Increased mass loss and asynchronous behavior of marine-terminating outlet glaciers at Upernavik Isstrøm, NW Greenland

In order to model and predict future behavior of marine terminating glaciers, it is essential to understand the different factors that control a glaciers response to climate change. Here we present a detailed study of the asynchronous changes in dynamic behavior of four adjacent marine-terminating glaciers at Upernavik Isstrøm (UI), northwest Greenland, between 1992 and 2013. Velocities were stable for all outlets at UI between 1992 and 2005. The northernmost glacier started to accelerate and thin in 2006 and continued to do so into 2011 after which time the velocities stabilized. The second most northerly glacier started to accelerate and thin in 2009 and continued to do so until the last observations in 2013, dramatically increasing the area affected by dynamically induced thinning. The southern glaciers show little change, with the most southerly glacier undergoing slight retreat and deceleration between 1992 and 2013. These observations point out the fact that the UI glaciers are reacting to climate change on different timescales. The asynchronous behavior of the four neighboring glaciers is explained in terms of the individual glaciers geometry and terminus position. The northernmost glacier is believed to have had a floating tongue between 1985 and 2007 which disintegrated in 2007-2008. This release of back stress destabilized the glacier causing it to accelerate and thin rapidly. We suggest that the ice tongue broke up due to ocean-warming-induced thinning in the late 1990s. Recent response on UI glaciers is found to be related to increased surface melt. Our investigations suggest that three out of the four main glaciers in the UI are likely to be in unstable positions and may have the potential to rapidly thin and accelerate and increase their contribution to sea level in the future.