Abstract: The Antarctic Vostok ice core provided compelling evidence of the nature of climate, and of climate feedbacks, over the past 420,000 years. Marine records suggest that the amplitude of climate variability was smaller before that time, but such records are often poorly resolved. Moreover, it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records. Here we report the recovery of a deep ice core from Dome C, Antarctica, that provides a climate record for the past 740,000 years. For the four most recent glacial cycles, the data agree well with the record from Vostok. The earlier period, between 740,000 and 430,000 years ago, was characterized by less pronounced warmth in interglacial periods in Antarctica, but a higher proportion of each cycle was spent in the warm mode. The transition from glacial to interglacial conditions about 430,000 years ago ( Termination V) resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases, but there are significant differences in the patterns of change. The interglacial stage following Termination V was exceptionally long - 28,000 years compared to, for example, the 12,000 years recorded so far in the present interglacial period. Given the similarities between this earlier warm period and today, our results may imply that without human intervention, a climate similar to the present one would extend well into the future.

Abstract: Thorium-230 ages and oxygen isotope ratios of stalagmites from Dongge Cave, China, characterize the Asian Monsoon and low-latitude precipitation over the past 160,000 years. Numerous abrupt changes in 18O/16O values result from changes in tropical and subtropical precipitation driven by insolation and millennial-scale circulation shifts. The Last Interglacial Monsoon lasted 9.7 +/- 1.1 thousand years, beginning with an abrupt (less than 200 years) drop in 18O/16O values 129.3 +/- 0.9 thousand years ago and ending with an abrupt (less than 300 years) rise in 18O/16O values 119.6 +/- 0.6 thousand years ago. The start coincides with insolation rise and measures of full interglacial conditions, indicating that insolation triggered the final rise to full interglacial conditions.

Abstract: The magnitude of heat and salt transfer between the Indian and Atlantic oceans through 'Agulhas leakage' is considered important for balancing the global thermohaline circulation. Increases or reductions of this leakage lead to strengthening or weakening of the Atlantic meridional overturning and associated variation of North Atlantic Deep Water formation. Here we show that modern Agulhas waters, which migrate into the south Atlantic Ocean in the form of an Agulhas ring, contain a characteristic assemblage of planktic foraminifera. We use this assemblage as a modern analogue to investigate the Agulhas leakage history over the past 550,000 years from a sediment record in the Cape basin. Our reconstruction indicates that Indian-Atlantic water exchange was highly variable: enhanced during present and past interglacials and largely reduced during glacial intervals. Coherent variability of Agulhas leakage with northern summer insolation suggests a teleconnection to the monsoon system. The onset of increased Agulhas leakage during late glacial conditions took place when glacial ice volume was maximal, suggesting a crucial role for Agulhas leakage in glacial terminations, timing of interhemispheric climate change and the resulting resumption of the Atlantic meridional overturning circulation.

Abstract: [1] Geochemical profiles from the North Atlantic Ocean suggest that the vertical δ13C structure of the water column at intermediate depths did not change significantly between glacial and interglacial time over much of the Pleistocene, despite large changes in ice volume and iceberg delivery from nearby landmasses. The most anomalous δ13C profiles are from the extreme interglaciations of the late Pleistocene. This compilation of data suggests that, unlike today (an extreme interglaciation), the two primary sources of northern deep water, Norwegian-Greenland Sea and Labrador Sea/subpolar North Atlantic, had different characteristic δ13C values over most of the Pleistocene. We speculate that the current open sea ice conditions in the Norwegian-Greenland Sea are a relatively rare occurrence and that the high-δ13C deep water that forms in this region today is geologically unusual. If northern source deep waters can have highly variable δ13C, then this likelihood must be considered when inferring past circulation changes from benthic δ13C records.

Abstract: Foraminiferal oxygen isotope and pollen analyses from a deep-sea sequence off southwest Portugal show that the duration of temperate stages on land over the past 350,000 years varied considerably. The record shows forest contractions during intervals of low ice volume, coeval with declines in atmospheric methane, after which tree populations did not always recover. What emerges is that, although the broad timing of interglacials is consistent with orbital theory, their specific duration may be dictated by millennial variability. This complicates the prediction of the natural duration of interglacials, at least until the origin of this climate variability is understood.

Abstract: Three east Antarctic ice cores (Dome B, EPICA-Dome C and Komsomolskaia) give evidence for a uniform dust input to the polar plateau during the last glacial maximum (LGM)/Holocene transition (20 to 10 kyr BP) and the 87Sr/86Sr versus 143Nd/144Nd isotopic signature of the mineral particles highlights a common provenance from southern South America at that time. However, the size distribution of dust from the three ice cores highlights important differences within the east Antarctic during the LGM and shows clearly opposite regional trends during the climatic transition. Between Dome B and Dome C the timing of these changes is also different. A geographical diversity also arises from the different phasing of the short-term (multi-secular scale) dust size oscillations that are superposed at all sites on the main trends of glacial to interglacial changes. We hypothesize the dust grading is controlled by size fractionation inresponse to its atmospheric pathway, either in terms of horizontal trajectory or in altitude of transport. Such mechanism is supported also by the dust size changes observed during a volcanic event recorded in Vostok ice. Ice core dust size data suggest preferential upper air subsidence over the EDC-KMS region and easier penetration of relatively lower air masses to the DB area during the LGM. At the end of the last glacial period and during the climatic transition the region of relatively higher subsidence progressively moved southward. The scenario proposed, supported also by the LGM/Holocene regional changes of snow accumulation, likely operates even at sub-millennial time scale.

Abstract: The Holocene climate of the Southern Ocean is not well un-derstood, mainly because of the lack of high-resolution reconstruc-tions of ocean surface properties. Here we present a 12,500-yr-long,decadal-scale record of Holocene sea-surface temperatures and sea-ice presence from the Polar Front of the East Atlantic SouthernOcean. The record shows gradual climate change, with no abruptNeoglacial cooling, and an unprecedented late Holocene warming.The dominant forcing factor appears to be precessional insolation;Northern Hemisphere summer insolation correlates to at least theearly to middle Holocene climate trend. Spectral analysis revealscentennial-scale cyclic climate changes with periods of 1220, 1070,400, and 150 yr. The record shows good correlation to East Ant-arctic ice cores and to climate records from South Georgia andBunger Oasis. However, the record shows out-of-phase behaviorwith regard to climate records from the western Antarctic Penin-sula and the Peru-Chile Current; such behavior hints at a climaticdivide through Patagonia, the Drake Passage, and between Westand East Antarctica.Keywords: Southern Ocean, paleoclimate, diatoms, modern analogtechnique, Holocene, insolation, Antarctic Polar Front.INTRODUCTIONThe Holocene climate variability has received less attention thanthe more dramatic changes during the last glacial period. The Holoceneis generally assumed to be a stable interglacial period when climatechanges in the North Atlantic are transmitted to the rest of the worldthrough a strong thermohaline circulation (Imbrie et al., 1992). Thelarge fluctuations of the last glacial period appear to continue into thisinterglacial, although in a subdued manner (Bond et al., 2001).The Southern Ocean has received even less attention than the highnorthern latitudes; oceanic records are few and coarse. They generallydisplay a warm early Holocene followed by cooling (Labracherie etal., 1989; Pichon et al., 1992; Hodell et al., 2001), similar to NorthAtlantic climate (e.g., Koc¸ and Jansen, 1994). High-resolution recordsare restricted to Antarctic ice cores, which mostly display little climatevariability during the Holocene (Jouzel et al., 2001). An exception isthe Taylor Dome deuterium record, in which the Holocene appears tobe split by an abrupt cooling event ca. 5.5–5 ka (Steig et al., 1998).This cooling appears to fit the late Holocene global cooling trend (Por-ter, 2000) as a nonlinear response from the climate system to insolationchanges (deMenocal et al., 2000; Hodell et al., 2001).High-resolution Holocene records available for Southern Oceanclimate reconstruction are rarely from the Antarctic Circumpolar Cur-rent proper (e.g., Domack et al., 2001; Stenni et al., 2001; Lamy et al.,2002), with the exception of a multiproxy approach to Holocene cli-mate that includes a high-resolution description of lithic fragments(Hodell et al., 2001).We present data from site TN057-17 near the Polar Front in theEast Atlantic Southern Ocean. It is based on quantitative estimates ofsummer sea-surface temperature (SSST) and sea-ice presence (SIP),utilizing the down-core variability of diatom assemblages. The recordshows good correlation to Antarctic ice cores, but a gradual change inphase relationships. During the early Holocene, the record shows anin-phase relationship with the Ross Sea region ice cores; during thelate Holocene, the record shows an in-phase relationship with the EastAntarctic region ice cores.Antarctic Polar FrontThe Antarctic Polar Front (APF, Fig. 1) is an important climateboundary in terms of air-sea fluxes and the heat and salt budgets ofthe oceans. At the surface, the APF is a steep sea-surface temperaturegradient, while the subsurface expression is the southern limit for sub-duction of cold, fresh Antarctic Surface Water below warmer and moresaline Subantarctic Surface Water (Orsi et al., 1995). Globally, the APFcould be the southern limit of synchrony with Northern Hemisphereclimate (Broecker, 1996). The APF is subject to large spring and sum-mer blooms of diatoms (Fischer et al., 2002), and achieves the largestbiogenic sedimentation rates of the diatom ooze belt of the SouthernOcean (Burckle and Cirilli, 1987). It is these high sedimentation ratesof diatomaceous oozes and the sensitivity of diatoms especially to lightand temperature that make sites in the APF region suitable for pro-ducing high-resolution records of climate change.

Abstract: Dating results from terrestrial records in the northern foreland of the Alps have been compiled in order to establish an independent chronostratigraphy for the climate history of this region. U/Th dates of peat deposited during the final phase of the Last Interglacial indicate that it lasted until at least c. 115 000 yr ago. The Early Wurmian started with a period of severe cold climate causing a substitution of forest by tundra-like vegetation. It is assumed that during this period glaciers advanced to the margin of the foreland of at least the Western Alps. Sediments attributed to this glaciation are dated to about 103 000 yr. Three subsequent interstadials, all characterized by coniferous forest, were interrupted by cold stadials with steppe to tundra-like vegetation. The first interstadial is dated to about 95 000 yr. There is evidence for an interstadial with open coniferous woodland and three phases of steppe vegetation during the Middle Wurmian, between c. 50000 and 30 000 yr ago. The last glaciation of the Alpine Foreland reached its maximum extension between 24 000 and 21 500 yr and glaciers rapidly collapsed before ˜17 500 yr ago. A series of minor re-advances during the Lateglacial is reported from within the Alps, but the glaciers barely reached the main Alpine valleys during this time. The last of these advances formed the Egesen moraine and occurred at about 11 800 yr ago during the Younger Dryas.

Abstract: Pennsylvanian tropical rain forests flourished during an icehouse climate mode. Although it is well established that Milankovitch-band glacial-interglacial rhythms caused marked synchronous changes in Pennsylvanian tropical climate and sea level, little is known of vegetation response to orbital forcing. This knowledge gap has now been addressed through sequence- stratigraphic analysis of megafloral and palynofloral assemblages within the Westphalian D–Cantabrian Sydney Mines Formation of eastern Canada. This succession was deposited in a low- accommodation setting where sequences can be attributed confidently to glacio-eustasy. Results show that long-lived, low-diversity peat mires dominated by lycopsids were initiated during deglaciation events, but were mostly drowned by rising sea level at maximum interglacial conditions. Only upland coniferopsid forests survived flooding without significant disturbance. Mid- to late interglacial phases witnessed delta-plain progradation and establishment of high-diversity, mineral-substrate rain forests containing lycopsids, sphenopsids, pteridosperms, cordaites, and tree ferns. Renewed glaciation resulted in sea-level fall, paleovalley incision, and the onset of climatic aridity. Glacial vegetation was dominated by cordaites, pteridosperms, and tree ferns; hydrophilic lycopsids and sphenopsids survived in paleovalley refugia. Findings clearly demonstrate the dynamic nature of Pennsylvanian tropical ecosystems and are timely given current debates about the impact of Quaternary glacial-interglacial rhythms on the biogeography of tropical rain forest.

Abstract: On the basis of two sedimentary records from the central Sea of Okhotsk, we reconstruct the closely coupled glacial/interglacial changes in terrigenous flux, marine productivity, and sea ice coverage over the past 11 Myr The correspondance of our sedimentary records to the China loess grain size record (China loess particle timescale, CHILOPARTS) suggests that environmental changes in both the Sea of Okhotsk area and in SE Asia were closely related via the Siberian atmospheric high-pressure cell During full glacial times our records point to a strong Siberian High causing northerly wind directions, the extension of the sea ice cover, and a reduced Amur River discharge Deglacial maxima of terrigenous flux were succeeded by or synchronous to high-productivity events Marine productivity was strengthened during glacial terminations because of an effective nutrient utilization at times of enhanced water column stratification and high nutrient supply from fluvial runoff and sea ice thawing During interglacials, SE monsoonal winds prevailed, analogous to today's summer situation of a pronounced Mongolian Heat Low and a strong Hawaiian High Strong freshwater discharge induced by high precipitation rates in the Amur drainage area and a seasonally reduced and mobile sea ice cover favored marine productivity (although being considerably lower than during the terminations) and a lowered flux of ice-rafted detritus

Abstract: [1] In order to study the variability of dry versus humid conditions resulting from the East Asian monsoon (EAM) we analyzed hematite and goethite from two high-resolution Chinese loess sections by diffuse reflectance spectroscopy. The hematite and goethite concentrations are higher in interglacial paleosols than in glacial loess sediments, whereas the hematite/goethite (Hm/Gt) ratios are lower in paleosols than in loess. Such changes are consistent with higher precipitation and temperature and increased pedogenesis during interglaciation and lower precipitation and temperature and decreased pedogenesis during glaciation. The Hm/Gt ratio can be employed as a tool to assess short-term variations in humidity and aridity of the EAM. The Hm/Gt ratios of the last glacial loess displays millennial-scale abrupt climate oscillations, revealing a pattern of significantly reduced and enhanced summer monsoon moisture. Our results indicate that the EAM responded to tropical Pacific climate by millennial-scale changes in precipitation during the last glaciation.

Abstract: A review of the aeolian sedimentary record of the Thar desert is presented. This includes a regional survey of the major dune forms, their genesis and their relationship to climate and other regional landforms. A key aspect of this work is the chronometry of the dunes using luminescence methods. Luminescence dating of sand has enabled quantification of the duration of the phases of sand aggradation and quiescence, time scales of dune migration and the dating of pedogenic carbonates. We demonstrate that the conventional wisdom of synchronicity of dune aggradation with glacial epoch is not true in the context of Thar sands and here only a short durationwindow of opportunity existed for dune aggradation. Luminescence ages further suggest that this window occurred during a transitional climatic regime from glacial to interglacial about 4–10 ka after the glacial epoch. Other inferences included are that:

Abstract: From the onset of rhythmic loess accumulation, at the turn from the Gauss to the Matuyama Epoch, a frequent variation from humid warm to dry cool climate with loess and occasional gravel accumulation occurred until the end of the Matuyama Epoch Remnants of four glaciations (Gunz, Mindel, Riss, Wurm) within the Eastern Alps and their foreland have long since been known More recently evidence for an additional cold stage between the two older ones was found As a result of a major cooling and build up of piedmont glaciers in the foreland, the four glaciations show a complete succession of terminal moraines with glaciofluvial terraces connected to them The last interglacial/glacial cycle can easily be reconstructed climatologically and by sediment development It may serve as a model for understanding the climatic conditions of the older ones, which had very similar successions

Abstract: [1] Atmospheric methane (CH4) recorded in Antarctic ice cores represents the closest ice proxy available for Greenland temperature changes beyond times when Greenland climate records are available. The record over four climatic cycles from the Vostok ice core offers the opportunity to study the phase relationship between Greenland and Antarctic climate changes through detailed CH4 profiles. Combining American and French analytical efforts, we have improved the time resolution of the existing CH4 record from Petit et al. [1999]. Spectral analyses reveal high- and low-frequency variability (including a strong precessional component). The phase relationship between CH4 and the Antarctic temperature proxy (δD) shows a systematic lag of CH4 versus temperature by 1100 ± 200 years, on long timescales (50–400 kyr) and a more complex behavior over shorter timescales (i.e., ≤25 kyr), suggesting that Dansgaard/Oeschger-type of climatic variability and associated interhemispheric linkage are robust features of late Quaternary climate.

Abstract: Warm‐water molluscs were transported to Wanganui Basin from the northeastern North Island during Pleistocene time as planktotrophic larvae. This is not possible at present, so their occurrence in Wanganui Basin correlates with breaches of the Auckland isthmus during high sea levels. The end of Nukumaruan time is clearly defined by the extinction of 29 genera of molluscs (most only locally) during this stage, including 15 at the end. The extinction likely was caused by the initial closure of the Auckland isthmus. Migrants to Wanganui from the northeastern North Island indicate that breaches of the isthmus during interglacials commenced in oxygen isotope stage (OIS) 25, just before the mid‐Pleistocene transition (MPT). Appearances of taxa from Australia at Wanganui during OIS 17–9 therefore indicate that warm‐water taxa were transported to New Zealand during interglacial maxima after the MPT. The migrants provide the first molluscan biostratigraphy at the OIS scale. The Castlecliffian/Nukumaruan bo...

Abstract: Drilling during Leg 119 (1988) and Leg 188 (2000; Sites 1165–1167) of the Ocean Drilling Program (ODP) provides direct evidence for longand short-term changes in Cenozoic paleoenvironments in the Prydz Bay region. Cores from across the continental margin reveal that in preglacial times the present shelf was an alluvial plain system with austral conifer woodland in the Late Cretaceous that changed to cooler Nothofagus rainforest scrub by the middle to late Eocene (Site 1166). Earliest recovered evidence of nearby mountain glaciation is seen in late Eocene–age grain textures in fluvial sands. In the late Eocene to early Oligocene, Prydz Bay permanently shifted from being a fluviodeltaic complex to an exclusively marine continental shelf environment. This transition is marked by a marine flooding surface later covered by overcompacted glacial sediments that denote the first advance of the ice sheet onto the shelf. Cores do not exist for the early Oligocene to early Miocene, and seismic data are used to infer the transition from a shallow to normal depth prograding continental shelf with submarine canyons on the slope and channel/levees on the rise. Cores from the continental rise at Site 1165 show long-term (millions of years) early Miocene and younger decreases in sedimentation rates as well as short-term (Milankovitch periods) cyclicity between principally biogenic and terrigenous sediment supply—resulting from the cyclic presence of onshore glaciers and changes in ocean circulation. Middle Miocene transitions include rapid decreases in sedimenta1Cooper, A.K., and O’Brien, P.E., 2004. Leg 188 synthesis: transitions in the glacial history of the Prydz Bay region, East Antarctica, from ODP drilling. In Cooper, A.K., O’Brien, P.E., and Richter, C. (Eds.), Proc. ODP, Sci. Results, 188, 1–42 [Online]. Available from World Wide Web: . [Cited YYYY-MM-DD] 2Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Building 320, Room 118, Stanford CA 94305, USA. akcooper@pangea.stanford.edu 3Geoscience Australia, GPO Box 378, Canberra ACT 2601, Australia. Initial receipt: 3 July 2003 Acceptance: 28 April 2004 Web publication: 20 July 2004 Ms 188SR-001 A.K. COOPER AND P. O’BRIEN LEG 188 SYNTHESIS: GLACIAL HISTORY OF THE PRYDZ BAY REGION 2 tion rates, increased ice-rafted debris, shifts in clays and other minerals, and regional erosion of the slope and rise. These transitions may reflect enhanced glacial erosion and reduced glacial meltwater from progressively colder ice. At this time, seismic data show that depocenters began to shift from the outer continental rise to the base of the continental slope coincident with the initial stages of the glacial erosion and overdeepening of the continental shelf. During the late Miocene to early Pliocene there was a transition to greater subglacial activity on the shelf and more pronounced cyclic facies variations on the continental rise. At this time, severe glacial morphologies initiated on the shelf with the erosion of Prydz Channel and other troughs by fast-moving ice and the deposition of overcompacted glacial diamictons by slow-moving ice on adjacent banks. The Prydz trough-mouth fan also began to form with alternating deposition of debris flows (ice at shelf edge) and muddy units (reduced ice) (Site 1167). The fan also records a transition during the late Pleistocene for times younger than 780 k.y. when short-term glacial variations continued but ice reached the shelf edge only a few times. Both short-term and long-term transitions characterize the Cenozoic evolution of the Prydz Bay region from the Cretaceous nonglacial to late Neogene full-glacial paleoenvironments. These transitions are known only from ODP cores, and further insights will require additional drilling. INTRODUCTION Three sites (1165, 1166, and 1167) were drilled during Ocean Drilling Program (ODP) Leg 188 in the Prydz Bay region of Antarctica (Fig. F1) to achieve three principal objectives: 1. Date the earliest evidence of glacial activity in the region and decipher the Paleogene environment of Antarctica by drilling on the continental shelf; 2. Link Oligocene and younger events in the East Antarctic Ice Sheet with changes in the Southern Ocean by drilling a transect of holes across the continental shelf, slope, and rise; and 3. Acquire a record of late Miocene and younger ice advances to the shelf edge and interglacial periods by drilling into the troughmouth fan built by advances of the Lambert Glacier–Amery Ice Shelf. Leg 188 is also notable for the many technical advances made in successfully acquiring the desired cores under unusually harsh operating conditions. This was the first Antarctic drilling leg to work without the aid of a support ship and conduct logging-while-drilling operations in polar-glacial sediments. Site 1165 is the deepest drill hole in Antarctica to date, and Site 1167 is the first drill hole to sample deeply into a polar trough-mouth fan. These accomplishments and others lay the path for future Antarctic one-ship drilling operations to more fully decipher south polar paleoenvironmental history. The East Antarctic Ice Sheet has a long-lived record of growth and decay since the Paleogene (Barron et al., 1991) and is now the largest ice mass on Earth. The ice sheet has been a significant driving force in global climates and sea level changes and in ocean and atmospheric circulation. The long-term cooling of the world’s oceans and climates over F1. Prydz Bay region, p. 28.

Abstract: Climate in northeast Qinghai–Tibetan Plateau is characterised by the alternation of summer and winter monsoon circulation, which is generated by thermodynamic and kinetic effects of the immense plateau. The Plateau Monsoon system during the recent geological past has been investigated through a 44-m loess–paleosol section and a 17-m well to obtain the Plateau Monsoon climate changes during the last glacial–interglacial cycle. Thermoluminescence (TL) and optically stimulated luminescence (OSL) methods, as well as field observations and stratigraphic correlation, are used to date the deposit. Magnetic susceptibility (MS), frequency-dependent magnetic susceptibility (FMS), and calcium carbonate content, which are regarded as proxy indicators of strength of the Plateau Summer Monsoon (PSM), are measured. Measurement of grain size distribution, which is regarded as a proxy index of strength of the Plateau Winter Monsoon (PWM), is also carried out. The results show that changes of the unique Plateau Monsoon system during the past 130 kyr are associated with the glacial and interglacial alternations in the Northern Hemisphere. The PSM was unusually strengthened during a period matching the marine oxygen isotope stage 5e (OIS 5e), but it was weak during the OIS 5a and OIS 5c, and was close to that of the OIS 3. The PWM was significantly depressed during OIS 3, and was as weak as that in the Holocene. The PWM and PSM circulations were not always coupled during the last glacial cycle. Changes of the Plateau Monsoon system did not always parallel the SE Asian monsoon, although linkage between them existed to some extent. There are millennial-scale variations in the Plateau Monsoon system, but this is not further discussed in this paper.

Abstract: At 10 locations on the Central Loess Plateau (CLP), the grain-size distribution of the loess was analysed in order to increase our understanding of the dynamics of the aeolian system that was driving the deposition of the huge amounts of loess. We focused on the upper 18 to 40 m of the loess sections representing the previous 250 ky. After chronostratigraphical subdivision of each section, the grain-size variations of the different loess sections have been compared with each other in two north–south transects. As a result, the regional variability of the grain size over the Central Loess Plateau is obtained for different periods in the last 250,000 years. This variability is linked to both climatic changes and topographic characteristics. Steep grain-size gradients were present during glacial periods with very large variation in deposition quantity, while dust deposition over the Plateau was much more uniform during interglacial periods, with regard to both grain size and dust flux. It means that the dust deposition was very sensitive to climate variations in the northern part of the Central Loess Plateau. In contrast, the variability in loess deposition between glacials and interglacials was decreasing towards the south.

Abstract: The last 10,000 years have been characterized by distinctly stable climates. For the earlier glacial period (up to 125,000 years ago), climate records show long-lasting large-amplitude oscillations, generally known as Dansgaard– Oeschger (D/O) or Heinrich events. These fluctuations are believed to be a result of freshwater anomalies in the North Atlantic which dramatically reduce the transport of the meridional overturning cell (MOC). They are followed by a recovery of the MOC. Here, we propose that such long lasting instabilities in the meridional circulation are only possible during glacial periods when the Bering Strait (BS) is closed. An analytical ocean model which includes both wind and thermohaline processes) is used to show that, during interglacial periods (when the BS is open) perturbations in North Atlantic Deep Water (NADW) formation are quickly damped out. This new mechanism involves the strong winds in the Southern Ocean (SO) which, with an open BS, quickly [O(1–10 years)] flush any large low salinity anomalies out of the Atlantic and into the Pacific Ocean. During glacial periods, the stabilizing effect is prevented by the closure of the BS which traps the anomalies within the Atlantic, causing long lasting perturbations. We also show that no continuous fresh-water flux is needed in order to keep the collapsed MOC froma recovery in the closed basin case, but a relatively large continuous flux of 0:19 Sv is required in order to keep the collapsed state in the open BS case. With a smaller freshwater transport, the open MOC quickly recovers. This also indicates that an open BS is more stable than the closed BS case. Process-oriented numerical simulations using idealized geometry in a two-layer ocean support our analytical solutions and show that the flushing mechanism is active even when the shallow BS sill is included. r 2004 Elsevier Ltd. All rights reserved.