Fjord Dynamics and Modulation of Ice/Ocean Exchange

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.