Ocean forcing of the Greenland Ice Sheet: Calving fronts and patterns of retreat identified by automatic satellite monitoring of eastern outlet glaciers

Abstract

[1] We have developed an automatic method to identify changes in the position of calving glacier margins using daily MODIS imagery. Application of the method to 32 oceanterminating glaciers in East Greenland produced 26,802 margin positions for a 10 year long period (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009). We report these high-resolution data and show that the glaciers exhibit seasonal cycles with magnitudes of advance and retreat proportional to glacier width. Despite similar seasonality there is a distinct difference between the interannual trends of calving front positions north and south of 69°N. All glaciers above this latitude showed very limited or no change when seasonality was excluded, while glaciers south of 69°N retreated significantly between 2001 and 2005 (∼2.3 km on average). Approximately 26% of the retreat of southern glaciers was regained by readvance from 2005 to 2009. To explain the latitudinal boundary of glacier dynamics, we review basic climatic factors, including summer and winter atmospheric forcing, sea ice conditions, and ocean temperature. We conclude that the southern retreats were strongly influenced by warm oceanic conditions associated with increased transport of subtropical waters to the Irminger Sea and to fjords and coastal regions south of 69°N. Northern glaciers remained stable despite significant increase in runoff in this region because fjords at latitudes higher than 69°N are less exposed to subtropical waters. The southern retreats illustrate sensitive behavior of calving glaciers, and we hypothesize that the calving fronts retreated because they were exposed to rapid ice-front melting.

Multidecadal to millennial marine climate oscillations across the Denmark Strait (~ 66° N) over the last 2000 cal yr BP

“…However, our estimates also include a calculation of the standard deviations of the estimate based on iterations of the 2 × 5 matrix (Andrews and Eberl, 2012); thus, we could account for nearly 100 % of the sediment composition by specific sample selection from the two source areas. Additional sediment sources would certainly be derived from icebergs that originated in Scoresby Sund and northeast Greenland and sediment entrained in sea ice from the Arctic Ocean (Andrews, 2011;Bigg, 1999;Darby and Bischof, 2004;Darby et al, 2011;Seale et al, 2011). Over the 100 yr interval ending ca.…”

“…Kangerlussuaq Fjord, the Geikie Plateau, and Scoresby Sund all contain fast-flowing tidewater glaciers that contribute icebergs from their tidewater margins (Dwyer, 1993;Nuttall, 1993;Seale et al, 2011). Several of the fast-flowing ice streams are buttressed by a sikussuaq, a mélange of sea ice, bergy bits, and icebergs (Mugford and Dowdeswell, 2010;Reeh, 2004;Reeh et al, 2001;Syvitski et al, 1996).…”

Distributed subglacial discharge drives significant submarine melt at a Greenland tidewater glacier

“…The Greenland Ice Sheet lost mass at an increasing rate during the last decade, in part due to the increase in ice loss from the fronts of large marine-terminating outlet glaciers Rignot et al, 2011;Shepherd et al, 2012;Enderlin et al, 2014]. A change in the ocean's forcing at the ice/ocean boundary is a leading hypothesis to explain these increased mass losses [Murray et al, 2010;Rignot et al, 2010;Straneo et al, 2011].…”

Dynamic changes in outlet glaciers in northern Greenland from 1948 to 2015

“…warmer compared to the 1948-1999 average, in both the northwest and northeast regions of the GrIS (Figure 11). These 10 changes coincide with Arctic-wide increased retreat rates (Carr et al, 2017b), acceleration and retreat in south-east Greenland Seale et al, 2011), and, to some extent, recent changes in north-west Greenland (e.g. Moon et al, 2012).…”

“…Despite not being exposed to warm subtropical waters like elsewhere around Greenland (e.g. east Greenland: Seale et al, 2011), increased ocean temperatures can markedly increase basal melt rates on 15 large floating tongues (Mouginot et al, 2015;Reeh et al, 1999;Rignot et al, 2001Rignot et al, , 1997. Early work highlighted the importance of basal melting for the mass balance of ice-shelves (Reeh et al, 2001;Rignot et al, 2001;Rignot and Steffen, 2008) and melt rates beneath the three remaining floating ice tongues (Nioghalvfjerdsfjorden, Petermann, and Ryder) are estimated to exceed ~50 m a -1 , which is >80% of the total melt flux at all three glaciers (Wilson et al, 2017).…”