Parameterizing the impact of fjord circulation on the ocean forcing of melting ice sheets

Melting of the Greenland ice sheet currently accounts for about a quarter of the observed global mean sea level rise (contributing approximately 7.5mm over the period 1992-2011), and therefore has significant impact on the large fraction of the global population who are influenced by changing sea level. Greenland ice melt is also increasing freshwater input to the North Atlantic, with the potential to alter ocean circulation and significantly influence the climate in north-west Europe. Predictions from state-of-the-art climate models incorporate the atmospherically-driven surface melt of ice sheets, but the component of marine melting is missing.

This marine melting occurs in hundreds of fjords around Greenland where glaciers meet the ocean. Observations suggest that decadal variability in regional ocean temperature causes significant variability in ice loss. Warm water arriving at the ice front drives increased melting of submerged glacier snouts and ice shelves, leading to acceleration of inland regions of the ice sheet. The increased flux of ice from the land into the ocean impacts sea level.

Due to the geometrical confinement in fjords, the transport of ocean heat towards the ice depends on fjord circulation occurring on scales too small to be represented in a modern global climate model. The representation of this missing process requires a parameterization scheme that is driven by and affects the modeled ocean properties. The lack of such a parameterization is a serious limitation of contemporary climate models: the oceans around Greenland are predicted to warm in the future, but we cannot accurately predict the impact on glacial melt and sea-level rise because we lack the tools required to address the problem. As a result, recent IPCC reports have struggled to accurately estimate this contribution to sea-level rise.

This project will develop and implement a simple parameterization of glacial melt in response to ocean forcing, that can be used to represent small-scale fjord processes in large-scale ocean and earth system models. Our team will develop a simplified model to capture the exchange rates of heat and salt between a fjord and the wider ocean, and their impact on ice sheet melting, using physical constraints and fluid dynamics theory. We will calibrate the response of this model to a range of ocean conditions and fjord geometries, using high-resolution ocean simulations in a localized fjord setting and comparing to ongoing measurements in Greenland fjords. The simplified model will act as a parameterization of melting that can be applied to a wide range of fjords, and we will implement this in the Met Office ocean model. The final coupled model will predict local ice melt rates that drive an ice sheet model and control freshwater fluxes to the ocean.

Our parameterization will provide an adaptable tool for immediate use in climate and Earth system models at the Met Office and other climate modelling centres worldwide. It will be of flexible design, providing initial predictions based on current knowledge, but allowing new constraints to be incorporated from future field campaigns and modeling studies that account for new processes.

We will enhance the training of a student from a Science, Technology, Engineering & Mathematics (STEM) background, and translate their skills to tackle environmental challenges and address a key UK skills gap. We will dovetail intensive training at Oxford University on the core knowledge and skills for environmental research, with hands on experience of high performance computing, code development, and working in industry at the Met Office.

In summary, our intensive researcher training will infuse STEM skills into environmental science, whilst simultaneously forging new understanding of the impact of ocean circulation on glacial melting in Greenland fjords, and developing a dynamically-based parameterization of these effects for use in future climate model projections.