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The last deglacial was marked by tremendous changes in ocean temperature and circulation as well as atmospheric CO 2 and 14 C. We employed the “ 14 C plateau-tuning technique” to a centennial-scale planktic 14 C record of core MD08-3180 retrieved S.W. of the Azores Islands at ∼3060 m water depth to establish both a new standard of absolute age control and a record of past 14 C reservoir ages of ocean surface waters. Both δ 18 O minima of G. bulloides and high planktic reservoir ages of ∼1600 to 2170 yr suggest two major melt water incursions that reached from the Labrador Sea up to the subtropics over Heinrich Stadial 1 (HS-1). In parallel, we established a record of (apparent) benthic ventilation ages that add the planktic 14 C reservoir ages together with the benthic-planktic 14 C age difference at the site and time of deposition, a sum finally adjusted to past changes in atmospheric 14 C that occurred since the time of deep-water formation. Near the Azores apparent deep-water ages of the Last Glacial Maximum were as low as 340–740 yr, which suggests a lateral advection of young North Atlantic Deep Waters (NADW) from subpolar regions south of Iceland, in harmony with recent model simulation and in contrast to a widely assumed major shoaling of glacial deep-water formation. During HS-1, local benthic ventilation ages increased up to 2200–2550 yr, thus suggest an incursion of old southern-source deep waters, an unstable regime that was interrupted by brief pulses of NADW incursion near 16, 15.6 cal. ka, and most salient, near 14.9/14.7 ka. [ABSTRACT FROM AUTHOR]

During glacial periods of the Late Pleistocene, an abundance of proxy data demonstrates the existence of large and repeated millennial-scale warming episodes, known as Dansgaard-Oeschger (DO) events. This ubiquitous feature of rapid glacial climate change can be extended back as far as 800,000 years before present (bp) in the ice core record, and has drawn broad attention within the science and policy-making communities alike. Many studies have been dedicated to investigating the underlying causes of these changes, but no coherent mechanism has yet been identified. Here we show, by using a comprehensive fully coupled model, that gradual changes in the height of the Northern Hemisphere ice sheets (NHISs) can alter the coupled atmosphere-ocean system and cause rapid glacial climate shifts closely resembling DO events. The simulated global climate responses-including abrupt warming in the North Atlantic, a northward shift of the tropical rainbelts, and Southern Hemisphere cooling related to the bipolar seesaw-are generally consistent with empirical evidence. As a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets, minor changes in the height of the NHISs and the amount of atmospheric CO2 can trigger the rapid climate transitions via a local positive atmosphere-ocean-sea-ice feedback in the North Atlantic. Our results, although based on a single model, thus provide a coherent concept for understanding the recorded millennial-scale variability and abrupt climate changes in the coupled atmosphere-ocean system, as well as their linkages to the volume of the intermediate ice sheets during glacials. [ABSTRACT FROM AUTHOR]

During the last glacial, major abrupt climate events known as Heinrich events left distinct fingerprints of ice rafted detritus, and are thus associated with iceberg armadas; the release of many icebergs into the North Atlantic Ocean. We simulated the impact of a large armada of icebergs on glacial climate in a coupled atmosphere-ocean model. In our model, dynamic-thermodynamic icebergs influence the climate through two direct effects. First, melting of the icebergs causes freshening of the upper ocean, and second, the latent heat used in the phase-transition of ice to water results in cooling of the iceberg surroundings. This cooling effect of icebergs is generally neglected in models. We investigated the role of the latent heat by performing a sensitivity experiment in which the cooling effect is switched off. At the peak of the simulated Heinrich event, icebergs lacking the latent heat flux are much less efficient in shutting down the meridional overturning circulation than icebergs that include both the freshening and the cooling effects. The cause of this intriguing result must be sought in the involvement of a secondary mechanism: facilitation of sea-ice formation, which can disturb deep water production at key convection sites, with consequences for the thermohaline circulation. We performed additional sensitivity experiments, designed to explore the effect of the more plausible distribution of the dynamic icebergs' melting fluxes compared to a classic hosing approach with homogeneous spreading of the melt fluxes over a section in the mid-latitude North Atlantic (NA) Ocean. The early response of the climate system is much stronger in the iceberg experiments than in the hosing experiments, which must be a distribution-effect: the dynamically distributed icebergs quickly affect western NADW formation, which synergizes with direct sea-ice facilitation, causing an earlier sea-ice expansion and climatic response. Furthermore, compared to dynamic-thermodynamic icebergs, a homogeneous hosing overestimates the fresh water flux in the Eastern Ruddiman belt, causing a fresh anomaly in the Eastern North Atlantic, leading to a delayed recovery of the circulation after the event. [ABSTRACT FROM AUTHOR]

A striking characteristic of glacial climate in the North Atlantic region is the recurrence of abrupt shifts between cold stadials and mild interstadials. These shifts have been associated with abrupt changes in Atlantic Meridional Overturning Circulation (AMOC) mode, possibly in response to glacial meltwater perturbations. However, it is poorly understood why they were more clearly expressed during Marine Isotope Stage 3 (MIS3, ~60-27 ka BP) than during Termination 1 (T1, ~18-10 ka BP) and especially around the Last Glacial Maximum (LGM, ~23-19 ka BP). One clue may reside in varying climate forcings, making MIS3 and T1 generally milder than LGM. To investigate this idea, we evaluate in a climate model how ice sheet size, atmospheric greenhouse gas concentration and orbital insolation changes between 56 ka BP (=56k), 21k and 12.5k affect the glacial AMOC response to additional freshwater forcing. We have performed three ensemble simulations with the earth system model LOVECLIM using those forcings. We find that the AMOC mode in the mild glacial climate type (56k and 12.5k), with deep convection in the Labrador Sea and the Nordic Seas, is more sensitive to a constant 0.15 Sv freshwater forcing than in the cold type (21k), with deep convection mainly south of Greenland and Iceland. The initial AMOC weakening in response to freshwater forcing is larger in the mild type due to an early shutdown of Labrador Sea deep convection, which is completely absent in the 21k simulation. This causes a larger fraction of the freshwater anomaly to remain at surface in the mild type compared to the cold type. After 200 years, a weak AMOC is established in both climate types, as further freshening is compensated by an anomalous salt advection from the (sub-)tropical North Atlantic. However, the slightly fresher sea surface in the mild type facilitates further weakening of the AMOC, which occurs when a surface buoyancy threshold (−0.6 kg m surface density anomaly to the 56k reference state) is stochastically crossed in the Nordic Seas. While described details are model-specific, our results imply that a more northern location of deep convection sites during milder glacial times may have amplified frequency and amplitude of abrupt climate shifts. [ABSTRACT FROM AUTHOR]

The Community Climate System Model version 3, (CCSM3) is used to investigate the effect of the high latitude North Atlantic subsurface ocean temperature response in idealized freshwater hosing experiments on the strength of the Atlantic meridional overturning circulation (AMOC). The hosing experiments covered a range of input magnitudes at two locations in a glacial background state. Subsurface subpolar ocean warms when freshwater is added to the high latitude North Atlantic (NATL cases) and weakly cools when freshwater is added to the Gulf of Mexico (GOM cases). All cases show subsurface ocean warming in the Southern Hemisphere (SH). The sensitivity of the AMOC response to the location and magnitude of hosing is related to the induced subsurface temperature response, which affects the magnitude of the large-scale meridional pressure gradient at depth through the effect on upper ocean density. The high latitude subsurface warming induced in the NATL cases lowers the upper ocean density in the deepwater formation region enhancing a density reduction by local freshening. In the GOM cases the effect of SH warming partially offsets the effect of the high latitude freshening on the meridional density gradient. Following the end of hosing, a brief convective event occurs in the largest NATL cases which flushes some of the heat stored in the subsurface layers. This fuels a rapid rise in AMOC that lasts less than a couple of decades before subsequent freshening from increases in precipitation and sea ice melt reverses the initial increase in the meridional density gradient. Thereafter AMOC recovery slows to the rate found in comparable GOM cases. The result for these glacial transient hosing experiments is that the pace of the longer recovery is not sensitive to location of the imposed freshwater forcing. [ABSTRACT FROM AUTHOR]

The meridional overturning circulation (MOC) of the Atlantic Ocean is considered to be one of the most important components of the climate system. This is because its warm surface currents, such as the Gulf Stream, redistribute huge amounts of energy from tropical to high latitudes and influence regional weather and climate patterns, whereas its lower limb ventilates the deep ocean and affects the storage of carbon in the abyss, away from the atmosphere. Despite its significance for future climate, the operation of the MOC under contrasting climates of the past remains controversial. Nutrient-based proxies and recent model simulations indicate that during the Last Glacial Maximum the convective activity in the North Atlantic Ocean was much weaker than at present. In contrast, rate-sensitive radiogenic 231Pa/230Th isotope ratios from the North Atlantic have been interpreted to indicate only minor changes in MOC strength. Here we show that the basin-scale abyssal circulation of the Atlantic Ocean was probably reversed during the Last Glacial Maximum and was dominated by northward water flow from the Southern Ocean. These conclusions are based on new high-resolution data from the South Atlantic Ocean that establish the basin-scale north to south gradient in 231Pa/230Th, and thus the direction of the deep ocean circulation. Our findings are consistent with nutrient-based proxies and argue that further analysis of 231Pa/230Th outside the North Atlantic basin will enhance our understanding of past ocean circulation, provided that spatial gradients are carefully considered. This broader perspective suggests that the modern pattern of the Atlantic MOC-with a prominent southerly flow of deep waters originating in the North Atlantic-arose only during the Holocene epoch. [ABSTRACT FROM AUTHOR]

Abstract: During the late Pliocene global climate changed drastically as the Northern Hemisphere glaciation (NHG) intensified. It remains poorly understood how the North Atlantic Current (NAC) changed in strength and position during this time interval. Such changes may alter the amount of northward heat transport and therefore have a large impact on climate in the circum-North Atlantic region and the growth of Northern Hemisphere ice sheets. Using the alkenone biomarker we reconstructed orbitally resolved sea surface temperature (SST) and productivity records at Integrated Ocean Drilling Project (IODP) Expedition 306 Site U1313 during the late Pliocene and early Pleistocene, 3.68–2.45million years ago (Ma). Before 3.1Ma, SSTs in the mid-latitude North Atlantic were up to 6°C higher than the present and surface water productivity was low, indicating that an intense NAC transported warm, nutrient-poor surface waters northwards. Starting at 3.1Ma, surface water characteristics changed drastically as the NHG intensified. During glacial periods at the end of the late Pliocene and beginning of the Pleistocene, SSTs decreased and surface water productivity in the mid-latitude North Atlantic increased, reflecting a weakened influence of the NAC at our site. At the same time the increase in surface productivity suggests that the Arctic Front (AF) reached down into the mid-latitudes. We propose that during the intensification of the NHG the NAC had an almost pure west to east flow direction in glacials and did not penetrate into the higher latitudes. The diminished northward heat transport would have led to a cooling of the higher latitudes, which may have encouraged the growth of large continental ice sheets in the Northern Hemisphere. [ABSTRACT FROM AUTHOR]

The last glacial period was punctuated by rapid climate shifts, known as Dansgaard–Oeschger events, with strong imprint in the North Atlantic sector suggesting that they were linked with the Atlantic meridional overturning circulation. Here an idealized single-hemisphere three-dimensional ocean–atmosphere–sea ice coupled model is used to explore the possible origin of the instability driving these abrupt events and to provide a plausible explanation for the relative stability of the Holocene. Focusing on the physics of noise-free millennial oscillations under steady external (solar) forcing, it was shown that cold climates become unstable, that is, exhibit abrupt millennial-scale transitions, for significantly lower freshwater fluxes than warm climates, in agreement with previous studies making use of zonally averaged coupled models. This fundamental difference is a direct consequence of the weaker stratification of the glacial ocean, mainly caused by upper-ocean cooling. Using a two-hemisphere configuration of a coupled climate model of intermediate complexity, it is shown that this result is robust to the added presence of a bottom water mass of southern origin. The analysis reveals that under particular conditions, a pronounced interdecadal variability develops during warm interstadials. While the nature of the instability driving the millennial oscillations is identical to that found in ocean models under mixed boundary conditions, these interstadial–interdecadal oscillations share the same characteristics as those previously found in ocean models forced by fixed surface fluxes. The wind stress forcing is shown to profoundly affect both the properties and bifurcation structure of thermohaline millennial oscillations across a wide range of variation of freshwater forcing. In particular, it is shown that the wind stress forcing favors the maintenance of thermally direct meridional overturning circulations during the cold stadial phases of Dansgaard–Oeschger cycles. [ABSTRACT FROM AUTHOR]

Abstract: Total organic carbon (TOC), δ 13C values of TOC (δ 13Corg) and glycerol dialkyl glycerol tetraethers (GDGTs) were analysed for a sediment core from the North Atlantic covering the last 30kyr to investigate organic matter deposition due to ice rafting. TOC content was low in sediments representing glacial times (0.2–0.4%) and even lower in Holocene sediments (< 0.2%). The δ 13Corg values varied from −24‰ in glacial times to −20‰ at the start of the Holocene (8kycal BP), with negative excursions to −26‰ during Heinrich events. The δ 13Corg values correlated non-linearly with % ice rafted debris in the sediments, suggestive of supply of continental organic matter by ice rafting. GDGT analysis revealed varying amounts of soil-derived branched GDGTs and the marine isoprenoid GDGT, crenarchaeol, which is expressed in the branched isoprenoid tetraether (BIT) index. The BIT index was relatively high (0.3) in sediments deposited during the glacial compared to those laid down at the start of the Holocene (0.1), suggesting enhanced delivery of terrestrial OM to the North Atlantic by ice rafting, in agreement with the δ 13Corg results. This was confirmed by analysis of the 14C content of TOC, which indicated substantially older ages (1–9kyr) than the sediment age inferred from planktonic foraminifera. BIT indices and δ 13Corg values show phase offsets during Heinrich events, suggestive of differences either in timing of supply or of different sources of organic matter, i.e. soil organic matter and ancient mature sedimentary organic matter. Alternatively it may reflect changing contributions of source areas. [Copyright &y& Elsevier]

Quantifying past circulation is a vital part of testing our understanding of the modern and future climate system. The isotopic composition of neodymium (Nd) in marine precipitates has considerable promise as a recorder of past circulation patterns, but its robust application requires knowledge of the end-member compositions in order to correctly deconvolute a downstream signal. We show here, using in situ, high temporal resolution analyses of ferromanganese crusts from the North Atlantic, that the Nd isotopic composition of deep water during times of much more extensive Northern Hemisphere ice cover was no different than the modern-day interglacial value. This result is surprising, but greatly simplifies the use of Nd isotopes as tracers of the strength and patterns of circulation in the Atlantic in the past. [ABSTRACT FROM AUTHOR]

Published reconstructions of last glacial maximum (LGM) sea surface temperatures and sea ice extent differ significantly. We here test the sensitivity of simulated North Atlantic climates to two different reconstructions by using these reconstructions as boundary conditions for model experiments. An atmospheric general circulation model has been used to perform two simulations of the (LGM) and a modern-day control simulation. Standard (CLIMAP) reconstructions of sea ice and sea surface temperatures have been used for the first simulation, and a set of new reconstructions in the Nordic Seas/Northern Atlantic have been used for the second experiment. The new reconstruction is based on 158 core samples, and represents ice-free conditions during summer in the Nordic Seas, with accordingly warmer sea surface temperatures and less extensive sea ice during winter as well. The simulated glacial climate is globally 5.7 K colder than modern day, with the largest changes at mid and high latitudes. Due to more intense Hadley circulation, the precipitation at lower latitudes has increased in the simulations of the LGM. Relative to the simulation with the standard CLIMAP reconstructions, reduction of the sea ice in the North Atlantic gives positive local responses in temperature, precipitation and reduction of the sea level pressure. Only very weak signatures of the wintertime Icelandic Low occur when the standard CLIMAP sea surface temperature reconstruction is used as the lower boundary condition in LGM. With reduced sea ice conditions in the Nordic Seas, the Icelandic Low becomes more intense and closer to its present structure. This indicates that thermal forcing is an important factor in determining the strength and position of the Icelandic Low. The Arctic Oscillation is the most dominant large scale variability feature on the Northern Hemisphere in modern day winter climate. In the simulation of the LGM with extensive sea ice this pattern is significantly changed and represents no systematic large scale variability over the North Atlantic. Reduction of the North Atlantic sea ice extent leads to stronger variability in monthly mean sea level pressure in winter. The synoptic variability appears at a lower level in the simulation when standard reconstructions of the sea surface in the LGM are used. A closer inspection of storm tracks in this model experiment shows that that the synoptic lows follow a narrow band along the ice edge during winter. The trajectories of synoptic lows are not constrained to the sea ice edge to the same degree when the sea ice extent is reduced. Seasonally open waters in the Nordic Seas in the new reconstruction apparently act as a moisture source, consistent with the current understanding of the rapid growth of the Fennoscandian and Barents Ice Sheets, during the LGM. The signal from the intensified thermal forcing in the North Atlantic in Boreal winter is carried zonally by upper tropospheric waves, and thus generates non-local responses to the changed sea ice cover. [ABSTRACT FROM AUTHOR]

Well-dated multidecadal- to centennial-scale sediment records from the subarctic northwest Pacific show that the early deglacial 18.5-15.0 ka was marked by 3 pronounced short-term warmings of ∼5 °C. They lasted 500-1500 yr each and were coeval with early to late stages of cold Heinrich event 1 in the North Atlantic. These regional climate windows may have promoted a pre-Clovis emigration of people from the cold-arid monsoon climate in East Asia to the climatically more favorable, then-emerged Beringian and Aleutian shelf regions and the Americas, as suggested by archeological findings. [ABSTRACT FROM AUTHOR]

The McGill Paleoclimate Model-2 (MPM-2) is employed to study climate–thermohaline circulation (THC) interactions in a pre -industrial climate, with a special focus on the feedbacks on the THC from other climate system components. The MPM-2, a new version of the MPM, has an extended model domain from 90S to 90N, active winds and no oceanic heat and freshwater flux adjustments. In the MPM-2, there are mainly two stable modes for the Atlantic meridional overturning circulation (MOC) under the ‘present-day’ forcing (present-day solar forcing and the pre-industrial atmospheric CO2 level of 280 ppm). The ‘on’ mode has an active North Atlantic deep water formation, while the ‘off’ mode has no such deep water formation. By comparing the ‘off’ mode climate state with its ‘on’ mode analogue, we find that there exist many large differences between the two climate states, which originate from large changes in the oceanic meridional heat transports. By suppressing or isolating each process associated with a continental ice sheet over North America, sea ice, the atmospheric hydrological cycle and vegetation, feedbacks from these components on the Atlantic MOC are investigated. Sensitivity studies investigating the role of varying continental ice growth and sea ice meridional transport in the resumption of the Atlantic MOC are also carried out. The results show that a fast ice sheet growth and an enhanced southward sea ice transport significantly favor the resumption of the Atlantic MOC in the MPM-2. In contrast to this, the feedback from the atmospheric hydrological cycle is a weak positive one. The vegetation-albedo feedback could enhance continental ice sheet growth and thus could also favor the resumption of the Atlantic MOC. However, before the shut-down of the Atlantic MOC, feedbacks from these components on the Atlantic MOC are very weak. [ABSTRACT FROM AUTHOR]

Abstract: During the glacial–interglacial transition that began subsequent to the Last Glacial Maximum approximately 21,000 calendar years ago, globally averaged (eustatic) sea-level rose by approximately 120m as climate warmed to its current (Holocene) state. This rise of relative sea-level (RSL) did not occur smoothly, however, but was characterized by the occurrence of one or more episodes of extremely rapid increase. The most extreme of these events has come to be referred to as meltwater pulse 1a, and was initially identified in the coral based record of RSL history from the island of Barbados in the Caribbean Sea. Although it has usually been assumed that this episode of rapid RSL rise was derivative of a partial collapse of the northern hemisphere ice sheets, it has recently been suggested that this pulse could have originated in a dramatic melt-back of the Antarctic Ice Sheet. In this paper the arguments presented in favour of the southern hemisphere source are revisited in order to assess the plausibility of this alternative scenario. Based upon the analyses presented, it is concluded that the evidence previously provided in support of the southern hemisphere scenario is in fact unable to rule out an entirely northern hemisphere source for the meltwater pulse 1a. Since explicit evidence does exist that both the Laurentide and Fennoscandian ice sheets contributed to this event and that Antarctic ice sheet melting occurred significantly later, the southern hemisphere appears not to have been a prime mover of northern hemisphere events. [Copyright &y& Elsevier]

Abstract: Rapid climatic changes, the rhythm of which is fully described in Greenland deep ice cores, are also very well documented in the ocean (in particular in the North Atlantic) and on the continent. At these timescales, ice cores, deep sea-cores and continental records are still difficult to precisely synchronize. From the GRIP results, we show how a multiparametric ice core study allows us to circumvent this difficulty. The co-isotopic analysis of the deuterium and oxygen-18 concentrations in ice gives access to temperature both at the site (central Greenland) and in the evaporative moisture source region (North Atlantic). Rapid changes occur more or less rapidly from one event to the next, but are generally simultaneous. Surprisingly, our results suggest that the site and source temperatures vary in antiphase. This implies a drastic reorganization of the hydrological cycle in the North Atlantic at the time of rapid changes. To cite this article: J. Jouzel et al., C. R. Geoscience 337 (2005). [Copyright &y& Elsevier]

Quantitative and qualitative analyses of nannofossil assemblages from ODP Site 999 in the Caribbean Sea were performed to reveal changes in upper seawater structures and implications for climatic changes during the last 300,000 years. Overall, there is an inverse relationship in stratigraphic fluctuations between the absolute abundance (AA) of a lower photic taxon, Florisphaera profunda, and δ18O; this fluctuation pattern is considered to represent climatic changes in the Subtropical Under Water (SUW) in the Caribbean. Cross-spectral analysis demonstrates that the SUW was characterized by nutrient-rich water during interglacials; changes in orbitally driven gyre circulation system strongly affected fluctuations in the SUW in the Caribbean. Conversely, the surface water was enriched in nutrients during glacials as the result of increased terrigenous materials and shallowing of the thermocline based on changes of the N ratio (abundance of reticulofenestrids relative to F. profunda) and results of cross-spectral analysis between them and δ18O. The relationship between the thermocline variation and the ice volume fluctuation suggests that changes in the subtropical gyre circulation system in the North Atlantic have had stronger influences on the Caribbean thermocline variations and there may be a little contribution of climatic fluctuations that originated in the Southern Ocean to the Caribbean Sea.A large floral turnover in nannofossil assemblages between oxygen isotope stages 6 and 5 was observed in Hole 999A, which corresponds to Termination II. On the basis of floral compositions, photosynthetic primary productions had been more active than today before Termination II. [Copyright &y& Elsevier]

The climate of the last glacial period was extremely variable, characterized by abrupt warming events in the Northern Hemisphere, accompanied by slower temperature changes in Antarctica and variations of global sea level. It is generally accepted that this millennial-scale climate variability was caused by abrupt changes in the ocean thermohaline circulation. Here we use a coupled ocean-atmosphere-sea ice model to show that freshwater discharge into the North Atlantic Ocean, in addition to a reduction of the thermohaline circulation, has a direct effect on Southern Ocean temperature. The related anomalous oceanic southward heat transport arises from a zonal density gradient in the subtropical North Atlantic caused by a fast wave-adjustment process. We present an extended and quantitative bipolar seesaw concept that explains the timing and amplitude of Greenland and Antarctic temperature changes, the slow changes in Antarctic temperature and its similarity to sea level, as well as a possible time lag of sea level with respect to Antarctic temperature during Marine Isotope Stage 3. [ABSTRACT FROM AUTHOR]

Studies of marine records from the northwestern European shelf and the northern North Atlantic suggest that last interglacial environments were less stable in this area than in the mid-latitude Atlantic. The influx of Atlantic water masses to the northern North Atlantic was generally higher, and the meridional temperature gradient was steeper, during the last interglaciation than during the Holocene. Strong north–south sea-surface-temperature gradients during the early Weichselian indicate a generally low influx of Atlantic water to the northern North Atlantic, even during interstades. [Copyright &y& Elsevier]

Examines the timing of dust fluxes to the North Atlantic Ocean in relation to the climate records from the Vostok ice core in Antartica around the time of the penultimate deglaciation. Pattern and timing of carbon dioxide variations recorded by the Vostok ice core; Measurement of the magnetic remanence acquired at high applied magnetic fields of the sediments; Methodology.

Investigates the presence of millennial-scale variability in climate and deep-water circulation in the western North Atlantic during marine isotope stages (MIS) 11 and 12. Characterization of MIS 11-12; Occurrence of millennial-scale climate instability and associated changes in North Atlantic Deep Water (NADW); Glacial-interglacial climate variability.

Focuses on the effects of changes in sea-surface temperatures of the North Atlantic Ocean prior to the Heinrich ice rafting event. Possible preexistence of glacial warming as compared to extensive climactic warming ca. 15.9 ka; Environmental effects of cold-ocean conditions on proximal terrestrial climates.

Presents evidence for a general relationship between low-latitude monsoonal climate variability and the rapid temperature fluctuations of high northern latitudes that are recorded in the Greenland ice records. How periods of lowered southwest monsoonal intensity are associated with intervals of high-latitude atmospheric cooling and the injection of melt water into the North Atlantic basin; Implications of the evidence.

Focuses on the influence of ocean current circulation changes in the glacial climates in the North Atlantic Ocean ranging along the Faroe Island-Shetland Island channel. Glacial sections correlating with current oscillations; Isotopic evidences of the correlation.

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.

Presents high-resolution records of foraminiferal assemblages and ice-rafted detritus from North Atlantic cores for the interval 65,000 to 135,000 years ago. Extension of surface-ocean record to Eemian period; Correlation with Greenland Ice Core Project (GRIP) ice-cores.

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.

The article discusses a research study by E. Bohm and colleagues on the link between ocean paleocirculation and climate change. Topics noted include the multimode modes concept of ocean circulation during the last glacial cycle, production of deep water in the North Atlantic, ratio of protactinium to thorium isotopes, and stability of oceanic heat transport.

One of the most commonly accepted views of the relation between climate and ocean circulation is known popularly as the "global conveyer," meaning that deep water forms in the North Atlantic Ocean in large amounts during interglacial periods and in smaller volumes during glacial intervals, producing significant changes in the rate of large-scale ocean circulation. Much of the evidence for this belief is based on studies of the carbon isotopic composition of benthic foraminifera, i.e., those that lived on the sea floor over the last glacial/interglacial cycle. Researchers examine this proposition in more detail by comparing and contrasting carbon isotopic profiles from seven sites in the North Atlantic covering the last 27 glacial cycles, a time span of nearly 2 million years.