News: Web Platform for Sharing Spatial Data, p. 118 About AGU: Exploration Station Brings Science to the Public, p. 119 About AGU: Patzert Receives 2010 Athelstan Spilhaus Award, p. 120 Book Review: Introduction to Water Resources and Environmental Issues, p. 121 Research Spotlight: Expansion of Corals, Rain in Pakistan, Fog on Mars, p. 124

volume 92 number 14 5 APRIL 2011

Context for the Recent Massive Petermann Glacier Calving Event

On 4 August 2010, about one fifth of the in steady state even allowing for sporadic floating ice tongue of Petermann Glacier calving that occurs on a decadal time (also known as “Petermann Gletscher”) scale. in northwestern Greenland calved (Fig- Rignot and Steffen [2008] have recently ure 1). The resulting “ice island” had an considered the Petermann ice tongue in mass area approximately 4 times that of Manhat- balance terms. Combining measured surface tan Island (about 253±17 square kilometers). velocity and thickness at the grounding line The ice island garnered much attention from during 2000–2006, they estimated that the the media, politicians, and the public, who ice sheet supplies about 12 cubic kilometers raised concerns about downstream implica- of ice per year to the tongue. Because Peter- tions for shipping, offshore oil and gas oper- mann is located in one of the driest regions ations, and possible connections to Arctic of the Greenland Ice Sheet, surface losses and global warming. from sublimation more than compensate for Does this event signal a change in the gla- the 10–15 centimeters of snow accumulation cier’s dynamics? Or can it be characterized per year, to result in 1.7 cubic kilometers of as part of the glacier’s natural variability? yearly surface ice loss. Time-­averaged calv- Understanding the known historical context ing losses are of similar magnitude (about of this event allows scientists and the public 1 cubic kilometer per year). to judge its significance. If one takes the system to be at steady state, these losses account for about 20% An Overview of Petermann Glacier of the supply estimated by Rignot and Stef- fen [2008]. Thus, ocean melting presum- Fig. 1. (a) NASA Aqua satellite Moderate Resolution Imaging Spectroradiometer true-­color image, Petermann Glacier is a major outlet ably drives loss of the remaining 80%. taken 0840 UTC on 5 August 2010, showing calving of Petermann Glacier, northwestern Green- that drains about 6% of the Greenland Ice Arctic seawater of Atlantic origin enters land. There was no sign of a break on 3 August (based on Envisat’s advanced synthetic aperture Sheet area. It is one of four such major out- Petermann Fjord via Nares Strait and deliv- radar data from its wide-­swath mode, observed at 1530 UTC), but Envisat imagery revealed the let glaciers surrounding Greenland that are ers ample heat to accomplish the basal break on 4 August 2010. (b) A map of 31 known frontal positions of the ice tongue (sources are grounded substantially (500 meters) below melting [Johnson et al., 2011]. Ocean in Table S1). The seaward red curve is the ice front in 1876; behind it in red are the locations of sea level and one of two that retain signifi- observations are very limited, so specific large “fissures” also observed at that time. The yellow curve shows the frontal position in 1922; cant floating ice tongues. The Petermann mechanisms of ocean–ice shelf interac- black curves represent frontal positions in 1948, 1952, 1953, 1959, 1963, 1975–1978, 1991–1999, ice tongue feeds into a high-­walled fjord, tion remain uncertain; further research is 1999–2010, and July 2010. Green dots represent the grounding line, and the black star is the 15–20 kilometers wide and about 80 kilo- required to reveal what limits basal melt- location of an automatic weather station [Rignot and Steffen, 2008]. The black arrow traces the meters in length. The main flow of ice that ing and whether the rising temperature of total movement of the glacier from 1922 to 2010. White is glacial ice. (c) Times series of ice shelf crosses the grounding line is augmented by Arctic intermediate water will affect melt- length as measured along the central axis from the grounding line. Lines connecting 1876 and 1922 are hypothetical trajectories. Blue arrows indicate steady ice advance velocities between smaller inflow glaciers descending along ing and calving rates. calving episodes (brown arrows). the sides of the fjord (Figure 1; see also Fig- ure S1 in the online supplement to this Eos Calving Variability and Dynamics issue (http://​www​.agu​.org/​­eos​_­elec/)). The illustrate this point. While the solid line is in break points. Surface water ponding has ice tongue thins substantially from about 600 Although loss due to calving has not been accord with the more detailed recent record, been reported on the Petermann ice tongue meters at the grounding line to 200 meters predominant to date, the question arises of the scenario indicated by the dashed line since the earliest observations and may approximately 20 kilometers downstream of whether the recent calving heralds a change cannot be ruled out for 1876–1922, 1922– promote surface cracking, as implicated in the line. It thins more gradually thereafter in the system. Historical evidence suggests 1947, and the 1980s. At current ice tongue the breakup of other ice shelves. Surface to 45–70 meters at the seaward edge, corre- that a conclusion cannot yet be drawn. Hig- velocities, it should take approximately temperatures in this region have risen dur- sponding to a height above sea level of only gins [1991] estimated ice tongue veloci- 2 decades for the ice front to return to its for- ing the past few decades [Box et al., 2009], 4–7 meters [Rignot and Steffen, 2008]. ties of 0.8–1.0 kilometer per year, based merly “stable” ice front position. with likely impact on surface melting. How- Petermann’s ice tongue is supplied by on displacements of persistent surface fea- The calving of an ice island is a dramatic ever, the sporadic nature of calving and the flow from the Greenland Ice Sheet and a tures identified in aerial photographs cov- event. Calving events at Petermann tend to relatively short record preclude establish- small amount of local precipitation. It loses ering 1947–1978. Rignot and Steffen [2008] involve the breakaway of a broad spine of ing a significant correlation with changing ice via sublimation, runoff or evaporation reported similar values of 1.0–1.1 kilometers the ice shelf that protrudes seaward once air temperature. Forces exerted by surface after surface melting, calving, and melting per year during 2000–2006, derived from ice near the sidewalls, calved into smaller winds, too weak to initiate a calving event, from contact with seawater. Members of the interferometric synthetic aperture radar. pieces, has drifted away (see Figure 1, and probably drive calved glacial ice out of the British Arctic Expedition first mapped the Near-­constant glacial advance rates and Table S1 in the online supplement). This fjord in the absence of a sea ice cover that tongue’s ice front in 1876. It had a similar ice shelf front position are consistent with sequence may result from the severe defor- is fixed in place. In fact, the “bright” sea sur- position in 1922 and was within 6 kilome- calving at roughly decadal intervals (see Fig- mation of ice along the margins as it moves face observed by European Remote Sens- ters of this position in 1962, leading to spec- ure 1c). In fact, calving of a magnitude com- (at 3 meters per day) down the progres- ing satellite (ERS-­1) synthetic aperture radar ulation that the Petermann ice front was rel- parable to the recent event was documented sively narrowing fjord. Landsat and aerial indicates that a strong wind at the mouth of atively stable despite regional warming dur- for 1991 [Gudmandsen, 2001]. The 2010 calv- images of the smaller (≤2-­kilometer-­wide) Petermann Fjord preceded the drift of an ice ing 1920–1950. Indeed, until the recent calv- ing is unusual in that the ice edge retreated glaciers feeding the tongue along the sides island out of the fjord in 1991. Simulations ing event, it had been presumed that the much closer to the grounding line than pre- of the fjord reveal highly fractured and with a regional atmospheric model [Samel- Petermann ice tongue was approximately viously observed (Figure 1). Gaps in the 134-­ likely thinner ice. Further, substantial trans- son and Barbour, 2008] for 3–6 August 2010 year record of ice front position and the spo- verse partial rifts tend to occur at intervals indicated wind speeds of 20 meters per sec- By K. K. Falkner, H. Melling, A. M. Münchow, radic nature of the calving process, however, behind the ice front, as first noted in 1876 ond at the glacier’s surface aligned along the J. E. Box, T. Wohlleben, H. L. Johnson, P. Gud- allow the possibility that the current position (Figure 1 and Figure S1). The currently fjord toward Nares Strait, which could have mandsen, R. Samelson, L. Copland, K. Steffen, of the ice front is not unprecedented. Hypo- most prominent rift extends halfway across been intensified by strong flows downslope E. Rignot, and A. K. Higgins thetical trajectories highlighted in Figure 1c the ice tongue, and 180 square kilometers of the local relief. of ice is encompassed between it and the Certainly, sea ice that crowds the ice front glacier margin. Whether this rift persists is an inhibitor of calving along the coasts of unchanged over the next few decades or Ellesmere Island and northern Greenland, propagates across the fjord and leads to resisting the free drift of ice islands and dis- continuing retreat of the ice tongue will be sipating the energy of gravity waves from important to monitor. distant storms that might flex the ice shelf Several factors are thought to influence to breaking point. It is possible, though, that calving. The geometry of Petermann Fjord the Petermann ice shelf responds to oce- likely contributes—­observed calving has anic change that has yet to be characterized been focused near its narrowest constric- at this location. Changing patterns of atmo- tion. Tidal flexing has been proposed as spheric pressure and temperature are affect- a mechanism for breaking Antarctic ice ing sea ice and ocean circulation in the Arc- shelves, but the separation of the Peter- tic. Indeed, stationary sea ice that typically mann ice island in 2010 occurred during forms in winter and prevents free movement the neap phase, when tidal amplitudes are of sea ice in Nares Strait for several months minimal. Crevassing that occurs both above and below the waterline may determine Petermann Glacier cont. on page 118

117 Eos VOLUME 92 NUMBER 14 5 APRIL 2011

Johnson, H. L., A. Münchow, K. K. Falkner, and Petermann Glacier H. Melling (2011), Ocean circulation and proper- cont. from page 117 ties in Petermann Fjord, Greenland, J. Geophys. Res., 116, C01003, doi:10.1029/​­2010JC006519. each year was virtually absent in 2006–2010 Implications of Further Calving Joughin, I., W. Abdalati, and M. Fahnestock (2004), except for a 60-­day period beginning in April Large fluctuations in speed on Greenland’s 2008 [Kwok et al., 2010]; such a sequence The glacial mass on the west side of north- Jakobshavn Isbrae glacier, Nature, 432, 608–610, does appear to be unusual. ern Greenland is thinning [Joughin et al., doi:10.1038/​­nature03130. TRANSACTIONS 2010] and contributing to a net ice mass flux Joughin, I., B. E. Smith, I. M. Howat, T. Scambos, AMERICAN GEOPHYSICAL UNION and T. Moon (2010), Greenland flow vari- The Newspaper of the Earth and Space Sciences Tracking the Recently Calved Ice Island to the ocean from Greenland, the absolute magnitude of which remains under refine- ability from ice-­sheet-­wide velo­city mapping, (197), 415–430, doi:10.3189/​ ment. Petermann Glacier has shown little J. Glaciol., 56 Editors Since breakup, the massive ice island ­002214310792447734. net change up to now, but if it loses its ice Anny Cazenave: Laboratoire d’Etudes en that calved in 2010 has drifted out of the Kwok, R., L. Toudal Pedersen, P. Gudmandsen, Géophysique et Océanographie Spatiales, fjord into Nares Strait, where, after briefly tongue, buttressed reinforcement against and S. S. Pang (2010), Large sea ice outflow into Toulouse, France; [email protected] hanging on Joe Island, it broke into two the ice sheet flow would be diminished and the Nares Strait in 2007, Geophys. Res. Lett., 37, there would be a direct oceanic conduit to L03502, doi:10.1029/​­2009GL041872. Christina M. S. Cohen: California Institute pieces. The larger fragment (about 155– of Technology, Pasadena, Calif., USA; cohen@ 160 square kilometers) remained wedged the depressed interior bedrock of Green- Rignot, E., and K. Steffen (2008), Channelized bot- srl.caltech.edu against Joe Island for a while before pass- land. As observed at Jakobshavn Isbrae tom melting and stability of floating ice shelves, ing southward into Kane Basin, while the in southwestern Greenland when it lost its Geophys. Res. Lett., 35, L02503, doi:10.1029/​ José D. Fuentes: Department of Meteorology, ­2007GL031765. Pennsylvania State University, University Park, floating shelf over the past decade Joughin[ smaller fragment (roughly 83 square kilo- Samelson, R. M., and P. L. Barbour (2008), Low-­ Pa., USA; [email protected] et al., 2004], this would most likely result in meters) immediately drifted south and level jets, orographic effects, and extreme events Wendy S. Gordon: Texas Parks and Wildlife passed into northern Baffin Bay. This is sim- accelerated land ice loss. Improved, more in Nares Strait: A model-­based mesoscale clima- Department, Austin, Tex., USA; wendy.gordon@ ilar to the documented 1991 calving event comprehensive observations of Petermann tology, Mon. Weather Rev., 136(12), 4746–4759, tpwd.state.tx.us that produced three ice islands with areas Glacier, its dynamics, and ocean interac- doi:10.1175/​­2007MWR2326.1. David Halpern: NASA Headquarters, Wash- of 73.5, 47.1, and 15.1 square kilometers as tions are needed to determine its vulnerabil- ington, D. C., USA; [email protected] well as many smaller icebergs [Gudmand- ity to retreat in the coming decades. Author Information Carol A. Stein: Department of Earth and sen, 2001]. Environmental Sciences, University of Illinois at Because of its relatively low profile Acknowledgments Kelly K. Falkner, College of Oceanic and Atmo- Chicago, Chicago, Ill., USA; [email protected] above sea level, ice calved from Peter- spheric Sciences, Oregon State University, Corvallis; We thank Luc Desjardins for knowledge- Editor in Chief mann Glacier can be difficult to detect. E-mail:­ kfalkner@­ nsf​­ .gov;​ Humfrey Melling, Institute Fragments that may reach the Grand able and timely updates regarding the frag- of Ocean Sciences, Fisheries and Oceans Canada, Barbara T. Richman: AGU, Washington, D. C., Banks off Newfoundland pose a serious ment trajectories and Dave Reinert for nim- Sidney, British Columbia, Canada; Andreas M. Mün- USA; eos_ [email protected] threat to shipping and offshore oil and ble assistance with the figures. chow, College of Earth, Ocean, and Environment, University of Delaware, Newark; Jason E. Box, gas rigs and so are of much concern to Editorial Advisory Board References Byrd Polar Research Center, Ohio State University, national ice services and the International Columbus; Trudy Wohlleben, Canadian Ice Ser- M. Lee Allison Earth and Space Science Ice Patrol. On 17 September 2010 the Cana- Informatics Box, J. E., L. Yang, D. H. Bromwich, and L.-­S. vice, Ottawa, Ontario, Canada; Helen L. Johnson, dian Ice Service succeeded in dropping a Bai (2009), Greenland Ice Sheet surface air Department of Earth Sciences, University of Oxford, Nathan T. Bridges Planetary Sciences beacon on the smaller fragment to aid in temperature variability: 1840–2007, J. Clim., 22, Oxford, UK; Preben Gudmandsen, Danish National Roland Bürgmann Tectonophysics tracking, and its progress can be followed 4029–4049, doi:10.1175/​­2009JCLI2816. Space Institute, Technical University of Denmark, Michael A. Ellis Earth and Planetary at http://sailwx​­ .info/​ shiptrack/​­ shipposition​­ ​ Gudmandsen, P. (2001), Major calving of Peter- Lyngby, Denmark; Roger Samelson, Oregon State Surface Processes .phtml­ ?​ call­ =​ 47557.­ As of this writing, the mann Gletscher, Greenland, in Proceedings of University, Corvallis; Luke Copland, Department of ice island had broken into more than a the 4th International POLLICHIA Symposium, Geography, University of Ottawa, Ottawa, Ontario, Arlene M. Fiore Atmospheric Sciences 24–26 June 2001: “Perspectives of Modern Polar Canada; Konrad Steffen, Cooperative Institute for dozen identifiable fragments, some of Nicola J. Fox Space Physics and Aeronomy Research and 175th Anniversary of Georg von Research in Environmental Sciences, Boulder, which have already transited more than Michael N. Gooseff Hydrology Neumeyer,” Mitt. Pollichia, 88, suppl., 81–86. Colo.; Eric Rignot, Jet Propulsion Laboratory, 1400 miles south in the Baffin Island Cur- Higgins, A. K. (1991), North Greenland glacier California Institute of Technology, Pasadena; and Seth S. Haines Near-Surface Geophysics rent and passed through or were within velocities and calf ice production, Polarfor­ Anthony K. Higgins, Geological Survey of Denmark Kristine C. Harper History of Geophysics Davis Strait as of March 2011. schung, 60(1), 1–23. and Greenland, Copenhagen, Denmark Keith D. Koper Seismology Xin-Zhong Liang Global Environmental Change Jung-Fu “Afu” Lin Mineral and Rock Physics Stephen Macko Education Stefan Maus Geomagnetism NEWS and Paleomagnetism Jerry L. Miller Ocean Sciences Peter Olson Study of the Earth’s Deep Interior Thomas H. Painter Cryosphere Sciences Roger A. Pielke Sr. Natural Hazards Web Platform for Sharing Spatial Data Len Pietrafesa Societal Impacts and Manipulating Them Online and Policy Sciences Michael Poland Geodesy To fill the need for readily accessible Data Basin users who create a free Paul R. Renne Volcanology, Geochemistry, conservation-­relevant spatial data sets, account are provided with a private area and Petrology the Conservation Biology Institute (CBI) (My Workspace) to organize the con- Sarah L. Shafer Paleoceanography launched in 2010 a Web-based platform tent they contribute to or find in the sys- and Paleoclimatology called Data Basin (http://​www​.­databasin​ tem. Users can create and edit personal Adrian Tuck Nonlinear Geophysics .org). It is the first custom application of profiles; track the creation of data sets, Jeffrey M. Welker Biogeosciences ArcGIS technology, which provides Web maps, and galleries; and manage their Earle Williams Atmospheric access to free maps and imagery using own group activity. 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