bluuebunny/crossref_metadata_2025 huggingface dataset:
Abrupt climate changes of the last deglaciation detected in a Western Mediterranean forest record
Authors: Fletcher W. J. , Sanchez Goñi M. F. , Peyron O. , Dormoy I.
Published: April 2010

Abstract. Abrupt changes in Western Mediterranean climate during the last deglaciation (20 to 6 cal ka BP) are detected in marine core MD95-2043 (Alboran Sea) through the investigation of high-resolution pollen data and pollen-based climate reconstructions by the modern analogue technique (MAT) for annual precipitation (Pann) and mean temperatures of the coldest and warmest months (MTCO and MTWA). Changes in temperate Mediterranean forest development and composition and MAT reconstructions indicate major climatic shifts with parallel temperature and precipitation changes at the onsets of Heinrich stadial 1 (equivalent to the Oldest Dryas), the Bölling-Allerød (BA), and the Younger Dryas (YD). Multi-centennial-scale oscillations in forest development occurred throughout the BA, YD, and early Holocene. Shifts in vegetation composition and (Pann reconstructions indicate that forest declines occurred during dry, and generally cool, episodes centred at 14.0, 13.3, 12.9, 11.8, 10.7, 10.1, 9.2, 8.3 and 7.4 cal ka BP. The forest record also suggests multiple, low-amplitude Preboreal (PB) climate oscillations, and a marked increase in moisture availability for forest development at the end of the PB at 10.6 cal ka BP. Dry atmospheric conditions in the Western Mediterranean occurred in phase with Lateglacial events of high-latitude cooling including GI-1d (Older Dryas), GI-1b (Intra-Allerød Cold Period) and GS-1 (YD), and during Holocene events associated with high-latitude cooling, meltwater pulses and N. Atlantic ice-rafting. A possible climatic mechanism for the recurrence of dry intervals and an opposed regional precipitation pattern with respect to Western-central Europe relates to the dynamics of the westerlies and the prevalence of atmospheric blocking highs. Comparison of radiocarbon and ice-core ages for well-defined climatic transitions in the forest record suggests possible enhancement of marine reservoir ages in the Alboran Sea by 200 years (surface water age 600 years) during the Lateglacial.
Climate in continental interior Asia during the longest interglacial of the past 500 000 years: the new MIS 11 records from Lake Baikal, SE Siberia
Authors: Prokopenko A. A. , Bezrukova E. V. , Khursevich G. K. , Solotchina E. P. , Kuzmin M. I. , Tarasov P. E.
Published: April 2010

Abstract. A synthesis of paleoclimate responses from Lake Baikal during the MIS 11 interglacial is presented based on proxy records from two drill sites 245 km apart. BDP-99 is located in vicinity of the delta of the major Baikal tributary, whereas the BDP-96 site represents hemipelagic setting distant from riverine influence. The comparison of thicknesses of interglacial intervals in these contrasting depositional settings confirms the extended ca. 33-kyr duration of the MIS 11 interglacial. The new BDP-99 diatom biostratigraphic record matches that of the BDP-96-2 holostratotype and thus allows establishing establishes robust correlation between the records on the same orbitally-tuned timescale. The first detailed MIS 11 palynological record from the BDP-99 drill core indicates the dominance of boreal conifer (taiga) forest vegetation in the Baikal region throughout the MIS 11 interglacial, since at least 424 ka till ca. 396 ka. The interval ca. 420–405 ka stands out as a "conifer optimum" with abundant Abies sibirica, indicative of climate significantly warmer and less continental than today. The closest Baikal analog to this type of vegetation in the history of the current Holocene interglacial is at ca. 9–7 ka. The warm conifer phase lasted for ca. 15 kyr during MIS 11 interrupted by two millennial-scale cooling episodes at ca. 411–410 and 405–404 ka. Reconstructed annual precipitation of 450–550 mm/yr during the MIS 11 interglacial is by ca. 100 mm higher than during the Holocene; regional climate was less continental with warmer mean temperatures both in summer and in winter. At both drill sites, the two-peak structure of the MIS 11 diatom abundance profiles reflects the orbital signature of precession in the interglacial paleoclimate record of continental Eurasia. MIS 11 interglacial was characterized by the sustained high level of primary production and accumulation of autochthonous organic matter at both study sites. The responses of paleoclimate-sensitive indices in the mineralogy of the MIS 11 sediments in BDP-96-2 are consistent with those during the Holocene. Illitization of secondary clay minerals in the Baikal watershed was an important process, but it appears to have been subdued during the first half of the MIS 11, apparently due to elevated humidity and muted seasonality of regional climate.
Potential analysis reveals changing number of climate states during the last 60 kyr
Authors: Livina V. N. , Kwasniok F. , Lenton T. M.
Published: April 2010

Abstract. We develop and apply a new statistical method of potential analysis for detecting the number of states of a geophysical system, from its recorded time series. Estimation of the degree of a polynomial potential allows us to derive the number of potential wells in a system. The method correctly detects changes in the number of wells in artificial data. In ice-core proxy records of Greenland paleotemperature, a reduction in the number of climate states from two to one is detected sometime prior to the last glacial maximum (LGM), 23–19 kyr BP. This result is also found in analysis of Greenland Ca data. The bifurcation can be interpreted as loss of stability of the warm interstadial state of the Dansgaard-Oeschger (DO) events. The proposed method can be applied to a wide range of geophysical time series exhibiting bifurcations.
Summer temperature trend over the past two millennia using air content in Himalayan ice
Authors: Hou S. , Chappellaz J. , Jouzel J. , Chu P. C. , Masson-Delmotte V. , Qin D. , Raynaud D. , Mayewski P. A. , Lipenkov V. Y. , Kang S.
Published: April 2010

Abstract. Two Himalayan ice cores display a factor-two decreasing trend of air content over the past two millennia, in contrast to the relatively stable values in Greenland and Antarctica ice cores over the same period. Because the air content can be related with the relative frequency and intensity of melt phenomena, its variations along the Himalayan ice cores provide an indication of summer temperature trend. Our reconstruction point toward an unprecedented warming trend in the 20th century but does not depict the usual trends associated with "Medieval Warm Period" (MWP), or "Little Ice Age" (LIA).
Synoptic climate change as a driver of late Quaternary glaciations in the mid-latitudes of the Southern Hemisphere
Authors: Rother H. , Shulmeister J.
Published: April 2010

Abstract. The relative timing of late Quaternary glacial advances in mid-latitude (40–55° S) mountain belts of the Southern Hemisphere (SH) has become a critical focus in the debate on global climate teleconnections. On the basis of glacial data from New Zealand and southern South America it has been argued that interhemispheric synchrony or asynchrony of Quaternary glacial events is due to Northern Hemisphere (NH) forcing of SH climate through either the ocean or atmosphere systems. Here we present a glacial snow-mass balance model that demonstrates that large scale glacial advances in the temperate and hyperhumid Southern Alps of New Zealand can be generated with very little thermal forcing. This is because the rapid conversion of precipitation from rainfall to snowfall drives massive ice accumulation at small thermal changes (1–4°C). Our model is consistent with recent paleo-environmental reconstructions showing that glacial advances in New Zealand during the Last Glacial Maximum (LGM) and the Last Glacial Interglacial Transition (LGIT) occurred under very moderate cooling. We suggest that such moderate cooling could be generated by changes in synoptic climatology, specifically through enhanced regional flow of moist westerly air masses. Our results imply that NH climate forcing may not have been the exclusive driver of Quaternary glaciations in New Zealand and that synoptic style climate variations are a better explanation for at least some Late Quaternary glacial events, in particular during the LGIT (e.g. Younger Dryas and/or Antarctic Cold Reversal).
Paleoclimatic reconstructions in Western Canada from subsurface temperatures: consideration of groundwater flow
Authors: Majorowicz J. , Grasby S. , Ferguson G. , Safanda J. , Skinner W.
Published: April 2010

Abstract. The surface temperature forcing is responsible for the majority of the observed deviation of temperature with depth. In some cases, differences higher than the error of measurements are observed between the model and measurements. These can be an indication that other factors than surface temperature change influence subsurface temperature. Groundwater flow is one of the possible candidates.
Proposing a mechanistic understanding of changes in atmospheric CO2 during the last 740 000 years
Authors: Köhler P. , Fischer H.
Published: April 2010

Abstract. Atmospheric carbon dioxide (CO2) measured in Antarctic ice cores shows a natural variability of 80 to 100 ppmv during the last four glacial cycles and variations of approximately 60 ppmv in the two cycles between 410 and 650 kyr BP. We here use dust and the isotopic temperature proxy deuterium (δD) from the EPICA Dome C Antarctic ice core covering the last 740 kyr together with other paleo-climatic records to force the ocean/atmosphere/biosphere box model of the global carbon cycle BICYCLE in a forward mode over this time in order to reconstruct the natural variability of pCO2. Our simulation results covered by our proposed scenario are based on process understanding gained previously for carbon cycle variations during Termination I. These results match the pCO2 measured in the Vostok ice core well (r2=0.80) and we predict prior to Termination V significantly smaller amplitudes in pCO2 variations mainly based on a reduced interglacial ocean circulation and reduced interglacial Southern Ocean sea surface temperature. These predictions for the pre-Vostok period match the new pCO2 data from the EPICA Dome C ice core for the time period 410 to 650 kyr BP equally well (r2=0.79). This is the first forward modelling approach which covers all major processes acting on the global carbon cycle on glacial/interglacial time scales. The contributions of different processes (terrestrial carbon storage, sea ice, sea level, ocean temperature, ocean circulation, CaCO3 chemistry, marine biota) are analysed.
Multiproxy records of climate variability for Kamchatka for the past 400 years
Authors: Solomina O. , Wiles G. , Shiraiwa T. , D’Arrigo R.
Published: April 2010

Abstract. Tree rings, ice cores and glacial geologic histories for the past several centuries offer an opportunity to characterize climate variability and to identify the key climate parameters forcing glacier expansions. A newly developed larch ring-width chronology is presented for Kamchatka that is sensitive to past summer temperature variability. This record provides the basis to compare with other proxy records of inferred temperature and precipitation change from ice core and glacier records, and to characterize climate for the region over the past 400 years. Individual low growth years in the larch record are associated with several known and proposed volcanic events that have been observed in other proxy records from the Northern Hemisphere. Comparison of the tree-rings with an ice core record of melt feature index for Kamchatka's Ushkovsky volcano confirms a 1–3 year dating accuracy for this ice core series over the late 18th to 20th centuries. Decadal variations of low summer temperatures (tree-ring record) and high annual precipitation (ice core record) are broadly consistent with intervals of positive mass balance measured and estimated at several glaciers, and with moraine building, provides a basis to interpret geologic glacier records.
Climate of the last glacial maximum: sensitivity studies and model-data comparison with the LOVECLIM coupled model
Authors: Roche D. M. , Dokken T. M. , Goosse H. , Renssen H. , Weber S. L.
Published: April 2010

Abstract. The Last Glacial Maximum climate is one of the classic benchmarks used both to test the ability of coupled models to simulate climates different from that ot the present-day and to better understand the possible range of mechanisms that could be involved in future climate change. It also bears the advantage of being one of the most well documented periods with respect to palaeoclimatic records, allowing a thorough data-model comparison. We present here an ensemble of Last Glacial Maximum climate simulations obtained with the Earth System model LOVECLIM, including coupled dynamic atmosphere, ocean and vegetation components. The climate obtained using standard parameter values is then compared to available proxy data for the surface ocean, vegetation, oceanic circulation and atmospheric conditions. Interestingly, the oceanic circulation obtained resembles that of the present-day, but with increased overturning rates. As this result is in contradiction with the "classic" palaeoceanographic view, we ran a range of sensitivity experiments to explore the response of the model and the possibilities for other oceanic circulation states. After a critical review of our LGM state with respect to available proxy data, we conclude that the balance between water masses obtained is consistent with the available data although the specific characteristics (temperature, salinity) are not in full agreement. The consistency of the simulated state is further reinforced by the fact that the mean surface climate obtained is shown to be generally in agreement with the most recent reconstructions of vegetation and sea surface temperatures, even at regional scales.
Social vulnerability to climate in the "Little Ice Age"?: an example from Central Europe in the early 1770s
Authors: Pfister C. , Brázdil R.
Published: April 2010

Abstract. The paper is oriented on social vulnerability to climate in Switzerland and in the Czech Lands during the early 1770s. Documentary sources of climate related to man-made archives are discussed. Methods of temperature and precipitation reconstruction based on this evidence as well as climate impact analyses are presented. Modelling of Little Ice Age-type Impacts (LIATIMP) is applied to highlight climate impacts during the period 1750–1800 in the Swiss Plateau and in the Czech Lands. LIATIMP are defined as adverse climate situations affecting grain production, mainly in terms of rainy autumns, cold springs and rainy harvest-periods. The most adverse weather patterns according to this model occurred from 1769 to 1771 causing two, in the case of the Czech Lands even three successive harvest failures. The paper addresses the social and economic consequences of this accumulation of climatic stress and explores how the authorities and the victims dealt with this situation.
Comparing transient, accelerated, and equilibrium simulations of the last 30 000 years with the GENIE-1 model
Authors: Lunt D. J. , Williamson M. S. , Valdes P. J. , Lenton T. M.
Published: April 2010

Abstract. We examine several aspects of the ocean-atmosphere system over the last 30 000 years, by carrying out simulations with prescribed ice-sheets, atmospheric CO2 concentration, and orbital parameters. We use the GENIE-1 model with a geostrophic ocean, dynamic sea-ice, an energy balance atmosphere, and a land-surface scheme with fixed vegetation. A transient simulation, with boundary conditions derived from ice-core records and ice-sheet reconstructions, is compared with equilibrium snapshot simulations, including the Last Glacial Maximum (21 000 years before present; 21 kyrBP), mid-Holocene (6 kyrBP) and pre-industrial. The equilibrium snapshot surface temperatures are all very similar to their corresponding time period in the transient simulation, suggesting that in the last 30 000 years, the ocean-atmosphere system has been close to equilibrium with its boundary conditions. We investigate the method of accelerating the boundary conditions of a transient simulation and find that the Southern Ocean is the region most affected by the acceleration. The Northern Hemisphere, even with a factor of 10 acceleration, is relatively unaffected.
On the importance of initial conditions for simulations of the Mid-Holocene climate
Authors: Renssen H. , Driesschaert E. , Loutre M. F. , Fichefet T.
Published: April 2010

Abstract. Three simulations of the Mid-Holocene (6 ka) climate were performed with the ECBilt-CLIO-VECODE coupled atmosphere-ocean-vegetation model to study the impact of initial conditions. These experiments were forced with identical 6 ka forcings (orbital parameters and atmospheric greenhouse gas concentrations) and differed only in initial conditions. Two simulations were designed as equilibrium experiments, with one being initialized with preindustrial conditions as required by the protocol of the Paleoclimate Modelling Intercomparison Project (PMIP), while in a second experiment early Holocene (9 ka) intial conditions were used. These equilibrium simulations were run for 2100 years with 6 ka forcings. The third experiment was set up as a transient simulation, also starting from early Holocene conditions, but forced with annually changing orbital parameters and greenhouse gas levels. The results of the last 100 years are compared and reveal no statistically significant differences, showing that in this model the initial conditions have no discernible impact on the 6 ka climate. This suggests that the PMIP set-up for 6 ka simulations is valid, with the condition that spin-up phase should be long enough (at least 600 years) to allow the deep ocean to adjust to the change in forcings.
Equatorial insolation: from precession harmonics to eccentricity frequencies
Authors: Berger A. , Loutre M. F. , Mélice J. L.
Published: April 2010

Abstract. Since the paper by Hays et al. (1976), spectral analyses of climate proxy records provide substantial evidence that a fraction of the climatic variance is driven by insolation changes in the frequency ranges of obliquity and precession variations. However, it is the variance components centered near 100 kyr which dominate most Upper Pleistocene climatic records, although the amount of insolation perturbation at the eccentricity driven 100-kyr period is much too small to cause directly a climate change of ice-age amplitude. Many attempts to find an explanation to this 100-kyr cycle in climatic records have been made over the last decades. Here we show that the double maximum which characterizes the daily irradiation received in tropical latitudes over the course of the year is at the origin in equatorial insolation of not only a strong 100-kyr, but also of a 11-kyr and a 5.5-kyr periods related respectively to eccentricity and to precession.
Glacial – interglacial atmospheric CO2 change: a simple "hypsometric effect" on deep-ocean carbon sequestration?
Authors: Skinner L. C.
Published: April 2010

Abstract. Given the magnitude and dynamism of the deep marine carbon reservoir, it is almost certain that past glacial – interglacial fluctuations in atmospheric CO2 have relied at least in part on changes in the carbon storage capacity of the deep sea. To date, physical ocean circulation mechanisms that have been proposed as viable explanations for glacial – interglacial CO2 change have focussed almost exclusively on dynamical or kinetic processes. Here, a simple mechanism is proposed for increasing the carbon storage capacity of the deep sea that operates via changes in the volume of southern-sourced deep-water filling the ocean basins, as dictated by the hypsometry of the ocean floor. It is proposed that a water-mass that occupies more than the bottom 3 km of the ocean will essentially determine the carbon content of the marine reservoir. Hence by filling this interval with southern-sourced deep-water (enriched in dissolved CO2 due to its particular mode of formation) the amount of carbon sequestered in the deep sea may be greatly increased. A simple box-model is used to test this hypothesis, and to investigate its implications. It is suggested that up to 70% of the observed glacial – interglacial CO2 change might be explained by the replacement of northern-sourced deep-water below 2.5 km water depth by its southern counterpart. Most importantly, it is found that an increase in the volume of southern-sourced deep-water allows glacial CO2 levels to be simulated easily with only modest changes in Southern Ocean biological export or overturning. If incorporated into the list of contributing factors to marine carbon sequestration, this mechanism may help to significantly reduce the "deficit" of explained glacial – interglacial CO2 change.
Historical droughts in Mediterranean regions during the last 500 years: a data/model approach
Authors: Brewer S. , Alleaume S. , Guiot J. , Nicault A.
Published: April 2010

Abstract. We present here a new method for comparing the output of General Circulation Models (GCMs) with proxy-based reconstructions, using time series of reconstructed and simulated climate parameters. The method uses k-means clustering to allow comparison between different periods that have similar spatial patterns, and a fuzzy logic-based distance measure in order to take reconstruction errors into account. The method has been used to test two coupled ocean-atmosphere GCMs over the Mediterranean region for the last 500 years, using an index of drought stress, the Palmer Drought Severity Index. The results showed that, whilst no model was able to exactly simulate the reconstructed changes, all simulations were an improvement over using the mean climate. Further, a good match was found after 1650 with a model run that took into account changes in volcanic forcing, solar irradiance, and greenhouse gases. A more detailed investigation of the output of this model showed the existence of a set of atmospheric circulation patterns linked to the patterns of drought stress: 1) a blocking pattern over northern Europe linked to dry conditions in the south prior to the Little Ice Age (LIA) and during the 20th century; 2) a NAO-positive like pattern with increased westerlies during the LIA; 3) a NAO-negative like period shown in the model prior to the LIA, but that occurs most frequently in the data during this period. The results of the comparison emphasise the importance of the inclusion of the various forcings in the models and help to understand the atmospheric changes connected to reconstructed climate changes.
Low-frequency oscillations of the Atlantic Ocean meridional overturning circulation in a coupled climate model
Authors: Schulz M. , Prange M. , Klocker A.
Published: April 2010

Abstract. Using a 3-dimensional climate model of intermediate complexity we show that the overturning circulation of the Atlantic Ocean can vary at multicentennial-to-millennial timescales for present-day boundary conditions. A weak and continuous freshwater input into the Labrador Sea pushes the overturning circulation of the Atlantic Ocean into a bi-stable regime, characterized by phases of active and inactive deep-water formation in the Labrador Sea. In contrast, deep-water formation in the Nordic Seas is active during all phases of the oscillations. The actual timing of the transitions between the two circulation states occurs randomly. The oscillations constitute a 3-dimensional phenomenon and have to be distinguished from low-frequency oscillations seen previously in 2-dimensional models of the ocean. A conceptual model provides further insight into the essential dynamics underlying the oscillations of the large-scale ocean circulation. The model experiments indicate that the coupled climate system can exhibit unforced climate variability at multicentennial-to-millennial timescales that may be of relevance for Holocene and future climate variations.
Predicting Pleistocene climate from vegetation
Authors: Loehle C.
Published: April 2010

Abstract. Climates at the Last Glacial Maximum have been inferred from fossil pollen assemblages, but these inferred climates are colder than those produced by climate simulations. Biogeographic evidence also argues against these inferred cold climates. The recolonization of glaciated zones in eastern North America following the last ice age produced distinct biogeographic patterns. It has been assumed that a wide zone south of the ice was tundra or boreal parkland (Boreal-Parkland Zone or BPZ), which would have been recolonized from southern refugia as the ice melted, but the patterns in this zone differ from those in the glaciated zone, which creates a major biogeographic anomaly. In the glacial zone, there are few endemics but in the BPZ there are many across multiple taxa. In the glacial zone, there are the expected gradients of genetic diversity with distance from the ice-free zone, but no evidence of this is found in the BPZ. Many races and related species exist in the BPZ which would have merged or hybridized if confined to the same refugia. Evidence for distinct southern refugia for most temperate species is lacking. Extinctions of temperate flora were rare. The interpretation of spruce as a boreal climate indicator may be mistaken over much of the region if the spruce was actually an extinct temperate species. All of these anomalies call into question the concept that climates in the zone south of the ice were very cold or that temperate species had to migrate far to the south. Similar anomalies exist in Europe and on tropical mountains. An alternate hypothesis is that low CO2 levels gave an advantage to pine and spruce, which are the dominant trees in the BPZ, and to herbaceous species over trees, which also fits the observed pattern. Most temperate species could have survived across their current ranges at lower abundance by retreating to moist microsites. These would be microrefugia not easily detected by pollen records, especially if most species became rare. These results mean that climate reconstruction based on terrestrial plant indicators will not be valid for periods with markedly different CO2 levels.
Precipitation variations of Longxi, northeast margin of Tibetan plateau since AD 960 and its relationship with solar activity
Authors: Tan L. , Cai Y. , Yi L. , An Z. , Ai L.
Published: April 2010

Abstract. The precipitation variations of Longxi area, northeast margin of Tibetan plateau since AD 960 are reconstructed from Chinese historical documentary records. It shows that since AD 960, the precipitation of Longxi fluctuantly decreased to the lowest in the end stage of 17th century and 18th century. After this period, the precipitation gradually increased. Three short wet periods of Longxi in the last millennium were: from the end of 10th century to the early of 11th century, from the end of 12th century to the early of 13th century and the first half of 20th century. The precipitation variations of Longxi coincide well with variations of the Northern Hemisphere temperature and the atmospheric 14C concentration, the modeled solar output, the reconstructed total solar irradiance, which shows that solar activity may be the main driving force of precipitation variations of Longxi on multi-decadal to centennial scales in the last millennium. Synchronous variations of Longxi precipitation and Northern Hemisphere temperature may be ascribed to the same control of solar activity. Solar activity controls remotion of the north edge of Asian summer monsoon by affecting Asia summer monsoon intensity, East Asian winter monsoon intensity and the locations of westerlies, thus further dominates precipitation variations of Longxi.
Maximum growing season temperature in Western Europe: multi proxy reconstructions in Fontainebleau from 1596 to 2000
Authors: Etien N. , Daux V. , Masson-Delmotte V. , Stievenard M. , Bernard V. , Durost S. , Guillemin M. T. , Mestre O. , Pierre M.
Published: April 2010

Abstract. In this study, we have combined a Burgundy grape harvest date record with new δ18O measurements conducted on timbers and living trees cellulose from Fontainebleau castle and forest. Our reconstruction is expected to provide a reference series for the variability of growing season temperature (from April to September) in Western Europe from 1596 to 2000. We have estimated an uncertainty of 0.55°C on individual growing season maximum temperature reconstructions. We are able to assess this uncertainty, which is not the case for many documentary sources (diaries etc.), and even not the case for early instrumental temperature data. We compare our data with a number of independent temperature estimates for Europe and the Northern Hemisphere. The comparison between our reconstruction and Manley mean growing season temperature data provides an independent control of the quality of CET data. We show that our reconstruction preserves more variance back in time, because it was not distorted/averaged by statistical/homogenisation methods. Further works will be conducted to compare the δ18O data from wood cellulose provided by transects of different tree species in Europe obtained within the EC ISONET project and the French ANR Program ESCARSEL, to analyse the spatial and temporal coherency between δ18O records. The decadal variability will be also compared with other precipitation δ18O records such as those obtained from benthic ostracods from deep peri-Alpine lakes or simulated by regional atmospheric models equipped with the modelling of water stable isotopes.
Strong summer monsoon during the cool MIS-13
Authors: Yin Q. Z. , Guo Z. T.
Published: April 2010

Abstract. The δ18O record in deep-sea sediments show a significant reduced amplitude of the ice volume variations before Marine Isotope Stage 11, about 400 kyr ago, with less warm interglacials and less cold glacials. The deuterium temperature and the greenhouse gases records in the Antarctic ice cores show the same feature. As the reduction in the amplitude of climate and greenhouse gases concentration variations before 400 kyr BP is present in both deep-sea and ice cores, it is tempting to conclude that this is a worldwide phenomenon. This is not necessarily true, at least as far as some of the records, in particular of China, are concerned. The loess in northern China, the sedimentary core in the eastern Tibetan Plateau and the palaeosols in southern China all record an unusually warm and wet climate during Marine Isotope Stage 13, indicating an extremely strong East Asian summer monsoon. During the same interglacial, unusually strong African and Indian monsoon are recorded in the sediments of the equatorial Indian Ocean and of the Mediterranean Sea. Other extreme climate events are also recorded in sediment cores of the equatorial Atlantic, the Pacific, the subtropical South Atlantic Ocean and in the Lake Baikal of Siberia.
Reconstructing glacier-based climates of LGM Europe and Russia – Part 3: Comparison with GCM and pollen-based climate reconstructions
Authors: Allen R. , Siegert M. J. , Payne A. J.
Published: April 2010

Abstract. Understanding past climates using GCM models is critical to confidently predicting future climate change. Although previous analysis of GCM simulations have shown them to under predicted European glacial temperature anomalies (the difference between modern and glacial temperatures) such analyses have focused primarily on results from glacial simulations alone. Here we compare glacial maximum GCM results with the palaeoenvironment derived from glacier-climate modelling. The comparison confirms that GCM anomalies are under predicted, and that this is due to modern conditions that are modelled too cold and glacial temperatures that are too warm. The result is that CGM results, if applied to a glacier mass balance model, over predict the extent of glaciers today, and under predict their extent at the last glacial (as depicted in glacial geological reconstructions). Effects such as seasonality and model parameterisation change the magnitude of the under prediction but still fail to match expected glacial conditions.
Spatial structure of the 8200 cal yr BP event in Northern Europe
Authors: Seppä H. , Birks H. J. B. , Giesecke T. , Hammarlund D. , Alenius T. , Antonsson K. , Bjune A. E. , Heikkilä M. , MacDonald G. M. , Ojala A. E. K. , Telford R. J. , Veski S.
Published: April 2010

Abstract. A synthesis of well-dated high-resolution pollen records suggests a spatial structure in the 8200 cal yr BP event in northern Europe. The temperate, thermophilous tree taxa, especially Corylus, Ulmus, and Alnus, decline abruptly between 8300 and 8000 cal yr BP at most sites located south of 61° N, whereas there is no clear change in pollen values at the sites located in the North-European tree-line region. Pollen-based quantitative temperature reconstructions and several other, independent palaeoclimate proxies, such as lacustrine oxygen-isotope records, reflect the same pattern, with no detectable cooling in the sub-arctic region. The observed pattern would challenge the general view of the wide-spread occurrence of the 8200 cal yr BP event in the North Atlantic region. An alternative explanation is that the cooling during the 8200 cal yr BP event took place mostly during the winter and spring, and the ecosystems in the south responded sensitively to the cooling during the onset of the growing season. In contrast, in the sub-arctic area, where the vegetation was still dormant and lakes ice-covered, the cold event is not reflected in pollen-based or lake-sediment-based records. The arctic regions may therefore not always be optimal for detecting past climate changes.
Ice flow modelling at EPICA Dome C and Dome Fuji, East Antarctica
Authors: Parrenin F. , Dreyfus G. , Durand G. , Fujita S. , Gagliardini O. , Gillet F. , Jouzel J. , Kawamura K. , Lhomme N. , Masson-Delmotte V. , Ritz C. , Schwander J. , Shoji H. , Uemura R. , Watanabe O. , Yoshida N.
Published: April 2010

Abstract. 1-D ice flow models are used to construct the age scales at the Dome C and Dome Fuji drilling sites (East Antarctica). The poorly constrained glaciological parameters at each site are recovered by fitting independent age markers identified on each core. We reconstruct past accumulation rates, that are larger than those modelled using the classical vapour saturation pressure relationship during glacial periods by up to a factor 1.5. During the Early Holocene, changes in reconstructed accumulation are not linearly related to changes in ice isotopic composition. A simple model of past elevation changes is developed and shows an amplitude variation of 110–120 m at both sites. We suggest that there is basal melting at Dome C (0.56±0.19 mm/yr). The reconstructed velocity profile is highly non linear at both sites, which suggests complex ice flow effects. This induces a non linear thinning function in both drilling sites, which is also characterized by bumps corresponding to variations in surface elevation with time.
On the verification of climate reconstructions
Authors: Bürger G.
Published: April 2010

Abstract. The skill of proxy-based reconstructions of Northern hemisphere temperature is reassessed. Using an almost complete set of proxy and instrumental data of the past 130 years a multi-crossvalidation is conducted of a number of statistical methods, producing a distribution of verification skill scores. The scores show considerable variation for all methods, but previous estimates, such as a 50% reduction of error (RE), appear as outliers and more realistic estimates vary about 25%. It is shown that the overestimation of skill is possible in the presence of strong persistence (trends). In that case, the classical "early" or "late" calibration sets are not representative for the intended (instrumental, millennial) domain. As a consequence, RE scores are generally inflated, and the proxy predictions are easily outperformed by random-based, a priori skill-less predictions. To obtain robust significance levels the multi-crossvalidation is repeated using predictors based on red noise. Comparing both distributions, it turns out that the proxies perform significantly better for almost all methods. The nonsense predictor scores do not vanish, nonetheless, with an estimated 10% of spurious skill based on representative samples. I argue that this residual score is due to the limited sample size of 130 years, where the memory of the processes degrades the independence of calibration and validation sets. It is likely that proxy prediction scores are inflated correspondingly, and have to be adjusted further. The consequences of the limited verification skill for millennial reconstructions is briefly discussed.
Surface thermal perturbations of the recent past at low latitudes – inferences based on borehole temperature data from Eastern Brazil
Authors: Hamza V. M. , Cavalcanti A. S. B. , Benyosef L. C. C.
Published: April 2010

Abstract. Borehole temperature data from the eastern parts of Brazil has been examined in an attempt to extract information on surface thermal perturbations of the recent past at low latitudes. Forward models were employed in the analysis of temperature logs from 16 localities and, in addition, inverse modeling was carried out for data from 10 selected sites. The model results have allowed determination of the magnitude as well as the duration of ground surface temperature (GST) changes in three major geographic zones of Brazil. Prominent among such events are the warming episodes that occurred over much of the subtropical highland regions in the southeastern parts of Brazil. The present magnitude of GST changes in this region are in the range of 2 to 3.5°C but have had their beginning during the early decades of the 20th century. Nearly similar trends are also seen in temperature-depth profiles of bore holes in the subtropical humid zones of the interior and coastal areas of southern Brazil. The data from semi arid zones of northeast Brazil also indicate occurrence of surface warming events but the magnitudes are in the range of 1.4 to 2.2°C while the duration of the warming event is larger, extending back into the last decades of the 19th century. There are indications that changes in both climate and vegetation cover contribute to variations in GST. Thus the magnitudes of GST variations are relatively large in localities which have undergone changes in vegetation cover. Also there are indications that GST changes are practically insignificant in areas of tropical rain forest. Another important result emerging from model studies is that the climate was relatively cooler during the 17th and 18th centuries. The climate histories, deduced from geothermal data, are found to be consistent with results of available meteorological records in southern Brazil. Comparative studies also indicate that the magnitudes and duration of recent climate changes in southern and eastern Brazil are similar to those found in other continental areas such as North America, Asia and Europe.
Direct North-South synchronization of abrupt climate change record in ice cores using beryllium 10
Authors: Raisbeck G. M. , Yiou F. , Jouzel J. , Stocker T. F.
Published: April 2010

Abstract. A new, decadally resolved record of the 10Be peak at 41 kyr from the EPICA Dome C ice core (Antarctica) is used to match it with the same peak in the GRIP ice core (Greenland). This permits a direct synchronisation of the climatic variations around 41 kyr BP, independent of uncertainties related to the ice age-gas age difference in ice cores. Dansgaard-Oeschger event 10 is in the period of best synchronisation and is found to be coeval with an Antarctic temperature maximum. Simulations using a thermal bipolar seesaw model agree reasonably well with the observed relative climate chronology in these two cores. They also reproduce three Antarctic warming events between A1 and A2.
Tropical cooling and the onset of North American glaciation
Authors: Huybers P. , Molnar P.
Published: April 2010

Abstract. We offer a test of the idea that gradual cooling in the eastern tropical Pacific led to cooling of North America and the initiation of glaciation ~3 Myr ago. Using modern climate data we estimate how warming of the eastern tropical Pacific affects North American temperature and ice-ablation. Assuming that the modern relationship holds over the past millions of years, an eastern tropical Pacific warmer by ~4° between 3–5 Ma would increase ablation in northern North America by approximately two meters per year. By comparison, a similar estimate of the ablation response to variations in Earth's obliquity gives less than half the magnitude of the tropically-induced change. Considering that variations in Earth's obliquity appear sufficient to initiate glaciations between ~1–3 Ma, we infer that the warmer eastern equatorial Pacific prior to 3 Ma suffices to preclude glaciation.
On the quality of climate proxies derived from newspaper reports – a case study
Authors: Gallego D. , García-Herrera R. , Prieto R. , Peña-Ortiz C.
Published: April 2010

Abstract. In this paper, the quality of a reconstruction of daily snow frequency in the central Andes is evaluated by studying the atmospheric patterns related to anomalies in the reconstructed series. The origin of precipitation anomalies in this part of the world is relatively well known and is has been related to the El Niño/Southern Oscillation cycle through the Pacific South American pattern, which implies changes in the subtropical jet across the Pacific, the blocking activity in the Southeastern Pacific and the ice formation around the Antarctic Peninsula. We found that the reconstructed series of snow frequency reproduces every expected anomaly pattern related to precipitation in the central Andes during the period 1958–1996. The methodology developed can help to validate reconstructed series in absence of instrumental data to perform a direct calibration. In addition, it provides a physical link between the variability of a climate proxy and the underlying atmospheric dynamics.
A nonlinear method for detecting climate mutation: a case study for summer climate change in China
Authors: Wan S. Q. , Feng G. L. , Wang L. , Gu C. H. , Hu Y. L. , Zhou G. H.
Published: April 2010

Abstract. In this paper, we explored the dynamical mechanism of anomalous summer climate late 1970s in China applying a new method, i.e., a dynamics index-Q based on phase-space reconstruction. The interesting results show that different climate variable have the similar dynamics property in different regions, they reflect an intrinsic dynamics interior climate system, which may be associated with the teleconnection wave trains mainly triggered by the Tibetan Plateau, and reveals some of causes making North China drought indirectly. However, the Phenomena are hardly possible found via any statistic methodology.
Strong asymmetry of hemispheric climates during MIS-13 inferred from correlating China loess and Antarctica ice records
Authors: Guo Z. T. , Berger A. , Yin Q. Z. , Qin L.
Published: April 2010

Abstract. The loess-soil sequence in northern China is among the best long-term terrestrial climate records in the Northern Hemisphere that documented the history of the Asian summer and winter monsoon circulations, dust emission and aridity of inland deserts. In the Southern Hemisphere, the Antarctica ice cores provided a 800-thousand year (ka) history of the atmospheric methane (CH4) and carbon dioxide (CO2) concentrations, eolian dust and Antarctica temperature. We correlate the two records to address the hemispheric climate link in the past 800 ka and the potential roles of Asian dust and monsoon on the atmospheric CO2 and CH4 levels. The results show a broad coupling between the Asian and Antarctic climates at the glacial-interglacial scale and support a potential role of Asian dust and monsoon in modulating the atmospheric concentration of greenhouse gases. However, a number of decoupled aspects are revealed, among which marine isotope stage (MIS) 13 exhibits the strongest anomalous link compared with the other interglacials. It is characterized by the greatest interglacial global ice volume, carbon isotope (δ13C) maxima in the world oceans, cooler Antarctic temperature, more extended sea ice in the Southern Ocean, lower CO2 and CH4 concentrations, but by unusually strengthened Asian, Indian and African monsoons, weakest Asian winter monsoon, lowest Asian dust and iron fluxes. Particularly warm conditions were also reported for the elevated Tibetan Plateau and northern high-latitude regions. These lines of evidence consistently suggest an increased ice volume in the Southern Hemisphere, a substantially reduced ice volume in the Northern Hemisphere during MIS-13, and hence, an enhanced hemispheric asymmetry of polar ice-conditions. This event has deeply affected the continental, marine and atmospheric conditions at the global scale. Similar anomalies of lesser extents also occurred during MIS-11 and MIS-5e. These suggest that hemispheric climate coupling at the glacial-interglacial scale was significantly unstable during the mid-Pleistocene, and that the degree of asymmetry of polar ice-conditions has prominent impacts on the global climate system, including the Asian monsoon climate. Because global sea ice is likely evolving towards a similar trend now, the scenario may also be helpful for future climate evaluation.
How did Marine Isotope Stage 3 and Last Glacial Maximum climates differ? Perspectives from equilibrium simulations
Authors: Van Meerbeeck C. J. , Renssen H. , Roche D. M.
Published: April 2010

Abstract. Dansgaard-Oeschger events occurred frequently during Marine Isotope Stage 3 (MIS3), as opposed to the following MIS2 period, which included the Last Glacial Maximum (LGM). Transient climate model simulations suggest that these abrupt warming events in Greenland and the North Atlantic region are associated with a resumption of the Thermohaline Circulation (THC) from a weak state during stadials to a relatively strong state during interstadials. However, those models were run with LGM, rather than MIS3 boundary conditions. To quantify the influence of different boundary conditions on the climates of MIS3 and LGM, we perform two equilibrium climate simulations with the three-dimensional earth system model LOVECLIM, one for stadial, the other for interstadial conditions. We compare them to the LGM state simulated with the same model. Both climate states are globally 2°C warmer than LGM. A striking feature of our MIS3 simulations is the enhanced Northern Hemisphere seasonality, July being 4°C warmer than in LGM. Also, despite some modification in the location of North Atlantic deep water formation, deep water export to the South Atlantic remains unaffected. To study specifically the effect of orbital forcing, we perform two additional sensitivity experiments spun up from our stadial simulation. The insolation difference between MIS3 and LGM causes half of the 30–60°N July temperature anomaly (+6°C). In a third simulation additional freshwater forcing halts the Atlantic THC, yielding a much colder North Atlantic region (−7°C). Comparing our simulation with proxy data, we find that the MIS3 climate with collapsed THC mimics stadials over the North Atlantic better than both control experiments, which might crudely estimate interstadial climate. These results suggest that freshwater forcing is necessary to return climate from warm interstadials to cold stadials during MIS3. This changes our perspective, making the stadial climate a perturbed climate state rather than a typical, near-equilibrium MIS3 climate.