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Ca isotope geochemistry has great potential for improving our understanding of magmatic systems and for tracing the deep Earth carbon cycle. There are still many open questions, however, regarding the proper application of this relatively novel proxy to the study of mantle-derived magmas, including (i) the possible effects of pressure on mineral-melt Ca isotope fractionation factors, and (ii) the potential for Ca isotopes to be used as tracers of recycled marine carbonates in mantle-derived magmas. Kimberlites are mantle-derived melts that are highly enriched in CO2 and are the deepest-sourced magmas (>200 km depth) known to erupt at Earth's surface, providing an excellent opportunity to explore these questions. We present Ca isotope data combined with detailed petrographic observations, bulk-carbonate C-O isotope data, and bulk-rock major element analyses, for a suite of 23 well-characterized kimberlite samples from their type-locality (Kimberley, South Africa). These kimberlites have abundant previous evidence for recycled surface materials in their mantle source, including low S isotope and moderately radiogenic Sr isotope compositions, yet display only limited variations in their Ca isotope compositions (δ44CaBSE of −0.08‰ to −0.27‰), with an average of −0.17 ± 0.02‰ (2SE, n = 21). This composition is indistinguishable from average carbonatites [−0.19 ± 0.03‰ (2SE, n = 106)] and OIB from recent studies [−0.16 ± 0.01‰ (2SE, n = 41)], and slightly lower than average MORB [−0.11 ± 0.02‰ (2SE, n = 31)]. Although our samples display a wide range of emplacement styles, alteration conditions, extents of magmatic differentiation, and degrees of mantle-cargo entrainment (i.e., xenocryst accumulation), we find no correlations between Ca isotopes and any of these factors. Instead, we find that low-degree partial melting of the likely kimberlite source lithology (i.e., carbon-bearing garnet lherzolite) yields modelled melt δ44CaBSE values ranging between −0.12‰ and −0.16‰ (at 1400–1500 °C), in agreement with the measured Ca isotope compositions of the Kimberley kimberlites. This observation, and the lack of heavy carbon isotope signatures in the examined samples, indicates that kimberlites do not require subducted carbonates in their mantle sources, despite their very high CO2 contents. Although several recent studies have suggested that equilibrium mineral-melt Ca isotope fractionation factors (e.g., 1000lnαgrt-melt) could be significantly different at higher pressures (i.e., due to pressure-induced changes in Ca[sbnd]O bond lengths and coordinations), our models successfully reproduce the kimberlite data using pressure-independent predictions for mineral-melt fractionations. It remains possible, however, that differences in isotopic fractionation due to the peculiar composition of kimberlite melts (e.g., high CO2, low SiO2) are effectively cancelled out by competing pressure effects, and future work independently targeting these factors will be especially important for our understanding of Ca isotope fractionation in mantle-derived melts and the Ca isotope systematics of Earth's mantle., Geochimica et Cosmochimica Acta, 348, ISSN:0016-7037, ISSN:1872-9533

Earth's carbon cycle is strongly influenced by subduction of sedimentary material into the mantle. The composition of the sedimentary subduction flux has changed considerably over Earth's history, but the impact of these changes on the mantle carbon cycle is unclear. Here, we show that the carbon isotopes of kimberlite magmas record a fundamental change in their deep-mantle source compositions during the Phanerozoic Eon. The 13C/12C of kimberlites before ∼250 Ma preserves typical mantle values, whereas younger kimberlites exhibit lower and more variable ratios-a switch coincident with a recognized surge in kimberlite magmatism. We attribute these changes to increased deep subduction of organic carbon with low 13C/12C following the Cambrian Explosion when organic carbon deposition in marine sediments increased significantly. These observations demonstrate that biogeochemical processes at Earth's surface have a profound influence on the deep mantle, revealing an integral link between the deep and shallow carbon cycles., Science Advances, 8 (9), ISSN:2375-2548

International audience; New high-resolution relative sea-level (RSL) proxy data obtained from Lithophyllum rims in the Adriatic allow usto distinguish major local, regional and global RSL driving processes during the past two millennia. RSL changeon the Elafiti islands in the Dubrovnik archipelago (Southern Adriatic) has been significantly affected by local tectonic contributions, which vary spatially and increase southeastwards from Jakljan to Grebeni. Consequently, the RSL change on northwestward islands, Jakljan and ˇSipan, is still dominantly driven by linear regional glacioisostatic adjustment (GIA) processes estimated at ~0.34 mm/yr. However, GIA effects are occasionally cancelled out by local, non-linear coseismic uplifts of small magnitude and by variations in the global mean sea level (GMSL). Thus the rapid fall in GMSL of 0.26 mm/yr offset the GIA effects between approximately ~1000–1250 cal CE, resulting in temporal hiatuses in algal rim formation. After ~1800 cal CE, GIA rates were significantly amplified by GMSL rise, which exceed 0.9 mm/yr at Jakljan and ˇSipan and goes up to 1.4 mm/yr at Koloˇcep and Grebeni, confirming the acceleration of RSL rise over the past two hundred years.The new GMSL records from the northern and southern Adriatic, allow us to reconstruct the first highresolutionGMSL curve for the Adriatic. We show that GMSL variability is in-phase with solar activity during the last two millennia, acting on cycles of ~350, 220 and 100-yrs. We also show that increased GMSL fall, which stopped the formation of algal rims around ~1000 and ~1600 cal CE, coincides with the global reduction in radiative forcing associated with the Oort and Maunder minima, with a drop in sea surface temperature (SST) and with increased salinity. Thus, our analyses revealed a consistent periodicity between the Adriatic GMSL signal, solar forcing, SST and salinity, with the most important cycle being the 350-year Great Solar Cycle.

The retreat of ice shelves and glaciers over the last century provides unequivocal evidence of recent global warming. Glacierets (miniature glaciers) and ice patches are important components of the cryosphere that highlight the global retreat of glaciers, but knowledge of their behaviour prior to the Little Ice Age is lacking. Here, we report the uranium–thorium age of subglacial carbonate deposits from a recently exposed surface previously occupied by the disappearing Triglav Glacier (southeastern European Alps) that may elucidate the glacier's presence throughout the entire Holocene. The ages suggest the deposits' possible preservation since the Last Glacial Maximum and Younger Dryas. These thin deposits, formed by regelation, are easily eroded if exposed during previous Holocene climatic optima. The age data indicate the glacier's present unprecedented level of retreat since the Last Glacial Maximum and the potential of subglacial carbonates as additional proxies to highlight the extraordinary nature of the current global climatic changes.

The 8.2 ka event is regarded as the most prominent climate anomaly of the Holocene and is thought to have been triggered by a meltwater release to the North Atlantic that was of sufficient magnitude to disrupt the Atlantic Meridional Overturning Circulation (AMOC). It is most clearly captured in Greenland ice-core records, where it is reported as a cold and dry anomaly lasting ∼ 160 years, from 8.25 ± 0.05 until 8.09 ± 0.05 ka (Thomas et al., 2007). It is also recorded in several archives in the North Atlantic region; however, its interpreted timing, evolution and impacts vary significantly. This inconsistency is commonly attributed to poorly constrained chronologies and/or inadequately resolved time series. Here we present a high-resolution speleothem record of early Holocene palaeoclimate from El Soplao Cave in northern Spain, a region pertinent to studying the impacts of AMOC perturbations on south-western Europe. We explore the timing and impact of the 8.2 ka event on a decadal scale by coupling speleothem stable carbon and oxygen isotopic ratios, trace element ratios (Mg / Ca and Sr / Ca), and growth rate. Throughout the entire speleothem record, δ18O variability is related to changes in effective recharge. This is supported by the pattern of changes in δ13C, Mg / Ca and growth rate. The 8.2 ka event is marked as a centennial-scale negative excursion in El Soplao δ18O, starting at 8.19 ± 0.06 ka and lasting until 8.05 ± 0.05 ka, suggesting increased recharge at the time. Although this is supported by the other proxies, the amplitude of the changes is minor and largely within the realm of variability over the preceding 1000 years. Further, the shift to lower δ18O leads the other proxies, which we interpret as the imprint of the change in the isotopic composition of the moisture source, associated with the meltwater flux to the North Atlantic. A comparison with other well-dated records from south-western Europe reveals that the timing of the 8.2 ka event was synchronous, with an error-weighted mean age for the onset of 8.23 ± 0.03 and 8.10 ± 0.05 ka for the end of the event. This compares favourably with the North Greenland Ice Core Project (NGRIP) record. The comparison also reveals that the El Soplao δ18O is structurally similar to the other archives in south-western Europe and the NGRIP ice-core record.

Speleothems represent important archives of terrestrial climate variation that host a variety of proxy signals and are also highly amenable to radiometric age determination. Although speleothems have been forming on Earth for at least 400 million years, most studies rely upon the U-Th chronometer which extends only to the mid Pleistocene, leaving important questions over their longer-term preservation potential. To date, older records, exploiting the advantages of the U-Pb chronometer, remain fragmentary ‘snapshots in time’. Here we demonstrate the viability of speleothems as deep time climate archives by showing that a vast system of shallow caves beneath the arid Nullarbor plain of southern Australia, the world’s largest exposed karst terrain, formed largely within the Pliocene epoch, with a median age of 4.2 Ma, and that, in these caves, even the most delicate formations date from this time. The long-term preservation of regional-scale cave networks such as this demonstrates that abundant speleothem archives do survive to permit the reconstruction of climates and environments for much older parts of Earth history than the ~600 ka period to which most previous studies have been limited.

Changes in the magnitude of millennial-scale climate variability (MCV) during the Late Pleistocene occur as a function of changing background climate state over tens of thousands of years, an indirect consequence of slowly varying incoming solar radiation associated with changes in Earth’s orbit. However, whether astronomical forcing can stimulate MCV directly (without a change in the background state) remains to be determined. Here we use a comprehensive fully coupled climate model to demonstrate that orbitally driven insolation changes alone can give rise to spontaneous millennial-scale climate oscillations under intermediate glacial conditions. Our results demonstrate that an abrupt transition from warm interstadial to cold stadial conditions can be triggered directly by a precession-controlled increase in low-latitude boreal summer insolation and/or an obliquity-controlled decrease in high-latitude mean annual insolation, by modulating North Atlantic low-latitude hydroclimate and/or high-latitude sea ice–ocean–atmosphere interactions, respectively. Furthermore, contrasting insolation effects over the tropical versus subpolar North Atlantic, exerted by obliquity or precession, result in an oscillatory climate regime, even within an otherwise stable climate. With additional sensitivity experiments under different glacial–interglacial climate backgrounds, we synthesize a coherent theoretical framework for climate stability, elaborating the direct and indirect (dual) control by Earth’s orbital cycles on millennial-scale climate variability during the Pleistocene. Millennial-scale climate oscillations can arise from orbital forcing alone during relatively stable glacial climate states, according to an analysis of high- and low-latitude climate proxy records as well as climate modelling.

For marine fishes of commercial interest, defining how individuals vary in certain attributes, through ontogeny, and across space and time, can help expose the structure of harvested populations and guide their management. The chemical markers locked within otoliths are, in principle, ideal for such applications, providing life-long, bio-environmental records for individuals and populations. However, substantial uncertainty still surrounds how intrinsic (i.e., within-individual) and extrinsic (i.e., environmental) processes shape chemical incorporation into otoliths, constraining our ability to predict marker variability when sampling is patchy. To tackle these issues, we measured otolith elemental (Li, Mg, Ca, Mn, Zn, Sr, Ba) and stable isotopic (δ13C, δ18O) concentrations from juvenile Atlantic herring (Clupea harengus) captured in Icelandic nursery sites, and built models to isolate ontogenetic (i.e., age-, growth-related) from environmental influences on otolith chemistry. Otolith Li:Ca, Mg:Ca, Mn:Ca and Sr:Ca declined with age within sites. Age slopes differed among sites for Li:Ca and Mg:Ca, and Sr:Ca was lower in larger fish within an age-class. Individual-level variation (i.e., within site, within age-class) was high for all markers, our models highlighting the importance of temperature and salinity (or proxies these represent) in explaining population-level δ13C and δ18O trends. Age- and year-specific predictions for each marker, at each site, generally accorded well with empirical observations, providing inference on island-wide heterogeneity in otolith chemistry across the juveniles’ full distributional range. Such ‘isoscapes’, generated from mechanistically-focused models as presented here, might benefit investigations of population structure for other exploited species, particularly where sampling limitations hamper fishery-management efforts.

The trace-element geochemistry of speleothems is becoming increasingly used for reconstructing palaeoclimate, with a particular emphasis on elements whose concentrations vary according to hydrological conditions at the cave site (e.g. Mg, Sr, Ba and U). An important step in interpreting trace-element abundances is understanding the underlying processes of their incorporation. This includes quantifying the fractionation between the solution and speleothem carbonate via partition coefficients (where the partitioning (D) of element X (D-X) is the molar ratio [X/Ca] in the calcite divided by the molar ratio [X/Ca] in the parent water) and evaluating the degree of spatial variability across time-constant speleothem layers. Previous studies of how these elements are incorporated into speleothems have focused primarily on stalagmites and their source waters in natural cave settings, or have used synthetic solutions under cave-analogue laboratory conditions to produce similar dripstones. However, dripstones are not the only speleothem types capable of yielding useful palaeoclimate information. In this study, we investigate the incorporation of Mg, Sr, Ba and U into a subaqueous calcite speleothem (CD3) growing in a natural cave pool in Italy. Pool-water measurements extending back 15 years reveal a remarkably stable geochemical environment owing to the deep cave setting, enabling the calculation of precise solution [X/Ca]. We determine the trace element variability of 'modern' subaqueous calcite from a drill core taken through CD3 to derive D-Mg, D-Sr, D-Ba and D-U then compare these with published cave, cave-analogue and seawater-analogue studies. The D-Mg for CD3 is anomalously high (0.042 +/- 0.002) compared to previous estimates at similar temperatures (similar to 8 degrees C). The D-Sr (0.100 +/- 0.007) is similar to previously reported values, but data from this study as well as those from Tremaine and Froelich (2013) and Day and Henderson (2013) suggest that [ Na/Sr] might play an important role in Sr incorporation through the potential for Na to outcompete Sr for calcite non-lattice sites. DBa in CD3 (0.086 +/- 0.008) is similar to values derived by Day and Henderson (2013) under cave-analogue conditions, whilst DU (0.013 +/- 0.002) is almost an order of magnitude lower, possibly due to the unusually slow speleothem growth rates (

The original article has been corrected. During proof correction of the article, mistakes in the author affiliations of Petra Bajo, John C. Hellstrom, Robert Wiśniewski, Anthony E. Fallick, Stefano Natali, and Marco Luppichini were introduced. Please find the correct affiliations here as well.

The end of the Younger Dryas (YD) was Earth’s last major abrupt climate event and is most vividly preserved in the water-isotope (ice δ18O), calcium (Ca2+) and methane-concentration (CH4) series of Greenland ice cores. Although numerous palaeoclimate records span this transition, surprisingly few have the dating precision necessary to test whether or not abrupt warming in Greenland was accompanied by synchronous climate changes beyond the Arctic. Speleothems, with their exceptional absolute chronologies, are well placed to conduct such a test.Here we apply a change-point detection algorithm to new and published speleothem δ18O records of the YD from the Indo-Australian summer monsoon and Asian summer monsoon domains to compare the synchronicity of hydroclimate changes across the YD termination. The algorithm, which identifies the age (and its uncertainty) of a regime shift in a time series, was applied to the 13 - 11 ka interval of each speleothem record. The results yield an error-weighted mean YD-termination age of 11.55 ± 0.02 ka BP (2σ), supporting the hypothesis of a closely coupled monsoon seesaw. Analysis of the Greenland NGRIP ice-core δ18O and Ca2+ records on the GICC05 chronology for the same interval produces a YD-termination age of 11.63 ± 0.10 ka BP. Although the NGRIP and speleothem ages overlap within uncertainties, this hints at a possible Arctic lead over the tropics. However, if we apply a correction to the GICC05 chronology based on recent ice-core 10Be and tree-ring 14C synchronisation, the change-point analysis gives a NGRIP termination age of 11.57 ± 0.02 ka BP. This revised timing is consistent with the Cariaco Basin greyscale record (11.56 ± 0.02 ka BP). It also brings the NGRIP and Antarctic WAIS Divide ice-core CH4 records into perfect alignment across the transition. This assemblage of ages from geographically dispersed regions suggests that hydroclimate changes associated with the YD termination were synchronous, at least to within a couple of decades. It also calls for a revision to the onset age of the Greenlandian Stage (the Pleistocene-Holocene boundary).

Australia is the driest continent outside of Antarctica yet relatively little is known about its long-term moisture history. Many local palaeoclimate archives suffer preservation problems, particularly in the arid centre of the continent, where weathering and erosion leave behind an incomplete record. In an attempt to redress the paucity of arid-zone palaeoclimate records, we investigate ‘pendulites’, subaqueous speleothems that grow episodically according to fluctuations in local groundwater levels. At Mairs Cave (central Flinders Ranges, South Australia), pendulites have formed around stalactites. During the first sustained episode of drowning, the stalactite is veneered by subaqueous calcite, sealing it and preventing further stalactitic growth after water levels fall. Once sealed, the pendulites only record periods of persistent drowning, assumed to correspond to major pluvial episodes.Age data from two pendulite samples collected from close to the ceiling where the highest water levels have reached reveal two main groundwater ‘high-stand’ phases centred on ~67 and ~48 ka, coincident with Southern Hemisphere summer insolation maxima. This suggests that precession-driven southward migration of the ITCZ resulted in regular and persistent incursions of tropical air masses to the central Flinders Ranges. Trace element, stable isotope and growth-rate changes reveal that these orbitally controlled growth intervals are superimposed by regional climate responses to Dansgaard-Oeschger and Heinrich events. The results from Mairs Cave shed new light on the moisture history of central Australia, in particular the competing influences of tropical and middle-latitude circulation systems. This provides a precisely dated regional palaeoclimate template for reconstructing ecosystem changes, understanding human migration/dispersal patterns of the first Australians, and the progressive demise of megafauna. We also highlight the utility of subaqueous speleothems more generally as important archives for investigating arid-zone palaeoclimate.

Under the current rapid global warming, studying how environments responded to past climate change becomes increasingly important to better understand what impact climate variability has on regional flora and fauna. Our new multi-proxy study to the World Heritage Naracoorte Caves in southern Australia provides a unique window into the past climate as they are heavily decorated with speleothems but also contain in-fill deposits rich in Pleistocene vertebrate fossils including the extinct Australian megafauna. Until now, these speleothems have been dated using U-Th series and the fossil-bearing sediments with Optical Stimulated Luminescence and Electro Spin Resonance techniques, but only up to ca. 500 ka. We have U-Pb dated speleothems from the Naracoorte Caves for the first time and extended the record beyond 500 ka. We combined precise chronology with analyses of pollen and charcoal within the speleothems which allows us to better understand how southern Australia’s climate and its vegetation changed during the Quaternary. It also provides a unique insight into the timing and extent of cave opening with important potential for much older vertebrate fossil deposits than previously thought.

Past climatic and environmental changes can be reconstructed thanks to paleoclimatic archives such as ice cores, marine sediment cores, lake sediment cores, speleothems, tree rings, corals, etc. The dating of these natural archives is crucial for deciphering the temporal sequence of events during past climate changes. It is also essential to estimate the absolute and relative errors of such estimated chronologies. This task is, however, complex since it involves the combination of different dating approaches on different paleoclimatic sites and often different types of archives. Here we present Paleochrono, a new probabilistic model to derive a common and probalistically optimal chronology for several paleoclimatic sites with potentially different types of archives. Paleochrono is based on the inversion of an archiving model: a varying deposition rate (also named sedimentation or accumulation rate) and also, for ice cores, a lock-in-depth of air bubbles (since air is not trapped at surface) and a thinning function (since ice undergoes flow). The model integrates several types of chronological information: prior knowledge of the archiving process, independently dated horizons, depth intervals of known duration, undated stratigraphic links between records, and, for ice cores, Δdepth observations (depth differences between synchronous events recorded in the bubbles and ice, respectively). The optimization is formulated as a least-squares problem, assuming that all densities of probabilities are near-Gaussian and that the model is almost linear in the vicinity of the best solution. Paleochrono is the successor of IceChrono, which was dealing only with ice-core records. Paleochrono performs better than IceChrono in terms of computational efficiency, ease of use, and accuracy. We demonstrate the ability of Paleochrono in a new AICC2012-Hulu dating experiment, which combines the AICC2012 dating experiment, based on records from five polar ice cores, with data from two U/Th-dated speleothems from Hulu Cave (China). We analyse the performance of Paleochrono in terms of computing time and memory usage in various dating experiments. Paleochrono is freely available under the MIT open source license.

We present the first stable isotope (δ13C and δ18O) speleothem record from continental Croatia retrieved from two coeval stalagmites from Nova Grgosova Cave. U-Th dates constrain the stalagmite growth history from 10 ka to the present, revealing coeval growth between 7.8 and 5.6 ka. We interpret δ18O as an autumn/winter hydrological proxy related to changes of vapor source, precipitation amount, and/or seasonal rainfall distribution, while δ13C predominantly responds to spring/summer vegetation status and soil microbial activity. We identify several centennial to millennial-scale hydroclimate oscillations during this period that result from multiple forcing factors. Along with amount and source effect, it appears that some centennial variations were governed also by seasonal moisture balance. From 9.2 to 8.8 ka BP, the local environmental setting was characterized by enhanced vegetation activity, while during the 8.2 ka event the main feature was a change in precipitation seasonality. The most prominent change, identified in both δ13C records, is a sudden decline of vegetation and soil biological activity around 7.4 ka, indicating a precipitation decrease at a time of maximum plant growth in spring and summer and likely also reduced precipitation in autumn and winter. Although small in magnitude in these speleothems, a peak in δ18O and δ13C values at 4.3–4.1 ka suggests that both summer and winter conditions were substantially drier during the 4.2 ka event, in accordance with increased Mediterranean aridity and consistent with other global climate changes reported at this time. Compared to the present North Atlantic Oscillation (NAO) influence, we assume that millennial Holocene NAO-like variations were persistent through the Holocene via their effect on modifying local/regional air temperature, vapor origin, and inter- and intrannual precipitation distribution. Anthropogenic deforestation, which was the first major human impact on the environment during the Neolithic agricultural revolution, is excluded as a leading factor in δ13C variability since the first sedentary settlements were established further to the east in more arable locations along river valleys. However, the impact of intensive mining around the cave site during the last millennium is evident, with substantial deforestation driving an increase in δ13C.

The timing, duration and evolution of sea level during the Marine Isotope Stage 5e (MIS 5e) highstand is a subject of intense debate. A major problem in resolving this debate is the difficulty of chronologically constraining the sea level fall that followed the peak of the highstand. This was mainly controlled by ice-sheet dynamics, the understanding of which is relevant for assessing future sea-level behavior due to global warming. Here we use stratigraphical and geochoronological (U/Th dating and tephra fingerprinting) evidence from the Infreschi archaeological cave (Marina di Camerota, Southern Italy) to constrain relative sea level (RSL) evolution during the MIS 5e highstand and younger stages. Uranium-thorium dating of speleothem deposition phases places the maximum highstand RSL at 8.90 ± 0.6m a.s.l., as indicated by the near-horizontal upper limit of Lithophaga boreholes measured for along a ∼3.5 km coastal cliff section. Geochronological data show that RSL fell more than 6 m before ∼120 ka, suggesting a duration of the Last Interglacial highstand significantly shorter than proposed in some previous studies. Modelling shows that the RSL trend predicted by the ICE-5G and ICE-6G ice-sheet simulations is consistent with our data, but requires an additional significant reduction of both Greenland and Antarctic ice sheets to match the height of the local maximum highstand if no correction for tectonics is applied. Reconciling field data and models requires an earlier and likely shorter duration of the MIS 5e highstand. This suggests that our new data can constrain global ice-volume variations during the penultimate deglaciation, as well as glacial inception at the end of the Last Interglacial. According to our chronology, there is no local evidence of higher-than-present-day sea levels after 120 ka.

Speleothems deposited from cave drip waters retain, in their calcite lattice, isotopic records of past environmental changes. Among other proxies, &delta, 18O is recognized as very useful for this purpose, but its accurate interpretation depends on understanding the relationship between precipitation and drip water &delta, 18O, a relationship controlled by climatic settings. We analyzed water isotope data of 17 caves from different latitudes and altitudes in relatively small but diverse Croatian karst regions in order to distinguish the dominant influences. Drip water &delta, 18O in colder caves generally shows a greater resemblance to the amount-weighted mean of precipitation &delta, 18O compared to warmer sites, where evaporation plays an important role. However, during glacial periods, today&rsquo, s &lsquo, warm&rsquo, sites were cold, changing the cave characteristics and precipitation &delta, 18O transmission patterns. Superimposed on these settings, each cave has site-specific features, such as morphology (descending or ascending passages), altitude and infiltration elevation, (micro) location (rain shadow or seaward orientation), aquifer architecture (responsible for the drip water homogenization) and cave atmosphere (governing equilibrium or kinetic fractionation). This necessitates an individual approach and thorough monitoring for best comprehension.

Many geographically dispersed records from across the globe reveal the occurrence of abrupt climate changes, called interstadial events, during the last glacial period. These events appear to have happened at the same time, but the difficulty of determining absolute dates in many of the records have made that proposition difficult to prove. Corrick et al. present results from 63 precisely dated speleothems that confirm the synchrony of those interstadial events. Their results also provide a tool with which to validate model simulations of abrupt climate change and calibrate other time series such as ice-core chronologies.Science, this issue p. 963Abrupt climate changes during the last glacial period have been detected in a global array of palaeoclimate records, but our understanding of their absolute timing and regional synchrony is incomplete. Our compilation of 63 published, independently dated speleothem records shows that abrupt warmings in Greenland were associated with synchronous climate changes across the Asian Monsoon, South American Monsoon, and European-Mediterranean regions that occurred within decades. Together with the demonstration of bipolar synchrony in atmospheric response, this provides independent evidence of synchronous high-latitude–to-tropical coupling of climate changes during these abrupt warmings. Our results provide a globally coherent framework with which to validate model simulations of abrupt climate change and to constrain ice-core chronologies.

A stalagmite (FR16) from Frasassi Cave, located near the Adriatic coast of the Italian peninsula, offers a 16 kyr petrographic and stable isotope record spanning from 112.8 ± 1.5 ka to 96.6 ± 1.0 ka, corresponding to the interval from marine isotope stage (MIS) 5c to MIS 5d. The physical characteristics of FR16 calcite, allowed for a thorough understanding of the processes controlling isotopic changes, because fabrics as well are controlled by the environmental parameters within the cave that reflect external climate forcing. The FR16 δ13C profile matches fabric changes where columnar fabric usually corresponds to more negative values and micrite/microsparite layers to less negative δ13C values, and with the North Greenland Ice-core Project (NGRIP) δ18O record with more negative δ13C values during interstadials GI24 and GI23. This suggests a hydrological sensitivity for the two proxies, and their variability can be linked to recharge changes. On the other hand, the response to Greenland events appears subdued in the δ18O record and the trend mimics instead the Northern Hemisphere (NH) summer insolation with more negative δ18O values corresponding to the maximum insolation centred at ca. 105 ka. This behaviour can be explained by the higher sensitivity of δ18O to rainfall seasonality, moisture source and trajectories, whose combined effect attenuated the stadials/intersadials signal in the stalagmite.

Urbanization disturbs groundwater flow through the sealing of native soils with impervious surfaces and through modifications to the subsoil by constructed drainage and other infrastructure (trenches and excavations, e.g. water supply). The impact of these disturbances on groundwater contributions to urban streams (i.e. baseflow) is poorly understood. While high flows caused by impervious runoff to streams are a common focus of urban studies, the route taken by groundwater to become streamflow in urban landscapes is not generally considered. To assess the impact of urbanization on groundwater sources to streams, both rainfall and baseflow were sampled weekly for stable isotopes of water in two nearby streams—one draining a peri-urban catchment and the other draining a forested, natural catchment. In addition, to study the rate of groundwater discharge to the stream, monthly baseflow recession behavior was investigated. We found that baseflow in the forested catchment was constant in stable isotope values (δ18O = −5.73‰ ± 0.14‰) throughout the year. Monthly baseflow recession constants were close to 1 and had little variation (ranging 0.951–0.992), indicating a well-mixed groundwater store and long residence times. In contrast, the urban baseflow isotopic composition featured distinct seasonal variations (δ18O = −3.35‰ ± 1.20‰ from October to March and δ18O = −4.54‰ ± 0.43‰ from April to September) and high week-to-week variability in summer, reflecting a contribution of recent rainfall to baseflow. Recession constants were lower (ranging 0.727–0.955) with pronounced seasonal variations, suggesting shorter residence times and the likely presence of a variety of stores and pathways. These results provide evidence that the urban catchment has diversified groundwater pathways, and its groundwater storage is drained faster than that of the forested catchment. It highlights some of the subsurface hydrological consequences of urbanization. Restoring low-flow aspects of the flow regime through nature-mimicking stormwater management requires careful consideration of how the behavior of natural groundwater pathways can be restored or replicated using innovative stormwater control measures.

MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside) and PIC (Phlogopite-Ilmenite-Clinopyroxene) xenoliths are thought to be formed by intense “primary” mantle metasomatism. These rocks also display secondary features, such as cross-cutting veins and geochemical zonation of matrix minerals, which probably reflect later metasomatic events. To investigate the nature and origin(s) of these secondary features, 28 MARID and PIC xenoliths from southern African kimberlites and orangeites have been studied. MARID-hosted veins contain both carbonate and Ti-rich phases (e.g., titanite, phlogopite), suggesting that they formed by the infiltration of a carbonated silicate melt. Elevated TiO2 contents in MARID matrix mineral rims are spatially associated with carbonate-dominated veins, suggesting a genetic relationship between vein formation and geochemical zonation. Spongy rims around primary MARID and PIC clinopyroxene are depleted in Na2O and Al2O3 relative to their cores, possibly reflecting mineral dissolution in the xenoliths during ascent and emplacement of the entraining kimberlite. The preservation of compositional differences between primary and secondary phases in MARID and PIC xenoliths indicates that metasomatism occurred shortly before, or broadly coeval with, kimberlite/orangeite magmatism; otherwise, at typical mantle temperatures, such features would have quickly re-equilibrated. Increased Na2O in some mineral rims (e.g., K-richterite) may therefore reflect equilibration with a more Na-enriched primitive kimberlite melt composition than is commonly suggested. Vein-hosted clinopyroxene 87Sr/86Sri (0.70539 ± 0.00079) in one MARID sample is intermediate between primary clinopyroxene in the sample (0.70814 ± 0.00002) and the host Bultfontein kimberlite (0.70432 ± 0.00005), suggesting that vein minerals are derived from interactions between primary MARID phases and kimberlite-related melts/fluids. Sulfur isotope compositions of barite (δ34SVCDT = +4.69 ‰) and sulfides (δ34SVCDT = −0.69 ‰) in carbonate veins reflect equilibration at temperatures of 850–900 °C, consistent with sulfur-rich melt/fluid infiltration in the lithospheric mantle. In contrast, vein carbonate C-O isotope systematics (δ13CVPDB = −9.18 ‰; δ18OVSMOW = +17.22 ‰) are not typical of kimberlites or other mantle carbonates (δ13CVPDB = −3 to −8 ‰; δ18OVSMOW = 6 to 9 ‰), and may represent post-emplacement hydrothermal interactions of the cooling kimberlite with crustal fluids. These constraints suggest protracted metasomatism of MARID rocks shortly before and during entrainment by the host kimberlite.

Reliable information on the structure of fished populations can help align management units with the ecology of target species. One way to attain such information lies in accurately defining the scales at which groups of fish vary in key attributes – the chemical markers within otoliths providing well known examples. Here, motivated by current uncertainties around stock status and population structure within the Icelandic summer spawning (ISS) herring (Clupea harengus) stock, we use simulations to derive quantitative rules for assessing the spatial and temporal scales of otolith chemical variation in a Bayesian modelling setting. We then apply these rules to empirical otolith chemistry data from ISS herring sampled across their full distributional range, over three years, to tackle some open questions on nursery connectivity, fidelity and contributions to the fishery. Bayesian multivariate linear models (BMLMs) exposed differences in otolith elemental (Li, Mg, Mn, Zn, Sr, Ba) and stable isotopic (δ13C, δ18O) concentrations in nursery-resident age-1 and age-2 juveniles that generally scaled with distance among nurseries, and time between sampling events. Our simulation-based rules built confidence in the application of BMLMs to characterise ‘source’ populations within the juvenile dataset. These sources were subsequently treated as baseline samples in mixture models that revealed 1) strong evidence for nursery-site fidelity between age-1 and age-2, and 2) multiple nurseries as contributors to a fished age-3 population, irrespective of presumed nursery quality. While additional sampling is required to confirm these results and their relevance for management of herring stocks in Iceland and further afield, we note that the rules and models presented here can be easily adapted for a broader suite of fisheries applications where reliable methods for evaluating differences in multiple attributes among individuals, populations or stocks are needed.

Conceptual models predict a tight coupling between the Intertropical Convergence Zone (ITCZ) and the Southern Westerly Winds (SWW) in response to glacial-interglacial transitions, yet little is known about this relationship under Holocene boundary conditions. Here we present a synthesis of Holocene pollen data from the southwest Pacific mid-latitudes that tracks changes in the SWW. Comparison of our SWW paleoclimate records with data tracking the ITCZ, oceanic circulation, and insolation reveals clearly synchronous and in-phase ITCZ-SWW dynamics between 12 and 5 ka, indicating a tight coupling between the tropics and southern mid-latitudes in response to ocean circulation and insolation. An apparent decoupling of the SWW and ITCZ in the Pacific region after 5 ka is attributable to the overriding influence of the El Niño–Southern Oscillation (ENSO) over the proxy data.

Non-annually resolved palaeoclimate records in the Australasian region were compiled to facilitate investigations of decadal to centennial climate variability over the past 2000 years. A total of 675 lake and wetland, geomorphic, marine, and speleothem records were identified. The majority of records are located near population centres in southeast Australia, in New Zealand, and across the maritime continent, and there are few records from the arid regions of central and western Australia. Each record was assessed against a set of a priori criteria based on temporal resolution, record length, dating methods, and confidence in the proxy–climate relationship over the Common Era. A subset of 22 records met the criteria and were endorsed for subsequent analyses. Chronological uncertainty was the primary reason why records did not meet the selection criteria. New chronologies based on Bayesian techniques were constructed for the high-quality subset to ensure a consistent approach to age modelling and quantification of age uncertainties. The primary reasons for differences between published and reconstructed age–depth models were the consideration of the non-singular distribution of ages in calibrated 14C dates and the use of estimated autocorrelation between sampled depths as a constraint for changes in accumulation rate. Existing proxies and reconstruction techniques that successfully capture climate variability in the region show potential to address spatial gaps and expand the range of climate variables covering the last 2000 years in the Australasian region. Future palaeoclimate research and records in Australasia could be greatly improved through three main actions: (i) greater data availability through the public archiving of published records; (ii) thorough characterisation of proxy–climate relationships through site monitoring and climate sensitivity tests; and (iii) improvement of chronologies through core-top dating, inclusion of tephra layers where possible, and increased date density during the Common Era.

Terrestrial data spanning the Last Glacial Maximum (LGM) and deglaciation from the southern Australian region are sparse and limited to discontinuous sedimentological and geomorphological records with relatively large chronological uncertainties. This dearth of records has hindered a critical assessment of the role of the Southern Hemisphere mid-latitude westerly winds on the region's climate during this time period. In this study, two precisely dated speleothem records for Mairs Cave, Flinders Ranges, are presented, providing for the first time a detailed terrestrial hydroclimatic record for the southern Australian drylands during 23–15 ka. Recharge to Mairs Cave is interpreted from the speleothem record by the activation of growth, physical flood layering, and δ18O and δ13C minima. Periods of lowered recharge are indicated by 18O and 13C enrichment, primarily affecting δ18O, argued to be driven by evaporation of shallow soil/epikarst water in this water-limited environment. A hydrological driver is supported by calcite fabric changes. These include the presence of laminae, visible organic colloids, and occasional dissolution features, related to recharge, as well as the presence of sediment bands representing cave floor flooding. A shift to slower-growing, more compact calcite and an absence of lamination is interpreted to represent reduced recharge. The Mairs Cave record indicates that the Flinders Ranges were relatively wet during the LGM and early deglaciation, particularly over the interval 18.9–15.8 ka. This wetter phase ended abruptly with a shift to drier conditions at 15.8 ka. These findings are in agreement with the geomorphic archives for this region, as well as the timing of events in records from the broader Australasian region. The recharge phases identified in the Mairs Cave record are correlated with, but antiphase to, the position of the westerly winds interpreted from marine core MD03-2611, located 550 km south of Mairs Cave in the Murray Canyons region. The implication is that the mid-latitude westerlies are located further south during the period of enhanced recharge in the Mairs Cave record (18.9–16 ka) and conversely are located further north when greater aridity is interpreted in the speleothem record. A further comparison with speleothem records from the northern Australasian region reveals that the availability of tropical moisture is the most likely explanation driving enhanced recharge, with further amplification of recharge occurring during the early half of Heinrich Stadial 1 (HS1), possibly influenced by a more southerly displaced Intertropical Convergence Zone (ITCZ). A rapid transition to aridity at 15.8 ka is consistent with a retraction of this tropical moisture source.

Here we present a multiproxy record (?13C, ?18O, major and minor element composition, mineralogy, and low-resolution biogenic silica content) from a lacustrine succession in the Sulmona Basin, central Italy. Based on previous tephrochronological constraints and a new 40Ar/39Ar dating of a tephra matching the widespread X-6 tephra, the record spans the ca. 129-92 ka period and documents at sub-orbital scale the climatic and environmental changes over the Last Interglacial and its transition to the Last Glacial period. The ?18O composition is interpreted as a proxy for the amount and seasonality of local precipitation, whereas variations in elemental and mineralogical composition are inferred to reflect climatic-driven changes in clastic sediment input. The observed variations are consistent among the different proxies, and indicate that periods of reduced precipitation were marked by enhanced catchment erosion, probably due to a reduction in vegetation cover. The first part of the Last Interglacial shows the most negative ?18O values. Comparison with pollen records from the Mediterranean suggests a greater seasonality of the precipitation at this time. At millennial-to-centennial time scales, comparison of the Sulmona record with speleothem ?18O records from central Italy highlights a highly coherent pattern of hydrological evolution, with enhanced variability and similar events of reduced precipitation consistently recorded by each isotope record. The observed intra-interglacial variability can potentially be linked, within the uncertainties associated with each age model, to similar variations observed in sea-surface temperature records from the Mediterranean and the North Atlantic, suggesting a link between Mediterranean hydrology and North Atlantic temperature and circulation patterns that persists during periods of low ice volume.

Primary carbonates in kimberlites are the main CO2 carriers in kimberlites and thus can be used to constrain the original carbon and oxygen-isotope composition of kimberlite melts and their deep mantle sources. However, the contribution of syn- and post-emplacement processes to the modification of the C–O-isotope composition of kimberlites is yet to be fully constrained. This study aims to shed new light on this topic through a detailed textural, compositional (major and trace elements), and in situ C–O–Sr isotopic characterisation of carbonates in the Benfontein kimberlite sills (Kimberley, South Africa). Our multi-technique approach not only reveals the petrographic and geochemical complexity of carbonates in kimberlites in unprecedented detail, but also allows identification of the processes that led to their formation, including: (1) magmatic crystallisation of Sr-rich calcite laths and groundmass; (2) crystallisation of late groundmass calcite from hydrothermal fluids; and (3) variable degrees of crustal contamination in carbonate-rich diapirs and secondary veins. These diapirs most likely resulted from a residual C–O–H fluid or carbonate melt with contributions from methane-rich fluids from the Dwyka shale wall rock, leading to higher 87Sr/86Sr and δ18O, but lower δ13C values than in pristine magmatic calcite. Before coalescing into the diapiric segregations, these fluids/melts also variably entrained early formed calcite laths and groundmass phases. Comparison between in situ and bulk-carbonate analyses confirms that O isotopic analyses of bulk carbonates from kimberlite rocks are not representative of the original isotopic signature of the kimberlite magma, whereas bulk C-isotope compositions are similar to those of the pristine magmatic carbonates. Calcite laths and most groundmass grains at Benfontein preserve isotopic values (δ18O = 6–8‰ and δ13C = − 4 to − 6‰), similar to those of unaltered carbonatites worldwide, which, therefore, probably correspond to those of their parental melts. This narrow range suggests kimberlite derivation from a mantle source with little contribution from recycled crustal material unless the recycled material had isotopic composition indistinguishable from typical mantle values.

RATIONALE: The suitability of organic matter (OM) removal pre-treatments in isotopic studies of lacustrine carbonates is currently under debate. Naturally occurring OM seems to have a negligible effect on the bulk isotopic composition of carbonates compared with changes induced by pre-treatments. This study provides further insights into the possible effects induced by commonly used pre-treatments on natural lacustrine carbonates. METHODS: Sixteen samples from the Fucino F1-F3 lacustrine succession (Abruzzo, central Italy) were characterised for their mineralogical and geochemical composition and each was split into three identical aliquots. One aliquot was left untreated while the remaining two were treated with NaOCl and H2 O2 dilutions. The same treatment was applied to an internal standard consisting of pure Carrara marble. The treated and untreated samples were analysed for their carbon (δ13 C values) and oxygen (δ18 O values) isotope compositions using an Analytical Precision AP2003 isotope ratio mass spectrometer. RESULTS: The samples had variable proportions of endogenic and detrital components, the detrital portion being more (less) abundant during colder (warmer) climate phases. We observed that neither the NaOCl nor the H2 O2 treatment was able to completely remove OM and therefore there was selective removal of compounds within the OM pool. A possible effect of pre-treatment is the loss of carbonates intimately interspersed within the OM, as suggested by the evolution of isotopic ratios towards the local detrital array. CONCLUSIONS: Our study highlights sample-specific changes in geochemistry associated with sample pre-treatments; however, such changes do not seem to lead to either systematic and/or predictable isotopic shifts. We suggest that the suitability of NaOCl or H2 O2 pre-treatments for OM removal should be evaluated on a case-by-case basis. In the specific case of lacustrine marls from palaeo-lake Fucino containing relatively low amounts of OM and in which both detrital and endogenic carbonates occur, both pre-treatments should be avoided.

Radiometric dating of glacial terminations over the past 640,000 years suggests pacing by Earth’s climatic precession, with each glacial-interglacial period spanning four or five cycles of ~20,000 years. However, the lack of firm age estimates for older Pleistocene terminations confounds attempts to test the persistence of precession forcing. We combine an Italian speleothem record anchored by a uranium-lead chronology with North Atlantic ocean data to show that the first two deglaciations of the so-called 100,000-year world are separated by two obliquity cycles, with each termination starting at the same high phase of obliquity, but at opposing phases of precession. An assessment of 11 radiometrically dated terminations spanning the past million years suggests that obliquity exerted a persistent influence on not only their initiation but also their duration. We acknowledge financial support from Australian Research Council Discovery Project grants 0664621 (to J.D.W.), 110102185 (to R.N.D., J.D.W., J.C.H., E.W., A.E.F., and S.F.), and 160102969 (to R.N.D., J.D.W., G.Z., E.W., and P.F.). We thank the Gruppo Speleologico Lucchese and the Federazione Speleologica Toscana for logistic and funding support. The SUERC contribution to this study falls within the framework of the Scottish Alliance for Geoscience, Environment and Society (SAGES). P.B. was the recipient of a University of Melbourne International Postgraduate Research Scholarship and Postgraduate Writing-Up Award supported by the Albert Shimmins Fund. J.C.H. was the recipient of an Australian Research Council Future Fellowship (FT130100801). P.F. acknowledges support from the European Union through a Marie-Curie Reintegration grant (PERG-GA-2010-272134 - MILLEVARIABILI). D.H. acknowledges support from the UK Natural Environmental Research Council. E.W. is supported by a Royal Society Professorship. A.H.L.V. and T.R. received financial support from Fundação para a Ciência e a Tecnologia (FCT, Portugal) projects MOWCADYN (PTDC/MAR-PRO/3761/2012), WarmWorld (PTDC/CTA-GEO/29897/2017), and CCMAR (UID/ Multi/04326/2019). Samples from the marine sites were provided by the Integrated Ocean Drilling Program to D.H., A.H.L.V., and T.R. info:eu-repo/semantics/publishedVersion

Few palaeoclimate archives beyond the polar regions preserve continuous and datable palaeotemperature proxy time series over multiple glacial-interglacial cycles. This hampers efforts to develop a more coherent picture of global patterns of past temperatures. Here we show that Mg concentrations in a subaqueous speleothem from an Italian cave track regional sea-surface temperatures over the last 350,000 years. The Mg shows higher values during warm climate intervals and converse patterns during cold climate stages. In contrast to previous studies, this implicates temperature, not rainfall, as the principal driver of Mg variability. The depositional setting of the speleothem gives rise to Mg partition coefficients that are more temperature dependent than other calcites, enabling the effect of temperature change on Mg partitioning to greatly exceed the effects of changes in source-water Mg/Ca. Subaqueous speleothems from similar deep-cave environments should be capable of providing palaeotemperature information over multiple glacial-interglacial cycles., Few palaeoclimate archives beyond the polar regions preserve continuous and datable paleotemperature proxy time series over multiple glacial-interglacial cycles. Here, the authors show that Mg concentrations in a subaqueous speleothem from an Italian cave track regional sea-surface temperatures over the last 350,000 years.

Flowstone speleothem growth beneath Mount Arthur, New Zealand shows a clear relationship to vegetation density and soil development on the surface above. Flowstone does not currently form beneath sub-alpine Nothofagus forest above ca. 1000–1100 m altitude but U-Th dating shows it has formed there during past intervals of warmer-than-present conditions including an early–mid Holocene optimum and the last interglacial from ca. 131–119 ka. Some flowstones growing beneath ca. 600 m surface altitude, currently mantled with dense broadleaf-podocarp forest, grew during full glacial conditions, indicating that local tree line was never below this altitude. This implies that Last Glacial Maximum annual temperature was no more than ca. 4 °C cooler than today. Flowstone growth appears to be a robust indicator of dense surface vegetation and well-developed soil cover in this setting, and indicates that past interglacial climates of MIS 7e, 5e, the early–mid Holocene and possibly MIS 5a were more conducive to growth of trees than was the late Holocene, reflecting regional temperature changes similar in timing to Antarctic temperature changes. Here, flowstone speleothem growth is a sensitive indicator of vegetation density at high altitude, but may respond to other factors at lower altitudes.

Long, continuous palaeoclimate records provide an opportunity to extend knowledge of decadal to multi-decadal scale climate variability beyond the limit of instrumental records. In this study, qual...

High-resolution U-Th and 14C dating of two calcite flowstones (RTf: Last Interglacial; RTy: Late Holocene) from the Re Tiberio – Monte Tondo karst system (North Italy) is presented to investigate the palaeoclimate potential of speleothems from gypsum caves. To date, there is a lack of information regarding the dating potential of calcite speleothems that have grown in such gypsum karst environment (e.g. no pseudokarst). High-resolution U-Th dating, aimed at establishing if these speleothems can provide robust radiometric age sequences, is first presented. Although both samples show promise for reliable radiometric dating, about 20% of the ages in the RTf dataset were excluded from the age-model as outliers. These outliers are best explained by post-depositional diagenetic processes affecting the U-Th system rather than anything specific to gypsum karst environment conditions. In contrast, outliers were not detected in the RTy sample, but U-Th analysis was not able to constrain its relatively young age (∼600 years before present, B.P.). Consequently, radiocarbon measurements were undertaken, and combined with the U-Th ages to build an age-model. The latter allowed the estimation of “dead carbon fraction” (DCF), which yields a constant value through time, and a magnitude comparable to other sites where climate is similar to Monte Tondo. Soils were considered the main source of carbon, because bedrock dissolution acted predominantly under open-system conditions, and soil organic matter (SOM) turnover rate appears above average compared to sites studied elsewhere.

K-Ar dating of illite in fault gouges is a useful tool for constraining the timing of brittle fault movement; however, this can be problematic in fault gouges hosted in clay-rich rocks due to the influence of host-rock material. Therefore, this study employs a multianalytical geochemical approach to unravel the influence of host-rock mineralogy, as well as fault zone development, on ages from fault-gouge samples in a shale detachment zone. K-Ar dating of the ≥2 μm fraction of 6 samples from the Sap Bon Formation detachment zone and associated fault zones in the Khao Khwang fold-thrust belt of central Thailand yielded an age range of 262 ± 5.4 to 208 ± 4.6 Ma. Carbon and oxygen stable isotope analysis along with X-ray diffraction mineralogy indicate that the samples with the youngest K-Ar ages are characterized by higher grade clay mineralogy, and hotter, orogenic fluid temperatures. Using these proxies and comparison to existing geochronology of the study area, we correlated K-Ar illite ages to one of three stages of fault zone evolution: detrital, diagenetic (burial), and authigenic (fault movement). The youngest K-Ar dates in the Sap Bon Formation are contemporaneous with recently published zircon province data indicating that faulting and detachment zone formation in the Sap Bon Formation were occurring by the mid-Late Triassic, with deformation continuing as late as the Rhaetian.

An important step in the implementation of paleoclimate reconstructions from speleothems (cave carbonate deposits) is to evaluate the sensitivity of the host cave environment to regional climate. Accordingly, we studied three caves at different altitudes (74 m, 570 m and 1250 m a.s.l.) along a transect from the Dalmatian islands to Velebit Mountain peaks in coastal Croatia to characterize their environments in terms of each cave’s suitability to host speleothems that would be capable of yielding robust paleoclimate reconstructions. We conducted cave microclimate (2-years) and dripwater (1-year) monitoring and analysed the isotopic composition of precipitation, cave dripwater and modern spelean calcite. As for the water isotopic imprints, the isotopic values of meteoric waters reaching the two lower-altitude caves, in spite of an altitude difference of 500 m, lie on local meteoric water lines (LMWLs) of similar slope and intercept (δ 2 H = 6.61 × δ 18 O + 4.92 and δ 2 H = 6.69 × δ 18 O + 6.86). Their slopes lower than that of GMWL indicate enhanced evaporation during the warm season. As expected, the LMWL of the highest cave region (δ 2 H = 7.83 × δ 18 O + 14.45) resembles the slope of the GMWL, but the values of deuterium excess obtained for all three caves (between 15.2‰ and 16.6‰) match that of western Mediterranean-sourced waters (∼15‰). Monthly d -excess values suggest Atlantic-sourced air masses can reach the sites throughout the year but never dominate the rainfall composition. The altitude effect was noted both in precipitation and in dripwater isotopic composition, but with notably different Δδ 18 O/100 m gradients (−0.33‰ and −0.11‰, respectively). Stable isotope variations of the dripwaters in all caves were attenuated in relation to the rainwater, even those of the drip sites with fracture-flow behaviour. Based on stable cave microclimate conditions, relatively steady discharges, and modern calcite apparently precipitated at or close to isotopic equilibrium with dripwater, the two caves at lower altitudes show the greatest potential for future paleoclimate studies. The cave at the highest altitude experiences large cave air temperature amplitudes (5.3 °C) and pronounced ventilation, making the isotopic signal susceptible to kinetic fractionation which might preclude quantification of environmental changes, but on the other hand it accentuates isotopic events, making them easier to identify.

The trace element and Sr isotope records in two coeval stalagmites characterized by different growth rates and flow regimes at Savi cave (Grotta Savi, NE Italy) reveal different sources and incorporation mechanisms for Mg and Sr. Mg is sourced primarily from dissolved cave host rock while particulate Mg derived from soil plays a subordinate role. The presence of particulate-borne Mg is inferred from the co-variation of Mg and particle-associated elements (Th, Al and Mn) which are preferentially concentrated in open columnar calcite layers. Variation in Mg concentrations corrected for particle-influenced components, the Mg c parameter, is controlled by water–rock interaction, with higher and lower Mg c during dry and wet phases, respectively. This is thought to reflect incongruent dissolution of Mg-rich phases. Correction of Sr concentrations for contributions from airborne exogenic Sr, based on 87 Sr/ 86 Sr ratios, yields the bedrock-only contribution (Sr c ). Sr c variation in stalagmite calcite is influenced by speleothem growth rate and by variation of the calcite-water Sr partitioning in wet and dry phases, and only to a minor extent by incongruent dissolution of Mg-rich phases. Concentration profiles for Mg c and Sr cg (corrected for growth rate effects) show inverse correlations and are inferred to show hydrological significance which is captured in a hydrological index, HI. We suggest HI provides robust information on water–rock interaction related to hydrological changes and can be utilized in both wet and semi-arid environments, provided the corrections for soil Mg and exogenic Sr can be applied with confidence. Application of the HI index allows correction of Grotta Savi oxygen isotope data, to yield a δ 18 O c time series that shows when changes in moisture sources and atmospheric reorganization, or changes in moisture amount, were significant. This is especially evident during the Younger Dryas (YD). The Savi record supports the concept of a two-phase YD, marked by an increase of moisture and stronger impact of Adriatic and Mediterranean Sea influences over the northern Adriatic region from 12.3 ka onwards. Then, a large-scale atmospheric reorganization and gradual northward shift of the Polar Front caused a progressive reduction of sea influence over the region from 12.1 ka, supporting the concept of a hemispheric change.

Gypsum beds host the majority of the caves in the north-eastern flank of the Apennines, in the Emilia Romagna region (Italy). More than six hundred of these caves have been surveyed, including the longest known epigenic gypsum cave systems in the world (Spipola-Acquafredda, ~11 km). Although this area has been intensively studied from a geological point of view, the age of the caves has never been investigated in detail. The rapid dissolution of gypsum and uplift history of the area have led to the long-held view that speleogenesis commenced only during the last 130 000 years. Epigenic caves only form when the surface drainage system efficiently conveys water into the underground. In the study area, this was achieved after the dismantling of most of the impervious sediments covering the gypsum and the development of protovalleys and sinkholes. The time necessary for these processes can by constrained by understanding when caves were first formed. The minimum age of karst voids can be indirectly estimated by dating the infilling sediments. U–Th dating of carbonate speleothems growing in gypsum caves has been applied to 20 samples from 14 different caves from the Spipola-Acquafredda, Monte Tondo-Re Tiberio, Stella-Rio Basino, Monte Mauro, and Castelnuovo systems. The results show that: (i) caves have been forming since at least ~600 kyr ago; (ii) the peak of speleogenesis was reached during relatively cold climate stages, when rivers formed terraces at the surface and aggradation caused paragenesis in the stable cave levels; (iii) ~200 000 years were necessary for the dismantling of most of the sediments covering the karstifiable gypsum and the development of a surface mature drainage network. Besides providing a significant contribution to the understanding of evaporite karst evolution in the Apennines, this study refines our knowledge on the timescale of geomorphological processes in a region affected by rapid uplifting. Copyright © 2016 John Wiley & Sons, Ltd.