References:

Tedesco, M., and A.J. Monaghan. 2009, An updated Antarctic melt record through 2009 and its linkages to high- latitude and tropical climate variability, Geophysical Research Letters, 36, L18502, doi:10.1029/2009GL039186.

Tedesco, M. and A.J. Monaghan. 2010. Climate and melting variability in Antarctica. Eos, Transactions, American Geophysical Union, 91, 1-2.

Wendt, A., G. Casassa, A. Rivera, and J. Wendt. 2009. Reassessment of ice mass balance at Horseshoe Valley, Antarctica. Antarctic Science, 21, 505–513.

World Climate Report: Recent News from Antarctica

The Register: Antarctic glacier melt maybe ‘not due to climate change’

Observations beneath Pine Island Glacier in West Antarctica and implications for its retreat

Adrian Jenkins, Pierre Dutrieux, Stanley S. Jacobs, Stephen D. McPhail, James R. Perrett, Andrew T. Webb & David White

Thinning ice in West Antarctica, resulting from acceleration in the flow of outlet glaciers, is at present contributing about 10% of the observed rise in global sea level1. Pine Island Glacier in particular has shown nearly continuous acceleration and thinning throughout the short observational record. The floating ice shelf that forms where the glacier reaches the coast has been thinning rapidly, driven by changes in ocean heat transport beneath it. As a result, the line that separates grounded and floating ice has retreated inland. These events have been postulated as the cause for the inland thinning and acceleration. Here we report evidence gathered by an autonomous underwater vehicle operating beneath the ice shelf that Pine Island Glacier was recently grounded on a transverse ridge in the sea floor. Warm sea water now flows through a widening gap above the submarine ridge, rapidly melting the thick ice of the newly formed upstream half of the ice shelf. The present evolution of Pine Island Glacier is thus part of a longer-term trend that has moved the downstream limit of grounded ice inland by 30 km, into water that is 300 m deeper than over the ridge crest. The pace and ultimate extent of such potentially unstable retreat are central to the debate over the possibility of widespread ice-sheet collapse triggered by climate change.

Nature Geoscience
Published online: 20 June 2010 | doi:10.1038/ngeo890

Hydrothermal vents spew volcanically heated seawater from the planet’s underwater mountain ranges — the vast mid-ocean ridge system, where lava erupts and new crust forms. Chemicals dissolved in those vents influence ocean chemistry and sustain a complex web of organisms, much as sunlight does on land. In recent decades more than 220 vents have been discovered worldwide, but so far no one has looked for them in the rough and frigid waters off Antarctica.

From her lab in Palisades, N.Y., geochemist Gisela Winckler recently took up the search. By analyzing thousands of oceanographic measurements, she and her Lamont colleagues pinpointed six spots on the remote Pacific Antarctic Ridge, about 2,000 miles from New Zealand, the closest inhabited country, and 1,000 miles from the west coast of Antarctica, where they think vents are likely to be found. The sites are described in a paper published in the journal Geophysical Research Letters.

Read more at Science Daily: Hydrothermal Vents Discovered Off Antarctica

Journal Reference:

Winckler, G., R. Newton, P. Schlosser, and T. J. Crone. Mantle helium reveals Southern Ocean hydrothermal venting. Geophysical Research Letters, 2010; 37 (5): L05601 DOI: 10.1029/2009GL042093

It is little wonder why, considering that the AR4 found that “Sea ice is projected to shrink in both the Arctic and Antarctic under all SRES scenarios.”

World Climate Report: Another IPCC Error: Antarctic Sea Ice Increase Underestimated by 50%

Peter Bromirski of Scripps Oceanography is the lead scientist in a new study published in the journal Geophysical Research Letters that describes how storms over the North Pacific Ocean may be transferring enough wave energy to destabilize Antarctic ice shelves. The California Department of Boating and Waterways and the National Science Foundation supported the study.

According to Bromirski, storm-driven ocean swells travel across the Pacific Ocean and break along the coastlines of North and South America, where they are transformed into very long-period ocean waves called “infragravity waves” that travel vast distances to Antarctica.

Bromirski, along with coauthors Olga Sergienko of Princeton University and Douglas MacAyeal of the University of Chicago, propose that the southbound travelling infragravity waves “may be a key mechanical agent that contributes to the production and/or expansion of the pre-existing crevasse fields on ice shelves,” and that the infragravity waves also may provide the trigger necessary to initiate the collapse process.

The researchers used seismic data collected on the Ross Ice Shelf to identify signals generated by infragravity waves that originated along the Northern California and British Columbia coasts, and modeled how much stress an ice shelf suffers in response to infragravity wave impacts. Bromirski said only recently has technology advanced to allow scientists to deploy seismometers for the extended periods on the ice shelf needed to capture such signals.

The study found that each of the Wilkins Ice Shelf breakup events in 2008 coincided with the estimated arrival of infragravity waves. The authors note that such waves could affect ice shelf stability by opening crevasses, reducing ice integrity through fracturing and initiating a collapse. “(Infragravity waves) may produce ice-shelf fractures that enable abrupt disintegration of ice shelves that are also affected by strong surface melting,” the authors note in the paper.

Whether increased infragravity wave frequency and energy induced by heightened storm intensity associated with climate change ultimately contribute to or trigger ice shelf collapse is an open question at this point, said Bromirski. More data from Antarctica are needed to make such a connection, he said.

In separate research published last year, Bromirski and Peter Gerstoft of Scripps Oceanography showed that infragravity waves along the West Coast also generate a curious “hum”-subsonic noise too low for humans to hear (see Scripps explorations story Earth Sounds from Central America).

Scripps News: Antarctic Ice Shelf Collapse Possibly Triggered by Ocean Waves, Scripps-led Study Finds Extremely long waves could have initiated 2008 collapse events

Scripps Institution of Oceanography / University of California, San Diego

# # #

Note to broadcast and cable producers: University of California, San Diego provides an on-campus satellite uplink facility for live or pre-recorded television interviews. Please phone or e-mail the media contact listed above to arrange an interview.

Scripps Institution of Oceanography, at University of California, San Diego, is one of the oldest, largest and most important centers for global science research and education in the world. The National Research Council has ranked Scripps first in faculty quality among oceanography programs nationwide. Now in its second century of discovery, the scientific scope of the institution has grown to include biological, physical, chemical, geological, geophysical and atmospheric studies of the earth as a system. Hundreds of research programs covering a wide range of scientific areas are under way today in 65 countries. The institution has a staff of about 1,300, and annual expenditures of approximately $155 million from federal, state and private sources. Scripps operates one of the largest U.S. academic fleets with four oceanographic research ships and one research platform for worldwide exploration.

Transoceanic infragravity waves impacting Antarctic ice shelves

Peter D. Bromirski

Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA

Olga V. Sergienko

AOS Program, Princeton University, Princeton, New Jersey, USA

Douglas R. MacAyeal

Department of the Geophysical Sciences, University of Chicago, Chicago, Illinois, USA

Long‐period oceanic infragravity (IG) waves (ca. [250, 50] s period) are generated along continental coastlines by nonlinear wave interactions of storm‐forced shoreward propagating swell. Seismic observations on the Ross Ice Shelf show that free IG waves generated along the Pacific coast of North America propagate transoceanically to Antarctica, where they induce a much higher amplitude shelf response than ocean swell (ca. [30, 12] s period). Additionally, unlike ocean swell, IG waves are not significantly damped by sea ice, and thus impact the ice shelf throughout the year. The response of the Ross Ice Shelf to IG‐wave induced flexural stresses is more than 60 dB greater than concurrent ground motions measured at nearby Scott Base. This strong coupling suggests that IG‐wave forcing may produce ice‐shelf fractures that enable abrupt disintegration of ice shelves that are also affected by strong surface melting. Bolstering this hypothesis, each of the 2008 breakup events of the Wilkins Ice Shelf coincides with wave‐model‐estimated arrival of IG‐wave energy from the Patagonian coast.

Citation: P. D. Bromirski, O. V. Sergienko, and D. R. MacAyeal (2010), Transoceanic infragravity waves impacting Antarctic ice shelves, Geophys. Res. Lett., 37, L02502, doi:10.1029/2009GL041488.

Sensors lowered through three holes drilled in the Fimbul Ice Shelf showed the sea water is still around freezing and not at higher temperatures widely blamed for the break-up of 10 shelves on the Antarctic Peninsula, the most northerly part of the frozen continent in West Antarctica.

“The water under the ice shelf is very close to the freezing point,” Ole Anders Noest of the Norwegian Polar Institute wrote after drilling through the Fimbul, which is between 250m and 400m thick.

“This situation seems to be stable, suggesting that the melting under the ice shelf does not increase,” he wrote of the first drilling cores.

The Australian: Antarctic sea water shows ‘no sign’ of warming

“Our work suggests that while West Antarctica is still losing significant amounts of ice, the loss appears to be slightly slower than some recent estimates,” said Ian Dalziel, lead principal investigator for WAGN. “So the take home message is that Antarctica is contributing to rising sea levels. It is the rate that is unclear.”

In 2006, another team of researchers used data from the Gravity Recovery and Climate Experiment (GRACE) satellites to infer a significant loss of ice mass over West Antarctica from 2002 to 2005. The GRACE satellites do not measure changes in ice loss directly but measure changes in gravity, which can be caused both by ice loss and vertical uplift of the bedrock underlying the ice.

Now, for the first time, researchers have directly measured the vertical motion of the bedrock at sites across West Antarctica using the Global Positioning System (GPS). The results should lead to more accurate estimates of ice mass loss.

Antarctica was once buried under a deeper and more extensive layer of ice during a period known as the Last Glacial Maximum. Starting about 20,000 years ago, the ice began slowly thinning and retreating. As the ice mass decreases, the bedrock immediately below the ice rises, an uplift known as postglacial rebound.

Postglacial rebound causes an increase in the gravitational attraction measured by the GRACE satellites and could explain their inferred measurements of recent, rapid ice loss in West Antarctica. The new GPS measurements show West Antarctica is rebounding more slowly than once thought. This means that the correction to the gravity signal from the rock contribution has been overestimated and the rate of ice loss is slower than previously interpreted.

“The published results are very important because they provide precise, ground-truth GPS observations of the actual rebound of the continent due to the loss of ice mass detected by the GRACE satellite gravity measurements over West Antarctica” said Vladimir Papitashvili, acting director for the Antarctic Earth Sciences Program at the National Science Foundation, which supported the research.

WAGN researchers do not yet know how large the overestimation was. A more definitive correction will be conducted by other researchers who specialize in interpreting GRACE data. Previous estimates of postglacial rebound were made with theoretical models. Assimilation of the direct GPS results into new models will therefore produce significant improvements in estimations of ice mass loss.

The results will appear in “Geodetic Measurements of Vertical Crustal Velocity in West Antarctica and the Implications for Ice Mass Balance” (M. Bevis et al., 2009), published in the electronic journal Geochemistry, Geophysics, Geosystems of the American Geophysical Union and the American Geochemical Society. [View the paper online.]

A team from The University of Texas at Austin’s Jackson School of Geosciences (Ian Dalziel, lead principal investigator), The Ohio State University’s School of Earth Sciences (Michael Bevis), and The University of Memphis’ Center for Earthquake Research and Information (Robert Smalley, Jr.) performed the WAGN project.

The network consists of 18 GPS stations installed on bedrock outcrops across West Antarctica. Precise, millimeter level, three-dimensional locations of the stations, which are bolted into the bedrock, were determined during measurements made from 2001 to 2003 and from 2004 to 2006, the two measurements being at least three years apart. The difference in the positions during the two time periods indicates the motion of the bedrock.

The WAGN data were supplemented with data from the first year of the Polar Earth Observing Network (POLENET) project, a project to establish a more sophisticated, continuously recording network of GPS and seismic stations, including the already established WAGN sites. POLENET will further improve our understanding of  the interaction between the solid earth and ice sheets at both poles. The lead principal investigator of the U.S. Antarctic contribution to POLENET is Terry Wilson of The Ohio State University.

The West Antarctic GPS Network and the U.S. Antarctic contribution to the Polar Earth Observing Network of the International Polar Year were both funded and logistically supported by the Office of Polar Programs of the National Science Foundation.

For more information, contact: J.B. Bird, Jackson School of Geosciences, 512-750-3512 (cell), 512-232-9623.

The University of Texas at Austin, News, October 19 2009

The above figure was adapted by World Climate Report from Tedesco M., and A. J. Monaghan, 2009. An updated Antarctic melt record through 2009 and its linkages to high-latitude and tropical climate variability. Geophysical Research Letters, 36, L18502, doi:10.1029/2009GL039186:

“A 30-year minimum Antarctic snowmelt record occurred during austral summer 2008–2009 according to spaceborne microwave observations for 1980–2009. Strong positive phases of both the El-Niño Southern Oscillation (ENSO) and the Southern Hemisphere Annular Mode (SAM) were recorded during the months leading up to and including the 2008–2009 melt season.”

Not a peep from the climate alarmist media. Now, if the melt had been a record high…….

Scientists from Western Australia’s Curtin University of Technology are using acoustic sensors developed to support the Comprehensive Nuclear Test Ban Treaty to listen for the sound of icebergs breaking away from the giant ice sheets of the south pole.

“More than six years of observation has not revealed any significant climatic trends,” CUT associate professor Alexander Gavrilov said yesterday.

The Australian: ‘Ice shelves stable over six years’

ANTARCTICA: Freeze-Dried Findings Support a Tale of Two Ancient Climates

A surprising cache of ancient plant material adds evidence for divergent climate histories of the East and West Antarctic ice sheets over the past 14 million years.

Excerpt: These findings appear to be contradictory at first glance, but in fact they buttress an evolving view among scientists that the two major features of the continent, the western and eastern ice sheets, have experienced vastly different climate histories. Data from the Dry Valleys reveals an East Antarctic Ice Sheet that is high, dry, cold, and stable, at least in its central area. And the ANDRILL cores suggest a more volatile West Antarctic Ice Sheet that is subject to the changing temperatures of the sea in which it wades. “It reaffirms the fragility of the West Antarctic Ice Sheet [WAIS] and the stability of the central part of the East Antarctic Ice Sheet,” says Peter Barrett, a sedimentologist at the Victoria University of Wellington (VUW) in New Zealand, who advised the ANDRILL project.