Rapid accelerations of Antarctic Peninsula outlet glaciers driven by surface melt

Atmospheric warming is increasing surface melting across the Antarctic Peninsula, with unknown impacts upon glacier dynamics at the ice-bed interface. Using high-resolution satellite-derived ice velocity data, optical satellite imagery and regional climate modelling, we show that drainage of surface meltwater to the bed of outlet glaciers on the Antarctic Peninsula occurs and triggers rapid ice flow accelerations (up to 100% greater than the annual mean). This provides a mechanism for this sector of the Antarctic Ice Sheet to respond rapidly to atmospheric warming. We infer that delivery of water to the bed transiently increases basal water pressure, enhancing basal motion, but efficient evacuation subsequently reduces water pressure causing ice deceleration. Currently, melt events are sporadic, so efficient subglacial drainage cannot be maintained, resulting in multiple short-lived (< 6 day) ice flow perturbations. Future increases in meltwater could induce a shift in glacier dynamic regime, characterised by seasonal-scale ice flow variations

Automated mapping of the seasonal evolution of surface meltwater and its links to climate on the Amery Ice Shelf, Antarctica

Surface meltwater is widespread around the Antarctic Ice Sheet margin and has the potential to influence ice shelf stability, ice flow and ice–albedo feedbacks. Our understanding of the seasonal and multi-year evolution of Antarctic surface meltwater is limited. Attempts to generate robust meltwater cover time series have largely been constrained by computational expense or limited ice surface visibility associated with mapping from optical satellite imagery. Here, we add a novel method for calculating visibility metrics to an existing meltwater detection method within Google Earth Engine. This enables us to quantify uncertainty induced by cloud cover and variable image data coverage, allowing time series of surface meltwater area to be automatically generated over large spatial and temporal scales. We demonstrate our method on the Amery Ice Shelf region of East Antarctica, analysing 4164 Landsat 7 and 8 optical images between 2005 and 2020. Results show high interannual variability in surface meltwater cover, with mapped cumulative lake area totals ranging from 384 to 3898 km2 per melt season. By incorporating image visibility assessments, however, we estimate that cumulative total lake areas are on average 42 % higher than minimum mapped values. We show that modelled melt predictions from a regional climate model provide a good indication of lake cover in the Amery region and that annual lake coverage is typically highest in years with a negative austral summer SAM index. Our results demonstrate that our method could be scaled up to generate a multi-year time series record of surface water extent from optical imagery at a continent-wide scale

Characteristics of the modelled meteoric freshwater budget of the western Antarctic Peninsula

Rapid climatic changes in the western Antarctic Peninsula (WAP) have led to considerable changes in the meteoric freshwater input into the surrounding ocean, with implications for ocean circulation, the marine ecosystem and sea-level rise. In this study, we use the high-resolution Regional Atmospheric Climate Model RACMO2.3, coupled to a firn model, to assess the various contributions to the meteoric freshwater budget of the WAP for 1979–2014: precipitation (snowfall and rainfall), meltwater runoff to the ocean, and glacial discharge. Snowfall is the largest component in the atmospheric contribution to the freshwater budget, and exhibits large spatial and temporal variability. The highest snowfall rates are orographically forced and occur over the coastal regions of the WAP (View the MathML source>2000mm water equivalent (w.e.) y−1y−1) and extend well onto the ocean up to the continental shelf break; a minimum View the MathML source(∼500mmw.e.y−1) is reached over the open ocean. Rainfall is an order of magnitude smaller, and strongly depends on latitude and season, being large in summer, when sea ice extent is at its minimum. For Antarctic standards, WAP surface meltwater production is relatively large View the MathML source(>50mmw.e.y−1), but a large fraction refreezes in the snowpack, limiting runoff. Only at a few more northerly locations is the meltwater predicted to run off into the ocean. In summer, we find a strong relationship of the freshwater fluxes with the Southern Annular Mode (SAM) index. When SAM is positive and occurs simultaneously with a La Niña event there are anomalously strong westerly winds and enhanced snowfall rates over the WAP mountains, Marguerite Bay and the Bellingshausen Sea. When SAM coincides with an El Niño event, winds are more northerly, reducing snowfall and increasing rainfall over the ocean, and enhancing orographic snowfall over the WAP mountains. Assuming balance between snow accumulation (mass gain) and glacial discharge (mass loss), the largest glacial discharge is found for the regions around Adelaide Island View the MathML source(10Gty−1), Anvers Island View the MathML source(8Gty−1) and southern Palmer Land View the MathML source(12Gty−1), while a minimum View the MathML source(<2Gty−1) is found in Marguerite Bay and the northern WAP. Glacial discharge is in the same order of magnitude as the direct freshwater input into the ocean from snowfall, but there are some local differences. The spatial patterns in the meteoric freshwater budget have consequences for local productivity and carbon drawdown in the coastal ocean

Regional climate of the Larsen B embayment 1980–2014

Understanding the climate response of the Antarctic Peninsula ice sheet is vital for accurate predictions of sea-level rise. However, since climate models are typically too coarse to capture spatial variability in local scale meteorological processes, our ability to study specific sectors has been limited by the local fidelity of such models and the (often sparse) availability of observations. We show that a high-resolution (5.5 km × 5.5 km) version of a regional climate model (RACMO2.3) can reproduce observed interannual variability in the Larsen B embayment sufficiently to enable its use in investigating long-term changes in this sector. Using the model, together with automatic weather station data, we confirm previous findings that the year of the Larsen B ice shelf collapse (2001/02) was a strong melt year, but discover that total annual melt production was in fact ~30% lower than 2 years prior. While the year before collapse exhibited the lowest melting and highest snowfall during 1980–2014, the ice shelf was likely pre-conditioned for collapse by a series of strong melt years in the 1990s. Melt energy has since returned to pre-1990s levels, which likely explains the lack of further significant collapse in the region (e.g. of SCAR Inlet)

The modelled surface mass balance of the Antarctic Peninsula at 5.5 km horizontal resolution.

This study presents a high-resolution (similar to 5.5 km) estimate of surface mass balance (SMB) over the period 1979-2014 for the Antarctic Peninsula (AP), generated by the regional atmospheric climate model RACMO2.3 and a firn densification model (FDM). RACMO2.3 is used to force the FDM, which calculates processes in the snowpack, such as meltwater percolation, refreezing and runoff. We evaluate model output with 132 in situ SMB observations and discharge rates from six glacier drainage basins, and find that the model realistically simulates the strong spatial variability in precipitation, but that significant biases remain as a result of the highly complex topography of the AP. It is also clear that the observations significantly underrepresent the high-accumulation regimes, complicating a full model evaluation. The SMB map reveals large accumulation gradients, with precipitation values above 3000 mm we yr(-1) in the western AP (WAP) and below 500 mm we yr(-1) in the eastern AP (EAP), not resolved by coarser data sets such as ERA-Interim. The average AP ice-sheet-integrated SMB, including ice shelves (an area of 4.1 x 10(5) km(2)), is estimated at 351 Gt yr(-1) with an interannual variability of 58 Gt yr(-1), which is dominated by precipitation (PR) (365 +/- 57 Gt yr(-1)). The WAP (2.4 x 10(5) km(2)) SMB (276 +/- 47 Gt yr(-1)), where PR is large (276 +/- 47 Gt yr(-1)), dominates over the EAP (1.7 x 10(5) km(2)) SMB (75 +/- 11 Gt yr(-1)) and PR (84 +/- 11 Gt yr(-1)). Total sublimation is 11 +/- 2 Gt yr(-1) and meltwater runoff into the ocean is 4 +/- 4 Gt yr(-1). There are no significant trends in any of the modelled AP SMB components, except for snowmelt that shows a significant decrease over the last 36 years (-0.36 Gt yr(-2))

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

High-resolution climate modelling of Antarctica and the Antarctic Peninsula

In this thesis we have used a high-resolution regional atmospheric climate model (RACMO2.3) to simulate the present-day climate (1979-2014) of Antarctica and the Antarctic Peninsula. We have evaluated the model results with several observations, such as in situ surface energy balance (SEB) observations by automatic weather stations and stake measurements of surface mass balance (SMB). After a recent physics update within the model, we show that the model is now better capable of realistically simulating the complex climate of the Antarctic ice sheet than a previous version of the model. The most important update is the inclusion of a scheme that allows for super-saturation of ice clouds, leading to the transportation of more clouds into the interior of the continent. As a result, modelled snowfall rates and downwelling longwave radiation have increased, and the model better represents the SEB and the SMB in East Antarctica. We have specifically applied RACMO2.3 to the Antarctic Peninsula (AP). For this purpose, the model is for the first time used at a high spatial resolution of 5.5 km in order to accurately represent the complex AP topography. RACMO2.3 is coupled to a sophisticated firn densification model that calculates processes in the snowpack such as meltwater percolation, refreezing and runoff into the ocean. By a comparison with weather stations and weather balloons, we first show that the model is capable of simulating AP wind and temperature. Secondly, we present a high-resolution estimate of the climatological (1979-2014) SMB of the AP. We show that the model is capable of resolving the distinct differences in snowfall rates between the western AP (WAP) and the eastern AP. For instance, the WAP receives nearly 80% of all AP snowfall, including snowfall rates of up to 40 meter per year. When integrated over the AP including ice shelves (an area of 410000 km2), the model calculates an average SMB of 351 gigaton per year (with an interannual variability of 58 gigaton per year) from 1979 to 2014, which mostly consists of snowfall (363 ± 56 gigaton per year). The other SMB components, sublimation, drifting snow erosion and meltwater runoff, are small in comparison (11, 0.5 and 4 gigaton per year, respectively). Finally, we applied the model to the northwestern AP, one of the most rapidly changing regions on Earth. In order to provide improved insight in the effects of these changes, we present the characteristics of the WAP meteoric freshwater budget. This budget consists of snowfall, rainfall, meltwater runoff and glacial discharge into the ocean. Changes in these processes have implications for the marine ecosystem, the surrounding sea-ice, ocean circulation and, ultimately, sea-level rise. Here, we present modelled estimates of the spatial and temporal variability of the freshwater budget, including a first estimate of glacial discharge into the ocean, assuming balance between snow accumulation and glacial discharge. We find that due to this process, locally between 2 and 11 gigaton of ice is lost to the ocean per year

High-resolution climate modelling of Antarctica and the Antarctic Peninsula

In this thesis we have used a high-resolution regional atmospheric climate model (RACMO2.3) to simulate the present-day climate (1979-2014) of Antarctica and the Antarctic Peninsula. We have evaluated the model results with several observations, such as in situ surface energy balance (SEB) observations by automatic weather stations and stake measurements of surface mass balance (SMB). After a recent physics update within the model, we show that the model is now better capable of realistically simulating the complex climate of the Antarctic ice sheet than a previous version of the model. The most important update is the inclusion of a scheme that allows for super-saturation of ice clouds, leading to the transportation of more clouds into the interior of the continent. As a result, modelled snowfall rates and downwelling longwave radiation have increased, and the model better represents the SEB and the SMB in East Antarctica. We have specifically applied RACMO2.3 to the Antarctic Peninsula (AP). For this purpose, the model is for the first time used at a high spatial resolution of 5.5 km in order to accurately represent the complex AP topography. RACMO2.3 is coupled to a sophisticated firn densification model that calculates processes in the snowpack such as meltwater percolation, refreezing and runoff into the ocean. By a comparison with weather stations and weather balloons, we first show that the model is capable of simulating AP wind and temperature. Secondly, we present a high-resolution estimate of the climatological (1979-2014) SMB of the AP. We show that the model is capable of resolving the distinct differences in snowfall rates between the western AP (WAP) and the eastern AP. For instance, the WAP receives nearly 80% of all AP snowfall, including snowfall rates of up to 40 meter per year. When integrated over the AP including ice shelves (an area of 410000 km2), the model calculates an average SMB of 351 gigaton per year (with an interannual variability of 58 gigaton per year) from 1979 to 2014, which mostly consists of snowfall (363 ± 56 gigaton per year). The other SMB components, sublimation, drifting snow erosion and meltwater runoff, are small in comparison (11, 0.5 and 4 gigaton per year, respectively). Finally, we applied the model to the northwestern AP, one of the most rapidly changing regions on Earth. In order to provide improved insight in the effects of these changes, we present the characteristics of the WAP meteoric freshwater budget. This budget consists of snowfall, rainfall, meltwater runoff and glacial discharge into the ocean. Changes in these processes have implications for the marine ecosystem, the surrounding sea-ice, ocean circulation and, ultimately, sea-level rise. Here, we present modelled estimates of the spatial and temporal variability of the freshwater budget, including a first estimate of glacial discharge into the ocean, assuming balance between snow accumulation and glacial discharge. We find that due to this process, locally between 2 and 11 gigaton of ice is lost to the ocean per year

High-resolution climate modelling of Antarctica and the Antarctic Peninsula

In this thesis we have used a high-resolution regional atmospheric climate model (RACMO2.3) to simulate the present-day climate (1979-2014) of Antarctica and the Antarctic Peninsula. We have evaluated the model results with several observations, such as in situ surface energy balance (SEB) observations by automatic weather stations and stake measurements of surface mass balance (SMB). After a recent physics update within the model, we show that the model is now better capable of realistically simulating the complex climate of the Antarctic ice sheet than a previous version of the model. The most important update is the inclusion of a scheme that allows for super-saturation of ice clouds, leading to the transportation of more clouds into the interior of the continent. As a result, modelled snowfall rates and downwelling longwave radiation have increased, and the model better represents the SEB and the SMB in East Antarctica. We have specifically applied RACMO2.3 to the Antarctic Peninsula (AP). For this purpose, the model is for the first time used at a high spatial resolution of 5.5 km in order to accurately represent the complex AP topography. RACMO2.3 is coupled to a sophisticated firn densification model that calculates processes in the snowpack such as meltwater percolation, refreezing and runoff into the ocean. By a comparison with weather stations and weather balloons, we first show that the model is capable of simulating AP wind and temperature. Secondly, we present a high-resolution estimate of the climatological (1979-2014) SMB of the AP. We show that the model is capable of resolving the distinct differences in snowfall rates between the western AP (WAP) and the eastern AP. For instance, the WAP receives nearly 80% of all AP snowfall, including snowfall rates of up to 40 meter per year. When integrated over the AP including ice shelves (an area of 410000 km2), the model calculates an average SMB of 351 gigaton per year (with an interannual variability of 58 gigaton per year) from 1979 to 2014, which mostly consists of snowfall (363 ± 56 gigaton per year). The other SMB components, sublimation, drifting snow erosion and meltwater runoff, are small in comparison (11, 0.5 and 4 gigaton per year, respectively). Finally, we applied the model to the northwestern AP, one of the most rapidly changing regions on Earth. In order to provide improved insight in the effects of these changes, we present the characteristics of the WAP meteoric freshwater budget. This budget consists of snowfall, rainfall, meltwater runoff and glacial discharge into the ocean. Changes in these processes have implications for the marine ecosystem, the surrounding sea-ice, ocean circulation and, ultimately, sea-level rise. Here, we present modelled estimates of the spatial and temporal variability of the freshwater budget, including a first estimate of glacial discharge into the ocean, assuming balance between snow accumulation and glacial discharge. We find that due to this process, locally between 2 and 11 gigaton of ice is lost to the ocean per year