bluuebunny/crossref_metadata_2025 huggingface dataset:
Glacier mass balance reconstruction by sublimation induced enrichment of chemical species on Cerro Tapado (Chilean Andes)
Authors: Ginot P. , Kull C. , Schotterer U. , Schwikowski M. , Gäggeler H. W.
Published: April 2010

Abstract. A 36 m long ice core down to bedrock from the Cerro Tapado glacier (5536 m a.s.l., 30°08' S, 69°55' W) was analyzed to reconstruct past climatic conditions for Northern Chile. Because of the marked seasonality in the precipitation (short wet winter and extended dry summer periods) in this region, major snow ablation and related post-depositional processes occur on the glacier surface during summer periods. They include predominantly sublimation and dry deposition. Under certain assumptions the chemical record along the ice core may be applied to reconstruct the history of such secondary processes. For the time period 1962–1999, a mean annual net accumulation of 316 mm water equivalent (weq) and 327 mm weq loss by sublimation was deduced by this method. This corresponds to an initial total annual accumulation of 539 mm weq. The annual variability of the accumulation and sublimation may exhibit a correlation with the Southern Oscillation Index (SOI). The deepest part of the ice record shows a time discontinuity; its age is unknown.
Where can the Arctic oscillation be reconstructed? Towards a reconstruction of climate modes based on stable teleconnections
Authors: Lohmann G. , Rimbu N. , Dima M.
Published: April 2010

Abstract. Proxy data can bring observed climate variability of the last 100 years into a long-term context. We identify regions of the Northern Hemisphere where the teleconnection patterns of the Arctic Oscillation are stationary. Our method provides a systematic way to examine optimal sites for the reconstruction of climate modes based on paleoclimatic archives that sensitively record temperature and precipitation variations. We identify the regions for boreal winter and spring that can be used to reconstruct the Arctic Oscillation index in the pre-instrumental period. Finally, this technique is applied to high resolution coral, tree ring, ice core and mollusk shell data to understand proxy-climate teleconnections and their use for climate reconstructions.
A studying of solar-ENSO correlation with southern Brazil tree-ring index (1955–1994)
Authors: Rigozo N. R. , Nordemann D. J. R. , Pereira de Souza Echer M. , Echer E. , Prestes A.
Published: April 2010

Abstract. Solar activity, volcanic aerosol, El Niño-Southern Oscillation and global temperature anomalies effects on Southern Brazil tree growth rings are presented through multiple linear analysis. Linear correlations were made on annual, 10 year running averages and band pass filter. For annual averages, the correlation coefficients were low, and the 10 years running average correlations the coefficient correlations were much higher. The multiple regression of 2 to 5 year band pass filter indicates that 60% of the variance in tree ring index was explained by volcanic eruptions, Southern Oscillation Index and temperature anomalies. The multiple regression of 10 year running averages indicates that 84% of the variance in tree ring index was explained by solar activity and another time series. These results indicate that the effects of solar activity, volcanic eruptions, ENSO and temperature anomalies on tree rings are better seen on long timescales than volcanic eruption, ENSO and temperature anomaly.
Effect of land albedo, CO2, orography, and oceanic heat transport on extreme climates
Authors: Romanova V. , Lohmann G. , Grosfeld K.
Published: April 2010

Abstract. Using an atmospheric general circulation model of intermediate complexity coupled to a sea ice-slab ocean model, we perform a number of sensitivity experiments under present-day orbital conditions and geographical distribution to assess the possibility that land albedo, atmospheric CO2, orography and oceanic heat transport may cause an ice-covered Earth. Changing only one boundary or initial condition, the model produces solutions with at least some ice-free oceans in the low latitudes. Using some combination of these forcing parameters, a full Earth's glaciation is obtained. We find that the most significant factor leading to an ice-covered Earth is the high land albedo in combination with initial temperatures set equal to the freezing point. Oceanic heat transport and orography play only a minor role for the climate state. Extremely low concentrations of CO2 also appear to be insufficient to provoke a runaway ice-albedo feedback, but the strong deviations in surface air temperatures in the Northern Hemisphere point to the existence of a strong nonlinearity in the system. Finally, we argue that the initial condition determines whether the system can go into a completely ice covered state, indicating multiple equilibria, a feature known from simple energy balance models.
Seasonal mean pressure reconstruction for the North Atlantic (1750–1850) based on early marine data
Authors: Gallego D. , Garcia-Herrera R. , Ribera P. , Jones P. D.
Published: April 2010

Abstract. Measures of wind strength and direction abstracted from European ships' logbooks during the recently finished CLIWOC project have been used to produce the first gridded Sea Level Pressure (SLP) reconstruction for the 1750-1850 period over the North Atlantic based solely on marine data. The reconstruction is based on a spatial regression analysis calibrated by using data taken from the ICOADS database. An objective methodology has been developed to select the optimal calibration period and spatial domain of the reconstruction by testing several thousands of possible models. The finally selected area, limited by the performance of the regression equations and by the availability of data, covers the region between 28°N and 52°N close to the European coast and between 28°N and 44°N in the open Ocean. The results provide a direct measure of the strength and extension of the Azores High during the 101 years of the study period. The comparison with the recent land-based SLP reconstruction by Luterbacher et al. (2002) indicates the presence of a common signal. The interannual variability of the CLIWOC reconstructions is rather high due to the current scarcity of abstracted wind data in the areas with best response in the regression. Guidelines are proposed to optimize the efficiency of future abstraction work.
Millennial temperature reconstruction intercomparison and evaluation
Authors: Juckes M. N. , Allen M. R. , Briffa K. R. , Esper J. , Hegerl G. C. , Moberg A. , Osborn T. J. , Weber S. L. , Zorita E.
Published: April 2010

Abstract. There has been considerable recent interest in paleoclimate reconstructions of the temperature history of the last millennium. A wide variety of techniques have been used. The interrelation between the techniques is sometimes unclear, as different studies often use distinct data sources as well as distinct methodologies. Recent work is reviewed with an aim to clarifying the import of the different approaches. A range of proxy data collections used by different authors are passed through two reconstruction algorithms: firstly, inverse regression and, secondly, compositing followed by variance matching. It is found that the first method tends to give large weighting to a small number of proxies and that the second approach is more robust to varying proxy input. A reconstruction using 18 proxy records extending back to AD 1000 shows a maximum pre-industrial temperature of 0.25 K (relative to the 1866 to 1970 mean). The standard error on this estimate, based on the residual in the calibration period is 0.149 K. Two recent years (1998 and 2005) have exceeded the estimated pre-industrial maximum by more than 4 standard errors.
The DO-climate events are noise induced: statistical investigation of the claimed 1470 years cycle
Authors: Ditlevsen P. D. , Andersen K. K. , Svensson A.
Published: April 2010

Abstract. The significance of the apparent 1470 years cycle in the recurrence of the Dansgaard-Oeschger (DO) events, observed in the Greenland ice cores, is debated. Here we present statistical significance tests of this periodicity. The detection of a periodicity relies strongly on the accuracy of the dating of the DO events. Here we use both the new NGRIP GICC05 time scale based on multi-parameter annual layer counting and the GISP2 time scale where the periodicity is most pronounced. For the NGRIP dating the recurrence times are indistinguishable from a random occurrence. This is also the case for the GISP2 dating, except in the case where the DO9 event is omitted from the record. Whether or not the record shows a truly periodic beating has strong implications for identifying the underlying cause. If the recurrence is periodic it suggests an external cause. If the recurrence of DO events is not periodic it points to triggering mechanisms internal to the climate system being manifested at the millennial timescale.
Application of sediment core modelling to understanding climates of the past: An example from glacial-interglacial changes in Southern Ocean silica cycling
Authors: Ridgwell A.
Published: April 2010

Abstract. Paleoceanographic evidence from the Southern Ocean reveals an apparent stark meridional divide in biogeochemical dynamics associated with the glacial-interglacial cycles of the late Neogene. South of the present-day position of the Antarctic Polar Front biogenic opal is generally much more abundant in sediments during interglacials compared to glacials. To the north, an anti-phased relationship is observed, with maximum opal abundance instead occurring during glacials. This antagonistic response of sedimentary properties is an important model validation target for testing hypotheses of glacial-interglacial change, particularly with respect to understanding the causes of the variability in atmospheric CO2. Here, I illustrate a time-dependent modelling approach to helping understand past climatic change by means of the generation of synthetic sediment core records. I find a close match between model-predicted and observed down-core changes in sedimentary opal content is achieved when changes in seasonal sea-ice extent is imposed, suggesting that the cryosphere is probably the primary driver of the striking features exhibited by the paleoceanographic record of this region.
A guide for digitising manuscript climate data
Authors: Brönnimann S. , Annis J. , Dann W. , Ewen T. , Grant A. N. , Griesser T. , Krähenmann S. , Mohr C. , Scherer M. , Vogler C.
Published: April 2010

Abstract. Hand-written or printed manuscript data are an important source for paleo-climatological studies, but bringing them into a suitable format can be a time consuming adventure with uncertain success. Before starting the digitising work, it is worthwhile spending a few thoughts on the characteristics of the data, the scientific requirements with respect to quality and coverage, and on the different digitising techniques. Here we briefly discuss the most important considerations and report our own experience. We describe different methods for digitising numeric or text data, i.e., optical character recognition (OCR), speech recognition, and key entry. Each technique has its advantages and disadvantages that may become important for certain applications. It is therefore crucial to thoroughly investigate beforehand the characteristics of the manuscript data, define the quality targets and develop validation strategies.
Coupled climate model simulation of Holocene cooling events: solar forcing triggers oceanic feedback
Authors: Renssen H. , Goosse H. , Muscheler R.
Published: April 2010

Abstract. The coupled global atmosphere-ocean-vegetation model ECBilt-CLIO-VECODE is used to perform transient simulations of the last 9000 years, forced by variations in orbital parameters, atmospheric greenhouse gas concentrations and total solar irradiance (TSI). The objective is to study the impact of decadal-centennial scale TSI variations on Holocene climate variability. The simulations show that negative TSI anomalies can trigger temporary reorganizations in the ocean circulation that produce centennial-scale cooling events that are consistent with proxy evidence for Holocene cold phases. In the model, reduced solar irradiance leads to a relocation of the site with deepwater formation in the Nordic Seas, causing an expansion of sea ice that produces additional cooling. The consequence is a characteristic climatic anomaly pattern, with cooling over most of the North Atlantic region and drying in the tropics. Our results suggest that the oceans play an important role in amplifying centennial-scale climate variability.
The origin of the European "Medieval Warm Period"
Authors: Goosse H. , Arzel O. , Luterbacher J. , Mann M. E. , Renssen H. , Riedwyl N. , Timmermann A. , Xoplaki E. , Wanner H.
Published: April 2010

Abstract. Using a combination of proxy records and results of a three dimensional climate model, we show that European summer temperatures roughly a millennium ago were comparable to those of the late 20th century. Those two relatively mild periods are separated by a rather cold era, supporting the existence of a summer ``Medieval Warm Period" in Europe. The long-term temperature history appears to result from the superposition of various anthropogenic forcings, the summer cooling associated with changes in land-use over the last 1000 years having the same magnitude as the net warming due to the combined increase in greenhouse gas concentration and in sulphate aerosols during the last 200 years. Volcanic and solar forcing plays a weaker role in this comparison between the late 20th century and the early second millennium. Evidence for winter is more equivocal. The forced response in the model displays a clear temperature maximum at the end of the 20th century but the uncertainties are too large to state that this period is the warmest of the past millennium in Europe in winter.
Recent warming inconsistent with natural association between temperature and atmospheric circulation over the last 2000 years
Authors: Mayewski P. A. , Maasch K. A.
Published: April 2010

Abstract. Comparison between proxies for atmospheric circulation and temperature reveals associations over the last few decades that are inconsistent with those of the past 2000 years. Notably, patterns of middle to high latitude atmospheric circulation in both hemispheres are still within the range of variability of the last 6–10 centuries while, as demonstrated by Mann and Jones (2003), Northern Hemisphere temperatures over recent decades are the highest of the last 2000 years. Further, recent temperature change precedes change in middle to high latitude atmospheric circulation unlike the two most notable changes in climate of the past 2000 years during which change in atmospheric circulation preceded or coincided with change in temperature. In addition, the most prominent change in Southern Hemisphere temperature and atmospheric circulation of the past 2000, and probably 9000 years, precedes change in temperature and atmospheric circulation in the Northern Hemisphere unlike the recent change in Northern Hemisphere temperature that leads. These findings provide new verification that recent rise in temperature is inconsistent with natural climate variability and is most likely related to anthropogenic activity in the form of enhanced greenhouse gases. From our investigation we conclude that the delayed warming over much of the Southern Hemisphere may be, in addition to other factors, a consequence of underpinning by natural climate variability. Further bipolar comparison of proxy records of atmospheric circulation demonstrates that change in atmospheric circulation in the Southern Hemisphere led by 400 years, the most abrupt change in Northern Hemisphere atmospheric circulation of the last 9000 years. This finding may be highly relevant to understanding a future when warming becomes more fully established in the Southern Hemisphere.
Past temperature reconstructions from deep ice cores: relevance for future climate change
Authors: Masson-Delmotte V. , Dreyfus G. , Braconnot P. , Johnsen S. , Jouzel J. , Kageyama M. , Landais A. , Loutre M.-F. , Nouet J. , Parrenin F. , Raynaud D. , Stenni B. , Tuenter E.
Published: April 2010

Abstract. Ice cores provide unique archives of past climate and environmental changes based only on physical processes. Quantitative temperature reconstructions are essential for the comparison between ice core records and climate models. Several methods have been developed to reconstruct past local temperatures from deep ice cores. Here we first analyse the long term fluctuations of temperature as depicted in the long Antarctic record from EPICA Dome C. The long term imprint of obliquity changes in the EPICA Dome C record is highlighted and compared to simulations conducted with the ECBILT-CLIO intermediate complexity climate model. We discuss the comparison between the current interglacial period and the long interglacial corresponding to marine isotopic stage 11, ~400 kyr BP. Previous studies had focused on the role of precession and the thresholds required to induce glacial inceptions. We suggest that, due to the low eccentricity configuration of MIS 11 and the Holocene, the effect of precession on the incoming solar radiation is damped and that changes in obliquity must be taken into account. The EPICA Dome C alignment of terminations I and VI published in 2004 corresponds to a phasing of the obliquity signals. A conjunction of low obliquity and minimum northern hemisphere summer insolation is not found in the next tens of thousand years, supporting the idea of an unusually long interglacial ahead. As a second point relevant for future climate change, we discuss the magnitude and rate of change of past temperatures reconstructed from Greenland (NorthGRIP) and Antarctic (Dome C) ice cores. Past episodes of temperatures above the present-day values by up to 5°C are recorded at both locations during the penultimate interglacial period. The polar warming simulated by coupled climate models forced by a CO2 increase of 1% per year is compared to ice-core-based temperature reconstructions. In Antarctica, the CO2-induced warming lies clearly beyond the natural rhythm of temperature fluctuations. In Greenland, the CO2-induced warming is as fast or faster than the most rapid temperature shifts of the last ice age. The magnitude of polar temperature change in response to a quadrupling of atmospheric CO2 is comparable to the magnitude of the polar temperature change from the Last Glacial Maximum to present-day. When forced by prescribed changes in ice sheet reconstructions and CO2 changes, climate models systematically underestimate the glacial-interglacial polar temperature change.
Changes in terrestrial carbon storage during interglacials: a comparison between Eemian and Holocene
Authors: Schurgers G. , Mikolajewicz U. , Gröger M. , Maier-Reimer E. , Vizcaîno M. , Winguth A.
Published: April 2010

Abstract. A complex earth system model (atmosphere and ocean general circulation models, ocean biogeochemistry and terrestrial biosphere) was used to perform transient simulations of two interglacial sections (Eemian, 128–113 ky B.P., and Holocene, 9 ky B.P.-present). The changes in terrestrial carbon storage during these interglacials were studied with respect to changes in the earth's orbit. The effect of different climate factors for the changes in carbon storage were studied in offline experiments in which the vegetation model was forced with only temperature, hydrological parameters, radiation, or CO2 concentration from the transient runs. Although temperature caused the largest anomalies in terrestrial carbon storage, the increase in storage due to forest expansion and increased photosynthesis in the high latitudes was nearly balanced by the decrease due to increased respiration. Large positive effects on carbon storage came from an enhanced monsoon circulation in the subtropics between 128 and 121 ky B.P. and between 9 and 6 ky B.P., and from increases in incoming radiation during summer for 45° to 70° N compared to a control run with present-day insolation. Compared to this control run, the net effect of these changes was a positive carbon storage anomaly of about 200 Pg C for 125 ky B.P. and 7 ky B.P., and a negative anomaly around 150 Pg C for 116 ky B.P. Although the net increases for Eemian and Holocene were rather similar, the causes of this differ substantially. The decrease in terrestrial carbon storage during the experiments was the main driver of an increase in atmospheric CO2 concentration for both the Eemian and the Holocene.
Agricultural sustainability in the semi-arid Near East
Authors: Hole F.
Published: April 2010

Abstract. Agriculture began in the eastern Mediterranean Levantine Corridor about 11 000 years ago toward the end of the Younger Dryas when aridity had diminished wild food resources. During the subsequent Climatic Optimum, agricultural villages spread rapidly but subsequent climatic changes on centennial to millennial scales resulted in striking oscillations in settlement, especially in marginal areas. Natural climate change thus alternately enhanced and diminished the agricultural potential of the land. Growing populations and more intensive land use, both for agriculture and livestock, have led to changes in the structure of vegetation, hydrology, and land quality. Over the millennia, political and economic interventions, warfare and incursions by nomadic herding tribes all impacted sustainability of agriculture and the ability of the land to support its populations. In much of the region today, agricultural land use is not sustainable given existing technology and national priorities. The Near Eastern case is instructive because of the quality of information, the length of the record, and the pace of modern change.
Climate-human-environment interactions: resolving our past
Authors: Dearing J. A.
Published: April 2010

Abstract. The paper reviews how we can learn from the past about climate-human-interactions at the present time, and in the future. It focuses on data sources for environmental change at local and regional/global spatial scales, and shows the scope and limitations of each. The use of parallel histories in local case-studies is described in a case-study from China, where independent records help unravel the complexity of interactions and provide a basis for assessing the resilience and sustainability of the landscape system. Holocene global records for Natural Forcings (e.g. climate and tectonics), Human Society and Ecosystems are reviewed, and the problems of reconstructing global records of processes that are only recorded at local scales examined. Existing regional/global records are used to speculate about the veracity of anthropogenic forcing of global climate. The paper concludes that a full understanding of causes of earth system change through (at least) the Holocene can come only through the most rigorous reconstructions of climate, human activities and earth processes, and importantly their interactions, at all locations and at all scales. It follows that we need to promote inter-scale learning: regionalisation and generalisation of existing data would be useful first steps. There is now a need to develop long-term simulation models that can help anticipate complex ecosystem behaviour and environmental processes in the face of global environmental change – and resolving our past is an essential element in that endeavour.
Simulating sub-Milankovitch climate variations associated with vegetation dynamics
Authors: Tuenter E. , Weber S. L. , Hilgen F. J. , Lourens L. J.
Published: April 2010

Abstract. Climate variability at sub-Milankovitch periods (between 2 and 15 kyr) is studied in a set of transient simulations with a coupled atmosphere/ocean/vegetation model of intermediate complexity (Climber-2). Focus is on the region influenced by the African and Asian summer monsoon. Pronounced variations at sub-Milankovitch periods of about 10 kyr (Asia and Africa) and about 5 kyr (Asia) are found in the monsoonal runoff in response to the precessional forcing. This is caused by the dynamic response of the vegetation. For low summer insolation (precession maximum) precipitation is low and desert expands at the expense of grass, while for high insolation (precession minimum) precipitation is high and the tree fraction increases thus reducing the grass fraction. This induces sub-Milankovitch variations in the grass fraction and associated variations in the water holding capacity of the soil. No sub-Milankovitch variability occurs in the runoff when vegetation is kept fixed. The high-latitude vegetation coverage also exhibits sub-Milankovitch variability under both obliquity as well as precessional forcing. We hypothesize that sub-Milankovitch variations found in terrestrial and marine records are related to variations in vegetation, soil characteristics and runoff influencing ocean salinity and circulation.
Reconstructing glacier-based climates of LGM Europe and Russia – Part 1: Numerical modelling and validation methods
Authors: Allen R. , Siegert M. J. , Payne A. J.
Published: April 2010

Abstract. The mountain environments of mid-latitude Europe and Arctic Russia contain widespread evidence of Late-Quaternary glaciers that have been prescribed to the Last Glacial Maximum (LGM). This glacial-geological record has yet to be used to quantitatively reconstruct the LGM climate of these regions. Here we describe a simple glacier-climate model that can be used to derive regional temperature and precipitation information from a known glacier distribution. The model was tested against the present day distribution of glaciers in Europe. The model is capable of adequately predicting the spatial distribution, snowline and equilibrium line altitude climate of glaciers in the Alps, Scandinavia, Caucasus and Pyrenees Mountains. This verification demonstrated that the model can be used to investigate former climates such as the LGM. Reconstructions of LGM climates from proxy evidence are an important method of assessing retrospective general circulation model (GCM) simulations. LGM palaeoclimate reconstructions from glacial-geological evidence would be of particular benefit to investigations in Europe and Russia, where to date only fossil pollen data have been used to assess continental-scale GCM simulations.
Climatic conditions for modelling the Northern Hemisphere ice sheets throughout the ice age cycle
Authors: Abe-Ouchi A. , Segawa T. , Saito F.
Published: April 2010

Abstract. The ice sheet-climate interaction as well as the climatic response to orbital parameters and atmospheric CO2 content are examined in order to drive an ice sheet model throughout an ice age cycle. Feedback processes between ice sheet and atmosphere are analyzed by numerical experiments using a high resolution General Circulation Model (GCM) under different conditions at the Last Glacial Maximum. Among the proposed processes, the ice albedo feedback, the elevation-mass balance feedback and the desertification effect over ice sheet were found to be the dominant processes for the ice-sheet mass balance. The temperature lapse rate over the ice sheet is proposed to be about 5 °C km–1, which is weaker than assumed in other studies. Within the plausible range of parameters related to these processes, the ice sheet response to orbital parameters and atmospheric CO2 content for the last glacial/interglacial cycle was simulated in terms of both ice volume and geographical distribution, using a three-dimensional ice-sheet model. Careful treatment related to climate-ice sheet feedback is essential for a reliable simulation of ice sheet changes during ice age cycles.
Increased aeolian activity during climatic regime shifts as recorded in a raised bog in south-west Sweden during the past 1700 years
Authors: de Jong R. , Schoning K. , Björck S.
Published: April 2010

Abstract. Analyses of testate amoebae and aeolian sediment influx (ASI) were used to reconstruct effective humidity changes and aeolian activity in the coastal zone of south-west Sweden. Cores were taken from an ombrotrophic peat sequence from the Undarsmosse bog. Since both types of analysis were carried out on the same core, a direct comparison between humidity fluctuations in the bog and aeolian activity was possible, potentially providing detailed information on atmospheric circulation changes in this region. Relatively stable wet bog surface conditions occurred from 1500 to 1230 and 770 to 380 cal. yrs BP, whereas dry conditions dominated from 1630 to 1530, 1160 to 830 and 300 to 50 cal. yrs BP. The transitions between these phases occurred within 60–100 years. ASI peak events were reconstructed around 1450, 1150, 850 and after 370 cal. yrs BP. Most interestingly, these aeolian activity peaks started during the recorded hydrological transitions, regardless of the direction of these shifts. Our results therefore suggest that climatic regime shifts in this region were associated with temporary intensifications of atmospheric circulation during the past 1700 years. Several ASI peaks apparently coincide with reduced solar activity, possibly suggesting a solar related cause for some of the observed events.
"EDML1": a chronology for the EPICA deep ice core from Dronning Maud Land, Antarctica, over the last 150 000 years
Authors: Ruth U. , Barnola J.-M. , Beer J. , Bigler M. , Blunier T. , Castellano E. , Fischer H. , Fundel F. , Huybrechts P. , Kaufmann P. , Kipfstuhl S. , Lambrecht A. , Morganti A. , Oerter H. , Parrenin F. , Rybak O. , Severi M. , Udisti R. , Wilhelms F. , Wolff E.
Published: April 2010

Abstract. A chronology called EDML1 has been developed for the EPICA ice core from Dronning Maud Land (EDML). EDML1 is closely interlinked with EDC3, the new chronology for the EPICA ice core from Dome-C (EDC) through a stratigraphic match between EDML and EDC that consists of 322 volcanic match points over the last 128 ka. The EDC3 chronology comprises a glaciological model at EDC, which is constrained and later selectively tuned using primary dating information from EDC as well as from EDML, the latter being transferred using the tight stratigraphic link between the two cores. Finally, EDML1 was built by exporting EDC3 to EDML. For ages younger than 41 ka BP EDML1/EDC3 is based on dated volcanic events and on a match to the Greenlandic GICC05 time scale via 10Be and methane. The internal consistency between EDML1 and EDC3 is estimated to be typically ~6 years and always less than 450 years over the last 128 ka (always less than 130 years over the last 60 ka), which reflects an unprecedented synchrony of time scales. EDML1 ends at 150 ka BP (2417 m depth) because the match between EDML and EDC becomes ambiguous further down. This hints to a complex ice flow history for the deepest 350 m of the EDML ice core, which amongst other reasons may be caused by spatial variations of the geothermal heat flux.
Anomalous flow below 2700 m in the EPICA Dome C ice core detected using δ18O of atmospheric oxygen measurements
Authors: Dreyfus G. B. , Parrenin F. , Lemieux-Dudon B. , Durand G. , Masson-Delmotte V. , Jouzel J. , Barnola J.-M. , Panno L. , Spahni R. , Tisserand A. , Siegenthaler U. , Leuenberger M.
Published: April 2010

Abstract. While there are no indications of mixing back to 800 000 years in the EPICA Dome C ice core record, comparison with marine sediment records shows significant differences in the timing and duration of events prior to stage 11 (~430 ka, thousand of years before 1950). A relationship between the isotopic composition of atmospheric oxygen (δ18O of O2, noted δ18Oatm) and daily northern hemisphere summer insolation has been observed for the youngest four climate cycles. Here we use this relationship with new δ18O of O2 measurements to show that anomalous flow in the bottom 500 m of the core distorts the duration of events by up to a factor of 2. By tuning δ18Oatm to orbital precession we derive a corrected thinning function and present a revised age scale for the interval corresponding to Marine Isotope Stages 11–20 in the EPICA Dome C ice core. Uncertainty in the phasing of δ18Oatm with respect to insolation variations in the precession band limits the accuracy of this new agescale to ±6 kyr (thousand of years). The previously reported ~30 kyr duration of interglacial stage 11 is unchanged. In contrast, the duration of stage 15.1 is reduced by a factor of 2, from 31 to 16 kyr.
Repeated temperature logs from the sites of the Czech, Slovenian and Portuguese borehole climate stations
Authors: Šafanda J. , Rajver D. , Correia A. , Dědeček P.
Published: April 2010

Abstract. Two borehole climate stations were established in Slovenia and Portugal within a joint Czech-Slovenian-Portuguese project in the years 2003–2005. They completed the older Czech station, which has been operating since the year 1994. We report here on the repeated temperature logs carried out within 6 boreholes at the sites of the stations and their surroundings within a time span of 8–20 years (1985–2005). The repeated logs revealed subsurface warming in all the boreholes amounting to 0.2–0.6°C below the depth of the annual run at 20 m. The depth of the Czech borehole (140 m) and the Portuguese borehole (180 m) was sufficient enough for a reconstruction of the ground surface temperature (GST) history of the last 150–200 years and their comparison with the surface air temperature (SAT) series measured in Prague (since 1771) and Lisbon (1856), respectively. The reconstructed histories reproduce reasonably well the amplitude of the recent warming, 1–1.5°C above the long-term mean. The depth of all four Slovenian boreholes, 100 m, did not allow the inversion, but it was possible to apply it to a deep borehole 5 km apart from the Slovenian station. The obtained GST history was compared with SAT series from Ljubljana (since 1851). Alternatively, a compatibility of the observed temporal changes of subsurface temperature with surface air temperature series measured in Prague, Ljubljana and Lisbon was checked by comparing differences of the repeated logs with the synthetic ones. These were calculated by using the SAT series as a forcing function at a surface of transient geothermal models of the borehole sites. A degree of agreement varies from very well to rather poor, probably depending on unaccounted site specific factors, which are to be specified by a long-term temperature monitoring at the established stations.
How unusual was autumn 2006 in Europe?
Authors: van Oldenborgh G. J.
Published: April 2010

Abstract. The temperatures in large parts of Europe have been record high during the meteorological autumn of 2006. Compared to the 1961–1990 normals it was more than three degrees Celsius warmer from the North side of the Alps to southern Norway. This made it by far the warmest autumn on record in the United Kingdom, Belgium, the Netherlands, Denmark, Germany and Switzerland, with the records in Central England going back to 1659, in the Netherlands to 1706 and in Denmark to 1768. Also in most of Austria, southern Sweden, southern Norway and parts of Ireland the autumn was the warmest on record. Under the obviously false assumption that the climate does not change, the observed temperatures for 2006 would occur with a probability of less than once every 10 000 years in a large part of Europe, given the distribution defined by the temperatures in the autumn 1901–2005. However, even taking global warming linearly into account the event was still very unusual, with return times of 200 years or more in most of this region using the most conservative extrapolation. Global warming and a southerly circulation were found to give the largest contributions to the anomalous temperature, with minor contributions of more sunshine and SST anomalies in the North Sea. Climate models that simulate the current circulation well do not simulate an increasing probability of warm events in autumn under global warming, implying that it either was a very rare coincidence or some non-linear physics is missing from these models.
Two millennia of climate variability in the Central Mediterranean
Authors: Taricco C. , Ghil M. , Vivaldo G.
Published: April 2010

Abstract. This experimental work addresses the need for high-resolution, long and homogeneous climatic time series that facilitate the study of climate variability over time scales of decades to millennia. We present a high-resolution record of foraminiferal δ18O from a Central Mediterranean sediment core that covers the last two millennia. The record was analyzed using advanced spectral methods and shows highly significant oscillatory components with periods of roughly 600, 350, 200, 125 and 11 years. Comparison with the spectra of composite temperature-proxy series over the last millennium reveals that the δ18O trend and 200-y components are well correlated with the long-term Northern Hemisphere temperature variations over the last millennium, showing a maximum at the Medieval Optimum and a shallower local minimum at the Little Ice Age. In the preceding millennium the same δ18O components also reveal a deep maximum (temperature minimum) at about 0 AD.
Millennium-long summer temperature variations in the European Alps as reconstructed from tree rings
Authors: Corona C. , Guiot J. , Edouard J. L. , Chalié F. , Büntgen U. , Nola P. , Urbinati C.
Published: April 2010

Abstract. This paper presents a reconstruction of the summer temperatures over the Greater Alpine Region (44.05°–47.41° N, 6.43°–13° E) during the last millennium based on a network of 36 multi-centennial larch and stone pine chronologies. Tree ring series are standardized using an Adaptative Regional Growth Curve, which attempts to remove the age effect from the low frequency variations in the series. The proxies are calibrated using the June to August mean temperatures from the HISTALP high-elevation temperature time series spanning the 1818–2003. The method combines an analogue technique, which is able to extend the too short tree-ring series, an artificial neural network technique for an optimal non-linear calibration including a bootstrap technique for calculating error assessment on the reconstruction. About 50% of the temperature variance is reconstructed. Low-elevation instrumental data back to 1760 compared to their instrumental target data reveal divergence between (warmer) early instrumental measurements and (colder) proxy estimates. The proxy record indicates cool conditions, from the mid-11th century to the mid-12th century, related to the Oort solar minimum followed by a short Medieval Warm Period (1200–1420). The Little Ice Age (1420–1830) appears particularly cold between 1420 and 1820 with summers are 0.8°C cooler than the 1901–2000 period. The new record suggests that the persistency of the late 20th century warming trend is unprecedented. It also reveals significant similarities with other alpine reconstructions.
Provenance changes of eolian dust at Lingtai section in the Chinese Loess Plateau since 7 Ma and its implication for desert development in East Asia
Authors: Isozaki Y. , Tada R. , Sun Y. , Nagashima K. , Zheng H. , Toyoda S. , Tani A.
Published: April 2010

Abstract. It is suggested that the uplift of Himalaya-Tibetan Plateau enhanced interior aridity in East Asia and resulted in development of middle latitude gobi and sandy deserts and accumulation of the eolian sediments in the Chinese Loess Plateau. Therefore, estimation of the provenance for eolian sediments in the Chinese Loess Plateau is critical to reconstruct the environmental changes in East Asia and their relation to the Himalaya-Tibetan Plateau uplift. We recently developed a new provenance tracing method by using a combination of Electron Spin Resonance (ESR) signal intensity and Crystallinity Index (CI) of quartz, and demonstrated that fine fraction of the surface sediments from nine major deserts in East Asia could be distinguished one another on the ESR signal intensity versus CI diagram. Here, we measured ESR signal intensity and CI of quartz in fine fractions of samples covering the last 7 Ma obtained from Lingtai section in the central Chinese Loess Plateau, and compared the results with those of the surface samples from nine major deserts in East Asia. The results suggest that the provenance of fine fraction of the eolian sediment in Lingtai section changed at 4.3, 2.1, 1.4, 1.1, 0.8 and 0.4 Ma. During 7 to 4.3 Ma, the dust might be have been supplied from Precambrian to Paleozoic metamorphic and granitic rocks and granite exposed in the present central to eastern part of the Tian Shan Mountains. The contribution from the Taklimakan desert appeared at 4.3 Ma, increased drastically at 1.1 Ma, and persisted till 0.8 Ma, whereas the main source of detrital material to the Taklimakan desert might have changed from eastern part of the Kunlun and the Altyn Mountains to western part of the Kunlun and the Tian Shan Mountains. During 0.8 to 0.4 Ma, contribution from the Badain Juran desert gradually increased. Finally, contribution from the Tengger desert appeared from 0.4 to 0 Ma. Together with tectonic evidences from literatures, the provenance changes from 4.3 to 0.8 Ma seem to reflect uplift of the Tian Shan and the Kunlun Mountains and consequent formation of the Taklimakan desert, whereas the change at 0.4 Ma may reflect uplift of the Qilian Mountains although formation of mountain glaciers could be an alternative possibility. These provenance changes will provide important constraints not only on the development of arid areas and evolution of monsoon but also on the uplift and erosion of mountains in East Asia.
Borehole paleoclimatology – the effect of deep lakes and "heat islands" on temperature profiles
Authors: Balobaev V. T. , Kutasov I. M. , Eppelbaum L. V.
Published: April 2010

Abstract. It is known that changes in ground surface temperatures could be caused by many non-climatic effects. In this study we propose a method based on utilization of Laplace equation with nonuniform boundary conditions. The proposed method makes possible to estimate the maximum effect of deep lakes and "heat islands" (areas of deforestation, urbanization, farming, mining and wetland drainage) on the borehole temperature profiles.
Anticyclonic atmospheric circulation as an analogue for the warm and dry mid-Holocene summer climate in central Scandinavia
Authors: Antonsson K. , Chen D. , Seppä H.
Published: April 2010

Abstract. Climate reconstructions from central Scandinavia suggest that annual and summer temperatures were rising during the early Holocene and reached their maximum after 8000 cal yr BP. The period with highest temperatures was characterized by increasingly low lake-levels and dry climate, with driest and warmest conditions at about 7000 to 5000 cal yr BP. We compare the reconstructed climate pattern with simulations of a climate model for the last 9000 yr and show that the model, which is predominantly driven by solar insolation patterns, fails to produce the reconstructed mid-Holocene dry and warm period in Scandinavia. As an alternative explanation for the reconstructed climate, we hypothesize that the trend from the moist early Holocene towards dry and warm mid-Holocene was caused by a changing atmospheric circulation pattern with a mid-Holocene dominance of summer-time anticyclonic circulation. An extreme case of the anticyclonic conditions is the persistent blocking high, an atmospheric pressure pattern that at present often causes long spells of particularly dry and warm summer weather, or "Indian summers". The hypothesis is tested with daily instrumental temperature and precipitation records in central Sweden and an objective circulation classification based on surface air pressure over the period 1900–2002. It is concluded that the differences between the precipitation and temperature climates under anticyclonic and non-anticyclonic conditions are significant. Further, warm and dry combination, as indicated by mid-Holocene reconstructions, is a typical pattern under anticyclonic conditions. These results indicate that the presented hypothesis for the mid-Holocene climate is likely valid.
Revisiting the absolute calibration of the Greenland ice-core age-scales
Authors: Skinner L.
Published: April 2010

Abstract. Recently, an absolute "calibration" was proposed for the GRIP and GISP2 Greenland ice-core time scales (Shackleton et al., 2004). This calibration attempted to reconcile the stratigraphic integration of ice-core, marine and speleothem archives with the absolute age constraints that marine and speleothem records incorporate. Here we revisit this calibration in light of the new layer-counted chronology of the NGRIP ice-core (GICC05). The GICC05 age-scale differs from the proposed absolute calibration by up to 1200 years late in the last glaciation, with implications both for radiocarbon cycling and the inferred timing of North Atlantic climate events relative to absolutely dated archives (e.g. relative sea-level). By precisely aligning the stratigraphy of Iberian Margin marine cores with that of the Greenland ice-cores, it appears that either: 1) the radiocarbon content of mid-latitude Atlantic surface-waters was extremely depleted (resulting in average surface reservoir ages up to 1700 years prior to ~22 ka BP); or 2) the GICC05 age-scale includes too few years (is up to 1200 years too young). It is shown here that both of these possibilities are in fact correct to some degree. Northeast Atlantic surface reservoir ages should be revised upward by ~350 years, while the NGRIP age-scale appears to be "missing" time. These findings illustrate the importance of integrated stratigraphy as a test for our chronologies, which are rarely truly "absolute". This is an important point, since probably the worst error that we can make is to entrench and generalise a precise stratigraphical relationship on the basis of erroneous absolute age assignations.
Constraining atmospheric CO2 content during the Middle Miocene Antarctic glaciation using an ice sheet-climate model
Authors: Langebroek P. M. , Paul A. , Schulz M.
Published: April 2010

Abstract. Foraminiferal oxygen isotopes from deep-sea sediment cores suggest that a rapid expansion of the Antarctic ice sheet took place in the Middle Miocene around 13.9 million years ago (Ma). The origin for this transition is still not understood satisfactorily. Among the proposed causes are a drop in the partial pressure of atmospheric carbon dioxide (pCO2) in combination with orbital forcing. An additional complication is the large uncertainty in the magnitude and age of the reconstructed pCO2 values and the low temporal resolution of the available record in the Middle Miocene. We used an ice sheet-climate model with an energy and mass balance module to assess variations in ice-sheet volume induced by pCO2 and insolation forcing and to better constrain atmospheric CO2 in the Middle Miocene. The ice-sheet sensitivity to atmospheric CO2 was tested in several scenarios using constant pCO2 forcing or a regular decrease in pCO2. Small, ephemeral ice sheets existed under relatively high atmospheric CO2 conditions (between 400–450 ppm), whereas more stable, large ice sheets occurred when pCO2 is less than 400 ppm. Transitions between the states were largely CO2-induced, but were enhanced by extremes in insolation. In order to explain the Antarctic glaciation in the Middle Miocene as documented by the oxygen isotope records from sediment cores, pCO2 must have decreased by approximately 150 ppm in about 30 ka, crossing the threshold pCO2 of 400 ppm around 13.9 Ma. Forcing the ice sheet-climate model with cyclic pCO2 variations at a period of 100 ka and amplitudes of approximately 40 ppm generated late Pleistocene glacial-interglacial like ice-volume variations, where the ice volume lagged pCO2 by 11–16 ka.