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The modern Indian summer monsoon (ISM) is characterized by exceptionally strong interhemispheric transport, indicating the importance of both Northern and Southern Hemisphere processes driving monsoon variability. Here, we present a high-resolution continental record from southwestern China that demonstrates the importance of interhemispheric forcing in driving ISM variability at the glacial-interglacial time scale as well. Interglacial ISM maxima are dominated by an enhanced Indian tow associated with global ice volume minima. In contrast, the glacial ISM reaches a minimum, and actually begins to increase, before global ice volume reaches a maximum. We attribute this early strengthening to an increased cross-equatorial pressure gradient derived from Southern Hemisphere high-latitude cooling. This mechanism explains much of the nonorbital scale variance in the Pleistocene ISM record. [ABSTRACT FROM AUTHOR]

The dominant period of Pleistocene glacial cycles changed during the mid-Pleistocene from 40,000 years to 100,000 years, for as yet unknown reasons. Here we present a 2.1-million-year record of sea surface partial pressure of CO2 (Pco2), based on boron isotopes in planktic foraminifer shells, which suggests that the atmospheric partial pressure of CO2 (pco2) was relatively stable before the mid-Pleistocene climate transition. Glacial Pco2 was ∼31 microatmospheres higher before the transition (more than 1 million years ago), but interglacial Pco2 was similar to that of late Pleistocene interglacial cycles (<450,000 years ago). These estimates are consistent with a close linkage between atmospheric CO2 concentration and global climate, but the lack of a gradual decrease in interglacial Pco2 does not support the suggestion that a long-term drawdown of atmospheric CO2 was the main cause of the climate transition. [ABSTRACT FROM AUTHOR]

The timing of sea-level change provides important constraints on the mechanisms driving Earth's climate between glacial and interglacial states. Fossil corals constrain the timing of past sea level by their suitability for dating and their growth position close to sea level. The coral-derived age for the last deglaciation is consistent with climate change forced by Northern Hemisphere summer insolation (NHI), but the timing of the penultimate deglaciation is more controversial. We found, means of uranium/thorium dating of fossil corals, that sea level during the penultimate deglaciation had risen to ∼85 meters below the present sea level by 137,000 years ago, and that it fluctuated on a millennial time scale during deglaciation. This indicates that the penultimate deglaciation occurred earlier with respect to NHI than the last deglacial, beginning when NHI was at a minimum. [ABSTRACT FROM AUTHOR]

Whether cooling occurred in the Southern Hemisphere during the Younger Dryas (YD) is key to understanding mechanisms of millennial climate change. Although Southern Hemisphere records do not reveal a distinct climate reversal during the late glacial period, many mountain glaciers readvanced. We show that the Puerto Bandera moraine (5005), which records a readvance of the Southern Patagonian Icefield (SPI), formed at, or shortly after, the end of the YD. The exposure age (10.8 ± 0.5 thousand years ago) is contemporaneous with the highest shoreline of Lago Cardiel (49°S), which records peak precipitation east of the Andes since 13 thousand years ago. Absent similar moraines west of the Andes, these data indicate an SPI response to increased amounts of easterly-sourced precipitation—reflecting changes in the Southern Westerly circulation—rather than regional cooling. [ABSTRACT FROM AUTHOR]

A high-resolution deuterium profile is now available along the entire European Project for Ice Coring in Antarctica Dome C ice core, extending this climate record back to marine isotope stage 20.2, ∼800,000 years ago. Experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation. We assessed the general correspondence between Dansgaard-Oeschger events and their smoothed Antarctic counterparts for this Dome C record, which reveals the presence of such features with similar amplitudes during previous glacial periods. We suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records. [ABSTRACT FROM AUTHOR]

Because animals require oxygen, an increase in late-Neoproterozoic oxygen concentrations has been suggested as a stimulus for their evolution. The iron content of deep-sea sediments shows that the deep ocean was anoxic and ferruginous before and during the Gaskiers glaciation 580 million years ago and that it became oxic afterward, The first known members of the Ediacara biota arose shortly after the Gaskiers glaciation, suggesting a causal link between their evolution and this oxygenation event. A prolonged stable oxic environment may have permitted the emergence of bilateral motile animals some 25 million years later. [ABSTRACT FROM AUTHOR]

A 13-million-year continuous record of Oligocene climate from the equatorial Pacific reveals a pronounced "heartbeat" in the global carbon cycle and periodicity of glaciations. This heartbeat consists of 405,000-, 127,000-, and 96,000-year eccentricity cycles and 1.2 million-year obliquity cycles in periodically recurring glacial and carbon cycle events. That climate system response to intricate orbital variations suggests a fundamental interaction of the carbon cycle, solar forcing, and glacial events. Box modeling shows that the interaction of the carbon cycle and solar forcing modulates deep ocean acidity as well as the production and burial of global biomass. The pronounced 405,000-year eccentricity cycle is amplified by the long residence time of carbon in the oceans. [ABSTRACT FROM AUTHOR]

Long-term variations in Northern Hemisphere summer insolation are generally thought to control glaciation. But the intensity of summer insolation is primarily controlled by 20,000-year cycles in the precession of the equinoxes, whereas early Pleistocene glacial cycles occur at 40,000-year intervals, matching the period of changes in Earth's obliquity. The resolution of this 40,000-year problem is that glaciers are sensitive to insolation integrated over the duration of the summer. The integrated summer insolation is primarily controlled by obliquity and not precession because, by Kepler's second law, the duration of the summer is inversely proportional to Earth's distance from the Sun. [ABSTRACT FROM AUTHOR]

We propose that from ∼3 to 1 million years ago, ice volume changes occurred in both the Northern and Southern Hemispheres, each controlled by local summer insolation. Because Earth's orbital precession is out of phase between hemispheres, 23,000-year changes in ice volume in each hemisphere cancel out in globally integrated proxies such as ocean δ18O or sea level, leaving the in-phase obliquity (41,000 years) component of insolation to dominate those records. Only a modest ice mass change in Antarctica is required to effectively cancel out a much larger northern ice volume signal. At the mid-Pleistocene transition, we propose that marine-based ice sheet margins replaced terrestrial ice margins around the perimeter of East Antarctica, resulting in a shift to in-phase behavior of northern and southern ice sheets as well as the strengthening of 23,000-year cyclicity in the marine δ18O record. [ABSTRACT FROM AUTHOR]

We present a detailed history of glacial to Holocene radiocarbon in the deep western North Atlantic from deep-sea corals and paired benthic-planktonic foraminifera. The deglaciation is marked by switches between radiocarbon-enriched and -depleted waters, leading to large radiocarbon gradients in the water column. These changes played an important role in modulating atmospheric radiocarbon. The deep-ocean record supports the notion of a bipolar seesaw with increased Northern-source deep-water formation linked to Northern Hemisphere warming and the reverse. In contrast, the more frequent radiocarbon variations in the intermediate/deep ocean are associated with roughly synchronous changes at the poles. [ABSTRACT FROM AUTHOR]

Laterally extensive black shales were deposited on the São Francisco craton in southeastern Brazil during low-latitude Neoproterozoic glaciation ∼740 to 700 million years ago. These rocks contain up to 3.0 weight % organic carbon, which we interpret as representing the preserved record of abundant marine primary productivity from glacial times. Extractable biomarkers reflect a complex and productive microbial ecosystem, including both phototrophic bacteria and eukaryotes, living in a stratified ocean with thin or absent sea ice, oxic surface waters, and euxinic conditions within the photic zone. Such an environment provides important constraints for parts of the "Snowball Earth" hypothesis. [ABSTRACT FROM AUTHOR]

Since the first evidence of low algal productivity during ice ages in the Antarctic Zone of the Southern Ocean was discovered, there has been debate as to whether it was associated with increased polar ocean stratification or with sea-ice cover, shortening the productive season. The sediment concentration of biogenic barium at Ocean Drilling Program site 882 indicates low algal productivity during ice ages in the Subarctic North Pacific as well. Site 882 is located southeast of the summer sea-ice extent even during glacial maxima, ruling out sea-ice-driven light limitation and supporting stratification as the explanation, with implications for the glacial cycles of atmospheric carbon dioxide concentration. [ABSTRACT FROM AUTHOR]

The direct and secondary effects of rapidly changing climate caused large rivers draining the Atlantic passive margin to incise quickly into bedrock beginning about 35,000 years ago. Measured in samples from bedrock fluvial terraces, 10-beryllium shows that both the Susquehanna and Potomac Rivers incised 10- to 20-meter-deep gorges along steep, convex lower reaches during the last glacial cycle. This short-lived pulse of unusually rapid downcutting ended by 13,000 to 14,000 years ago. The timing and rate of downcutting are similar on the glaciated Susquehanna and unglaciated Potomac Rivers, indicating that regional changes, not simply glacial meltwater, initiated incision. [ABSTRACT FROM AUTHOR]

A newly discovered Paleolithic site on the Yana River, Siberia, at 71 °N, lies well above the Arctic circle and dates to 27,000 radiocarbon years before present, during glacial times. This age is twice that of other known human occupations in any Arctic region. Artifacts at the site include a rare rhinoceros foreshaft, other mammoth foreshafts, and a wide variety of tools and flakes. This site shows that people adapted to this harsh, high-latitude, Late Pleistocene environment much earlier than previously thought. [ABSTRACT FROM AUTHOR]

Two hypotheses have been put forward to explain the large and abrupt climate changes that punctuated glacial time. One attributes such changes to reorganizations of the ocean's thermohaline circulation and the other to changes in tropical atmosphere-ocean dynamics. In an attempt to distinguish between these hypotheses, two lines of evidence are examined. The first involves the timing of the freshwater injections to the northern Atlantic that have been suggested as triggers for the global impacts associated with the Younger Dryas and Heinrich events. The second has to do with evidence for precursory events associated with the Heinrich ice-rafted debris layers in the northern Atlantic and with the abrupt Dansgaard-Oeschger warmings recorded in the Santa Barbara Basin. [ABSTRACT FROM AUTHOR]

We use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from Ocean Drilling Program cores to reconstruct salinity and temperature of the deep ocean during the Last Glacial Maximum (LGM). Our data show that the temperatures of the deep Pacific, Southern, and Atlantic oceans during the LGM were relatively homogeneous and within error of the freezing point of seawater at the ocean's surface. Our chloride data show that the glacial stratification was dominated by salinity variations, in contrast with the modern ocean, for which temperature plays a primary role. During the LGM the Southern Ocean contained the saltiest water in the deep ocean. This reversal of the modern salinity contrast between the North and South Atlantic implies that the freshwater budget at the poles must have been quite different. A strict conversion of mean salinity at the LGM to equivalent sea-level change yields a value in excess of 140 meters. However, the storage of fresh water in ice shelves and/or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The occurrence of carbon isotope minima at the beginning of glacial terminations is a common feature of planktic foraminifera carbon isotopic records from the Indo-Pacific, sub-Antarctic, and South Atlantic. We use the δ[sup 13]C record of a thermocline-dwelling foraminifera, Neogloboquadrina dutertrei, and surface temperature estimates from the eastern equatorial Pacific to demonstrate that the onset of δ[sup 13]C minimum events and the initiation of Southern Ocean warming occurred simultaneously. Timing agreement between the marine record and the δ[sup 13]C minimum in an Antarctic atmospheric record suggests that the deglacial events were a response to the breakdown of surface water stratification, renewed Circumpolar Deep Water upwelling, and advection of low δ[sup 13]C waters to the convergence zone at the sub-Antarctic front. On the basis of age agreement between the absolute δ[sup 13]C minimum in surface records and the shift from low to high δ[sup 13]C in the deep South Atlantic, we suggest that the δ[sup 13]C rise that marks the end of the carbon isotope minima was due to the resumption of North Atlantic Deep Water influence in the Southern Ocean. [ABSTRACT FROM AUTHOR]

In contrast to the relatively stable climate of the past 10,000 years, during glacial times the North Atlantic region experienced large-amplitude transitions between cold (stadial) and warm (interstadial) states. In this modeling study, we demonstrate that hydrological interactions between the Atlantic thermohaline circulation (THC) and adjacent continental ice sheets can trigger abrupt warming events and also limit the lifetime of the interstadial circulation mode. These interactions have the potential to destabilize the THC, which is already more sensitive for glacial conditions than for the present-day climate, thus providing an explanation for the increased variability of glacial climate. [ABSTRACT FROM AUTHOR]

Discusses the extension of a precise relative chronology for Greenland and West Antarctic paleotemperature to 90,000 years ago, based on correlation of atmospheric methane records from the Greenland Ice Sheet Project 2 and Byrd ice cores. Climate change during the last Glacial Period; Oceanic teleconnection between the hemispheres on millennial time scales.

Documents climate shifts during the last deglaciation using carbon 14 time scales from the Cariaco Basin in Venezuela. Hydrography of the Cariaco Basin; Increase and decline of carbon 14 during the Younger Dryas; Forcing mechanisms corresponding to carbon 14 variations; Climate effect of solar irradiance.

Uses the model-derived equilibrium line attitudes (ELA) of former tropical glaciers to examine the climate of tropical regions during glacial periods. Sensitivity tests suggesting average sea surface temperatures; Comparison of the climates in the Peruvian Andes and Papua New Guinea.

Presents a study which demonstrated that a marine sediment core from the Iberian margin was affected by cooling and advection of arctic water masses during some Heinrich events in the North Atlantic region as of August 2000. Implications of high-resolution paleoclimatic records to glacial climate; Influence of Heinrich events.

Presents a report on the variations in atmospheric nitrous oxide (N2O) concentration during abrupt climatic changes. Records covering the last glacial-interglacial transition and a fast climatic change during the last ice age showing that the N2O concentration changed in parallel with fast temperature variations in the Northern hemisphere; Information about the response of the environment to global climatic changes.

Presents research which concluded that during the Earth's last glacial period, the climate underwent frequent and abrupt changes due to the ability of the ocean's thermohaline circulation to assume more than one mode of operation. Record in ancient sedimentary rocks; Possible trigger mechanism for such reorganizations; Impact of another such reorganization due to an increase in atmospheric carbon dioxide levels.

Discusses the ice record provided by the Guliya ice cap on the Qinghai-Tibetan Plateu. The information about the regional climatic conditions over the last glacial cycle; The development of a time scale for the interpretation of the paleoclimatic information; The evidence for old ice; Abrupt climate changes.

Reports the absolute age of the Younger Dryas-Preboreal climactic shift, or the time marking the end of the last ice age in the North Atlantic, as being 11450 to 11390 plus-or-minus 80 years before the present. Dating methods used; Suggestion that the Younger Dryas may have begun as an anomalous meltwater event.

Discusses climatic changes during the Glacial Age. Period of southwest monsoon intensification; Teleconnections in the evolution of monsoonal and high-latitude climates; Frequency of monsoonal climate variability.

The article discusses research by Z. An et al. which used analysis of the organic carbon content of ancient lake sediments in the Heqing Basin in southwestern China to study the Indian summer monsoon (ISM) annual climate cycle during the Pleistocene period. Previous research indicated that the expansion of glaciers in the Northern Hemisphere (NH) led to a weaker ISM, but the data gathered by An et al. suggests that ISM development during glacial periods was driven by cooling in the Southern Hemisphere (SH).

The free-air gravity trend over Canada, derived from the Gravity Recovery and Climate Experiment (GRACE) satellite mission, robustly isolates the gravity signal associated with glacial isostatic adjustment (GIA) from the longer-time scale mantle convection process. This trend proves that the ancient Laurentian ice complex was composed of two large domes to the west and east of Hudson Bay, in accord with one of two classes of earlier reconstructions. Moreover, GIA models that reconcile the peak rates contribute ∼25 to ∼45% to the observed static gravity field, which represents an important boundary condition on the buoyancy of the continental tectosphere. [ABSTRACT FROM AUTHOR]

Glacial refuge areas are expected to harbor a large fraction of the intraspecific biodiversity of the temperate biota. To test this hypothesis, we studied chloroplast DNA variation in 22 widespread European trees and shrubs sampled in the same forests. Most species had genetically divergent populations in Mediterranean regions, especially those with low seed dispersal abilities. However, the genetically most diverse populations were not located in the south but at intermediate latitudes, a likely consequence of the admixture of divergent lineages colonizing the continent from separate refugia. [ABSTRACT FROM AUTHOR]

The last deglaciation was marked by large, hemispheric, millennial-scale climate variations: the Bølling-Allerød and Younger Dryas periods in the north, and the Antarctic Cold Reversal in the south. A chronology from the high-accumulation Law Dome East Antarctic ice core constrains the relative timing of these two events and provides strong evidence that the cooling at the start of the Antarctic Cold Reversal did not follow the abrupt warming during the northern Bølling transition around 14,500 years ago. This result suggests that southern changes are not a direct response to abrupt changes in North Atlantic thermohaline circulation, as is assumed in the conventional picture of a hemispheric temperature seesaw. [ABSTRACT FROM AUTHOR]

Explores glacial surface temperatures of the Southeast Atlantic ocean. Discussion of the presence on brisk cyclonic currents; Use of marine records in identifying long-term cooling in the Last Glacial Maximum; Documentation of Cape Basin records in terms of substantial temperature ocean warming.

Features a record of atmospheric carbon dioxide concentration during the transition from the Last Glacial Maximum to the Holocene, obtained from the Dome Concordia, Antarctica, ice core. Increase of 76 parts per million by volume over a period of 6000 years in four clearly distinguishable intervals; Correlation between carbon dioxide concentration and Antarctic temperature.

Reports on pollen records of deglacial sequences from northwest Nelson, New Zealand demonstrates that there was no significant temperature decline associated with the Younger Dryas in New Zealand. When the Younger Dryas (YD) occurred; Observations of vegetation change during the YD.

Reports on the findings indicating that meridonal atmospheric circulation intensity increased in the polar South Pacific and North Atlantic at the beginning of the Holocene rapid climate change event known as the Little Ice Age (LIA). How the date of 1400 A.D. was determined; How the LIA may still be effecting climate and weather patterns at the end of the 20th century; Possible causes of the LIA.

Proposes explanations for the greater cooling in the tropics during glacial cycles. Earth's climate during the Pleistocene glaciations; Cooling of deep waters; Glacial-to-interglacial change.

Examines the temperature response to Milankovitch forcing at 2000-year intervals covering the critical time period of the last interglacial with the use of a climate model. Role of geographic response to total isolation changes in the differences between the insolation record at 65 degrees North and the sea-level record; Measurement of orbital-climate linkage.

The article explores how the Antarctic ice sheet has changed in recent years by tracking mass changes. The methods for measuring mass changes mentioned in the article include subtracting the melt and ice flow from the total snowfall, sensing changes in the strength of gravity using pairs of satellites, and repeat mapping of surface elevations from satellites. A study cited in this article, which applied the repeated mapping method, showed that a correction must be made for changes in the density of the firn layer on the ice sheet surface.

The article explores whether spruce grew in southern Greenland during the Pleistocene period and thus provided evidence that the ice sheet was sufficiently reduced to allow for regional development of boreal forests. It says that there is independent evidence to prove that spruce lived in Greenland in the mid-Pleistocene. Meanwhile, it cites pollen data suggesting that the Greenland ice sheet was much smaller during previous warm periods. It predicts that the Arctic region will likely become warmer than it was during the Pleistocene period and will remain warmer for thousands of years if greenhouse gas concentrations continue to increase over the next century.

The article discusses the causes of glacial cycle in earth. It has been stated according to the Milankovitch theory that the changes of insolation is the cause of ice age cycle. Insolation is described as the exposure of the earth's surface to the rays of the sun. It varies on time scales of thousands of years as a result of regular changes in earth's orbit around the sun, in the tilt of earth's axis, and in the direction of earths axis of rotation. An example has been cited that between 3 and 1 million years before present, glacial oscillations follows a 41,000-year cycle and that these oscillations correspond to insolation changes driven by obliquity changes. Other information related to the topic are discoursed in the paper.

Studies the bird ivory gull observed in arctic islands based on a research by biologist Grant Gilchrist of Canadian Wildlife Service. Occurrence of the bird in glacial climates; Effect of climatic factors on reduction in gulls.

Focuses on the factors affecting biological diversity. Impact of glacial-interglacial cycles on biodiversity; Effects of climatic changes on geographic distribution of species; Importance of southern refugia on the survival of biodiversity.

Presents a study on the probable length of the warm interglacial climate. Information on the Eemian and Holocene interglacial periods; Implications of the greenhouse effect to the climate; Effect of anthropogenic carbon dioxide emissions on the dynamics of ice-age cycles.

Glaciation in the humid tropical Andes is a sensitive indicator of mean annual temperature. Here, we present sedimentological data from lakes beyond the glacial limit in the tropical Andes indicating that deglaciation from the Last Glacial Maximum led substantial warming at high northern latitudes. Deglaciation from glacial maximum positions at lake Titicaca, Peru/Bolivia (16°S), and Lake Junin, Peru (11°S), occurred 22,000 to 19,500 calendar years before the present, several thousand years before the Bølling-Allerød warming of the Northern Hemisphere and deglaciation of the Sierra Nevada, United States (36.5° to 38°N). The tropical Andes deglaciated white climatic conditions remained regionally wet, which reflects the dominant control of mean annual temperature on tropical glaciation. [ABSTRACT FROM AUTHOR]

Investigates the roles of glacial meltwater and continental drainage in glacial and climatic instability. Review of numerical modeling studies of ocean circulation; Suggestion on the themohaline circulation of the oceans; Changes in the amount and location of freshwater discharge.

Reports developments related to science as of January 2002. Increase in the availability of iron during glacial periods in Southern Ocean; Occurrence of virulent infections due to soil fungus Cryptococcus neoformans; Effects of initial cell division of plant zygote.

Provides information on the Younger Dryas (YD) period. Hypotheses on the effect of YD; How to identify oceanic and atmospheric teleconnections that linked regional climates during glacial-interglacial cycles; Climate indicators from both South and North America that reveal climatic reversals of glacial-interglacial transition.

Comments on the article `An Appealing Snowball Earth That's Still Hard to Swallow,' by Richard A. Kerr. Information on the glacial deposits found in low latitudes; Assumption of the snowball Earth hypothesis and Precambrian climate; Indications of the earliest glacial deposits.

Examines patterns of biodiversity in refugial areas of the Amazonian rain forest, or where temperate fauna and flora existed during full-glacial conditions. Categories of research done on full-glacial refugia; What accounts for the geographic patterns of the genetic variations in fauna and flora; Postulation of the full-glacial refugia theory.