Petermann Glacier is one of the largest glaciers of the Greenland ice sheet, and yet, relatively little is known about it or the surrounding area. Petermann Fjord lies in an ice-choked and remote corner of northern Greenland, it is difficult to access by ship, even in the relatively benign summer months.
Figure 1: Location of Petermann Glacier and Fjord. Bathymetry from IBCAO v3 . Petermann Glacier catchment from S. Bevan, Swansea University. Box shows extent of Figure 2.
Petermann Glacier drains ice from the centre of the vast Greenland Ice Sheet to the ocean in the 90 km long Petermann Fjord (Figure 1). Sparse depth measurements show that the fjord bed lies up to 1100 m below sea level – it is one of the deepest fjords in Greenland, testament to many millenia of intense glacial erosion. However, much of the inner-fjord remains unexplored; knowing the shape of the fjord is really important for understanding how the glacier will behave in the future. Shallow fjords allow glaciers to rest on the bed, which has a stabilising effect. In contrast, deep fjords permit ice to float in seawater, making the ice prone to breaking away in the form of icebergs or large ice islands. One of the many goals of the Petermann 2015 expedition is to survey the inner-fjord and produce high-resolution bathymetric maps of this area. This will greatly improve predictions of the future behaviour of the glacier system.
Figure 2: Petermann Glacier and Fjord, view looking approximately NW. Landsat 8 OLI imagery (NASA) projected on the GIMP 30 m resolution digital elevation model . 5x vertical exaggeration.
Petermann Glacier is vast, it drains more than 4% of the total ice sheet – an area larger than the state of West Virginia (see drainage basin in Figure 1). The glacier flows like a river of ice towards the sea at a speed of approximately 1 km per year and delivers 12 billion tonnes of ice to the ocean annually; enough freshwater to supply London for nearly 25 years* (Figure 3 – [5, 6, 7]). Once the glacier hits Petermann Fjord, the ice begins to float, forming an ice tongue which currently covers an area of 900 km2. The ice tongue thins, from nearly 600 m thickness where it enters the fjord, to around 100 m at the glacier front . The ice thinning is primarily (~85%) caused by melting from the underside of the ice by relatively warm ocean waters [5, 3]. Consequently, it is crucial to know what is happening in the ocean in order to predict how the glacier might behave in the future. Current oceanographic data are sparse, providing only a “snapshot” of conditions, [5, 3, 8] and almost nothing is known about how the oceanography of the fjord varies over time – does warm water permanently circulate beneath the floating tongue? Does turbulence in the fjord help melt the ice? We hope to address these unknowns by collecting a wide range of ocean measurements, including drilling through the floating ice tongue to measure water properties beneath the ice.
Figure 3: Figure from  – Panchromatic Landsat 7 image of Petermann Glacier shortly after the 2010 calving event; (b) example of TerraSAR-X feature tracking showing the hinge line (red; Rignot, 1996), the flowline transect (black) and locations (purple) above and below the grounding line selected for observation/model comparison. Black circles illustrate the positions of the recently deployed GPS units. Date format is day/month/year.
Two huge glacier calving events have occurred at Petermann Glacier over the past 5 years, one in 2010 and another in 2012 [9, 10]. During each event a large portion of the floating ice tongue broke away and drifted out of the fjord, before finally melting and disintegrating in Baffin Bay. These twin calving events resulted in a glacier retreat of 35 km, the most retreated position since the area was first surveyed in 1875 [11, 8]. Glacier calving and retreat has prompted speculation about the glaciers future, a major motivation for the Petermann 2015 expedition. It is crucial that we understand whether these calving events are part of the natural cyclical behaviour of the glacier, or stem from external influences – either through climate or ocean warming. We hope to answer these questions by reconstructing the behaviour of the glacier, oceans, and climate over timescales of thousands of years, providing valuable context against which to assess the magnitude of current changes.
*Based on average water consumption of 167 litres per person, per day, and a population of 8 million people.
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