Abstract: Today9s comparatively warm climate has been the exception more than the rule during the last 500,000 years or more. If recent warm periods (or interglacials) are a guide, then we may soon slip into another glacial period. But Berger and Loutre argue in their Perspective that with or without human perturbations, the current warm climate may last another 50,000 years. The reason is a minimum in the eccentricity of Earth9s orbit around the Sun.

Abstract: [1] Nitrous oxide (N 2 O) concentration records exist for the last 1000 years and for time periods of rapid climatic changes like the transition from the last glacial to today's interglacial and for one of the fast climate variations during the last ice age. Little is known, however, about possible N 2 O variations during the more stable climate of the present interglacial (Holocene) spanning the last 11 thousand years. Here we fill this gap with a high-resolution N 2 O record measured along the European Project for Ice Coring in Antarctica (EPICA) Dome C Antarctic ice core. On the same ice we obtained high-resolution methane and carbon dioxide records. This provides the unique opportunity to compare variations of the three most important greenhouse gases (after water vapor) without any uncertainty in their relative timing. The CO 2 and CH 4 records are in good agreement with previous measurements on other ice cores. The N 2 O concentration started to decrease in the early Holocene and reached minimum values around 8 ka (<260 ppbv) before a slow increase to its preindustrial concentration of ∼265 ppbv.

Abstract: Insoluble dust concentrations and volume-size distributions have been measured for the new 581 m deep Dome C-EPICA ice core (Antarctica). Over the 27000 years spanned by the record, microparticle measurements from 169 levels, to date, confirm evidence of the drastic decrease in bulk concentration from the Last Glacial Maximum (LGM) to the Holocene (interglacial) by a factor of more than 50 in absolute value and of about 26 in flux. Unique new features revealed by the EPICA profile include a higher dust concentration during the Antarctic Cold Reversal phase (ACR) by a factor of 2 with respect to the Holocene average. This event is followed by a well-marked minimum that appears to be concomitant with the methane peak that marks the end of the Younger Dryas in the Northern Hemisphere. Particle volume-size distributions show a mode close to 2 μm in diameter, with a slight increase from the LGM to the Holocene; the LGM/Holocene concentration ratio appears to be dependent on particle size and for diameters from 2 to 5 μm it changes from 50 to 6. Glacial samples are characterised by well-sorted particles and very uniform distributions, while the interglacial samples display a high degree of variability and dispersion. This suggests that different modes of transport prevailed during the two climatic periods with easier penetration of air masses into Antarctica in the Holocene than during Glacial times. Assuming that southern South America remained the main dust source for East Antarctica over the time period studied, the higher dust content recorded during the ACR which preceded the Younger Dryas period, represents evidence of a change in South America environmental conditions at this time. A wet period and likely mild climate in South America is suggested at circa 11.5–11.7 kyr BP corresponding to the end of the Younger Dryas. The Holocene part of the profile also shows a slight general decrease in concentration, but with increasingly large particles that may reflect gradual changes at the source.

Abstract: 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 Bolling-Allerod warming of the Northern Hemisphere and deglaciation of the Sierra Nevada, United States (36.5° to 38°N). The tropical Andes deglaciated while climatic conditions remained regionally wet, which reflects the dominant control of mean annual temperature on tropical glaciation.

Abstract: Located in a tectonically stable, intraplate setting and in the far field of former ice sheets, the southern Australian passive continental margin represents a globally important region for quantifying sea level during Pleistocene highstands. The stratigraphical record of the southern Australian margin is dominated by geographically extensive coastal barrier, estuarine and peritidal landforms of bioclastic, temperate carbonate affinity, a function of regional aridity. Siliciclastic successions dominate the eastern Australian coastline. Despite the generally high level of tectonic stability, regional contrasts are evident in the elevation of Pleistocene shoreline deposits that largely relate to pre-Quaternary geotectonic setting. The most complete record of Pleistocene highstand deposits occurs in the Murray Basin–Coorong Coastal Plain region, and indicates that interglacial sea-level highstands, for at least the past 11 interglacials, did not deviate by more than 6 m from present sea-level. The Pleistocene marginal marine record of southern Australia is dominantly represented by coastal successions deposited during marine oxygen isotope stages 5e and 7, equating with relative sea-level maxima of 2–6 m and greater than 1 m above present sea-level (APSL) respectively. Intertidal facies of Late Pleistocene interstadial successions rarely occur above present sea level. The most reliable record of glacio-eustatic (ice equivalent) sea level is registered on coastlines developed on stable Precambrian cratons such as the Gawler Craton (Eyre Peninsula), where a consistent elevation of 2 m APSL is registered for over 500 km for the last interglacial shoreline (125 ka). Copyright © 2002 John Wiley & Sons, Ltd.

Abstract: At several times during marine oxygen isotope stage 6, the eastern Mediterranean region was influenced by two extreme climatic systems: the large ice sheet over northern Europe and the wet tropics associated with African monsoons. During this interval, two major climatic events occurred in the region; the sapropel S6 layer formed ca. 176 ka in the eastern Mediterranean basin owing to the increase in the African monsoon, and another event, although not large enough to form sapropel, occurred ca. 151 ka. The isotopic composition of Soreq Cave speleothems seems to record these events as very low δ 18 O-δ 13 C values dated as ca. 178 and 152 ka. The very low δ 18 O-δ 13 C values of −6‰ and −11‰ to −12‰, respectively, are typical of interglacial intervals, but here they were recorded during a glacial interval. Such low peaks indicate that in this part of the eastern Mediterranean region, i.e., Israel, the rainfall amount increased dramatically. Moreover, the isotopic record of the speleothems also shows that during the entire stage 6, although the climate was as cold as much of the last glacial, the conditions were never as dry.

Abstract: High-resolution sequence stratigraphy provides a framework to interpret unconformity-bounded depositional sequences in the stream-dominated Kings River alluvial fan, located near Fresno, California. Depositional units in the fan are analogous to systems tracts described from marine deposits. Fan sequences reflect changes in accumulation space (Blum and Tornqvist 2000) associated with Pleistocene glacial cycles in the Sierra Nevada and preservation space created by tectonic subsidence in the San Joaquin basin. Adjustments in accumulation space are driven by changes in the ratio of sediment supply to discharge during glacial advances and retreats. At the end of glacial periods and the beginning of interglacial periods, declines in the ratio of sediment supply to discharge led to fan incision, a basinward shift in the fan intersection point, and loss of accumulation space. In mid- and upper-fan settings, incised valleys and laterally extensive, moderately mature paleosols formed, marking the unconformable base of the depositional sequence. Throughout the interglacial period, relatively low accumulation space existed and deposition was confined to the distal areas of the fan. Rapid aggradation and, thus, accumulation space increase, in response to increased sediment supply during the next glacial event initially filled the incised valley with a fining-upward succession of relatively coarse-grained channel and overbank deposits that contain rare, immature paleosols. Upon filling of the incised valley, the intersection point stabilized near the fan apex. This led to unconfined, open-fan deposition, indicating that widespread accumulation space was available across most of the fan surface. These high-accumulation-space units consist of fluvial deposits from multiple, large glacial outwash channels that radiated outward from the proximally located intersection point. Sequence boundaries and units associated with accumulation-space cycles can be used to understand and predict facies distributions and stratigraphic packaging within glacially influenced fans similar to the Kings River alluvial fan.

Abstract: This study addresses the mechanisms of climatic change in the northern high latitudes during the last interglacial (126-115 kyr BP) using the earth system model of intermediate complexity "MoBidiC". Two series of sensitivity experiments have been performed to assess (a) the respective roles played by different feed-backs represented in the model and (b) the respective impacts of obliquity and precession. The model simulates important environmental changes at northern high latitudes prior the last glacial inception, i.e.: (a) an annual mean cooling of 5 degreesC, mainly taking place between 122 and 120 kyr BP; (b) a southward shift of the northern treeline by 14degrees in latitude; (c) accumulation of perennial snow starting at about 122 kyr BP and (d) gradual appearance of perennial sea ice in the Arctic. As summer sea ice, summer snow and vegetation are particularly sensitive to spring and summer insolation, their evolution is mainly controlled by precession. Furthermore, these environmental changes cause variations in surface albedo that nearly quadruple the direct effect of the astronomical forcing. We conclude that in MoBidiC, precession is the main contributor to climatic change during the last interglacial. The feedback analysis reveals that the synergy between snow and vegetation is crucial for the gradual settlement of perennial snow at northern high latitudes. The interactions between the ocean and the continent are less critical, but the gradual growth of summer sea ice throughout the Eemian hastens the transition between taiga and tundra by about 1000 years. The model also simulates a 5% weakening of the North Atlantic branch of the thermohaline circulation throughout the study interval. This is a consequence of a slight warming of sub-surface Atlantic water at mid-latitudes caused by a decrease in winter heat exchanges between the ocean and the atmosphere. It is partly compensated for by a salinity increase at polar latitudes caused by a decrease in the local freshwater balance. Such a slight change in the thermohaline circulation does not have any significant impact on the heat balance of the northern high latitudes between 126 and 115 kyr BP.

Abstract: SUMMARY A Late Quaternary loess/palaeosol sequence at Kurtak in the Yenisey River valley, southern Siberia, has been studied magnetically. The 34 m section (340 samples) exhibits variations in magnetic susceptibility which can be correlated with oxygen isotope stages 1‐7. A detailed sampling of stage 5 (a further 209 samples) permits the identification of substages 5a‐e. The susceptibility variations themselves are in the opposite sense to that found in the classic sections of the Chinese Loess Plateau, but are in agreement with the ‘wind-intensity’ model which has been put forward to explain similar findings in loess sequences in Alaska. Published results for the susceptibility of magnetite imply volume fractions of #0.2 per cent in glacial stages 2 and 4, dropping to #0.05 per cent in stages 1, 3 and 5. These fluctuations match the aeolian flux variations observed in core V21‐146 from the north Pacific. Even though the warmer intervals are characterized by lower susceptibilities, the observed frequency dependence of susceptibility indicates that new magnetic material is produced as a result of pedogenesis during interglacial and interstadial times.

Abstract: The pH of the ocean is controlled by the chemistry of calcium carbonate. This system in turn plays a large role in regulating the CO2 concentration of the atmosphere on timescales of thousands of years and longer. Reconstructions of ocean pH and carbonate-ion concentration are therefore needed to understand the ocean's role in the global carbon cycle. During the Last Glacial Maximum (LGM), the pH of the whole ocean is thought to have been significantly more basic1, as inferred from the isotopic composition of boron incorporated into calcium carbonate shells, which would partially explain the lower atmospheric CO2 concentration at that time. Here we reconstruct carbonate-ion concentration—and hence pH—of the glacial oceans, using the extent of calcium carbonate dissolution observed in foraminifer faunal assemblages as compiled in the extensive global CLIMAP data set2. We observe decreased carbonate-ion concentrations in the glacial Atlantic Ocean, by roughly 20 µmol kg-1, while little change occurred in the Indian and Pacific oceans relative to today. In the Pacific Ocean, a small (5 µmol kg-1) increase occurred below 3,000 m. This rearrangement of ocean pH may be due to changing ocean circulation from glacial to present times, but overall we see no evidence for a shift in the whole-ocean pH as previously inferred from boron isotopes1.

Abstract: The large difference in carbon and oxygen isotope data from the marine record between marine oxygen isotope stage 12 (MIS 12) and MIS 11, spanning the interval between about 480 and 380 kyr ago, has been interpreted as a transition between an extremely cold glacial period and an unusually warm interglacial period, with consequences for global ice volume, sea level and the global carbon cycle1,2,3,4. The extent of the change is intriguing, because orbital forcing is predicted to have been relatively weak at that time5. Here we analyse a continuous sediment record from Lake Baikal, Siberia, which reveals a virtually continuous interglacial diatom assemblage, a stable littoral benthic diatom assemblage and lithogenic sediments with ‘interglacial’ characteristics for the period from MIS 15a to MIS 11 (from about 580 to 380 kyr ago). From these data, we infer significantly weaker climate contrasts between MIS 12 and 11 than during more recent glacial–interglacial transitions in the late Pleistocene epoch (about 130 to 10 kyr ago). For the period from MIS 15a to MIS 11, we also infer an apparent lack of extensive mountain glaciation.