Ian Joughin's research while affiliated with University of Washington Seattle and other places
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Publications (295)
Ice losses from the Greenland and Antarctic ice sheets have accelerated since the 1990s, accounting for a significant increase in the global mean sea level. Here, we present a new 29-year record of ice sheet mass balance from 1992 to 2020 from the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE). We compare and combine 50 independent estima...
Seasonal terminus-position variability of Greenland's marine-terminating outlet glaciers is superimposed on multidecadal trends of glacier retreat. To characterize this seasonal variability, we manually digitized terminus positions for 219 marine-terminating glaciers in Greenland from January 2015 through December 2021 using Sentinel-1 synthetic ap...
Earlier studies have shown that seasonal terminus-position variability is superimposed on multi-decadal trends of glacier retreat. To characterize this seasonal variability, we manually digitized terminus positions for 219 marine-terminating glaciers in Greenland from January 2015 through December 2021 using Sentinel-1 SAR mosaics. We digitized at...
Ice losses from the Greenland and Antarctic Ice Sheets have accelerated since the 1990s, accounting for a significant increase in global mean sea level. Here, we present a new 29-year record of ice sheet mass balance from 1992 to 2020 from the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE). We compare and combine 50 independent estimates...
Marine-terminating outlet glacier terminus traces, mapped from satellite and aerial imagery, have been used extensively in understanding how outlet glaciers adjust to climate change variability over a range of timescales. Numerous studies have digitized termini manually, but this process is labor intensive, and no consistent approach exists. A lack...
In order to determine whether the calving flux of an ice shelf is changing, the long-term calving flux needs to be established. Methods used to estimate the calving flux either take into account non-steady-state behaviour by capturing movement of the calving-front location (e.g., using satellite observations), or they assume the calving front is st...
The retreat and acceleration of marine-terminating outlet
glaciers in Greenland over the past 2 decades have been widely attributed
to climate change. Here we present a comprehensive annual record of glacier
terminus positions in northwest and central-west Greenland and compare it
against local and regional climatology to assess the regional sensit...
The spatial distribution of ocean-induced melting beneath buttressing ice shelves is often cited as an important factor controlling Antarctica’s sea-level contribution. Using numerical simulations, we investigate the relative sensitivity of grounded-ice loss to the spatial distribution and overall volume of ice-shelf melt over two centuries. Contra...
Marine-terminating outlet glacier terminus traces, mapped from satellite and aerial imagery, have been used extensively in understanding how outlet glaciers adjust to climate change variability over a range of time scales. Numerous studies have digitized termini manually, but this process is labor-intensive, and no consistent approach exists. A lac...
We introduce a new software package called “icepack” for modeling the flow of glaciers and ice sheets.
The icepack package is built on the finite element modeling library Firedrake, which uses the Unified Form Language (UFL), a domain-specific language embedded into Python for describing weak forms of partial differential equations.
The diagnostic...
The retreat and acceleration of marine-terminating outlet glaciers in Greenland over the past two decades has been widely attributed to climate change. Here we present a comprehensive annual record of glacier terminus positions in northwest and central-west Greenland and compare it against local and regional climatology to assess the regional sensi...
Speedup of Pine Island Glacier over the past several decades has made it Antarctica’s largest contributor to sea-level rise. The past speedup is largely due to grounding-line retreat in response to ocean-induced thinning that reduced ice-shelf buttressing. While speeds remained fairly steady from 2009 to late 2017, our Copernicus Sentinel 1A/B–deri...
The recent influx of remote sensing data provides new opportunities for quantifying spatiotemporal variations in glacier surface velocity and elevation fields. Here, we introduce a flexible time series reconstruction and decomposition technique for forming continuous, time-dependent surface velocity and elevation fields from discontinuous data and...
We introduce a new software package called icepack for modeling the flow of glaciers and ice sheets. Icepack is built on the finite element modeling library Firedrake, which uses the domain-specific language UFL for describing weak forms of partial differential equations. The diagnostic models in icepack are formulated through action principles tha...
A system of subglacial lakes drained on Thwaites Glacier from 2012–2014. To improve coverage for subsequent drainage events, we extended the
elevation and ice-velocity time series on Thwaites Glacier through austral winter 2019. These new observations document a second drainage cycle in
2017/18 and identified two new lake systems located in the wes...
The recent influx of remote sensing data provides new opportunities for quantifying spatiotemporal variations in glacier surface velocity and elevation fields. Here, we introduce a flexible time series reconstruction and decomposition technique for forming continuous, time-dependent surface velocity and elevation fields from discontinuous data and...
The recent influx of remote sensing data provides new opportunities for quantifying spatiotemporal variations in glacier surface velocity and elevation fields. Here, we introduce a flexible time series reconstruction and decomposition technique for forming continuous, time-dependent surface velocity and elevation fields from discontinuous data and...
Abstract. A system of subglacial lakes drained on Thwaites Glacier from 2012–2014. To improve coverage for subsequent drainage events, we extended the elevation and ice velocity time series on Thwaites Glacier through austral winter 2019. These new observations document a second drainage cycle and identified two new lake systems located in the west...
Glaciers and ice sheets shape Earth's surface and are important components of the climate system. Among the notable effects of glacier flow are erosion and sedimentation of Earth's surface and variations in sea level as glaciers lose or gain mass. These effects depend on the slip of glaciers along their beds, which is accompanied by drag at ice-bed...
In recent decades, the Greenland Ice Sheet has been a major contributor to global sea-level rise1,2, and it is expected to be so in the future³. Although increases in glacier flow4–6 and surface melting7–9 have been driven by oceanic10–12 and atmospheric13,14 warming, the degree and trajectory of today’s imbalance remain uncertain. Here we compare...
The speed of Greenland's fastest glacier, Jakobshavn Isbræ, has varied substantially since its speed-up in the late 1990s. Here
we present observations of surface velocity, mélange rigidity, and
surface elevation to examine its behaviour over the last decade. Consistent
with earlier results, we find a pronounced cycle of summer speed-up and
thinnin...
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 determ...
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-me...
The speed of Greenland’s fastest glacier, Jakobshavn Isbrae, has varied substantially since its speedup in the late 1990s. Here we present observations of surface velocity, mélange rigidity, and surface elevation to examine its behaviour over the last decade. Consistent with earlier results, we find a pronounced cycle of summer speedup and thinning...
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 i...
Plain Language Summary
Although much effort has gone into improving numerical simulations of ice‐sheet behavior for sea‐level projection, the best choice for the friction law that governs the sliding of ice over its bed remains poorly known. As a consequence, a wide range of friction laws is used by the ice‐sheet modeling community. Here we take ad...
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 determ...
Ocean-induced basal melting is directly and indirectly 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)...
We describe several new ice velocity maps produced by the
Greenland Ice Mapping Project (GIMP) using Landsat 8 and Copernicus Sentinel
1A/B data. We then focus on several sites where we analyse these data in
conjunction with earlier data from this project, which extend back to the
year 2000. At Jakobshavn Isbræ and Køge Bugt, we find good agreement...
Systematically monitoring Greenland's outlet glaciers is central to
understanding the timescales over which their flow and sea level
contributions evolve. In this study we use data from the new Sentinel-1a/b
satellite constellation to generate 187 velocity maps, covering four key outlet
glaciers in Greenland: Jakobshavn Isbræ, Petermann Glacier,
Ni...
Ice velocity is one of the products associated with the Ice Sheets Essential Climate Variable. This paper describes the intercomparison and validation of ice-velocity measurements carried out by several international research groups within the European Space Agency Greenland Ice Sheet Climate Change Initiative project, based on space-borne Syntheti...
Geometry strongly controls the dynamic behavior of marine-terminating (tidewater) glaciers, significantly influencing advance and retreat cycles independent of climate. Yet the recent, nearly ubiquitous retreat of tidewater glaciers suggests that changes in atmospheric and oceanic forcing may also drive dynamic change. To isolate the influence of g...
The Antarctic Ice Sheet is an important indicator of climate change and driver of sea-level rise. Here we combine satellite observations of its changing volume, flow and gravitational attraction with modelling of its surface mass balance to show that it lost 2,720 ± 1,390 billion tonnes of ice between 1992 and 2017, which corresponds to an increase...
Interferometric synthetic aperture radar (InSAR) has become an essential tool for measuring ice sheet velocity in the Polar Regions. At low radar frequencies, e.g. L-band (1.2 GHz) but also at higher frequency, e.g. C-band (5.6 GHz), the ionosphere has been documented to be an important source of noise in these data. In this paper, we employ a spli...
Crosson and Dotson ice shelves are two of the most rapidly changing outlets in West Antarctica, displaying both significant thinning and grounding-line retreat in recent decades. We used remotely sensed measurements of velocity and ice geometry to investigate the processes controlling their changes in speed and grounding-line position over the past...
We describe several new ice velocity maps produced by the Greenland Ice Sheet Mapping Project (GIMP) using Landsat 8 and Copernicus Sentinel 1A/B data. We then focus on several sites where we analyse these data in conjunction with earlier data from this project, which extend back to the year 2000. At Jakobshavn Isbrae and Koge Bugt, we find good ag...
Systematically monitoring Greenland’s outlet glaciers is central to understanding the timescales over which their flow and sea level contributions evolve. In this study we use data from the new Sentinel-1a/b satellite constellation to generate 187 velocity maps, covering 4 key outlet glaciers in Greenland; Jakobshavn Isbræ, Petermann Glacier, Niogh...
Crosson and Dotson Ice Shelves are two of the most rapidly changing outlets in West Antarctica, displaying both significant thinning and grounding-line retreat in recent decades. We used remotely sensed datasets to investigate the processes controlling their changes in speed and grounding-line position over the past 20 years. We combined these obse...
While numerous maps of Greenland ice flow velocity exist, most have gaps in coverage and/or accuracy is limited. We processed a large volume of synthetic aperture radar and Landsat 8 imagery collected between 1995 and 2015 to produce a nearly complete map of ice flow velocity for Greenland at a far greater accuracy than most prior products. We eval...
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...
The dynamic response of Greenland tidewater glaciers to oceanic and atmospheric change has varied both spatially and temporally. While some of this variability is likely related to regional climate signals, glacier geometry also appears to be important. In this study, we investigated the environmental and geometric controls on the seasonal and inte...
A decrease in the mass and volume of Western Palmer Land has raised the prospect that ice speed has increased in this marine-based sector of Antarctica. To assess this possibility, we measure ice velocity over 25 years using satellite imagery and an optimised modelling approach. More than 30 unnamed outlet glaciers drain the 800 km coastline of Wes...
We present conventional and swath altimetry data from
CryoSat-2, revealing a system of subglacial lakes that drained between June 2013 and January 2014 under the central part of Thwaites Glacier, West
Antarctica (TWG). Much of the drainage happened in less than 6 months,
with an apparent connection between three lakes spanning more than 130 km.
Hyd...
A firn aquifer in the Helheim Glacier catchment of Southeast Greenland lies directly upstream of a crevasse field. Previous measurements show that a 3.5-km long segment of the aquifer lost a large volume of water (26,000–65,000 m2 in cross section) between spring 2012 and spring 2013, compared to annual meltwater accumulation of 6000–15,000 m2. The...
In the last two decades, Pine Island Glacier (PIG) experienced marked speedup, thinning, and grounding-line retreat, likely due to ice-shelf basal melt and marine ice-sheet instability. To better understand these processes, we analyzed 2008–2010 and 2012–2014 in-situ GPS records for PIG to constrain surface mass balance, firn compaction, and basal...
We present subannual observations (2009–2014) of a major West Antarctic glacier (Pine Island Glacier) and the neighboring ocean. Ongoing glacier retreat and accelerated ice flow were likely triggered a few decades ago by increased ocean-induced thinning, which may have initiated marine ice-sheet instability. Following a subsequent 60% drop in ocean...
Surface meltwater can refreeze within firn layers and crevasses to warm ice through latent-heat transfer on decadal to millennial timescales. Earlier work posited that the consequent softening of the ice might accelerate ice flow, potentially increasing ice-sheet mass loss. Here, we calculate the effect of meltwater refreezing on ice temperature an...
We use observations of ice-sheet surface motion from a Global Positioning System (GPS) network operating from 2006–2014 around North Lake in west Greenland to investigate the dynamical response of the Greenland Ice Sheet's ablation area to inter-annual variability in surface melting. We find no statistically significant relationship between runoff...
We produced a 6-year time series of differential tidal displacement for Pine Island Ice Shelf, Antarctica, using speckle-tracking methods applied to fine-resolution TerraSAR-X data. These results reveal that the main grounding line has maintained a relatively steady position over the last 6 years, following the speedup that terminated in ~2009. In...
We present conventional and swath altimetry data from Cryosat-2 revealing a system of subglacial lakes that drained between June 2013 and January 2014 under the central part of Thwaites Glacier, West Antarctica. Much of the drainage happened in less than six months, with an apparent connection between three lakes spanning more than 130 km. Hydropot...
An international team produced an integrated assessment of polar ice mass losses in 2012. Now efforts to provide an up-to-date assessment are under way, with an open invitation for participation.
We adapted the automated, open source NASA Ames Stereo Pipeline (ASP) to generate digital elevation models (DEMs) and orthoimages from very-high-resolution (VHR) commercial imagery of the Earth. These modifications include support for rigorous and rational polynomial coefficient (RPC) sensor models, sensor geometry correction, bundle adjustment, po...
Rapid dynamic changes of ocean-terminating outlet glaciers of the Greenland ice sheet are related to atmospheric and oceanic warming but the detailed link to external forcing is not well understood. Observations show high variability in dynamic changes and are mainly limited to the past three decades with dense satellite observations. Here we compi...
Rapid dynamic changes of ocean-terminating outlet glaciers of the Greenland ice sheet are related to atmospheric and oceanic warming but the detailed link to external forcing is not well understood. Observations show high variability in dynamic changes and are mainly limited to the past three decades with dense satellite observations. Here we compi...
Glaciers in Greenland are changing rapidly. To better understand these changes, we have produced a series of seven synthetic aperture radar (SAR) backscatter mosaics for seven winters during the period from 2000 to 2013. Six of the mosaics were created using RADARSAT Fine-Beam data and the seventh used ALOS-PALSAR Fine-Beam Single-Polarization data...
Resistance at the ice-bed interface provides a strong control on the response of ice streams and outlet glaciers to external forcing, yet it is not observable by remote sensing. We used inverse methods constrained by satellite observations to infer the basal resistance to flow underneath three of the Greenland Ice Sheet's largest outlet glaciers. I...
A glacial flow model of Smith, Pope and Kohler Glaciers is calibrated by means of control methods against time varying, annually resolved observations of ice height and velocities, covering the period 2002 to 2011. The inversion – termed "transient calibration" – produces an optimal set of time-mean, spatially varying parameters together with a tim...
A glacial flow model of Smith, Pope and Kohler Glaciers has been calibrated by means of inverse methods against time-varying, annualy resolved observations of ice height and velocities, covering the period 2002 to 2011. The inversion – termed "transient calibration" – produces an optimal set of time-mean, spatially varying parameters together with...
Water-driven fracture propagation beneath supraglacial lakes rapidly transports large volumes of surface meltwater to the base of the Greenland Ice Sheet. These drainage events drive transient ice-sheet acceleration and establish conduits for additional surface-to-bed meltwater transport for the remainder of the melt season. Although it is well est...