latest news

11.04.2013

David Clemens-Sewall '14 has arrived at McMurdo Station, Antarctica, after spending over 25 hours in four different aircraft. David, who is currently working with Bob Hawley on the Roosevelt Island Climate Evolution (RICE) Project, is currently keeping the world abreast of his goings-on in his blog "Adventures at the Ends of the Earth".

08.08.2013

Kristin has recently returned from Greenland. She was participating in the summer field seminar portion of the IGERT Polar Environmental Change program. Read about their adventures here.

04.11.2013

One of this year's two recipients of the Graduate Faculty Mentoring Award is our very own Professor Bob Hawley! Check it out: here

other information

Last updated 08.01.2013

Research

Bob's research has primarily focused on the firn layer of polar ice sheets, frequently at the locations of deep ice cores. His investigations into techniques for measuring in-situ densification profiles of polar firn led to the development of a new technique called Borehole Optical Stratigraphy, in which a video camera is lowered down a borehole in the ice, and a recording is made of the patterns of light and dark in the borehole walls. These patterns of light and dark are associated with variations in ice grain size and density, and thus can be related to the annual layers commonly used to date ice cores in high-accumulation locations. Additionally, these layers can be used as natural markers, and their movements tracked through time as the firn column compresses. This provides a continuous profile of the vertical motion of the firn, which can allow the calculation of an independent depth-age scale. The firn is also of major importance to altimetry studies like the NASA's current ICEsat mission and ESA's CryoSat-2. Fluctuations of firn density might affect the height of the surface measured by the altimeter, and penetration of the radar wave into the firn can also have other interpretable results. Among other projects, Bob is currently working with ESA data to define new ways to use the interferometric information from the SIRAL radar altimeter, the primary payload of CryoSat-2.

Projects

We are always developing, seeking funding for, and working on new projects. The following is an overview of a few of our current pursuits.

Ground-truthing of satellite altimetry
Understanding the spatial variability of snow and firn
Subglacial controls on margin stability
Analysis and ground validation of CryoSat-2 data
Deglaciation of the Ross Sea embayment from geophysics at Roosevelt Island, Antarctica


Ground-truthing of satellite altimetry

GPS surveying setup

The study of Earth's ice sheets by satellite altimeter is of primary importance in the effort to quantify the contribution to sea level rise, the sensitivity to climate change, and the changing nature of the Earth's cryosphere. In order to interpret satellite altimetry data, some comparison with known elevations must be performed. In addition, the change in elevation at the surface of an ice sheet (such as Greenland) is affected by several factors, not all of which directly correspond with actual mass changes in the ice sheet. ICESat is the flagship US altimetry satellite.

This project utilizes a combination of existing firn-compaction data sets from a previous NSF-funded project, along with ongoing monitoring of surface elevation and accumulation along an existing ICESat ground track (track 412 near Summit Station, Greenland), to investigate the relationships between elevation change (as measured by DGPS and ICESat's laser altimeter), accumulation (as measured at an array of bamboo poles), firn compaction (as measured in an array of boreholes), and ice flow (the remaining component of elevation change, neglecting crustal deformation).

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Understanding the spatial variability in near-surface snow and firn, Northern Greenland

traverse route

The Greenland Ice Sheet (GIS) is a key component in the effort to understand climate change. The state of the GIS is determined by its response to climate, and as such it is an important indicator of the response of the cryosphere to current climate forcings. The two key questions that must be asked in any assessment of the state of an ice sheet are: "What has it been doing in the past?" and "What is it doing right now?"

This project seeks to help answer these two defining questions by investigating the physical properties of surface and near-surface snow and firn along a traverse from Thule, North coastal Greenland, to Summit camp, central Greenland. The traverse is an already-funded logistics project, aimed at bringing fuel and supplies to Summit camp, and our participation will add a science component to the existing traverse, by making highly detailed observations of snow pit and shallow borehole stratigraphy. The route crosses through several facies of the ice sheet, which makes the route scientifically relevent, crossing through areas of margin, percolation zone, and the interior of the ice sheet. Comparison of the measurements that we propose to those done by Benson (1962) from 1952 to 1955 provides a unique insight into the changes these regions have undergone in the last 50 years.

The traverse is underway! Check out the real-time mission tracker!

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Subglacial controls on Greenland Ice Sheet marginal acceleration

Field location

This is a joint project, in collaboration with Dr. Ginny Catania of the University of Texas Institute for Geophysics, Dr. Martin Luthi of the Swiss Federal Institute of Technology, Zurich, and Dr. Tom Neumann, of NASA Goddard Space Flight Center. Our goal in this project is to examine the nature of short-term ice velocity changes near Swiss Camp, Greenland, to assess the impact of these changes on the stability of the ice sheet interior. Our work will focus on the interaction between the ice sheet, the atmosphere and the bed through an integrated observational approach which involves remote sensing, borehole geophysics, surface-based GPS and ice-penetrating radar.

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Analysis and ground validation of CryoSat-2 data

first data from CryoSat-2

The primary payload of CryoSat-2 is the Synthetic aperture Interferometric Radar Altimeter(SIRAL), a new type of radar altimeter that uses dual receive antennas and synthetic aperture processing to improve resolution in the across-track and along-track directions,respectively, overcoming drawbacks of previous designs. This, combined with the all-weather nature of radar altimetry and the high-inclination orbit, will allow mapping of the changes of the polar ice sheets with great accuracy. In advance of the launch of both CryoSat-1 and CryoSat-2, airborne campaigns have been organized with a prototype of the SIRAL instrument. Data from these campaigns have been invaluable in learning about the likely response of the SIRAL instrument over ice, and several interesting discoveries have illuminated the possibility of gleaning more insight into the ice sheet than previously thought.First, the airborne radar revealed that in addition to detecting the surface, multiple subsurfaceechoes could be resolved in the radar waveforms. Subsequent analysis revealed these subsurface echoes to be annual layers, allowing the mapping of mass inputs to the ice sheets over long spatial scales. Additionally, in areas of relatively high slope (high slope for a radar altimeter is greater than 2-3 degrees), the phase signal from the interferometric mode of the altimeter could be interpreted to provide not just a single elevation point, but multiple points across the instrument ground track. Both of these two methods offer significant added value to the CryoSat-2 dataset. In order to understand the results from these unique new data products, they must be be supported by ground-based validation in the field.

This project will use a series of targeted Greenland field campaigns to develop the ground-based observational dataset needed for validation and calibration of these new products.

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Deglaciation of the Ross Sea embayment from geophysics at Roosevelt Island, Antarctica

Radar transect of Roosevelt Island

The potential for rapid deglaciation of the West Antarctic IceSheet remains a major uncertainty in predictions of future sea-level rise, with additional implications for ocean circulation and global climate. Assessment of the past evolution of the ice sheet provides clues about its present and future stability. This project will provide a much-needed constraint on the former ice thickness and the history of deglaciation in the eastern Ross Sea. This history from the Eastern Ross Sea, combined with those from Siple Dome and Byrd, together with the existing geologic record from the Western Ross Sea, will allow us to develop a significantly improved representation of the former thickness and configuration of grounded ice in the Ross Sea Embayment, and the timing and pattern of deglaciation.

This collaborative project, led by Howard Conway of the glaciology group of the University of Washington, with partners Ed Waddington (UW) and Ed Brook of the Oregon State University department of Geosciences, levereges the drilling efforts of an international collaboration with Nancy Bertler of the University of Wellington Antarctic Research Centre. Nancy and her team will drill an ice core at the divide of Roosevelt Island, and the US collaborators will perform geophysical investigations in the area, including radio echo sounding, GPS surveying, and geophysical borehole logging, with the goal of determining the date of the onset of divide flow at Roosevelt Island, which will help us understand when this divide emerged from a thinning ice cover of the Ross Sea embayment.

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