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An active microbial assemblage cycles sulfur in a sulfate-rich, ancient marine brine beneath Taylor Glacier, an outlet glacier of the East Antarctic Ice Sheet, with Fe(lll) serving as the terminal electron acceptor. Isotopic measurements of sulfate, water, carbonate, and ferrous iron and functional gene analyses of adenosine 5'-phosphosulfate reductase imply that a microbial consortium facilitates a catalytic sulfur cycle. These metabolic pathways result from a limited organic carbon supply because of the absence of contemporary photosynthesis, yielding a subglacial ferrous brine that is anoxic but not sulfidic. Coupled biogeochemical processes below the glacier enable subglacial microbes to grow in extended isolation, demonstrating how analogous organic-starved systems, such as Neoproterozoic oceans, accumulated Fe(II) despite the presence of an active sulfur cycle.

Evidence from high-sedimentation-rate South Atlantic deep-sea cores indicates that global and Southern Ocean carbon budget shifts preceded thermohaline circulation changes during the last ice age initiation and termination and that these were preceded by ice-sheet growth and retreat, respectively. No consistent lead-lag relationships are observed during abrupt millennial warming events during the last ice age, allowing for the possibility that ocean circulation triggered some millenial climate changes. At the major glacial-interglacial transitions, the global carbon budget and thermohaline ocean circulation responded sequentially to the climate changes that forced the growth and decline of continental ice sheets., Records of past global climate preserve evidence of large-scale changes in temperature and ice volume at glacial-interglacial boundaries. Although the timing of ice ages is broadly driven by Milankovich orbital [...]

Surface exposure ages of glacial deposits in the Ford Ranges of western Marie Byrd Land indicate continuous thinning of the West Antarctic Ice Sheet by more than 700 meters near the coast throughout the past 10,000 years. Deglaciation lagged the disappearance of ice sheets in the Northern Hemisphere by thousands of years and may still be under way. These results provide further evidence that parts of the West Antarctic Ice Sheet are on a long-term trajectory of decline. West Antarctic melting contributed water to the oceans in the late Holocene and may continue to do so in the future., Melting of ice sheets at the end of the last glacial period raised the world's oceans by about 120 m between 19,000 and 6000 years ago (1). Antarctica's contribution is [...]

Ice flow at a location in the equilibrium zone of the west-central Greenland Ice Sheet accelerates above the midwinter average rate during periods of summer melting. The near coincidence of the ice acceleration with the duration of surface melting, followed by deceleration after the melting ceases, indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice-bedrock interface. Interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting, with larger increases accompanying higher amounts of summer melting. The indicated coupling between surface melting and ice-sheet flow provides a mechanism for rapid, large-scale, dynamic responses of ice sheets to climate warming., The time scale for dynamic responses of ice sheets to changes in climate (e.g., snow accumulation and surface temperature) is typically considered to be hundreds to thousands of years (1). [...]

A 420-year history of strontium/calcium, uranium/calcium, and oxygen isotope ratios in eight coral cores from the Great Barrier Reef, Australia, indicates that sea surface temperature and salinity were higher in the 18th century than in the 20th century. An abrupt freshening after 1870 occurred simultaneously throughout the southwestern Pacific, coinciding with cooling tropical temperatures. Higher salinities between 1565 and 1870 are best explained by a combination of advection and wind-induced evaporation resulting from a strong latitudinal temperature gradient and intensified circulation. The global Little Ice Age glacial expansion may have been driven, in part, by greater poleward transport of water vapor from the tropical Pacific., The Little Ice Age (LIA) appears in most Northern Hemisphere paleoclimate reconstructions as multiple, century-scale periods of anomalously cold, dry conditions between the 15th and late 19th centuries (1-4). Glacial [...]

Age-depth relations from internal layering reveal a large region of rapid basal melting in Greenland. Melt is localized at the onset of rapid ice flow in the large ice stream that drains north off the summit dome and other areas in the northeast quadrant of the ice sheet. Locally, high melt rates indicate geothermal fluxes 15 to 30 times continental background. The southern limit of melt coincides with magnetic anomalies and topography that suggest a volcanic origin., Basal melt and meltwater exert a strong influence on ice flow (1-4). Our limited knowledge of basal melt is derived from models and sparse observations of bed properties (5-7). Here [...]

A corrected radiocarbon age of 11,050 ± 14 years before present for an advance of the Franz Josef Glacier to the Waiho Loop terminal moraine on the western flank of New Zealand's Southern Alps shows that glacier advance on a South Pacific island was synchronous with initiation of the Younger Dryas in the North Atlantic region. Hence, cooling at the beginning of the Younger Dryas probably reflects global rather than regional forcing. The source for Younger Dryas climatic cooling may thus lie in the atmosphere rather than in a North Atlantic thermohaline switch., The Younger Dryas cooling was a short-lived climatic reversal [ 10,000 to 11,000 [sup.14]C years before present (B.P.)] superimposed on the last deglaciation. It featured rapid shifts of North Atlantic [...]

Most earthquakes follow a simple scaling relationship such that the duration of fault movement is proportional to [10.sup.M/2], where M is the earthquake moment magnitude. The typical duration of an [...], We have detected dozens of previously unknown, moderate earthquakes beneath large glaciers. The seismic radiation from these earthquakes is depleted at high frequencies, explaining their nondetection by traditional methods. Inverse modeling of the long-period seismic waveforms from the best-recorded earthquake, in southern Alaska, shows that the seismic source is well represented by stick-slip, downhill sliding of a glacial ice mass. The duration of sliding in the Alaska earthquake is 30 to 60 seconds, about 15 to 30 times longer than for a regular tectonic earthquake of similar magnitude.

Earth's dynamic oblateness ([J.sub.2]) has been decreasing due to postglacial rebound (PGR). However, [J.sub.2] began to increase in 1997, indicating a pronounced global-scale mass redistribution within Earth's system. We have determined that the observed increases in [J.sub.2] are caused primarily by a recent surge in subpolar glacial melting and by mass shifts in the Southern, Pacific, and Indian oceans. When these effects are removed, the residual trend in [J.sub.2] (-2.9 x [10.sup.-11] [year.sup.-1]) becomes consistent with previous estimates of PGR from satellite and eclipse data. The climatic significance of these rapid shifts in glacial and oceanic mass, however, remains to be investigated., Earth is a dynamic system; it has a fluid, mobile atmosphere and oceans; a continually changing global distribution of ice, snow, and ground water; a fluid core that is undergoing [...]

Satellite radar interferometry reveals that the speed of the Ryder Glacier increased roughly threefold and then returned to normal (100 to 500 meters/year) over a 7-week period near the end of the 1995 melt season. The accelerated flow represents a substantial, though short-lived, change in ice discharge. During the period of rapid motion, meltwater-filled supraglacial lakes may have drained, which could have increased basal water pressure and caused the mini-surge. There are too few velocity measurements on other large outlet glaciers to determine whether this type of event is a widespread phenomenon in Greenland, but because most other outlet glaciers are at lower latitudes, they should experience more extensive melting, making them more susceptible to meltwater-induced surges., Discharge of ice through outlet glaciers represents a substantial part of the mass loss of the Greenland and Antarctic ice sheets and thus has a major impact on their mass [...]

Physical Conditions at the Base of a Fast Moving Antarctic Ice Stream THE DEMONSTRATION OF RAPID MOTIONS in the great Antarctic ice streams [1] has added an important new element [...]

Large millennial-scale fluctuations of the southern margin of the North American Laurentide Ice Sheet occurred during the last deglaciation, when the margin was located between about 43 ° and 49 ° N. Fluctuations of the ice margin triggered episodic increases in the flux of freshwater to the North Atlantic by rerouting continental runoff from the Mississippi River drainage to the Hudson or St. Lawrence Rivers. We found that periods of increased freshwater flow to the North Atlantic occurred at the same time as reductions in the formation of North Atlantic Deep Water, thus providing a mechanism for observed climate variability that may be generally characteristic of times of intermediate global ice volume., A leading hypothesis about the origin of the large and abrupt fluctuations in high-latitude climate on millennial time scales invokes changes in the rate of formation of North Atlantic Deep [...]

Isotope studies show that the Vostok ice core consists of ice refrozen from Lake Vostok water, from 3539 meters below the surface of the Antarctic ice sheet to its bottom at about 3750 meters. Additional evidence comes from the total gas content, crystal size, and electrical conductivity of the ice. The Vostok site is a LikeLy place for water freezing at the Lake-ice interface, because this interface occurs at a higher Level here than anywhere else above the Lake. Isotopic data suggest that subglacial Lake Vostok is an open system with an efficient circulation of water that was formed during periods that were slightly warmer than those of the past 420,000 years. Lake ice recovered by deep drilling is of interest for preliminary investigations of Lake chemistry and bedrock properties and for the search for indigenous Lake microorganisms. This Latter aspect is of potential importance for the exploration of icy planets and moons., The Vostok ice core in central Antarctica has provided the longest record of past changes in climate and atmospheric composition, showing four glacial-interglacial cycles down to a depth of 3310 [...]

Oxygen-isotope ratios of precipitation (Δ[sup.18][O.sub.p]) inferred from deep-lake ostracods from the Ammersee (southern Germany) provide a climate record with decadal resolution. The record in detail shows many of the rapid climate shifts seen in central Green[and ice cores between 15,000 and 5000 years before the present (B.P.). Negative excursions in the estimated Δ[sup.18][O.sub.p] from both of these records likely reflect short weakenings of the thermohaline circulation caused by episodic discharges of continental freshwater into the North Atlantic. Deviating millennial-scale trends, however, indicate that climate gradients between Europe and Green[and changed systematically, reflecting a gradual rearrangement of North At[antic circulation during deglaciation., The Greenland ice cores show strong quasiperiodic climatic oscillations during the longer term interglacial-glacial and glacial-interglacial transitions. These Dansgaard-Oeschger events (DOEs) (1) are characterized by rapid warmings of almost glacial-interglacial [...]

Like coffee in your morning mug, or beer in your evening pint, the level at which the sea rests is controlled both by the shape of the vessel and by [...]

The notion of a large ice sheet is familiar to many through descriptions of the vast expanses of ice that once covered much of Canada, the northern United States, and [...]

Sea level records contain fundamental information on Earth's climatic changes and the relative motion between the sea surface and the topography of the sea floor. On a global scale, they [...]

The EPILOG (Environmental Processes of the Ice Age: Land, Oceans, Glaciers) program originated in 1998, under the aegis of the IMAGES (International Marine Global Change Study) program of IGBP/PAGES (International [...]

Catastrophic Landslide Deposits in the Karakoram Himalaya THREE LARGE ROCK AVALANCHES descended to the surface of Bualtar Glacier in the central Karakoram Himalaya between 29 and 31 July 1986. Approximately [...]

Global Sea Level and Earth Rotation DURING THE PAST 100 YEARS, GLOBAL SEA LEVEL HAS apparently risen by 10 to 15 cm, roughly 50% of which is attributed to the [...]

Antarctica: Measuring Glacier Velocity from Satellite Images MONITORING THE DYNAMICS OFthe Greenland and Antarctic ice sheets is an important scientific task because significant changes in the storage of ice within [...]

Glacier surging--popularly called 'galloping'--is one of the most dramatic phenomena of glacier motion. A surging-type glacier, after flowing along in an apparently normal manner for years, speeds up for a [...]

A record of oxygen isotopes in biogenic opal, 4200 to 1200 calibrated years before the present, from a high-altitude proglacial lake on Mount Kenya, East Africa, exhibits short-term fluctuations on a time scale of centuries as well as tong-term variations. The short-term fluctuations are attributed to changes in the glacier meltwater input, and the long-term variations are related to changes in lake temperature. The record indicates that the climate was warm in Equatorial East Africa from 2300 to 1500 years before the present., The Holocene, although relatively more stable than the Late Pleistocene, was also subject to abrupt climatic changes (1, 2). Small, low-latitude glaciers are especially sensitive to such climatic changes (3). [...]

Subhourly measurements of bed deformation, bed shear strength, subglacial water pressure, and surface speed at Storglaciaren, a glacier in northern Sweden, showed that the shear-strain rates of the bed decrease during periods of high water pressure and surface speed. High water pressures appear to be accompanied by a reduction in the coupling of ice with the bed that is sufficient to reduce or eliminate shearing. The instability of large ice masses may result from similar decoupling rather than from pervasive bed deformation, as has been commonly thought., Many glaciers are underlain, at least in part, by unlithified sediment that may deform readily if basal water pressures are near the ice overburden pressure. Such deformation has been invoked [...]

If, in the common vernacular, to move glacially is to move slowly, is fast glacier flow an oxymoron? Apparently not, according to research on modern glaciers and ice sheets and [...]

In their efforts to determine whether physical processes provide any evidence that anthropogenic activity has begun to affect Earth's climate, researchers have long pointed out that the historical and geologic [...]