Glacier dynamics near the calving front of Bowdoin Glacier, northwestern Greenland

Abstract

To better understand recent rapid recession of marine-terminating glaciers in Greenland, we performed satellite and field observations near the calving front of Bowdoin Glacier, a 3 km wide outlet glacier in northwestern Greenland. Satellite data revealed a clear transition to a rapidly retreating phase in 2008 from a relatively stable glacier condition that lasted for >20 years. Ice radar measurements showed that the glacier front is grounded, but very close to the floating condition. These results, in combination with the results of ocean depth soundings, suggest bed geometry in front of the glacier is the primary control on the rate and pattern of recent rapid retreat. Presumably, glacier thinning due to atmospheric and/or ocean warming triggered the initial retreat. In situ measurements showed complex short-term ice speed variations, which were correlated with air temperature, precipitation and ocean tides. Ice speed quickly responded to temperature rise and a heavy rain event, indicating rapid drainage of surface water to the bed. Semi-diurnal speed peaks coincided with low tides, suggesting the major role of the hydrostatic pressure acting on the calving face in the force balance. These observations demonstrate that the dynamics of Bowdoin Glacier are sensitive to small perturbations occurring near the calving front

Initiation of a major calving event on the Bowdoin Glacier captured by UAV photogrammetry

“…Its present-day position is no more than 2 km upstream of its 1897 position (Chamberlin, 1897). However, from July 2008 to September 2013, a rapid retreat of the calving front at a rate of 220 m yr −1 was recorded, while no significant changes occurred during the previous 20 years (Sugiyama et al, 2015). From 2013, the calving front has stabilized to about its current position.…”

“…It is approximately 10 km long and 3 km wide with an average surface slope of less than 1 • . The glacier discharges into the Bowdoin Fjord through a 3 km wide, most-likely grounded calving front (Sugiyama et al, 2015). At the centre of the calving front, the Bowdoin Glacier was about 250 m thick, and its maximal flow speed was about 1.5 m day −1 in 2013.…”

“…There exist a variety of image matching methods to derive glacier surface speed (Heid and Kääb, 2012). Here, we have used an algorithm of crosscorrelation in frequency domain on orientation images (Abe et al, 2016;Heid and Kääb, 2012;Sugiyama et al, 2015). On the one hand, a 30 m resolution velocity field, averaged between 14 June and 1 August (see Fig.…”

“…This included ice radar and GPS measurements (Sugiyama et al, 2015;Tsutaki et al, 2016), seismic records (Podolskiy et al, 2016), automatic camera installations and borehole drilling (to record in-ternal ice deformation, englacial temperature and water pressure).…”

Acoustic water bottom investigation with a remotely operated watercraft survey system

“…In addition, the data are recordable with simultaneous positional information, so a wide range of scientific data can be collected at a relatively low cost; moreover, the equipment can be used on small boats because of their small size and light weight. Thus, these modern fish finders have been used in a variety of research fields, including marine engineering (Uchida et al 2008;Tabusa et al 2013), glaciology (Sugiyama et al 2015), marine biology (Heyman et al 2007), and archeology and geology (Yamasaki and Kamai 2015).…”