates were similar to those at LCIS even though the depth-specific rates were lower. Mixed-layer nitrification was below detection at all stations such that nitrate uptake can be used as a proxy for carbon export potential <em>sensu</em> the new production paradigm – this was highest near FIS in late summer. Our observations can be explained by melting sea ice near the ice shelves that supplies iron and enhances water column stratification, thus alleviating iron and/or light limitation of phytoplankton and allowing them to consume the abundant surface macronutrients. That the sea ice melted completely at FIS but not LCIS may explain why late-summer productivity and carbon export potential were highest near FIS, more than double the rates measured in early summer and near LCIS. The early-to-late summer progression near the ice shelves contrasts that of the open Southern Ocean where iron is depleted by late summer, driving a shift towards smaller phytoplankton that facilitate less carbon export.</p>

scholarly journals Coupling a thermodynamically active ice shelf to a regional simulation of the Weddell Sea

2013 ◽  
Vol 6 (4) ◽  
pp. 1209-1219 ◽  
Author(s):  
V. Meccia ◽  
I. Wainer ◽  
M. Tonelli ◽  
E. Curchitser
Keyword(s):  
Ocean Model ◽  
Weddell Sea ◽  
Future Climate Change ◽  
Climate Change Scenarios ◽  
Ice Shelf ◽  
Model Framework ◽  
Promising Tool ◽  
Regional Ocean Model System ◽  
Enhanced Resolution ◽  
Regional Ocean Model

Abstract. A thermodynamically interactive ice shelf cavity parameterization is coupled to the Regional Ocean Model System (ROMS) and is applied to the Southern Ocean domain with enhanced resolution in the Weddell Sea. This implementation is tested in order to assess its degree of improvement to the hydrography (and circulation) of the Weddell Sea. Results show that the inclusion of ice shelf cavities in the model is feasible and somewhat realistic (considering the lack of under-ice observations for validation). Ice shelf–ocean interactions are an important process to be considered in order to obtain realistic hydrographic values under the ice shelf. The model framework presented in this work is a promising tool for analyzing the Southern Ocean's response to future climate change scenarios.

Recent glacial advance in the western Weddell Sea Sector driven by anomalous sea ice circulation

2020 ◽  
Author(s):  
Frazer Christie ◽  
Toby Benham ◽  
Julian Dowdeswell
Keyword(s):  
Sea Ice ◽  
Antarctic Peninsula ◽  
Ice Sheet ◽  
Weddell Sea ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Total Contribution ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
The Antarctic

<p>The Antarctic Peninsula is one of the most rapidly warming regions on Earth. There, the recent destabilization of the Larsen A and B ice shelves has been directly attributed to this warming, in concert with anomalous changes in ocean circulation. Having rapidly accelerated and retreated following the demise of Larsen A and B, the inland glaciers once feeding these ice shelves now form a significant proportion of Antarctica’s total contribution to global sea-level rise, and have become an exemplar for the fate of the wider Antarctic Ice Sheet under a changing climate. Together with other indicators of glaciological instability observable from satellites, abrupt pre-collapse changes in ice shelf terminus position are believed to have presaged the imminent disintegration of Larsen A and B, which necessitates the need for routine, close observation of this sector in order to accurately forecast the future stability of the Antarctic Peninsula Ice Sheet. To date, however, detailed records of ice terminus position along this region of Antarctica only span the observational period c.1950 to 2008, despite several significant changes to the coastline over the last decade, including the calving of giant iceberg A-68a from Larsen C Ice Shelf in 2017.</p><p>Here, we present high-resolution, annual records of ice terminus change along the entire western Weddell Sea Sector, extending southwards from the former Larsen A Ice Shelf on the eastern Antarctic Peninsula to the periphery of Filchner Ice Shelf. Terminus positions were recovered primarily from Sentinel-1a/b, TerraSAR-X and ALOS-PALSAR SAR imagery acquired over the period 2009-2019, and were supplemented with Sentinel-2a/b, Landsat 7 ETM+ and Landsat 8 OLI optical imagery across regions of complex terrain.</p><p>Confounding Antarctic Ice Sheet-wide trends of increased glacial recession and mass loss over the long-term satellite era, we detect glaciological advance along 83% of the ice shelves fringing the eastern Antarctic Peninsula between 2009 and 2019. With the exception of SCAR Inlet, where the advance of its terminus position is attributable to long-lasting ice dynamical processes following the disintegration of Larsen B, this phenomenon lies in close agreement with recent observations of unchanged or arrested rates of ice flow and thinning along the coastline. Global climate reanalysis and satellite passive-microwave records reveal that this spatially homogenous advance can be attributed to an enhanced buttressing effect imparted on the eastern Antarctic Peninsula’s ice shelves, governed primarily by regional-scale increases in the delivery and concentration of sea ice proximal to the coastline.</p>

scholarly journals Explicit and parametrised representation of under ice shelf seas in a z<sup>*</sup> coordinate ocean model

2017 ◽  
Author(s):  
Pierre Mathiot ◽  
Adrian Jenkins ◽  
Christopher Harris ◽  
Gurvan Madec
Keyword(s):  
Sea Ice ◽  
Continental Shelf ◽  
Weddell Sea ◽  
Depth Range ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Antarctic Continental Shelf ◽  
Shelf Seas ◽  
Ocean Properties ◽  
The Antarctic

Abstract. Ice shelf/ocean interactions are a major source of fresh water on the Antarctic continental shelf and have a strong impact on ocean properties, ocean circulation and sea ice. However, climate models based on the ocean/sea ice model NEMO currently do not include these interactions in any detail. The capability of explicitly simulating the circulation beneath ice shelves is introduced in the non-linear free surface model NEMO. Its implementation into the NEMO framework and its assessment in an idealised and realistic circum-Antarctic configuration is described in this study. Compared with the current prescription of ice shelf melting (i.e. at the surface) inclusion of open sub-ice-shelf leads to a decrease sea ice thickness along the coast, a weakening of the ocean stratification on the shelf, a decrease in salinity of HSSW on the Ross and Weddell Sea shelves and an increase in the strength of the gyres that circulate within the over-deepened basins on the West Antarctic continental shelf. Mimicking the under ice shelf seas overturning circulation by introducing the meltwater over the depth range of the ice shelf base, rather than at the surface is also tested. It yields similar improvements in the simulated ocean properties and circulation over the Antarctic continental shelf than the explicit ice shelf cavity representation. With the ice shelf cavities opened, the widely-used “3 equations” ice shelf melting formulation enables an interactive computation of melting that has been assessed. Comparison with observational estimates of ice shelf melting indicates realistic results for most ice shelves. However, melting rates for Amery, Getz and George VI ice shelves are considerably overestimated.

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

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

&lt;p&gt;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&amp;#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.&lt;/p&gt;

Causes and consequences of Southern Ocean change: the IPCC SROCC assessment

2020 ◽  
Author(s):  
Michael Meredith ◽  
Martin Sommerkorn ◽  
Sandra Cassotta ◽  
Chris Derksen ◽  
Alexey Ekaykin ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Sea Level ◽  
Ocean Circulation ◽  
Global Climate ◽  
Ice Sheets ◽  
The Arctic ◽  
Polar Regions ◽  
Ice Shelves

&lt;p&gt;Climate change in the polar regions exerts a profound influence both locally and over all of our planet.&amp;#160; Physical and ecosystem changes influence societies and economies, via factors that include food provision, transport and access to non-renewable resources.&amp;#160; Sea level, global climate and potentially mid-latitude weather are influenced by the changing polar regions, through coupled feedback processes, sea ice changes and the melting of snow and land-based ice sheets and glaciers.&lt;/p&gt;&lt;p&gt;Reflecting this importance, the IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) features a chapter highlighting past, ongoing and future change in the polar regions, the impacts of these changes, and the possible options for response.&amp;#160; The role of the polar oceans, both in determining the changes and impacts in the polar regions and in structuring the global influence, is an important component of this chapter.&lt;/p&gt;&lt;p&gt;With emphasis on the Southern Ocean and through comparison with the Arctic, this talk will outline key findings from the polar regions chapter of SROCC. It will synthesise the latest information on the rates, patterns and causes of changes in sea ice, ocean circulation and properties. It will assess cryospheric driving of ocean change from ice sheets, ice shelves and glaciers, and the role of the oceans in determining the past and future evolutions of polar land-based ice. The implications of these changes for climate, ecosystems, sea level and the global system will be outlined.&lt;/p&gt;

Quantifying uncertainty in future projections of ice loss from the Filchner-Ronne Ice Shelf System

2020 ◽  
Author(s):  
Emily Hill ◽  
Sebastian Rosier ◽  
Hilmar Gudmundsson ◽  
Matthew Collins
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Weddell Sea ◽  
Future Climate Change ◽  
Model Parameters ◽  
Climate Change Scenarios ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Future Projections

&lt;p&gt;Mass loss from the Antarctic Ice Sheet is the main source of uncertainty in projections of future sea-level rise, with important implications for coastal regions worldwide. Enhanced melt beneath ice shelves could destabilise large parts of the ice sheet, and further increase ice loss. Despite advances in our understanding of feedbacks in the ice sheet-ice shelf-ocean system, future projections of ice loss remain poorly constrained in many parts of Antarctica. In particular, there is ongoing debate surrounding the future of the Filchner-Ronne Ice Shelf (FRIS) region. The FRIS has remained relatively unchanged in recent decades, but an increase in air and ocean temperatures in the neighbouring Weddell Sea, could force rapid retreat in the near future. Indeed, previous modelling work has suggested the potential for widespread infiltration of warm water beneath the ice shelf in the second half of the twenty-first century, leading to a drastic increase in basal melting.&lt;/p&gt;&lt;p&gt;Here, we use the ice flow model &amp;#218;a alongside the ocean box model PICO (Potsdam Ice-shelf Cavity mOdel) to understand the key physical processes and model variability in future projections of sea level rise from the FRIS region. We investigate uncertain model parameters associated with ice dynamics, surface melting and precipitation, ocean temperature forcing, and parameters relating to the strength of basal melt generated by PICO. We optimise the prior distributions of parameters in PICO using observations and a Bayesian approach, leading to improved posterior distributions for use in the following stages of uncertainty quantification. We then run our forward model through the 21&lt;sup&gt;st&lt;/sup&gt; century for various RCP scenarios and extensive random sampling of uncertain parameters to train an emulator. From this, we present probabilistic projections of potential sea level rise from the FRIS region for different future climate change scenarios, together with a sensitivity analysis to identify the most important parameters that contribute to uncertainty in these projections.&lt;/p&gt;

Investigating the climate variability in the Totten area using NEMO-LIM regional model.

2020 ◽  
Author(s):  
Guillian Van Achter ◽  
Charles Pelletier ◽  
Thierry Fichefet
Keyword(s):  
Sea Ice ◽  
Ocean Circulation ◽  
Ice Sheet ◽  
Regional Model ◽  
East Antarctica ◽  
Shelf Area ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Landfast Ice ◽  
The Impact

&lt;p&gt;The Totten ice shelf drains over 570 000 km&amp;#178; of East Antarctica. Most of the ice sheet that drains through the Totten ice-shelf is from Aurora Subglacial Basin and is marine based making the region potentially vulnerable to rapid ice sheet colapse.&lt;br&gt;Understanding how the changes in ocean circulation and properties are causing increased basal melt of Antarctic ice shelves is crucial for predicting future sea level rise.&lt;br&gt;In the context of the The PARAMOUR project (decadal predictability and variability of polar climate: the role of atmosphere-ocean-cryosphere multiscale interaction), we use a high resolution NEMO-LIM 3.6 regional model to investigate the variability and the predictability of the coupled climate system over the Totten area in East Antarctica.&lt;br&gt;In this poster, we will present our on-going work about the impact of landfast ice over the variability of the system. Landfast ice is sea ice that is fastened to the coastline, to the sea floor along shoals or to grouded icebergs. Current sea ice models are unable to represent very crudely the formation, maintenance and decay of coastal landfast ice. We applyed several parameterization for modeling landfast ice over the Totten ice shelf area.&lt;/p&gt;

scholarly journals Intercomparison of Antarctic ice-shelf, ocean, and sea-ice interactions simulated by MetROMS-iceshelf and FESOM 1.4

2018 ◽  
Vol 11 (4) ◽  
pp. 1257-1292 ◽  
Author(s):  
Kaitlin A. Naughten ◽  
Katrin J. Meissner ◽  
Benjamin K. Galton-Fenzi ◽  
Matthew H. England ◽  
Ralph Timmermann ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Water Mass ◽  
Horizontal Resolution ◽  
Ocean Model ◽  
Small Scale ◽  
Ice Shelf ◽  
Vertical Coordinate ◽  
Ice Shelves ◽  
Basal Melting

Abstract. An increasing number of Southern Ocean models now include Antarctic ice-shelf cavities, and simulate thermodynamics at the ice-shelf/ocean interface. This adds another level of complexity to Southern Ocean simulations, as ice shelves interact directly with the ocean and indirectly with sea ice. Here, we present the first model intercomparison and evaluation of present-day ocean/sea-ice/ice-shelf interactions, as simulated by two models: a circumpolar Antarctic configuration of MetROMS (ROMS: Regional Ocean Modelling System coupled to CICE: Community Ice CodE) and the global model FESOM (Finite Element Sea-ice Ocean Model), where the latter is run at two different levels of horizontal resolution. From a circumpolar Antarctic perspective, we compare and evaluate simulated ice-shelf basal melting and sub-ice-shelf circulation, as well as sea-ice properties and Southern Ocean water mass characteristics as they influence the sub-ice-shelf processes. Despite their differing numerical methods, the two models produce broadly similar results and share similar biases in many cases. Both models reproduce many key features of observations but struggle to reproduce others, such as the high melt rates observed in the small warm-cavity ice shelves of the Amundsen and Bellingshausen seas. Several differences in model design show a particular influence on the simulations. For example, FESOM's greater topographic smoothing can alter the geometry of some ice-shelf cavities enough to affect their melt rates; this improves at higher resolution, since less smoothing is required. In the interior Southern Ocean, the vertical coordinate system affects the degree of water mass erosion due to spurious diapycnal mixing, with MetROMS' terrain-following coordinate leading to more erosion than FESOM's z coordinate. Finally, increased horizontal resolution in FESOM leads to higher basal melt rates for small ice shelves, through a combination of stronger circulation and small-scale intrusions of warm water from offshore.

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

1998 ◽  
Vol 27 ◽  
pp. 99-104 ◽  
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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