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Mountains cover 25% of Earth's land surface, and their snow and ice stores act as water towers for more than a billion people worldwide. Many are locations of especially hazardous [...]

A carbon-rich black layer, dating to [approximately equal to] 12.9 ka, has been previously identified at [approximately equal to] 50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it. Causes for the extinctions, YD cooling, and termination of Clovis culture have long been controversial. In this paper, we provide evidence for an extraterrestrial (ET) impact event at [congruent to] 12.9 ka, which we hypothesize caused abrupt environmental changes that contributed to YD cooling, major ecological reorganization, broad-scale extinctions, and rapid human behavioral shifts at the end of the Clovis Period. Clovis-age sites in North American are overlain by a thin, discrete layer with varying peak abundances of (i) magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal, (iv) soot, (v) carbon spherules, (vi) glass-like carbon containing nanodiamonds, and (vii) fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at [approximately equal to] 12.9 ka. This layer also extends throughout at least 15 Carolina Bays, which are unique, elliptical depressions, oriented to the northwest across the Atlantic Coastal Plain. We propose that one or more large, low-density ET objects exploded over northern North America, partially destabilizing the Laurentide Ice Sheet and triggering YD cooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food limitations) contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America. comet | iridium | micrometeorites | nanodiamonds | spherules

The most prominent Holocene climatic event in Greenland ice-core proxies, with approximately half the amplitude of the Younger Dryas, occurred [approximately]8000 to 8400 yr ago. This Holocene event affected regions well beyond the North Atlantic basin, as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane. Widespread proxy records from the tropics to the north polar regions show a short-lived cool, dry, or windy event of similar age. The spatial pattern of terrestrial and marine changes is similar to that of the Younger Dryas event, suggesting a role for North Atlantic thermohaline circulation. Possible forcings identified thus far for this Holocene event are small, consistent with recent model results indicating high sensitivity and strong linkages in the climatic system.

Greenland, far north land of the Atlantic, has often been beyond the limit of European farming settlement. One of its Norse settlements, colonized just before AD 1000, is astonishingly - [...]

Sulfate concentrations from continuous biyearly sampling of the GISP2 Greenland ice core provide a record of potential climate-forcing volcanism since 7000 B.C. Although 85 percent of the events recorded over the last 2000 years were matched to documented volcanic eruptions, only about 30 percent of the events from 1 to 7000 B.C. were matched to such events. Several historic eruptions may have been greater sulfur producers than previously thought. There are three times as many events from 5000 to 7000 B.C. as over the last two millennia with sulfate deposition equal to or up to five times that of the largest known historical eruptions. This increased volcanism in the early Holocene may have contributed to climatic cooling., Volcanic aerosols have an important role in the Earth's climate, beginning with their contribution to the development of the primordial atmosphere (1). More recently, much interest has focused on the [...]

High-resolution, continuous multivariate chemical records from a central Greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41,000 years. These chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to Greenland [defined here as the polar circulation index (PCI)] and in the extent of ocean ice cover. Massive iceberg discharge events previously defined from the marine record are correlated with notable expansions of ocean ice cover and increases in PCI. During stadials without discharge events, ocean ice cover appears to reach some common maximum level. The massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling., During the last glaciation, the North Atlantic region experienced major changes in climate relative to the Holocene (the most recent 10,000 years). The most obvious and dramatic of these changes [...]

Global climate underwent frequent changes in the last 40,000 years as shown by ice core drillings from Greenland. The core samples were analyzed for electrical conductivity, which indicated the degree of acidity or dustiness, which indicated climate. The results showed that changes occurred in periods as small as ten or three years, while the overall climate made transitions between glacial and interglacial.

Analysis of ice from Dye-3, Greenland, has demonstrated that the transition between the Younger Dryas and Holocene climate periods occurred over a 40-year period. A near annually resolved, multiparameter record of the transition recorded in the GISP2 core from Summit, Greenland, shows that most of the transition occurred in a series of steps with durations of about 5 years. Some climate proxies associated with mid-latitude sources appear to have changed about 15 years before climate proxies associated with more northern regions. Changes in atmospheric water vapor are likely to have played a large role in the climate transition., The Greenland Ice Sheet Project II (GISP2) and Greenland Ice Core Project (GRIP) ice cores were collected at the summit of the Greenland ice sheet at locations selected to obtain [...]

Paleoclimatic records from equatorial East Africa, Antarctica, and Greenland reveal that atmospheric circulation changed abruptly at the early to mid-Holocene transition to full postglacial conditions. A climatic reorganization occurred at [...]

Greenland ice core records provide clear evidence of rapid changes in climate in a variety of climate indicators. In this work, rapid climate change events in the Northern and Southern hemispheres are compared on the basis of an examination of changes in atmospheric circulation developed from two ice cores. High-resolution glaciochemical series, covering the period 10,000 to 16,000 years ago, from a central Greenland ice core and a new site in east Antarctica display similar variability. These findings suggest that rapid climate change events occur more frequently in Antarctica than previously demonstrated., Among the rapid climate change events, the Younger Dryas (YD, a return to near glacial conditions during the last deglaciation) has received considerable attention because it is the most dramatic [...]

Glaciochemical time series developed from Summit, Greenland, indicate that the chemical composition of the atmosphere was dynamic during the Holocene epoch. Concentrations of sea salt and terrestrial dusts increased in Summit snow during the periods 0 to 600, 2400 to 3100, 5000 to 6100, 7800 to 8800, and more than 11,300 years ago. The most recent increase, and also the most abrupt, coincides with the Little Ice Age. These changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods, and that temperatures in the mid to high northern latitudes were potentially the coldest since the Younger Dryas event., Our ability to predict the environmental consequences of anthropogenic emissions first requires a thorough understanding of natural atmospheric and climatic variability. Records from Summit, Greenland, ice cores reveal that climate [...]

A depth-age scale and an accumulation history for the Holocene have been established on the Greenland Ice Sheet Project 2 (GISP2) deep core, providing the most continuously dated record of annual layer accumulation currently available. The depth-age scale was obtained with the use of various independent techniques to count annual layers in the core. An annual record of surface accumulation during the Holocene was obtained by correcting the observed layer thicknesses for flow-thinning. Fluctuations in accumulation provide a continuous and detailed record of climate variability over central Greenland during the Holocene. Climate events, including 'Little Ice Age' type events, are examined., The GISP2 ice core was drilled from surface to bedrock to obtain a paleoclimatic history spanning the last 200,000 years. The summit drilling site is located at 72.6N, 38.5 ° [...]

One of the most dramatic climate change events observed in marine and ice core records is the Younger Dryas, a return to near-glacial conditions that punctuated the last deglaciation. High-resolution, continuous glaciochemical records, newly retrieved from central Greenland, record the chemical composition of the arctic atmosphere at this time. This record shows that both the onset and the termination of the Younger Dryas occurred within 10 to 20 years and that massive, frequent, and short-term (decadal or less) changes in atmospheric composition occurred throughout this event. Changes in atmospheric composition are attributable to changes in the size of the polar atmospheric cell and resultant changes in source regions and to the growth and decay of continental biogenic source regions. During the last 70,000 to 10,000 years, the North Atlantic experienced rapid, changes in sea-surface temperature coincident with rapid changes in the bulk chemistry, dust concentration, and temperature of precipitation, which are unparalleled in the Holocene record[1-4]. Some of these events have [...]

The results of the Greenland ice core GISP2 showing that snow accumulated within one to three years from the Younger Dryas event to the subsequent Preboreal interval is reported. It is well-known that the warming at the end of the last glaciation was punctuated by shifts to glacial climate, of which the 50-year-long Younger Dryas event is the most well-known. The extreme rapidity of climate change indicated by the GISP2 data is remarkable because it suggests that events in the last glaciation may have been a response to a sudden trigger in the North Atlantic climate system.

Sulfate and Nitrate Concentrations from a South Greenland Ice Core ONE OF THE MAJOR PROBLEMS ASSOCIATED with determining the effects of fossil fuel burning and acid deposition through time has [...]