Abstract: Sea ice and dust flux increased greatly in the Southern Ocean during the last glacial period. Palaeorecords provide contradictory evidence about marine productivity in this region, but beyond one glacial cycle, data were sparse. Here we present continuous chemical proxy data spanning the last eight glacial cycles (740,000 years) from the Dome C Antarctic ice core. These data constrain winter sea-ice extent in the Indian Ocean, Southern Ocean biogenic productivity and Patagonian climatic conditions. We found that maximum sea-ice extent is closely tied to Antarctic temperature on multi-millennial timescales, but less so on shorter timescales. Biological dimethylsulphide emissions south of the polar front seem to have changed little with climate, suggesting that sulphur compounds were not active in climate regulation. We observe large glacial-interglacial contrasts in iron deposition, which we infer reflects strongly changing Patagonian conditions. During glacial terminations, changes in Patagonia apparently preceded sea-ice reduction, indicating that multiple mechanisms may be responsible for different phases of CO2 increase during glacial terminations. We observe no changes in internal climatic feedbacks that could have caused the change in amplitude of Antarctic temperature variations observed 440,000 years ago.

Abstract: An analysis of 1516 radiocarbon dates demonstrates that the development of the current circumarctic peatlands began ∼16.5 thousand years ago (ka) and expanded explosively between 12 and 8 ka in concert with high summer insolation and increasing temperatures. Their rapid development contributed to the sustained peak in CH 4 and modest decline of CO 2 during the early Holocene and likely contributed to CH 4 and CO 2 fluctuations during earlier interglacial and interstadial transitions. Given the decreased tempo of peatland initiation in the late Holocene and the transition of many from fens (which generated high levels of CH 4 ) to ombrotrophic bogs, a neoglacial expansion of northern peatlands cannot explain the increase in atmospheric CH 4 that occurred after 6 ka.

Abstract: Evidence from a North Atlantic deep-sea sediment core reveals that the largest climatic perturbation in our present interglacial, the 8200-year event, is marked by two distinct cooling events in the subpolar North Atlantic at 8490 and 8290 years ago. An associated reduction in deep flow speed provides evidence of a significant change to a major downwelling limb of the Atlantic meridional overturning circulation. The existence of a distinct surface freshening signal during these events strongly suggests that the sequenced surface and deep ocean changes were forced by pulsed meltwater outbursts from a multistep final drainage of the proglacial lakes associated with the decaying Laurentide Ice Sheet margin.

Abstract: Eustatic sea-level variation is the primary index of global ice volume over glacial cycles. Here, we review recent studies of eustatic sea level during interglacial periods. This review includes in-depth discussion of the variability, magnitude and duration of the last five interglacial periods and a summary of evidence for the last nine interglacial periods. The last nine interglacial periods differ not only in height and variability of sea level, but also in timing relative to northern summer insolation peaks. Some interglacials have a single peak and others have several, while MIS 11 persisted with little variation for at least 30 kyr. Estimates of interglacial sea levels remain subject to uncertainties. There is an outstanding need for glacio-hydro-isostatic modelling for all glacial cycles of interest, as well as improvements in dating and dating-correction techniques.

Abstract: A high-resolution study of mineralogy and major element geochemistry combined with Sr and Nd isotopes has been conducted on high sedimentation rate cores collected off the Irrawaddy River mouth in the Andaman Sea and the Bay of Bengal to reconstruct the erosional and weathering history of the Irrawaddy River basin. In both cores, ɛNd(0) values imply that both glacial and interglacial sediments share a common crustal source: the Irrawaddy River. Strong glacial/interglacial cycles are recorded by 87Sr/86Sr: interglacial periods yield values between 0.713 and 0.717, whereas glacial periods show higher values between 0.717 and 0.719. Variations of the pedogenic clays (smectite and kaolinite) to primary mineral (feldspar, quartz, illite, and chlorite) ratios show strong precessional cycles, suggesting a control by past changes in the summer monsoon intensity. Each increase in pedogenic clays content is also associated with a net loss of labile elements (Na, K, and Ca) from the detrital minerals under chemical weathering. Wet periods of summer monsoon reinforcement correspond to an increase in weathering of the Irrawaddy plain soils and a decrease of 87Sr/86Sr ratio. Plotting 87Sr/86Sr versus 87Rb/86Sr gives a pseudo-isochrons interpreted as a mixing line representing the strength of chemical weathering. During glacial stages, enhanced physical erosion induced by glacier scour and frost action in the highland of the Irrawaddy River basins produced high volumes of unaltered, Rb-rich minerals. The low sea level of glacial times constricted the river to the main channel in the lower reaches and permitted an efficient transport of unaltered Rb-rich minerals with high radiogenic Sr composition from the high relief of the Indo-Burman Ranges and the Tibetan plateau to the Indian Ocean.

Abstract: [1] The sources and sinks of atmospheric carbon dioxide over glacial/interglacial cycles are under debate. Variation in productivity of the Antarctic Circumpolar Current (ACC) could potentially play a significant role, but current interpretations of sedimentary geochemical proxies suggest that glacial productivity was not higher than today. We present areal and down-core distribution patterns of previously overlooked diatom resting spores that indicate the occurrence of extensive phytoplankton blooms across the entire Atlantic sector of the ACC, particularly in the seasonal ice zone (SIZ), linked to higher iron input during the last glacial. Sea ice acts as an effective transporter of iron and enhances its bioavailability. The dominance of the deep living radiolarian Cyladophora davisiana in glacial SIZ sediments indicates that organic carbon export to mesopelagic depths was at least tenfold higher than today.

Abstract: The Permian Cedar Mesa Sandstone represents the product of at least 12 separate aeolian erg sequences, each bounded by regionally extensive deflationary supersurfaces. Facies analysis of strata in the White Canyon area of southern Utah indicates that the preserved sequences represent erg-centre accumulations of mostly dry, though occasionally water table-influenced aeolian systems. Each sequence records a systematic sedimentary evolution, enabling phases of aeolian sand sea construction, accumulation, deflation and destruction to be discerned and related to a series of underlying controls. Sand sea construction is signalled by a transition from damp sandsheet, ephemeral lake and palaeosol deposition, through a phase of dry sandsheet deposition, to the development of thin, chaotically arranged aeolian dune sets. The onset of the main phase of sand sea accumulation is reflected by an upward transition to larger-scale, ordered sets which represent the preserved product of climbing trains of sinuous-crested transverse dunes with original downwind wavelengths of 300–400 m. Regularly spaced reactivation surfaces indicate periodic shifts in wind direction, which probably occurred seasonally. Compound co-sets of cross strata record the oblique migration of superimposed slipfaced dunes over larger, slipfaceless draa. Each aeolian sequence is capped by a regionally extensive supersurface characterized by abundant calcified rhizoliths and bioturbation and which represents the end product of a widespread deflation episode whereby the accumulation surface was lowered close to the level of the water table as the sand sea was progressively cannibalized by winds that were undersaturated with respect to their potential carrying capacity. Aeolian sequence generation is considered to be directly attributable to cyclical changes in climate and related changes in sea level of probable glacio-eustatic origin that characterize many Permo-Carboniferous age successions. Sand sea construction and accumulation occurred during phases of increased aridity and lowered sea level, the main sand supply being former shallow marine shelf sediments that lay to the north-west. Sand sea deflation and destruction would have commenced at, or shortly after, the time of maximum aridity as the available sand supply became exhausted. Restricted episodes of non-aeolian accumulation would have occurred during humid (interglacial) phases, accumulation and preservation being enabled by slow rises in the relative water table. Subsidence analysis within the Paradox Basin, together with comparisons to other similar age successions suggests that the climatic cycles responsible for generating the Cedar Mesa erg sequences could be the product of 413 000 years so-called long eccentricity cycles. By contrast, annual advance cycles within the aeolian dune sets indicate that the sequences themselves could have accumulated in just a few hundred years and therefore imply that the vast majority of time represented by the Cedar Mesa succession was reserved for supersurface development.

Abstract: . Ice cores provide unique archives of past climate and environmental changes based only on physical processes. Quantitative temperature reconstructions are essential for the comparison between ice core records and climate models. We give an overview of the methods that have been developed to reconstruct past local temperatures from deep ice cores and highlight several points that are relevant for future climate change. We first analyse the long term fluctuations of temperature as depicted in the long Antarctic record from EPICA Dome C. The long term imprint of obliquity changes in the EPICA Dome C record is highlighted and compared to simulations conducted with the ECBILT-CLIO intermediate complexity climate model. We discuss the comparison between the current interglacial period and the long interglacial corresponding to marine isotopic stage 11, ~400 kyr BP. Previous studies had focused on the role of precession and the thresholds required to induce glacial inceptions. We suggest that, due to the low eccentricity configuration of MIS 11 and the Holocene, the effect of precession on the incoming solar radiation is damped and that changes in obliquity must be taken into account. The EPICA Dome C alignment of terminations I and VI published in 2004 corresponds to a phasing of the obliquity signals. A conjunction of low obliquity and minimum northern hemisphere summer insolation is not found in the next tens of thousand years, supporting the idea of an unusually long interglacial ahead. As a second point relevant for future climate change, we discuss the magnitude and rate of change of past temperatures reconstructed from Greenland (NorthGRIP) and Antarctic (Dome C) ice cores. Past episodes of temperatures above the present-day values by up to 5°C are recorded at both locations during the penultimate interglacial period. The rate of polar warming simulated by coupled climate models forced by a CO2 increase of 1% per year is compared to ice-core-based temperature reconstructions. In Antarctica, the CO2-induced warming lies clearly beyond the natural rhythm of temperature fluctuations. In Greenland, the CO2-induced warming is as fast or faster than the most rapid temperature shifts of the last ice age. The magnitude of polar temperature change in response to a quadrupling of atmospheric CO2 is comparable to the magnitude of the polar temperature change from the Last Glacial Maximum to present-day. When forced by prescribed changes in ice sheet reconstructions and CO2 changes, climate models systematically underestimate the glacial-interglacial polar temperature change.

Abstract: This is part 2 of a study examining southwest African continental margin sediments from nine sites on a north-south transect from the Congo Fan (4°S) to the Cape Basin (30°S) representing two glacial (MIS 2 and 6a) and two interglacial stages (MIS 1 and 5e). Contents, distribution patterns, and molecular stable carbon isotope signatures of long-chain n-alkanes (C27-C33) and n-alkanols (C22-C32) as indicators of land plant vegetation of different biosynthetic types were correlated with concentrations and distributions of pollen taxa in sediments of the same time horizons. Selected single pollen type data reveal details of vegetation changes, but the overall picture is best illustrated by summing pollen known to predominantly derive from C4 plants or C4 plus CAM plants. The C4 plant signals in the biomarkers are recorded in the δ13C data and in the abundances of C31 and C33n-alkanes, and the C32n-alkanol. Calculated clusters of wind trajectories for austral summer and winter situations for the Holocene and the Last Glacial Maximum afford information on the source areas for the lipids and pollen and their transport pathways to the ocean. This multidisciplinary approach provides clear evidence of latitudinal differences in leaf wax lipid and pollen composition, with the Holocene sedimentary data paralleling the current major phytogeographic zonations. The northern sites (Congo Fan area and northern Angola Basin) get most of their terrestrial material from the Congo Basin and the Angolan highlands dominated by C3 plants. Airborne particulates derived from the western and central South African hinterland dominated by deserts, semideserts, and savannah regions are rich in organic matter from C4 plants. As can be expected from the present and glacial positions of the phytogeographic zones, the carbon isotopic signatures of n-alkanes and n-alkanols both become isotopically more enriched in 13C from north to south. In the northern part of the transect the relative importance of C4 plant indicators is higher during the glacials than in the interglacials, indicating a northward extension of arid zones favoring grass vegetation. In the south, where grass-rich vegetation merges into semidesert and desert, the difference in C4 plant indicators is small.