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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

Publications

2000-present and while at APL-UW

Further speedup of Jakobshavn Isbrae

Joughin, I., B.E. Smith, D.E. Shean, and D. Floricioiu, "Further speedup of Jakobshavn Isbrae," The Cryosphere, 8, 209-214, doi:doi:10.5194/tc-8-209-2014, 2014.

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3 Feb 2014

We have extended the record of flow speed on Jakobshavn Isbrae through the summer of 2013. These new data reveal large seasonal speedups, 30 to 50% greater than previous summers. At a point a few kilometres inland from the terminus, the mean annual speed for 2012 is nearly three times as great as that in the mid-1990s, while the peak summer speeds are more than a factor of four greater. These speeds were achieved as the glacier terminus appears to have retreated to the bottom of an over-deepened basin with a depth of ~ 1300 m below sea level. The terminus is likely to reach the deepest section of the trough within a few decades, after which it could rapidly retreat to the shallower regions ~ 50 km farther upstream, potentially by the end of this century.

Ice-sheet mass balance and climate change

Hanna, E., and 11 others, including B. Smith, "Ice-sheet mass balance and climate change," Nature, 498, 51-59, doi:10.1038/nature12238, 2013.

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6 Jun 2013

Since the 2007 Intergovernmental Panel on Climate Change Fourth Assessment Report, new observations of ice-sheet mass balance and improved computer simulations of ice-sheet response to continuing climate change have been published. Whereas Greenland is losing ice mass at an increasing pace, current Antarctic ice loss is likely to be less than some recently published estimates. It remains unclear whether East Antarctica has been gaining or losing ice mass over the past 20 years, and uncertainties in ice-mass change for West Antarctica and the Antarctic Peninsula remain large. We discuss the past six years of progress and examine the key problems that remain.

A reconciled estimate of ice-sheet mass balance

Shepherd, A., and 46 others, including I. Joughin and B. Smith, "A reconciled estimate of ice-sheet mass balance," Science, 338, 1183-1189, doi:10.1126/science.1228102, 2012.

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30 Nov 2012

We combined an ensemble of satellite altimetry, interferometry, and gravimetry data sets using common geographical regions, time intervals, and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of Earth's polar ice sheets. We find that there is good agreement between different satellite methods—especially in Greenland and West Antarctica—and that combining satellite data sets leads to greater certainty. Between 1992 and 2011, the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula changed in mass by –142 ± 49, +14 ± 43, –65 ± 26, and –20 ± 14 gigatonnes year-1, respectively. Since 1992, the polar ice sheets have contributed, on average, 0.59 ± 0.20 millimeter year-1 to the rate of global sea-level rise.

More Publications

Glaciology: Repeat warming in Greenland

Smith, B.E., "Glaciology: Repeat warming in Greenland," Nature Geosci., 5, 369-370, doi:10.1038/ngeo1488, 2012.

27 May 2012

Seasonal to decadal scale variations in the surface velocity of Jakobshavn Isbrae, Greenland: Observation and model-based analysis

Joughin, I., B.E. Smith, I.M. Howat, D. Floriciolu, R.B. Alley, M. Truffer, and M. Fahnestock, "Seasonal to decadal scale variations in the surface velocity of Jakobshavn Isbrae, Greenland: Observation and model-based analysis," J. Geophys. Res., 117, doi:10.1029/2011JF002110, 2012.

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25 May 2012

Using new data, we build upon the nearly two-decade long record of observations from Jakobshavn Isbrae to investigate the processes driving its dynamic evolution. While winter flow speed has not increased substantially over the last three winters, there remains a strong seasonal variation in flow speed that coincides with a cycle of summer thinning and winter thickening. We relate changes in glacier speed to geometry through variations in basal traction and horizontal stresses, using ice-flow models constrained by satellite and airborne observations. These results suggest that the bed provides little flow resistance along the main trough within about 20 km of the terminus. While the loss of buttressing from the retreat of grounded and floating ice likely contributed to the initial speedup, other processes are of comparable significance at seasonal to decadal time scales. From analysis of the models, we hypothesize that thinning-induced change in basal effective pressure is the dominant process influencing near-terminus behavior, while diffusive processes drive the upstream response. The apparent need for the terminus to thin to near flotation before it can calve may limit the rate at which retreat occurs. Our analysis of the processes controlling the speed suggests little potential for further large acceleration. Thinning and elevated speeds may continue at rates similar to present, however, putting the glacier on course to retreat to the head of its deep trough in about a century, at which point it likely would stabilize with a thinner terminus.

21st-century evolution of Greenland outlet glacier velocities

Moon, T., I. Joughin, B. Smith, and I. Howat, "21st-century evolution of Greenland outlet glacier velocities," Science, 336, 576-578, doi:10.1126/science.1219985, 2012.

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4 May 2012

Earlier observations on several of Greenland%u2019s outlet glaciers, starting near the turn of the 21st century, indicated rapid (annual-scale) and large (>100%) increases in glacier velocity. Combining data from several satellites, we produce a decade-long (2000 to 2010) record documenting the ongoing velocity evolution of nearly all (200 ) of Greenland%u2019s major outlet glaciers, revealing complex spatial and temporal patterns. Changes on fast-flow marine-terminating glaciers contrast with steady velocities on ice-shelf%u2013terminating glaciers and slow speeds on land-terminating glaciers. Regionally, glaciers in the northwest accelerated steadily, with more variability in the southeast and relatively steady flow elsewhere. Intraregional variability shows a complex response to regional and local forcing. Observed acceleration indicates that sea level rise from Greenland may fall well below proposed upper bounds.

Changes in the dynamics of marine terminating outlet glaciers in west Greenland (2000-2009)

McFadden, E.M., I.M. Howat, I. Joughin, B.E. Smith, and Y. Ahn, "Changes in the dynamics of marine terminating outlet glaciers in west Greenland (2000-2009)," J. Geophys. Res., 116, doi:10.1029/2010F001757, 2011.

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23 Jun 2011

Recent changes in the dynamics of Greenland's marine terminating outlet glaciers indicate a rapid and complex response to external forcing. Despite observed ice front retreat and recent geophysical evidence for accelerated mass loss along Greenland's northwestern margin, it is unclear whether west Greenland glaciers have undergone the synchronous speed-up and subsequent slow-down as observed in southeastern glaciers earlier in the decade. To investigate changes in west Greenland outlet glacier dynamics and the potential controls behind their behavior, we derive time series of front position, surface elevation, and surface slope for 59 marine terminating outlet glaciers and surface speeds for select glaciers in west Greenland from 2000 to 2009. Using these data, we look for relationships between retreat, thinning, acceleration, and geometric parameters to determine the first-order controls on glacier behavior. Our data indicate that changes in front positions and surface elevations were asynchronous on annual time scales, though nearly all glaciers retreated and thinned over the decade. We found no direct relationship between retreat, acceleration, and external forcing applicable to the entire region. In regard to geometry, we found that, following retreat, (1) glaciers with grounded termini experienced more pronounced changes in dynamics than those with floating termini and (2) thinning rates declined more quickly for glaciers with steeper slopes. Overall, glacier geometry should influence outlet glacier dynamics via stress redistribution following perturbations at the front, but our data indicate that the relative importance of geometry as a control of glacier behavior is highly variable throughout west Greenland.

Committed sea-level rise for the next century from Greenland ice sheet dynamics during the past decade.

Price, S.F., A.J. Payne, I.M. Howat, and B.E. Smith, "Committed sea-level rise for the next century from Greenland ice sheet dynamics during the past decade." P. Natl. Acad. Sci. USA, 108, 8978-8983, doi:10.1073/pnas.1017313108, 2011.

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31 May 2011

We use a three-dimensional, higher-order ice flow model and a realistic initial condition to simulate dynamic perturbations to the Greenland ice sheet during the last decade and to assess their contribution to sea level by 2100. Starting from our initial condition, we apply a time series of observationally constrained dynamic perturbations at the marine termini of Greenland's three largest outlet glaciers, Jakobshavn Isbrae, Helheim Glacier, and Kangerdlugssuaq Glacier. The initial and long-term diffusive thinning within each glacier catchment is then integrated spatially and temporally to calculate a minimum sea-level contribution of approximately 1 plus/minus 0.4 mm from these three glaciers by 2100. Based on scaling arguments, we extend our modeling to all of Greenland and estimate a minimum dynamic sea-level contribution of approximately 6 plus/minus 2 mm by 2100. This estimate of committed sea-level rise is a minimum because it ignores mass loss due to future changes in ice sheet dynamics or surface mass balance. Importantly, > 75% of this value is from the long-term, diffusive response of the ice sheet, suggesting that the majority of sea-level rise from Greenland dynamics during the past decade is yet to come. Assuming similar and recurring forcing in future decades and a self-similar ice dynamical response, we estimate an upper bound of 45 mm of sea-level rise from Greenland dynamics by 2100. These estimates are constrained by recent observations of dynamic mass loss in Greenland and by realistic model behavior that accounts for both the long-term cumulative mass loss and its decay following episodic boundary forcing.

Light propagation in firn: Application to borehole video

Fudge, T.J., and B.E. Smith, "Light propagation in firn: Application to borehole video," J. Glaciol., 56, 614-624, doi:10.3189/002214310793146205, 2010.

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1 Oct 2010

Borehole optical stratigraphy (BOS) is a borehole video system and processing routine for investigating polar firn. BOS records brightness variations in the firn and is effective at identifying stratigraphic markers. BOS brightness logs have been used to count annual layers and measure vertical strain, even though a specific cause of the brightness variations has not been determined. Here we combine two models of light transport to examine potential errors with BOS and identify improvements which will allow the system to estimate optical grain size. We use a Monte Carlo radiative transfer model to estimate the influence of firn microstructure variations on borehole reflectance. We then use a ray-tracing algorithm to model the multiple reflections within the borehole that cause measured brightness variations.

Multiple reflections cause the brightness measured at a point on the borehole wall to not necessarily be equal to the local wall reflectance. The ray tracing further shows that wall imperfections or variations in the camera position can produce brightness variations that are unrelated to changes in firn properties. Smooth walls and good stabilization of the camera help ensure that brightness variations result from variations in firn properties, and thus are a measure of firn stratigraphy, rather than artifacts.

Greenland flow variability from ice-sheet-wide velocity mapping

Joughin, I., B.E. Smith, I.M. Howat, T. Scambos, and T. Moon, "Greenland flow variability from ice-sheet-wide velocity mapping," J. Glaciol., 56, 415-430, doi:10.3189/002214310792447734, 2010.

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1 Aug 2010

Using RADARSAT synthetic aperture radar data, we have mapped the flow velocity over much of the Greenland ice sheet for the winters of 2000/01 and 2005/06. These maps provide a detailed view of the ice-sheet flow, including that of the hundreds of glaciers draining the interior. The focused patterns of flow at the coast suggest a strong influence of bedrock topography. Differences between our two maps confirm numerous early observations of accelerated outlet glacier flow as well as revealing previously unrecognized changes. The overall pattern is one of speed-up accompanied by terminus retreat, but there are also several instances of surge behavior and a few cases of glacier slowdown. Comprehensive mappings such as these, at regular intervals, provide an important new observational capability for understanding ice-sheet variability.

An inventory of active subglacial lakes in Antarctica detected by ICESat (2003-2008)

Smith, B.E., H.A. Fricker, I.R. Joughin, and S. Tulaczyk, "An inventory of active subglacial lakes in Antarctica detected by ICESat (2003-2008)," J. Glaciol., 55, 573-595, doi:10.3189/002214309789470879, 2009.

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1 Sep 2009

Through the detection of surface deformation in response to water movement, recent satellite studies have demonstrated the existence of subglacial lakes in Antarctica that fill and drain on timescales of months to years. These studies, however, were confined to specific regions of the ice sheet. Here we present the first comprehensive study of these 'active' lakes for the Antarctic ice sheet north of 86°S, based on 4.5 years (2003-08) of NASA's Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data. Our analysis has detected 124 lakes that were active during this period, and we estimate volume changes for each lake. The ICESat-detected lakes are prevalent in coastal Antarctica, and are present under most of the largest ice-stream catchments. Lakes sometimes appear to transfer water from one to another, but also often exchange water with distributed sources undetectable by ICESat, suggesting that the lakes may provide water to or withdraw water from the hydrologic systems that lubricate glacier flow. Thus, these reservoirs may contribute pulses of water to produce rapid temporal changes in glacier speeds, but also may withdraw water at other times to slow flow.

Continued evolution of Jakobshavn Isbrae following its rapid speedup

Joughin, I., I. Howat, M. Fahnestock, B. Smith, W. Krabill, R. Alley, H. Stern, and M. Truffer, "Continued evolution of Jakobshavn Isbrae following its rapid speedup," J. Geophys. Res., 113, doi:10.1029/2008JF001023, 2008.

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28 Oct 2008

Several new data sets reveal that thinning and speedup of Jakobshavn Isbrae continue, following its recent rapid increase in speed as its floating ice tongue disintegrated. The present speedup rate of –5% a-1 over much of the fast-moving region appears to be a diffusive response to the initial much larger speedup near the front. There is strong seasonality in speed over much of the fast-flowing main trunk that shows a good inverse correlation with the seasonally varying length of a short (typically ~6 km) floating ice tongue. This modulation of speed with ice front position supports the hypothesis that the major speedup was caused by loss of the larger floating ice tongue from 1998 to 2003. Analysis of image time series suggests that the transient winter ice tongue is formed when sea ice bonds glacier ice in the fjord to produce a nearly rigid mass that almost entirely suppresses calving. Major calving only resumes in late winter when much of this ice clears from the fjord. The collapse of the ice tongue in the late 1990s followed almost immediately after a sharp decline in winter sea-ice concentration in Disko Bay. This decline may have extended the length of the calving season for several consecutive years, leading to the ice tongue's collapse.

Seasonal speedup along the western flank of the Greenland ice sheet

Joughin, I., S.B. Das, M.A. King, B.E. Smith, I.M. Howat, and T. Moon, "Seasonal speedup along the western flank of the Greenland ice sheet," Science, 320, 791-883, 2008.

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9 May 2008

It has been widely hypothesized that a warmer climate in Greenland would increase the volume of lubricating surface meltwater reaching the ice-bedrock interface, accelerating ice flow and increasing mass loss. We have assembled a data set that provides a synoptic-scale view, spanning ice-sheet to outlet-glacier flow, with which to evaluate this hypothesis. On the ice sheet, these data reveal summer speedups (50 to 100%) consistent with, but somewhat larger than, earlier observations. The relative speedup of outlet glaciers, however, is far smaller (<15%). Furthermore, the dominant seasonal influence on Jakobshavn Isbrae's flow is the calving front's annual advance and retreat. With other effects producing outlet-glacier speedups an order of magnitude larger, seasonal melt's influence on ice flow is likely confined to those regions dominated by ice-sheet flow.

In The News

Glacier that sank the Titanic is really on the move, say scientists

The Christian Science Monitor, Sudeshna Chowdhury

Jakobshavn Glacier has bagged the tile of Greenland's Fastest Glacier in Greenland: In the summer of 2012 it reached a record speed of over 150 feet per day.

4 Feb 2014

Greenland glacier hits speed record

BBC News, Paul Rincon

A river of ice in Greenland has become the fastest-flowing glacier currently known in the world, a study suggests. Ian Joughin and Ben Smith of the University of Washington's Polar Science Center in Seattle analysed pictures from the German TerraSAR-X satellites to measure the speed of the glacier.

4 Feb 2014

Greenland's fastest glacier sets new speed record

UW News and Information, Hannah Hickey

The latest observations of Jakobshavn Glacier show that Greenland's largest glacier is moving ice from land into the ocean at a speed that appears to be the fastest ever recorded.

3 Feb 2014

More News Items

UW researchers mapping changes in glacier ice

KING5 News, Seattle, Adam Mertz

University of Washington researchers are working with NASA to create digital maps of glaciers in Greenland.

25 Nov 2013

Post-shutdown, UW Arctic research flights resume

UW News and Information, Hannah Hickey

After a couple of stressful weeks during the federal government shutdown, University of Washington researchers are back at work monitoring conditions near the North Pole. November has been busy for UW scientists studying winter storms, glacier melt and floating sea ice.

18 Nov 2013

International study provides more solid measure of shrinking in polar ice sheets

UW News and Information, Hannah Hickey

Dozens of climate scientists have reconciled their measurements of ice sheet changes in Antarctica and Greenland during the past two decades. The results, published Nov. 29 in the journal Science, roughly halve the uncertainty and discard some conflicting observations.

29 Nov 2012

80-year-old aerial images show retreat of Greenland glaciers

Los Angeles Times, Thomas H. Maugh II

Long-abandoned 80-year-old aerial photographs found in a Danish basement document the unexpectedly rapid response of Greenland glaciers to changes in average temperatures.

30 May 2012

Data sheds light on speed of Greenland's glaciers

BBC News, Mark Kinver

Greenland's glaciers are not speeding up as much as previously thought, researchers have estimated. A team of US researchers based their findings on data stretching back to 2000-2001, collected from more than 200 outlet glaciers. "So far, on average, we are seeing about a 30% speed-up in 10 years," observed lead author Twila Moon.

4 May 2012

Greenland ice melt could raise seas less than feared, study says

CNN, Matt Smith

Greenland's glaciers are sliding into oceans at a faster pace than previously known, but they may contribute less to an expected rise in global sea level than feared, scientists reported Thursday.

4 May 2012

Greenland glaciers shrinking quickly, but not worst case

The Washington Post (Associated Press)

Greenland's glaciers are hemorrhaging ice at an increasingly faster rate but not at the breakneck pace that scientists once feared, a new study says.

3 May 2012

Greenland's ice melting more slowly than expected

NPR 'All Things Considered', RIchard Harris

The flow of Greenland glaciers to the sea has increased by 30 percent over the past decade. But Polar Science Center researchers report in Science that they aren't seeing a runaway meltdown of Greenland that some have feared.

3 May 2012

Increasing speed of Greenland glaciers gives new insight for rising sea level

UW Today, Vince Stricherz

Changes in the speed that ice travels in more than 200 outlet glaciers indicates that Greenland's contribution to rising sea level in the 21st century might be significantly less than the upper limits some scientists thought possible, a new study shows.

3 May 2012

Sea-level rise 'may not be as high as worst-case scenarios have predicted'

The Guardian, Damian Carrington

New research published in Science suggests that Greenland's glaciers are slipping into the sea more slowly than was previously thought. But scientists warn that ice loss still sped up by 30% and is driving rises in sea levels that endanger low-lying coasts around the world.

3 May 2012

Go to the poles in your imagination at annual Polar Science Weekend

University Week

Hands-on exhibits, UW polar experts and a bit of imagination will transport you and your family to the extreme environments of the Arctic and Antarctica later this month during Polar Science Weekend at Pacific Science Center.

11 Feb 2010

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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