Fluctuations of the West Greenland Ice Sheet, independent ice caps and mountain glaciers during the twentieth century

Abstract

The Greenland Ice Sheet contains enough water to raise global sea levels by ~7 metres, but predictions of the actual potential future contribution in a warming climate vary widely. These can be improved through a better understanding of how the whole ice sheet and its outlet glaciers have responded to past and present climate fluctuations. Recent studies have observed that Greenland Ice Sheet outlet glaciers have been retreating and thinning at increasingly faster rates since the 1990s. However, few studies have investigated the behaviour of the numerous independent ice caps that surround the ice sheet, or the land-terminating outlet glaciers. In addition, recent retreat is rarely put into context with long-term twentieth century fluctuations. This study has mapped ice sheet outlet glaciers and margins, independent ice cap outlets and mountain/valley glaciers at 11 time steps between the Little Ice Age and 2009 in northwest and southwest Greenland. Length changes of different glacier classes and terminus environments are examined, and overall glacier fluctuations compared to regional air temperatures and precipitation. Glaciers in the northwest have retreated further than those in the southwest at most time periods, with the exception of 1943/53-1964 when southwest glaciers underwent their most rapid rate of retreat. Length changes in both regions are driven by air temperature and precipitation changes. Tidewater outlet glaciers have generally retreated shorter distances than land-terminating glaciers in both absolute and relative terms over long time periods. These results imply that recent rapid retreat of many tidewater outlet glaciers in Greenland is not unprecedented, and may represent natural cyclical fluctuations rather than a long-term shift in behaviour. Ice sheet outlet glaciers have retreated shorter relative distances than independent ice caps and mountain/valley glaciers. Ice sheet margins advanced in the southwest between 1964 and 2001, and a slight advance of many independent glaciers was observed from ~1964-1987. It is unclear why this advance occurred. This study highlights the need for more research into the fluctuations of the independent ice caps and land-terminating glaciers in all regions of Greenland. In addition, more detailed research into the response of glaciers of all classes and terminus environments to climate change during the whole of the twentieth century is required to put recent changes into context.