Influence of fast ice on future ice shelf melting in the Totten Glacier area, East Antarctica

The Totten Glacier in East Antarctica is of major climatic interest because of the large fluctuations in its grounding line and potential vulnerability to climate change. Here, we use a series of high-resolution, regional NEMO-LIM-based (Nucleus for European Modelling of the Ocean coupled with the Louvain-la-Neuve sea ice model) experiments, which include an explicit treatment of ocean–ice shelf interactions, as well as a representation of grounded icebergs and fast ice, to investigate the changes in ocean–ice interactions in the Totten Glacier area between the recent past (1995–2014) and the end of the 21st century (2081–2100) under SSP4–4.5 climate change conditions. By the end of the 21st century, the wide areas of multiyear fast ice simulated in the recent past are replaced by small patches of first year fast ice along the coast, which decreases the total summer sea ice extent. The Antarctic Slope Current is accelerated by about 116 %, which decreases the heat exchange across the shelf and tends to reduce the ice shelf basal melt rate, but this effect is counterbalanced by the effect of the oceanic warming. As a consequence, despite the accelerated Antarctic Slope Current, the Totten ice shelf melt rate is increased by 91 % due to the intrusion of warmer water into its cavity. The representation of fast ice dampens the ice shelf melt rate increase throughout the 21st century, as the Totten ice shelf melt rate increase reaches 136 % when fast ice is not taken into account. The Moscow University ice shelf melt rate increase is even more impacted by the representation of fast ice, with a 36 % melt rate increase with fast ice, compared to a 75 % increase without a fast ice representation. This influence of the representation of fast ice in our simulations on the basal melting rate trend over the 21st century is explained by the large impact of the fast ice for present-day conditions (∼25 % difference in m yr−1), while the impact decreases significantly at the end of the 21st century (∼4 % difference in m yr−1). As a consequence, the reduction in the fast ice extent in the future induces a decrease in the fast ice effect on the ice shelf melt rate that partly compensates for the increase due to warming of the ocean. This highlights the importance of including a representation of fast ice to simulate realistic ice shelf melt rate increase in East Antarctica under warming conditions.</p

Influence of fast ice on future ice shelf melting in the Totten Glacier area, East Antarctica

The Totten Glacier in East Antarctica is of major climatic interest because of the large fluctuations in its grounding line and potential vulnerability to climate change. Here, we use a series of high-resolution, regional NEMO-LIM-based (Nucleus for European Modelling of the Ocean coupled with the Louvain-la-Neuve sea ice model) experiments, which include an explicit treatment of ocean–ice shelf interactions, as well as a representation of grounded icebergs and fast ice, to investigate the changes in ocean–ice interactions in the Totten Glacier area between the recent past (1995–2014) and the end of the 21st century (2081–2100) under SSP4–4.5 climate change conditions. By the end of the 21st century, the wide areas of multiyear fast ice simulated in the recent past are replaced by small patches of first year fast ice along the coast, which decreases the total summer sea ice extent. The Antarctic Slope Current is accelerated by about 116 %, which decreases the heat exchange across the shelf and tends to reduce the ice shelf basal melt rate, but this effect is counterbalanced by the effect of the oceanic warming. As a consequence, despite the accelerated Antarctic Slope Current, the Totten ice shelf melt rate is increased by 91 % due to the intrusion of warmer water into its cavity. The representation of fast ice dampens the ice shelf melt rate increase throughout the 21st century, as the Totten ice shelf melt rate increase reaches 136 % when fast ice is not taken into account. The Moscow University ice shelf melt rate increase is even more impacted by the representation of fast ice, with a 36 % melt rate increase with fast ice, compared to a 75 % increase without a fast ice representation. This influence of the representation of fast ice in our simulations on the basal melting rate trend over the 21st century is explained by the large impact of the fast ice for present-day conditions (∼25 % difference in m yr−1), while the impact decreases significantly at the end of the 21st century (∼4 % difference in m yr−1). As a consequence, the reduction in the fast ice extent in the future induces a decrease in the fast ice effect on the ice shelf melt rate that partly compensates for the increase due to warming of the ocean. This highlights the importance of including a representation of fast ice to simulate realistic ice shelf melt rate increase in East Antarctica under warming conditions.</p

Modelling ice–ocean interactions in the Totten Glacier area, East Antarctica, under present and future conditions

The Antarctic Climate is characterized by strong interactions between the ocean, cryosphere and atmosphere and it plays a key role in the Earth’s Climate by driving the storage and redistribution of heat, freshwater and CO2. However, our understanding of the Antarctic Climate processes are still limited due to the scarcity of in-situ observations. In addition, climate models are biased when simulating the current state of the climate and disagree on the future of Antarctica. The missing piece of the puzzle might be the small-scale processes. These climate processes, that take place at scale smaller than 100 km, are particularly hard to observe and cannot be explicitly resolved by most climate models due to they coarse horizontal resolution. In this thesis, we study the role of some small-scale processes in the interactions between the ocean and the cryosphere using a high-resolution numerical model. We focus on the Totten Glacier area in East Antarctica, a region of Antarctic fast ice, grounded icebergs, coastal polynyas, ice shelves and modified Circumpolar Deep Water. With the development of a regional configuration, high-resolution ocean-ice sheet-sea ice model, we investigate a first formulation to represent the Antarctic fast ice, the effect of a warming climate on the ice-ocean interactions and the effect of the ice sheet-ocean coupling on the ice-ocean interactions. Our findings indicate that these small-scale processes could have significant implications for the dynamics of the Antarctic Climate and its response to anthropogenic forcing. This thesis contributes to our comprehension of rarely observed processes and underscores the importance of including them in climate models. By recognizing the significance of these processes, we can improve the accuracy of climate projections and ultimately make more informed decisions to address climate change.(SC - Sciences) -- UCL, 202

Brief communication: Arctic sea ice thickness internal variability and its changes under historical and anthropogenic forcing

We use model simulations from the CESM1-CAM5-BGC-LE dataset to characterise the Arctic sea ice thickness internal variability both spatially and temporally. These properties, and their stationarity, are investigated in three different contexts: (1) constant pre-industrial, (2) historical and (3) projected conditions. Spatial modes of variability show highly stationary patterns regardless of the forcing and mean state. A temporal analysis reveals two peaks of significant variability, and despite a non-stationarity on short timescales, they remain more or less stable until the first half of the 21st century, where they start to change once summerice-free events occur, after 2050

Statistical predictability of the Arctic sea ice volume anomaly: identifying predictors and optimal sampling locations

This work evaluates the statistical predictabilityof the Arctic sea ice volume (SIV) anomaly – here definedas the detrended and deseasonalized SIV – on the interan-nual timescale. To do so, we made use of six datasets, fromthree different atmosphere–ocean general circulation models,with two different horizontal grid resolutions each. Basedon these datasets, we have developed a statistical empiricalmodel which in turn was used to test the performance of dif-ferent predictor variables, as well as to identify optimal lo-cations from where the SIV anomaly could be better recon-structed and/or predicted. We tested the hypothesis that anideal sampling strategy characterized by only a few optimalsampling locations can provide in situ data for statisticallyreproducing and/or predicting the SIV interannual variabil-ity. The results showed that, apart from the SIV itself, thesea ice thickness is the best predictor variable, although totalsea ice area, sea ice concentration, sea surface temperature,and sea ice drift can also contribute to improving the pre-diction skill. The prediction skill can be enhanced furtherby combining several predictors into the statistical model.Applying the statistical model with predictor data from fourwell-placed locations is sufficient for reconstructing about70 % of the SIV anomaly variance. As suggested by theresults, the four first best locations are placed at the tran-sition Chukchi Sea–central Arctic–Beaufort Sea (79.5◦N,158.0◦W), near the North Pole (88.5◦N, 40.0◦E), at the tran-sition central Arctic–Laptev Sea (81.5◦N, 107.0◦E), and off-shore the Canadian Archipelago (82.5◦N, 109.0◦W), in thisrespective order. Adding further to six well-placed locations,which explain about 80 % of the SIV anomaly variance, thestatistical predictability does not substantially improve tak-ing into account that 10 locations explain about 84 % of thatvariance. An improved model horizontal resolution allows abetter trained statistical model so that the reconstructed val-ues better approach the original SIV anomaly. On the otherhand, if we inspect the interannual variability, the predictorsprovided by numerical models with lower horizontal reso-lution perform better when reconstructing the original SIVvariability. We believe that this study provides recommenda-tions for the ongoing and upcoming observational initiatives,in terms of an Arctic optimal observing design, for studyingand predicting not only the SIV values but also its interannualvariability

Ocean–Ice Sheet Coupling in the Totten Glacier Area, East Antarctica: Analysis of the Feedbacks and Their Response to a Sudden Ocean Warming

We coupled together high-resolution versions of the ocean–sea ice model NEMO and the ice sheet model BISICLES configured to the Totten Glacier area and ran a series of simulations over the recent past (1995–2014) and under warming conditions (2081–2100; SSP4-4.5) with NEMO in stand-alone mode and with the coupled model to assess the effects of the coupling. During the recent past, the ocean–ice sheet coupling has increased the time-averaged value of the basal melt rate in both the Totten and Moscow University ice shelf cavities by 6.7% and 14.2%, respectively. The relationship between the changes in ice shelf thickness and ice shelf basal melt rate suggests that the effect of the coupling is not a linear response to the melt rate but rather a more complex response, driven partly by the dynamical component of the ice sheet model. The response of the ice sheet–ocean coupling due to the ocean warming is a 10% and 3% basal melt rate decrease in the Totten and Moscow University ice shelf cavities, respectively. This indicates that the ocean–ice sheet coupling under climate warming conditions dampens the basal melt rates. Our study highlights the importance of incorporating ocean–ice sheet coupling in climate simulations, even over short time periods.info:eu-repo/semantics/publishe

Modelling landfast sea ice and its influence on ocean–ice interactions in the area of the Totten Glacier, East Antarctica

The Totten Glacier in East Antarctica is of major climate interest because of the large fluctuation of its grounding line and of its potential vulnerability to climate change. The ocean above the continental shelf in front of the Totten ice shelf exhibits large extents of landfast sea ice with low interannual variability. Landfast sea ice is either crudely or not at all represented in current climate models. These models are potentially omitting or misrepresenting important effects related to this type of sea ice, such as its influence on coastal polynya locations. Yet, the impact of the landfast sea ice on the ocean–ice shelf interactions is poorly understood. Using a series of high-resolution, regional NEMO-LIM-based experiments, including an explicit treatment of ocean–ice shelf interactions, over the years 2001–2010, we simulate a realistic landfast sea ice extent in the area of Totten Glacier through a combination of a sea ice tensile strength parameterisation and a grounded iceberg representation. We show that the presence of landfast sea ice impacts seriously both the location of coastal polynyas and the ocean mixed layer depth along the coast, in addition to favouring the intrusion of mixed Circumpolar Deep Water into the ice shelf cavities. Depending on the local bathymetry and the landfast sea ice distribution, landfast sea ice affects ice shelf cavities differently. The Totten ice shelf melt rate is increased by 16% on average and its variance decreased by 38%, while the Moscow University ice shelf melt rate is increased by in winter. This highlights the importance of including an accurate landfast sea ice representation in regional and eventually global climate models

The potential of numerical prediction systems to support the design of Arctic observing systems: insights from the APPLICATE and YOPP projects

Numerical systems used for weather and climate predictions have substantially improved over past decades. We argue that despite a continued need for further addressing remaining limitations of their key components, numerical prediction systems have reached a sufficient level of maturity to examine and critically assess the suitability of Earth's current observing systems – remote and in situ, for prediction purposes; and that they can provide evidence-based support for the deployment of future observational networks. We illustrate this point by presenting recent, co-ordinated international efforts focused on Arctic observing systems, led in the framework of the Year of Polar Prediction and the H2020 project APPLICATE. The Arctic, one of the world's most rapidly changing regions, is relatively poorly covered in terms of in situ data but richly covered in terms of satellite data. In this study, we demonstrate that existing state-of-the-art datasets and targeted sensitivity experiments produced with numerical prediction systems can inform us of the added value of existing or even hypothetical Arctic observations, in the context of predictions from hourly to interannual time-scales. Furthermore, we argue that these datasets and experiments can also inform us how the uptake of Arctic observations in numerical prediction systems can be enhanced to maximise predictive skill. Based on these efforts we suggest that (a) conventional in situ observations in the Arctic play a particularly important role in initializing numerical weather forecasts during the winter season, (b) observations from satellite microwave sounders play a particularly important role during the summer season, and their enhanced usage over snow and sea ice is expected to further improve their impact on predictive skill in the Arctic region and beyond, (c) the deployment of a small number of in situ sea-ice thickness monitoring devices at strategic sampling sites in the Arctic could be sufficient to monitor most of the large-scale sea-ice volume variability, and (d) sea-ice thickness observations can improve the simulation of both the sea ice and near-surface air temperatures on seasonal time-scales in the Arctic and beyond