Palaeoclimatic Studies Research Articles

Climatic controls on the equilibrium-line altitudes of Scandinavian cirque glaciers

The equilibrium-line altitudes (ELAs) of reconstructed palaeoglaciers have been widely used to assess palaeoclimatic conditions, yet this concept has rarely been tested using modern glaciers. To address this shortcoming, correlations between the ELAs of 513 modern cirque glaciers and present-day climatic and topographic variables across Scandinavia, as well as regional trends in ELA and climate, are analysed. ELAs are calculated using the Area-Altitude-Balance-Ratio method, with a ratio of 1.5 ± 0.4. Results indicate that glacier ELAs are strongly correlated with distance from the coast. This reflects the present-day precipitation pattern of the region (characterised by high precipitation near the sea) and demonstrates a climate dominated by a maritime-continental transition. Temperature explains differences in glacier ELA regional trends as well as ELA changes with latitude. Following standard meteorological convention, Scandinavia is divided into two macro-climate regions and analyses are run within the macro-regions as well as the complete dataset. The strength of correlations between ELA and precipitation increases when the study is divided into northern and southern macro-regions. These results test long held assumptions about relationships between climate and cirque glacier ELA, which is of particular relevance to palaeoclimatic studies based on the reconstruction of former cirque glaciers.

GLOBAL WARMING AND CLIMATE CHANGE AND SPORTS

Climate change is not the new phenomenon. The palaeo-climatic studies reveal that during the Pleistocene and Holocene periods several warm and cold periods occurred, resulted change of sea level and change in climatic processes like rise and fall of global average temperature and rainfall. The last medieval warm period was observed from 950 to 1350 AD, followed by the little Ice Age from 1400 to 1900 AD. Occurrence of these climatic changes and their impacts are considered due to natural processes that are geological and astronomical. In 1970s environmentalists and some climate scientists pointed that earth’s average temperature is rising linked with the anthropogenic causes of global warming and emission of carbon dioxide through fossil fuels. In late 1980s the problem was discussed in politics and media. To examine and monitor the global rise of temperature and its impacts due to the emission of carbon dioxide an organization of Intergovernmental Panel on Climate Change (IPCC) was created in 1988 by United Nations Environment Programme (UNEP). The IPCC released several reports based upon anthropogenic causes of climate change and their impacts. According to IPCC, 2007 report on climate change during the last 100 years the earth’s average temperature has increased up to 0.6 degree Celsius and if emission of greenhouse gases particularly carbon dioxide continues to rise, global temperature will rise up to 5.8 degrees Celsius by the end of 2100 AD. Similarly as a result of this threat of global warming, glaciers will disappear even from Antarctica and Arctic sea will open for navigation throughout the year. Many islands and coastal cities will submerge as a result of sea level rise. In 2004 Canadian Broadcasting T.V presented a documentary with the name “ The doomsday called off” in which leading climate scientists, astrophysicist and geophysicist presented evidences that science of global warming presented by IPCC scientists is incomplete and incorrect based upon computer models and stimulations which are deliberately exaggerated. Many climate scientists have shown disassociation with the IPCC views and speculations on the basis of its doubtful manipulated and exaggerated figures of global warming and some consider it a climate scam. Since then debate between UN pro man-made global warming scientists and anti-man-made global warming climate scientists continue.

Evidence for wetter climate recorded in the Jingxian red clay section since approximately 840 ka ago and its relationship with the East Asian summer monsoon intensity

The Quaternary red clay (QRC) is one of the typical terrestrial sediments in southern China which contains abundant palaeoclimatic information. A natural QRC outcrop, named the Jingxian red clay section (JRCS), was developed in Jingxian City on the northern piedmont of Mt. Huangshan, offering a valuable archive for long-term palaeoclimatic study from a southern China perspective. The objective of this study is to reveal palaeoclimatic information of regional precipitation from the JRCS and its correlation with the East Asian summer monsoon (EASM) intensity, using grain-size measurements combined with dating via Electron Spin Resonance (ESR) and palaeomagnetism. The results indicate that: (1) Ten palaeoclimatic wetter periods (PWPs) designated as PWPI to PWPX from top to bottom were detected from the grain-size analysis results of the upper 9.4 m JRCS. These PWPs span a period from approximately 840 ka ago to present; (2) three PWPs (PWPVIII to PWPX) were basically determined to approximately 612–690, 720–762 and 792–822 ka ago, basically corresponding to China loess layers of L6, L7 and L8 and deep-sea isotope stages of MIS16, MIS18 and MIS20, respectively. Data suggests that the PWPs in the study area were observed mainly during glaciations; (3) regional precipitation in the study area should be negatively related to the EASM intensity since approximately 840 ka ago as a result of variations in North Hemisphere solar insolation and uplifts of the Tibetan Plateau; (4) the modern anti-phase of monsoonal rainfall at glacial-interglacial timescales seemed to have existed between northern China and southern China since the late Early Pleistocene (approximately 840 ka ago).

The effects of diagenetic aromatization on the carbon and hydrogen isotopic composition of higher plant di- and triterpenoids: Evidence from buried wood

The widely distributed aromatic di- and triterpenoids from higher plants occurring in sediments are formed by diagenetic microbial processes affecting their precursor plant lipids. These compounds and their stable isotopic composition (δ13C and δ2H) have the potential to be used for palaeoenvironmental and palaeoclimatic studies. In the present study, the isotopic composition of di- and triterpenoids aromatized to different extents has been measured to specifically examine the isotopic effects associated with the aromatization reaction. To overcome the possibility of multiple higher plant sources, as is generally the case with sedimentary lipids, the δ13C and δ2H values of aromatized di- and triterpenoids from lipid extracts recovered from conifer and angiosperm buried wood have been determined, allowing an unambiguous substrate/product relationship along the aromatization pathway to be assured. The results show that the δ13C compositions of both di- and triterpenes do not seem to be significantly affected by progressive aromatization, whereas the situation is different for δ2H values. In the case of diterpenoids related to abietic acid, a significant increase of the δ2H values by up to 86‰ with ongoing aromatization was measured. This is in contrast to what is expected for dehydrogenated compounds which should be globally more 2H-depleted than their precursor molecules (e.g., biosynthesized unsaturated fatty acids vs. their saturated precursors). This 2H enrichment of aromatized diterpenoids could indicate that they represent only minor residual intermediates, the majority having been further degraded by processes favoring the degradation of the 1H-containing substrates and having a moderately pronounced 12C/13C selectivity. With triterpenoids, preservation of the δ2H values was observed whatever the nature and extent of the aromatization process considered, which may be related to enzymatic reactions showing a limited influence on the hydrogen stable isotopic composition of the aromatized compounds.

Mud deposition and diagenesis within an Early Palaeozoic clinothem: Power Steps Formation, Newfoundland, Canada

AbstractThe early Ordovician (∼385 Ma) Power Steps Formation, Newfoundland, Canada, exposes a well-preserved mudstone-dominated clinothem that serves as an excellent archive for understanding how mud has been produced, transported and converted into mudstone prior to the evolution of globally widespread, deep soil horizons. Sedimentological analysis of four sandstone and five mudstone facies, along the Ochre Cove clinothem, reveal that mud and sand were delivered by unidirectional currents and experienced episodic reworking by storm waves. Petrographic examination and X-ray diffraction from described mudstone facies reveal significant variability in the distribution of illite versus chlorite between the lower and upper part of the Ochre Cove clinothem. This research highlights that in the present-day clay mineral fraction, illite is often detrital whereas chlorite originated via the alteration of silt-sized, highly unstable, mafic (volcanoclastic?) grains. Throughout all sedimentologic facies, albeit in different proportions, these mafic lithic grains were diagenetically altered via in situ weathering before significant compaction occurred, resulting in the precipitation of significant volumes of pore-bridging, silica- and iron-rich chlorite cement. Compositional, diagenetic and textural attributes across the Ochre Cove mud clinothem vary as a function of starting composition, hydrodynamic sorting and grain density. Given that a significant proportion of clay minerals has been generated via in situ transformation of a mafic, non-stable precursor assemblage, we recommend future studies to incorporate detailed petrographic description along with X-ray diffraction analyses when aiming to employ trends in whole-rock clay mineral data as a proxy in provenance and palaeoclimate studies of very old (pre-Devonian) mudstones and sandstones.

Quantifying faulting and base level controls on syn‐rift sedimentation using stratigraphic architectures of coeval, adjacent Early‐Middle Pleistocene fan deltas in Lake Corinth, Greece

AbstractQuantification of allogenic controls in rift basin‐fills requires analysis of multiple depositional systems because of marked along‐strike changes in depositional architecture. Here, we compare two coeval Early‐Middle Pleistocene syn‐rift fan deltas that sit 6 km apart in the hangingwall of the Pirgaki‐Mamoussia Fault, along the southern margin of the Gulf of Corinth, Greece. The Selinous fan delta is located near the fault tip and the Kerinitis fan delta towards the fault centre. Selinous and Kerinitis have comparable overall aggradational stacking patterns. Selinous comprises 15 cyclic stratal units (ca. 25 m thick), whereas at Kerinitis 11 (ca. 60 m thick) are present. Eight facies associations are identified. Fluvial and shallow water facies dominate the major stratal units in the topset region, with shelfal fine‐grained facies constituting ca. 2 m thick intervals between major topset units and thick conglomeratic foresets building down‐dip. It is possible to quantify delta build times (Selinous: 615 kyr; Kerinitis: >450 kyr) and average subsidence and equivalent sedimentation rates (Selinous: 0.65 m/kyr; Kerinitis: >1.77 m/kyr). The presence of sequence boundaries at Selinous, but their absence at Kerinitis, enables sensitivity analysis of the most uncertain variables using a numerical model, ‘Syn‐Strat’, supported by an independent unit thickness extrapolation method. Our study has three broad outcomes: (a) the first estimate of lake level change amplitude in Lake Corinth for the Early‐Middle Pleistocene (10–15 m), which can aid regional palaeoclimate studies and inform broader climate‐system models; (b) demonstration of two complementary methods to quantify faulting and base level signals in the stratigraphic record—forward modelling with Syn‐Strat and a unit thickness extrapolation—which can be applied to other rift basin‐fills; and (c) a quantitative approach to the analysis of stacking patterns and key surfaces that could be applied to stratigraphic pinch‐out assessment and cross‐hole correlations in reservoir analysis.

Quantifying age and model uncertainties in palaeoclimate data and dynamical climate models with a joint inferential analysis.

The study of palaeoclimates relies on information sampled in natural archives such as deep sea cores. Scientific investigations often use such information in multi-stage analyses, typically with an age model being fitted to a core to convert depths into ages at stage one. These age estimates are then used as inputs to develop, calibrate or select climate models in a second stage of analysis. Here, we show that such multi-stage approaches can lead to misleading conclusions, and develop a joint inferential approach for climate reconstruction, model calibration and age estimation. As an illustration, we investigate the glacial-interglacial cycle, fitting both an age model and dynamical climate model to two benthic sediment cores spanning the past 780 kyr. To show the danger of a multi-stage analysis, we sample ages from the posterior distribution, then perform model selection conditional on the sampled age estimates, mimicking standard practice. Doing so repeatedly for different samples leads to model selection conclusions that are substantially different from each other, and from the joint inferential analysis. We conclude that multi-stage analyses are insufficient when dealing with uncertainty, and that to draw sound conclusions the full joint inferential analysis should be performed.

Western Mediterranean hydro-climatic consequences of Holocene ice-rafted debris (Bond) events

Abstract. Gerard C. Bond established a Holocene series of North Atlantic ice-rafted debris events based on quartz and haematite-stained grains recovered from subpolar North Atlantic marine cores. These so-called “Bond events” document nine large-scale and multi-centennial North Atlantic cooling phases that might be linked to a reduced thermohaline circulation. Regardless of the high prominence of the Holocene North Atlantic ice-rafted debris record, there are critical scientific comments on the study: the Holocene Bond curve has not yet been replicated in other marine archives of the North Atlantic and there exist only very few palaeoclimatic studies that indicate all individual Bond events in their own record. Therefore, evidence of consistent hydro-climatic teleconnections between the subpolar North Atlantic and distant regions is not clear. In this context, the Western Mediterranean region presents key hydro-climatic sites for the reconstruction of a teleconnection with the subpolar North Atlantic. In particular, variability in Western Mediterranean winter precipitation might be the result of atmosphere–ocean coupled processes in the outer-tropical North Atlantic realm. Based on an improved Holocene δ18O record from Lake Sidi Ali (Middle Atlas, Morocco), we correlate Western Mediterranean precipitation anomalies with North Atlantic Bond events to identify a probable teleconnection between Western Mediterranean winter rains and subpolar North Atlantic cooling phases. Our data show a noticeable similarity between Western Mediterranean winter rain minima and Bond events during the Early Holocene and an opposite pattern during the Late Holocene. There is evidence of an enduring hydro-climatic change in the overall Atlantic atmosphere–ocean system and the response to external forcing during the Middle Holocene. Regarding a potential climatic anomaly around 4.2 ka (Bond event 3) in the Western Mediterranean, a centennial-scale winter rain maximum is generally in-phase with the overall pattern of alternating “wet and cool” and “dry and warm” intervals during the last 5000 years.

Extensive elemental mapping unlocks Mg/Ca ratios as climate proxy in seasonal records of Mediterranean limpets

Elemental analysis of biogeochemical archives is an established technique used to study climate in a range of applications, including ocean circulation, glacial/interglacial climates, and anthropogenic climate change. Data from mollusc archives are especially important because of their global abundance and sub-annual resolution. Despite this potential, they are underrepresented among palaeoclimate studies, due to enigmatic physiological influences skewing the elemental record. Understanding the patterns behind these influences will improve data interpretation and lead to the development of new climate proxies. Here, we show for the first time that extensive spatial mapping of multiple mollusc specimens using Laser Induced Breakdown Spectroscopy (LIBS) across a wider region can resolve enigmatic patterns within the elemental record caused by physiological influences. 2D elemental (Mg/Ca) maps of whole limpet shells (Patella caerulea) from across the Mediterranean revealed patterns of variability within individual mollusc records as well as within isochronous parts of specimens. By registering and quantifying these patterns, we established previously uninterpretable correlations with temperature (R2 > 0.8, p < 0.01). This outcome redefines the possibilities of accessing sub-annual climate proxies and presents the means to assess annual temperature ranges using oxygen isotope analysis requiring only 2 samples per shell.

Palynology of Cenozoic successions of Kerala Basin: a review from the perspective of biostratigraphy and palaeoclimatic studies

The Kerala Basin is only onshore opportunity to study Cenozoic palaeoclimate and palaeoenvironment of southwest India encompassing Neogene global events such as Mid Miocene Climate Optimum (MMCO) and even older times of Palaeogene. The global warming during ~17–15 Ma (MMCO), enhanced annual surface temperature 3–4° C higher than the present, is equivalent to the warming predicted for the next century. Since the palaeogeographical and other general conditions have not been much changed from the Miocene Period, Neogene palaeoclimate of Kerala Basin can be considered as a possible analogue for future climate. Many workers have studied the Cenozoic sedimentary successions of surface and subsurface for stratigraphic classification of the rocks, but still, discrepancy persists in the chronostratigraphic relationship in sedimentary successions. The palynological investigations have also been limited mainly to palynofloral and palaeoecological inferences except a few in which palynostratigraphy, correlation and age have been attempted on the basis of spore–pollen only. Major three Cenozones namely, Triangulorites bellus and Crassoretitriletes vanraadshooveni (Eocene–Oligocene) and Malvacearumpollis bakonyensis (Miocene) have been established. The palynological studies done in the region broadly suggest warm and humid climate with heavy rainfall. However, the recent quantitative studies have highlighted the complexity of palaeoclimatic evolution in the tropics in terms of monsoon. A time–constrained quantitative palaeovegetation and palaeoclimate reconstructions on the basis of palynology is required for evaluation of response and changes in the tropical flora of northwestern India across the major climate events. For that, the biostratigraphy of finer resolution based on systematic and integrated multi–biotic proxy is needed to establish an age model for these sedimentary successions.

Potential of shells of three species of eastern Australian freshwater mussels (Bivalvia: Hyriidae) as environmental proxy archives

Freshwater mussels in Australia are rarely studied for their life history and potential as palaeoclimate proxy archives. Therefore, we studied three freshwater mussel species from the Williams River, Hunter Valley, Australia, namely Alathyria profuga, Cucumerunio novaehollandiae and Hyridella drapeta, to identify their potential as new environmental proxy archives from Australian freshwater bodies. Growth analysis revealed that A. profuga and C. novaehollandiae produce distinctive growth lines, which allow the first identification of age and growth structure of these species. The oxygen isotope ratio in A. profuga shells and high-resolution element concentrations in all three species show cyclic, annual variations. A high correlation between growth rates and the combined winter air temperature and annual rainfall, as well as accurate temperature reconstruction using oxygen isotope values in the shells suggest that A. profuga has good potential as an environmental proxy archive. However, the low correlation observed between the Sr:Ca ratio and temperature limited the usefulness of the Sr:Ca ratio in A. profuga shells as a water temperate proxy. In contrast, growth rates and element ratios of C. novaehollandiae do not indicate a significant relationship with environmental variables, suggesting that this species, together with H. drapeta, is probably not suitable for palaeoclimatic studies.

High-Resolution Peat Core Chronology Covering the Last 12 KYR Applying an Improved Peat Bog Sampling

ABSTRACTThis work focuses on building a high-resolution age-depth model for quantitative palaeoclimate study from the Mohos peat bog, East Carpathian mountains. The investigated core presents a continuous peat profile for the last 12 kyr. The chronology was based on 36 accelerator mass spectrometry radiocarbon (AMS14C) analyses of the separatedSphagnumsamples from different depths of the profile. DrySphagnumsamples for AMS dating were prepared using the classic acid-base-acid (ABA) method followed with an oxidative bleaching step to get clean cellulose.Sphagnumcellulose samples were measured by AMS using the EnvironMICADAS at the ICER (Debrecen, Hungary). A high-resolution chronology was obtained with the use of Bayesian age-depth modeling. Peat accumulation rate has been calculated and the sections with variable accumulation rate values were observed along the profile.

Timing of glacial retreat in the Wicklow Mountains, Ireland, conditioned by glacier size and topography

ABSTRACTReconstructing the deglacial history of palaeo‐glaciers provides vital information on retreat processes, information which can inform predictions of the future behaviour of many of the world's glaciers. On this basis, this paper presents 170 Schmidt Hammer exposure ages from moraine boulders and glacially sculpted bedrock to reveal the post‐Last Glacial Maximum (LGM) history of the Wicklow Mountains, Ireland. These data suggest that large ice masses survived for 4–7 ka after retreat of the Irish Sea Ice Stream and were sustained by summit ice fields until ∼16.6 ka. Post‐LGM retreat was driven by climate and involved numerous short‐term ice front oscillations (≤1 ka), with widespread moraine deposition during Heinrich Stadial 1. In contrast, marked asynchroneity in the timing of Younger Dryas deglaciation is closely linked to snow redistribution which demonstrates the sensitivity of small cirque glaciers (≤1 km2) to local topography. This result has important implications for palaeoclimate reconstructions as cirque glacier dynamics may be (at least partly) decoupled from climate. This is further complicated by post‐depositional processes which can result in moraine ages (e.g. 10Be) which post‐date retreat. Future palaeoclimate studies should prioritize cirques where snow‐contributing areas are small and where post‐depositional disturbance of moraines is limited.

Growth patterns of the topshell Phorcus lineatus (da Costa, 1778) in northern Iberia deduced from shell sclerochronology

Combined shell growth pattern and oxygen isotope analysis has become a powerful approach in palaeoclimate and archaeological studies for reconstructing palaeoclimate conditions and littoral exploitation patterns, respectively. Recent investigations have shown that the gastropod Phorcus lineatus (da Costa, 1778) forms its shell in conditions of near equilibrium with the oxygen isotope signature of the seawater environment, demonstrating the utility of this species for reconstruction of sea surface temperature and determination of the season of harvest in archaeological studies. In contrast, the shell growth patterns of this species have received virtually no attention despite providing information on the rate and timing of shell growth that is crucial for correctly interpreting environmental proxies derived from shell geochemistry. In this paper, we compare microgrowth patterns and isotopic profiles of four modern individuals of the gastropod P. lineatus from northern Iberia to determine the timing and periodicity of subannual growth markers within the shells. Results of this sclerochronological study showed the presence of two types of growth lines/increments: i) large-scale accretionary units formed with variable periodicity, and ii) small-scale accretionary units formed by micro growth lines and increments determined by semidiurnal tidal cycles. Results suggest that shells grew uninterruptedly during early ontogeny. However, older specimens exhibited growth cessation/slowdown during summer and winter/spring. Therefore, shell growth rate is not only controlled by environmental conditions, but also by ontogenetic age and/or endogenous rhythms. A high correlation was found between seawater temperature derived from shell oxygen isotopes and instrumental seawater temperature (r2 = 0.88–0.98; p-values < 0.0001). This study shows that establishing accurate growth patterns of the topshell P. lineatus is essential for correctly reconstructing past seawater temperature conditions in palaeoclimate studies and for determining with higher precision the season(s) when the subfossil shells were collected by humans.

Stalagmites from western Thailand: preliminary investigations and challenges for palaeoenvironmental research

Locating suitable caves and stalagmites for palaeoenvironmental and palaeoclimatic studies can be challenging. Isotopic geochemical analyses, albeit commonly performed for palaeoclimatic reconstruction, are also time consuming and costly. Therefore, petrographic and non‐destructive morphological studies on speleothems are desirable to facilitate sample selection for further analysis. In this study, 20 caves were surveyed in Ban Rai district, Uthai Thani province in western Thailand. After external physical observations in the field, three stalagmite samples were collected from Tham Nam Cave to test their potential for palaeoclimatic research. Firstly, the stalagmites were scanned by X‐ray computed tomography (CT scanning) and subsequently the CT images were compared with petrographic inspections. Columnar fabrics show the highest density, whereas closed and open dendritic fabrics have medium and the lowest densities, respectively. Layers near the top and bottom of the three stalagmites were dated by U‐Th mass spectrometric techniques. All three samples were deposited between c. 87 and c. 105 ka ago; therefore, they are probably the oldest stalagmites that have been reported so far from mainland Southeast Asia. However, their physical features indicate that all the samples have suffered from postdepositional dissolution, and are unlikely to be suitable for palaeoclimatic research. The internal dissolution feature of stalagmites, however, cannot be identified by visual inspection of uncut samples. We hereby argue that CT images are useful to characterize stalagmite petrography, in particular fabric, porosity and density. Such features can be used to select the ideal plane of a stalagmite for sectioning, to maximize the chances of robust climatic reconstruction.

A 3 million year index for North African humidity/aridity and the implication of potential pan-African Humid periods

Mediterranean sediments are valuable archives of both African monsoon variability and higher-latitude climate processes, and can also be used to provide an environmental context for early human migrations and settlements. However, the long history of Mediterranean palaeoclimate studies largely pre-dates the advent of widespread x-ray fluorescence (XRF) core-scanning, so there are few continuous and high-resolution geochemical records from this key region that extend beyond the last glacial cycle. Here we present XRF core-scanning results for ODP Site 967 (Eastern Mediterranean) that have been fully-calibrated into element concentrations spanning the last 3 million years (My). Comparison with independent geochemical data from conventional XRF highlights disparities for certain element/element ratios, thus suggesting the need for caution when taking ratios of scanning XRF data. Principal component analysis of the calibrated XRF dataset reveals two dominant components: detrital inputs (PC1) and a ‘sapropel’ (≈monsoon run-off) signal (PC2), which we use to establish a new orbitally-tuned chronology. We observe inverse covariation between PC2 and a previously published aeolian dust record from ODP Site 967 (Larrasoaña et al., 2003), and combine these records to produce a composite index of humidity and aridity for the wider North African region over the past 3 My. We propose that by combining run-off and dust signals in a single metric, our index captures the effects of both strengthening/northward migration (increased run-off) and weakening/southward retreat (increased dust) of the North African monsoon. Comparison of the index with published records of Northwest and East African palaeohumidity suggests that it tracks the timing of “Green Sahara Periods” throughout the Plio-Pleistocene, and that at least 30 of these intervals coincided with increased humidity across East Africa. We tentatively suggest that these specific episodes may be termed “pan-African Humid Periods”, as a means to highlight large-scale climate trends and to provide an environmental framework for palaeo-anthropological research.

Geochemistry of the brachiopod Hemithiris psittacea from the Canadian Arctic: Implications for high latitude palaeoclimate studies

Fossil shell material from high palaeo-latitudes is increasingly studied for environmental forcings specific to these latitudes and as sensitive archives of climate change. However, more detailed studies of modern analogues are necessary for putting findings into global and high latitude perspectives.Here we present δ13C and δ18O values, as well as Mg, Sr, Na, Mn and Fe contents for the rhynchonellide brachiopod Hemithiris psittacea from Friday Harbor, U.S.A. and twenty-five sites from Canada ranging in latitude from 48° to 71°N. Median Mn/Ca ratios are below 0.1mmol/mol and Fe/Ca ratios are below 0.3mmol/mol, with no strong correlation between ratios and no apparent geographical relationship. Mg/Ca and Sr/Ca ratios vary within relatively narrow limits and yield median ratios of 3.7mmol/mol and 1.13mmol/mol. Na/Ca ratios vary widely amongst the sites with median values ranging from 9 to 20mmol/mol. Relatively uniform median δ13C values of +1.8±0.6‰ (2 sd, n=25) are observed for the Canadian sites, whereas at Friday Harbor the signature of 13C depletion in local DIC is imprinted in the shell calcite. Median δ18O values of −0.5 to +2.7‰ are more variable than carbon isotope signatures and point to precipitation of shell material in seawater diluted by variable amounts of freshwater and affected by seasonal sea ice.Our results imply that robust elemental patterns and carbon isotope signatures of high latitude brachiopod fossils can be expected for most palaeogeographic situations. In contrast, δ18O signatures of shell material from high latitude marginal seas, particularly during glacial periods, would yield unreasonably high seawater temperature estimates unless the oxygen isotopic composition of the ambient water is accurately accounted for in palaeotemperature calculations.

A 25,000-year record of environmental change from Welsby Lagoon, North Stradbroke Island, in the Australian subtropics

There are few continuous Australian palaeoclimate records that extend beyond the Last Glacial Maximum (LGM), meaning that knowledge of regional climates before, during and after this period is limited. Understanding late-Pleistocene climates of the subtropics is important because of the fundamental role the region plays in the large-scale, global transfer of energy from low latitudes. Palaeoclimate studies of subtropical regions can help define the extent of warming/cooling during the large global climatic events which characterise the late-Pleistocene. Here we report the results from a multi-proxy analysis of a sediment record from Welsby Lagoon on North Stradbroke Island, in the eastern Australian subtropics, spanning the past ca. 25,000 years. Stable C and N isotope analysis and high resolution contiguous records of macrocharcoal deposition and sediment organic content are interpreted in conjunction with a previously published pollen record. Sediment organic content displayed a very strong correlation with total organic carbon (TOC) content as determined through elemental analysis and, given the peaty nature of the sediment, is interpreted as indicative of moisture balance. The proxies reflect wet subtropical climates in the lead up to the LGM which led to an expansion of the wetland. This was followed by a cool, dry and windy LGM (ca. 22.3–19.7'000 years before present; kyr BP), which was punctuated by a brief wet phase ca. 21.7–20.4 kyr BP. A salient feature of the deglacial period is a rapid increase in TOC around 15 kyr BP, coincident with the Antarctic Cold Reversal and Bølling-Allerød warm phase. Increased fire frequency is evident in the Holocene, which is characterised by otherwise stable climate and vegetation. This study supports the notion of variable climates during the LGM and finds an onset of deglacial warming in the Australian subtropics that predates the Holocene.

The youngest volcanic eruptions in East‐Central Europe—new findings from the Ciomadul lava dome complex, East Carpathians, Romania

Violent explosive eruptions occurred between c. 51 and 29 thousand years ago—during the Last Glacial Maximum in East‐Central Europe—at the picturesque volcano of Ciomadul, located at the southernmost tip of the Inner Carpathian Volcanic Range in Romania. Field volcanology, glass geochemistry of tephra, radiocarbon and optically stimulated luminescene dating, along with coring the lacustrine infill of the two explosive craters of Ciomadul (St Ana and Mohos), constrain the last volcanic activity to three subsequent eruptive stages. The explosivity was due to the silicic composition of the magma producing Plinian‐style eruptions, and the interaction of magma with the underlying, water‐rich rocks resulting in violent phreatomagmatic outbursts. Tephra (volcanic ash) from these eruptions are interbedded with contemporaneous loess deposits, which form thick sequences in the vicinity of the volcano. Moreover, tephra layers are also preserved in the older Mohos crater infill, providing an important archive for palaeoclimate studies. Identifying the final phreatomagmatic eruption of Ciomadul at c. 29.6 ka, which shaped the present‐day landform of the 1600‐m‐wide St Ana explosion crater, we were able to correlate related tephra deposits as far as 350 km from the source within a thick loess‐palaeosol sequence at the Dniester Delta in Roxolany, Ukraine. A refined tephrostratigraphy, based on a number of newly found exposures in the Ciomadul surrounding region as well as correlation with the distal terrestrial and marine (e.g. Black Sea) volcano‐sedimentary record, is expected from ongoing studies.

North Atlantic Oscillation controls on oxygen and hydrogen isotope gradients in winter precipitation across Europe; implications for palaeoclimate studies

Abstract. Winter (October to March) precipitation δ18OP and δDP values in central Europe correlate with the winter North Atlantic Oscillation index (wNAOi), but the causal mechanisms remain poorly understood. Here we analyse the relationships between precipitation-weighted δ18OP and δDP datasets (δ18Opw and δDpw) from European GNIP and ANIP stations and the wNAOi, with a focus on isotope gradients. We demonstrate that longitudinal δ18Opw and δDpw gradients across Europe (“continental effect”) depend on the wNAOi state, with steeper gradients associated with more negative wNAOi states. Changing gradients reflect a combination of air temperature and variable amounts of precipitable water as a function of the wNAOi. The relationships between the wNAOi, δ18Opw and δDpw can provide additional information from palaeoclimate archives such as European speleothems that primarily record winter δ18Opw. Comparisons between present-day and past European longitudinal δ18O gradients inferred from Holocene speleothems suggest that atmospheric pressure configurations akin to negative wNAO modes dominated the early Holocene, whereas patterns resembling positive wNAO modes were more common in the late Holocene, possibly caused by persistent shifts in the relative locations of the Azores High and the Icelandic Low.