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Ian Joughin

Publications and source records attributed to Ian Joughin.

6 recordsLinked to original sources
PubMed2006

Integrating satellite observations with modelling: basal shear stress of the Filcher-Ronne ice streams, Antarctica.

Using inverse methods constrained by recent satellite observations, we have produced a comprehensive estimate of the basal shear stress beneath the Filchner-Ronne ice streams. The inversions indicate that a weak bed (approx. 4-20kPa) underlies much of these ice streams. Compared to the Ross ice streams, the distribution of weak subglacial till is more heterogeneous, with 'sticky spots' providing much of the resistance to flow. A weak bed beneath Recovery ice stream extends several hundred kilometres inland with flow. Along this ice stream, discrepancies between thickness measurements and flux estimates suggest the existence of a deep (-1400m) trough not resolved by existing maps of subglacial topography. We hypothesize that the presence of this and other deep troughs is a major influence on this sector of the ice sheet that is not fully incorporated in current models of ice-sheet evolution.

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PubMed2005

Ice-sheet and sea-level changes.

Future sea-level rise is an important issue related to the continuing buildup of atmospheric greenhouse gas concentrations. The Greenland and Antarctic ice sheets, with the potential to raise sea level approximately 70 meters if completely melted, dominate uncertainties in projected sea-level change. Freshwater fluxes from these ice sheets also may affect oceanic circulation, contributing to climate change. Observational and modeling advances have reduced many uncertainties related to ice-sheet behavior, but recently detected, rapid ice-marginal changes contributing to sea-level rise may indicate greater ice-sheet sensitivity to warming than previously considered.

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PubMed2004

Large fluctuations in speed on Greenland's Jakobshavn Isbrae glacier.

It is important to understand recent changes in the velocity of Greenland glaciers because the mass balance of the Greenland Ice Sheet is partly determined by the flow rates of these outlets. Jakobshavn Isbrae is Greenland's largest outlet glacier, draining about 6.5 per cent of the ice-sheet area, and it has been surveyed repeatedly since 1991 (ref. 2). Here we use remote sensing data to measure the velocity of Jakobshavn Isbrae between 1992 and 2003. We detect large variability of the velocity over time, including a slowing down from 6,700 m yr(-1) in 1985 to 5,700 m yr(-1) in 1992, and a subsequent speeding up to 9,400 m yr(-1) by 2000 and 12,600 m yr(-1) in 2003. These changes are consistent with earlier evidence for thickening of the glacier in the early 1990s and rapid thinning thereafter. Our observations indicate that fast-flowing glaciers can significantly alter ice discharge at sub-decadal timescales, with at least a potential to respond rapidly to a changing climate.

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PubMed2004

Ice flow direction change in interior West Antarctica.

Upstream of Byrd Station (West Antarctica), ice-penetrating radar data reveal a distinctive fold structure within the ice, in which isochronous layers are unusually deep. The fold has an axis more than 50 kilometers long, which is aligned up to 45 degrees to the ice flow direction. Although explanations for the fold's formation under the present flow are problematic, it can be explained if flow was parallel to the fold axis approximately 1500 years ago. This flow change may be associated with ice stream alterations nearer the margin. If this is true, central West Antarctica may respond to future alterations more than previously thought.

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PubMed2002

Positive mass balance of the Ross Ice Streams, West Antarctica.

We have used ice-flow velocity measurements from synthetic aperture radar to reassess the mass balance of the Ross Ice Streams, West Antarctica. We find strong evidence for ice-sheet growth (+26.8 gigatons per year), in contrast to earlier estimates indicating a mass deficit (-20.9 gigatons per year). Average thickening is equal to approximately 25% of the accumulation rate, with most of this growth occurring on Ice Stream C. Whillans Ice Stream, which was thought to have a significantly negative mass balance, is close to balance, reflecting its continuing slowdown. The overall positive mass balance may signal an end to the Holocene retreat of these ice streams.

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