Samstag, 26. Januar 2008

Fire and Ice: Antarctic Volcano

The British Antarctic Survey has been flying routine surveying missions over the western Antarctic ice sheets for several years. They've covered the area pretty thoroughly, so it might sound odd that they've only recently discovered a volcano. But, explains David Vaughan, a glaciologist with the BAS, it wasn't the easiest thing to spot, given that it's buried under several hundred meters of ice. Dr. Vaughan and his colleagues recently discovered the volcano when radar images revealed a layer of volcanic ash, like a layer of icing in a wedding cake, buried half-way down in the ice. Beneath the ice, says Dr. Vaughan, is a tuya, a flat-topped volcano, like the kind found under the glaciers in Iceland. It turns out that the volcano in Antarctica last erupted during the lifetime of Alexander the Great and sent a plume of ash and steam about 12 kilometers into the sky.

mp3 (Canadian Broadcast)

The British Antarctic Survey

Donnerstag, 17. Januar 2008

Glacier mass balance values for the year 2006

Preliminary mass balance values for the year 2006 are now available from more than 80 glaciers worldwide. The continuous mass balance statistics below are calculated based on the 30 glaciers in 9 mountain ranges with long-term data series back to 1980. The statistics for the year 2005 are based on 29 glaciers from 9 regions, and the preliminary values for the year 2006 result from 25 glaciers in 7 regions. The related statistics and figures will be updated as soon as the missing data becomes available.
The average mass balance of the glaciers with available long-term mass balance series around the world continues to decrease, with tentative figures indicating a further thickness reduction of 1.4 m w.e. during the hydrological year 2006. This continues the trend in accelerated ice loss during the past two and a half decades and brings the total loss since 1980 at more than 10.5 m w.e.

Pingos and lakes

Dzhangyskol is a small lake of glacial origin in the central part of the Altai Mountains in southern Siberia. Pollen stratigraphies and chronologies of two cores record the vegetational development of the area from the Late Glacial treeless landscape to the forest and steppe of today. The modern lake is a remnant of a much larger ice-dammed lake, which was reduced in size and then temporarily drained after diversion of the inflowing mountain meltwater stream, which had low d18O values. The dry lake floor allowed development of permafrost and small pingos (frozen mounds of lake sediments). With the onset of greater climatic humidity in the mid-Holocene, the input of local water with higher d18O caused a rise in lake level, drowning the earlier pingos. Growth of a broad fen on the margin of the lake led to formation of a modern pingo complex.

BLYAKHARCHUK et al. (2007): The role of pingos in the development of the Dzhangyskol lake–pingo complex, central Altai Mountains, southern Siberia. Palaeogeography, Palaeoclimatology, Palaeoecology Vol. 257, 4

Changes related to frost and snow in Europe

Changes in indices related to frost and snow in Europe by the end of the twenty-first century were analyzed based on experiments performed with seven regional climate models (RCMs). All the RCMs regionalized information from the same general circulation model (GCM), applying the IPCC-SRES A2 radiative forcing scenario. In addition, some simulations used SRES B2 radiative forcing and/or boundary conditions provided by an alternative GCM. Ice cover over the Baltic Sea was examined using a statistical model that related the annual maximum extent of ice to wintertime coastal temperatures. Fewer days with frost and snow, shorter frost seasons, a smaller liquid water equivalent of snow, and milder sea ice conditions were produced by all model simulations, irrespective of the forcing scenario and the driving GCM. The projected changes have implications across a diverse range of human activities. Details of the projections were subject to differences in RCM design, deviations between the boundary conditions of the driving GCMs, uncertainties in future emissions and random effects due to internal climate variability. A larger number of GCMs as drivers of the RCMs would most likely have resulted in somewhat wider ranges in the frost, snow and sea ice estimates than those presented in this paper.

JYLHA et al. (2008): Changes in frost, snow and Baltic sea ice by the end of the twenty-first century based on climate model projections for Europe. Climatic Change Vol. 86, 3-4

Mittwoch, 16. Januar 2008

Tracing glacier wastage in the Northern Tien Shan

Tracing glacier wastage in the Northern Tien Shan (Kyrgyzstan/Central Asia) over the last 40 years

The status and dynamics of glaciers are crucial for agriculture in semiarid parts of Central Asia, since river flow is characterized by major runoff in spring and summer, supplied by glacier- and snowmelt. Ideally, this coincides with the critical period of water demand for irrigation. The present study shows a clear trend in glacier retreat between 1963 and 2000 in the Sokoluk watershed, a catchment of the Northern Tien Shan mountain range in Kyrgyzstan. The overall area loss of 28% observed for the period 1963–2000, and a clear acceleration of wastage since the 1980s, correlate with the results of previous studies in other regions of the Tien Shan as well as the Alps. In particular, glaciers smaller than 0.5 km2 have exhibited this phenomenon most starkly. While they registered a medium decrease of only 9.1% for 1963–1986, they lost 41.5% of their surface area between 1986 and 2000. Furthermore, a general increase in the minimum glacier elevation of 78 m has been observed over the last three decades. This corresponds to about one-third of the entire retreat of the minimum glacier elevation in the Northern Tien Shan since the Little Ice Age maximum.

Dienstag, 15. Januar 2008

Recent Antarctic ice mass loss

Recent Antarctic ice mass loss from radar interferometry and regional climate modelling

Large uncertainties remain in the current and future contribution to sea level rise from Antarctica. Climate warming may increase snowfall in the continent's interior, but enhance glacier discharge at the coast where warmer air and ocean temperatures erode the buttressing ice shelves. Here, we use satellite interferometric synthetic-aperture radar observations from 1992 to 2006 covering 85% of Antarctica's coastline to estimate the total mass flux into the ocean. We compare the mass fluxes from large drainage basin units with interior snow accumulation calculated from a regional atmospheric climate model for 1980 to 2004. In East Antarctica, small glacier losses in Wilkes Land and glacier gains at the mouths of the Filchner and Ross ice shelves combine to a near-zero loss of 461 Gt /yr. In West Antarctica, widespread losses along the Bellingshausen and Amundsen seas increased the ice sheet loss by 59% in 10 years to reach 13260 Gt/yr in 2006. In the Peninsula, losses increased by 140% to reach 6046 Gt /yr in 2006. Losses are concentrated along narrow channels occupied by outlet glaciers and are caused by ongoing and past glacier acceleration. Changes in glacier flow therefore have a significant, if not dominant impact on ice sheet mass balance.

Nature Geoscience
Landsat Image Mosaic Of Antarctica (LIMA)

Freitag, 11. Januar 2008

Dinosaurs on the rocks?

In this week's issue of Science (Science 11 January 2008:Vol. 319. no. 5860, p. 145), paleoceanographers present new data that make the case for polar ice at the height of the Cretaceous hothouse 90 million years ago.

The study by researchers at Scripps Institution of Oceanography at UC San Diego provides strong evidence that a glacial antarctic ice cap, about half the size (until 60%) of the modern day glacial ice sheet, existed 91 million years ago during a period of high mean global temperatures.

The new study is titled, “Isotopic Evidence for Glaciation During the Cretaceous Supergreenhouse,” and examines geochemical and sea level data retrieved from marine microfossils deposited on the ocean floor 91 million years ago during the Cretaceous Thermal Maximum.

This extreme warming event in Earth’s history raised tropical ocean temperatures to 35-37°C, about 10°C warmer than today, thus creating an intense greenhouse climate. But 90 milion years ago the sealevel dropped worldwide by 40 m - how, and why?

Using two independent isotopic techniques, researchers at Scripps Oceanography studied the microfossils to gather geochemical data on the growth and eventual melting of large Cretaceous ice sheets (Stable isotopes of oxygen molecules (d18O) in bottom-dwelling and near-surface marine foraminifera as proxy for large waterstorages other than the oceans, and the chemical composition of fossil archeobacteria-membranes as proxy for water-temperatures).

These independent methods provided Andre Bornemann, lead author of the study, with strong evidence to conclude that an ice sheet about 50-60 percent the size of the modern Antarctic ice cap existed for about 200,000 years. Bornemann conducted this study as a postdoctoral researcher at Scripps Oceanography and continues this research at Universitat Leipzig in Germany.

“Until now it was generally accepted that there were no large glaciers on the poles prior to the development of the Antarctic ice sheet about 33 million years ago,” said Richard Norris, professor of paleobiology at Scripps Oceanography and co-author of the study. “This study demonstrates that even the super-warm climates of the Cretaceous Thermal Maximum were not warm enough to prevent ice growth.”

Researchers are still unclear as to where such a large mass of ice could have existed in the Cretaceous or how ice growth could have started. The temperatures where much to high for icefields in or on the oceans. So the authors suggest that climate cycles may have favored ice growth during a few times in the Cretaceous when natural climate variations produced unusually cool summers, likewise on high mountains or on the continent of Antarctica.

But anyway ice sheets were much less common during the Cretaceous Thermal Maximum than during more recent “icehouse” climates. Paradoxically, past greenhouse climates may have aided ice growth by increasing the amount of moisture in the atmosphere and creating more winter snowfall at high elevations and high latitudes, according to the paper’s authors.

The results from the study are consistent with other studies from Russia and New Jersey that show sea level fell by about 25-40 m at the same time that the ice sheets were growing during the Cretaceous period. Sea level is known to fall as water is removed from the oceans to build continental ice sheets; conversely, sea level rises as ice melts and returns to the sea.
The presence or absence of sea ice has major environmental implications, specifically in terms of sea level rise and global circulation patterns.