The Greenland Ice Sheet (GrIS), which stores freshwater equal to more than seven meters of potential sea level rise, strongly interacts with the global, Arctic and North Atlantic climate. In a warming climate, the GrIS has been losing mass and is projected to lose mass at an increasing rate. The interactions between the GrIS and the climate have the potential to amplify or dampen GrIS mass balance responses to a CO2 forcing. We investigate the impact of ice sheet-climate interactions on the mass balance and climate of the GrIS using the Community Ice Sheet Model version 2 (CISM2) coupled to the Community Earth System Model version 2 (CESM2). We compare idealized simulations with a non-evolving and evolving ice sheet topography in which we apply an annual 1 % increase until we reach four times pre-industrial (PI) CO2 concentrations. Furthermore, we analyze an idealized simulation in which we first apply a 4x PI CO2 forcing and thereafter annually reduce atmospheric CO2 by 5 % until PI concentrations are reached. By comparison of a 1- and 2-way coupled simulation, we find significant changes in atmospheric blocking, precipitation and cloud formation over Greenland as the GrIS topography evolves, acting as negative feedback mechanisms on mass loss. Besides, we find that a uniform temperature lapse rate misrepresents temperature changes in the ablation area, leading to an overestimation of the positive melt-elevation and melt-albedo feedback in 1-way coupled simulations, resulting in an overestimation of mass loss. During a 350 year 4xPI CO2 forcing period, the ice sheet loses a total mass of 1.1 m sea level equivalent, and part of its margins retreat land inward. When applying an annual 5 % decrease in CO2 to 1xPI CO2 concentrations, melt reduces rapidly. The small discharge concerned with the retreated state of the ice sheet allows for halting the GrIS mass loss, despite a surface mass balance that is only slightly positive under a remaining global warming of 2 K. During a complex transitional phase towards a colder climate, the GrIS, Arctic and North Atlantic ocean strongly interact, causing the area south of the GrIS to transition from a ’warming hole’ towards a ’cooling hole’. Elevated atmospheric temperatures, larger ocean heat transport and a poorer state of the snowpack, compared to the initial pre-industrial state, result in limited regrowth of the ice sheet under reintroduced PI CO2 conditions.

The Greenland Ice Sheet (GrIS) is an ice sheet situated on the island of Greenland. It has a surface area of about 1.74 million km² and contains a volume of ice equivalent to 7.4 m of global mean sea level rise. The GrIS is vulnerable to climate disruptions such as anthropogenic climate change. As a result of increased greenhouse gas emissions, the mass of the GrIS is observed to be decreasing starting in the 1990.
Our research uses output from a climate model called Community Earth System Model version 2.1 (CESM2.1). CESM is an earth system model, meaning that it tries to model the whole earth for its major physical, chemical and biological functions. Importantly for our research, it models the GrIS such that its shape can change, so that it can model changes in atmospheric flow. This is known as an “interactive ice sheet”.
This research three scenarios run on an interactive ice sheet to find its results. It uses a historical run to evaluate the model. Then it also uses two hypothetical scenarios called 3xCO2 and 4xCO2. Each starts at the pre-industrial concentration of 285 ppm CO2, and then increases the concentration by 1\% per year until reaching 3 and 4 times pre-industrial concentrations respectively, after which the concentration is maintained constant.
This thesis focuses on the mass balance (MB) of the GrIS, as these differ strongly between 3xCO2 and 4xCO2. In the scenarios we researched, this mass balance is dominated by the surface mass balance (SMB). SMB is in turn primarily driven by the ice melt. Negative SMB is called Ablation Area SMB
The thesis makes two important observations. Firstly, area distribution can be split up into a total surface area component, which depends on time, and a relative elevation distribution component, which depends on elevation. Secondly, the area normalised AASMB is linear with elevation, but the gradient varies with time.
Typically, increased melt is explained as a result of ablation area expansion. However, this does not capture the elevation distribution of the AASMB. Using the two results drawn from above, we create a new mental model which results in a more detailed explanation of the GrIS mass loss.

Ice, a pervasive element across the Solar System, holds immense importance in understanding the response of the Earth to ongoing climate change as well as the dynamics of planetary bodies. This dissertation investigates ice fractures on terrestrial and planetary ice bodies, focusing on their impact on the melting of ice shelves in Antarctica and their dynamics on Europa, one of Jupiter’s moons.

The urgency to understand the behavior of terrestrial ice shelves under environmental forcing is driven by the ongoing climate crisis. Antarctica is experiencing a rapid loss of mass, primarily due to increasing ocean-induced melting at the base of its ice shelves in response to global warming. The release of glacier meltwater into the world’s oceans contributes to arising the global sea level. However, the rate and magnitude of sea-level rise are highly uncertain and the potential ice mass-loss from Antarctica could significantly accelerate sea-level rise throughout this century due to the instability of its ice shelves. Thus, accurately projecting Antarctica’s contribution to global sea level necessitates a better understanding of the processes behind the loss of its ice shelves.

In this dissertation, I examine the thinning of Antarctic ice shelves caused by enhanced melting at their base due to warming oceans. Intrusion of ocean heat beneath the ice shelves indeed plays a crucial role in projecting their future. Through idealized ocean modeling using the Massachussetts Institute of Technology general circulation model (MITgcm), I simulate ocean dynamics under the ice, investigating the impact of fractures and ice front retreat on the sub-shelf ocean circulation. Results indicate that fractures may act as barriers, inhibiting the intrusion of warm water towards the inland sections of the ice shelves, and thereby reducing basal melt. Furthermore, I examine the impact of the separation of iceberg A-68 from the Larsen C ice shelf in July 2017 on the sub-shelf ocean dynamics. This specific retreat event leads to the redistribution of heat under the ice, resulting in enhanced melting in specific sections of the ice shelf, suggesting future destabilisation of Larsen C. These findings highlight the importance of considering updated ice-shelf coastlines to accurately project ocean circulation and its implications for ice shelf stability.

Furthermore, this dissertation explores the dynamics of specific lineament features observed on the surface of Europa, which are identified as ice fractures. Although limited observations restrict our understanding of ice fracturing events on this moon, insights from studying terrestrial ice sheets provide valuable knowledge. By extend ing an existing terrestrial-based numerical model of fracture propagation on ice shelves, I show that some lineaments on the surface of Europa exhibit a behavior that is similar to ice fractures on Antarctic ice shelves. The model depicts the evolution of these lineament features as bursts of fracture propagation events interspersed with periods of inactivity, which is a typical behavior of fractures on terrestrial ice shelves.

Overall, this dissertation shows the potential for synergy between Earth and planetary science. By leveraging advances in our understanding of physical processes on Earth, terrestrial-based models and theories contribute to expanding our knowledge of physics on other celestial bodies. This interdisciplinary approach, supported and validated by remote sensing and in-situ missions, is fundamental in order to advance our understanding of ice fractures, their interaction with the surrounding environment and their dynamics throughout the Solar System. On Earth, a better understanding of the dynamics of Antarctic ice shelves is imperative to correctly project Antarctica’s contribution to global sea level.@en

Floating ice shelves regulate Antarctic ice sheet mass loss by buttressing land ice discharge toward the ocean. Next to basal melting, iceberg calving following the propagation of rifts has the potential to reduce this buttressing effect. However, rift propagation is largely unpredictable and generally not resolved in coarse climate models. The sub-shelf ocean circulation is believed to play an important role in rift propagation as it is closely related to ice shelf melting and freezing. Previous work suggests that the sub-shelf circulation of an intact ice shelf is altered by the presence of km-wide basal channels. As it could impact freezing and melting, the potential effect of basal channels on a rifted Antarctic ice shelf should be explored.

In this study, the Massachusetts Institute of Technology general circulation model was applied to explore for the first time the potential effect of basal channels on the melting and freezing of a rifted Antarctic ice shelf. To this end, four simulations were performed with a high-resolution ocean model for the domain of an ice shelf cavity with idealized boundary conditions. These simulations correspond to a cavity with melt channels, a prominent rift close to the ice shelf front, both, and none of them. The effects of channels, a rift or the combination of both on melt, freezing and ocean circulation in the cavity were assessed through a comparison of these four simulations. Following previous research, results show that basal channels decrease ice shelf basal melting. We found that the addition of only a rift does not change the melt intensity or pattern. In addition, it was found that basal channels increase the freezing inside a rift. A sub-shelf boundary current on the Coriolis favoured side of the domain without channels is reformed to a clockwise circulation in each channel, resulting in an adjusted flow pattern inside the rift from one single large clockwise return flow to a smaller one behind each channel. Hence, buoyant cold shelf meltwater does not only enter the rift in the boundary current but after every topographic incision, and the thermal forcing is increased. Furthermore, the multiple return flow pattern enlarges the average frictional velocity inside the rift, which is positively related to the freezing rate intensity. In an offline calculation, it was found that the contribution of the thermal forcing to the total freezing amount is approximately three times larger than the friction velocity.

From our simulations, we conclude that the presence of basal channels in a rifted ice shelf decreases basal melting at the grounding line and increases freezing inside rifts. Previous work on rift propagation suggests that these results imply that marine ice accretion inside the rift could increase, and fracture propagation could be reduced. Given these connections between ice shelf processes, this study stresses the importance of including basal channels and rifts in ice shelf cavity models to robustly reproduce Antarctic sub-shelf circulation and basal melt.

The Greenland ice sheet (GrIS) is an important component of the climate system and is a key contributor to future sea level rise, as it is storing frozen water that would raise sea levels by 7.4 m should it all melt (Bamber et al., 2018). Of particular concern is the amount of global warming we are facing now and in the future, as it is becoming more likely that even if our emissions are significantly reduced, global warming will reach at least 2∘𝐶 (Arias et al., 2021). Much research concerns the future contribution of the GrIS to sea level rise for high emissions scenarios and low emission scenarios, but there are few studies giving the main focus to what is becoming a more likely future, the moderate emissions scenarios. This research aims to quantify the mass loss of the Greenland ice sheet and subsequent contribution to future sea level rise under a moderate CO2 concentration scenario over a multimillennia timescale. An idealised simulation of 3000 years, where CO2 concentrations are increased by 1% annually until reaching two times pre-industrial values and then kept constant, is run with the high-resolution Community Earth System Model version 2.1 (CESM2.1) and Community Ice Sheet Model version 2.1 (CISM2.1). The climate, run with CESM2.1, is simulated for 1000 years. After 500 years, it is assumed that the climate is close to equilibrium, and thus one climate year is used for five years of forcing the ice sheet in CISM2.1, resulting in 3000 years of ice sheet simulation. At the end of the simulation, the global mean annual temperature has increased by 5∘𝐶 and the temperature over Greenland is 9∘𝐶 warmer than pre-industrial. The rate of sea level contribution in the first centuries is lower than the observed contemporary mass loss of 0.7 mm/yr (Shepherd et al., 2020) but increases after year 710 to a rate of 1 mm/yr. Another increase in mass loss is happening from the year 1380 until the end of the simulation where the rate is 2 mm/yr and the total contribution to sea level rise is 4.1 m. The limited mass loss in the period between years 71-400 and its increase thereafter is found to relate to temporal strong weakening and posterior recovery of the NAMOC. This study projects that the GrIS is a major contributor to future sea level rise, even in a moderate warming scenario, and that the changing NAMOC has a noteworthy effect on the GrIS mass budget.

The Greenland Ice Sheet is the world’s second largest ice sheet, storing an equivalent of 7.3 meters of sea level rise. Due to climate change, the Greenland ice sheet is currently losing mass at an accelerated rate. Ice sheet models are used to project long term melt of the ice sheet, which are often forced by output from climate models. Most of the multi-millennium time scale ice sheet simulations conducted in the past used SMB calculations based on empirical relationships between melt and temperature (Positive-Degree Day schemes). In this thesis, I address the question of the future evolution of the Greenland ice sheet by means of an ice sheet model forced with an elevation dependent SMB field that accounts for the energy available for melt. This work focuses on key variables such as ice thickness, ice area, velocity and contribution to eustatic sea level rise, and assesses the reversibility of the mass loss. For this thesis, I performed uncoupled CISM2.1 simulations which were forced by the elevation- SMB field from a coupled CESM-CISM simulation. The coupled simulation used to force the ice sheet has a length of 160 years and a CO2 concentration that is increased with 1% per year from pre-industrial levels and capped at 4 times CO2. Time segments with 2x, 3x and 4x pre-industrial CO2 concentrations of this CESM-CISM run were used to force the ice sheet on multi-millennium time-scales. In addition, a Recovery from 4x CO2 was conducted in which the pre-industrial forcing from a coupled CESM-CISM simulation is re-introduced after 55% mass loss. The 2x, 3x and 4x CO2 scenarios resulted in a cumulative sea level rise of 0.49 m, 3.0 m, and 8.2 m by year 4,000. The 2x CO2 scenario resulted in limited retreat and stability within 4,000 years. No stability of the ice sheet was attained by year 8,000 in the 3x CO2 simulation, with a final Mass Balance of -108.8 Gt/yr (0.30 ± mm/yr). The 4x CO2 simulation resulted in the complete deglaciation of the ice sheet within 3,000 years. Despite the lower initial topography compared to the pre-industrial ice sheet, the Recovery from 4x CO2 simulation resulted into expansion of the ice sheet. Within 4,000 years, the mass increased from 46% to 67% relative to the pre-industrial ice sheet.

The Greenland Ice Sheet has a total volume of 2900000 km3. In recent decades, the ice-sheet has been losing mass rapidly and has nearly doubled its contribution to sea-level rise. One main contributing factor has been the recent widespread acceleration of the tidewater glaciers that terminate in deep and narrow glacial fjords. However, our understanding of the subsurface water properties causing this acceleration has been extremely limited owing to the lack of observations around these locations. We hypothesize that while the ice-sheet is not coupled to the ocean in the current General Circulation Models (GCMs), they can still be used to improve our understanding of the subsurface warming around these regions. In this study, we first evaluate two GCMs (HADGEM2-ES and GISS-E2-R) around three tidewater glacier locations, by interpolating the high resolution CTD data to the GCM grid. Our results substantiate that GISS-E2-R performs better than the HADGEM2-ES model along the Western Margin. However, along the Eastern Margin, we find that the HADGEM2-ES model is more consistent with the observations. The modelled spatio-temporal variability of water masses was investigated in a Pre-Industrial and Historical simulation, later used to quantify the evolution of subsurface warming under a future warming (RCP 8.5) scenario. Our results show that the Kangerlussuaq glacier (shelf) is more sensitive to greenhouse gas (GHG) forcings than Helheim and Jakobshavn. With respect to the Pre-Industrial climate, the mean warming of the Kangerlussuaq shelf under the RCP 8.5 scenario is 3.76°C, which is considerably greater than Helheim (2.38°C) and Jakobshavn (1.92°C). This is predominantly driven by the subsurface Return Waters of the Arctic Atlantic which are seen to warm the most under a future warming (RCP 8.5) scenario. For each of the three simulation, we decompose the Ocean Heat Content (OHC) time-series into intrinsic oscillatory modes so as to discern and quantify the high frequency variability from the multi-year/decadal variability and trends in the OHC. Where the contribution from the high-frequency modes to the total energy contained in the OHC signal is considerable in a Pre-Industrial scenario; the Historical and RCP 8.5 derived OHC are seen to contain a very dominant low-frequency response to GHG forcings, which contains (almost) all of the energy contained in the signal. For the RCP 8.5 scenario, we infer that at Kangerlussuaq, such a response is considerably greater than other locations. Furthermore, a consistent long-term increasing trend is seen in the upper ocean heat content for Kangerlussuaq, throughout the 21st century (1.01 × 10^8 J/m^2/month), unlike our inferences from other locations. This trend is found to be an order of magnitude higher than Helheim (2.36 × 10^7 J/m^2/month) and Jakobshavn (1.27 × 10^7 J/m^2/month). Our results also indicate that sea-ice free months at the Nares Strait (A.D. 2055 onwards) allows for a relatively greater mixing of the Lincoln Sea and Baffin Bay waters, which is consistent with the decline and stagnation of the rising OHC at Jakobshavn.