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High latitude deep water upwelling has the potential to control global climate over glacial timescales through the biological pump and ocean-atmosphere CO 2 exchange. However, there is currently a lack of continuous long nutrient upwelling records with which to assess this mechanism. Here we present geochemical proxy records for nutrient upwelling and glacial North Pacific Intermediate Water (GNPIW) formation in the Bering Sea over the past 850 kyr, which demonstrates that glacial periods were characterised by reduced nutrient upwelling, when global atmospheric CO 2 and temperature were also lowered. We suggest that glacial expansion of sea ice in the Bering Sea, and the simultaneous expansion of low nutrient GNPIW, inhibited vertical mixing and nutrient supply across the subarctic Pacific Ocean. Our findings lend support to the suggestion that high latitude sea ice and the resultant intermediate water formation, modulated deep water upwelling and ocean-atmosphere CO 2 exchange on glacial-interglacial timescales. • Increased Bering Sea sea ice caused expansion of intermediate water in glacials. • Intermediate water expansion inhibited deep water nutrient supply to surface waters. • Region contributed to global ocean-air CO 2 exchange on glacial timescales. • Tight correlation between subarctic nutrient upwelling and global CO 2. [ABSTRACT FROM AUTHOR]

The present-day ocean ventilation in the Arctic Mediterranean (Nordic Seas and Arctic Ocean), via transformation of northward inflowing warm Atlantic surface water into cold deep water, affects regional climate, atmospheric circulation and carbon storage in the deep ocean. Here we study the glacial evolution of the Arctic Mediterranean circulation and its influence on glacial climate using radiocarbon reservoir-age reconstructions on deep-sea cores from the Fram Strait that cover the late glacial period (33,000–20,000 yr ago; 33–20 ka). Our results show high Benthic-Planktic 14C age differences of ∼1500 14C years 33–26.5 ka suggesting significant water column stratification between ∼100–2600 m water depth, and reduction and/or shoaling of deep-water formation. This phase was followed by break-up of the stratification during the Last Glacial Maximum (LGM; 26–20 ka), with Benthic-Planktic 14C age differences of ∼250 14C years, likely due to enhanced upwelling. These ocean circulation changes potentially contributed to the final intensification phase of glaciation via positive cryosphere-atmosphere-ocean circulation-carbon cycle feedbacks. Our data also do not support 'extreme aging' of >6000 14C years in the deep Arctic Mediterranean, and appear to rule out the proposed outflow of very old Arctic Ocean water to the Nordic Seas during the LGM and to the subpolar North Atlantic Ocean during the deglacial period. • Strong ocean stratification in the Fram Strait during the late glacial (33–26 ka). • Breakup of ocean stratification during the LGM (26–20 ka) due to enhanced upwelling. • No extreme aging of >6000 yr in the Arctic Mediterranean as previously suggested. [ABSTRACT FROM AUTHOR]

• A multi-biomarker record from Lake Elsinore, CA sediment core spans 32–9 ka. • Deglacial warming and storm-track shifts are consistent with prior studies nearby. • Plant wax hydrogen isotopes indicate storm-track changes during the last glacial. • Lipids show temperatures varied during the last glacial, including extreme warmth. Reconstructions of past hydroclimate provide a means to understand precipitation responses to global ocean-atmosphere climate dynamics beyond the scope of that in the instrumental record. Late glacial climate was characterized by abrupt variability in ice and ocean dynamics, however the implications for hydroclimate are not as well known. Here we present organic geochemical proxy evidence for precipitation isotopes based on plant leaf wax hydrogen isotopic compositions (δ D wax) and temperature proxy evidence based upon the branched glycerol dialkyl glycerol tetraethers (brGDGTs), that derive from the membrane lipids of bacteria, each extracted from a sedimentary archive in Lake Elsinore, California spanning 32–9 ka. We add proxy evidence for vegetation and salinity from additional biomarker analyses and compare to prior pollen and sedimentological evidence from the same core. Our record indicates a strong deglacial warming of 10 °C in Lake Elsinore (beginning at 14.5 ka) that accompanied a D-enrichment of precipitation of +90‰ and more C 4 vegetation (12–10 ka), after a cold, wet and C 3 -dominated phase (20–14.5 ka), indicating winter-dominated precipitation during the Last Glacial Maximum and Heinrich Stadial 1. During the late glacial (32–20 ka) we find abrupt variability, with precipitation isotopic shifts (∼70‰) that are independent of temperature swings implicating changes in storm track, rather than local temperature as drivers of the precipitation isotope signal. Temperature is however not irrelevant for hydroclimate: we find extreme warmth at 29.4 ka and 26.8 ka, the latter coincident with existing reports of an extended dry period (27.5–25.5 ka), suggesting a long hot and dry interlude during the generally cooler glacial period. We compare δ D wax with speleothem δ 18 O from Nevada, also within the winter-dominated precipitation region. Our results corroborate the Last Glacial Maximum and deglacial signals, and fill gaps revealing storm-track instability from 32–20 ka, however the pacing and magnitude of the biomarker signals merit cautious interpretation. [ABSTRACT FROM AUTHOR]

Abstract Millennial scale events marked by the contribution of detrital sand are recorded in North Atlantic sediments during the Last Glacial Maximum (LGM), between Heinrich events (HE) 1 and 2, and left their imprint on Laurentian Fan (LF – 43°N) sediments off eastern Canada. The LF counterpart of the well-known detrital events consist of glacial red-brick sediments resulting from subglacial flows separated by olive-grey sediments appears at ∼21.4–19.9 and ∼19.5–18.65 cal kyr BP. High-resolution analyses of diatom assemblages and lithic grains coupled with planktonic oxygen isotopic records reveal that while the red sediment is almost barren of diatoms, foraminifera and lithics (>150 μm), they are abundant in the olive-grey sediment. Diatom assemblages reveal three phases during these events: (1) initial relatively warm/temperate conditions followed by (2) very cold surface water and drifting ice, and (3) a final phase characterized by relatively warmer waters and the appearance of detrital carbonate. Although these events possibly reflect the variability specific to the slope water region, they are likely the response to Atlantic Meridional Overturning Circulation perturbations and ice-sheet instability. Through a chain of mechanisms, meltwater inputs into the North Atlantic led ultimately to an increased volume of tropical waters and part of the heat stored in the subsurface was flushed by a brief convective episode that was not sustained, accounting for the return of cold conditions after the events. The sequence of mechanisms deduced from the paleo data here and elsewhere is consistent with previous modeling results. These data suggest that the detrital events between Heinrich event 1 and 2 may be synchronous across the North Atlantic, and that the LGM was probably not a time of prolonged steady state in the climate system. Highlights • Detailed description oceanographic changes of some LGM detrital events. • Diatom records evidence the presence of relatively warmer waters at the beginning and by the end of the events. • Possible links between detrital events, ice-sheets instability and AMOC perturbations. [ABSTRACT FROM AUTHOR]

Abstract Glacial deposits on the high-altitude, arid southern Central Andean Plateau (CAP), the Puna in northwestern Argentina, document past changes in climate, but the associated geomorphic features have rarely been directly dated. This study provides direct age control of glacial moraine deposits from the central Puna (24°S) at elevations of 3900–5000 m through surface exposure dating with cosmogenic nuclides. Our results show that the most extensive glaciations occurred before 95 ka and an additional major advance occurred between 46 and 39 ka. The latter period is synchronous with the highest lake levels in the nearby Pozuelos basin and the Minchin (Inca Huasi) wet phase on the Altiplano in the northern CAP. None of the dated moraines produced boulder ages corresponding to the Tauca wet phase (24–15 ka). Additionally, the volcanic lithologies of the deposits allow us to establish production ratios at low latitude and high elevation for five different nuclide and mineral systems: 10Be, 21Ne, and 26Al from quartz (11 or 12 samples) and 3He and 21Ne from pyroxene (10 samples). We present production ratios for all combinations of the measured nuclides and cross-calibrated production rates for 21Ne in pyroxene and quartz for the high, (sub-)tropical Andes. The production rates are based on our 10Be-normalized production ratios and a weighted mean of reference 10Be production rates calibrated in the high, tropical Andes (4.02 ± 0.12 at g−1 yr−1). These are, 21Ne qtz : 18.1 ± 1.2 at g−1 yr−1 and 21Ne px : 36.6 ± 1.8 at g−1 yr−1 (En 88 – 94) scaled to sea level and high latitude using the Lal/Stone scheme, with 1 σ uncertainties. As 3He and 26Al have been directly calibrated in the tropical Andes, we recommend using those rates. Finally, we compare exposure ages calculated using all measured cosmogenic nuclides from each sample, including 11 feldspar samples measured for 36Cl, and a suite of previously published production rates. Highlights • The most extensive glaciations in the southern Central Andean Plateau predate 95 ka. • Another glacial advance occurred between 46 and 39 ka during the Minchin wet phase. • None of the dated moraines produced boulder ages corresponding to the Tauca wet phase (24–15 ka). • Production rates were cross-calibrated for five different nuclide/mineral pairs. • Exposure ages from six nuclide/mineral pairs from the same samples were compared. [ABSTRACT FROM AUTHOR]

Dunefields have a great potential to unravel past regimes of atmospheric circulation as they record direct traces of this component of the climate system. Along the Portuguese coast, transgressive dunefields represent relict features originated by intense and frequent westerly winds that largely contrast with present conditions, clearly dominated by weaker northwesterly winds. Optical dating and subsurface stratigraphy document three age clusters indicating main episodes of dune mobilization during: the last termination (20–11.6 ka), Middle Holocene (5.6 ka), and Late Holocene (1.2–0.98 and 0.4–0.15 ka). We find reconstructed windfields to be analogous during all episodes and dominated by strong westerlies. Yet, larger grain size diameters and dune volumes documented for the last termination support amplified patterns compatible with a southward shift and intensification of the North Atlantic westerlies during winters. Conversely, dunes deposited after the Middle Holocene are compatible with more variable windfields and weakened patterns controlled by interannual shifts towards low values of the North Atlantic Oscillation (NAO). This work demonstrates that present windfield regimes in southern Europe are not compatible with past aeolian activity. Indeed, present day analogs indicate that wind intensities compatible with past aeolian activity are rare at present (sediment transport potentials below estimates in the aeolian record), but can occur if the jet stream is diverted to the south (i.e. 30°N with negative NAO index) or if very deep cyclones anchor around 50°N, extending their influence to the western Portuguese coast (relatively low NAO index). However, these conditions represent temporary patterns lasting around one day, while we suggest that the identified episodes of aeolian activity may represent semi-permanent conditions. [ABSTRACT FROM AUTHOR]

One of the key processes for modulating ice flow is the interaction between the ice and the bed, but direct observations of the subglacial environment are sparse and difficult to obtain. In this study we use information from an extensive radio-echo sounding dataset to identify areas of the Greenland Ice Sheet where internal layers have been influenced by near-bed processes. Based on an automatic algorithm for calculating the slope of the internal radio-echo layers, we identify areas with disrupted layer stratigraphy. We find that large parts of the northern portion of the ice sheet are influenced by locally confined mechanisms that produce up-warping or folds in the layer stratigraphy inconsistent with the surface and bed topography. This is particularly evident at the onset of ice streams, although less dynamic areas close to the ice divide also contain imprints of layer disturbances. Our results show that the disturbances are found in many different flow and thermal regimes, and underscore the need to understand the mechanisms responsible for creating them. [ABSTRACT FROM AUTHOR]

The circulation of intermediate waters plays an important role in global heat and carbon transport in the ocean and changes in their distribution are closely tied to glacial–interglacial climate change. Coupled radiocarbon and U/Th measurements on deep-sea Desmophyllum dianthus corals allow for the reconstruction of past intermediate water ventilation. We present a high-resolution time series of Antarctic Intermediate Water radiocarbon from 44 corals spanning 30 ka through the start of the Holocene, encompassing the transition into the Last Glacial Maximum (LGM) and the last deglaciation. Corals were collected south of Tasmania from water depths between 1430 and 1950 m with 80% of them between 1500 and 1700 m, giving us a continuous record from a narrow depth range. The record shows three distinct periods of circulation: the MIS 3–2 transition, the LGM/Heinrich Stadial 1 (extending from ∼22 to 16 kyr BP), and the Antarctic Cold Reversal (ACR). The MIS 3–2 transition and the ACR are characterized by abrupt changes in intermediate water radiocarbon while the LGM time period generally follows the atmosphere at a constant offset, in support of the idea that the LGM ocean was at steady state for its 14 C distribution. Closer inspection of the LGM time period reveals a 40‰ jump at ∼19 ka from an atmospheric offset of roughly 230‰ to 190‰, coincident with an observed 10–15 m rise in sea level and a southward shift of the Subantarctic and Polar Fronts, an abrupt change not seen in deeper records. During the ACR time period intermediate water radiocarbon is on average less offset from the atmosphere ( ∼ 110 ‰ ) and much more variable. This variability has been captured within the lifetimes of three individual corals with changes of up to 35‰ over ∼40 yr, likely caused by the movement of Southern Ocean fronts. This surprising result of relatively young and variable intermediate water radiocarbon during the ACR seems to go against the canonical idea of reduced circulation and ventilation in the south during this time period. However comparisons with other records from the Southern Ocean highlight zonal asymmetries, which can explain the deviation of our Tasmanian record from those in Drake Passage and the eastern Pacific. These signals seen in Tasmanian intermediate water Δ 14 C can also be found in Greenland ice core δ 18 O and East Asian monsoon strength. Throughout the LGM and the deglaciation, our Tasmanian intermediate water record is sensitive to times when the upper and lower cells of the meridional overturning circulation are more or less interconnected, which has important implications for the global climate system on glacial–interglacial time scales. [ABSTRACT FROM AUTHOR]

Abstract: The potential influence of low latitude ocean primary productivity on glacial atmospheric carbon dioxide levels has proven challenging to deduce using mass accumulation rates (MARs) of biogenic particulates in deep sea sediment cores. Benthic foraminiferal B/Ca serves as a proxy for past seawater calcite saturation state, and thereby provides a fresh perspective on this outstanding paleoceanographic problem. Here we employ Cibicidoides wuellerstorfi B/Ca in the Panama Basin region of the eastern equatorial Pacific (EEP) to investigate the nature of deep tropical Pacific carbon storage over the past 50 ka BP. We present evidence for persistently lower deep Panama Basin calcite saturation state, reflecting an increase in total carbon dioxide storage, during the last ice age relative to the Holocene. These results reflect the modification of inflowing deep waters by overlying export productivity, and support the concept of an invigorated glacial EEP soft-tissue pump possibly driven by oceanic nutrient (iron and silica) redistribution. Benthic Cibicidoides spp. carbon-13 is consistent with this conclusion by exhibiting substantially lighter values during glacial time, reflecting the accumulation of metabolic carbon dioxide in the deep tropical Pacific. Counterintuitively, downcore application of the Globorotalia menardii calcite fragmentation index (MFI) reveals enhanced glacial sedimentary calcite preservation in the Panama Basin. Together these results point towards a systematic decoupling of bottom water chemistry from biogenic burial fluxes: the crux of the aforementioned traditional paleoproductivity problem. [Copyright &y& Elsevier]

Abstract: The freshwater budget of the Arctic Ocean is a key component governing the deep water formation in the North Atlantic and the global climate system. We analyzed the isotopic composition of neodymium (ε Nd) in authigenic phases of marine sediments on the Mendeleev Ridge in the western Arctic Ocean spanning an estimated time interval from present to about 75ka BP. This continuous record was used to reconstruct the ε Nd of the polar deep water (PDW) and changes in freshwater sources to the PDW through time. Three deviations in ε Nd from a long term average of −10.2 were identified at estimated 46–51, 35–39 and 13–21ka BP. The estimated 46–51ka BP event can be traced to bursting of ice-dammed lakes accompanying the collapse of the Barents–Kara Ice Sheet, which would have released radiogenic Nd to the eastern Arctic Ocean. The cyclonic surface circulation in the eastern Arctic Ocean must have been stronger than at present for the event to be recorded on the Mendeleev Ridge. For the 35–39 and 13–21ka BP events, it is likely that the Laurentide Ice Sheet (LIS) supplied the unradiogenic freshwater. The configuration of the anticyclonic circulation in the western Arctic was probably similar to today or expanded eastward. Our simple mass balance calculations suggest that large amounts of freshwater were released but due to significant deep water formation within the Arctic Ocean, the effect on the formation of NADW was probably minor. [Copyright &y& Elsevier]

Abstract: A long-standing debate concerning Neogene Antarctic climate in the McMurdo Dry Valleys relies largely on evidence from landscape evolution, glacial modeling and stratigraphy. We provide new evidence from meteoric 10Be for the onset of frozen, hyper-arid conditions on a high elevation (1840m) interfluve at Table Mountain. A simple decay model for the co-occurrence of meteoric 10Be and illuviated clay in cores of ice-cemented glacial sediments indicates that the clays were actively migrating down from the surface in a warm climate until the system froze between 6 and 9Ma. Although this age range may be sensitive to possible interference by in situ produced 10Be, the implied minimum age of 6Ma for the Sirius Group indicates that the Dry Valleys were permanently frozen down to this elevation at this time. The model also suggests denudation rates of 1–6cmMyr−1 since freezing. These data provide an independent test of glacial-stratigraphic evidence used to determine Antarctic paleoclimate. [Copyright &y& Elsevier]

Abstract: Significant uncertainty exists concerning the efficiency of alpine glacial erosion relative to fluvial and hillslope processes. Latitudinal variations in temperature are important for determining the extent of glaciers, as are the rates of tectonic uplift that influence the elevation (and hence temperatures) that glaciers can form. The acute sensitivity of glacial erosion to temperature has complicated previous interpretations because temperatures must be cool enough to maintain ice yet warm enough to allow glacial sliding. Here we quantify the influence of climate and tectonics on glacial landscape evolution with a coupled glacial, fluvial, and hillslope landscape evolution model that systematically explores variations in rock-uplift rate and periodic variations in climate (i.e. glacial–interglacial periods) over million-year time scales. Emphasis is placed on understanding when a particular climate is either more (e.g. “buzzsaw” conditions) or less erosive than its preglacial landscape. Results indicate that the erosional efficiency of glaciers varies as a function of latitudinal controlled temperature and rock-uplift rate. An order of magnitude increase in erosion rates occurs in some scenarios for both localized (valley bottom) erosion and short-term (one glacial period) durations of glaciation. However, when averaged over the entire landscape for 2Ma, increases in glacial erosion are typically less than double that of the preglacial landscape. In some scenarios, average glacial erosion rates are less than preglacial rates due to either small, inefficient glaciers or extensive cold-based glaciation. Model predictions are compared with a compilation of long-term denudation rates from glaciated mountain ranges and indicate models perform well at explaining patterns of glacial erosion efficiency. The findings presented here have clear implications for the impact of glaciations on the evolution of landscapes including: (1) the climatic “window” in which glaciers are more erosive compared to pre-glacial rates; (2) spatial and temporal variations in denudation that can lead to pulses of erosion; and (3) predictions of glacial erosional efficiency at different latitudes. We conclude that latitudinal and elevation dependent variations in temperature control the efficiency of glacial denudation and explain discrepancies between previous studies. [Copyright &y& Elsevier]

Abstract: The calcium carbonate (CaCO3) content of deep-sea sediments in the Pacific Ocean increases during glacials of the late Pleistocene in comparison to interglacials, whereas records of sedimentary CaCO3 in the Atlantic Ocean show an anticorrelated pattern across glacial-interglacial cycles. Here we show that this anticorrelation in inter-ocean CaCO3 cycles arose comparatively recently, at ~1.10million years ago (Ma), during the mid-Pleistocene transition. Before this time, we show that the CaCO3 content of Pacific and Atlantic Ocean sediments experienced in-phase cyclicity, both having ‘Atlantic-style’ phasing with respect to glacial–interglacial cycles. The onset of anticorrelated cyclicity at 1.10Ma involved a twofold switch in the Pacific''s CaCO3 cycles: glacial CaCO3 preservation became consistently better while interglacial preservation became consistently worse. We demonstrate that the cause of this glacial–interglacial ‘mirror imaging’ of Pacific CaCO3 dissolution cyclicity at 1.10Ma was a switching over of the relative ventilation state of abyssal South Pacific waters between glacials and interglacials. Specifically, we suggest that a consistent strengthening of deep water ventilation within the Pacific sector of the Southern Ocean during glacials drove glacial Pacific CaCO3 dissolution to diminish, while a contemporaneous weakening of very well-ventilated ‘upstream’ North Atlantic Deep Water during interglacials drove interglacial Pacific CaCO3 dissolution ‘downstream’ to intensify. We propose that the increased mean alkalinity of the global deep ocean (driven by the geographically and bathymetrically vast Pacific Ocean) during glacials after 1.10Ma may explain part of the drawdown in glacial atmospheric CO2 levels hypothesised to have been linked to the increased severity of these late Pleistocene glacials. [Copyright &y& Elsevier]

Abstract: One of the earliest discoveries in palaeoceanography was the observation in 1935 that the (sub)tropical planktic foraminifer Globorotalia menardii became absent or extremely rare in the Atlantic Ocean during glacials of the late Pleistocene. Yet a mechanistic explanation for G. menardii''s extraordinary biogeographic behaviour has eluded palaeoceanographers for 75years. Here we show that modern G. menardii, along with two other species that also suffer Atlantic population collapses during glacials, track poorly ventilated waters globally in their thermocline habitats. The ventilation states of low latitude thermoclines are ‘set’, to a first order, by intermediate water masses originating at high latitudes. In the modern Atlantic this control on low latitude thermocline ventilation is exerted by relatively poorly ventilated, southern-sourced Antarctic Intermediate Water (AAIW) and sub-Antarctic Mode Water (SAMW). We suggest that the glacial Atlantic foraminifer population collapses were a consequence of a low latitude thermocline that was better ventilated during glacials than it is today, in line with geochemical evidence, and driven primarily by a well-ventilated, northern-sourced intermediate water mass. A ventilation mechanism driving the glacial population collapses is further supported by our new constraints on the precise timing of these species'' Atlantic proliferation during the last deglaciation — occurring in parallel with a wholesale, bipolar reorganisation of the Atlantic''s thermocline-to-abyssal overturning circulation. Our findings demonstrate that a bipolar seesaw in the formation of high latitude intermediate waters has played an important role in regulating the population dynamics of thermocline-dwelling plankton at lower latitudes. [Copyright &y& Elsevier]

Abstract: When calculated with the commonly accepted average Northern Hemisphere production rate, 10Be dates of surface boulders on moraines in the Lago Argentino area of Patagonia are younger than minimum-limiting 14C ages for the same landforms. This disagreement could result from the lack of a regional 10Be production-rate calibration site. To assess this possibility, we here present high-precision measurements of 10Be in samples collected from surface boulders on the Herminita and Puerto Bandera moraine complexes deposited alongside Lago Argentino on the eastern flank of the Andes at 50°S in Patagonia. Together with maximum- and minimum-limiting 14C ages for the two moraine systems, these measurements confine the local 10Be production rate to between 3.60 and 3.82atoms/g/yr (midpoint=3.71±0.11atoms/g/yr) when using a time-dependent scaling method that incorporates a high-resolution geomagnetic model. This range includes upper and lower error bounds of acceptable production rates derived from both the Herminita and the Puerto Bandera sites. The upper limit of this range is more than 12% below the average Northern Hemisphere production rate, as calculated using the same scaling method, given in Balco et al. [Quat. Geochron 3 (2008) 174–195]. Other scaling models yield production rates with similarly large offsets from the Balco et al. (2008) rate. On the other hand, the range of acceptable production rate values determined from Patagonia overlaps at 1σ with, and encompasses, the production rate recently derived in Macaulay valley in the Southern Alps of New Zealand [A. Putnam et al., Quat. Geochron. 5 (2010a) 392–409]. Within uncertainties (i.e., overlap at 1 sigma) this Patagonian production rate range also agrees with a recently determined production rate from low-elevation sites in northeastern North America and northern Norway. When the Macaulay production rate is used to calculate Patagonian exposure dates, 14C and 10Be chronologies are mutually compatible for late-glacial moraine systems. Both chronologies then indicate that outlet glaciers of the Southern Patagonian Icefield achieved a late-glacial maximum in the western reaches of Lago Argentino at 13,000cal. yr BP at the end of the Antarctic Cold Reversal (14,500–12,900cal. yr BP). Outlet glaciers subsequently receded to near present-day ice margins during the Younger Dryas stadial (12,900–11,700cal. yr BP). This general retreat was interrupted about 12,200cal. yr BP when Upsala Glacier constructed an interlobate complex of moraine ridges on Herminita Peninsula. Mountain glaciers in Patagonia and New Zealand, on both sides of the South Pacific Ocean, exhibited a coherent pattern of late-glacial ice-margin fluctuations. [Copyright &y& Elsevier]

Abstract: The seasonal cycle is a fundamental aspect of climate, with a significant influence on mean climate and on human societies. Assessing seasonality in different climate states is therefore important but, outside the tropics, very few palaeoclimate records with seasonal resolution exist and there are currently no glacial-age seasonal-resolution sea-surface-temperature (SST) records at mid to high latitudes. Here we show that both Mg/Ca and oxygen isotope (δ18O) ratios in modern limpet (Patella) shells record the seasonal range of SST in the western Mediterranean — a region particularly susceptible to seasonal change. Analysis of a suite of fossil limpet shells from Gibraltar shows that SST seasonality was greater during the last glacial by ~2°C as a result of greater winter cooling. These extra-tropical seasonal-resolution SST records for the last glacial suggest that the presence of large ice-sheets in the northern hemisphere enhances winter cooling. This result also indicates that seasonality in the Mediterranean is not well-represented in most palaeoclimate models, which typically show little change in seasonal amplitude, and provides a new test for the accuracy of climate models. [Copyright &y& Elsevier]

Abstract: Chronologies of sediments that document the last glacial history of the Black Sea “Lake” are hampered by issues relating to reservoir age. Regulated by basin hydrology, reservoir ages represent a tool that could potentially be used to better understand the response of Black Sea “Lake” hydrology to climate change. Therefore, deciphering reservoir age evolution is crucial both for better constraining the basin chronological framework and for providing new insights into our understanding of Black Sea “Lake” hydrology. By tuning a meaningful new high-resolution geochemical dataset (obtained from core MD04-2790) to a climate reference record, here, we propose a reliable chronology spanning the last 32kyr BP. The chronology is compared to a large AMS radiocarbon dataset (n=51). Pairs of calendar and radiocarbon ages allowed us to compute reservoir ages, and to, then, reconstruct a high-resolution quantitative reservoir age record for the last glacial history of the Black Sea “Lake”. The main factor controlling reservoir ages in lakes is the Hard Water Effect (HWE), which is regulated by basin hydrology. Therefore, changes in the reconstructed reservoir age record have been qualitatively interpreted in terms of the hydrologic responses of the Black Sea “Lake” to climate change. Our results allowed us to determine periods of complete isolation or outflow for the Black Sea “Lake”. During Heinrich Event 2 (HE2) and during the Last Glacial Maximum (LGM) the basin was strictly isolated, whereas prior to HE2 and during HE1 it outflowed into the Marmara Sea. Following the onset of the Bølling–Allerød, factors other than the HWE are thought to have influenced the reservoir age, preventing conclusive interpretations. We also determined an undocumented, to date, phase of Black Sea “Lake” stratification during the full glacial (HE2 and LGM). Our results indicate that reservoir age is a powerful tool for investigating and better understanding past hydrologic changes in lakes and inland seas. [Copyright &y& Elsevier]

Abstract: The Little Ice Age (LIA) is one of the most prominent climate shifts in the past 5000yrs. It has been suggested that the LIA might be the most recent of the Dansgaard–Oeschger events, which are better known as abrupt, large scale climate oscillations during the last glacial period. If the case, then according to Broecker (2000a, 2000b) Antarctica should have warmed during the LIA, when the Northern Hemisphere was cold. Here we present new data from the Ross Sea, Antarctica, that indicates surface temperatures were ~2°C colder during the LIA, with colder sea surface temperatures in the Southern Ocean and/or increased sea-ice extent, stronger katabatic winds, and decreased snow accumulation. Whilst we find there was large spatial and temporal variability, overall Antarctica was cooler and stormier during the LIA. Although temperatures have warmed since the termination of the LIA, atmospheric circulation strength has remained at the same, elevated level. We conclude, that the LIA was either caused by alternative forcings, or that the sea-saw mechanism operates differently during warm periods. [Copyright &y& Elsevier]

Abstract: A set of 40 Uranium-series datings obtained on the reef-forming scleractinian cold-water corals Lophelia pertusa and Madrepora oculata revealed that during the past 400kyr their occurrence in the Gulf of Cádiz (GoC) was almost exclusively restricted to glacial periods. This result strengthens the outcomes of former studies that coral growth in the temperate NE Atlantic encompassing the French, Iberian and Moroccan margins dominated during glacial periods, whereas in the higher latitudes (Irish and Norwegian margins) extended coral growth prevailed during interglacial periods. Thus it appears that the biogeographical limits for sustained cold-water coral growth along the NE Atlantic margin are strongly related to climate change. By focussing on the last glacial–interglacial cycle, this study shows that palaeo-productivity was increased during the last glacial. This was likely driven by the fertilisation effect of an increased input of aeolian dust and locally intensified upwelling. After the Younger Dryas cold event, the input of aeolian dust and productivity significantly decreased concurrent with an increase in water temperatures in the GoC. This primarily resulted in reduced food availability and caused a widespread demise of the formerly thriving coral ecosystems. Moreover, these climate induced changes most likely caused a latitudinal shift of areas with optimum coral growth conditions towards the northern NE Atlantic where more suitable environmental conditions established with the onset of the Holocene. [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]

Abstract: The circulation patterns of the deep glacial Pacific Ocean are still debated. Difficulties arise due to the scarcity of reliable paleoceanographic records that can document the past movements and properties of Pacific Ocean water masses. Here, we jointly use δ13C and δ18O measured on the epibenthic foraminifer Cibicidoides wuellerstorfi, from the MD02-2529 sediment core collected at 1619m water depth in the eastern equatorial Pacific, to monitor changes in water mass circulation spanning the past 150kyrBP. After the extraction of short-term (centennial to millennial-scale) δ13C and δ18O changes, which were ~1.0 and 0.5‰, respectively, we observed that these rapid δ13C and δ18O shifts were closely interrelated during the last 150kyrBP. A comparison of MD02-2529 with other benthic δ13C records localized to the north and south of the core location revealed that MD02-2529 was alternately bathed by a northern nutrient-rich and a southern nutrient-poor water mass. The comparison provided a diagnostic for the latitudinal movements of a sharp water mass front that was particularly evident during marine isotope stages 4 and 3 on the millennial timescale. By considering that δ13C is an indicator of the northern vs. southern origin of the water that bathed the MD02-2529 coring site in the past, we found that a North Pacific water mass, that occasionally spreads to the eastern Pacific Ocean as deep as 1600m and as far south as 8°N, was responsible for shifts toward the positive δ18O we observed in the past. We then used the δ13C/δ18O relationship to reconstruct latitudinal temperature and/or salinity gradients of the water mass that were linked to changes in the northern and/or the southern water mass end-members. Evolution of the δ13C/δ18O relationship spanning the past 150kyrBP has shed light on how hydrological processes occurring at northern and southern high latitudes are transmitted to the ocean''s interior through water mass advection. [Copyright &y& Elsevier]

Abstract: Recent studies of the eolian deposits in northern China have extended the East Asian monsoon history back to the early Miocene. However, the relative intensities of monsoonal winds and precipitation and the extent of their coupling prior to the Pleistocene epoch remain poorly constrained, mainly due to uncertainties in the interpretation of proxy indices generated from the Mio–Pliocene Red Clay sequences. Here we reconstruct East Asian monsoon oscillations over the past 7Ma using magnetic susceptibility and carbonate content as summer monsoon (precipitation) proxies, and quartz grain size as a winter monsoon (wind intensity) index. Our results suggest that precipitation and wind intensity exhibited significant orbital-scale variations prior to 4.2Ma, followed by slightly damped variability between 4.2 and 2.75Ma. Subsequently, East Asian monsoon circulation experienced two large shifts at about 2.75 and 1.25Ma, characterized by stepwise strengthening of glacial wind and interglacial precipitation. A remarkable change in East Asian monsoon seasonality occurred around 3.15–2.75Ma. Prior to 3.15Ma, strong winds were positively correlated with high effective precipitation, whereas after 2.75Ma strong winds were negatively correlated with heavy precipitation. This shift was probably induced by a change from an insolation-forced system to one strongly influenced by the combined effects of the phased uplift of the Himalaya–Tibetan Plateau and the simultaneous development of the Northern Hemisphere ice sheets. [ABSTRACT FROM AUTHOR]

Abstract: Subglacial conditions of large polar ice sheets remain poorly understood, despite recent advances in satellite observation. Major uncertainties related to basal conditions, such as the temperature field, are due to an insufficient knowledge of geothermal heat flow. Here, a hybrid method is presented that combines numerical modeling of the ice sheet thermodynamics with a priori information using a simple assimilation technique. Additional data are essentially vertical temperature profiles measured in the ice sheet at selected spots, as well as the distribution of subglacial lakes. In this way, geothermal heat-flow datasets are improved to yield calculated temperatures in accord with observations in areas where information is available. Results of the sensitivity experiments show that 55% of the grounded part of the Antarctic ice sheet is at pressure melting point. Calculated basal melt rates are approximately 65Gtyear−1, which is 3% of the total surface accumulation. Although these sensitivity experiments exhibit small variations in basal melt rates, the impact on the ice age of basal layers is quite important. In areas that are characterized by relatively low melt rates, this may lead to standard deviations up to 50% (in a model run over a period of 106 years). Subglacial water flow is concentrated underneath the large outlet glaciers of Antarctica. The larger subglacial lakes are perched at the head of these subglacial water systems. An exception, however, is the lake system of the Recovery Ice Stream Catchment, that receives a substantial amount of subglacial melt water from the upstream catchment. [Copyright &y& Elsevier]

Abstract: Reliable reconstructions of deep ocean carbonate ion concentration, [CO3 2−], and pH are crucial to understand mechanisms responsible for the past atmospheric CO2 variations observed in ice cores. However, it is challenging to reconstruct past deep water [CO3 2−] and pH and literature results from different proxies conflict, warranting careful investigations on possible reasons for the existing inconsistencies. Here, we present the first down core B/Ca and δ11B records measured in an epifaunal benthic foraminifer Cibicidoides wuellerstorfi from the Caribbean Sea during the last 160kyr. The two proxies yield quantitatively comparable deep water [CO3 2−] and pH results, showing high values during glacials relative to inter-glacials (differences in [CO3 2−] and pH are ∼35μmol/kg and ∼0.15, respectively), consistent with past ocean circulation changes in the Caribbean Sea. Our data provide convincing evidence that both proxies serve as faithful proxies to estimate deep ocean [CO3 2−] and pH, despite our incomplete understanding of boron incorporation into foraminiferal carbonates. [Copyright &y& Elsevier]

Abstract: The Mid-Pleistocene transition (MPT) was the time when quasi-periodic (∼100kyr), high-amplitude glacial variability developed in the absence of any significant change in the character of orbital forcing, leading to the establishment of the characteristic pattern of late Pleistocene climate variability. It has long been known that the interval around 900ka stands out as a critical point of the MPT, when major glaciations started occurring most notably in the northern hemisphere. Here we examine the record of climatic conditions during this significant interval, using high-resolution stable isotope records from benthic and planktonic foraminifera from a sediment core in the North Atlantic (Integrated Ocean Drilling Program Expedition 306, Site U1313). We have considered the time interval from late in Marine Isotope Stage (MIS) 23 to MIS 20 (910 to 790ka). Our data indicate that interglacial MIS 21 was a climatically unstable period and was broken into four interstadial periods, which have been identified and correlated across the North Atlantic region. These extra peaks tend to contradict previous studies that interpreted the MIS 21 variability as consisting essentially of a linear response to cyclical changes in orbital parameters. Cooling events in the surface record during MIS 21 were associated with low benthic carbon isotope excursions, suggesting a coupling between surface temperature changes and the strength of the Atlantic meridional overturning circulation. Time series analysis performed on the whole interval indicates that benthic and planktonic oxygen isotopes have significant concentrations of spectral power centered on periods of 10.7kyr and 6kyr, which is in agreement with the second and forth harmonic of precession. The excellent correspondence between the foraminifera δ 18O records and insolation variations at the Equator in March and September suggests that a mechanism related to low-latitude precession variations, advected to the high latitudes by tropical convective processes, might have generated such a response. This scenario accounts for the presence of oscillations at frequencies equal to precession harmonics at Site U1313, as well as the occurrence of higher amplitude oscillations between the MIS22/21 transition and most of MIS 21, times of enhanced insolation variability. [Copyright &y& Elsevier]

Abstract: The aim is to investigate the evolution of the subglacial landscape of Antarctica using an ice sheet and erosion model. We identify different stages of continental glaciation and model the erosion processes associated with each stage. The model links erosion to the basal thermal regime and indicates that much of the Antarctic interior may have been subject to less than 200m of erosion. The depth of erosion reflects the presence or absence of warm-based ice and the consistency of ice flow direction. This information, linked with knowledge about landscapes of glaciation in the northern hemisphere and some simple but robust assumptions about initial topography, is used to generate a map of the subglacial Antarctic landscape in which much of the lowland interior resembles the landscapes of areal scouring typical of the Laurentian and Scandinavian shields. Near the continental margins selective linear erosion has overdeepened pre-existing river valleys by as much as 2.8km. High elevation plateaus adjacent to such drainage systems have survived largely unmodified under cold-based ice. High erosion rates result from steep thermal gradients in basal ice. Mountain regions such as the Gamburtsev Mountains, uplands in Dronning Maud Land and massifs in West Antarctica are likely to bear features of local alpine glaciation. Such landscapes may have been protected under cold-based ice for the last 34Myrs or possibly longer. [Copyright &y& Elsevier]

Abstract: The exceptionally long interglacial warm period known as Marine Isotope Stage 11 (MIS-11; 428–397ky ago vs. ky vs. kyr) is often considered as a potential analogue for future climate development in the absence of human influence. We use a new high-resolution sea-level record—a globally integrated ice-volume signal—to compare MIS-11 and the current interglacial (Holocene). It is found that sea-level rise into both interglacials started over similar timescales relative to the respective insolation increases, and progressed up to −50m at similar rates of 1.0–1.2m per century. Subsequent weak insolation changes anomalously prolonged the MIS-11 deglaciation over more than 20ky. The main sea-level highstand was achieved at the second MIS-11 insolation maximum, with a timing closely equivalent to that of the Holocene highstand compared to its single insolation maximum. Consequently, while MIS-11 was an exceptionally long period of interglacial warmth, its ice-volume minimum/sea-level highstand lasted less than 10ky, which is similar to the duration of other major interglacials. Comparison of the ends of MIS-11 and the Holocene based on timings relative to their respective maxima in mean 21 June insolation at 65°N suggests that the end of Holocene conditions might have been expected 2.0–2.5ky ago. Instead, interglacial conditions have continued, with CO2, temperature, and sea level remaining high or increasing. This apparent discrepancy highlights the need to consider that: (a) comparisons may need to focus on other orbital control indices, in which case the discrepancy can vanish; and/or (b) the feedback mechanisms that dominate the planetary energy balance may have become decoupled from insolation during the past 2millennia. [Copyright &y& Elsevier]

Abstract: Two stalagmites (C996-1 and C996-2) collected from the Jiuxian Cave in the Shaanxi Province in central China have been studied with U-series dating and stable isotope analysis. Thirty-eight 230Th dating results showed that the stalagmite C996-1 was continuously deposited through the last 8.5ka BP (thousand years before present, present=1950AD), and C996-2 was deposited through the last 19ka BP excluding two growth hiatuses between 8.3 and 5.7ka BP, and 15.4 and 11.9ka BP. With a relatively stable boundary condition, we interpret the δ 18O of speleothem calcite as most indicative of the amount of summer monsoon precipitation, although temperature and other factors might have some minor impact. The δ 18O records show notable changes within the last glacial maximum (LGM), resembling other East Asian monsoon records such as those from the Hulu and Sanbao Caves, suggesting that significant monsoonal climate changes occurred in eastern Asia as far north as the Qinling Mountains during the LGM interval. A comparison of our records to precisely dated contemporaneous speleothem records from other caves shows that the increasing trend of δ 18O during the Holocene commenced as early as ∼7.5ka BP in the low-latitude monsoonal area, i.e. the Hoti Cave, while at higher latitudes this shift occurred later, such as ∼7.0ka BP in the Dongge Cave, ∼5.3ka BP in the Heshang Cave, ∼4.7ka BP in the Sanbao Cave and ∼4.5ka BP in the Jiuxian Cave. These results imply an asynchronous change of the summer monsoon precipitation occurred in East Asia during the Holocene. The asynchrony may be related to the responses of a coupled tropical and subtropical monsoon system to changes of the insolation and the differences in thermal forcing, which result from the complex geographical configuration. The variation of sea surface temperature (SST) in the western tropical Pacific may also have important impacts on the summer monsoon precipitation changes in central and northern China because it affects the Northwestern Pacific Subtropical High, a monsoon-front regulator. More robust tests are needed to confirm this phenomenon and to evaluate the contribution of different factors in detail. [Copyright &y& Elsevier]

Abstract: The Adelaide rift complex in South Australia contains the type sections for Sturtian and Marinoan glacial deposits. The litho- and chemo-stratigraphy of these deposits play a central role in evaluating global Neoproterozoic ice age hypotheses and Rodinia supercontinent reconstructions, but reliable depositional age constraints have been extremely limited. We report results of in situ Th–U–total Pb (electron microprobe) dating of detrital and authigenic monazite in two samples from the Umberatana Group (Sturtian Holowilena Ironstone and pre-Marinoan Enorama Shale) in the Central Flinders Ranges. Several texturally and chemically distinct detrital and authigenic populations are recognized. Detrital dates range from 1600Ma to 760Ma and most relate to well-known orogenic or igneous events in surrounding cratonic regions. Authigenic monazite grew in three or more pulses ranging from 680Ma to 500Ma. The date of 680±23Ma (2σ) for the earliest generation of authigenic monazite in sandstone from the Enorama Shale (1) provides an estimate for the age of the base of the Trezona carbon isotopic anomaly just beneath the Marinoan glacial deposits, (2) provides an absolute minimum age constraint on the underlying Sturtian glacial deposits, and (3) supports proposed correlations between type Marinoan deposits and precisely dated glacial deposits in Namibia and China, which bracket the presumed Marinoan equivalents between 655 and 635Ma. This age is inconsistent with a Re–Os isochron age of 643±2.4Ma (2σ) on shales near the bottom of the Sturtian–Marinoan interglacial succession, stratigraphically >3000m below the Enorama Shale sample, and militate against the hypothesis that the type Marinoan is correlative with the 580Ma Gaskiers glaciation. Monazite growth near 600Ma and again at about 500Ma probably represent hydrothermal fluid-flow events, the latter of which also corresponds to the well-known Delamerian Orogeny during which the Adelaide sediments were folded into their present structural pattern. [Copyright &y& Elsevier]

Abstract: The Indian Ocean is an important part of the global thermohaline circulation system, receiving deep waters sourced from the Southern Ocean and being the location of upwelling and surface-ocean current flow which returns warm and salty waters to the Atlantic. It is also an ideal location to reconstruct the link between thermohaline circulation and deep-water nutrient contents. No mixing occurs between major deep-water masses along flow paths within the Indian Ocean, so changes in water-mass provenance reflect changes in deep-ocean circulation while nutrient contents reflect addition and dissolution of organic matter. We present neodymium (Nd) and carbon (C) isotope records from an equatorial Indian Ocean core (SK129–CR2) spanning the last 150 kyr. The Nd isotope record shows that an increased proportion of North Atlantic Deep Water (NADW) reached the Indian Ocean during interglacials (Marine Isotope Stages; MIS 1 and 5), and a reduced proportion during glacials (MIS 2, 4, and 6), and also that changes occurred during MIS 3. The magnitude and timing of deglacial and some MIS 3 variability is very similar to those in the RC11–83/TNO57–21 South Atlantic deep Cape Basin Nd isotope record (). Since the deep Cape Basin is oceanographically upstream of the Indian Ocean from a deep water circulation perspective, the Nd isotopes suggest that Atlantic meridional overturning circulation changes were effectively propagated from the southeastern Atlantic into the central Indian Ocean via the Southern Ocean. Comparison of the Nd and C isotope records shows that deep-ocean circulation was decoupled from nutrient-content changes on glacial–interglacial timescales, in particular suggesting higher productivity during MIS 5. Increased equatorial productivity during MIS 5 is supported by benthic infaunal–epifaunal foraminiferal δ 13C gradients, as well as benthic foraminiferal δ 13C gradients along deep-water flow. Concurrent warming, indicated by planktonic foraminiferal Mg/Ca during MIS 5 at the site is consistent with changing thermocline temperature and may indicate a link to surface-ocean hydrographic changes. [Copyright &y& Elsevier]

Abstract: During the last glacial period, polar ice cores indicate climate asynchrony between the poles at the millennial time-scale. Yet, surface ocean circulation in large parts of the globe varied in tune with Greenland temperature fluctuations suggesting that any anti-phase behavior to a substantial degree must lie in the deeper global ocean circulation which is poorly understood outside the Atlantic Ocean. Here we present data from the north-western Indian Ocean which indicate that the timing of maxima in northward extensions of glacial Antarctic Intermediate Water (GAAIW) coincides with dramatically reduced thermohaline overturn in the North Atlantic associated with the Heinrich-ice surge events (HE). The repeated expansion of the GAAIW during HEs, recorded far north of the equator in the Arabian Sea, suggests that southern hemisphere driven intermediate water mass variability forms an integral part of the inter-hemisphere asynchronous climate change behavior at the millennial time-scale. [Copyright &y& Elsevier]

Abstract: In northern China, the history of desert migration provides a good measure of the East-Asian summer monsoon variations, since the desert margin environment is very sensitive to changes in summer monsoon rainfall. Desert margin migration can be well documented in the downwind loess deposits, since the grain size of Chinese loess is principally controlled by source-to-sink distance and hence the loess grain size is an effective proxy for reconstructing the history of the East-Asian summer monsoon. In order to investigate the pattern and migration of the summer monsoon rainfall belt over northern China during the past two glacial–interglacial cycles, contour maps of loess grain size were constructed for MIS 2, 3, 4, 5, 6 and 7. All the grain-size isolines show a near north–south gradient for both glacials and interglacials, indicating a dominant dust source region in north and an approximately north–south dust transport pathway for dust deposits in the main body of the Loess Plateau, at least for the past two glacial–interglacial cycles. The reconstructed southeast desert margin for MIS 2, 3, 4, 5, 6 and 7 roughly parallels the present isohyets, implying that the pattern of the East-Asian summer monsoon rainfall belt during the past two glacial–interglacial cycles is similar to the present, i.e. a northeast–southwest trend for the isohyets of the summer monsoon, despite the glacial–interglacial cycles. Using the grain-size isolines of MIS 2 as a reference, we derive a northerly desert retreat of ∼160 km, ∼19 km, ∼225 km and ∼223 km for MIS 3, 4, 5 and 7, respectively, and a southerly desert advance of ∼29 km for MIS 6, that could be preliminarily regarded as the relative migration distance for the East-Asian summer monsoon rainfall belt. In addition, the inferred climate conditions in MIS 3 are cool and humid in northern China, while the driest and coldest interval of the last two glacial periods occurs in MIS 6. [Copyright &y& Elsevier]

Abstract: Atmospheric dust levels may play important roles in feedbacks linking continental source areas, tropical convection, marine productivity, and global climate. These feedbacks appear to be particularly significant in the tropical Pacific, where variations in local convection and productivity have been demonstrated to have impacts on climate at higher latitudes. Modeling of past dust levels and related feedbacks has been limited, however, by a paucity of observational data. In this study we present a temporal and spatial survey of dust fluxes to the eastern equatorial Pacific over the past 30 kyr. Glacial and Holocene fluxes of 232Th, a proxy for continental material, were calculated by normalization to 230Th from a north–south transect of cores along 110°W between 3°S and 7°N (ODP sites 848–853). Fluxes were 30–100% higher during the last glacial, suggesting increased dustiness in both hemispheres during the glacial period. In both time periods, dust fluxes decrease towards the south, reflecting scavenging of Northern Hemisphere dust by precipitation at the ITCZ. The Holocene meridional dust flux gradient between 7°N and 3°S is characterized by a steep drop in dust levels at the southern edge of the modern range of the ITCZ, while the gradient is shallower and more nearly linear during the last glacial. This change may indicate that the glacial ITCZ in this region was a less effective barrier to inter-hemispheric dust transport, most likely due to a decrease in convective intensity and precipitation during the last glacial; alternatively, the change in gradient may be explained by increased variability in the location of the glacial ITCZ. Our data do not appear to require a mean southerly displacement of the glacial ITCZ, as suggested by the results of other studies. [Copyright &y& Elsevier]

Abstract: Assessing risk from tropical cyclones and predicting the impact of this hazard under a human altered climate is based exclusively upon the behaviour of these events over the past 50–100 yr and often less. Critical to these determinations is an understanding of the full extent of the natural variability of this hazard. The coarse resolution of millennial scale sedimentary records, brevity of the instrumental register, imprecision of longer historical accounts and lack of any long-term, high resolution records has led to the assumption that the total variability of tropical cyclone behaviour is encompassed within the seasonal to multi-decadal oscillations observed to date. We present a near 800 yr long, annual resolution isotope record of tropical cyclones in northeast Australia which displays marked centennial scale regimes. Our record demonstrates that the frequency variability of intense landfalling cyclones is greatest at centennial scale compared to seasonal and decadal oscillations. Switching between centennial scale regimes in this record occurred rapidly (10–20 yr) highlighting the importance of accounting for this phenomenon in coastal planning and risk assessment. Our study highlights the importance of obtaining high resolution multi-century records of tropical cyclone activity in order to more accurately assess future impacts of this hazard to human society. [Copyright &y& Elsevier]

Abstract: Throughout the last ∼ 900 kyr, the Late Pleistocene, Earth has experienced periods of cold glacial climate, punctuated by seven abrupt transitions to warm interglacials, the so-called terminations. Although most of glacial ice is located in the Northern Hemisphere (NH), the Southern Hemisphere (SH) seems to play a crucial role in deglaciation. Variation in the seasonal distribution of solar insolation is one candidate for the cause of these climatic shifts. But so far, no simple mechanism has been identified. Here we present a mathematical analysis of variations in midsummer insolation in both hemispheres at 65° latitude. Applying this analysis to the entire Pleistocene, the last 2 Myr, we find that prior to each termination the insolation in both hemispheres increases in concert, with a SH lead. Introducing time and energy thresholds to these overlaps, calculated times for the onsets of the seven terminations by this insolation canon (exceptional overlaps meeting the two threshold prerequisites) are ∼ 23, 139, 253, 345, 419, 546 and 632 kyr BP, perfectly matching the geologic record. The timing originates from the interplay between the two orbital parameters obliquity and precession, explaining why terminations occur at integer multiple of the precessional cycle. There is no such constellation between 1 and 2 Myr BP, the Early Pleistocene, in agreement with Earth''s climate at that time. This change in orbital forcing coincides with the Mid Pleistocene Revolution, separating the Late from the Early Pleistocene. Therefore, we hypothesize that the insolation canon is the trigger for glacial terminations. [Copyright &y& Elsevier]

Abstract: Rates of continental erosion may be reconstructed from variations in the rate of accumulation of clastic sediment, most of which lies offshore. Global rates of marine sedimentation are usually considered to have reached a maximum after 3–4 Ma, driven by enhanced erosion in a variable glacial–interglacial climate. However, a new compilation of seismic data from the marginal seas of Asia now shows that only the Red River reached its historic peak after 4 Ma. Sediment flux from Asia first peaked in the early–middle Miocene (24–11 Ma), well before the initiation of a glacial climate, indicating that rock uplift and especially precipitation are the key controls on erosion, at least over long periods of geologic time. Reconstructions of weathering in East Asia show that faster erosion correlates with more humid, warm climates in the early–middle Miocene, changing to less erosive, drier climates after 14 Ma when Antarctic glaciation begins. Average rates of sedimentation on most east Asian continental margins since 1.8 Ma are 5–6 times less than the modern fluvial flux, implying that the flux to the oceans varies sharply on short timescales and is not always buffered over timescales of ∼104 yr by storage in flood plains. [Copyright &y& Elsevier]

Abstract: The lack of temporal resolution and accurate chronology of Southern Ocean marine cores has hampered comparison of glacial millennial-scale oscillations between the Southern Ocean, Antarctic ice and other records from both hemispheres. In this study, glacial climate variability is investigated over the last 50 ka using a multi-proxy approach. A precise chrono-stratigraphy was developed on the high-sedimentation rate core MD94-103 (Indian Southern Ocean, 45°35′S 86°31′E, 3560 m water depth) by geomagnetic synchronization between the later core and NAPIS75, and 14C dates. High-resolution time-series of δ18O in planktonic foraminifera Globigerina bulloides and Neogloboquadrina pachyderma, and sea surface temperatures (SSTs) estimated from the alkenone UK′37 index and foraminifera assemblages have been generated. Temporal evolution of the two temperature proxy records is notably different during the last glacial period. While foraminifera data indicate a consistent cooling towards the last glacial maximum, anomalous warm glacial alkenone temperatures suggest a strong advection of 〈warm〉 “detrital” alkenones by surface waters of the Agulhas current. Superimposed to this general trend, during Heinrich events, foraminiferal SSTs point to warmer surface waters, while concurrent alkenone SSTs exhibit apparent coolings probably caused by enhanced local alkenone production. By analogy to modern observations, possible influence of ENSO-like conditions on the subantarctic Southern Ocean SSTs is discussed. [Copyright &y& Elsevier]

Abstract: Our observations show that extreme uplift in southeast Alaska began about 1770 AD, with relative sea level (RSL) change to 5.7 m and current uplift rates to 32 mm/yr. This region experienced widespread glacial melting following the Little Ice Age (LIA), with the collapse of the Glacier Bay Icefield alone equivalent to 8 mm of global sea level rise. Geodynamic modelling links the uplift to post-LIA isostatic rebound, with the extreme uplift signal and a priori knowledge of ice load changes requiring the presence of a low viscosity asthenosphere (3.7×1018 Pa s). These crustal deformations are triggered by climate change through glacier wastage. [Copyright &y& Elsevier]

Abstract: The first detailed stratigraphic record from a deep-water carbonate mound in the Northeast Atlantic based on absolute datings (U/Th and AMS 14C) and stable oxygen isotope records reveals that its top sediment sequences are condensed by numerous hiatuses. According to stable isotope data, mainly sediments with an intermediate signal are preserved on the mound, while almost all fully glacial and interglacial sediments have either not been deposited or have been eroded later. The resulting hiatuses reduce the Late Pleistocene sediment accumulation at Propeller Mound to amounts smaller than the background sedimentation. The hiatuses most likely result due to the sweeping of the mound in turn with the re-establishment of vigour interglacial circulation patterns after sluggish current regimes during glacials. Thus, within the discussion if internal, fluid-driven or external environmentally driven processes control the evolution of such carbonate mounds, our findings for Propeller Mound clearly point to environmental forcing as the dominant mechanism shaping deep-water carbonate mounds in the NE Atlantic during the Late Pleistocene and Holocene. [Copyright &y& Elsevier]

A new physical mechanism involving the Antarctic ice-sheet extent is able to link climatic and CO2 glacial–interglacial changes. It is furthermore able to explain many features of the glacial cycles, like the 100 kyr oscillations or the peculiarities of stage 11 (about 400 kyr BP). Indeed, from recent results, the glacial ocean bottom waters were possibly much more saline and consequently, may have an unsuspected large density. This glacial deep stratification could account for a significant part of the glacial–interglacial CO2 difference. The formation of these waters around Antarctica involves brine rejection over the continental shelves and is directly linked to changes in sea ice formation and Antarctic ice-sheet extent. Using this new scenario, we formulate a conceptual model that reproduce the succession and the amplitude of glaciations over the last few million years. This new mechanism furthermore provides the clue to understanding the changes in the main climatic frequency from 23 to 41 ka about 3 Myr ago and from 41 to 100 ka about 1 Myr ago. The Antarctic ice-sheet influence on bottom water formation could provide the “missing piece” to complete the astronomical theory of Quaternary climates. [Copyright &y& Elsevier]

New Re–Os isotopic data were obtained from chlorite-grade black shales from the upper Old Fort Point Formation (Windermere Supergroup), a post-glacial Neoproterozoic marker horizon in western Canada. A Re–Os isochron date of 634±57 Ma (MSWD=65, n=5) was determined using the conventional inverse aqua regia digestion medium. However, dissolution of the same samples with a new CrO3–H2SO4 dissolution technique [Chem. Geol. 200 (2003) 225] yielded a much more precise date of 607.8±4.7 Ma (MSWD=1.2). Both dates are in agreement with existing U–Pb age constraints that bracket the Old Fort Point Formation between ∼685 and ∼570 Ma. The distinctive Re–Os systematics recorded by the two analytical protocols is explained by dissolution of a variably radiogenic, detrital Os component by the aqua regia method. In contrast, the CrO3–H2SO4 technique minimizes this detrital component by selectively dissolving organic matter that is dominated by hydrogenous (seawater) Re and Os. The date of 607.8±4.7 Ma is thus interpreted as the depositional age for the upper Old Fort Point Formation providing a minimum age constraint for the timing of the second Windermere glaciation in western Canada. This ice age is correlative with the Marinoan (∼620–600 Ma) ice age and older than the ∼580-Ma Gaskiers glaciation of northeastern North America. The new Re–Os age determined from the CrO3–H2SO4 digestion technique thus provides further support to a growing body of evidence for a global Marinoan glacial episode. Such an interpretation would not be discernable from the imprecise Re–Os date obtained with the aqua regia protocol. These results also indicate the potential for Re–Os radiometric dating of black shales that was not previously recognized. Importantly, neither chlorite-grade metamorphism nor the low organic content (TOC <1%) of the Old Fort Point Formation precluded the determination of a precise Re–Os depositional age using the CrO3–H2SO4 analytical protocol. [Copyright &y& Elsevier]

The spatial distribution of warm surface water in the Atlantic Ocean reflects the state of the thermohaline circulation. The Azores Current/Front, which is a recirculation of the Gulf Stream, marks the northeastern boundary of the North Atlantic subtropical gyre. Its position is therefore diagnostic of the width of the Atlantic warm water sphere. Here we report high resolution stable isotope and faunal abundance records of planktonic foraminifera in a sediment core from the Gulf of Cadiz (southwest Spain) which reflects shifting of the Azores Front since the Last Glacial Maximum (LGM). Today, the Azores Front does not penetrate into the Gulf of Cadiz, even though the front resides at the same latitude as the Gulf of Cadiz in the Atlantic. Our results indicate that the Azores Front is a robust feature of the Atlantic surface circulation, and that is present both in interglacial times and during the LGM at roughly the same latitude. However, during the LGM prior to 16 ka BP and during the Younger Dryas, the Azores Front did penetrate eastward into the Gulf of Cadiz. [Copyright &y& Elsevier]

ODP Site 1089 is optimally located in order to monitor the occurrence of maxima in Agulhas heat and salt spillage from the Indian to the Atlantic Ocean. Radiolarian-based paleotemperature transfer functions allowed to reconstruct the climatic history for the last 450 kyr at this location. A warm sea surface temperature anomaly during Marine Isotope Stage (MIS) 10 was recognized and traced to other oceanic records along the surface branch of the global thermohaline (THC) circulation system, and is particularly marked at locations where a strong interaction between oceanic and atmospheric overturning cells and fronts occurs. This anomaly is absent in the Vostok ice core deuterium, and in oceanic records from the Antarctic Zone. However, it is present in the deuterium excess record from the Vostok ice core, interpreted as reflecting the temperature at the moisture source site for the snow precipitated at Vostok Station. As atmospheric models predict a subtropical Indian source for such moisture, this provides the necessary teleconnection between East Antarctica and ODP Site 1089, as the subtropical Indian is also the source area of the Agulhas Current, the main climate agent at our study location.The presence of the MIS 10 anomaly in the δ13C foraminiferal records from the same core supports its connection to oceanic mechanisms, linking stronger Agulhas spillover intensity to increased productivity in the study area. We suggest, in analogy to modern oceanographic observations, this to be a consequence of a shallow nutricline, induced by eddy mixing and baroclinic tide generation, which are in turn connected to the flow geometry, and intensity, of the Agulhas Current as it flows past the Agulhas Bank.We interpret the intensified inflow of Agulhas Current to the South Atlantic as responding to the switch between lower and higher amplitude in the insolation forcing in the Agulhas Current source area. This would result in higher SSTs in the Cape Basin during the glacial MIS 10, due to the release into the South Atlantic of the heat previously accumulating in the subtropical and equatorial Indian and Pacific Ocean. If our explanation for the MIS 10 anomaly in terms of an insolation variability switch is correct, we might expect that a future Agulhas SSST anomaly event will further delay the onset of next glacial age. In fact, the insolation forcing conditions for the Holocene (the current interglacial) are very similar to those present during MIS 11 (the interglacial preceding MIS 10), as both periods are characterized by a low insolation variability for the Agulhas Current source area. Natural climatic variability will force the Earth system in the same direction as the anthropogenic global warming trend, and will thus lead to even warmer than expected global temperatures in the near future. [Copyright &y& Elsevier]

A box model of the North Atlantic Ocean exhibits self-sustained oscillations of the large-scale ocean circulation, which are reminiscent of Dansgaard–Oeschger (DO)-style oscillations. The freshwater forcing of this ocean model depends on mean climate state, represented by global ice volume. This is computed by a one-dimensional ice-sheet model, subject to changes in high-latitude northern hemisphere summer insolation. At low/large ice volume, the ocean–ice system stays in a permanent interstadial/stadial mode. Millennial scale DO-style oscillations result at intermediate ice-volume values, which thus define a “DO window”. During an interglacial-to-glacial transition, this DO window is crossed sufficiently slow to allow for sustained DO-style oscillations to develop. In contrast, during a glacial termination, the system moves relatively rapid through the DO window, resulting in an intermittent re-appearance of DO-style oscillations, which resemble the sequence of events surrounding the Younger Dryas (YD). When forced with modeled ice-volume evolution over the last 800 thousand years, our model predicts Younger-Dryas-type cooling events for each major glacial termination. Accordingly, the Younger Dryas does not appear to be a one-time event. [Copyright &y& Elsevier]

Deep-sea sediment pore fluids contain a record of past glaciations in their [Cl] and δ18O. The signal of the Last Glacial Maximum (LGM) ice volume increase remains in the pore fluids as a local peak in each of these species. Using a one-dimensional model to account for the diffusive and advective transport within the sediment column since the LGM, the past bottom water salinity and δ18Oseawater values can be estimated. The model is most sensitive to the shape of the forcing function used to represent bottom water variations through time, the effective diffusion coefficient, and the scatter in the data. Assuming steady-state compaction, the model is relatively insensitive to the initial condition, the bulk sedimentation rate and the assumed porosity profile, though these last two are measured independently. Overall uncertainties in the relative [Cl] increase at the LGM are between 0.1 and 0.5%, where the mean ocean change is about 3.5%. [Copyright &y& Elsevier]

Data from ice cores suggest that Late-glacial and early Holocene atmospheric CO2 variations were rather conservative, the most important change being a gradual Younger Dryas increase. By contrast, palaeo-CO2 records based on the inverse relationship between CO2 partial pressure and stomatal frequency of terrestrial plant leaves reflect a more dynamic CO2 evolution, including an abrupt decrease at the Allerød/Younger Dryas transition. Here we present a Late-glacial and early Holocene CO2 record based on stomatal index data from leaves preserved in the sediments of a small lake in southwestern Sweden. Three independent records constructed from stomatal index data of Salix polaris, Salix herbacea and Betula nana leaves were combined to form a high-resolution CO2 reconstruction for the period 12 800–10 800 cal yr BP. Atmospheric CO2 concentrations were found to have decreased rapidly from c. 260 ppmv to 210–215 ppmv within 200 years during the Allerød (GI-1)/Younger Dryas (GS-1) transition. After 100–200 years, CO2 concentration started to gradually increase to 270–290 ppmv at the end of the Younger Dryas stadial (GS-1). CO2 concentrations were relatively stable during the early Holocene, except for a short-lived period of lower (240–250 ppmv) values c. 11 350–11 200 cal yr BP. This Late-glacial and early Holocene CO2 evolution partly resembles previous stomatal-based CO2 reconstructions, and the overall trend is almost identical to that seen in ice-core records. The amplitude of change is, however, markedly higher in the Swedish stomatal-based record compared to the ice cores. This difference may partly be accounted for by the inherent smoothing of ice-core CO2 records caused by diffusion, but a major part of the difference in amplitude between ice-core and stomatal-based records still remains to be explained. Based on our reconstruction, atmospheric CO2 may have played an important role in climate dynamics during the last deglaciation. [Copyright &y& Elsevier]

Pb isotopic compositions of bulk sediment cores from the Tropical Atlantic are used here to infer variations in the provenance of terrigenous input to the Tropical Atlantic during Pleistocene climate cycles. The 200-ka high precision (2σ∼100 ppm) Pb isotope records of the Ceara´ Rise (Western Atlantic) and Sierra Leone Rise (Eastern Atlantic) cores show a clear glacial–interglacial cyclicity, reflected by alternating unradiogenic Pb and radiogenic Pb in both cores. The glacial–interglacial Pb isotopic contrast is also observed in Pb–Pb space and can be explained in terms of binary mixing - variations along the mixing lines reflecting changes in the relative proportions of the glacial (unradiogenic) and interglacial (radiogenic) Pb source(s). The Pleistocene Pb isotopic variability of the terrigenous input to the Ceara´ Rise can be linked to changes in the weathering styles in the Amazon Basin and, as a result, in the Amazon river discharge. These changes are reflected by a greater contribution from the highlands (Andes) Pb source during glacial times, and strengthening of the lowlands (Shield) Pb source during interglacials. On the other hand, Pb isotopic variations in the Sierra Leone Rise core indicate increased Pb inputs from the Saharan dust plume during glacial times, in agreement with the wind patterns over Africa. Furthermore, this result bears some implications on the cause of the enhanced glacial terrigenous fluxes to the Tropical Atlantic, which we infer to be due to increase in winter wind transport rather than glacial hyperaridity. The cyclicity of the Ceara´ Rise and Sierra Leone Rise Pb isotopic records together with changes in the proportions of mixing sources throughout the last 200 ka monitor changes in the hydrological cycle over South America and the wind systems over Africa, respectively, both of which are linked to the seasonal latitudinal migration of the Intertropical Convergence Zone. The correlation found between Pb isotope cycles and other paleoclimate proxies suggests that Pb isotopes may be responding to variations in Earth’s orbital parameters. [Copyright &y& Elsevier]

Analyzing simulations of glacial ocean circulation and radiocarbon distribution I show that increased sea ice cover over the Southern Ocean reduces ventilation and radiocarbon content of the deep ocean. Two simulations, one present-day and one glacial, tuned to have similar rates of North Atlantic Deep Water formation are used. Insulation from air–sea gas exchange due to more extended sea ice cover increases Southern Ocean radiocarbon ages by more than 100 yr. Higher rates of sea ice formation and export from high southern latitudes lead to a salinification of Antarctic Bottom Water (AABW), making it the most saline deep water mass of the glacial world oceans. This increases the density of AABW and hence its rate of formation. Mass and radiocarbon fluxes to the deep ocean are thus decoupled. Both older Southern Ocean waters and a stronger flux of AABW increase radiocarbon ages of glacial bottom waters by up to 300 yr. Available reconstructions of glacial bottom water properties are broadly consistent with the simulation. These results question previous inferences from radiocarbon distributions on glacial deep water formation rates. [Copyright &y& Elsevier]

Previous studies of lateral viscosity variations on postglacial rebound often neglect the spherical shape of the Earth and the self-gravity of the solid earth and oceans. In this paper, the consistent sealevel equation is solved by the coupled Laplace–finite element method for a spherical, self-gravitating incompressible Maxwell earth. It confirms the importance of self-gravity in the oceans on sealevel computation near the ice margin where the data are most sensitive to the existence of lateral variations in lithospheric thickness and asthenospheric viscosity. The effects of lateral variations in lower mantle viscosity, asthenospheric viscosity and lithospheric thickness are investigated. This paper confirms the finding of earlier investigations. The combined effect of lateral viscosity variations in the lower mantle with reverse viscosity contrasts in the upper mantle is also investigated. For sealevel data near the center of rebound, the effect of lateral viscosity contrast in the lower mantle can be masked by the existence of a reverse lateral viscosity contrasts in the upper mantle. However, this is not the case for sealevel data just outside the ice margin. [Copyright &y& Elsevier]

• We introduce a new valley network parameter accounting for elevation-drainage area distribution. • We develop a new 1D model for coupled glacial-fluvial topography in steady state. • Tectonics and climate control the shape of both glacial and fluvial topography. • Temperate glaciers erode more efficiently than rivers for typical parameter sets. • The influence of tectonics and climate on glacial relief is compatible with the glacial buzzsaw. Studies on relief and hypsometry in glaciated mountain ranges have recognized the equilibrium line altitude of glaciers as a major control on mountain height. This has led to the belief that, in contrast to fluvial topography, glacial topography is limited by climate, with tectonics playing a secondary role. This concept is known as the glacial buzzsaw. However, the understanding of controls on glacial relief has remained mainly qualitative, in part because a reference scenario for glacial landscape evolution — a glacial topographic steady state linked to the base level by a fluvial topographic steady-state downstream of the glacier terminus - and its dependencies have not yet been defined. Here we define such a reference and compare steady state longitudinal profiles in a coupled system of glacial and fluvial erosion that involves both tectonics and climate. Our model is based on the stream power law for fluvial erosion, the shallow ice approximation in combination with a glacial erosion rule, and an empirically determined drainage area-flow length relationship for both rivers and glaciers. Further, we introduce a new approach to incorporate dendritic glacier network structures into the one-dimensional model. Modeling of coupled glacial-fluvial steady-state profiles with empirical glacial and fluvial erosion parameters shows that the difference between glacial and fluvial relief depends on climate, tectonics and the applied erosion laws. Our results imply that glacial erosion can typically balance tectonic uplift rates at lower relief and topographic slopes than fluvial erosion. This steady state equivalent of the glacial buzzsaw effect suggests that glaciers may indeed be more efficient erosional agents than rivers increasing erosion in a cooling climate. [ABSTRACT FROM AUTHOR]