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Benjamin Smith

Principal Physicist

Affiliate Associate Professor, Earth and Space Sciences

Email

bsmith@apl.washington.edu

Phone

206-616-9176

Department Affiliation

Polar Science Center

Education

B.S. Physics, University of Chicago, 1997

M.S. Geology & Geophysics, University of Wisconsin - Madison, 1999

Ph.D. Earth & Space Sciences/Geophysics, University of Washington - Seattle, 2005

Publications

2000-present and while at APL-UW

Melt at grounding line controls observed and future retreat of Smith, Pope, and Kohler glaciers

Lilien, D.A., I. Joughin, B. Smith, and N. Gourmelen, "Melt at grounding line controls observed and future retreat of Smith, Pope, and Kohler glaciers," The Cryosphere, 13, 2817-2834, doi:10.5194/tc-13-2817-2019, 2019.

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5 Nov 2019

Smith, Pope, and Kohler glaciers and the corresponding Crosson and Dotson ice shelves have undergone speedup, thinning, and rapid grounding-line retreat in recent years, leaving them in a state likely conducive to future retreat. We conducted a suite of numerical model simulations of these glaciers and compared the results to observations to determine the processes controlling their recent evolution. The model simulations indicate that the state of these glaciers in the 1990s was not inherently unstable, i.e., that small perturbations to the grounding line would not necessarily have caused the large retreat that has been observed. Instead, sustained, elevated melt at the grounding line was needed to cause the observed retreat. Weakening of the margins of Crosson Ice Shelf may have hastened the onset of grounding-line retreat but is unlikely to have initiated these rapid changes without an accompanying increase in melt. In the simulations that most closely match the observed thinning, speedup, and retreat, modeled grounding-line retreat and ice loss continue unabated throughout the 21st century, and subsequent retreat along Smith Glacier's trough appears likely. Given the rapid progression of grounding-line retreat in the model simulations, thinning associated with the retreat of Smith Glacier may reach the ice divide and undermine a portion of the Thwaites catchment as quickly as changes initiated at the Thwaites terminus.

Ice shelf basal melt rates from a high-resolution digital elevation model (DEM) record for Pine Island Glacier, Antarctica

Shean, D.E., I.R. Joughin, P. Dutrieux, B.E. Smith, and E. Berthier, "Ice shelf basal melt rates from a high-resolution digital elevation model (DEM) record for Pine Island Glacier, Antarctica," Cryosphere, 13, 2633-2656, doi:10.5194/tc-13-2633-2019, 2019.

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10 Oct 2019

Ocean-induced basal melting is responsible for much of the Amundsen Sea Embayment ice loss in recent decades, but the total magnitude and spatiotemporal evolution of this melt is poorly constrained. To address this problem, we generated a record of high-resolution digital elevation models (DEMs) for Pine Island Glacier (PIG) using commercial sub-meter satellite stereo imagery and integrated additional 2002–2015 DEM and altimetry data. We implemented a Lagrangian elevation change (Dh∕Dt) framework to estimate ice shelf basal melt rates at 32–256 m resolution. We describe this methodology and consider basal melt rates and elevation change over the PIG ice shelf and lower catchment from 2008 to 2015. We document the evolution of Eulerian elevation change (dh∕dt) and upstream propagation of thinning signals following the end of rapid grounding line retreat around 2010. Mean full-shelf basal melt rates for the 2008–2015 period were ~82–93 Gt yr-1, with ~200–250 m yr-1 basal melt rates within large channels near the grounding line, ~10–30 m yr-1 over the main shelf, and ~0–10 m yr-1 over the North shelf and South shelf, with the notable exception of a small area with rates of ~50–100 m yr-1 near the grounding line of a fast-flowing tributary on the South shelf. The observed basal melt rates show excellent agreement with, and provide context for, in situ basal melt-rate observations. We also document the relative melt rates for kilometer-scale basal channels and keels at different locations on the ice shelf and consider implications for ocean circulation and heat content. These methods and results offer new indirect observations of ice–ocean interaction and constraints on the processes driving sub-shelf melting beneath vulnerable ice shelves in West Antarctica.

Measuring height change around the periphery of the Greenland Ice Sheet with radar altimetry

Gray, L., and 10 others including I. Joughin and B. Smith, "Measuring height change around the periphery of the Greenland Ice Sheet with radar altimetry," Front. Earth Sci., 7, 146, doi:10.3389/feart.2019.00146, 2019.

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11 Jun 2019

Ice loss measurements around the periphery of the Greenland Ice Sheet can provide key information on the response to climate change. Here we use the excellent spatial and temporal coverage provided by the European Space Agency (ESA) CryoSat satellite, together with NASA airborne Operation IceBridge and automatic weather station data, to study the influence of changing conditions on the bias between the height estimated by the satellite radar altimeter and the ice sheet surface. Surface and near-surface conditions on the ice sheet periphery change with season and geographic position in a way that affects the returned altimeter waveform and can therefore affect the estimate of the surface height derived from the waveform. Notwithstanding the possibility of a varying bias between the derived and real surface, for the lower accumulation regions in the western and northern ice sheet periphery (< ~1 m snow accumulation yearly) we show that the CryoSat altimeter can measure height change throughout the year, including that associated with ice dynamics, summer melt and winter accumulation. Further, over the 9-year CryoSat lifetime it is also possible to relate height change to change in speed of large outlet glaciers, for example, there is significant height loss upstream of two branches of the Upernavik glacier in NW Greenland that increased in speed during this time, but much less height loss over a third branch that slowed in the same time period. In contrast to the west and north, winter snow accumulation in the south-east periphery can be 2 – 3 m and the average altimeter height for this area can decrease by up to 2 m during the fall and winter when the change in the surface elevation is much smaller. We show that vertical downward movement of the dense layer from the last summer melt coupled with overlying dry snow, are responsible for the anomalous altimeter height change. However, it is still possible to estimate year-to-year height change measurements in this area by using data from the late-summer to early-fall when surface returns dominate the altimeter signal.

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In The News

Key data for NASA's ice-monitoring satellite in trouble thanks to shutdown

Gizmodo, Maddie Stone

the spring campaign for NASA’s Operation IceBridge — a series of airborne flights over the Arctic and Antarctic the space agency has been conducting since 2009 — would likely be delayed thanks to President Trump’s fictitious crisis at the U.S. southern border.

23 Jan 2019

Shutdown imperils NASA's decadelong ice-measuring campaign

Science, Paul Voosen

The partial U.S. government shutdown threaten to shorten IceBridge missions, a decadelong NASA aerial campaign meant to secure a seamless record of ice loss. Ben Smith comments that this will imperil the plan to collect overlapping data with the new ice-monitoring satellite called the Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2).

18 Jan 2019

UW glaciologist gets first look at NASA's new measurements of ice sheet elevation

UW News, Hannah Hickey

Less than three months into its mission, NASA's Ice, Cloud and land Elevation Satellite-2, or ICESat-2, is already exceeding scientists’ expectations. Benjamin Smith, a member of the ICESat-2 science team, shared the first look at the satellite's performance at the American Geophysical Union's annual meeting Dec. 11 in Washington, D.C.

14 Dec 2018

More News Items

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
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