SPECIAL ISSUE ON OCEAN-ICE INTERACTION THE ICE SHELF OF PETERMANN GLETSCHER, NORTH GREENLAND, AND ITS CONNECTION TO THE ARCTIC AND ATLANTIC OCEANS NORTH GREENLAND,By Andreas Münchow, Laurie Padman, AND Peter Washam,ITS andCONNECTION Keith W. Nicholls TO THE ICE SHELF OF PETERMANN GLETSCHER, Petermann Gletscher, August 10, 2015. View is to the northeast from the center of the glacier. 84 Oceanography | Vol.29, No.4 …the new remotely sensed and in situ data identify the Petermann ice-ocean system as a dynamically “ rich and rapidly changing environment. ” ABSTRACT. Petermann Gletscher in North Greenland features the second largest there as the gateway to North Greenland. floating ice shelf in the Northern Hemisphere. This paper describes the history of its It is also the only deepwater port within a exploration and presents new ocean and glacier observations. We find that the floating 1,600 km radius, allowing US, Canadian, ice shelf is strongly coupled to the ocean below and to Nares Strait at time scales from Danish, and Swedish ships to receive tidal to interannual. Our observations cover the 2012 to 2016 period after two large and discharge their sailors and scien- calving events took place in 2010 and 2012 that reduced the ice shelf area by 380 km2 to tists. Since 2009, Thule AFB has also about 870 km2 today. A potential third breakup, of an additional 150 km2, is anticipated served as the northern base for annual by a large fracture that extends from the margin to the center of the glacier. Operation IceBridge flights over North Greenland that map the changing ice HISTORY OF EXPLORATION expeditions, the onset of the Cold War sheets and glaciers. brought airplanes and radar to North The establishment of military weather In 1921 owing to starvation I had to go Greenland. Even further north, the Arctic stations and airfields in the high Arctic directly from Cape Heiberg-Juergensen to Ocean along with the bordering land and coincided with the discovery of mas- our cache at Cape Agassiz…during this ice masses of Greenland and Canada sive ice islands (large tabular icebergs) journey the greater part of the glacier became a battle space. To support mil- drifting freely in the Arctic Ocean. was mapped. – Lauge Koch itary aviation, weather stations were On August 14, 1946, airmen of the Traveling by dog sled, Danish geolo- established in 1947 at Eureka and in 1950 46th Strategic Reconnaissance Squadron gist Lauge Koch mapped Petermann at Alert (J. Johnson, 1990). In 1951, more of the US Air Force discovered a moving Gletscher in 1921 as he crossed it with than 12,000 US military men and women ice island with an area of about 200 km2 three Inuit companions on a journey to descended on the small trading post of that was kept secret until November 1950 explore northern North Greenland. They Thule (Figure 1) that Knud Rasmussen (Hattersley-Smith et al., 1952). Most ice discovered and named Steensby, Ryder, and Peter Freuchen had established islands originated from ice shelves to the and H.C. Ostenfeld Glaciers (Figure 1) 40 years earlier to support their dog-sled north of Ellesmere Island whose area was that, like Petermann Gletscher, had float- expeditions across Greenland (Freuchen, reduced over the last century from about ing ice shelves (Ahnert, 1963; Higgins, 1935). “Operation Blue Jay” built Thule 8,900 km2 to 1,000 km2 (Jeffries, 1992; 1990). All four starved travelers returned Air Force Base (AFB) as a forward station Antoniades et al., 2011). Franz Boas pro- home safely in 1921; however, their pre- for fighter jets, nuclear-armed bomb- vided the first historical description of vious expedition in 1917 had not been so ers, and early warning radar systems. an ice island from Petermann Gletscher lucky, because two traveling companions The radars were designed to detect bal- in 1883 when he established a German died (Rasmussen, 1921). Figure 2 shows listic missiles crossing the Arctic Ocean station in Cumberland Sound at 65°N, the 1917 and 1921 survey tracks along from Eurasia to North America, while 65°W as part of the First International with the historic Koch (1928) map and the bombers were to retaliate in case of a Polar Year (Boas, 1885). Without know- a modern remotely sensed mapping of nuclear attack from the Soviet Union. ing the source of the massive tabular ice- Petermann Gletscher and its fjord. Today, the jets, bombers, and Soviet berg, Boas (1885) made measurements Only 30 years after these dog-sled Union are all gone, but Thule AFB is still of ice thickness (120–150 m), extent Oceanography | December 2016 85 AWS: EA KMJ below it. These new observations are nei- ther complete nor fully understood in their dynamical implications; however, P S R O the new remotely sensed and in situ data identify the Petermann ice-ocean system as a dynamically rich and rapidly chang- Baffin Is N 80°N CS Z ing environment. These tantalizing obser- 1000 vations suggest strong ocean impacts Greenland on the ice shelf as the coupled system Labrador responds to larger-scale change observed over Greenland (Hanna et al., 2013) and the Arctic Ocean (Polyakov et al., 2010). 70°N PETERMANN ICE SHELF 1000 3000 Historically, the floating section of Petermann Gletscher oscillated in length 60 °W 50 °N °N °W 60 °W between 70 km and 85 km from the 40 20 84°N grounding line at decadal time scales (Münchow et al., 2014) as the glacier’s ter- minus moved steadily seaward at speeds Lincoln Sea of 900–1,000 m yr–1 (Higgins, 1990). This changed when two large calving Alert events reduced the length of the ice shelf Ellesmere Is in 2010 and 2012 from 81 km to 46 km (Münchow et al., 2014). The ice lost from 2010 to 2012, 36 ± 4 Gt, represents three 82°N years of ice flux across the grounding line (Rignot and Steffen, 2008); however, it H.C. will take the glacier roughly two decades Steensby Ostenfeld to reach its former terminus location, if it Ryder continues to advance at its current speed Petermann of ~1.2 km yr–1 (Nick et al., 2012). 80°N The structure and extent of the ice shelf °W °W 60 40 depend on the interactions of numer- FIGURE 1. (top) Map of the study area from the Arctic to the Atlantic Ocean with bathymetry con- ous processes, including atmospheric and toured in 1,000 m intervals. The red square indicates Petermann Gletscher, and red tracks show oceanic forcing, sea ice and mélange (the the 2010/11 path of Petermann Ice Island PII-2010A. Blue dots show locations of weather stations (west to east near 80°N) at Eureka (E), Alert (A), and Kap Morris Jesup (KMJ). Thule Air Force Base combination of sea ice and small iceberg is located near 76°N and shown as a black triangle. Red dots indicate glaciers with current float- fragments) in the fjord, and the dynam- ing ice shelves or that have had floating ice shelves within the last 20 years, includes Petermann ics of ice sheet flow across the grounding (P), Steensby (S), Ryder (R), and H.C. Ostenfeld (O), 79 North Glacier (N), and Zachariae Isstrom (Z). The red triangle in Cumberland Sound (CS) shows the location of the ice island described by Boas line (Straneo et al., 2013). Here, we pro- (1885). The bottom panel shows details west of 40°W. The northern sill in the Lincoln Sea is indicated vide new observations on the most dif- by a red star. Bathymetry contours of 250 m (rose), 300 m (cyan), and 350 m (blue) are plotted over ficult of these processes to observe, the a MODIS image from August 2015. interactions between the ocean and the ice shelf. H. Johnson et al. (2011) and (78 km2), surface undulations (150 m expedition in 1874/75. Croppinger identi- Münchow (2016) discuss the regional wavelength over several kilometers), and fied the terminus of Petermann Gletscher oceanography of Petermann Fjord and rocks both on the ice surface and within as a floating ice shelf when he noticed Nares Strait, respectively, with data col- the upper 1–2 m of the ice. All these vertical tidal motions of the glacier from lected prior to the 2010 calving event. features match scales and characteris- sextant measurements (Nares, 1876). Our new observations were obtained tics of the Petermann Gletscher ice shelf Here, we extend these initial explora- since the 2012 calving event, and extend as they were first described by Richard tions with modern observations of the throughout Petermann Fjord and Croppinger, surgeon of a British Naval shape of the ice shelf as well as the ocean under the ice shelf. 86 Oceanography | Vol.29, No.4 Petermann Fjord connects the glacier reveal identical glacier thinning between 2013/14 terminus speed also represents to Nares Strait, which in turn is connected 2007 and 2010 (Münchow et al., 2014), glacier speeds at those locations. to the Arctic Ocean in the north and the prior to the large calving events. More Between August 20, 2015, and Atlantic Ocean via Baffin Bay in the south recently, as part of NASA’s Operation February 11, 2016, we measured glacier (Figure 1). The path of Petermann Ice IceBridge, a laser altimeter was used speeds 16 km from the grounding zone Island PII-2010A emphasizes this con- to measure surface elevation from the with a single-frequency GPS as part of nection, as the 60 m thick section of the grounded ice to the ice front on a repeat an ocean weather observatory (discussed ice island reached the Labrador Sea in the path along the glacier in April 2013 and below).