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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. [ABSTRACT FROM AUTHOR]

A multi-proxy record is presented for approximately the last 4500 cal a BP from Lake Shkodra, Albania/Montenegro. Lithological analyses, C/N ratio and δ13C of the organic and inorganic carbon component suggest that organic matter and bulk carbonate are predominantly authigenic. The δ18O record of bulk carbonate indicates the presence of two prominent wet periods: one at ca. 4300 cal a BP and one at ca. 2500-2000 cal a BP. The latter phase is also found in southern Spain and Central Italy, and represents a prominent event in the western and central Mediterranean. In the last 2000 years, four relatively wet intervals occurred between ca. 1800 and 1500 cal a BP (150-450 AD), 1350-1250 (600-700 AD), 1100-800 (850-1150 AD), and at ca. 90 cal a BP (1860 AD). Between ca. 4100 and 2500 cal a BP δ18O values are relatively high, with three prominent peaks indicating drier conditions at ca. 4100-4000 cal a BP, ca. 3500 and at ca. 3300 cal a BP. Four additional drier events are identified at 1850 (ca. 100 AD), 1400 (ca. 550 AD), 1150 (800 AD) and ca.750 cal a BP (1200 AD). The pollen record does not show changes in accordance with these episodes owing to the poor sensitivity of vegetation in this area, which is dominated by an orographic rainfall effect and where changes in altitudinal vegetation belts do not affect the pollen rain in the lake catchment. However, since ca. 900 cal a BP a significant decrease in the percentage arboreal pollen and in pollen concentrations suggest major deforestation produced by human activities. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We have applied a new technique to analyze the oxygen (δ 18O) and hydrogen (δD) isotope ratios in speleothem fluid inclusions to reconstruct the temperature and rainfall history of southern Indonesia during the Younger Dryas (YD) event and the Holocene. The 12,640-year speleothem record, anchored by 33 uranium-series dates, shows that fluid-inclusion δ 18O values vary in phase with speleothem calcite δ 18O during the Holocene, suggesting that the speleothem calcite δ 18O primarily reflects variations in the δ 18O of local rainfall. Significant early to mid-Holocene decreases in both δ 18O series are interpreted as an intensification of Australian–Indonesian summer monsoon rainfall in response to deglacial eustatic sea-level rise and flooding of the Sunda Shelf. Cave drip-water temperatures reconstructed from coupled measurements of δ 18O in speleothem calcite and fluid inclusions remained relatively constant through the Holocene. This is consistent with reconstructions of Indo-Pacific sea-surface temperature (SST) based on analysis of Mg/Ca ratios in planktonic foraminifera. However, during the YD event, drip-water (i.e. cave) temperature was ∼5°C cooler than modern, which is substantially cooler than SSTs inferred from foraminiferal Mg/Ca, but consistent with coral Sr/Ca reconstructions of SST and terrestrial evidence for high-elevation snow-line depressions. Lower fluid-inclusion δ 18O values during the YD indicate that the cooling was accompanied by increased monsoon rainfall. Taken together, the results suggest that the southerly penetration of the intertropical convergence zone (ITCZ) was largely influenced by the cross-equatorial temperature gradient, rather than local SSTs (and air temperatures). Our results provide new evidence for a rapid cooling of deep tropical air temperatures and repositioning of the ITCZ during the YD event. [Copyright &y& Elsevier]

Abstract: Trace element and stable isotope ratios from an active stalagmite (LR06-B1) recovered from Liang Luar Cave on the island of Flores (eastern Indonesia) are used to reconstruct the position of the austral summer inter-tropical convergence zone and Australian-Indonesian summer monsoon variability during the Holocene. Uranium-series dating of the stalagmite shows that it commenced growth 12,640years ago, with hiatuses spanning 8,560 to 6,420 and 3,670 to 2,780years ago. Stalagmite Mg/Ca and Sr/Ca ratios correlate significantly with one another, and with δ 18O and δ 13C, throughout the record. This suggests that the Mg/Ca and Sr/Ca ratios are dominated by prior calcite precipitation, a process whereby degassing in the vadose zone during periods of low recharge causes deposition of calcite and disproportionate loss of Ca2+ ions (relative to Mg2+ and Sr2+) ‘upstream’ of the stalagmite. The degree of initial 234U/238U disequilibrium also appears to have been controlled by recharge to the overlying aquifer. Together with the Mg/Ca, Sr/Ca, and δ 18O values, the initial uranium isotope activity ratios ([234U/238U]I) imply a generally drier early Holocene, coincident with a lower sea level and lower Southern Hemisphere summer insolation. Comparison of speleothem δ 18O time-series from Flores and Borneo shows that they vary in unison for much of the Holocene. However, there is a significant decrease in the Borneo δ18O record ~6,000 to 4,000 years ago that does not occur in the Flores record. This anomaly may be related to a change in the Australian-Indonesian summer monsoon circulation in response to a protracted positive phase of the Indian Ocean Dipole. Under this scenario, stronger upwelling off of western Indonesia would, based on present-day effects, result in reduced summer convective activity over Flores and a subsequent northward shift of the intertropical convergence zone. [Copyright &y& Elsevier]

A severe drought in parts of low-latitude northeastern Africa and southwestern Asia ∼4200 yr ago caused major disruption to ancient civilizations. Stable isotope, trace element, and organic fluorescence data from a calcite flowstone collected from the well-watered Alpi Apuane karst of central-western Italy indicate that the climatic event responsible for this drought was also recorded in mid-latitude Europe. Although the timing of this event coincides with an episode of increased ice-rafted debris to the subpolar North Atlantic, the regional ocean-atmosphere response seems atypical of similar Holocene icerafting events. Furthermore, comparison of the flowstone data with other regional proxies suggests that the most extreme part of the dry spell occurred toward the end of a longerterm climate anomaly. [ABSTRACT FROM AUTHOR]

Speleothems deposited from cave drip waters retain, in their calcite lattice, isotopic records of past environmental changes. Among other proxies, δ18O is recognized as very useful for this purpose, but its accurate interpretation depends on understanding the relationship between precipitation and drip water δ18O, 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 δ18O in colder caves generally shows a greater resemblance to the amount-weighted mean of precipitation δ18O compared to warmer sites, where evaporation plays an important role. However, during glacial periods, today's 'warm' sites were cold, changing the cave characteristics and precipitation δ18O 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. [ABSTRACT FROM AUTHOR]

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 CO 2 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 (δ44Ca BSE 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 δ44Ca BSE 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 CO 2 contents. Although several recent studies have suggested that equilibrium mineral-melt Ca isotope fractionation factors (e.g., 1000lnα grt-melt) could be significantly different at higher pressures (i.e., due to pressure-induced changes in Ca 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 CO 2 , low SiO 2) 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. [ABSTRACT FROM AUTHOR]

Detailed petrographic observations have been coupled with trace element and δ13C - δ18O analyses in order to investigate their dynamics in two Holocene Bosnian speleothems. The potential of this multiproxy approach in providing a means to extract palaeo-environmental information from stalagmites whose stable isotope signals are noisy and without obvious trends has been tested. The studied stalagmites are mostly characterized by columnar microcrystalline fabric. At the sub-millimetre scale of lamination, different microcrystalline columnar sub-types (open and closed) have been detected and classified on the basis of the observed porosity and the crystallite size. The presence of variations in crystallite arrangement at the lamina scale suggests the occurrence of small-scale environmental changes recorded in the studied samples. A positive correlation was found found between Mg concentration, δ13C and fabric variations, while a negative correlation relates those parameters with Sr concentration. Both δ13C and fabric changes appear to be directly related to changes in hydrology. The detailed observation of calcite fabrics combined with stable isotope and trace element profiles allowed for the interpretation of the conditions under which the speleothems were deposited. [ABSTRACT FROM AUTHOR]

Abstract Aragonite speleothems are increasingly being used as high-resolution climate proxies; however, aragonite is unstable and susceptible to diagenetic transformation into calcite leading to mineralogical, textural and geochemical alterations that have not been fully investigated. To provide some insights to these modifications, this study combines stable isotope geochemistry and U-series dating with petrological observations and EMPA elemental analyses to characterize a stalagmite from Castañar Cave (Cáceres, Spain) that shows primary aragonite diagenetically altered and with reverse ages. The diagenetic processes include recrystallization to calcite, micritization and dissolution. Characterization and interpretation of the chemistry and nature of the waters from which the aragonite precipitated, and of the ones that subsequently formed the calcite, indicates that both polymorphs formed from the same fluids. These fluids hydrochemically evolved from an "aragonite mode" to a "calcite mode" along a diagenetic path within the sample. The results show that during transformation the system stayed close in one of the stages, and open in the other with the same textural result. Reverse ages are found either in the recrystallized areas or in the primary aragonite, caused by two different U-remobilization mechanisms, U-leaching due to flowing waters on the surface, and U-loss during the transformation process. These results highlight the complex behavior of speleothems during diagenesis and the impact on the geochemical information of the primary and secondary phases, and thus the importance of petrological and geochemical characterization of speleothems for paleoclimatic studies. [ABSTRACT FROM AUTHOR]

Abstract Three stalagmites, which grew in the high altitude (∼1800 m a.s.l.) Piani Eterni karst system (northern Italy), represent the longest speleothem palaeoclimate-environmental record from the southern Alps. U-Th dating shows their discontinuous formation during Marine Isotope Stage (MIS) 10, 8, 7d, 6 and 5d–b, with carbonate deposition prevented during both full interglacial and full glacial stages. Speleothem formation was inhibited during interglacial peaks because local base level rise, connected to global climate changes, caused the alluviation of the main epiphreatic levels of the cave system. Drainage of the hydrological pathways, caused by the progressive decrease of rainfall and the accumulation of a perennial snow pack, stopped carbonate deposition during glacials. Thus, Piani Eterni speleothems function as indicators of transitional interglacial to glacial (IG–G) climate periods over the last ∼400 thousand years (kyrs). Analysis of δ18O and δ13C suggest that: i) seasonal snow melt occurred in these high altitude terrains during IG–G times, allowing meteoric water to efficiently penetrate the karst network; ii) soils were restored during MIS 5c–b, but absent during MIS 10, 8, 7d and 6 due to denudation of the karst surfaces; and iii) rainfall perturbations modulated the IG–G shifts in the southern Alps. Rainfall variation is connected to solar radiation changes at orbital timescales during MIS 5c–b, and mimics Dansgaard-Oeschger (DO) cycle variability during DO 23 and 22. DO cycle-like variability is also suspected during MIS 10, 8 and 6. The most important result is that, from a geochemical perspective, this study demonstrates that drivers of δ18O in southern alpine speleothems are similar to Mediterranean, Middle Eastern and Asian speleothems in that they are prevalently controlled by the rainfall amount effect. This contrasts with speleothem records from the more continental northern alpine sector where the air temperature effect on δ18O of precipitation dominates. Highlights • The longest speleothem palaeoclimate-environmental record from the Southern Alps. • Speleothems as indicators of interglacial-to-glacial transition over the last ∼400 kyr. • Seasonal snow melting occurred during interglacial-to-glacial times. • Soils restored during MIS 5c-b, but were absent during MIS 10, 8, 7d and 6. • Mediterranean response of δ18O in Southern Alpine speleothems (rainfall amount). [ABSTRACT FROM AUTHOR]

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 (δ 18 O = −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 (δ 18 O = −3.35‰ ± 1.20‰ from October to March and δ 18 O = −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. [ABSTRACT FROM AUTHOR]

The period corresponding to Marine Isotope Stages 9 (MIS 9) offers the opportunity to study orbital and sub-orbital scale climate variability under boundary conditions different from those of better studied intervals such as the Holocene and the Last Interglacial. Yet, it is poorly represented in independently-dated continental archives around the Mediterranean Region. Here, we present a speleothem stable isotope record (δ 18 O and δ13 C) from the Former Yugoslavian Republic of Macedonia (F.Y.R.O.M., southern Balkans), which consists of two periods of growth broadly covering the ca. 332 to 292 ka and the ca. 264 to 248 ka intervals (MIS 9e-b and late MIS 8). We interpret the speleothem δ 18 O as mostly related to regional hydrology, with variations that can be interpreted as due to changes in rainfall amount, with higher/lower values associated to drier/wetter condition. This interpretation is corroborated by a change in mineralogical composition between aragonite and calcite at ca. 328 ka, which marks increasing precipitation at the onset of MIS 9 and occurs within a trend of decreasing δ 18 O values. Also the comparison with the multiproxy climate record available from the nearby Lake Ohrid seems to support the proposed interpretation. The MIS 9e interglacial appears to be characterized by wettest conditions between ca. 326 and 321 ka, i.e. lasting ca. 5 kyr. Decreasing precipitation and enhanced millennial scale variability matches the glacial inception (MIS9 d to b), with drier events at ca. 319 ka (ca. 2 kyr long) and 310 ka (ca. 1 kyr long), and a major rainfall reduction between 306 and 298 ka. The latter is followed by a prominent wetter period between 298 and 295 ka, for which carbon data values suggest high infiltration rate. Rainfall decreases again after 295 ka, and remain low until the growth interruption at ca. 292 ka. Resumption of the growth and progressive soil development, expressed by the carbon isotope record, occurred during the late part of MIS 8. Despite the rather high temporal uncertainty (average 6 ka), the speleothem hydrological record complements the environmental information provided by the Lake Ohrid record and also fits well to the framework of regional and extra-regional variability, showing similarities with pollen records from southern and western Europe, both at orbital and at sub-orbital time scale. [ABSTRACT FROM AUTHOR]

Here we present a multiproxy record (δ 13 C, δ 18 O, 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 40 Ar/ 39 Ar 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 δ 18 O 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 δ 18 O 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 δ 18 O 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The quality of climate proxy data from speleothem archives depends to varying degrees on crystallization processes, which result in diverse fabrics. Here, we document shifts in calcite growth mechanisms, from ion-by-ion to nanoparticle/nanocrystal attachment, in stalagmites from the tropical island of Atiu (South Pacific). Changes in solution stoichiometry and organic matter content result in the development of two columnar fabrics that are common elsewhere in settings characterized by seasonal contrast. A porous columnar fabric, characterized by intracrystalline micro and nanoporosity grows via a non-classical pathway through amorphous calcium carbonate (ACC) nanoparticles (∼2–4 nm in diameter) and calcite nanocrystal attachment. Despite subsequent transformation of nanoparticles/crystals into a large calcite crystal, the porous columnar fabric appears to preserve a δ18O signal that faithfully reflects that of the parent fluid via quasi-equilibrium fractionation. Furthermore, the porous fabric shows random and fuzzy lateral distributions of Sr, another hydrological proxy, yet this element's incorporation follows equilibrium partitioning. The chemical properties of compact columnar fabrics, which appear to grow by classical ion-by-ion attachment, may not directly reflect those of the original depositional environment because of degassing, the presence of growth inhibitors (such as Na) and very early diagenetic modifications. Columnar porous calcite fabrics that formed through non-classical pathways in other settings may faithfully record the original properties of the parent drip water, whereas compact fabrics that formed through classical pathways elsewhere may not. It is concluded that the study of fabrics at the nano-scale is a necessary complement to speleothem research to identify the influence of crystallization pathways on the accuracy of proxy data. • Stalagmite calcite forms through complex crystallization pathways. • Both classical and non-classical processes are involved. • Particle and nanocrystal attachment operate to yield a porous fabric. • Columnar porous calcite may faithfully record the original properties of the parent drip water. • Oxygen isotopes and trace element concentration correlate with fabrics through crystallization. [ABSTRACT FROM AUTHOR]

Oxygen isotopic (δ18O) variations in stalagmite records have the potential to provide new insights about past climates beyond the instrumental record. This paper presents the first high-resolution oxygen isotope time series of three coeval stalagmite records from the alpine region of south-eastern Australia covering the period 1922–2006 CE. We use extended surface and cave monitoring datasets, petrographic investigation, modelled recharge time series and farmed calcite precipitates to assess the controls on speleothem δ18O and investigate the coherence between three records from Harrie Wood Cave. The drip water response to recent interannual rainfall variability shows that cave drip water Cl−, δ18O and drip rate display a clear response to an increase in rainfall recharge. It is demonstrated that stalagmites from the same drip sites also record variability in interannual recharge, where an increase in δ18O values is observed with lower recharge, while a decrease in δ18O values correspond to higher recharge amounts. The three stalagmite δ18O records are in broad agreement, showing common responses to relatively higher recharge between 1945 and 1995 CE and the low recharge periods between 1937 and 1945 CE (World War II drought) and late 1996 to 2006 CE (beginning of the Millennium Drought). However, differences in the magnitude of the relative response of each stalagmite δ18O record varies. Based on evidence from our cave monitoring study and farmed calcites, we conclude that the differences between the three stalagmite records is attributed to variability in the contribution of preferential flows during recharge events and the store reservoir volume supplying the drip site. When the δ18O decreases in response to enhanced recharge, the speleothem δ13C also decreases, and this is interpreted to reflect a soil respiration response to changes in soil moisture availability due to recharge. Hence, stalagmite δ18O from the Australian alpine region can be applied to reconstruct periods of relatively higher and lower rainfall recharge and thus extend our knowledge of the timing and relative magnitude of droughts as well as past periods of higher recharge in this region. [Display omitted] • Three replicated 20th - 21stC stalagmite δ18O records from Harrie Wood Cave, SE Australia. • Modern speleothems are examined using insights from cave monitoring datasets in this region. • Stalagmite δ18O records from the Australian Alps are archives of regional recharge. [ABSTRACT FROM AUTHOR]

The hydroclimate of the South Pacific is highly variable on a range of timescales, however, the brevity of instrumental data in the region complicates the detection and attribution of this variability. Annually laminated speleothems may fill this knowledge gap by providing paleo-hydroclimate proxy data extending beyond the instrumental period. In this study, replicated oxygen isotope (δ18O) time series from two stalagmites from Pouatea (Pu17) and Nurau (Nu16) caves in the southern Cook Islands were used to reconstruct the variability of effective infiltration over the past 350 years (1672–2019 CE) based on observational rainfall data and cave monitoring and calcite farming experiments. The reconstructed infiltration was then compared to available reconstructions of known climate drivers of the South Pacific. Significant dry and wet periods over the last 350 years were identified based on the δ18O signal of compact/porous calcite fabric and their δ13C signals. The hydroclimate significance of these proxies was validated through comparison with the instrumental records. We could not reach an annual resolution of reconstructed infiltration, due to a combination of stable isotope sampling limitations and mixing effects within the aquifer. Nevertheless, the combined δ18O record of Pu17 and Nu16 identifies that the main driver of infiltration and, hence rainfall variability, in the southern Cook Islands is the location of the South Pacific Convergence Zone (SPCZ), which in turn is modulated by the El Niño Southern Oscillation (ENSO). This study demonstrates the hydroclimate significance of speleothem fabrics when combined with O and C stable isotopes, and adds paleoclimate information to a region that has a paucity of data. • ENSO and movements of the SPCZ are the main drivers of rainfall in the southern Cook Islands. • Joint use of speleothem fabrics, δ18O and δ13C serves as a proxy of effective infiltration. • Reconstruction of effective infiltration variability over the past 350 years (1672–2019 CE). • Insights into large-scale controls on rain and speleothem δ18O variability. [ABSTRACT FROM AUTHOR]

Late Pleistocene and Holocene archaeological deposits from the central Mediterranean regions contain abundant terrestrial gastropod shell remains. Stable isotope studies of their shell carbonate are valuable proxies for various aspects of climate and environmental change such as temperature, hydrological sources and balance, as well as vegetation. Here we present stable carbon and oxygen isotope data of snail shells from several archaeological deposits in the western Mediterranean (Iberian, Italian Peninsula and Sicily). Isotope ratios differ remarkably between the Late Pleistocene, Holocene and modern shells. The results can be interpreted in terms of hydrological variations and changes in vegetation over time. Fossil shells offer the opportunity to examine the effects of past climate change on local and regional environments. [ABSTRACT FROM AUTHOR]

Two flowstone cores from Tana che Urla Cave (TCU, central Italy), preserve an interval of continuous growth between ca. 159 and 121 ka. Stable isotope time series show an abrupt shift toward lower values at ca. 132 ka, coincident with an increase in growth rate and a marked change in speleothem fabric. This shift is consistent with the profound climate changes associated with the glacial-interglacial transition (i.e. shift to warmer and wetter conditions). The TCU record also shows significant variability (alternation between wetter and drier periods), both for glacial and interglacial portions of the record. Glacial MIS 6 is characterized by a wetter period between ca. 154 and 152 ka, while the early to middle last interglacial period shows several drier events (at ca. 129, 126 and 122 ka) which can be placed in the wider context of climatic instability emerging from North Atlantic marine and NW European terrestrial records. [ABSTRACT FROM AUTHOR]

Abstract: Carbon and oxygen isotope ratios were measured in fossil and recent shells of the land snail Helix ligata. Fossil shells were recovered from the archaeological excavations of Grotta della Serratura and recent specimens collected adjacent to the cave. The record is discontinuous and spans from ca 14 to 7 ka cal BP. The oxygen isotope composition of the fossil shells suggests they were grown from environmental waters (e.g. precipitation) isotopically similar to the present during the recorded part of the Late Glacial. A notable exception is represented by a layer at ca 13.4 ka cal BP, with shells characterised by 18O-enriched values, suggesting drier conditions, with rainfall perhaps reduced by 25% compared to the present day. This layer could correspond in part with the GI-1b event of the Greenland ice-core records. The onset of the Holocene was marked by a decrease of δ18O, suggesting an increase in humidity. Significantly lower δ18O values occur at ca 7.4 ka cal BP, in agreement with other stable isotope records, which suggests enhanced rainfall over the Mediterranean region at that time. [Copyright &y& Elsevier]