Abstract
ABSTRACTThe increasingly negative mass balance of the Greenland ice sheet (GrIS) over the last ~25 years has been associated with enhanced surface melt and increased ice loss from marine-terminating outlet glaciers. Accelerated retreat during 2000–2010 was concentrated in the southeast and northwest sectors of the ice sheet; however, there was considerable spatial and temporal variability in the timing and magnitude of retreat both within and between these regions. This behaviour has yet to be quantified and compared for all glaciers in both regions. Furthermore, it is unclear whether retreat has continued after 2010 in the northwest, and whether the documented slowdown in the southeast post-2005 has been sustained. Here, we compare spatial and temporal patterns of frontal change in the northwest and southeast GrIS, for the period 2000–2015. Our results show near-ubiquitous retreat of outlet glaciers across both regions for the study period; however, the timing and magnitude of inter-annual frontal position change is largely asynchronous. We also find that since 2010, there is continued terminus retreat in the northwest, which contrasts with considerable inter-annual variability in the southeast. Analysis of the role of glacier-specific factors demonstrates that fjord and bed geometry are important controls on the timing and magnitude of glacier retreat.
Highlights
Since the early 1990s, the rate of ice loss from the Greenland ice sheet (GrIS) has accelerated in synchrony with both elevated air temperatures (e.g. Hanna and others, 2008, 2012b, 2013; Fettweis and others, 2013) and warmer ocean waters reaching marine margins (e.g. Murray and others, 2010; Straneo and others, 2012, 2016; Sutherland and Straneo, 2012)
Understanding the patterns of retreat in the northwest and southeast regions of the GrIS is especially important because together, these regions currently contribute over 80% of the ice sheets total annual dynamic discharge (Enderlin and others, 2014) and are important contributors to ice loss and overall ice-sheet mass balance
Mean regional annual retreat rates were higher in the northwest (−90 m a−1, SD = 110 m) compared with the southeast (−70 m a−1, SD = 190 m), and this was reflected in the proportion of glaciers that experienced retreat rates of >−200 m a−1 (13% in the northwest and 7% in the southeast) (Fig. 4)
Summary
Since the early 1990s, the rate of ice loss from the Greenland ice sheet (GrIS) has accelerated in synchrony with both elevated air temperatures (e.g. Hanna and others, 2008, 2012b, 2013; Fettweis and others, 2013) and warmer ocean waters reaching marine margins (e.g. Murray and others, 2010; Straneo and others, 2012, 2016; Sutherland and Straneo, 2012). The average annual mass loss from the GrIS between 1991 and 2015 was 0.47 ± 0.23 mm SLE (Van den Broeke and others, 2016) and was driven by negative surface mass balance (primarily the result of increased air temperatures, leading to enhanced surface melt) and increasing ice discharge from outlet glaciers (channels of fast flowing ice draining the ice sheet and terminating at a marine margin) (Meier and Post, 1987; van den Broeke and others, 2009; Post and others, 2011) These glaciers contribute to ice loss through enhanced retreat of the calving front (Meier and Post, 1987; Pfeffer, 2007; Post and others, 2011) and associated thinning and accelerated ice motion that further enhances retreat (Van der Veen, 2002; Pritchard and others, 2009; van den Broeke and others, 2009; Enderlin and others, 2014). While Moon and others (2015) analysed the behaviour of a small sample of glaciers in the northwest beyond 2010, other observations of glacier retreat after this year are limited
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