The 1.7 million km2 Greenland Ice Sheet is divided into a series of major drainage basins, each typically about 50-100,000 km2 in area. Most of these basins drain into the marine waters of fjord systems via relatively narrow and heavily crevassed outlet glaciers that dissect the mountains fringing the island. Over the past few years it has become clear that the Ice Sheet is losing mass and has become a significant contributor to global sea-level rise. This is related to, first, the doubling in speed of several outlet glaciers, increasing ice flux to the sea and, secondly, a major increase in the area affected by summer melting and runoff from the ice-sheet surface. Both of these changes have taken place in the past decade and have been linked with warmer air and water temperatures over and around Greenland. A major question for both scientists and policymakers is how the Greenland Ice Sheet will continue to react to the temperature rises that are predicted for the coming century by a suite of climate models, particularly in the context that the Arctic is likely to warm at a greater rate than the global average due to the continuing loss of its surrounding sea-ice cover and the changes in ocean albedo and, therefore, energy balance that will result. We will acquire geophysical data from a series of ten outlet glaciers of the Greenland Ice Sheet using airborne ice-penetrating radar, laser altimeter, gravimeter, and magnetometer and GPS instruments. These glacier systems have been selected because: (a) they are major drainage basins within the ice sheet which provide a high ice flux to the sea; and (b) they represent different sub-environments within the Greenland Ice Sheet and its related climate and ocean setting. We will focus our investigations on three key areas of each outlet glacier: first, the heavily crevassed fast-flowing outlet glaciers themselves, that flow in narrow channels through Greenland's fringing mountains; secondly, an upper transition zone between the ice-sheet interior and these narrow outlet glaciers; and thirdly, the grounding zone marking the transition of fast-flowing outlet glaciers to floating ice tongues that are present at the head of many Greenland fjords. Our scientific objectives are: 1. To determine ice surface elevation and subglacial bed elevation, including measurement beneath areas of heavy crevassing in fast-flowing outlet glaciers. 2. To characterize the substrate beneath the ice, in particular whether it is crystalline bedrock or deformable sediments. 3. To establish the distribution of subglacial melting and characterize the subglacial hydrological system where water is present. 4. To identify the transition zones between inland ice, outlet glaciers and the grounding zone and reveal basal character changes associated with them. 5. To describe the three-dimensional nature of internal ice layering within transition zone from inland ice to outlet glacier to measure the distribution of accumulation, strain, and basal melting. This information will make a fundamental contribution to the computer modelling of ice sheets, and how Greenland in particular may respond in future to changes in air and ocean temperate over the coming decades. This because these models require information, known as boundary conditions, on the shape of the bed and also the processes that are going on there in order to make useful predictions. To date, we know little about, for example, the distribution of water beneath these outlet glaciers. The changing amount of ice lost from the ice sheet by surface melting and iceberg production is important, in turn, for predictions on the future contributions of Greenland to sea-level rise in a warming Arctic. This is of significance beyond the academic community. In the UK and elsewhere, governments at national and regional level are requiring information about rates of sea-level rise and the remediation measures, such as sea defences, that are needed.

The Greenland Ice Sheet (GrIS) has been losing mass over the past three decades and is now a significant contributor to global sea-level rise. In recent decades, the ice sheet's rate of mass (or ice) loss has accelerated, driven by a warming climate and substantial increases both in: 1) the flow speed and retreat rate of many large glaciers that drain the ice sheet and terminate in the ocean; and 2) the surface melt rates and area of the ice sheet experiencing summer melting. However, a critical area of future potential dynamic change and ice-mass loss, which is unaccounted for in our current model projections of the Greenland Ice Sheet's future evolution, concerns the influence of ice-marginal (or proglacial) lake formation on the dynamic stability of outlet glaciers. It is well known from numerous observations elsewhere, that glaciers which terminate in proglacial lakes typically flow much faster than similar sized glaciers that terminate on land. It is now also clear that the number and size of proglacial lakes around the margins of the GrIS are increasing and that trend will continue in to the future. There is therefore the clear potential for the development of more lake-terminating glaciers affecting the ice-sheets' ice-dynamics and long-term stability with the possibility of a dramatic (or 'catastrophic') acceleration in ice-mass loss from these hitherto slowly changing ice-margins. Greenland's land-terminating ice-sheet margins currently flow rather slowly (~100 m/yr) and their mass loss is controlled almost entirely by surface-melt processes. Since the climate is warming, these land-terminating glaciers are thinning and retreating slowly. However, in numerous glaciated regions around the globe, glacier termini are accelerating (by a factor of 2 or more) where glaciers terminate in lakes as opposed to adjacent land-terminating glaciers. This occurs because when a glacier terminates in a lake, it experiences processes which lead to glacier calving, thinning and acceleration. These processes lead to enhanced ice mass loss from the terminus calving and retreat but also through the glacier acceleration which brings ice more rapidly from higher to lower elevations on the ice-sheet thereby exposing the ice to warmer temperatures that promote increased surface melt. As such, a rather simple change in glacier terminus morphology can have a dramatic impact on the glaciers' ice dynamics and mass loss. This project will determine the extent to which these developing proglacial lakes will impact future ice-sheet mass loss, and thus contribute to sea-level rise, over the coming century. We have already undertaken a proof-of-concept study revealing contrasting behaviour at two adjacent lake- and land-terminating glaciers in SW Greenland. Using satellite data to derive glacier velocities, our study shows that ice-motion at the lake-terminating margin more than doubled between 2017-2021 (to ~200 m/yr); by contrast, the neighbouring land-terminating glacier decelerated over the same time-period. We now aim to determine the extent to which these observations of recent acceleration are typical at Greenland's numerous lake terminating margins and more importantly, investigate how important ice-marginal lake terminating glacier dynamics will become in the future for ice-sheet mass loss. In order to achieve this broad aim, the project will use a range of satellite data in conjunction with surface mass balance and ice-sheet modelling to determine: i) how glacier terminus position, motion and surface elevation have changed, both at the ice-margin and inland, in recent decades in response to glacier termination in proglacial lakes; ii) what processes are driving these observed changes in terminus behaviour; and iii) the impact of proglacial lake-induced ice-margin acceleration, thinning and retreat, on the Greenland Ice Sheet's sea level rise contributions, under projected climate warming over the next century.

The greenhouse world of the Late Cretaceous to mid-Paleogene (~100 - 40 million years ago) is of particular interest to earth scientists because there is good geological evidence to show that at this time tropical/subtropical conditions extended into Antarctica in the south and into the Arctic in the north. At this time the south polar ice cap was either much smaller or absent. Many modern groups of plants and animals have their evolutionary roots in this greenhouse world and it is possible that their expansion related directly to this prolonged period of global warmth. This greenhouse world was punctuated by a mass extinction event at 65Ma at the Cretaceous - Paleogene boundary (K-Pg). In addition, this warm world was interrupted by a series of abrupt extreme warming events, or hyperthermals, probably caused by the sudden release of massive amounts of CO2 into the atmosphere and oceans. The K-Pg mass extinction event probably had a much longer-lasting effect on global ecosystems than the more transient hyperthermals but we will test this idea by investigating the geological record from the polar regions, the regions on Earth most sensitive to environmental and climate change. Much of the geological record for this time interval for the polar regions comes from deep sea drill sites but the best onshore exposure is found on Seymour Island, Antarctica. We have recently investigated this locality in detail and now have a high resolution geological record from the end of the Cretaceous period, across the K-Pg boundary and into the mid-Paleogene period. Analysis of large collections of sediments and plant and invertebrate fossils will provide us with new information about climates on land and temperatures in shallow seas around Antarctica at that time. The fossils also allow us to reconstruct the composition of faunas and floras that lived in the polar regions and to determine how their diversity changed over time. We will produce a new palaeotemperature curve for the latest Cretaceous - mid-Paleogene interval in Antarctica, and will assess whether the hyperthermal events occurred so far south. By matching fossil diversity with the climate record we will assess the time taken for plants and animals to recover from the K-Pg mass extinction and investigate whether times of high biodiversity were linked to episodes of warming. For example, do sub-tropical plant fossils and an unusual marine fossil assemblage represent poleward incursions of warmth-loving biotas during a global warming event 55 million years ago, only to go extinct when cooler conditions returned? Some studies indicate that the K-Pg mass extinction reset the global evolutionary clock forever, with new species subsequently appearing at a much higher rate in the tropics than at the poles. We will test this important theory by adding our new Antarctic fossil data to a global database for the latest Cretaceous to the mid-Paleogene. Was the radiation of species through this interval really slower at the poles, and if so, why did the change in rates occur immediately after the K-Pg boundary? How does our record of palaeoclimate and biodiversity from Antarctica compare to that from the Arctic and from low latitude sites - were high latitude communities particularly sensitive to climate change and environmental disturbance, even in a greenhouse world? How did forests at the poles affect the climate system? Does our fossil record match the evolutionary history derived from modern marine faunas by molecular studies? By using a range of palaeoenvironmental indicators and analytical techniques (isotope geochemistry, sedimentary facies analysis, palaeobotany, palaeobiology, climate modelling) we will reconstruct the greenhouse world of the past and assess the impact of dramatic global events on the evolution of life, particularly in the polar regions.

The dominant driver of anthropogenic global warming is the increasing amount of the greenhouse gas carbon dioxide in the atmosphere. This is increasing because it is being emitted by the burning of fossil fuel, deforestation and cement making, with only ~45% staying in the atmosphere. The rest is stored in other reservoirs at or near Earth's surface including the ocean, trees, soils, permafrost and methane ice, as well as sediments and rock. Carbon flows naturally between the atmosphere and these reservoirs by processes like photosynthesis, decay, weathering, burial and ocean circulation. Collectively, the exchange of carbon between these reservoirs is termed the carbon cycle. One of the biggest uncertainties about future climate change is how the carbon cycle will respond to (or 'feed back' on) our warming planet. It is possible, for example, that if global warming exceeds a threshold, permafrost and methane ice stored at the seafloor will melt rapidly, adding further greenhouse gases to the atmosphere and accelerating the warming. It is very difficult to predict whether 'tipping point' behaviour like this will occur in the global carbon cycle. C-FORCE will measure how the global carbon cycle responded from start to finish during a past period of global warming that was driven by emissions of carbon-based greenhouse gases to the atmosphere. The Paleocene-Eocene Thermal Maximum (PETM) is the largest natural climate change event of the last 65 million years, and the closest natural comparator to the modern rates of global warming and carbon greenhouse gas emissions. During the PETM, initial global warming of 4-5 degrees Celsius over a few thousand years was partially driven by carbon emissions from an unusually massive episode of volcanism, and the climate then gradually recovered to its pre-existing state over more than 100 thousand years. C-FORCE will use a novel model of the global carbon cycle to compare the carbon supplied by volcanism with the total PETM carbon budget; the difference between these two budgets can be attributed to carbon cycle feedbacks. We will make new high-resolution estimates of the rate at which volcanism supplied carbon to the atmosphere throughout the PETM by measuring the processes that generated the magma. We will calculate the total budget of carbon emissions to the atmosphere that caused the climate change by generating new high-resolution records of ocean acidification. Our carbon cycle modelling will allow the scientists who make these two sets of measurements to interface effectively to solve the net global carbon cycle feedback problem for the first time. Furthermore, because Earth's carbon reservoirs differ in isotopic composition, we can fingerprint which reservoirs most likely acted as carbon sources or sinks over the course of the PETM. Thus C-FORCE will determine how the global carbon cycle evolved throughout the PETM, and show whether or not tipping point behaviour occurred. Understanding how Earth's carbon reservoirs respond to global warming is crucial for predicting atmospheric carbon dioxide concentrations and climate change long into the future. Ultimately, an improved understanding of the carbon cycle affects future carbon budgets to limit global warming to 1.5 or 2 degrees Celcius and is therefore necessary for shaping mitigation targets and government policy. Beyond delivering a research product, C-FORCE challenges current understanding of the carbon cycle and we see our role as an empowering force in this space. The public discourse on climate change is a mixture of disaffection and anxiety, so C-FORCE will take a different direction to traditional public engagement, by partnering with community organisers and local government to train, mentor and co-develop our public engagement with young people.

The Greenland Ice Sheet is the largest ice mass on Earth outside of Antarctica, containing enough ice to raise sea levels by 7 m if it were to melt completely. The ice sheet is connected to the surrounding ocean at marine-terminating (or tidewater) outlet glaciers, with significant implications for both systems. Heat is transferred to the ice from comparatively warm ocean waters, melting the part of the glaciers that is in contact with the ocean. In recent decades this melting has accelerated in response to ocean warming, triggering glacier retreat and accelerating ice sheet mass loss and sea level rise. In return, the ice sheet transfers fresh water to the ocean in the form of liquid meltwater and solid icebergs, modifying ocean water properties and currents around Greenland. As ice melting increases in a warming climate, these effects are predicted to become more significant, potentially impacting ocean circulation and climate on a regional to global scale. It is thus of critical importance that exchanges between the ice sheet and ocean are understood and can be predicted. A key barrier to achieving this aim lies in the long, narrow and deep fjords that connect Greenland's tidewater outlet glaciers to the open ocean. These fjords are subject to a specific set of processes that modify the exchange between the ice sheet and ocean. For example, meltwater draining along the bed of the ice sheet enters fjords at great depth below the sea surface, where it rises vigorously, mixing with fjord waters in the process. The properties of this meltwater, and consequently the impacts it has on the ocean, are thus significantly modified during its journey down-fjord. Similarly, fjords act to obstruct and modify warm waters flowing from the ocean towards the ice sheet, meaning that the temperature of waters reaching Greenland's tidewater glaciers may differ significantly from that circulating off the coast. It is therefore critical that fjord processes are taken into account if interaction between the ice sheet and ocean is to be effectively understood and predicted. In this project, we will therefore use a newly developed numerical fjord model, in conjunction with data on ice sheet, fjord and ocean properties, to systematically examine the impact of fjords on a Greenland-wide scale. We will use this model to identify the fjord processes which have greatest effect on the exchange of heat and freshwater between the ice sheet and ocean, and how these differ between fjords and over time. Using this knowledge, we will examine the impact of these processes on glacier retreat and regional ocean properties. We will also look into the future to consider how fjord processes and their impacts will evolve over the 21st century, and how this may be incorporated into the large-scale models that are used to predict the impacts of climate change on our society.