Modelling ice dynamic sea-level rise from the Antarctic Peninsula Ice Sheet

The Antarctic Peninsula (AP) has been one of the most rapidly warming regions on this planet. This warming has been accompanied by major glaciological changes such as tidewater glacier retreat, ice-shelf retreat and collapse alongside acceleration of outlet glaciers in response to ice-shelf removal. As faster owing glaciers deliver more ice from the ice sheet's interior to the margins, the AP has been identified as an important contributor to global sea-level rise (SLR). However, comprehensible SLR projections of the AP induced by ice dynamics over the next three centuries are still lacking. In this thesis, numerical ice-sheet models are utilised to present scenario-based ice dynamic SLR projections for the AP

Modelling ice dynamic contributions to sea level rise from the Antarctic Peninsula

The future ice dynamical contribution to sea-level rise (SLR) from 210 ice shelf nourishing drainage basins of the Antarctic Peninsula Ice Sheet (APIS) is simulated, using the British Antarctic Survey Antarctic Peninsula Ice Sheet Model. Simulations of the grounded ice sheet include response to ice-shelf collapse, estimated by tracking thermal ice shelf viability limits in 14 IPCC Global Climate Model ensemble temperature projections. Grounding line retreat in response to ice shelf collapse is parameterized with a new multivariate linear regression model utilizing a range of glaciological and geometric predictor variables. Multi-model means project SLR up to 9.4 mm sea-level equivalent (SLE) by 2200, and up to 19 mm SLE by 2300. Rates of SLR from individual drainage basins throughout the peninsula are similar to 2100, yet diverge between 2100 and 2300 due to individual basin characteristics. Major contributors to SLR are the outlet glaciers feeding southern George VI Ice Shelf, accounting for >75% of total SLR in some model runs. Ice sheet thinning induced by ice-shelf removal is large (up to ∼500 m), especially in Palmer Land in the Southern Antarctic Peninsula, and may propagate as far as 135 km inland. These results emphasize the importance of the ice dynamical contribution to future sea level of the APIS on decadal to centennial timescales

Hysteretic evolution of ice rises and ice rumples with variations in sea level

Ice rises and ice rumples are locally grounded features found in coastal Antarctica and are surrounded by otherwise freely floating ice shelves. An ice rise has an independent flow regime, whereas the flow regime of an ice rumple conforms to that of the ice shelf and merely slows the flow of ice. In both cases, local highs in the bathymetry are in contact with the ice shelf from below, thereby regulating the large-scale ice flow, with implications for the upstream continental grounding line position. This buttressing effect, paired with the suitability of ice rises as a climate archive, necessitates a better understanding of the transition between ice rise and ice rumple, their evolution in response to a change in sea level, and their dynamic interaction with the surrounding ice shelf. We investigate this behaviour using a three-dimensional full Stokes ice flow model. The simulations span end-member basal friction scenarios of almost stagnant and fully sliding ice at the ice-bed interface. We analyse the coupling with the surrounding ice shelf by comparing the deviations between the non-local full Stokes surface velocities and the local shallow ice approximation (SIA). Deviations are generally high at the ice divides and small on the lee sides. On the stoss side, where ice rise and ice shelf have opposing flow directions, deviations can be significant. Differences are negligible in the absence of basal sliding where the corresponding steady state ice rise is larger and develops a fully independent flow regime that is well described by SIA. When sea level is increased and a transition from ice rise to ice rumple is approached, the divide migration is more abrupt the higher the basal friction. In each scenario, the transition occurs after the stoss side grounding line has moved over the bed high and is positioned on a retrograde slope. We identify a hysteretic response of ice rises and ice rumples to changes in sea level, with grounded area being larger in a sea level increase scenario than in a sea level decrease scenario. This hysteresis not only shows irreversibility following an equal increase and subsequent decrease in sea level, but also has important implications for ice flow model initialisation. The initial grounded area needs to be carefully considered, as this will determine the formation of either an ice rise or an ice rumple, thereby causing different buttressing effects

Dynamic response of Antarctic Peninsula Ice Sheet to potential collapse of Larsen C and George VI ice shelves

Ice shelf break-up and disintegration events over the past 5 decades have led to speed-up, thinning, and retreat of upstream tributary glaciers and increases to rates of global sea-level rise. The southward progression of these episodes indicates a climatic cause and in turn suggests that the larger Larsen C and George VI ice shelves may undergo a similar collapse in the future. However, the extent to which removal of the Larsen C and George VI ice shelves will affect upstream tributary glaciers and add to global sea levels is unknown. Here we apply numerical ice-sheet models of varying complexity to show that the centennial sea-level commitment of Larsen C embayment glaciers following immediate shelf collapse is low ( < 2.5 mm to 2100,  < 4.2 mm to 2300). Despite its large size, Larsen C does not provide strong buttressing forces to upstream basins and its collapse does not result in large additional discharge from its tributary glaciers in any of our model scenarios. In contrast, the response of inland glaciers to a collapse of the George VI Ice Shelf may add up to 8mm to global sea levels by 2100 and 22mm by 2300 due in part to the mechanism of marine ice sheet instability. Our results demonstrate the varying and relative importance to sea level of the large Antarctic Peninsula ice shelves considered to present a risk of collapse

Towards interpretation of the radio-stratigraphy of Antarctic ice shelves from modeling and observations: A case study for the Roi Baudouin Ice Shelf, East Antarctica

Ice shelves surrounding the Antarctic perimeter buttress ice flow from the continent towards the ocean, and their disintegration leads to an increase in ice discharge and sea level rise. The evolution and integrity of ice shelves is governed by surface accumulation, basal melting, and ice dynamics. We find history of these processes imprinted in the ice-shelf stratigraphy, which is mapped using isochrones imaged with radar. As an observational archive, the radar obtained stratigraphy combined with ice flow modeling has high potential to assist model calibration and reduce uncertainties in projections for the ice-sheet evolution. In this study we use a simplistic and observationally driven ice-dynamic forward model to predict the ice-shelf stratigraphy. We validate this approach with the full Stokes ice-flow model Elmer/Ice, and present a test-case for the Roi Baudouin Ice Shelf (East Antarctica) - where our model predictions agree well with radar obtained observations. The presented method enables us to investigate whether ice shelves are in steady-state, as well as to map spatial variations of how much of the ice-shelf volume is determined by its local surface mass balance. In the case of Roi Baudouin, we find the ice-shelf volume in the western part to be dominated by ice inflowing from the ice sheet, while the eastern part of the ice shelf is dominated by ice locally accumulated on the shelf. Such analysis serves as a metric for the susceptibility of ice shelves to climate change. We further apply our approach to other ice shelves in Antarctica

Analysis of the surface mass balance for deglacial climate simulations

A realistic simulation of the surface mass balance (SMB) is essential for simulating past and future ice-sheet changes. As most state-of-the-art Earth system models (ESMs) are not capable of realistically representing processes determining the SMB, most studies of the SMB are limited to observations and regional climate models and cover the last century and near future only. Using transient simulations with the Max Planck Institute ESM in combination with an energy balance model (EBM), we extend previous research and study changes in the SMB and equilibrium line altitude (ELA) for the Northern Hemisphere ice sheets throughout the last deglaciation. The EBM is used to calculate and downscale the SMB onto a higher spatial resolution than the native ESM grid and allows for the resolution of SMB variations due to topographic gradients not resolved by the ESM. An evaluation for historical climate conditions (1980–2010) shows that derived SMBs compare well with SMBs from regional modeling. Throughout the deglaciation, changes in insolation dominate the Greenland SMB. The increase in insolation and associated warming early in the deglaciation result in an ELA and SMB increase. The SMB increase is caused by compensating effects of melt and accumulation: the warming of the atmosphere leads to an increase in melt at low elevations along the ice-sheet margins, while it results in an increase in accumulation at higher levels as a warmer atmosphere precipitates more. After 13 ka, the increase in melt begins to dominate, and the SMB decreases. The decline in Northern Hemisphere summer insolation after 9 ka leads to an increasing SMB and decreasing ELA. Superimposed on these long-term changes are centennial-scale episodes of abrupt SMB and ELA decreases related to slowdowns of the Atlantic meridional overturning circulation (AMOC) that lead to a cooling over most of the Northern Hemisphere

Predicting the steady-state isochronal stratigraphy of ice shelves using observations and modeling

Ice shelves surrounding the Antarctic perimeter moderate ice discharge towards the ocean through buttressing. Ice-shelf evolution and integrity depend on the local surface accumulation, basal melting and on the spatially variable ice-shelf viscosity. These components of ice-shelf mass balance are often poorly constrained by observations and introduce uncertainties in ice-sheet projections. Isochronal radar stratigraphy is an observational archive for the atmospheric, oceanographic and ice-flow history of ice shelves. Here, we predict the stratigraphy of locally accumulated ice on ice shelves with a kinematic forward model for a given atmospheric and oceanographic scenario. This delineates the boundary between local meteoric ice (LMI) and continental meteoric ice (CMI). A large LMI to CMI ratio hereby marks ice shelves whose buttressing strength is more sensitive to changes in atmospheric precipitation patterns. A mismatch between the steady-state predictions of the kinematic forward model and observations from radar can highlight inconsistencies in the atmospheric and oceanographic input data or be an indicator for a transient ice-shelf history not accounted for in the model. We discuss pitfalls in numerical diffusion when calculating the age field and validate the kinematic model with the full Stokes ice-flow model Elmer/Ice. The Roi Baudouin Ice Shelf (East Antarctica) serves as a test case for this approach. There, we find a significant east–west gradient in the LMI / CMI ratio. The steady-state predictions concur with observations on larger spatial scales (>10 km), but deviations on smaller scales are significant, e.g., because local surface accumulation patterns near the grounding zone are underestimated in Antarctic-wide estimates. Future studies can use these mismatches to optimize the input data or to pinpoint transient signatures in the ice-shelf history using the ever growing archive of radar observations of internal ice stratigraphy

The BALANCE Study Clinical Benefit and Long-Term Outcome After Intracoronary Autologous Bone Marrow Cell Transplantation in Patients With Acute Myocardial Infarction

ObjectivesThe aim of this study was to investigate the quantitative amount of improvement of ventricular hemodynamic status, geometry, and contractility as well as the long-term clinical outcome of cell-treated patients after acute myocardial infarction (AMI).BackgroundAnimal experiments as well as clinical studies have demonstrated that autologous bone marrow cell (BMC) transplantation might improve ventricular function and prevent remodeling.MethodsSixty-two patients underwent intracoronary autologous BMC transplantation 7 ± 2 days after AMI. Cells were infused directly into the infarct-related artery. The control group consisted of 62 patients with comparable left ventricular (LV) ejection fraction (EF) and diagnosis. All patients had several examinations (e.g., coronary angiography, right heart catheterization, biplane left ventriculography, electrocardiogram [ECG] at rest and exercise, echocardiography, late potential [LP], heart rate variability [HRV], and 24-h Holter ECG). The therapeutic follow-up was performed 3, 12, and 60 months after BMC therapy.ResultsThree months after BMC therapy there was significant improvement of EF and stroke volume index. The infarct size was significantly reduced by 8%. Contraction velocities (lengths/second, volumes/second) increased significantly and the slope of the ventricular function curve (systolic pressure/end-systolic volume) became steeper. There was significant improvement of contractility in the infarct zone, as evidenced by a 31% increase of LV velocity of shortening (VCF), preferably in the border zone of the infarct zone. In contrast, the noninfarcted area showed no difference in VCF before and after BMC therapy. Furthermore, decreases of abnormal HRV, LP, and ectopic beats were documented after BMC therapy. Twelve and 60 months after BMC therapy the parameters of contractility, hemodynamic status, and geometry of the LV were stable. The exercise capacity of treated patients was significantly augmented, and the mortality was significantly reduced in comparison with the control group.ConclusionsBMC therapy leads to significant and longstanding improvements of LV performance as well as quality of life and mortality of patients after AMI. After BMC therapy, no side effects were observed, showing that BMC therapy is safe

Ocean Response in Transient Simulations of the Last Deglaciation Dominated by Underlying Ice‐Sheet Reconstruction and Method of Meltwater Distribution

The last deglaciation was characterized by drastic climate changes, most prominently melting ice sheets. Melting ice sheets have a significant impact on the atmospheric and oceanic circulation, due to changes in the topography and meltwater release into the ocean. In a set of transient simulations of the last deglaciation with the Max Planck Institute for Meteorology Earth System Model we explore differences in the climate response that arise from different boundary conditions and implementations suggested within the Paleoclimate Modeling Intercomparison Project - Phase 4 (PMIP4) deglaciation protocol. The underlying ice-sheet reconstruction dominates the simulated deglacial millennial-scale climate variability in terms of timing and occurrence of observed climate events. Sensitivity experiments indicate that the location and timing of meltwater release from the ice sheets into the ocean are crucial for the ocean response. The results will allow a better interpretation of inter-model differences that arise from different implementations proposed within the PMIP4 protocol

Quantifying the effect of ocean bed properties on ice sheet geometry over 40 000 years with a full-Stokes model

Simulations of ice sheet evolution over glacial cycles require integration of observational constraints using ensemble studies with fast ice sheet models. These include physical parameterisations with uncertainties, for example, relating to grounding-line migration. More complete ice dynamic models are slow and have thus far only be applied for  50 % under almost equal forcing. Grounding-line positions differ by up to 49 km, show significant hysteresis, and migrate non-steadily in both scenarios with long quiescent phases disrupted by leaps of rapid migration. The simulations quantify the evolution of two different ice sheet geometries (namely thick and slow vs. thin and fast), triggered by the variable grounding-line migration over the differing ocean beds. Our study extends the timescales of 3D full-Stokes by an order of magnitude compared to previous studies with the help of parallelisation. The extended time frame for full-Stokes models is a first step towards better understanding other processes such as erosion and sediment redistribution in the ice shelf cavity impacting the entire catchment geometry