GRIP Ice Core Research Articles

Volcanism and the Greenland ice cores: A new tephrochronological framework for the last glacial-interglacial transition (LGIT) based on cryptotephra deposits in three ice cores

Chemical profiles from Greenland ice cores show that the frequency of volcanism was higher during the last glacial-interglacial transition (LGIT) and early Holocene, (17–9 ka b2k) than in any other period during the last 110 kyr. This increased frequency has partly been linked to climate-driven melting of the Icelandic ice sheet during the last deglaciation, with regional isostatic changes thought to alter mantle viscosity and lead to more eruptions. Our study is the first to construct a comprehensive tephrochronological framework from Greenland ice cores over the LGIT to aid in the reconstruction of volcanic activity over this period. The framework is based on extensive high-resolution sampling of three Greenland ice cores between 17.4 and 11.6 ka b2k and comprises a total of 64 cryptotephra deposits from the NGRIP, GRIP and NEEM ice cores. We show that many of these tephras are preserved within the core without an associated chemical signature in the ice, which implies that reconstructions of volcanism based solely on glacio-chemical indicators might underestimate the number of events. Single glass shards from each deposit were geochemically characterised to trace the volcanic source and many of these deposits could be correlated between cores. We show that the 64 deposits represent tephra deposits from 42 separate volcanic events, and of these, 39 are from Iceland, two from the north Pacific region (Japan and USA) and one has an unknown source. Six deposits can be correlated to terrestrial and/or marine tephra deposits in the Northern Hemisphere and the remaining 36 are unreported in other archives. We did not locate tephra from the compositionally distinctive Laacher See eruption (∼13 ka b2k) in our records. Combining our new discoveries with the previously published tephra framework, raises the number of individual tephra horizons found in Greenland ice over this interval to 50. This significantly improves the regional tephrochronological framework, our knowledge of the eruptive history of Iceland during the LGIT and provides new tephra constraints over key LGIT climate events. Consequentially, this framework can guide sampling strategies of future tephra studies in the terrestrial and marine realms aiming to link these records to the Greenland ice cores to assess regional climate synchroneity.

A latest Pleistocene and Holocene composite tephrostratigraphic framework for northeastern North America

Lakes and bogs in northeastern North America preserve tephra deposits sourced from multiple volcanic systems in the Northern Hemisphere. However, most studies of these deposits focus on specific Holocene intervals and the latest Pleistocene, providing snapshots rather than a full picture. We combine new data with previous work, supplemented by a broad review of the characteristics and ages of potential source regions and volcanoes, to develop the first composite tephrostratigraphic framework covering the last ∼14,000 years for this region. We report new cryptotephra records from three ombrotrophic peat bogs—Irwin Smith (Michigan), Bloomingdale (New York), and Sidney Bog (Maine)—as well as new analyses and age models from previously reported sites, Nordan's Pond Bog (Newfoundland) and Thin-Ice Pond (Nova Scotia). A new tephra (Iliinsky) from the NGRIP and GRIP ice cores is also presented as it can be correlated to new data from these terrestrial records and helps validate radiocarbon age models. We identify 21 new tephra in addition to the 15 already known, several of which cover the entire region – the White River Ash east, Newberry Pumice, Ruppert (NDN-230), and Mazama. For the first time we find Mount St. Helens Yn (ca. 3660 cal yr BP) and a set P tephra (∼3000–2550 cal yr BP), and confirm the presence of Jala Pumice from Volcan Ceboruco, Mexico, and KS1 from Ksudach volcano, Kamchatka. We describe new “ultra-distal” tephra, including the early Holocene KS2 eruption, and propose correlations to volcanoes Iliinsky and Shiveluch of Kamchatka, and Ushishir of the Kurile Islands. Not all of these tephra represent large eruptions, with several plausible correlations to sub-Plinian events. Using Bayesian age-modeling, we present new age estimates for the newly described tephra, for tephra with previously poor age control, and for several proximal correlatives. Overall, we demonstrate northeastern North America's importance for providing transcontinental linkages between paleoenvironmental records and providing insights into ash distribution from different styles and sizes of eruptions.

The Influence of Orbital Forcing on 10Be Deposition in Greenland Over the Glacial Period

Understanding the transport and deposition of the cosmogenic isotope10Be is vital for the application of the isotope data to infer past changes of solar activity, to reconstruct past Earth’s magnetic field intensity and climate change. Here, we use data of the cosmogenic isotope10Be from the Greenland ice cores, namely the NEEM and GRIP ice cores, to identify factors controlling its distribution. After removing the effects of the geomagnetic field on the cosmogenic radionuclide production rate, the results expose imprints of the 20–22 ka precession cycle on the Greenland10Be records of the last glacial period. This finding can further improve the understanding of10Be variability in ice sheets and has the prospect of providing better reconstructions of geomagnetic and solar activity based on cosmogenic radionuclide records.

Deglaciation of Penobscot Bay, Maine, USA

The Pond Ridge and Pineo Ridge moraines in downeast Maine likely formed at ~16.1 and ~15.7 ka respectively, during cold episodes recorded by δ18O dips in the GRIP ice core. The elapsed time between these ages is broadly consistent with retreat rates recorded by intervening De Geer moraines, which are readily visible on LiDAR imagery and are believed to be approximately annual. North-northwestward from the southwesterly extension of the Pond Ridge moraine there are three pairs of prominent moraines that are relatively continuous across the study area and could be reliably extrapolated across intervening water bodies. Retreat rates recorded by De Geer moraines suggest that these pairs formed at 15.7-15.8 ka, 15.5-15.6 ka, and ~15.5 ka. Although retreat appears to have occurred slightly faster across Penobscot Bay, a significant calving bay does not seem to have developed there. Instead, the ice margin remained relatively straight, retreating to the north-northwest. De Geer moraines become more widely spaced northward and vanish after ~15.5 ka when the ice margin was north of the head of Penobscot Bay and of Pineo Ridge. This likely reflects higher retreat rates during the initial phases of the Bølling warm period. Just south of Pineo Ridge there were two ice lobes; one retreated to the north and one to the northwest. The latter retreated more rapidly, while the former experienced numerous minor readvances and stillstands until finally pausing at the location of Pineo Ridge. A stillstand of this lobe then resulted in deposition of the Pineo Ridge moraine complex.

In search of stratigraphic subdivision of the period 8–0 ka in Greenland ice cores

The δ18O data for the last 8000 years in the Greenland NGRIP1, GRIP, DYE-3 and GISP2 ice cores have been analyzed stratigraphically in search of potentially meaningful boundaries and units. Pattern matching of the profiles is supported by using graphical display enhancements, calculating spectral trend curves and generating a compound profile. Techniques routinely used in subsurface geology have been applied in correlating the profiles. Four major stratigraphic units are identified (8.1–4.9, 4.9–3.3, 3.3–1.9 and 1.9–0.1 ka b2k), resulting in an improved understanding of the climate change after the Holocene Climate Optimum. Correlatable higher-order boundaries are identified within these units. The layers between the boundaries show δ18O patterns which generally are similar in character, the differences being ascribed to lateral variations in the factors that control the isotope content of the ice. The layering forms a series of short-lived low-amplitude aperiodic oscillations on a centennial time scale. The suggestion is that these higher-order boundaries and δ18O oscillations have climatic significance. Equivalent units are tentatively identified in ice-core data from the Agassiz and Renland ice caps. Comparison with other climate proxies or stratigraphies from the Northern Hemisphere is expected to render support for the here proposed scheme. It will then serve to guide and constrain the analysis of the dynamics of the climatic fluctuations for the study period.

Simulation of the future sea level contribution of Greenland with a new glacial system model

Abstract. We introduce the coupled model of the Greenland glacial system IGLOO 1.0, including the polythermal ice sheet model SICOPOLIS (version 3.3) with hybrid dynamics, the model of basal hydrology HYDRO and a parameterization of submarine melt for marine-terminated outlet glaciers. The aim of this glacial system model is to gain a better understanding of the processes important for the future contribution of the Greenland ice sheet to sea level rise under future climate change scenarios. The ice sheet is initialized via a relaxation towards observed surface elevation, imposing the palaeo-surface temperature over the last glacial cycle. As a present-day reference, we use the 1961–1990 standard climatology derived from simulations of the regional atmosphere model MAR with ERA reanalysis boundary conditions. For the palaeo-part of the spin-up, we add the temperature anomaly derived from the GRIP ice core to the years 1961–1990 average surface temperature field. For our projections, we apply surface temperature and surface mass balance anomalies derived from RCP 4.5 and RCP 8.5 scenarios created by MAR with boundary conditions from simulations with three CMIP5 models. The hybrid ice sheet model is fully coupled with the model of basal hydrology. With this model and the MAR scenarios, we perform simulations to estimate the contribution of the Greenland ice sheet to future sea level rise until the end of the 21st and 23rd centuries. Further on, the impact of elevation–surface mass balance feedback, introduced via the MAR data, on future sea level rise is inspected. In our projections, we found the Greenland ice sheet to contribute between 1.9 and 13.0 cm to global sea level rise until the year 2100 and between 3.5 and 76.4 cm until the year 2300, including our simulated additional sea level rise due to elevation–surface mass balance feedback. Translated into additional sea level rise, the strength of this feedback in the year 2100 varies from 0.4 to 1.7 cm, and in the year 2300 it ranges from 1.7 to 21.8 cm. Additionally, taking the Helheim and Store glaciers as examples, we investigate the role of ocean warming and surface runoff change for the melting of outlet glaciers. It shows that ocean temperature and subglacial discharge are about equally important for the melting of the examined outlet glaciers.

Simulating the Last Interglacial Greenland stable water isotope peak: The role of Arctic sea ice changes

Last Interglacial (LIG), stable water isotope values (δ18O) measured in Greenland deep ice cores are at least 2.5‰ higher compared to the present day. Previous isotopic climate simulations of the LIG do not capture the observed Greenland δ18O increases. Here, we use the isotope-enabled HadCM3 (UK Met Office coupled atmosphere-ocean general circulation model) to investigate whether a retreat of Northern Hemisphere sea ice was responsible for this model-data disagreement. Our results highlight the potential significance of sea ice changes on the LIG Greenland isotopic maximum. Sea ice loss in combination with increased sea surface temperatures, over the Arctic, affect δ18O: water vapour enriched in heavy isotopes and a shorter distillation path may both increase δ18O values over Greenland. We show, for the first time, that simulations of the response to Arctic sea ice reduction are capable of producing the likely magnitude of LIG δ18O increases at NEEM, NGRIP, GIPS2 and Camp Century ice core sites. However, we may underestimate δ18O changes at the Renland, DYE3 and GRIP ice core locations. Accounting for possible ice sheet changes is likely to be required to produce a better fit to the LIG ice core δ18O values.

Setting a chronology for the basal ice at Dye-3 and GRIP: Implications for the long-term stability of the Greenland Ice Sheet

The long-term stability of the Greenland Ice Sheet (GIS) is an important issue in our understanding of the climate system. Limited data suggest that the northern and southern sections extend well back into the Pleistocene, but most age constraints do not definitively date the ice. Here, we re-examine the GRIP and Dye-3 ice cores to provide direct ice core observations as to whether the GIS survived previous interglacials known to be warmer (∼130 ka) or longer (∼430 ka) than the present interglacial. We present geochemical analyses of the basal ice from Dye-3 (1991–2035 m) and GRIP (3020–3026 m) that characterize and date the ice. We analyzed the elemental and isotopic composition of O2, N2, and Ar, of trapped air in these two cores to assess the origin of trapped gases in silty ice. Dating of the trapped air was then achieved by measuring the paleoatmospheric δ40Ar/38Ar and the 17O anomaly (Δ17) of O2. The resulting age is a lower limit because the trapped air may be contaminated with crustal radiogenic 40Ar. The oldest average age of replicates measured at various depths is 970±140 ka for the GRIP ice core and 400 ka±170 ka for Dye-3. Δ17 data from Dye-3 also argue strongly that basal ice in this core predates the Eemian. This confirms that the Greenland Ice Sheet did not completely melt at Southern Greenland during the last interglacial, nor did it completely melt at Summit Greenland during the unusually long interglacial ∼430 kyr before present.

Millennial changes in North American wildfire and soil activity over the last glacial cycle

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

Consistently dated records from the Greenland GRIP, GISP2 and NGRIP ice cores for the past 104 ka reveal regional millennial-scale δ18O gradients with possible Heinrich event imprint

We present a synchronization of the NGRIP, GRIP and GISP2 ice cores onto a master chronology extending back to 104 ka before present, providing a consistent chronological framework for these three Greenland records. The synchronization aligns distinct peaks in volcanic proxy records and other impurity records (chemo-stratigraphic matching) and assumes that these layers of elevated impurity content represent the same, instantaneous event in the past at all three sites. More than 900 marker horizons between the three cores have been identified and our matching is independently confirmed by 24 new and previously identified volcanic ash (tephra) tie-points. Using the reference horizons, we transfer the widely used Greenland ice-core chronology, GICC05modelext, to the two Summit cores, GRIP and GISP2. Furthermore, we provide gas chronologies for the Summit cores that are consistent with the GICC05modelext timescale by utilizing both existing and new gas data (CH4 concentration and δ15N of N2). We infer that the accumulation contrast between the stadial and interstadial phases of the glacial period was ∼10% greater at Summit compared to at NGRIP. The δ18O temperature-proxy records from NGRIP, GRIP, and GISP2 are generally very similar and display synchronous behaviour at climate transitions. The δ18O differences between Summit and NGRIP, however, changed slowly over the Last Glacial–Interglacial cycle and also underwent abrupt millennial-to-centennial-scale variations. We suggest that this observed latitudinal δ18O gradient in Greenland during the glacial period is the result of 1) relatively higher degree of precipitation with a Pacific signature at NGRIP, 2) increased summer bias in precipitation at Summit, and 3) enhanced Rayleigh distillation due to an increased source-to-site distance and a potentially larger source-to-site temperature gradient. We propose that these processes are governed by changes in the North American Ice Sheet (NAIS) volume and North Atlantic sea-ice extent and/or sea-surface temperatures (SST) on orbital timescales, and that changing sea-ice extent and SSTs are the driving mechanisms on shorter timescales. Finally, we observe that maxima in the Summit–NGRIP δ18O difference are roughly coincident with prominent Heinrich events. This suggests that the climatic reorganization that takes place during stadials with Heinrich events, possibly driven by a southward expansion of sea ice and low SSTs in the North Atlantic, are recorded in the ice-core records.

Fabric along the NEEM ice core, Greenland, and its comparison with GRIP and NGRIP ice cores

Abstract. Fabric (distribution of crystallographic orientations) along the full NEEM ice core, Greenland was measured in the field by an automatic ice texture analyzer every 10 m, from 33 m down to 2461 m depth. The fabric evolves from a slightly anisotropic fabric at the top, toward a strong single maximum at about 2300 m, which is typical of a deformation pattern mostly driven by uniaxial compression and simple shearing. A sharp increase in the fabric strengthening rate is observed at the Holocene to Wisconsin (HW) climatic transition. From a simple model we estimate that this depth is located at a transition from a state dominated by vertical compression to a state dominated by vertical shear. Comparisons are made to two others ice cores drilled along the same ridge; the GRIP ice core, drilled at the summit of the ice sheet, and the NGRIP ice core, drilled 325 km to the NNW of the summit along the ridge, and 365 km upstream from NEEM. This comparison tends to demonstrate that the ice viscosity change with the HW climatic transition must be associated with the shear-dominated state to induce the abrupt fabric strengthening observed at NEEM. This comparison therefore reflects the increasing role of shear deformation on the coring site when moving NW along the ridge from GRIP to NGRIP and NEEM. The difference in fabric profiles between NEEM and NGRIP also evidences a stronger lateral extension associated with a sharper ridge at NGRIP. Further along the core, centimeter scale abrupt texture (fabric and microstructure) variations are observed in the bottom part of the core. Their positions are in good agreement with the observed folding layers in Dahl-Jensen et al. (2013).

Arctic Ocean perennial sea ice breakdown during the Early Holocene Insolation Maximum

Arctic Ocean sea ice proxies generally suggest a reduction in sea ice during parts of the early and middle Holocene (∼6000–10,000 years BP) compared to present day conditions. This sea ice minimum has been attributed to the northern hemisphere Early Holocene Insolation Maximum (EHIM) associated with Earth's orbital cycles. Here we investigate the transient effect of insolation variations during the final part of the last glaciation and the Holocene by means of continuous climate simulations with the coupled atmosphere–sea ice–ocean column model CCAM. We show that the increased insolation during EHIM has the potential to push the Arctic Ocean sea ice cover into a regime dominated by seasonal ice, i.e. ice free summers. The strong sea ice thickness response is caused by the positive sea ice albedo feedback. Studies of the GRIP ice cores and high latitude North Atlantic sediment cores show that the Bølling–Allerød period (c. 12,700–14,700 years BP) was a climatically unstable period in the northern high latitudes and we speculate that this instability may be linked to dual stability modes of the Arctic sea ice cover characterized by e.g. transitions between periods with and without perennial sea ice cover.

New findings regarding the Saksunarvatn Ash in Germany

ABSTRACTThe Saksunarvatn Ash is an important tephra layer for the correlation of Early Holocene environmental records in northern Europe, the North Atlantic and Greenland. The Saksunarvatn Ash is believed to have been produced by eruptions of the Grimsvötn volcanic system ∼10.3 ka BP, which had two axes of dispersal, one plume in a north‐west direction over northern Iceland and into Greenland, and a second southerly plume covering the Faroe Isles, Shetland Isles, western Norway and northern Germany. Here we present data from Potremser Moor, north‐east Germany, extending the easterly margin of the ash fallout zone. We also present single grain trace element data from the type site at Saksunarvatn as well as from Potremser Moor. The Saksunarvatn Ash is indistinguishable between Potremser Moor and Saksunarvatn, suggesting the two tephras were produced by the same eruption. Trace element compositions from both sites are similar to data from the North Atlantic marine core (LINK 14:185), but different from the GRIP ice core (GRIP 1528.61 m), indicating that the south‐east and north‐west plumes may have arisen from separate eruption events. Copyright © 2013 John Wiley & Sons, Ltd.

On the gas-ice depth difference (Δdepth) along the EPICA Dome C ice core

Abstract. We compare a variety of methods for estimating the gas/ice depth offset (Δdepth) at EPICA Dome C (EDC, East Antarctica). (1) Purely based on modelling efforts, Δdepth can be estimated combining a firn densification with an ice flow model. (2) The diffusive column height can be estimated from δ15N and converted to Δdepth using an ice flow model and assumptions about past average firn density and thickness of the convective zone. (3) Ice and gas synchronisation of the EDC ice core to the GRIP, EDML and TALDICE ice cores shifts the ice/gas offset problem into higher accumulation ice cores where it can be more accurately evaluated. (4) Finally, the bipolar seesaw hypothesis allows us to synchronise the ice isotopic record with the gas CH4 record, the later being taken as a proxy of Greenland temperature. The general agreement of method 4 with methods 2 and 3 confirms that the bipolar seesaw antiphase happened during the last 140 kyr. Applying method 4 to the deeper section of the EDC core confirms that the ice flow is complex and can help to improve our reconstruction of the thinning function and thus, of the EDC age scale. We confirm that method 1 overestimates the glacial Δdepth at EDC and we suggest that it is due to an overestimation of the glacial lock-in depth (LID) by the firn densification model. In contrast, we find that method 1 very likely underestimates Δdepth during Termination II, due either to an underestimated thinning function or to an underestimated LID. Finally, method 2 gives estimates within a few metres of methods 3 and 4 during the last deglacial warming, suggesting that the convective zone at Dome C cannot have been very large at this time, if it existed at all.

Grain-size characteristics and climate variability in TMS5e sequence of Tumen section in southern Tengger Desert, northwestern China

The TMS5e sequence from the Tumen section, at the southern edge of Tengger Desert in the northwestern China, is synchronous with Marine Isotope Stage 5e (MIS5e). It consists of 16 layers of aeolian dune sands, 11 layers of lacustrine loess-like facies, and 5 layers of lacustrine facies. The results of grain-size analysis shows that the palaeo-mobile dune sands, palaeo-fixed to semi-fixed dune sands and loess-like sandy loams are mainly composed of sands, ranging from 70% to 96%; their silt contents ranged from 4% to 20%, and their clay contents ranged from 1% to 5%; the climate under which the aeolian dune sands were deposited is similar to that under which modern mobile dune sands form, which is caused by the dominance of the cold, dry East Asian winter monsoon. In contrast, the lacustrine loess-like facies and lacustrine facies had a lower sand contents than those of the three aeolian dune sands, but have higher silt and clay contents, most of their sand content ranged from 30% to 60%, their silt contents ranged from 35% to 55%, and their clay contents ranged from 6% to 20%. The lacustrine loess-like facies and lacustrine facies formed under the influence of the warm, humid East Asian summer monsoon based on their similarity with modern sediments. The grain-size indicator Mz (mean grain diameter) and the SC/D value in the TMS5e sequence indicate climatic instability at the southern edge of the Tengger Desert during MIS5e, with at least 14 fluctuations between a warm, humid climate and a cold, dry climate, divided into five stages: TMS5e5 (139 kyr to 129.3 kyr B.P.), TMS5e4 (129.3 kyr to 124 kyr B.P.), TMS5e3 (124 kyr to 119.5 kyr B.P.), TMS5e2 (119.5 kyr to 116.5 kyr B.P.), and TMS5e1 (116.5 kyr to 113.7 kyr B.P.). These correspond roughly to MIS5e5, MIS5e4, MIS5e3, MIS5e2, and MIS5e1, respectively, in the GRIP ice core data.

Magnetization of polar ice: a measurement of terrestrial dust and extraterrestrial fallout

Laboratory-induced remanent magnetization of polar ice constitutes a measurement of the magnetization carried by the ferromagnetic dust particles in the ice. This non-destructive technique provides a novel kind of information on the dust deposited on the surface of polar ice sheets. Measurements made on ice samples from Greenland (North GRIP ice core) and Antarctica (Vostok and EPICA-Dome C ice cores) allowed the recognition of a fraction of magnetic minerals in ice whose concentration and magnetic properties are directly related to that of insoluble dust. The source of this fraction of magnetic minerals thus appears closely related to terrestrial dust transport and deposition and its magnetic properties are informative of the dust provenance areas. The rock-magnetic properties of the dust may reflect distinct changes of dust source areas from glacial to interglacial periods in agreement with and adding further information to the isotopic (87Sr/86Sr and 143Nd/144Nd) analyses. A second magnetic fraction consists of particles of nanometric size, which are superparamagnetic at freezer temperature and whose concentration is independent of the mass of aerosol dust found in the ice. The source of these nanometric-sized magnetic particles is ascribed to fallout of “meteoric smoke” and their concentration in ice was found to be compatible with the extraterrestrial fallout inferred from Ir concentrations. The diameter of the smoke particles as inferred from magnetic measurements is in the range of about 7–20 nm.

The Veldwezelt site (province of Limburg, Belgium): environmental and stratigraphical interpretations

AbstractUphill and drainage line environments reveal many hiatuses or discordances, because of truncation by erosion. In downslope position accumulation often prevailed outside the drainage lines and prevented erosion, even during unstable periods. Consequently, downslope sections yield the most detailed environmental data, but often lack contact with uphill series. However, for stratigraphical correlation the contact between downslope and uphill series is essential. In the Veldwezelt loess sequence this contact is intact, which provides additional data on transitional processes. In view of these special palaeoenvironmental conditions, exhibiting a transition between downslope and uphill areas and a south-east trending stream, an extraordinarily detailed Late Saalian, Eemian and Weichselian loess sequence could be reconstructed. The Veldwezelt series furnished important pedological, sedimentological, faunal, tephrochronological and cryogenic data, on the basis of which palaeoenvironmental conclusions could be drawn and six types of pedo-sedimentological cycles distinguished. A stratigraphical overview was obtained by correlating the Veldwezelt section with other west European loess frameworks and tephra sequences; the sedimentary series at Harmignies (Mons Basin, southern Belgium) and the Greenland GRIP ice core.

The Medieval Climate Anomaly in Greenland ice core data

Temperature signals in ice core data Greenland ice core data can be used to derive information on past climatic conditions in the Greenland area. Recently, Vinther et al. (2010) demonstrated a high correlation between δ18O data and Greenland coastal temperature observations even on seasonal timescales, reaffirming the ability of ice core δ18O to capture local temperatures, first proposed by Dansgaard (1954). The Vinther et al. (2010) analysis of the seasonal ice core δ18O data showed that the winter δ18O contains the strongest temperature signal, and that even annual average Greenland temperatures are more accurately captured in the winter δ18O rather than annual average δ18O data. This surprising fact is partly explained by the observation that Greenland winter temperatures are much more variable than summer temperatures and thus dominate the annual average variability (Vinther et al., 2010). Past Greenland climatic conditions can also be derived directly from Greenland ice core borehole temperature observations, by solving the equation of heat conduction in moving ice and firn (Dahl-Jensen et al., 1998). Using a Monte Carlo inversion technique, Dahl-Jensen et al. (1998) derived temperature histories from both southern and central Greenland from high precision borehole temperature measurements obtained at the DYE-3 and GRIP ice core drill sites. A third way of estimating past Greenland temperature conditions is to measure isotopes on nitrogen and argon trapped in air-bubbles within the ice (Severinghaus et al., 1998). These gases undergo a temperature dependent mass fractionation in the snow column before the air-bubbles are formed in the ice, thus retaining a retrievable temperature signal.

Age of the MGS5 segment of the Milanggouwan stratigraphical section and evolution of the desert environment on a kiloyear scale during the Last Interglacial in China's Salawusu River Valley: Evidence from Rb and Sr contents and ratios

The MGS5 segment of the Milanggouwan stratigraphical section in China's Salawusu River Valley records 8.5 sedimentary cycles consisting of dune sands alternating with fluviolacustrine facies or/and paleosols. Based on a comprehensive analysis of the distribution of Rb and Sr within the segment and paleoecological evidence (fossils), it appears that the observed sedimentation cycles mainly resulted from fluctuations between dry-cold and warm-humid climates, which indicates that the MGS5 segment experienced at least eight cold-dry and nine warm-humid climatic fluctuations. Of these, 12 cold–warm climate fluctuations correspond to DO20–DO25 and stadia 21–26 recorded by the NGRIP ice cores. Another five cold–warm climatic fluctuations that occurred during MGS5e correspond to five substages (5e1–5e5) recorded by the GRIP ice cores from Greenland. This kind of high-frequency climatic fluctuation on a kiloyear scale was mainly subject to variations in the strength of the East Asian winter and summer monsoons.

Climate variability recorded by n-alkanes of paleolake sediment in Qaidam Basin on the northeast Tibetan Plateau in late MIS3

Here we combine n-alkanes preserved in a shell bar section from Qarhan paleolake, Qaidam Basin with the other sedimentary proxies to elucidate the lake evolution process during the period 39.7 to 17.5 14C ka BP (calibrated age ranges from 43.5 to 22.4 cal. ka BP). In different stages, the n-alkane homologues exhibited different distribution modes indicative of variations in the surrounding vegetation and the hydrologic condition of the lake. The n-alkanes proxies (CPIh, ACLh, Paq) have the same trends as the summer solar insolation variation, implying that the summer insolation is the most important climatic factor driving the environmental changes and also indirectly controls lake evolution on the Tibetan Plateau. CPIh and ACLh as well as the total pollen concentration appear to show a trend comparable with methane concentration record from the GRIP ice core that reflected the Dansgaard-Oeschger events. This demonstrates that the paleoclimate variations in Qarhan area generally agree with global climate change and show rapid oscillations in late MIS3. These findings provide the latest molecular fossil evidence from paleolake sediments to confirm that lake evolution on Tibetan Plateau in late MIS3 was closely associated with enhanced summer insolation.