Controls on late Holocene and 20th century ice shelf dynamics in northeast Greenland

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Over the past three decades satellite observations over Greenland and Antarctica have revealed that marine terminating glaciers and ice shelves have been thinning at an accelerating rate in response to both increased air and ocean temperatures. Thinner ice shelves are less able to buttress inland ice, leading to grounding line retreat, increased ice sheet thinning and ultimately, sea-level rise. This process, known as the marine ice sheet instability, has the potential to drive rapid and irreversible ice sheet collapse. Indeed, some ice sheet models indicate that these processes are already underway in Antarctica. In Greenland, several studies have linked recent ice shelf thinning/loss and accelerated ice flow to the incursion of warm Atlantic water. However, understanding the nature and rate of this recent grounding line response to ocean forcing (and other perturbations) requires knowledge of how these processes have evolved over recent centuries. In Antarctica, some changes are known to have started prior to satellite observations, highlighting the need to understand the recent (centennial) history in order to understand the interplay between changing ocean properties and ice sheet dynamics. Such knowledge is essential if we are to accurately predict future ice sheet behaviour as well as the ocean feedbacks in the North Atlantic region. This project will explore the twentieth century evolution of the 79N ice shelf, which currently buttresses the Northeast Greenland ice stream (NEGIS). The NEGIS drains the northeast sector of the Greenland ice Sheet (GrIS) and contains approximately 1.2 m sea-level equivalent (sle). Its future stability is pivotal not only to future mass balance of the GrIS but also the freshwater flux to the northeast Atlantic and specifically, to the North Atlantic Deep Water overturning circulation. Starting in the early 2000s, the ice shelves that front NEGIS (Zachariae Isstrom and 79N) have started to destabilise, but while ZI has disintegrated, 79N has remained relatively stable. Some modelling studies suggest that the 'relative' stability of 79N could continue over the next century, but recent oceanographic observations have shown that ocean heat flux and melt rates maybe increasing. Thus, there is great concern that 79N will be the next ice shelf to disintegrate and if this occurs, it will result in a substantial increase in ice discharge to the ocean.This project will use existing sediment gravity, box and lake sediment cores collected from beneath and adjacent to the 79N ice shelf to reconstruct ice shelf history and Atlantic Water circulation over the last ~200 years. The available material was collected in 2016 and 2017 as part of the NERC project (Greenland in a Warmer Climate) in collaboration with the Alfred Wegener Institute in Germany. Specifically the student will employ a multi-proxy examination of key cores including analyses of sediment properties (physical properties, grain size), geochemical proxies (oxygen, carbon isotopes, XRF, clay mineral) and microfossil content (diatoms, foraminifera) to determine ice shelf presence/absence, changes in ice shelf thickness and water mass characteristics. Foraminiferal and oxygen and carbon stable isotope analyses will be used to investigate the variability in meltwater flux and Atlantic Water adjacent to and beneath the ice shelf. A geochronological framework for changing ice shelf dynamics and incursions of warm water will be determined using radiometric (Pb, Cs) and radiocarbon (C) dating methods. Pb analysis will be critical to establish a chronology twentieth century ice shelf dynamics. Integration of these datasets will enable the processes controlling retreat behaviour to be determined. The successful student will be trained in all aspect of multi-proxy core analyses and wherever possible spend time at key facilities and partner laboratories.In addition, the student will benefit from a large and energetic Polar research communities.