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The Indian Ocean exhibits multiple modes of interannual climate variability, whose future behaviour is uncertain. Recent analysis of glacial climates has uncovered an additional El Niño-like equatorial mode in the Indian Ocean, which could also emerge in future warm states. Here we explore changes in the tropical Indian Ocean simulated by the Paleoclimate Model Intercomparison Project (PMIP4). These simulations are performed by an ensemble of models contributing to the Coupled Model Intercomparison Project 6 and over four coordinated experiments: three past periods – the mid-Holocene (6000 years ago), the Last Glacial Maximum (21 000 years ago), the last interglacial (127 000 years ago) – and an idealized forcing scenario to examine the impact of greenhouse forcing. The two interglacial experiments are used to characterize the role of orbital variations in the seasonal cycle, whilst the other pair focus on responses to large changes in global temperature. The Indian Ocean Basin Mode (IOBM) is damped in both the mid-Holocene and last interglacial, with the amount related to the damping of the El Niño–Southern Oscillation in the Pacific. No coherent changes in the strength of the IOBM are seen with global temperature changes; neither are changes in the Indian Ocean Dipole (IOD) nor the Niño-like mode. Under orbital forcing, the IOD robustly weakens during the mid-Holocene experiment, with only minor reductions in amplitude during the last interglacial. Orbital changes do impact the SST pattern of the Indian Ocean Dipole, with the cold pole reaching up to the Equator and extending along it. Induced changes in the regional seasonality are hypothesized to be an important control on changes in the Indian Ocean variability. [ABSTRACT FROM AUTHOR]

Paleoclimate change can be quantified by modelling the paleoglacier extents at well-dated moraines. However, previous studies typically use paleo-precipitation changes derived from climate proxies in other locations to constrain paleo-temperature changes. This approach may lead to significant uncertainties due to the lack of a physical basis and spatial-temporal representativeness. To address this issue, we developed a two-step approach to better constrain the paleo-temperature and precipitation changes. The first step is to identify all potential scenarios for temperature-precipitation changes using a coupled glacial-mass-balance and ice-flow model. In the second step, we incorporate a physics-based parameter k , reflecting the sensitivity of precipitation and temperature change, to determine the most probable temperature-precipitation change. We demonstrate our new approach by reconstructing paleoclimate changes of two valley glaciers in the Bhutanese Himalaya (BH). This approach derives a set of temperature reductions of −4.14 °C, −4.08 °C, −0.93 °C, −0.33 ∼ −0.57 °C, and − 0.31 ∼ −0.52 °C, with their corresponding precipitation decreases of 21.4%, 21.0%, 5.2%, 1.7–3.3%, and 1.6–3.0% relative to the present, during the Last Glacial Maximum, Heinrich event 1, Younger Dryas, Neoglacial, and Little Ice Age in BH, respectively. The reconstructed cold and dry climates in BH are consistent with the paleoclimate reconstructions across the Tibetan Plateau, but our approach improved the accuracy of regional paleoclimate reconstructions. These results suggest that temperature change dominates the glacial fluctuations in BH, with additional influences from solar insolation, oceanic and atmospheric circulation changes, and volcanic eruptions. • A new approach to constrain the paleo-temperature and paleo-precipitation changes was proposed. • The reconstructed paleoclimates during the last glacial cycle were colder and dryer than the present. • The collective effect of external and internal variabilities was the potential triggers of glacial fluctuations. [ABSTRACT FROM AUTHOR]

Studies on long‐chain n‐alkan‐2‐ones from lake sediments remain sparse. In this study, we present an n‐alkan‐2‐one record from Qionghai Lake, southwest China, to assess the paleoclimate significance of variations in their compositions. A homologous series of n‐alkan‐2‐ones ranging from C21 to C35 were identified, with maximum concentrations of the C29 or C31 chain lengths and a strong odd‐over‐even predominance. This type of n‐alkan‐2‐one is considered to derive mainly from microbial oxidation of the corresponding n‐alkanes, and partial inputs from plants. The n‐alkan‐2‐one‐derived average chain length (ACL) and carbon preference index (CPI) values changed significantly over the past 28k cal a bp, consistent with the sediment grain size and n‐alkane proxies from the same core. Generally, the high CPI27‐33‐ket and low ACL27‐33‐ket values indicated cold and dry climates such as for the Last Glacial Maximum (23.2–19.7k cal a bp), Heinrich 1 event (17.6–15.6k cal a bp) and Younger Dryas (12.8–11.6k cal a bp), but low CPI27‐33‐ket and high ACL27‐33‐ket values denoted a warm and humid Holocene Climatic Optimum (7.0–4.3k cal a bp). Therefore, n‐alkan‐2‐ones have great paleoclimatic potential and can be applied together with other biomarkers to reconstruct a reliable paleoclimate record in lake sediments. [ABSTRACT FROM AUTHOR]

In order to better explore quantitative reconstructions of net primary productivity (NPP) conditions using a dinoflagellate cyst (dinocyst)-based transfer function method, we revised the tropical Atlantic modern dinocyst database n  = 208 (Marret et al., 2008). Modern assemblages from the worldwide dinocyst atlas (Zonneveld et al., 2013) were added to provide a better geographical coverage of the South Atlantic Ocean. The environmental dataset was updated using the World Ocean Atlas 2013 for sea-surface temperature (SST) and sea-surface salinity (SSS) data, as well as for 1997–2017 mean NPP values recorded during SeaWifs and MODIS spatial programs. New environmental datasets were tested using anomalies regarding mean latitudinal SST as a potential index to track past upwelling activity. Finally, preindustrial NPP values, simulated with the IPSL-CM5A-LR model developed at the Institut Pierre Simon Laplace (IPSL) have been added to the dinocyst environmental database to provide NPP values consistent with the mean age of “modern” dinocyst assemblages. The transfer function method using the updated modern database was then applied to fossil dinocyst assemblages of core KZAI-01, retrieved off the Congo River mouth and covering the last 43.2 kyr. Our results indicate a dominant orbital forcing, with higher primary productivity values reconstructed during precession minima (MIS 3 and the last deglaciation) and enhanced by a maximum of obliquity during the last deglaciation and the Holocene. The synchronicity between high upwelling intensity and high terrigenous inputs during high NPP period (e.g. during the last Deglaciation) highlighted the prevalent role of river-induced upwelling activity, which is specific to the Congo River. These results have improved our understanding of the environmental forcing leading to major trophic changes in the intertropical area. [ABSTRACT FROM AUTHOR]

In the Subarctic Pacific, variability in productivity on glacial-interglacial timescales is often attributed to changes in stratification and nutrient delivery to the surface, but the mechanisms driving this relationship are poorly constrained. Records extending beyond the last glacial maximum from both the open ocean and the marginal seas are required to investigate the timing and magnitude of different influential processes through the full glacial cycle. In this study we generated 231Pa/230Th over 210,000 years in order to capture two full glacial cycles of paleoproductivity on the Juan de Fuca Ridge in the East Subarctic Pacific. The sedimentary 231Pa/230Th ratios are always equal to or greater than the seawater production ratio (0.093), consistent with enhanced biological scavenging in this region. The temporal pattern of 231Pa/230Th burial is remarkably coherent with changes in climate, with high values (0.20) during peak interglacial periods descending to low values (0.10) during peak glacial conditions, consistent with other long productivity records from this region. We investigate the possible contributions of temperature, sea ice formation, Bering Strait closure, wind strength, upwelling, and subsurface nutrient concentrations as possible mechanisms by which physical and/or chemical stratification emerged during glacial periods. Due to the low sea surface salinity in the North Pacific, cooling actually weakens the density gradient in surface (0–200 m) waters. To create the steep density profiles that characterize physical stratification, additional processes to reduce the salinity of surface waters must occur during glacial periods. We suggest that regional sea ice formation and Bering Strait closure may have contributed to freshening surface waters and enhancing physical stratification during glacial periods. Additionally, simulated weak winds in this region due to the southward shift of the glacial westerlies may have further reduced surface mixing depths in the Subarctic Pacific. Finally, previous model simulations suggest strong glacial wind stress curl in the Subarctic Pacific, but enhanced Ekman divergence of nutrient-poor subsurface waters would have little impact on stimulating productivity in surface waters of the Subarctic Pacific. We therefore suggest that the combined effects of surface freshening, weak winds, and lower subsurface nutrient concentrations may all have contributed to lower productivity during glacial periods in the Subarctic Pacific. Key Points: Productivity is highest during interglacial periodsProductivity varies in step with global climateGlacial stratification may be driven by a strong pycnocline, weak winds, and/or reduced subsurface nutrient concentrations [ABSTRACT FROM AUTHOR]

South Westland, New Zealand, and southern Chile, are two narrow continental corridors effectively confined between the Pacific Ocean in the west and high mountain ranges in the east which impart significant influence over regional climate, vegetation and soils. In both these southern mid-latitude regions, evidence for extensive and repeated glaciations during cold phases of the Quaternary is manifested by arrays of successively older glacial drift deposits with corresponding outwash plain remnants. In South Westland, these variably aged glacial landforms are mantled by layered (multisequal) soils characterised by slow loess accretion and pedogenesis in an extreme leaching and weathering environment. These cover-bed successions have undergone repeated coupled phases of topdown and upbuilding soil formation that have been related to fluctuating cycles of interglacial/warm and glacial/cold climate during the Quaternary. In this study, we recognise multisequal soils overlying glacial landforms in southern continental Chile but, unlike the spodic (podzolic) soil sequences of South Westland, these are of dominantly volcanigenic (andic) provenance and are very similar to multisequal soils of andic provenance that predominate in, and adjacent to, areas of rhyolitic to andesitic volcanism in North Island, New Zealand. Here we develop a soil-stratigraphic model to explain the observed occurrence of multisequal soils mantling dominantly glacial landforms of southern continental Chile. Based on proxy data from southern Chile, we propose that persistent vegetation cover and high precipitation on the western side of the Andes, during colder-than-present episodes tended to suppress the widespread production of glacially-derived loessial materials despite the pervasive occurrence of glacial and glacio-fluvial deposits that have frequently inundated large tracts of this landscape during the Quaternary. Given the lack of loess cover-beds that have traditionally assisted in the relative dating of glacial episodes prior to the Late Quaternary, surface exposure dating techniques could provide another chronological alternative to address this issue. However, there have been two main obstacles to successfully apply this dating technique in Patagonia. First, minimum exposure ages may be obtained on moraines older than the last glacial cycle due to erosion, although dating outwash plains is more robust. Second, on the wet western side adjacent to the Andes, persistent vegetation cover during both glacial and post-glacial times, as well as widespread inundation by volcanic mass-flows, appear preventive. We make a case that soil genesis within this region appears to be dominated by a constant flux of intermittently erupted Andean-sourced tephra which has continued to upbuild soils at the ground surface separated by intervals where topdown weathering processes are intensified. As already demonstrated by New Zealand studies, multisequal soil successions have a clear implied connection to coupled glacial and interglacial climate cycles of the Quaternary. On this basis, similar sequences in northwest Patagonia provide a relatively untapped archive to enable Quaternary glacial and environmental changes in this pervasively glaciated volcanic region to be constructed. [ABSTRACT FROM AUTHOR]

Aim The regional co-occurrence of contrasting bioclimatic elements (warm-temperate, continental, boreal, arctic-alpine) may be shaped by the distribution of their glacial or post-glacial refugia. We tested this hypothesis using pollen proxies in a region where such refugia are expected, but not unequivocally demonstrated. Location East-Central Europe (Western Carpathians and adjacent regions). Methods We compiled pollen spectra from 112 sites distributed across various landscapes for six time-periods from the Late Glacial to the present. Compositional patterns were assessed by principal coordinates analyses ( PCoA) with a sensitivity analysis based on a bootstrap technique. Site PCoA scores were interpolated geographically and correlated with palaeoclimatic models. Results Consistently over the last 15,000 years, the first ordination axis sorted samples according to the proportion of deciduous temperate trees, while the second axis consistently followed an altitudinal gradient that coincided with temperature. The principal gradient was more important than the altitudinal gradient except for the Late Glacial and Bronze & Iron Ages, when both gradients were of similar importance. The fine-grained pattern in the present mountain landscape was formed as late as during early modern colonization. Main conclusions Since the Late Glacial, the landscape has been differentiated into temperate, continental and cold regions. This finding supports the hypothesis that refugia are a key factor for understanding current biogeography in Central Europe. The Late Glacial occurrence of temperate trees is unlikely to be explained only by gradual migrations from southern Europe. Humid but relatively warm mountains hence might have acted as glacial refugia of temperate forest species, while lowlands and leeward basins might have acted as post-glacial refugia of steppe grasslands. The strong contrast between forested (temperate) and more open continental landscapes during the Early Holocene seems to correspond with recent diversity patterns. Our results highlight the relevance of integrating past landscape trajectories into modern biogeographical models. [ABSTRACT FROM AUTHOR]

ABSTRACT A flowstone from the central European Abaliget Cave (Mecsek Mts, Hungary) provides a record of uninterrupted calcite deposition between ∼160 and ∼124 ka, covering most of Marine Isotope Stage (MIS) 6 and part of 5e. δ18O values of three lateral drill cores show synchronous high-frequency (millennial-scale) variability during MIS 6, interpreted as stadials and interstadials, and a 3.4‰ rise at the MIS 6/5e boundary. The interstadials are mostly symmetrical in shape and show consistently lower δ18O values than calcite formed during MIS 5e. The rises (decreases) in δ18O are followed by drops (increases) in δ13C with a delay of 1-2 ka, implying enhanced (reduced) soil bioproductivity. This period of highly variable climate is bracketed by two broad δ18O minima. The first minimum between ∼160 and ∼148 ka coincided with a maximum in ice-rafted detritus in the eastern North Atlantic. The second one from ∼134 to ∼129 ka occurred during Heinrich 11, before the rapid and large δ18O increase at ∼128 ka. [ABSTRACT FROM AUTHOR]

Numerical glacier models applied to moraine chronologies provide an opportunity to quantify past climate change. Here we apply a two-dimensional coupled mass balance – ice flow model to well-dated moraine sequences deposited by former alpine glaciers at two central Patagonian sites: Cerro Riñón (43.97°S, 71.64°W) and Río Tranquilo (47.50°S, 72.38°W), to reconstruct the local temperatures during both the Antarctic Cold Reversal (14.7–13 ka) and the Younger Dryas (12.9–11 ka). Modelled temperature anomalies during the Antarctic Cold Reversal are −2.6 ± 0.4 °C at 44°S, and −2.9 ± 0.6 °C at 47°S. At both locations this cold event is followed by temperature increases of +0.6–0.7 °C or precipitation reductions of c. 20% to drive glacier retreat to moraines deposited during Younger Dryas time. The consistent climatic anomalies between these two latitudes suggest this region of Patagonia was responding to a common climatic event. Further, the late-glacial temperature anomalies found here compare well to those determined by similar glacier modelling techniques in New Zealand, at 43–44° S. These results support a trans-Pacific response throughout the southern mid to high latitudes (43–47° S) during the ACR that is best explained by a northward expansion of the south westerly winds. • Glacier modelling reconstructs Patagonian temperatures during late-glacial. • Cooling of −2.7 to −2.9 ° C below modern during the Antarctic Cold Reversal. • Warming of +0.6 ° C from the Antarctic Cold Reversal into the Younger Dryas period. • Climate trends parallel New Zealand glaciers implicating southern westerly winds. [ABSTRACT FROM AUTHOR]

Past cold climates are often thought to have been drier than today on land, which appears to conflict with certain recent studies projecting widespread terrestrial drying with near-future warming. However, other work has found that, over large portions of the continents, the conclusion of future drying versus wetting strongly depends on the physical property of interest. Here, it is shown that this also holds in simulations of the Last Glacial Maximum (LGM): the continents have generally wetter topsoils and higher values of common climate wetness metrics than in the preindustrial, as well as generally lower precipitation and ubiquitously lower photosynthesis (likely driven by the low CO2), with streamflow responses falling in between. Using a large existing global pollen and plant fossil compilation, it is also confirmed that LGM grasslands and open woodlands grew at many sites of present-day forest, seasonal forests at many sites of present-day rain forest, and so forth (116-144 sites out of 302), while changes in the opposite sense were very few (9-17 sites out of 302) and spatially confined. These vegetation changes resemble the model photosynthesis responses but not the hydroclimate responses, while published lake-level changes resemble the latter but not the former. Thus, confidence in both the model hydrologic and photosynthesis projections is increased, and there is no significant conflict. Instead, paleo- and modern climate researchers must carefully define 'wetting' and 'drying' and, in particular, should not assume hydrologic drying on the basis of vegetation decline alone or assume vegetation stress on the basis of declines in hydroclimatic indicators. [ABSTRACT FROM AUTHOR]

The behavior of subtropical glaciers during Middle to Late Pleistocene global glacial maxima and abrupt climate change events, specifically in Earth's most arid low-latitude regions, remains an outstanding problem in paleoclimatology. The present-day climate of Cordillera Oriental, in arid northwestern Argentina, is influenced by shifts in subtropical climate systems, including the South American Summer Monsoon. To understand better past glacier-subtropical climates during the global Last Glacial Maximum (LGM, 26.5–19 ka) and other time periods, we combined geomorphic features with forty-two precise 10 Be ages on moraine boulders and reconstructed paleo-equilibrium line altitudes (ELA) at Nevado de Chañi (24°S) in the arid subtropical Andes. We found a major glacial expansion at ∼23 ± 1.6 ka, that is, during the global LGM. Additional glacial expansions are observed before the global LGM (at ∼52–39 ka), and after, at 15 ± 0.5 and 12 ± 0.6 ka. The ∼15 ka glacial event was found on both sides of Chañi and the ∼12 ka event is only recorded on the east side. Reconstructed ELAs of the former glaciers exhibit a rise from east to west that resembles the present subtropical climate trajectory from the Atlantic side of the continent; hence, we infer that this climate pattern must have been present in the past. Based on comparison with other low-latitude paleoclimate records, such as those from lakes and caves, we infer that both temperature and precipitation influenced past glacial occurrence in this sector of the arid Andes. Our findings also imply that abrupt deglacial climate events associated with the North Atlantic, specifically curtailed meridional overturning circulation and regional cooling, may have had attendant impacts on low subtropical Southern Hemisphere latitudes, including the climate systems that affect glacial activity around Nevado de Chañi. [ABSTRACT FROM AUTHOR]

Glaciers offer the potential to reconstruct past climate over timescales from decades to millennia. They are found on nearly every continent, and at the Last Glacial Maximum, glaciers were larger in all regions on Earth. The physics of glacier-climate interaction are relatively well understood, and glacier models can be used to reconstruct past climate from geological evidence of past glacier extent. This can lead to significant insights regarding past, present, and future climate. For example, glacier modeling has demonstrated that the near-ubiquitous global pattern of glacier retreat during the last few centuries resulted from a global-scale climate warming of ∼1°C, consistent with instrumental data and climate proxy records. Climate reconstructions from glaciers have also demonstrated that the tropics were colder at the Last Glacial Maximum than was originally inferred from sea surface temperature reconstructions. Future efforts to reconstruct climate from glaciers may provide new constraints on climate sensitivity to CO2 forcing, polar amplification of climate change, and more. [ABSTRACT FROM AUTHOR]

The characterization of Last Glacial millennial-timescale warming phases, known as interstadials or Dansgaard-Oeschger events, requires precise chronologies for the study of paleoclimate records. On the European continent, such chronologies are only available for several Last Glacial pollen and rare speleothem archives principally located in the Mediterranean domain. Farther north, in continental lowlands, numerous high-resolution records of loess and paleosols sequences show a consistent environmental response to stadial-interstadial cycles. However, the limited precision and accuracy of luminescence dating methods commonly used in loess deposits preclude exact correlations of paleosol horizons with Greenland interstadials. To overcome this problem, a radiocarbon dating protocol has been developed to date earthworm calcite granules from the reference loess sequence of Nussloch (Germany). Its application yields a consistent radiocarbon chronology of all soil horizons formed between 47 and 20 ka and unambiguously shows the correlation of every Greenland interstadial identified in isotope records with specific soil horizons. Furthermore, eight additional minor soil horizons dated between 27.5 and 21 ka only correlate with minor decreases in Greenland dust records. This dating strategy reveals the high sensitivity of loess paleoenvironments to Northern Hemisphere climate changes. A connection between loess sedimentation rate, Fennoscandian ice sheet dynamics, and sea level changes is proposed. The chronological improvements enabled by the radiocarbon "earthworm clock" thus strongly enhance our understanding of loess records to a better perception of the impact of Last Glacial climate changes on European paleoenvironments. [ABSTRACT FROM AUTHOR]

Dansgaard-Oeschger oscillations constitute one of the most enigmatic features of the last glacial cycle. Their cold atmospheric phases have been commonly associated with cold sea-surface temperatures and expansion of sea ice in the North Atlantic and adjacent seas. Here, based on dinocyst analyses from the 48-30 ka interval of four sediment cores from the northern Northeast Atlantic and southern Norwegian Sea, we provide direct and quantitative evidence of a regional paradoxical seesaw pattern: cold Greenland and North Atlantic phases coincide with warmer sea-surface conditions and shorter seasonal sea-ice cover durations in the Norwegian Sea as compared to warm phases. Combined with additional palaeorecords and multi-model hosing simulations, our results suggest that during cold Greenland phases, reduced Atlantic meridional overturning circulation and cold North Atlantic sea-surface conditions were accompanied by the subsurface propagation of warm Atlantic waters that re-emerged in the Nordic Seas and provided moisture towards Greenland summit. [ABSTRACT FROM AUTHOR]

A new detailed pollen and oxygen isotope record of the penultimate interglacial-glacial cycle, corresponding to the marine isotope stage (MIS) 7-6, has been generated from the Ahlat Ridge (AR) sediment core at Lake Van, Turkey. The presented Lake Van pollen record (ca. 250.2-128.8 ka) displays the highest temporal resolution in this region with a mean sampling interval of ~540 years. The integration of all available proxies shows three temperate intervals of high effective soil moisture availability. This is evidenced by the predominance of steppe-forested landscapes (oak steppe-forest) similar to the present interglacial vegetation in this sensitive semiarid region between the Black Sea, the Caspian Sea, and the Mediterranean Sea. The wettest and warmest stage, as indicated by highest temperate tree percentages, can be broadly correlated with MIS 7c, while the amplitude of the tree population maximum during the oldest penultimate interglacial (MIS 7e) appears to be reduced due to warm but drier climatic conditions. The detailed comparison of the penultimate interglacial complex (MIS 7) to the last interglacial (Eemian, MIS 5e) and the current interglacial (Holocene, MIS 1) provides a vivid illustration of possible differences in the successive climatic cycles. Intervening periods of treeless vegetation can be correlated with MIS 7d and 7a, in which open landscapes favor local erosion and detrital sedimentation. The predominance of steppe elements (e.g., Artemisia, Chenopodiaceae) during MIS 7d indicates very dry and cold climatic conditions. In contrast, the occurrence of higher temperate tree percentages (mainly deciduous Quercus) throughout MIS 7b points to relatively humid and mild conditions, which is in agreement with other pollen sequences in southern Europe. Despite the general dominance of dry and cold desert-steppe vegetation during the penultimate glacial (broadly equivalent to MIS 6), this period can be divided into two parts: an early stage (ca. 193-157 ka) with higher oscillations in tree percentages and a later stage (ca. 157-131 ka) with lower tree percentages and subdued oscillations. This subdivision of the penultimate glacial is also seen in other pollen records from southern Europe (e.g., MD01-2444 and I-284; Margari et al., 2010; Roucoux et al., 2011). The occurring vegetation pattern is analogous to the division of MIS 3 and MIS 2 during the last glacial in the same sediment sequence. Furthermore, we are able to identify the MIS 6e event (ca. 179-159 ka) as described in marine pollen records, which reveals clear climate variability due to rapid alternation in the vegetation cover. In comparison with long European pollen archives, speleothem isotope records from the Near East, and global climate parameters (e.g., insolation, atmospheric CO2 content), the new high-resolution Lake Van record presents an improved insight into regional vegetation dynamics and climate variability in the eastern Mediterranean region. [ABSTRACT FROM AUTHOR]

In this study, we provide combined biochronologic and chronostratigraphic constraints to the fluvial-lacustrine succession cropping out near the village of Rignano Flaminio, 35 km north of Rome, where two bone instruments have been recovered along with several vertebrate fossil remains. The presence of bone tools is characteristic of the Latium region, whereas it is rare in the rest of Italy, but very few sites in which such artifacts occur have precise geochronological constraints. In the investigated site, the presence of Cervus elaphus eostephanoceros , among other taxa, indicates a time interval limited to Marine Isotopic Stage (MIS) 13 and MIS 11. The occurrence of the Tufo Rosso a Scorie Nere pyroclastic-flow deposit, dated 449 ± 2 ka, at the base of the sedimentary deposits hosting the faunal assemblage allows us at restricting the interval to MIS 11. Moreover, applying a recently validated conceptual model accounting for an aggradational mechanism linked with sea-level rise during glacial termination for the sedimentary successions of the Tiber River and its tributaries in a relatively wider area around Rome, we further constrain the age to 430–405 ka. Following this approach, we present a review of the archaeological sites of Latium yielding bone instruments, remarking that only other four sites have been recently provided with geochronological constraints, through the application of the multidisciplinary methodology applied here. [ABSTRACT FROM AUTHOR]

Well-preserved Late Glacial moraines in the Barenduo and Yuqiongqu valleys on the eastern slope of the Samdainkangsang Peak present an opportunity to reconstruct glacier extents and examine the character of the climate during the Late Glacial stage in the Nyaiqentanggulha Mountains. This study employs a coupled mass-balance and ice-flow model to reconstruct the glacier extents in the two valleys and assess the magnitudes of temperature and precipitation change during the Late Glacial period. Model results indicate that during the Late Glacial, the Barenduo valley contained an ice volume of 1.67×108 m3, with the equilibrium-line altitude (ELA) being ~5500 m asl; and the Yuqiongqu valley had an ice volume of 5.56×108 m3, with the ELA being ~5470 m asl. A climate scenario, temperature depression of 2.6-2.8°C and 60-70%, percent of modern (1981-2010) precipitation, can sustain both of the Late Glacial glacier extents in the two valleys. A 50% increase or decrease from modern precipitation would have been coupled with the respective Late Glacial temperature depressions of 1.6 and 3.0°C in the Barenduo valley, and 2.1 and 2.8°C in the Yuqiongqu valley. [ABSTRACT FROM AUTHOR]

This paper is the first analysis of differences between Last Glacial Maximum (LGM) and present climates in southern South America considering the state-of-the-art PMIP3 paleoclimatic models. The study is focused on characteristics of temperature and precipitation over the portion of the continent to the south of 20°S at both sides of the Andes Cordillera. Results demonstrate that model outputs coincide with glacial conditions inferred from the very few paleorecords available in the region. Consequently, these models are a valuable tool for inferring additional conditions in areas where there is a lack of proxy information allowing the reconstruction of the past climate at regional scales. The analyzed PMIP3 models expose an LGM cooling of ∼2-5 °C throughout the year over almost all southern South America but differences are even more pronounced in areas around the southern Andes. Models also suggest that LGM precipitation was substantially lower than present over the portion of southern South America to the east of the Andes inferring reductions of ∼20–30% with respect to present-day values in subtropical areas and ∼40–50% in the southern tip of the continent. [ABSTRACT FROM AUTHOR]

On the basis of detailed analysis (sedimentological, palynological, macroremains, geochemical and GIS analysis) the development of the Sumowskie Paleolake was reconstructed. Obtained results led to distinguish three main stages of the evolution of the basin and its catchment during the Late Glacial and the Holocene: the lacustrine stage, the lake overgrowth stage and the post lacustrine stage. Study site is located in the western part of the Brodnica Lakeland, North-Eastern Poland, within the former Sumowskie Lake bottom. Multidisciplinary research was conducted for two cores (sedimentological, palynological, plant macroremains): SUM A (149 cm) and SUM C (51 cm) and the soil profile – SUM 3 (sedimentological, geochemical). GIS analyses (land cover and water level changes) were carried out for the nowadays Sumowskie Lakes catchment. It was confirmed, that climate was the most important factor influencing the evolution of the lake and its surrounding. Although the role of this factor decreased in the Neo-Holocene period in favor of rapidly growing human impact. Changes of the water level were much more abrupt and lasted longer (e.g. 9500? – 5000? BP hiatus caused by the water level decrease) than in other described basins of the region due to the specific geomorphologic situation. Shallow kettle basins could alternately act as lakes and wetlands. As they are well-spread in the young glacial area, the strong influence of this abrupt and long term events should be reconsidered. [ABSTRACT FROM AUTHOR]

Latest Pleistocene fossil soils and deposits have been described in the geoarchaeological site Divnogorie 9 (the Middle Don drainage basin) under the name of Divnogorie pedolithocomplex. For the first time, a soil-sediment series with 2–3 levels of soil formation has been described in the forest-steppe of the Russian Plain and dated to the Bølling–Allerød interval (BØ–AL). That was the last soil formation of Pre-Holocene time. The soils are weakly developed (immature), of meadow and burozem genesis. They formed for a few hundreds of years in periglacial steppe environments, under forest-steppe vegetation. The lower soil (attributed to Bølling) is dated at 13.5–14 ka cal BP and defined as a weakly developed Petrocalcic Skeletic Colluvic Siltic Chernozem. Under coniferous-broadleaf forests the middle soil is described as Umric Calcaric Colluvic Siltic Leptosol and dated at Dryas-2. The uppermost soil dated at Allerød is weakly developed Skeletic Calcaric Colluvic Siltic Cambisol formed under coniferous-broadleaf forest-steppe. The data obtained made possible reconstructions of the Late Glacial climates and landscapes. The underlying sediments are the deposits of Divnogorie paleo-lake. The deposits include seven bone-bearing horizons with Late Upper Palaeolithic lithic tools. They are dated to the interval 17–14 ka Cal BP. [ABSTRACT FROM AUTHOR]

The Magdalen Islands (Québec, Canada) are a key location for unravelling the glacial and sea-level history of the Maritime Provinces of eastern Canada. Although many sedimentary sequences have been described in the literature, absolute ages are lacking, impeding an accurate interpretation of the deposits and the establishment of a precise chronological framework. This study provides a detailed description of 21 stratigraphical sequences located throughout the archipelago, as well as the first comprehensive luminescence chronology from the Last Glacial Maximum (LGM) to c. 10 ka. In addition to the five samples collected for age control purposes, 34 luminescence samples were taken from 17 different sites in glacial, periglacial and coastal deposits. The stratigraphical and chronological data reveal that the islands were at the crossroads of two icecaps during the LGM; the southern islands were glaciated by the Escuminac icecap located in the western Gulf of St. Lawrence whereas the northern archipelago was glaciated at the end of the LGM by an ice flow from Newfoundland. The glacial deposit covering the northern Magdalen Islands was associated with the Newfoundland icecap; here it is named the Grande-Entrée till and is dated to c. 20 ka. OSL ages between c. 23 and 17 ka acquired from cryopediment and coastal deposits on the southern islands indicate that this part of the archipelago was deglaciated shortly after the LGM and was affected by a high sea level and periglacial processes. Around 15 ka, the entire archipelago was deglaciated and partially submerged until c. 10 ka. This data set is the first major contribution to a detailed chronology of the Magdalen Islands and constitutes the first step towards interpreting the glacial and sea-level history of the central area of the Gulf of St. Lawrence; this new understanding will provide input to regional marine and glacial modelling. [ABSTRACT FROM AUTHOR]

In this study, we report standard quartz SAR OSL and post-IR infrared (IR) stimulated luminescence (post-IR IRSL; pIRIR290) measurements made on sand-sized quartz and K-feldspar extracts from the loess-palaeosol sequence at Niuyangzigou in northeastern China. The quartz OSL characteristics are satisfactory. Extensive pIRIR50,290 dose recovery tests were performed by adding doses on top of the natural dose. We found that dose recovery ratios improve significantly when the test dose ranges between ∼15 and ∼80% of the total dose, and good dose recovery (within ±5% of unity) can be obtained up to ~800 Gy. Otherwise, the dose recovery ratio deviates from unity. The De values also depend on the test dose size and so we conclude that the effect of test dose size should be routinely considered in pIRIR dating. First IR stimulation plateau pIRIR290 results are compared with multiple elevated temperature-pIRIR (MET-pIRIR) data. It appears that the low temperature MET-pIRIR data are strongly affected by poor dose recovery, but this is not the case for the pIRIR290 results. Natural signal measurements at the highest (first IR) stimulation temperature on a sample expected to be in field saturation suggest that ∼10% signal loss occurs in pIRIR signals. Long-term laboratory bleaching experiments (>80 days) show that a constant (or very difficult to bleach) residual pIRIR290 signal is reached after ∼300 h, corresponding to a dose of 6.2±0.7 Gy. Quartz OSL and feldspar pIRIR50,290 ages are in good agreement at least back to c. 70 ka. Beyond this the quartz ages begin to underestimate but the feldspar ages are in agreement with the expected Last Interglacial age palaeosol. [ABSTRACT FROM AUTHOR]

The Kapp Ekholm site, in central Spitsbergen, shows alternating units of glaciomarine sandy silt and diamicton representing three glacial cycles and is key in reconstructing the Late Pleistocene glacial history of Svalbard. Part of the site is reinvestigated here by focusing on re-dating two units (B and F) interpreted as interglacial/interstadial glaciomarine deposits, in order to constrain the controversial chronology. A combination of Optical Stimulated Luminescence (OSL) on quartz, infrared stimulated luminescence with a 50 °C readout temperature (IRSL50) and post infrared-infrared stimulated luminescence (pIR), both on feldspar, was applied. While Formation B was beyond the dateable range of OSL, IRSL50 and pIR ages lead to the conclusion that this unit represents the Last Interglacial, Marine Isotope Stage (MIS) 5e, and the underlying diamicton the MIS 6 glacial. Formation F yielded ages implying that the formation represents the MIS 5a interstadial and the underlying diamicton is interpreted to represent the MIS 5b stadial. This agrees with conclusions drawn concerning the Pleistocene glaciations elsewhere on Svalbard. [ABSTRACT FROM AUTHOR]

Palynology of fossil faeces is still extremely rare and its contribution to the interpretation of the environment undervalued. In this paper we present the results of pollen analysis performed on cave hyena coprolites [ Crocuta crocuta spelaea (Goldfuss, 1832)] from Marine Isotope Stage 3 (MIS 3) sites of Cava Muracci (Cisterna di Latina, central Italy) and Tana delle Iene (Ceglie Messapica, southern Italy). This study provides new insights into the vegetation of the Late Pleistocene of peninsular Italy, until now known only through long pollen records. It also shows how the content of coprolites, combined with faunal data and geochronological investigations, can represent a potential integrative source of palaeoclimatic proxy data. Our results indicate that the surroundings of both of the hyena dens were characterised by a patchy landscape with open lowlands dominated by steppe and grassland vegetation, while a few mesophilous and thermophilous trees were present in more humid areas, probably along the marine coast and inland. The harsh glacial climate appears to have been milder at Cava Muracci than at Tana delle Iene. This could be due either to the different environmental features of the two sites or to the high climatic variability that occurred during MIS3. [ABSTRACT FROM AUTHOR]

Numerous ice-sheet reconstructions of the last glacial cycle have been proposed, however due to limited geological evidence, reconstructing older Northern Hemisphere ice sheets remains a difficult exercise. Here we focus on the penultimate glacial maximum (PGM; ~140 ka BP) over the Northern Hemisphere. While some evidence of the PGM Eurasian ice-sheet extent were found, this is not the case for the corresponding Laurentide ice sheet. To improve the glaciological reconstructions of the PGM Northern Hemisphere ice sheets, we explore the parameter space of ice-sheet model uncertainties and carry out numerous univariate ice-sheet steady-state sensitivity simulations. We use two PGM climate simulations to force the ice-sheet model, differing in the prescribed Laurentide ice topography (small and large). The simulated Northern Hemisphere ice volume ranges from 124.7 to 152 m SLE when using the climate accounting for a small Laurentide ice sheet, which is compatible with global sea-level reconstructions of this period (−92 to −150 m). Conversely, using the climate simulation with a Laurentide ice sheet comparable in size to that of the last glacial maximum results in too large ice volumes. Changes in basal drag provide the upper bound ice volume of our experiments, whereas changes in the distribution of ice streams provide the lower bound. [ABSTRACT FROM AUTHOR]

Using simulations performed by all available climate models participating in the latest Paleoclimate Modelling Intercomparison Project (PMIP) phase 3 (PMIP3), we revisited the climate over China and the East Asian monsoon during the last glacial maximum (LGM; 21,000 years ago). Similar to previous results obtained from the PMIP phases 1 and 2 (PMIP1/2) models, all nine models reproduced colder than the pre-industrial annual and seasonal temperatures over China during the LGM and underestimated the annual cooling as evidenced by proxy data. The LGM annual and seasonal precipitation and evaporation over China consistently decreased in the models, whereas the very small LGM change in net precipitation (precipitation minus evaporation) differed among models. The annual net precipitation change during the LGM was broadly consistent with reconstructed moisture conditions over most parts of China, especially over the western Tibetan Plateau where the PMIP1/2 models disagreed with the proxy data. Moreover, the LGM winter monsoon circulation weakened (strengthened) over the East Asian continent in four (one) of five models; the summer monsoon circulation generally weakened in two models, whereas it weakened north and strengthened south of about 30°N over East Asia in three models. The spatial patterns of the LGM change in East Asian winter and summer monsoons in the PMIP3 models differed somewhat from those in the PMIP1/2 simulations. [ABSTRACT FROM AUTHOR]

Vegetation and climate during the last ice age and the Last Glacial Maximum (LGM, ∼23,000–19,000 cal BP) were considerably different than during the current interglacial (Holocene). Cold climatic conditions and growing ice-sheets during the last glaciation radically reduced forest extent in Europe to a restricted number of so-called “refugia”, mostly located in the southern part of the continent. On the basis of paleobotanical analyses the Euganian Hills (Colli Euganei) in northeastern Italy have previously been proposed as one of the northernmost refugia of temperate trees (e.g. deciduous Quercus, Tilia, Ulmus, Fraxinus excelsior, Acer, Abies alba, Fagus sylvatica, Carpinus and Castanea ) in Europe. In this study we provide the first quantitative, vegetation independent summer air temperature reconstruction for Northern Italy spanning the time ∼31,000–17,000 cal yr BP, which covers the coldest periods of the last glacial, including the LGM and Heinrich stadials 1 to 3. Chironomids preserved in a lake sediment core from Lago della Costa (7m a.s.l.), a small lake at the south-eastern edge of the Euganean Hills, allowed quantitative reconstruction of Full and Late Glacial summer air temperatures using a combined Swiss-Norwegian temperature inference model based on chironomid assemblages from 274 lakes. Chironomid and pollen evidence from Lago della Costa derives from finely stratified autochthonous organic gyttja sediments, which excludes major sediment mixing or reworking. After reconstructing paleo-temperatures, we address the question whether climate conditions were warm enough to permit the local survival of temperate tree species during the LGM and whether local expansions and pollen-inferred contractions of temperate tree taxa coincided with chironomid-inferred climatic changes. Our results suggest that chironomids at Lago della Costa have responded to major climatic fluctuations such as temperature decreases during the LGM and Heinrich stadials. The vegetation of the Euganean Hills shows responses to these climatic oscillations although the effects of temperature changes were probably also strongly influenced by changes in humidity. Reconstructed July air temperatures at Lago della Costa never fell below 10–13 °C (error range of reconstruction ∼ ±1.5–1.6 °C), which is considerably above the limit considered necessary for forest growth (8–10 °C). Instead rather mild climatic conditions prevailed ∼31,000–17,000 cal yr BP with average summer temperatures between ∼12 and 16 °C, which most likely allowed survival of temperate tree taxa in the warmest (and moistest) microhabitats of the Euganean Hills during the LGM. Only assuming local survival is it possible to explain the repeated expansions and collapses of temperate trees at Lago della Costa which faithfully accompanied the climatic oscillations. [ABSTRACT FROM AUTHOR]

The late Jurassic–early Cretaceous is commonly considered the only cold climatic interval in Earth history without any direct evidence of polar ice. A newly discovered dropstone-bearing interval from the subtropical Iberian Basin (western Tethys) is described and provides evidence of contemporaneous polar glaciation. This interval is correlated laterally for 4.8 km and contains a boulder and two cobble-sized quartzite dropstones that are encased in mid-Cretaceous fissile black shales and fine-grained sandstones. Based on previously published dimensions of similar large clasts, only glacial dropstones and impact ejecta blocks reach the dimensions of the boulder-sized dropstone reported from Iberia. The dropstones show morphological features compatible with glacial transport and abrasion in a subglacial setting which closely resembles the features observed in recent glacial boulders exposed near the snouts of glaciers in Iceland. These Late Aptian dropstones from Spain correlate with many other similar erratics in the northern and southern palaeohemispheres, and suggest that ice sheets formed around the palaeo-North Pole during certain periods of the early Cretaceous. Our results and associated evidence such as the occurrence of glendonites, tillites, moderate- to high-amplitude sea-level oscillations worldwide, minimum pCO 2 concentrations, variation in calcareous nannofossil assemblages from low and high latitudes and isotopic excursions suggest that during the mid-Cretaceous there were periods of ice growth and decay that influenced the palaeotemperature, palaeoecology and sedimentology of the marine realm. The new data from Iberia are supported by recent results from Arctic Canada that indicate cool shelves and a mid-Cretaceous cold snap that developed for ~ 6 Myr between 118 and 112 Ma. The late Aptian dropstones reported in eastern Iberia were likely transported from high northern latitudes towards subtropical ones in the western Tethys by an extreme iceberg drift similar to those occurring at the present day in the Atlantic Ocean. Icebergs released from a northern fringing ice sheet may have travelled southwards through the Greenland–Norwegian Seaway. [ABSTRACT FROM AUTHOR]

This study investigates the possibility of Holocene glaciation on Mount Olympus (Greece) with a respective local temperature–precipitation equilibrium line altitude (TP-ELA) at c. 2200 m a.s.l., based on geomorphologic and paleoclimatic evidence. At present, the local TP-ELA is situated above the mountain’s summit (c. 2918 m a.s.l.), but permanent snowfields and ice bodies survive within Megala Kazania cirque between c. 2400 and c. 2300 m a.s.l., because of the cirque’s maritime setting that results from its close proximity (c. 18 km) to the Aegean Sea and of the local topographical controls. The snow and ice bodies occupied a considerably larger area and attained a stabilization phase between AD 1960 and 1980, also manifested from aerial photographs, a period characterized by increased winter precipitation (Pw) with subsequent TP-ELA depression to c. 2410 m a.s.l. Mid- to late-20th-century Pw and TP-ELA variations exhibit negative correlations with the winter North Atlantic Oscillation index (NAOw) at annual and multidecadal (30 years) timescales. Late Holocene (AD 1680–1860) reconstructed summer mean temperatures were lower by Ts < 1.1°C in relation to the reference period between AD 1960 and 1980 and were also superimposed to negative NAOw phases, thus bracketing this time interval as a favorable one to glacial formation and/or advance. Millennial-scale annual precipitation reconstructions at the hypothesized TP-ELA (c. 2200 m a.s.l.) point the period between 8 and 4 kyr BP as another glacier-friendly candidate. The mid-Holocene rather simplistic sequence of potential glacial advance phase was disturbed by short-lived cold climatic deteriorations, well-documented over the northern Aegean region that may partly explain the multicrested shape of the highest (c. 2200 m a.s.l.) morainic complex of Megala Kazania cirque. [ABSTRACT FROM AUTHOR]

Deglaciation chronology of the Bystra catchment (Western Tatra Mountains) has been reconstructed based on 10 Be exposure age dating. Fourteen rock samples were collected from boulders located on three moraines that limit the horizontal extent of the LGM maximum advance and the Lateglacial recessional stage. The oldest preserved, maximum moraine was dated at 15.5 ± 0.8 ka, an age that could be explained more likely by post-depositional erosion of the moraine. Such scenario is supported by geomorphologic and palaeoclimatological evidence. The younger cold stage is represented by well-preserved termino-lateral moraine systems in the Kondratowa and Sucha Kasprowa valleys. The distribution of the moraine ridges in both valleys suggest a complex history of deglaciation of the area. The first Late-glacial re-advance (LG1) was followed by a cold oscillation (LG2), that occurred at around 14.0 ± 0.7–13.7 ± 1.2 ka. Glaciers during both stages had nearly the same horizontal extent, however, their thickness and geometry changed significantly, mainly due to local climatic conditions triggered by topography, controlling the exposition to solar radiation. The LG1 stage occurred probably during the pre-Bølling cold stage (Greenland Stadial 2.1a), however, the LG2 stage can be correlated with the cooling at around 14 ka during the Greenland Interstadial 1 (GI-1d – Older Dryas). This is the first chronological evidence of the Older Dryas in the Tatra Mountains. The ELA of the maximum Bystra glacier was located at 1480 m a.s.l. in accordance with the ELA in the High Tatra Mountains during the LGM. During the LG1 and LG2 stages, the ELA in the catchment rose up to 1520–1530 m a.s.l. and was located approximately 100–150 m lower than in the eastern part of the massif. Climate modelling results show that the Bystra glacier (maximum advance) could have advanced in the catchment when mean annual temperature was lower than today by 11–12 °C and precipitation was reduced by 40–60%. This is in accordance with LGM conditions previously reported for the High Tatras. During the LG1 and LG2 stages the temperature decrease in the study area reached 10 °C and precipitation was lower by ∼30% compare to modern conditions. This resulted in slightly higher accumulation (20–30%) in the Western Tatra Mountains compare to the High Tatra Mountains. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of glaciation on mineral weathering, the stream water chemistry and the bacterial community composition were analysed in two catchments containing nominally identical sedimentary formations but which differed in the extent of glaciation. The stream waters were analysed for major ions, δ 34 S, δ 18 O SO4 and δ 18 O H2O and associated stream sediments were analysed by 16S rRNA gene tagged sequencing. Sulphate comprised 72–86% and 35–45% of the summer anion budget (in meq) in the unglaciated and glaciated catchments respectively. This indicates that sulfuric acid generated from pyrite weathering is a significant weathering agent in both catchments. Based on the relative proportions of cations, sulphate and bicarbonate, the stream water chemistry of the unglaciated catchment was found to be consistent with a sulphide oxidation coupled to silicate dissolution weathering process whereas in the glaciated catchment both carbonates and silicates weathered via both sulfuric and carbonic acids. Stable isotope measurements of sulphate, together with inferences of metabolic processes catalysed by resident microbial communities, revealed that the pyrite oxidation reaction differed between the two catchments. No δ 34 S fractionation relative to pyrite was observed in the unglaciated catchment and this was interpreted to reflect pyrite oxidation under oxic conditions. In contrast, δ 34 S and δ 18 O SO4 values were positively correlated in the glaciated catchment and were positively offset from pyrite. This was interpreted to reflect pyrite oxidation under anoxic conditions with loss of S intermediates. This study suggests that glaciation may alter stream water chemistry and the mechanism of pyrite oxidation through an interplay of biological, physical and chemical factors. [ABSTRACT FROM AUTHOR]

The influence of obliquity, the tilt of the Earth's rotational axis, on incoming solar radiation at low latitudes is small, yet many tropical and subtropical palaeoclimate records reveal a clear obliquity signal. Several mechanisms have been proposed to explain this signal, such as the remote influence of high-latitude glacials, the remote effect of insolation changes at mid- to high latitudes independent of glacial cyclicity, shifts in the latitudinal extent of the tropics, and changes in latitudinal insolation gradients. Using a sophisticated coupled ocean--atmosphere global climate model, EC-Earth, without dynamical ice sheets, we performed two idealized experiments of obliquity extremes. Our results show that obliquity-induced changes in tropical climate can occur without high-latitude ice sheet fluctuations. Furthermore, the tropical circulation changes are consistent with obliquity-induced changes in the cross-equatorial insolation gradient, suggesting that this gradient may be used to explain obliquity signals in low-latitude palaeoclimate records instead of the classical 65°N summer insolation curve. [ABSTRACT FROM AUTHOR]

Lying at the transition between temperate Mediterranean domain and subtropical deserts, the Levant is a key area to study the palaeoclimatic response over glacial-interglacial cycles. This paper presents a dated last interglacial (MIS 5) stalagmite (129-84 ka) from the Kanaan Cave, Lebanon. Variations in growth rate, morphology and petrology have been measured to derive a palaeoclimatic record. The speleothem growth curve shows rapid growth rates during the peak of MIS 5e (126-124 ka), moderate growth rates between 103.5 and 99 ka and very low growth rates from 99 to 84 ka. On the basis of the good correlation between the speleothem morphology and growth rates with the isotopic response of continental records from northern and southern Levant, we relate high growth rate to wet conditions during the maximum MIS 5e and MIS 5c. The peak in growth rates corresponds to sapropel events in the eastern Mediterranean. Low growth rates during MIS 5d and 5b indicate a transition to drier conditions. [ABSTRACT FROM AUTHOR]

The phenomenon of the Middle Pleistocene Transition (MPT)-a change of 41 k.y. periodicity of Pleistocene glacial cycles to 100 k.y. ones at about 1.24 Ma-is studied. Some MPT mechanisms proposed earlier by different authors are considered. It is concluded that the resonant MPT mechanism, implying the change in eigen (resonant) frequency of glacial sheets in the Northern Hemisphere due to the change in size of these sheets, is the least contradicting and fits the best the relevant empirical data. With respect to this mechanism, climate variations in the Early Pleistocene, until 1.24 Ma, resonantly responded to 41 k.y. insolation oscillations, which were caused by variations in Earth's axial tilt. After 1.24 Ma, owing to the growth of the global ice sheet volume and the increase in the period of eigen oscillations of the ice sheets, the direct eccentricity insolation signal characterized by the 100 k.y. (not 400 k.y.) periodicity was resonantly strengthened first. Some problems that emerged in the basis of the proposed mechanism are discussed. This mechanism explains the MPT phenomenon, the unsolved '100 k.y. period problem,' and the absence of the 400 k.y. periodicity in the Pleistocene climate oscillations from a common viewpoint. [ABSTRACT FROM AUTHOR]

Two global glaciations occurred during the Neoproterozoic. Snowball Earth theory posits that these were terminated after millions of years of frigidity when initial warming from rising atmospheric CO2 concentrations was amplified by the reduction of ice cover and hence a reduction in planetary albedo. This scenario implies that most of the geological record of ice cover was deposited in a brief period of melt-back. However, deposits in low palaeo-latitudes show evidence of glacial-interglacial cycles. Here we analyse the sedimentology and oxygen and sulphur isotopic signatures of Marinoan Snowball glaciation deposits from Svalbard, in the Norwegian High Arctic. The deposits preserve a record of oscillations in glacier extent and hydrologic conditions under uniformly high atmospheric CO2 concentrations. We use simulations from a coupled three-dimensional ice sheet and atmospheric general circulation model to show that such oscillations can be explained by orbital forcing in the late stages of a Snowball glaciation. The simulations suggest that while atmospheric CO2 concentrations were rising, but not yet at the threshold required for complete melt-back, the ice sheets would have been sensitive to orbital forcing. We conclude that a similar dynamic can potentially explain the complex successions observed at other localities. [ABSTRACT FROM AUTHOR]

Climate changes in the North Atlantic region during the last glacial cycle were dominated by the slow waxing and waning of the North American ice sheet as well as by intermittent, millennial-scale Dansgaard-Oeschger climate oscillations. However, prior to the last deglaciation, the responses of North American vegetation and biomass burning to these climate variations are uncertain. Ammonium in Greenland ice cores, a product from North American soil emissions and biomass burning events, can help to fill this gap. Here we use continuous, high-resolution measurements of ammonium concentrations between 110,000 to 10,000 years ago from the Greenland NGRIP and GRIP ice cores to reconstruct North American wildfire activity and soil ammonium emissions. We find that on orbital timescales soil emissions increased under warmer climate conditions when vegetation expanded northwards into previously ice-covered areas. For millennial-scale interstadial warm periods during Marine Isotope Stage 3, the fire recurrence rate increased in parallel to the rapid warmings, whereas soil emissions rose more slowly, reflecting slow ice shrinkage and delayed ecosystem changes. We conclude that sudden warming events had little impact on soil ammonium emissions and ammonium transport to Greenland, but did result in a substantial increase in the frequency of North American wildfires. [ABSTRACT FROM AUTHOR]

ABSTRACT The local last glacial maximum (LGML) on Dalijia Shan occurred during mid-marine isotope stage 3 (MIS3), which is consistent with some Tibetan Plateau records, but asynchronous with the MIS2 global Last Glacial Maximum (LGMG). Paleoclimatic reconstructions are key to advancing understanding such spatial and temporal patterns of paleoglaciation. Using multiple methods we reconstructed mid-MIS3 equilibrium-line altitude (ELA) on Dalijia Shan and inferred temperature depressions. Geomorphic ELA reconstructions combined with empirical data on current ELA temperature and precipitation yield a mid-MIS3 ELA of 4000 ± 78 m a.s.l. (618-851 m lower than current, and a temperature depression of 3.3-6.8 °C). Independent glacial modeling using the degree-day approach suggests a mid-MIS3 ELA between 3971 and 4024 m a.s.l. and a temperature depression of 4.2-5.6 °C. The consistency of these results indicate that mid-MIS3 temperature depressions in the Dalijia Shan region were 3.3-6.8 °C, which is less than the LGMG temperature depression inferred from regional climatic proxy data. Combined with other proxy data, this suggests that the LGML glacial advance in Dalijia Shan resulted from lower temperatures and slightly reduced precipitation compared with present, whereas the LGMG advance was more restricted because much colder conditions were combined with much lower precipitation. [ABSTRACT FROM AUTHOR]

Sea-surface temperatures (SSTs) based on radiolarian assemblage changes are estimated for the last 160 kyr, from a sediment core (Y9) recovered from Pukaki Saddle, northeast of Campbell Plateau. Site Y9 lies beneath Subantarctic Surface Water (SAW) immediately to the north of the Subantarctic Front (SAF), which in this region is bathymetrically constrained by the edges of Campbell Plateau and defines the northern boundary of the Antarctic Circumpolar Current (ACC). Radiolarian assemblages are characterised by an exceptionally high abundance of the Antarctic to subantarctic species Antarctissa spp. (up to 68%), especially during glacial intervals. SST estimates are derived using Factor Analysis and the Modern Analog Technique. Both methods capture the glacial-interglacial (G-I) pattern. The SST reconstructions show the changing relative influence of distinct water masses during the past G-I cycle, with major temperature variations of the order of 7–9 °C at glacial Terminations. Glacials (marine isotope stages (MIS) 6 and 2) are associated with particularly cool SSTs that are indicative of a more vigorous SAF/ACC and an enhancement of the inflow through Pukaki Saddle and/or frequent development of cold-core eddies at the SAF. By contrast, the influence of warmer waters and relaxation of the ACC during interglacials can be inferred from temperatures slightly warmer (e.g., mid-Holocene) and/or comparable to present day (e.g., MIS 5e). During these intervals, relatively warmer temperatures most likely indicate a higher warm-core eddy activity due to a strengthened Subtropical Front and/or a weakened inflow of cool water through Pukaki Saddle and/or an increased stratification in the Campbell Plateau region. Furthermore, the SST record is characterised by an abrupt warming at ca. 10 kyr (i.e., Termination I), the occurrence of a reversal at Termination I, and a warming event at the end of MIS 4, coinciding with the A4 event in the Byrd ice core. These characteristics, together with the pronounced G-I cycle shown by the SST estimates, suggest that Site Y9 is influenced by major oceanographic changes in the SW Pacific and responds to thermal changes at high southern latitudes. [ABSTRACT FROM AUTHOR]

The Levant, a transition zone between the temperate Mediterranean domain and subtropical deserts, is a key area to study the latitudinal migrations of zonal climatic belts in response to glacial-interglacial conditions. The region underwent large climatic shifts during the Late Quaternary, with dramatic impacts on water resources and human populations. This paper presents the unique long-term hydroclimatic record (ca. 400 ka) from Northern Levant, derived from a sediment core taken from a small tectonic basin of northern Lebanon, the currently wettest area of the Levant. Combined biotic (pollen, biologic aquatic remains) and abiotic proxies (sediment properties, carbonate oxygen isotopes) reveal relatively high water availability during interglacials and generally drier glacials periods during the past four climate cycles. These general trends are in line with pollen records from southeastern and near east Mediterranean areas, but differ from some paleohydrological records from the southern Levant. Southward migrations of the rain-bearing mid-latitude westerlies during glacial periods and regional land topography are likely to explain the observed regional climate signatures. In addition, distinctive climate signatures of the successive wetter/drier intervals reflect interactions between global forcing (insolation, atmospheric greenhouse gas concentration), eastern Mediterranean Sea surface conditions intimately linked to North Atlantic climate and to ice-sheet and sea-ice extent at high northern latitudes, land topography, and local hydrogeological processes. Our record brings new benchmarks for understanding the spatial heterogeneity of eastern Mediterranean responses to global climate changes. [ABSTRACT FROM AUTHOR]

Time-equivalent Early Permian sedimentary successions from high-latitude Gondwana basins and from equatorial accumulations in North China, covering the glacial to postglacial transition, display correlatable trends in continental weathering intensity based on chemical index of alteration (CIA) values. The successions display a pattern of CIA values that varies with latitude, similar to modern estuarine suspended sediments. Based on the modern-day CIA-temperature correlation, the glacial Early Permian low- to high-latitude land surface temperature gradient is estimated as ~20 °C, slightly higher than the calculated values for the contemporaneous sea-surface temperature gradient. [ABSTRACT FROM AUTHOR]

Abstract: The last 6000 years are of particular interest to the understanding of the Earth System because the boundary conditions of the climate system did not change dramatically (in comparison to larger glacial–interglacial changes), and because abundant, detailed regional palaeoclimatic proxy records cover this period. Here, we present fossil pollen data and examine their climatic interpretation based on a 200-cm-deep trenched sedimentary profile from Mahanadi river side, located near the Barpahar hillock of Bargarh District, Odisha, which is influenced by the South-west and North-east monsoon. The 5840 y chronology of the sediment core is based on three 14C dates on soil samples. During 5840–4380 BP, dense tropical mixed deciduous forest consisting of Madhuca, Syzygium and Acacia flourished in the region along with Rhizophora under a warm and humid climate governed by high monsoonal activity. This phase of climate is associated with the Holocene Climatic Optimum which falls within the temporal range of 8000–5000 BP. Subsequently, an increase in humidity was discerned between 4380 and 3230 BP, as evident by increase in forest elements, under warm and relatively humid climate in response to an increased monsoon. The climate during 3230–1860 BP was mild and in general less humid than today. This climate event was inevitably influenced by a notable global cold event 4200 years ago, which is synchronous with the collapse of the world's first human empire in Mesopotamia. After this event, there was a return of more humid climate from 1860 to 1300 BP, marked by high values of Potamogeton, Myriophyllum, Nymphoides, and fungal and trilete fern spores. This is further supported by the presence of Rhizophora and Sonneratia indicating high precipitation under the influence of coastal habitation. A striking signal of the Little Ice age (LIA) was observed since 1300 BP when the climate became relatively dry, as recognized in a sudden decline in major arboreals, along with high frequency of occurrence of dry herbs. This changing pattern of humidity was also reflected in the proportions of marshy/aquatic taxa, as well as ruderal taxa which is a result of human impact. The study will be helpful to display the palaeovegetation and climate in the region between Bengal and the Ganga plain. [Copyright &y& Elsevier]

The article focuses on a research related to the use of palaeo-climate comparisons for future climate projections of the Coupled Model Intercomparison Project. Research analyzes the correlation between three periods including last glacial maximum, mid-holocene and last millennium. It presents a table depicting researches done by organizations including the U.S. National Center for Atmospheric Research and the Japan Agency for Marine-Earth Science and Technology and the Hadley Center.

The IceCube Neutrino Observatory and its prototype, AMANDA, were built in South Pole ice, using powerful hot-water drills to cleanly bore >100 holes to depths up to 2500 m. The construction of these particle physics detectors provided a unique opportunity to examine the deep ice sheet using a variety of novel techniques. We made high-resolution particulate profiles with a laser dust logger in eight of the boreholes during detector commissioning between 2004 and 2010. The South Pole laser logs are among the most clearly resolved measurements of Antarctic dust strata during the last glacial period and can be used to reconstruct paleoclimate records in exceptional detail. Here we use manual and algorithmic matching to synthesize our South Pole measurements with ice-core and logging data from Dome C, East Antarctica. We derive impurity concentration, precision chronology, annual-layer thickness, local spatial variability, and identify several widespread volcanic ash depositions useful for dating. We also examine the interval around ∼74 ka recently isolated with radiometric dating to bracket the Toba (Sumatra) supereruption [ABSTRACT FROM AUTHOR]

Abstract: Fully understanding the timing and climate of Last Glacial Maximum (LGM) is still lack in the head of the Tashkurgan Valley, northwest Tibetan Plateau (TP). The recent improvements in cosmogenic 10Be exposure dating and glacier modeling present an opportunity to estimate the LGM climatic conditions. In the paper, we investigated the moraines and used the 10Be exposure dating on the moraine boulders to constrain the timing of the LGM, the Kuzigun glacial stage in the head of the Tashkurgan Valley. Then, we used a coupled mass-balance and ice-flow model to quantify the paleoclimate from past glacier extents constrained by mapped and dated Kuzigun glacial moraines in the area. We showed that the glaciers terminated at an elevation of 4100–4200 m asl during the Kuzigun glacial stage and the glacial stage occurred during or slightly before 15–23 ka, corresponding to the timing of the global LGM. The modeled mass balances indicated that present-day equilibrium line altitude (ELA) ranges from 5150 to 5250 m asl, and LGM ELA is between 4550 and 4600 m asl in the area, suggesting an ELA lowering of ∼600 m during the LGM. Model results suggested that the temperature during the LGM in the head of the Tashkurgan Valley is 5–8 °C colder than today, considering a 30–70% reduction in precipitation compared to today. The paleoclimate estimates are generally consistence with previous studies that showed the LGM climate was colder and drier than today on the TP. [Copyright &y& Elsevier]

Abstract: Based on a new, centennial-scale-resolution pollen record from the terrestrial site of Tenaghi Philippon (NE Greece) we report a series of high-amplitude millennial-scale forest expansion events during the interval from 312 to 240 ka (equivalent to isotopic substages c–a of Marine Isotope Stage [MIS] 9, MIS 8, and the onset of MIS 7e). Pollen-based indices support the climatic interpretation of the forest expansion events as indicators of abrupt increases in temperature and moisture availability in the Mediterranean region. Long-term changes in vegetation cover and composition during the studied interval permit the definition of glacial substages (early, middle and late) analogous to the glacial substages of the last climatic cycle. Within this framework, forest expansion events occurred during the early glacial (equivalent to MIS 9c-a) and the later part of the middle glacial (mid to late MIS 8), but are absent from the early part of the middle glacial (early MIS 8). Forest expansion events are also detected during the Lateglacial and onset of MIS 7, associated with a millennial-scale climate oscillation across the glacial–interglacial transition, i.e. Termination III (T-III). A peak-for-peak match between forest expansion events and Antarctic temperature maxima suggests interhemispheric coupling of millennial-scale climate variability via global oceanic circulation change and synergistic variability in atmospheric circulation consistent with the bipolar see-saw. The resolution of our record (mean: 290 yr) also permits the characterisation of climate evolution over the course of interstadial episodes following forest expansion events, and highlights differences in the characteristics of early and middle glacial interstadials (saw-tooth vs. plateau profile). These differences point to an influence of long-term boundary conditions, especially global ice volume, on the characteristics of millennial-scale events. [Copyright &y& Elsevier]

Abstract: Speleothem growth requires humid climates sufficiently warm to stimulate soil CO2 production by plants. We compile 283 U/Th dates on 21 stalagmites from six cave systems in the NW coast of Spain to evaluate if there are patterns in stalagmite growth that are evidence of climatic forcing. In the oldest stalagmites, from marine oxygen isotope stage (MIS) 7–5, growth persists through the glacial period. Hiatuses and major reductions in growth rate occur during extreme minima in summer insolation. Stalagmites active during the last interglaciation cease growth at the MIS 5–4 boundary (74ka), when regional sea-surface temperature cooled significantly. During MIS 3, only two stalagmites grew; rates were highest between 50 and 60ka during the maximum in summer insolation. One stalagmite grew briefly at 41ka, 36.5 and 28.6ka, all during warm phases of the Dansgaard–Oeschger cycles. A pronounced Holocene optimum in stalagmite growth occurs from 9 to 6ka. The cessation of most growth by 4.1ka, coincident with broad increases in aridity over the Mediterranean and areas influenced by the North African Monsoon, suggest that regions such as NW Spain, with dominant Atlantic moisture sources, also experienced increased aridity at this time. [Copyright &y& Elsevier]

The model of Paillard and Parrenin (Earth Planet Sci Lett 227:263-271, ) was modified to obtain a closer fit to δO and CO time series for the last 800 kyr. The model performance can be improved if its CO sensitivity to I insolation is eliminated and if different response times are assumed for ablation/accumulation of ice. Correlations between simulated and experimental time series for CO and ice volume V increase from 0.59 and 0.63 to 0.79 and 0.88, respectively. According to these models, terminations are produced by I amplification through CO-T and T-CO feedbacks, in synergy with an extra CO contribution from the deep ocean. This contribution is strongly dependent on ice-sheet extent and ice volume (or alternatively, CO concentration, which is a good proxy of Antarctic temperature) but is insensitive to Southern Ocean (SO) insolation on 21 February (I). Change of deep SO state may be the 'order parameter' for nonlinear deglacial changes. According to these models, 100 kyr periodicity of glacial cycles arises from the characteristic time of Antarctic ice sheet advance to the continental slope. [ABSTRACT FROM AUTHOR]