OS1.9 | Under cover: The Southern Ocean’s connection to sea ice and ice shelves
EDI
Under cover: The Southern Ocean’s connection to sea ice and ice shelves
Co-organized by CR4
Convener: Nadine Steiger | Co-conveners: Stefanie Arndt, Tiago Dotto, Moritz Kreuzer, Torge Martin
Orals
| Thu, 27 Apr, 16:15–18:00 (CEST)
 
Room 1.14
Posters on site
| Attendance Wed, 26 Apr, 14:00–15:45 (CEST)
 
Hall X5
Orals |
Thu, 16:15
Wed, 14:00
The interaction between the ocean and the cryosphere in the Southern Ocean has become a major focus in climate research. Antarctic climate change has captured public attention, which has spawned a number of research questions, such as: Is Antarctic sea ice becoming more vulnerable in a changing climate? Where and when will ocean-driven melting of ice shelves yield a tipping point in the Antarctic climate? How does the Antarctic Slope Current interact with the continental shelf and connect the basins around the continent? What role do ice-related processes play in nutrient upwelling on the continental shelf and in triggering carbon export to deep waters? Recent advances in observational technology, data coverage, and modeling provide scientists with a better understanding of the mechanisms involving ice-ocean interactions in the far South. Processes on the Antarctic continental shelf have been identified as missing links between the cryosphere, the global atmosphere and the deep open ocean that need to be captured in large-scale and global model simulations.

This session calls for studies on physical and biogeochemical oceanography and interactions between ice shelves, sea ice and the ocean. This includes work on all scales, from local to basin-scale to circumpolar; as well as paleo, present-day and future applications. Studies based on in-situ observations, remote sensing and regional to global models are welcome. We particularly invite cross-disciplinary topics involving glaciology and biological oceanography as well as contributions from the PALMOD project and the SCAR INSTANT program.

Orals: Thu, 27 Apr | Room 1.14

Chairpersons: Nadine Steiger, Tiago Dotto, Moritz Kreuzer
16:15–16:20
Sea ice & stratification
16:20–16:30
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EGU23-419
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ECS
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Highlight
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On-site presentation
Bianca Mezzina, Hugues Goosse, Pierre-Vincent Huot, Sylvain Marchi, and Nicole Van Lipzig

The observed evolution of Antarctic sea ice extent is marked by an abrupt decrease in 2016/2017. After several years of gradual increase culminated in an all-time record high in 2014/2015, a rapid decline in 2016 led to an unprecedented minimum, and unusual low extents have been observed since then. Even though this record has now been beaten, the sudden drop from extreme high values to a minimum in less than two years is unique to this event, whose dynamics are still uncertain. While it was likely triggered by anomalous atmospheric conditions in the prior months, the contribution of the ocean conditions, as a preconditioning which amplified the response of the sea ice or helped to maintain the anomalies for a longer period, still needs to be quantified. 

To evaluate the respective influences of the atmosphere and ocean on this 2016 event, we have performed sensitivity experiments using the circum-Antarctic fully coupled model (ice-sheet–ocean–sea-ice–atmosphere) PARASO. First, a control experiment with the model forced by lateral boundary conditions derived from observations (ERA5 in the atmosphere, ORAS5 in the ocean) is performed over the period 1985-2018. In such a set-up, the model correlates well with the observations and is able to capture the 2016 drop. Then, the model is integrated again between 2016 and 2018 with the same atmospheric boundary forcing, but with different initial conditions in the ocean: namely, ocean conditions from previous years in the control run are used as initial state in 2016 in the sensitivity experiments, producing an ensemble of 5 members.

Preliminary results indicate that the 2016 drop is captured by all members, suggesting the atmospheric boundary forcing as the dominant driver and confirming that the event is induced by large-scale atmospheric dynamics. However, some variability is present in the amplitude and timing of the drop, as well as in the evolution and recovery of the sea ice in the following months, which may be influenced by the different states of the ocean. Related processes are further investigated by examining different oceanic and atmospheric fields, focussing on the role of ocean preconditioning by identifying the differences between the members and their impact. 

How to cite: Mezzina, B., Goosse, H., Huot, P.-V., Marchi, S., and Van Lipzig, N.: Contributions of atmospheric forcing and ocean preconditioning in the 2016 Antarctic sea ice extent drop, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-419, https://doi.org/10.5194/egusphere-egu23-419, 2023.

16:30–16:40
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EGU23-480
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ECS
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On-site presentation
Milo Bischof, Daniel Goldberg, Sian Henley, and Neil Fraser

The impacts of upper-ocean mixing on primary productivity are complex and range from an entrainment of nutrients to modulating light limitations. Sea ice in turn plays an important role in determining mixing conditions through its cycles of formation and melt, and by moderating wind forcing. With sea ice conditions in the Southern Ocean projected to undergo large changes over the course of the century, understanding the relationship between sea ice and upper-ocean mixing is crucial for understanding the impacts of climate change on biological production in this region. Due to the inaccessibility of sea ice-covered waters however, mixed layer depth observations are often not available at a high temporal and spatial resolution. Here we present an analysis of sea ice-mixed layer depth relationships during a 40-year regional ocean-sea ice simulation of the  West Antarctic Peninsula (WAP) and Bellingshausen Sea, a highly biologically productive region of global importance. The relationship between winter sea ice and spring mixed layer depth shows clear differences on and off the WAP continental shelf, with decadal variations in the location of the boundary between negative and positive correlations. Potential mechanisms causing this effect are considered in detail, including the nonlinear relationship between sea ice cover and turbulent mixing, the transport of sea ice within the region, and a difference in the timing of the sea ice seasonal cycle between the two regions. The transport of warm Circumpolar Deep Water onto the shelf is also discussed. The presented findings have implications for the spatial distribution of primary producers in a more ice-free future WAP.

How to cite: Bischof, M., Goldberg, D., Henley, S., and Fraser, N.: Spatial variations in the sea ice-mixed layer depth relationship in the West Antarctic Peninsula, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-480, https://doi.org/10.5194/egusphere-egu23-480, 2023.

16:40–16:50
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EGU23-12482
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On-site presentation
Prasanta Sanyal and Ajay ajay

The local temperarturecannot explain the inter-annual variation in δ18Oprecip in the coastal Antarctic in past few decades. To understand this enigmatic variation, we have used long-term modern δ18Oprecip value of three coastal Antarctic sites. Using the δ18O-d-excess relationship and modelled δ18O value of vapor at source, we have shown that δ18Oprecip inherits the signature of moisture source parameters (MSPs). Furthermore, the wavelet analysis suggests that the variation in the MSPs impacts the seasonal cycle of δ18Oprecipwhich lead to disparity in the seasonal isotope-temperature relationship. The Southern Ocean surface stratification, due to increase in the freshwater flux by glacier melting, led to alignment of MSPs in such a manner that altogether significantly lowered the isotopic composition of initially formed vapor, which is reflected in δ18Oprecip at inter-annual scale.Our observations suggest that the palaeothermometry will underestimate the Antarctic temperature change for the periods characterized by warming and high glacier-melt.

How to cite: Sanyal, P. and ajay, A.: The Imprint of Southern Ocean Stratification on the Isotopic Composition of Antarctic Precipitation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12482, https://doi.org/10.5194/egusphere-egu23-12482, 2023.

Cross-shelf exchange
16:50–17:00
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EGU23-5080
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ECS
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Highlight
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On-site presentation
Jennifer Cocks, Alessandro Silvano, Alice Marzocchi, Alberto Naveira-Garabato, and Anna Hogg

Deep convection from dense water formation in the Southern Ocean drives the lower limb of the global overturning circulation, sequesters anthropogenic heat and carbon from the atmosphere and ventilates the abyssal ocean. The rate and location of dense water formation and its trajectory to the deep ocean is determined by changes in ocean density and stratification and influenced by ocean-ice-atmosphere interactions such as polynya openings (both open-ocean and coastal), sea ice formation and ice shelf collapse.

Signatures of deep convection are logistically difficult to measure. The highest-quality observations of water column density are currently provided by in-situ moorings and profiles from Argo floats or CTDs mounted on elephant seals (MEOP data[1]), but these data are spatially and temporally sparse. Satellite products providing complete coverage of high latitudes at regular repeat periods are becoming more readily available and offer an alternative method for capturing changes the extent and variability of deep-water formation in polar regions.

 

We compute steric height anomalies in the Southern Ocean from 2002-2018 using a novel method combining satellite altimetry and gravimetry data. We use these to explore density changes, focussing on deep water formation regions including the Weddell and Ross seas, the Adelie coastline and Amery shelf region, and infer multi-decadal changes in deep convective processes. Long term changes in the steric height anomalies can be linked to recorded ocean-ice events, such as the 2010 collapse of the Mertz glacier, the 2017 Maud Rise polynya and recent recovery of Ross Sea Bottom Water. The satellite-derived steric height anomalies have been validated against in-situ Argo and MEOP profiles and show good agreement in regions with a high data density.


[1]https://meop.net/meop-portal/

How to cite: Cocks, J., Silvano, A., Marzocchi, A., Naveira-Garabato, A., and Hogg, A.: Multi-decadal trends in Antarctic deep convection from satellite-derived steric height, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5080, https://doi.org/10.5194/egusphere-egu23-5080, 2023.

17:00–17:10
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EGU23-12791
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ECS
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On-site presentation
Julius Lauber, Laura de Steur, Tore Hattermann, and Elin Darelius

The Antarctic Slope Front and the associated Antarctic Slope Current shield the continental shelves in East Antarctica from offshore warm water that holds the potential for considerable ice shelf melting and, consequently, sea level rise. Here, we present two-year-long records of temperature, salinity, and velocity (2019-2020), obtained from two oceanographic moorings located within the slope front/current over bathymetries of around 1000m and 2000m slightly east of the prime meridian. The two-year data record reveals clear differences in the seasonality of the thermocline depth and the baroclinicity of the current between the deep and shallow mooring locations. In combination with climatologies of hydrography and satellite-derived surface geostrophic currents, we use the new data to refine the baroclinic seasonality of the ASF. The results highlight the role of surface buoyancy fluxes via seasonal sea ice melt and freeze. Finally, the slope current is shown to control flow into and out of the cavity of the close-by Fimbulisen Ice Shelf on seasonal time scales depending on the orientation of the entrances of the cavity. Our findings contribute to a better understanding of the processes controlling the slope front/current seasonality and resulting inflow into the East-Antarctic ice shelf cavities.

How to cite: Lauber, J., de Steur, L., Hattermann, T., and Darelius, E.: Observed Seasonal Evolution of the Antarctic Slope Current System at the Coast of Dronning Maud Land, East Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12791, https://doi.org/10.5194/egusphere-egu23-12791, 2023.

17:10–17:20
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EGU23-11864
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ECS
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Virtual presentation
Vanessa Teske, Ralph Timmermann, and Tido Semmler

The Filchner Trough on the continental shelf in the southern Weddell Sea is a region of great importance for the water mass exchange between the open ocean and the Filchner Ronne Ice Shelf cavity. Observations of the last 20 years and modelling studies show seasonal variations and longer lasting pulses of warm water intruding into the trough and reaching the Filchner Ice Shelf front. In this study, we evaluate the evolution of these intrusions in four climate scenarios defined for CMIP6 and simulated with the AWI Climate Model. We show that a warming climate will lead to more frequent pulses in the mitigation scenarios SSP1-2.6 and SSP2-4.5. For the high emission scenarios SSP3-7.0 and SSP5-8.5, hydrography in Filchner Trough will shift to a substantially warmer state during the second half of the 21st century with a temperature rise of 2°C in the trough until 2100. We demonstrate that the system‘s tipping into a warmer state is primarily caused by changes in the local sea ice formation and the depth of the Antarctic Slope Front. Our results show that a regime shift can be avoided by reaching the 2°C climate goal.

How to cite: Teske, V., Timmermann, R., and Semmler, T.: Evolution of warm water intrusions in the Filchner Trough, Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11864, https://doi.org/10.5194/egusphere-egu23-11864, 2023.

17:20–17:30
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EGU23-10081
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ECS
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Virtual presentation
Eliza Dawson and Earle Wilson

Ocean circulation patterns along the continental shelf in the Australian Antarctic Basin remain poorly understood due to the scarcity of in-situ observations and limited modeling studies. In this dynamically complex and climatically important region, the Ross Gyre, Antarctic Slope Current, and Antarctic Circumpolar Current converge just offshore of the George V Land continental shelf. If warm deep water could access the continental shelf and increase basal melt rates along the George V Land coastline, marine-terminating glaciers in the region could retreat and threaten the stability of the vast Wilkes Subglacial Basin. Here, we explore potential pathways for warm deep water to access the shelf along the George V Land coastline using output from the Southern Ocean State Estimate (SOSE) model. We use the SOSE output to map bottom temperatures and identify where warm bottom water could come close to the grounding line due to bathymetric steering. While SOSE provides observationally constrained hydrographic estimates along the George V Land continental shelf, there are substantial discrepancies between the model’s estimates and observations. Most notably, SOSE does not reproduce the dense, high salinity shelf waters observed in the region. SOSE is a model-generated best fit to Southern Ocean observations, so biases could be present in sparsely sampled regions like this one. To further examine the dynamics of this region, we also present preliminary results from an idealized ocean circulation model that explores the sensitivity of cross-shelf heat transport to changes in local heat and wind forcing.

How to cite: Dawson, E. and Wilson, E.: Exploring oceanic heat pathways along the George V Land continental shelf, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10081, https://doi.org/10.5194/egusphere-egu23-10081, 2023.

Ice shelf - ocean interaction
17:30–17:40
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EGU23-9657
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Highlight
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On-site presentation
Karen J. Heywood, Esther Portela, Walker Smith, Gillian Damerell, Peter Sheehan, and Meredith Meyer

Relatively warm modified Circumpolar Deep Water accesses the southern Ross Sea steered by bathymetric troughs. There it provides nutrients to support phytoplankton blooms in spring, and heat to melt the Ross Ice Shelf.  Here we present new observations collected by two ocean gliders during December 2022 and January 2023, in the Ross Sea polynya adjacent to the Ross Ice Shelf.  The gliders surveyed the full depth of the water column (about 700 m depth) carrying sensors measuring temperature, salinity, dissolved oxygen, chlorophyll fluorescence and optical backscatter, and also yielded estimates of the dive-average-current which we use to reference geostrophic shear.  Repeated quasi-meridional high resolution (profiles approximately every 1.5 km) sections along the sea ice edge allow analysis of the spatial and temporal variability, as well capturing the dynamic field of eddies, tides and coastal current. We discuss the influence of the sea ice and the atmospheric forcing on the water properties. One glider made an unauthorised foray beneath the Ross Ice Shelf, surveying the upper 200 m of the water column in high resolution beneath an ice shelf base at about 80 m depth. We observe solar-warmed water penetrating beneath the ice shelf with significant signatures of elevated chlorophyll fluorescence and optical backscatter, and low oxygen and salinity. We discuss the likely mechanisms involved in advecting this water beneath the ice shelf and its importance for physical and biogeochemical processes of ocean-ice interaction.



How to cite: Heywood, K. J., Portela, E., Smith, W., Damerell, G., Sheehan, P., and Meyer, M.: Spatial and temporal variability of water masses in the Southern Ross Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9657, https://doi.org/10.5194/egusphere-egu23-9657, 2023.

17:40–17:50
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EGU23-6731
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ECS
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On-site presentation
Pengyang Song, Patrick Scholz, Gregor Knorr, Dmitry Sidorenko, Ralph Timmermann, and Gerrit Lohmann

The melting of the Antarctic ice shelves becomes critical in a warming climate. However, the ocean component of climate models do not consider the effect of the Antarctic ice-shelf cavities. Here, we implement ice-shelf cavity features into the new AWI Earth system model (AWI-ESM2) based on unstructured meshes allowing for varying resolution in a multi-scale approach. We create a global mesh explicitly resolving the Antarctic ice-shelf cavities and evaluate the effect of the cavities under global warming scenarios. The new mesh provides a more realistic freshwater input into the Antarctic coast and the Southern Ocean. In an extreme warming climate scenario, the melting of the Antarctic ice shelves gets stronger by a factor of ~3, affecting the North Atlantic salinity and the overturning circulation. We conclude that the incorporation of ice-cavity feedback is essential to study the past, present, and future. Our approach might be seen as a prototype for the next phase of the Coupled Model Intercomparison Project.

How to cite: Song, P., Scholz, P., Knorr, G., Sidorenko, D., Timmermann, R., and Lohmann, G.: The ice-cavity feedback in an Earth system model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6731, https://doi.org/10.5194/egusphere-egu23-6731, 2023.

17:50–18:00
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EGU23-15622
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ECS
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Highlight
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Virtual presentation
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Ole Richter, Ben Galton-Fenzi, Kaitlin Naugthen, and Ralph Timmermann

Understanding the processes involved in basal melting of Antarctic ice shelves is important to quantify the rate at which Antarctica will lose mass. Current research of ice shelf-ocean interaction highlights deep warm water intrusions and melting along narrow grounding lines. The majority of the ice, however, lies in much shallower waters. Here we analyse the vertical structure of previously published Antarctic-wide estimates of ice shelf basal melting derived from satellites and ice shelf buttressing derived from ice sheet flow modelling. The results show that ice shelf regions with a draft shallower than 500 m account for more than 60 % of the total basal mass loss and more than 30 % of the total buttressing flux response. The oceanic processes that drive melting in shallow regions might be very different compared to the ones at depth and how well these are represented in large-scale models of Antarctic ice shelf-ocean interaction is not clear. This gap should be addressed for more accurate predictions of the Antarctic response to climate change.

 

How to cite: Richter, O., Galton-Fenzi, B., Naugthen, K., and Timmermann, R.: Ice shelf-ocean interaction at shallow depths needs more attention, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15622, https://doi.org/10.5194/egusphere-egu23-15622, 2023.

Posters on site: Wed, 26 Apr, 14:00–15:45 | Hall X5

Chairpersons: Torge Martin, Nadine Steiger
X5.360
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EGU23-13222
Verena Haid, Ralph Timmermann, Simon Schöll, Torsten Albrecht, and Hartmut H. Hellmer

A potential tipping point on the Antarctic continental shelves, in which cold shelf water is replaced by (modified) Circumpolar Deep Water (CDW) / Warm Deep Water (WDW), is currently the subject of many studies. Such a regime shift entails a drastic increase of basal melt for the fringing ice shelves and could ultimately destabilize large portions of the Antarctic ice sheet.

From the results of a large suite of experiments conducted with the Finite Element Sea ice-Ocean Model (FESOM), we identified for the Weddell Sea the density balance between the densest shelf water produced on the continental shelf and the WDW present on the continental slope at sill depth (shallowest depth of deepest connection to the cavity) as the crucial criterion for a shift in on-shelf circulation leading to a substantially increased heat flux into the cavity. This finding holds true for model runs using both z-level and sigma vertical coordinates as well as ocean-ice sheet (with the Parallel Ice Sheet Model, PISM) coupled model runs. We also find evidence that the same principle is valid in other Antarctic regions with a backward-sloping continental shelf.

Apart from the shelf water characteristics that largely depend on sea ice formation, the development of CDW/WDW characteristics  is crucial, but often neglected, in this context, especially in regional model studies. If under the influence of the globally warming climate the continental slope current becomes warmer and fresher, the associated density decrease could keep the continental shelf stable. Even if none of the on-shelf water classifies as High Salinity Shelf Water any more, as long as it is denser than the off-shelf CDW/WDW, it will block access to the cavity and prevent a regime shift.

How to cite: Haid, V., Timmermann, R., Schöll, S., Albrecht, T., and Hellmer, H. H.: The role of WDW density for a regime shift in the FRIS cavity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13222, https://doi.org/10.5194/egusphere-egu23-13222, 2023.

X5.361
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EGU23-16106
Svein Østerhus

Long term observations of the flow of dense waters from their area of formation to the abyss of the World Ocean, and the return flow of warm waters, are central to climate research. For the Weddell Sea an important component of such a system entail monitoring the formation of High Salinity Shelf Water (HSSW) on the continental shelf north of Ronne Ice Front, the transformation to Ice Shelf Water (ISW) beneath the floating Filchner-Ronne ice shelf, and the flux of ISW overflowing the shelf break to the deep Weddell Sea. Equally important is the return flow of warm water toward the Filchner-Ronne Ice Shelf system.

We operate several monitoring stations in the southern Weddell Sea. The systems build upon techniques and methods developed over several decades and have a proven record of high data return. Here we present plans for extending, integrating, and operating the existing long-term observatories to increase our knowledge of the natural variability of the ocean-ice shelf system, and to allow early identification of possible changes of regional or global importance.

How to cite: Østerhus, S.: Weddell Watch, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16106, https://doi.org/10.5194/egusphere-egu23-16106, 2023.

X5.362
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EGU23-3111
Markus Janout, Mathias van Caspel, Elin Darelius, Tore Hattermann, Svein Østerhus, Jean-Baptiste Sallée, and Nadine Steiger

The southern Weddell Sea features a vast perennially ice-covered continental shelf with polynyas, strong sea ice formation, first- and multi-year ice. Sea ice and the general ocean circulation maintain predominantly near-freezing waters on the shelf, which help to maintain the comparatively moderate basal melt rates of the Filchner-Ronne Ice Shelf (FRIS), Antarctica’s largest ice shelf by volume. In contrast to FRIS, other West Antarctic ice shelves show strong basal melt rates, caused by warm intruding ocean waters. In the southern Weddell Sea, however, warm water inflows occur episodically and spatially limited, when modified warm deep water enters the continental shelf through incisions in the shelf break and flows southward towards the FRIS front. Overall, the majority of the shelf is dominated by dense and cold water masses such as High Salinity Shelf Water (HSSW) and Ice Shelf Water (ISW), which are precursors of Antarctic Bottom Water and thus relevant for the global ocean circulation. In 2018, a comprehensive CTD survey found unprecedented (in the available observations) volumes of ISW in Filchner Trough. The ISW was exported from underneath the Filchner Ice Shelf (FIS) following a shift to enhanced cavity circulation due to strong sea ice formation in front of the Ronne Ice Shelf. These Filchner Trough conditions are summarized as the “Ronne-mode”, which is in contrast to the “Berkner-mode”, characterized by a greater influence of locally-formed waters. In this presentation, we introduce new multi-year time series from an international mooring network from various Southeast Weddell Sea locations (sub-FIS, Filchner Trough and Sill), to highlight the temporal and spatial extent of the recent Ronne-mode event, which lasted from 2018-2020, before shifting back into a Berkner-mode. The dominance of either circulation mode is controlled by large-scale atmospheric forcing and has implications on ice shelf basal melt and dense water export into the Weddell Sea. 

How to cite: Janout, M., van Caspel, M., Darelius, E., Hattermann, T., Østerhus, S., Sallée, J.-B., and Steiger, N.: On the 2018-2020 Ice Shelf Water outflow event in the southeastern Weddell Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3111, https://doi.org/10.5194/egusphere-egu23-3111, 2023.

X5.363
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EGU23-11464
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ECS
DongYoub Shin, Doshik Hahm, Tae-Wan Kim, Tae Siek Rhee, SangHoon Lee, Keyhong Park, Jisoo Park, Young Shin Kwon, Mi Seon Kim, and Tongsup Lee

To estimate the glacial meltwater distribution, we used five noble gases as tracers for optimum multiparameter analysis (OMPA) of the water masses in the Amundsen Sea, Antarctic. The increased number of tracers allowed us to define additional source waters at the surface, which have not been possible with a limited number of tracers. The highest fraction of submarine meltwater (SMW, ~0.6%) was present at the depth of 400 -- 500 m near the Dotson Ice Shelf. The SMW appeared to travel along an isopycnal layer to the continental shelf break >300 km away from the ice shelf. Ventilated SMW (VMW) and surface melts (up to 1.5%) were present in the surface layer <100 m. The distribution of SMW indicates that upwelled SMW, known as an important carrier of iron to the upper layer, amounts for 29% of the SMW in the Dotson Trough. The distinction between SMW and VMW made it possible to clearly distinguish the locally-produced SMW since the previous Winter Water formation from the fresh water (VMW) originated from the upstream; the production rate of the former was estimated as 53-94 G ton yr-1. The Meteoric Water fractions, consisted of SMW and VMW, comprised 24% of those derived from oxygen isotopes. This indicates that the annual input from basal melting is far less than the inventory of meteoric water derived from oxygen istopes.

How to cite: Shin, D., Hahm, D., Kim, T.-W., Rhee, T. S., Lee, S., Park, K., Park, J., Kwon, Y. S., Kim, M. S., and Lee, T.: Identification of ventilated and submarine glacial meltwaters in the Amundsen Sea, Antarctica, using noble gases, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11464, https://doi.org/10.5194/egusphere-egu23-11464, 2023.

X5.364
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EGU23-3627
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ECS
Irena Vankova, Xylar Asay-Davis, and Stephen Price

In-situ observations from the Filchner-Ronne Ice Shelf (FRIS) have uncovered dominant time scales of variability in basal melting and circulation beneath this extensive ice shelf. In particular, the data characterize mechanisms of seasonal and inter-annual variability in sub-ice shelf properties, and show that the amplitude of the variability over the past thirty years is very modest.
Because accurate representation of variability under present-day climate is an obvious prerequisite for earth system models that aim to project climate under a future change, this new observational understanding presents an opportunity for critical evaluation and improvement of existing models. We focus on the Energy Exascale Earth System Model (E3SM) and through a series of simulations we investigate the impact of ocean mixing parameterizations on the variability in the FRIS cavity.

How to cite: Vankova, I., Asay-Davis, X., and Price, S.: Sub-ice shelf circulation and melt rate variability in the Energy Exascale Earth System Model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3627, https://doi.org/10.5194/egusphere-egu23-3627, 2023.

X5.365
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EGU23-13262
Xylar Asay-Davis, Carolyn Begeman, Darren Engwirda, Holly Han, Matthew Hoffman, and Stephen Price

We present our approach to coupling an ocean component (MPAS-Ocean, Model for Prediction Across Scales-Ocean) to an ice sheet component (MALI, MPAS-Albany Land Ice) within an Earth System Model (E3SM, the Energy Exascale Earth System Model) developed by the US Department of Energy.  First, we present an extrapolation technique, similar to the ISMIP6 (Ice Sheet Modeling for CMIP6) protocol, that can be used in the absence of evolving grounding lines in the ocean component.  This technique, while crude, can be used in both Greenland fjords and ice-shelf cavities as a stop-gap in situations where the ocean component cannot capture the topographic evolution (e.g. because the ocean grid is too coarse or full coupling has not yet been completed).  Second, we demonstrate progress on a fully conservative wetting-and-drying technique using the idealized MISOMIP1 (Marine Ice Sheet-Ocean Intercomparison Project, phase 1) experiments within E3SM.

How to cite: Asay-Davis, X., Begeman, C., Engwirda, D., Han, H., Hoffman, M., and Price, S.: Ice sheet-ocean coupling in an Earth System Model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13262, https://doi.org/10.5194/egusphere-egu23-13262, 2023.

X5.366
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EGU23-4468
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ECS
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Antonino Ian Ferola, Yuri Cotroneo, Peter Wadhams, Giannetta Fusco, Pierpaolo Falco, Giorgio Budillon, and Giuseppe Aulicino

Monitoring the Antarctic sea-ice is essential for improving our knowledge of the Southern Ocean. We used satellite sea-ice concentration data for the 2002-2020 period to retrieve the sea-ice extent (SIE) and analyze its variability in the Pacific sector of the Southern Ocean. Results provide observational evidence of the recurring formation of a sea-ice protrusion that extends to 60° S at 150° W during the winter season. These activities are carried on in the framework of the ACCESS and SWIMMING projects of the PNRA.
Our findings show that the northward deflection of the southern Antarctic Circumpolar Current front is driven by the Pacific Antarctic Ridge (PAR) and is associated with the enhanced sea-ice advance. The PAR also constrains anticyclonic and cyclonic eddy trajectories, limiting their interaction with the sea-ice edge. These factors, within the 160° W - 135° W sector, determine an average SIE increase of 61,000 km2 and 46,293 km2 per year more than the upstream and downstream areas, respectively.

How to cite: Ferola, A. I., Cotroneo, Y., Wadhams, P., Fusco, G., Falco, P., Budillon, G., and Aulicino, G.: The role of the Pacific-Antarctic Ridge in establishing the northward extent of Antarctic sea-ice, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4468, https://doi.org/10.5194/egusphere-egu23-4468, 2023.

X5.367
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EGU23-6398
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ECS
Relevance of inherent snow property variability for the large-scale Antarctic sea ice mass budget
(withdrawn)
Stefanie Arndt, Marcel Nicolaus, and Christian Haas