A Review of Recent Changes in Major Marine-Terminating Outlet Glaciers in Northern Greenland
- 1School of Geography, Politics and Sociology, Newcastle University, Newcastle upon Tyne, UK
- 2Department of Geography, Durham University, Durham, UK
Over the past two decades, mass loss from the Greenland Ice Sheet (GrIS) has accelerated and contributed to global sea level rise. This has been partly attributed to dynamic changes in marine terminating outlet glaciers. Outlet glaciers at the northern margin of the ice sheet drain 40% of its area but are comparatively less well-studied than elsewhere on the ice sheet (e.g., central-west or south-east). In order to improve our understanding of this region of the GrIS, this paper synthesizes previously-published research on 21 major marine terminating outlet glaciers. Over the last 130 years, there has been a clear pattern of glacier retreat, particularly over the last two decades. This was accompanied by velocity increases on the majority of glaciers for which records exist. Despite a distinct signal of retreat, however, there is clear variability within the region, which has complicated efforts to determine the precise drivers of recent changes, such as changes in ice tongue buttressing, atmospheric and/or oceanic warming, in addition to the possibility of glacier surging. Thus, there is an important need for further work to ascertain the precise drivers of glacier change, which is likely to require datasets on recent changes in the ocean-climate system (particularly sub-surface ocean temperatures) and numerical modeling of glacier sensitivity to these various forcings. Objective identification of surge-type glaciers is also required. Given that Northern Greenland is predicted to undergo greater warming due to Arctic Amplification during the twenty-first century, we conclude that the region has the potential to become an increasingly important source of mass loss.
Mass loss from the Greenland Ice Sheet (GrIS) has doubled in the last two decades (Shepherd et al., 2012) as a result of both increased ice discharge and increased surface melt (van den Broeke et al., 2016). Together, these processes currently contribute ~0.6 mm per year to global sea level rise (Fürst et al., 2015). The increased ice discharge is associated with marine-terminating outlet glaciers that have undergone thinning, retreat and acceleration since the mid-1990s (Rignot and Kanagaratnam, 2006; Moon and Joughin, 2008; Joughin et al., 2010a). Their retreat between 2000 and 2010 was considered exceptional over the past half century (Howat and Eddy, 2011), and dynamic discharge from outlet glaciers was thought to be responsible for ~40% of mass loss from the ice sheet between 1991 and 2015 (van den Broeke et al., 2016). The recent rapid outlet glacier retreat and flow acceleration is understood to be in response to ocean-climate forcing (McFadden et al., 2011; Cook et al., 2014). Potential mechanisms by which atmospheric temperatures may promote retreat through glacier calving are the drainage of supraglacial lakes or water-filled crevasses fracturing through the full ice thickness (van der Veen, 2007; Das et al., 2008). Alongside this, ocean warming may increase rates of submarine melting at marine-terminating glaciers (Holland et al., 2008), which may be further enhanced by submarine meltwater plume discharge (Motyka et al., 2003; Jenkins, 2011). In addition, sea ice removal or decline may promote calving and a longer ice-free season may allow greater volumes of ice to be lost during the year (e.g., Carr et al., 2013b, 2014; Moon et al., 2015).
However, the magnitude of individual glacier responses to these forcings is known to be modulated by local topographic factors (Howat et al., 2007; Moon et al., 2012; Carr et al., 2013b). For example, fjord width is a key local control on glacier retreat, where a narrow fjord can delay the removal of icebergs from the terminus (e.g., Warren and Glasser, 1992; Jamieson et al., 2012; Carr et al., 2014). Another important glacier-specific factor is basal topography, whereby a