IAP-25-096

Investigating the oceanic impacts of Greenland’s meltwater

The connection between oceans and ice sheets is a key coupling in the climate system. Warm ocean waters can drive rapid ice melt and glacier retreat, creating an influx of meltwater that in turn has the potential to affect ocean properties and circulation. Concerningly, it has been suggested that the increase in meltwater draining from the Greenland Ice Sheet as the climate warms could affect the Atlantic Meridional Overturning Circulation (AMOC) over the coming decades, slowing the poleward transport of warm ocean water that contributes to Europe’s mild climate (Golledge et al, 2019). However, our knowledge of the processes controlling exchange between the Greenland Ice Sheet and ocean remains limited, hindering our ability to understand and project these impacts.

In ‘hosing experiments’ which simulate the addition of freshwater to the North Atlantic using a numerical ocean model, ice sheet meltwater is typically treated as an input to the ocean surface over a large area of the ocean surrounding Greenland (Jackson et al, 2022). However, in reality much of Greenland’s meltwater drains into fjords – long, deep and narrow inlets that connect marine terminating outlet glaciers to the ocean. These fjords modify the properties and distribution of meltwater reaching the open ocean with potentially profound implications for its impact on ocean properties and circulation.

Because most of the meltwater forming on the ice sheet surface drains subglacially (at the bed), it enters into fjords at the base of marine-terminating outlet glaciers. Rather than freshening the ocean surface, the freshwater may thus enter at depths of several hundred metres below the surface, driving vigorous upwelling of and mixing with deep ocean waters. On the other hand, icebergs, often found in high concentrations within fjords, may contribute relatively large amounts of meltwater directly to the sea surface. It is important that these processes are captured if the effects of ice sheet meltwater on the ocean are to be accurately constrained.

Despite their importance, exploring the impact of fjord processes on Greenland’s freshwater export has proven challenging. To address this issue, we have recently developed a numerical model which captures key fjord processes whilst remaining sufficiently computationally efficient and user-friendly to be applied on a Greenland-wide scale. This PhD project will use this model to conduct the first Greenland-wide investigation into how a realistic representation of fjord process modifies the export of freshwater from the Greenland ice sheet to the ocean. It will then use this knowledge to explore the potential impact of this exported freshwater on the ocean around Greenland. Through this, it provides an exciting opportunity to advance our understanding of how meltwater export from Greenland ice sheet may affect ocean circulation, and by extension climate, over the coming century.

The project will utilise the newly developed Fjord Reduced Physics Model, known as FjordRPM (Slater et al, 2025), which represents fjords as a set of vertically-stacked layers whose temperature and salinity evolve in time according to parameterized exchange processes. The model is written in Matlab and can be run on a standard laptop (avoiding the need for knowledge of High Performance Computing systems), and has shown promising results in initial comparisons with more complex models (Slater et al, 2025) and in situ observations (Mas e Braga et al, 2025).

Phase 1. Investigate the form, timing and location of meltwater export from Greenland’s fjords

The initial aim of the project is to use FjordRPM to explore how freshwater released from the ice sheet (as runoff and icebergs) is modified as it transits through fjords to the shelf. To do this, the model will be used to generate timeseries of simulated fjord-to-shelf fluxes over a period of multiple years across a large sample of Greenland’s fjords. These will be analysed to investigate how freshwater is transformed by processes occurring in fjords, and to identify the key controls on this transformation.
This will provide a detailed picture of the glacial freshwater exported from Greenland’s fjords to the shelf, and the role of fjords in modifying this export.

Phase 2. Investigate the impact of exported freshwater on stratification and circulation of shelf seas

Having undergone modification during transit through the fjords, glacial meltwaters will impact the stratification and circulation of the Greenland shelf seas in unknown ways. Using a novel, salinity-coordinate framework (Goldsworth, 2025), this the impacts of glacial meltwaters will be compared with other processes operating in the shelf seas, including sea ice processes, lateral ocean currents, exchange with the open ocean, and tide-driven mixing. To do so, the outputs of FjordRPM from Phase 1 will be quantified in the context of other processes operating in the ASTE state estimate (Nguyen et al., 2021). The sensitivity of impacts to the meltwater modification occurring in fjords will be investigated, considering the extreme cases of unmodified meltwater entering at the ocean surface versus meltwaters strongly mixed throughout the water column, and all cases in between.

Further work:

After investigating the impact of glacial meltwater on the shelf seas stratification and circulation, it may be possible to interrogate knock-on impacts on the export of that meltwater from the shelf seas and into the open ocean. It has been established recently that the major fraction of glacial meltwater remains on the Greenland shelf rather than being transported offshore (Beaird et al., 2024), but it is unclear to what extent this is influenced by the modification of meltwater during the transition through the fjord. This question could be investigated with a combination of ocean circulation theory and idealised and realistic numerical circulation models.

Year 1

Literature review, begin work on Phase 1

Year 2

Complete Phase 1, begin Phase 2

Year 3

Complete Phase 2, pursue any further research directions

Year 3.5

Completion of experiments, complete thesis write up

The student will develop the skills necessary to undertake the modelling and data analysis outlined in the project description, delivered primarily through in-house expertise. No existing experience in numerical modelling is required. The student will also be encouraged to attend a relevant summer school such as the Greenland Ice Sheet-Ocean Interactions Summer School (https://griso.ucsd.edu/griso-summer-school-2025/) or an Advanced Climate Dynamics Course (https://www.uib.no/en/rs/acdc/174760/acdc-2025) as well as training and networking opportunities organised through the Scottish Alliance for Geoscience, Environment and Society (https://sages.ac.uk/). Through the supervisor team, the student will be linked to larger projects on related themes (e.g. https://www.bas.ac.uk/project/giant/) and will benefit from the experience of working as part of a team spanning several institutions. Although no fieldwork is included as part of the PhD project, there may be the opportunity to join other groups undertaking fieldwork at this time, with recent PhD students gaining fieldwork experience in Antarctica, Greenland and Svalbard.

Further training in transferable skills, including project management, oral and written presentation and media and outreach engagement is available through the International Education and Lifelong Learning Institute at the University of St Andrews. The student will be expected to present their work at appropriate national and international conferences throughout their PhD research.