Description: Five Ocean Drilling Program sites (657-661), which form a north-south transect off the western periphery of the Sahara, were selected. Nearshore mean flux of opal off Cap Blanc (21°N) showed an abrupt increase about 3 Ma that appears to reflect the main onset of coastal upwelling fertility and enhanced trade winds. At the same time, the input of river-borne clay strongly decreased, suggesting a dry up of the central Saharan rivers. Later, marked short-lived spikes of clay and opal may indicate ongoing ephemeral pulses of fluvial runoff linked to peak interglacial stages. Aridification of the south Sahara and Sahel increased in several steps: at 4.6, 4.3 and especially at 4.0, 3.6 and 2.1 Ma, and again, at 0.8 Ma. The late Miocene and earliest Pliocene were humid. Central and north Sahara climate appears to be linked to the glaciation history of the Northern Hemisphere. Spatial distribution of quartz accumulation suggests that the dust outbreaks linked to the Intertropical Convergence Zone during summer did not shift in latitude back to 4.0 Ma, at least. Short-term variations of dust output over the last 0.5 my followed orbital scale pulses with a strong precessional signal, showing a link of Sahelian humidity changes to the variation of sea-surface temperature and evaporation in the tropical Atlantic.

Description: At the western continental margin of the Barents Sea, 75°N, hemipelagic sediments provide a record of Holocene climate change with a time resolution of 10–70 years. Planktic foraminifera counts reveal a very early Holocene thermal optimum 10.7–7.7 kyr BP, with summer sea surface temperatures (SST) of 8°C and a much enhanced West Spitsbergen Current. There was a short cooling between 8.8 and 8.2 kyr BP. In the middle and late Holocene summer, SST dropped to 2.5°-5.0°C, indicative of reduced Atlantic heat advection, except for two short warmings near 2.2 and 1.6 kyr BP. Distinct quasi-periodic spikes of coarse sediment fraction (with large portions of lithic grains, benthic and planktic foraminifera) record cascades of cold, dense winter water down the continental slope as a result of enhanced seasonal sea ice formation and storminess on the Barents shelf over the entire Holocene. The spikes primarily cluster near recurrence intervals of 400–650 and 1000–1350 years, when traced over the entire Holocene, but follow significant 885–/840– and 505–/605-year periodicities in the early Holocene. These non-stationary periodicities mimic the Greenland-10Be variability, which is a tracer of solar forcing. Further significant Holocene periodicities of 230, (145) and 93 years come close to the deVries and Gleissberg solar cycles.

Description: High-resolution planktonic and epibenthic stable isotope records from Ocean Drilling Program site 658 off northwest Africa provide a basis for a detailed study of glacial terminations I-VI during the last 650,000 years. The duration of the terminations was about one half to one quarter of an orbital precession cycle (5800–10,700 years), when its amplitude was high. At low amplitudes, the terminations lasted longer than half an obliquity cycle (29,000 years). Marked climatic rebounds similar to the Younger Dryas, each with a duration of 1000–2500 years, subdivided all six terminations into distinct steps A, B, and C. Important parts of the deglacial steps were as brief as 700–1000 years. The speed of climatic change suggests that special associations existed between orbital forcing and inherent instability of the ice sheets. In harmony with published models, the more rapid pulses of glacial meltwater incursions to the northern North Atlantic led to one or more brief short-term shut-downs of North Atlantic Deep Water formation. This process is reflected by pronounced benthic δ13C minima that precisely coincide, in most cases, with the end of the δ18O deglaciation steps and immediately terminate with succeeding Younger Dryas-style cooling events. Thus we conclude that the rebounds resulted from a short-term antecedent estuarine circulation regime in the North Atlantic, except for the Younger Dryas itself, which succeeded the Alleröd with its well ventilated Atlantic deepwater circulation and hence continues to be an enigma.

Description: Based on detailed reconstructions of global distribution patterns, both paleoproductivity and the benthic δ13C record of CO2, which is dissolved in the deep ocean, strongly differed between the Last Glacial Maximum and the Holocene. With the onset of Termination I about 15,000 years ago, the new (export) production of low- and mid-latitude upwelling cells started to decline by more than 2-4 Gt carbon/year. This reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric CO2 as recorded in ice cores and, with a slight delay of more than 1000 years, to a large-scale gradual CO2 depletion of the deep ocean by about 650 Gt C. This estimate is based on an average increase in benthic δ13C by 0.4–0.5‰. The decrease in new production also matches a clear 13C depletion of organic matter, possibly recording an end of extreme nutrient utilization in upwelling cells. As shown by Sarnthein et al., [1987], the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades, which in turn was linked via a shrinking extent of sea ice to a massive increase in high-latitude insolation, i.e., to orbital forcing as primary cause.

Description: The late Pliocene phase of large-scale climatic deterioration about 3.2-2.4 Ma BP is well documented in a number of (benthic) 〈latex〉$\delta^{18}$〈/latex〉O records. To test the global implications of this event, we have mapped the distribution patterns of various sediment variables in the Pacific and Atlantic Oceans during two time slices, 3.4-3.18 and 2.43-2.33 Ma BP. The changes of bulk sedimentation and bulk sediment accumulation rates are largely explained by the variations of CaCO〈latex〉$_3$〈/latex〉-accumulation rates (and the accumulation rates of the complementary siliciclastic sediment fraction near continents in higher latitudes). During the late Pliocene, the CaCO〈latex〉$_3$〈/latex〉-accumulation rate increased along the equatorial Pacific and Atlantic and in the northeastern Atlantic, but decreased elsewhere. The accumulation rate of organic carbon (C〈latex〉$_{org}$〈/latex〉) and net palaeoproductivity also increased below the high-productivity belts along the equator and the eastern continental margins. From these patterns we may conclude that (trade-) wind-induced upwelling zones and upwelling productivity were much enhanced during that time. This change led to an increased transfer of CO〈latex〉$_2$〈/latex〉 from the surface ocean to the ocean deep water and to a reduction of evaporation, which resulted in an aridification of the Saharan desert belt as depicted in the dust sediments off northwest Africa.

Description: Marine molluscan shells from para-type and other loclities of the Holsteinian interglaciation were dated by ThU and the electron spin resonance (ESR) method to more than 350,000 and 370,000 yr B.P., beyond the limit of ThU dating. The high age estimate is corroborated by a KAr age of 420,000 yr B.P. determined from volcanic ash near the base of the Ariendorf paleosol in the Middle Rhine valley believed to be a pedostratigraphic equivalent of the Holsteinian. Shells from the Herzeele marine unit III, an equivalent of the Wacken (Dömnitz) warm stage in northern France and subsequent to the Holsteinian, revealed ages between 300,000 and 350,000 yr B.P. A correlation of these two warm stages with marine oxygen-isotope stages 11 and 9 on the SPECMAP and CARTUNE time scales is suggested. From the benthic oxygen-isotope record one may infer that no exceptionally high global sea-level rise corresponds to the large transgressions of the Holstein Sea in northern Germany. Therefore, a significant proportion of the transgression was probably the result of an unusually large local glacial-isostatic depression caused by the extreme buildup of ice during the preceding Elster glaciation (stage 12). According to the deep-sea record, it lasted approximately 50% longer than the subsequent cold stage 10. The outstanding soil formation with Braunlehm and the well-developed thermal optimum of the Holsteinian are tentatively related to a phase of minimum sea-ice cover in the Norwegian-Greenland Sea, as deduced from long benthic carbon-isotope records from the central Atlantic.

Description: The past 20,000 yr have witnessed tremendous climatic changes, a glacial maximum at about 18,000 yr BP and a climatic optimum centred on about 6,000 yr BP, both of which mark extreme situations for the Quaternary. This paper attempts to show that active sand dunes were extensive 18,000 yr ago. Conversely, it seems that sand dunes were generally dormant 6,000 yr ago. Thus the former textbook concept1,2 of an arid climatic optimum and a pluvially active glacial maximum is reversed.

Description: Analysis of aeolo-marine dust deposits in the subtropical eastern Atlantic enables the strength of the major wind patterns during the late Quaternary to be evaluated and gives an insight into the climate of North Africa.

Description: Late Pliocene changes in the advection of Mediterranean Outflow Water (MOW) derivates were reconstructed at northeast Atlantic DSDP/ODP sites 548 and 982 and compared to records of WMDW at West Mediterranean Site 978. Neodymium isotope (εNd) values more positive than −10.5/−11 reflect diluted MOW derivates that spread almost continuously into the northeast Atlantic from 3.7 to 2.55 Ma, reaching Rockall Plateau Site 982 from 3.63 to 2.75 Ma. From 3.4 to 3.3 Ma average MOW temperature and salinity increased by 2°–4 °C and ~1 psu both at proximal Site 548 and distal Site 982. The rise implies a rise in flow strength, coeval with a long-term rise in both west Mediterranean Sea surface salinity by almost 2 psu and average bottom water salinity (BWS) by ~1 psu, despite inherent uncertainties in BWS estimates. The changes were linked with major Mediterranean aridification and a drop in African monsoon humidity. In contrast to model expectations, the rise in MOW salt discharge after 3.4 Ma did not translate into improved ventilation of North Atlantic Deep Water, since it possibly was too small to significantly influence Atlantic Meridional Overturning Circulation. Right after ~2.95 Ma, with the onset of major Northern Hemisphere Glaciation, long-term average bottom water temperature (BWT) and BWS at Site 548 dropped abruptly by ~5 °C and ~1–2 psu, in contrast to more distal Site 982, where BWT and BWS continued to oscillate at estimates of ~2 °C and 1.5–2.5 psu higher than today until ~2.6 Ma. We relate the small-scale changes both to a reduced MOW flow and to enhanced dilution by warmwaters of a strengthenedNorth Atlantic Current temporarily replacingMOWderivates at Rockall Plateau.

Description: Eight time slices of surface-water paleoceanography were reconstructed from stable isotope and paleotemperature data to evaluate late Quaternary changes in density, current directions, and sea-ice cover in the Nordic Seas and NE Atlantic. We used isotopic records from 110 deep-sea cores, 20 of which are accelerator mass spectrometry (AMS)-14C dated and 30 of which have high (〉8 cm /kyr) sedimentation rates, enabling a resolution of about 120 years. Paleotemperature estimates are based on species counts of planktonic foraminifera in 18 cores. The δ18O and δ13C distributions depict three main modes of surface circulation: (1) The Holocene-style interglacial mode which largely persisted over the last 12.8 14C ka, and probably during large parts of stage 3. (2) The peak glacial mode showing a cyclonic gyre in the, at least, seasonally ice-free Nordic Seas and a meltwater lens west of Ireland. Based on geostrophic forcing, it possibly turned clockwise, blocked the S-N flow across the eastern Iceland-Shetland ridge, and enhanced the Irminger current around west Iceland. It remains unclear whether surface-water density was sufficient for deepwater formation west of Norway. (3) A meltwater regime culminating during early glacial Termination I, when a great meltwater lens off northern Norway probably induced a clockwise circulation reaching south up to Faeroe, the northward inflow of Irminger Current water dominated the Icelandic Sea, and deepwater convection was stopped. In contrast to circulation modes two and three, the Holocene-style circulation mode appears most stable, even unaffected by major meltwater pools originating from the Scandinavian ice sheet, such as during δ18O event 3.1 and the Bölling. Meltwater phases markedly influenced the European continental climate by suppressing the “heat pump” of the Atlantic salinity conveyor belt. During the peak glacial, melting icebergs blocked the eastward advection of warm surface water toward Great Britain, thus accelerating buildup of the great European ice sheets; in the early deglacial, meltwater probably induced a southward flow of cold water along Norway, which led to the Oldest Dryas cold spell.