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Benjamin Smith

Principal Physicist

Affiliate Associate Professor, Earth and Space Sciences





Department Affiliation

Polar Science Center


2000-present and while at APL-UW

GPS-derived estimates of surface mass balance and ocean-induced basal melt for Pine Island Glacier ice shelf, Antarctica

Shean, D.E., K. Christianson, K.M. Larson, S.R.M. Ligtenberg, I.R. Joughin, B.E. Smith, C.M. Stevens, M. Bushuk, and D.M. Holland, "GPS-derived estimates of surface mass balance and ocean-induced basal melt for Pine Island Glacier ice shelf, Antarctica," Cryosphere, 11, 2655-2674, doi:10.5194/tc-11-2655-2017, 2017.

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21 Nov 2017

In the last 2 decades, Pine Island Glacier (PIG) experienced marked speedup, thinning, and grounding-line retreat, likely due to marine ice-sheet instability and ice-shelf basal melt. To better understand these processes, we combined 2008–2010 and 2012–2014 GPS records with dynamic firn model output to constrain local surface and basal mass balance for PIG. We used GPS interferometric reflectometry to precisely measure absolute surface elevation (zsurf) and Lagrangian surface elevation change (Dzsurf∕ Dt). Observed surface elevation relative to a firn layer tracer for the initial surface (zsurf – zsurf0′) is consistent with model estimates of surface mass balance (SMB, primarily snow accumulation). A relatively abrupt  ~0.2–0.3 m surface elevation decrease, likely due to surface melt and increased compaction rates, is observed during a period of warm atmospheric temperatures from December 2012 to January 2013. Observed Dzsurf∕ Dt trends (–1 to –4 m yr-1) for the PIG shelf sites are all highly linear. Corresponding basal melt rate estimates range from  ~10 to 40 m yr-1, in good agreement with those derived from ice-bottom acoustic ranging, phase-sensitive ice-penetrating radar, and high-resolution stereo digital elevation model (DEM) records. The GPS and DEM records document higher melt rates within and near features associated with longitudinal extension (i.e., transverse surface depressions, rifts). Basal melt rates for the 2012–2014 period show limited temporal variability despite large changes in ocean temperature recorded by moorings in Pine Island Bay. Our results demonstrate the value of long-term GPS records for ice-shelf mass balance studies, with implications for the sensitivity of ice–ocean interaction at PIG.

Seasonal to multiyear variability of glacier surface velocity, terminus position, and sea ice/ice melange in northwest Greenland

Moon, T., I, Joughin, and B. Smith, "Seasonal to multiyear variability of glacier surface velocity, terminus position, and sea ice/ice melange in northwest Greenland," J. Geophys. Res., 120, 818-833, doi:10.1002/2015JF003494, 2015.

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13 May 2015

Glacier ice discharge, which depends on ice velocity and terminus fluctuations, is a primary component of Greenland Ice Sheet mass loss. Some research suggests that ice melange influences terminus calving, in turn affecting glacier velocity. The details and broad spatiotemporal consistency of these relationships, however, is undetermined. Focusing on 16 northwestern Greenland glaciers during 2009 through summer 2014, we examined seasonal surface velocity changes, glacier terminus position, and sea ice and ice melange conditions. For a longer-term analysis, we also produced extended records of four glaciers from 1999 to 2014. There is a strong correspondence between seasonal near-terminus sea ice/melange conditions and terminus change, with rigid ice melange conditions associated with advance and open water associated with retreat. Extended sea ice-free periods and reduced rigid melange are also linked with anomalously large terminus retreat. In all but one case, sustained multiyear retreat of greater than 1 km during both the 15-year and 6-year records was accompanied by interannual velocity increases. Seasonal velocity patterns, however, correspond more strongly with runoff changes than terminus behavior. Projections of continued warming and longer sea ice-free periods around Greenland indicate that notable retreat over wide areas may continue. This sustained retreat likely will contribute to multiyear speedup. Longer melt seasons and earlier breakup of melange may also alter the timing of seasonal ice flow variability.

Marine ice sheet collapse potentially underway for the Thwaites Glacier Basin, West Antarctica

Joughin, I., B.E. Smith, and B. Medley, "Marine ice sheet collapse potentially underway for the Thwaites Glacier Basin, West Antarctica," Science, 344, 735-738, doi: 10.1126/science.1249055, 2014

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16 May 2014

Resting atop a deep marine basin, the West Antarctic Ice Sheet has long been considered prone to instability. Using a numerical model, we investigate the sensitivity of Thwaites Glacier to ocean melt and whether unstable retreat is already underway. Our model reproduces observed losses when forced with ocean melt comparable to estimates. Simulated losses are moderate (<0.25 mm per year sea level) over the 21st Century, but generally increase thereafter. Except possibly for the lowest-melt scenario, the simulations indicate early-stage collapse has begun. Less certain is the timescale, with onset of rapid (> 1 mm per year of sea-level rise) collapse for the different simulations within the range of two to nine centuries.

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In The News

Hidden lakes drain below West Antarctica's Thwaites Glacier

UW News and Information, Hannah Hickey

Thwaites Glacier on the edge of West Antarctica is one of the planet’s fastest-moving glaciers. Research shows that it is sliding unstoppably into the ocean, mainly due to warmer seawater lapping at its underside.

8 Feb 2017

What Antarctica's incredible "growing" icepack really means

National Geographic, Brian Clark Howard

Are the Antarctic's ice sheets shrinking or growing? And what does that mean for global sea-level rise? Ben Smith, who was not involved with the study, notes that the technology used to collect surface elevation measurements might not be up to the task of distinguishing snowpack volume based on differences of one or two centimeters.

3 Nov 2015

Antarctica accumulates more ice than it melts

Business Insider, Rebecca Harrington

The snow that falls on Antarctica every year is accumulating as ice faster than it's melting on the continent, a new study from NASA found. Ben Smith, not involved in the study, notes that precise records of snow accumulation are needed to fully understand the nature of the net ice gains and losses.

2 Nov 2015

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Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center