Search

• A speleothem record from Eastern North America spans three glacial/interglacial cycles. • The oxygen isotope record displays strong cyclicity in the precession band. • The record lags summer insolation at 65°N by ∼5000 yr. • The record is in phase with Northern Hemisphere fall insolation. • Our findings are consistent with North American climates being forced by global ice volumes. The nature and controls of orbital-scale climate variability in North America (NA) are subjects of ongoing debates. On the basis of previous cave records from Southwestern United States, two mutually incompatible hypotheses have been proposed. One links NA orbital-scale climate variability to Northern Hemisphere (NH) summer insolation forcing in a manner analogous to low-latitude monsoon systems, while the other suggests that it is not causally tied to either changes in global ice-volumes or NH summer insolation. Here we report new cave oxygen isotope (δ 18 O) records from Buckeye Creek Cave (BCC), West Virginia, east central North America, covering most of the past three glacial-interglacial periods (∼335 to 45 kyr ago). The BCC δ 18 O record exhibits a strong precession-band cycle, which is in-phase with changes in global ice-volumes (i.e., sea level), sea surface temperatures in the NE Gulf of Mexico and is consistent with the results from published cave records from Nevada and Devils Hole. As with global ice-volume, the BCC records lag summer insolation at 65°N by ∼5000 yr, which stands in contrast with records of low-latitude monsoon variability in South America and Asia, which are in phase and out-of-phase with changes in summer insolation and sea level, respectively. Provided the degree of lag to summer insolation provides a measure of competing forcing from global ice-volume and summer insolation, our data suggest that NA orbital-scale climate variability is dominantly driven by ice-volume forcing. In addition, the sea surface temperatures in the NE Gulf of Mexico and changes in northern high-latitude cryosphere may be also important in explaining the unusually low δ 18 O values at times of the intermediate ice-volume periods in BCC and other NA cave records. [ABSTRACT FROM AUTHOR]

Abstract The timing and structure of Termination II (T-II) is still debatable as the number of high-quality records is insufficient. This study presents precisely dated stalagmite δ 18 O data between 133.4 ± 0.3 to 126.6 ± 0.3 ka BP (covering most of T-II) from north China, near the northern limit of the East Asian summer monsoon (EASM), an area sensitive to climate change. The onset of the last interglacial is constrained at 129.4 ± 0.3 ka BP, consistent with south Chinese speleothem records, further supporting the idea that Northern Hemisphere summer insolation plays an important role in initiating glacial terminations. An extended interval of heavy δ 18 O is observed immediately prior to this abrupt transition, named as the "Weak Monsoon Interval" (WMI) in south Chinese cave records, which was associated with the Heinrich Stadial 11 (H11) in the North Atlantic. A significant millennial-scale interstadial peaking at 132.7 ± 0.3 ka BP is identified preceding the weakest phase of the WMI. A synchronous counterpart is also found in some south Chinese speleothem and North Atlantic alkenone Mg/Ca SST records. It is inferred that the main H11 freshwater penetration possibly occurred after 131.5 ka BP, leaving some aspects of ocean and atmospheric circulation still in interstadial mode from 134 to 131.5 ka BP. Following the onset of the last interglacial, there was a millennial-scale "pause" in our δ 18 O record, synchronized with a "slowdown" in the rate of decrease in δ 18 O in south Chinese cave records. This is possibly a large regional climate oscillation, as it is also identified in some North Atlantic records, but one which is too weak to be a Younger Dryas (YD)-type event. In summary, compared to south Chinese cave records, significant millennial-scale climate oscillations before and after the synchronous onset of the last interglacial is the main feature of our record. Nevertheless, the sequence of these climate events remains very different from Termination I (T-I), which is possibly ascribed to the stronger insolation, higher atmosphere CO 2 , and the resultant faster and greater meltwater pulse to the North Atlantic during T-II than during T-I. Highlights • Termination II (T-II) in north China recorded by a precisely dated stalagmite. • The last interglacial onset was at around 129 ka BP in both north and south China. • Millennial-scale event of T-II in north China is more significant than south China. • Evolution of T-II is different from Termination-I shown by Chinese cave records. [ABSTRACT FROM AUTHOR]

This study presents the first well-dated high resolution stable isotope ( δ 18 O and δ 13 C ) and trace element (Mg and Sr) speleothem records from southwestern Morocco covering the last 1000 yrs. Our records reveal substantial decadal to multidecadal swings between dry and humid periods, consistent with regional paleorecords with prevailing dry conditions during the Medieval Climate Anomaly (MCA), wetter conditions during the second part of the Little Ice Age (LIA), and a trend towards dry conditions during the current warm period. These coherent regional climate signals suggest common climate controls. Statistical analyses indicate that the climate of southwestern Morocco remained under the combined influence of both the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO) over the last millennium. Interestingly, the generally warmer MCA and colder LIA at longer multidecadal timescales probably influenced the regional climate in North Africa through the influence on Sahara Low which weakened and strengthened the mean moisture inflow from the Atlantic Ocean during the MCA and LIA respectively. [ABSTRACT FROM AUTHOR]

We have developed techniques for measuring 234U and 230Th on Faraday cups with precisions of 1–3 epsilon units (1 ε-unit=1 part in 104) using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Using a Thermo-Scientific Neptune with desolvation nebulization, we obtained ionization/transmission efficiencies of 1–2% for both U and Th. We set up protocols to correct for tailing, prepared U and Th gravimetric standards, tested a Th mass fractionation correction procedure based on U isotopes, and identified natural calcite samples likely to be in U–Th isotopic secular equilibrium. The measured atomic ratios, 234U/238U=54.970 (±0.019)×10−6 and 230Th/238U=16.916 (±0.018)×10−6, for these calcite samples were identical within errors (quoted 2σ uncertainties calculated combining all sources of error). Half-life values calculated from these ratios are consistent with previous values, but have much smaller errors: 245,620±260a for 234U and 75,584±110a for 230Th (quoted 2σ uncertainties calculated using all sources of error). In calculating a 230Th age, some of the systematic errors included in estimating the full error in the half-lives effectively cancel. Removing these uncertainties (uncertainty in the 238U half-life value, uncertainty in our gravimetric uranium and thorium standards, and uncertainty in the absolute isotopic composition of the uranium standard), yields effective uncertainties for the purposes of 230Th dating of ±70a for the 234U half-life value and ±30a for the 230Th half-life value. Under ideal circumstances, with our methods, the 2σ uncertainty in age, including uncertainty in half-life values is ±10a at 10ka, ±100a at 130ka, ±300a at 200ka, ±1ka at 300ka, ±2ka at 400ka, ±6ka at 500ka, and ±12ka at 600ka. The isotopic composition of a sample with an age <800ka can clearly be resolved from the isotopic composition of a sample in secular equilibrium, assuming closed system behavior. Using these techniques, we analyzed a Sanbao Cave (Hubei, China) stalagmite that formed between 510 and 640ka ago. As the half-life values were determined independent of the Sanbao Cave ages, the observed co-variation between stalagmite δ18O and Northern Hemisphere summer insolation is consistent with accurate ages and half-life values. [ABSTRACT FROM AUTHOR]

The upper Hanjiang River region is the recharge area of the middle route of South-to-North Water Transfer Project. The region is under construction of the Hanjiang-Weihe River Water Transfer Project in China. Monsoon precipitation variations in this region are critical to water resource and security of China. In this study, high-resolution monsoon precipitation variations were reconstructed in the upper Hanjiang River region over the past 6650 years from δ 18 O and δ 13 C records of four stalagmites in Xianglong cave. The long term increasing trend of stalagmite δ 18 O record since the middle Holocene is consistent with other speleothem records from monsoonal China. This trend follows the gradually decreasing Northern Hemisphere summer insolation, which indicates that solar insolation may control the orbital-scale East Asian summer monsoon (EASM) variations. Despite the declined EASM intensity since the middle Holocene, local precipitation may not have decreased remarkably, as revealed by the δ 13 C records. A series of centennial- to decadal-scale cyclicity was observed, with quasi-millennium-, quasi-century-, 57-, 36- and 22-year cycles by removing the long-term trend of stalagmite δ 18 O record. Increased monsoon precipitation during periods of 4390–3800 a BP, 3590–2960 a BP, 2050–1670 a BP and 1110–790 a BP had caused four super-floods in the upper reach of Hanjiang River. Dramatically dry climate existed in this region during the 5.0 ka and 2.8 ka events, coinciding with notable droughts in other regions of monsoonal China. Remarkably intensified and southward Westerly jet, together with weakened summer monsoon, may delay the onset of rainy seasons, resulting in synchronous decreasing of monsoon precipitation in China during the two events. During the 4.2 ka event and the Little Ice Age, the upper Hanjiang River region was wet, which was similar to the climate conditions in central and southern China, but was the opposite of drought observed in northern China. We propose that weakened summer monsoon and less strengthened or normal Westerly jet may cause rain belt stay longer in the southward region, which reduced rainfall in northern China but enhanced it in central and southern China. [ABSTRACT FROM AUTHOR]

Abstract: Two stalagmites (C996-1 and C996-2) collected from the Jiuxian Cave in the Shaanxi Province in central China have been studied with U-series dating and stable isotope analysis. Thirty-eight 230Th dating results showed that the stalagmite C996-1 was continuously deposited through the last 8.5ka BP (thousand years before present, present=1950AD), and C996-2 was deposited through the last 19ka BP excluding two growth hiatuses between 8.3 and 5.7ka BP, and 15.4 and 11.9ka BP. With a relatively stable boundary condition, we interpret the δ 18O of speleothem calcite as most indicative of the amount of summer monsoon precipitation, although temperature and other factors might have some minor impact. The δ 18O records show notable changes within the last glacial maximum (LGM), resembling other East Asian monsoon records such as those from the Hulu and Sanbao Caves, suggesting that significant monsoonal climate changes occurred in eastern Asia as far north as the Qinling Mountains during the LGM interval. A comparison of our records to precisely dated contemporaneous speleothem records from other caves shows that the increasing trend of δ 18O during the Holocene commenced as early as ∼7.5ka BP in the low-latitude monsoonal area, i.e. the Hoti Cave, while at higher latitudes this shift occurred later, such as ∼7.0ka BP in the Dongge Cave, ∼5.3ka BP in the Heshang Cave, ∼4.7ka BP in the Sanbao Cave and ∼4.5ka BP in the Jiuxian Cave. These results imply an asynchronous change of the summer monsoon precipitation occurred in East Asia during the Holocene. The asynchrony may be related to the responses of a coupled tropical and subtropical monsoon system to changes of the insolation and the differences in thermal forcing, which result from the complex geographical configuration. The variation of sea surface temperature (SST) in the western tropical Pacific may also have important impacts on the summer monsoon precipitation changes in central and northern China because it affects the Northwestern Pacific Subtropical High, a monsoon-front regulator. More robust tests are needed to confirm this phenomenon and to evaluate the contribution of different factors in detail. [Copyright &y& Elsevier]

Abstract: The growth of carbonate formations in caves (speleothems) is sensitive to changes in environmental conditions at the surface (temperature, precipitation and vegetation) and can provide useful paleoclimatic and paleoenvironmental information. We use 73 230Th dates from speleothems collected from a cave in southwestern Oregon (USA) to constrain speleothem growth for the past 380000 years. Most speleothem growth occurred during interglacial periods, whereas little growth occurred during glacial intervals. To evaluate potential environmental controls on speleothem growth we use two new modeling approaches: i) a one-dimensional thermal advection–diffusion model to estimate cave temperatures during the last glacial cycle, and ii) a regional climate model simulation for the Last Glacial Maximum (21000 years before present) that assesses a range of potential controls on speleothem growth under peak glacial conditions. The two models are mutually consistent in indicating that permafrost formation did not influence speleothem growth during glacial periods. Instead, the regional climate model simulation combined with proxy data suggest that the influence of the Laurentide and Cordilleran ice sheets on atmospheric circulation induced substantial changes in water balance in the Pacific Northwest and affected speleothem growth at our location. The overall drier conditions during glacial intervals and associated periods of frozen topsoil at times of maximum surface runoff likely induced drastic changes in cave recharge and limited speleothem growth. This mechanism could have affected speleothem growth in other mid-latitude caves without requiring the presence of permafrost. [Copyright &y& Elsevier]

Abstract: An annual layer-counted and 230Th-dated stalagmite oxygen isotope record from Qingtian Cave in Hubei province, central China, provides an Asian Monsoon (AM) history across the Allerød to Younger Dryas (YD) transition, with an average 2.5-year resolution. Seasonal δ 18O profiles indicate that the calcite δ 18O is a sensitive proxy for AM changes, and the close similarity between the Qingtian and other cave records from eastern China suggests a large-scale regional coherence of monsoonal precipitation δ 18O variations associated with the temperature changes in high-northern latitudes. The annually-resolved chronology with a U–Th age uncertainty of less than 100 yr defines the timing, duration and transition of the early Allerød, the intra-Allerød cold period (IACP), the late Allerød, and the start of the YD. The 160-yr-long IACP, with two brief reversals, is clearly shown in both δ 18O and lamina thickness records. The early and late Allerød, separated by the IACP, are characterized by several decadal to centennial cycles of δ 18O variations, each punctuated by sub-cycles. These decadal to centennial monsoon variations correlate with the Greenland temperature changes, supporting a model simulation that the decadal North Atlantic Oscillation (NAO) and North Pacific Oscillation (NPO) are coupled via atmospheric circulation under glacial boundary conditions, perhaps affecting tropical/subtropical monsoon changes. However, the monsoon transition between the late Allerød and YD lasted 380 yr, longer than the analogous Greenland temperature shift by at least 130 yr [Stuiver, M., Grootes, P.M., GISP2 oxygen isotope ratios. Quat. Res. 53 (2000) 277–284]. This implicates other links besides the direct link between Greenland and the AM, which is now well documented. One possibility is the influence by Southern Hemisphere climate via cross-equatorial air flow [An, Z.S., The history and variability of the East Asian paleomonsoon climate. Quat. Sci. Rev. 19 (2000) 171–187]. [Copyright &y& Elsevier]

Abstract: Understanding the full range of past monsoon variability, with reference to specific monsoon seasons, is essential to test coupled climate models and improve their predictive capabilities. We present a 54-year long, high-resolution skeletal oxygen isotope (δ 18O) record extracted from a well-preserved, massive Porites sp. coral at Hainan Island, South China Sea, to investigate East Asian monsoon variability during summer and winter ∼4400 calendar yr ago. Analysis of modern coral δ 18O confirms that Porites from Hainan Island are well positioned to record winter monsoon forcing of sea surface temperature (SST), as well as the influence of summer monsoon rainfall on sea surface salinity (SSS). The coral record for ∼4400 yr ago shows ∼9% amplification of the annual cycle of δ 18O, in good agreement with coupled ocean–atmosphere models showing higher summer rainfall (lower coral δ 18O) and cooler winter SSTs (higher coral δ 18O) in response to greater Northern Hemisphere insolation seasonality during the Middle Holocene. Mean SSTs in the South China Sea during the Mid-Holocene were within 0.5 °C of modern values, yet the mean δ 18O for the fossil coral is ∼0.6‰ higher than that for the modern coral, suggesting that the δ 18O of surface seawater was higher by at least ∼0.5‰, relative to modern values. The 18O-enrichment is likely to be driven by greater advection of moisture towards the Asian landmass, enhanced monsoon wind-induced evaporation and vertical mixing, and/or invigorated advection of saltier 18O-enriched Pacific water into the relatively fresh South China Sea. The 18O-enrichment of the northern South China Sea ∼4400 yr ago contributes to mounting evidence for recent freshening of the tropical Western Pacific. Today, winter SST and summer SSS variability in the South China Sea reflect the interannual influence of ENSO and the biennial variability inherent to monsoon precipitation. Spectral analysis of winter SSTs ∼4400 yr ago reveals a strong ENSO cycle at 6.7 y, which is significantly longer than the average 3.6 y cycle observed since 1970. The results suggest that the influence of ENSO on winter SSTs in the South China Sea was well established by ∼4400 yr ago. However, spectral analysis of summer SSS ∼4400 yr ago shows no significant ENSO cycle, suggesting that teleconnections between ENSO and summer monsoon rainfall were restricted. Taken together, the results indicate marked differences in ENSO–monsoon interactions during the winter and summer monsoon seasons in the past. The fossil coral δ 18O record also shows that the amplitude of interannual SST and SSS variability was stronger ∼4400 yr ago, despite ENSO variability being significantly weaker in the Pacific region. Thus it appears that the strengthened Mid-Holocene monsoon was sensitive to forces, other than ENSO, that acted as alternative drivers of interannual monsoon variability. If this is the case, greater interannual climate variability could accompany the strengthening of the Asian monsoon predicted to occur during the 21st century as transient greenhouse warming preferentially warms Eurasia, even if ENSO perturbations remain relatively stable. [Copyright &y& Elsevier]

Abstract: We present a continuous record of the Asian monsoon over the last 16 ka from δ18O measurements of stalagmite calcite. Over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230Th dates. δ18O and therefore Asian monsoon intensity generally follows changes in insolation, although changes in δ18O are generally accommodated in abrupt shifts in contrast to smoothly varying insolation, indicating that threshold effects may be important. δ18O decreased dramatically (∼3‰) at the start of the Holocene (∼11.5 ka) and remained low for ∼6 ka. Four positive δ18O events centered at 11225±97 yr BP (1.05‰), 10880±117 yr BP (1.15‰), 9165±75 yr BP (1.4‰), and a double event centered at 8260±64 yr BP (1.1‰) and 8080±74 yr BP (1.0‰) punctuated this period of high monsoon intensity. All four events correlate within error with climate changes in Greenland ice cores. Thus, the relationship between the Asian monsoon and the North Atlantic observed during the glacial period appears to continue into the early Holocene. In addition, three of the four events correlate within error with outburst events from Lake Agassiz. The decline of monsoon intensity in the mid-late Holocene is characterized by an abrupt positive shift in δ18O which occurs at 3550±59 yr BP (1.1‰ in ∼100 yr). In addition, the Holocene is punctuated by numerous centennial- and multi-decadal-scale events (amplitudes 0.5 to 1‰) up to half the amplitude of the glacial interstadial events seen in the last glacial period. Thus, Holocene centennial- and multi-decadal-scale monsoon variability is significant, although not as large as glacial millennial-scale variability. The monsoon shows a strong connection with northern South American hydrological changes related by changes in ITCZ position. Spectral analysis of the δ18O record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing. However, there are numerous other significant peaks including peaks at El Niño frequencies (observed for high-resolution portions of the record between 8110 and 8250 yr) which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling Holocene monsoon climate. In addition, for this high-resolution portion, we observe a distinctive biennial oscillation of the Asian monsoon, which has been associated with the Tropospheric Biennial Oscillation (TBO). [Copyright &y& Elsevier]

We report concentrations of 231Pa, 230Th, and 232Th measured in unfiltered seawater samples from three stations occupied during the 1994 Arctic Ocean Section; at the western edge of the Canada Basin, in the Makarov Basin, and in the Amundsen Basin at the North Pole. The North Pole data agree well with previously published profiles from the Amundsen Basin. 230Th and 231Pa concentrations in the Canada and Makarov Basins are intermediate between those reported previously for the Beaufort Sea and the Alpha Ridge, reinforcing the observation that scavenging rates are variable in the western and central Arctic and can be as rapid as in the Eurasian Basin and other oceans. Thorium-232 data indicate that relatively high rates of scavenging under the permanent ice cover are driven at least in part by offshore transport of detrital particulate material. A comparison of water column 230Th 231Pa ratios throughout the Arctic suggests that there may be little basin-scale fractionation of these two isotopes in this ocean, contrary to expectations based on the relatively large area of the continental shelves and their contrasts with the deep basins. Models of shelf–basin exchange and 230Th/231Pa scavenging, incorporating available constraints, support this suggestion and point to the need for more data from the Arctic shelves, where the imprint of Th/Pa fractionation, if any, is expected be most pronounced. [Copyright &y& Elsevier]

This study evaluates the accuracy of U/Th dates for young (< a few thousand years old) reef corals, both living and fossil, and explores strategies for refining those dates. The high precision of the U/Th method (±1–2%) for dating young corals is well-established. Earlier studies have demonstrated the method’s accuracy for select samples of known age. However, these studies have focused on typical samples that have extremely low 232Th concentrations (tens of pg/g). Here we study the dating systematics of young corals that have low but significant amounts of 232Th (up to 1000 pg/g), indicating the presence of small fractions of non-radiogenic 230Th (i.e. 230Th not generated by in situ U decay). We report U/Th ages for living and subaerially exposed fossil corals from Palmyra Island, located in the central tropical Pacific, that range from 50 to 700 yr old. The Palmyra corals contain varying amounts of 232Th and small fractions of associated non-radiogenic 230Th. Uncertainty associated with the correction for non-radiogenic 230Th can lead to significant errors in U/Th dates. We have characterized non-radiogenic 230Th/232Th values, (230Th/232Th)nr, as a means of minimizing this source of error. We calculate (230Th/232Th)nr values ranging from 0 to 2×10−5 for the Palmyra living corals by comparing measured U/Th dates to absolute dates for the living coral, whose chronology is well-established. For the fossil corals, we employ three different approaches to arrive at (230Th/232Th)nr estimates. First, we compare measured U/Th dates to absolute dates in samples from a young fossil coral that overlaps the living coral. Next, we use the firm relative dating constraints imposed by five overlapping fossil corals from the 14th–15th centuries to calculate (230Th/232Th)nr values. Finally, we attempt to anchor the 14th–15th century floating coral chronology to an absolute chronology by correlating the climate signals in the coral records to those in absolutely dated climate proxy records. All lines of evidence point to a range of (230Th/232Th)nr for fossil corals that overlaps the range determined for the living coral, suggesting that most of the thorium is primary or is added while the coral is still alive. Our work also demonstrates the utility of multiple (230Th/232Th)nr estimates. Most importantly, we demonstrate a method by which accurate (±5 yr) U/Th-based chronologies can be obtained for young fossil corals with significant 232Th concentrations. [Copyright &y& Elsevier]

Abstract Maritime Continent (MC) convection drives zonal and meridional climate modes, including the Australasian monsoon system, but its role in past global climate change remains uncertain. Here we use speleothem oxygen isotope (δ 18 O) records from a latitudinal transect across the MC, and a new critically located record for southwest Sulawesi, Indonesia, to reconstruct spatial hydroclimate variability in the Australasian monsoon domain over the last 40,000 yr. Our results show that atmospheric convection in the core MC region was reduced from ∼40,000 to 12,000 yr ago and strengthened rapidly only after the inundation of shallow continental shelves in the region, well after the onset of deglaciation. Interestingly, the millennial-scale climatic impacts of North Atlantic Heinrich events are not evident in Sulawesi. Together with climate model simulations, we demonstrate that changes in deep atmospheric convection dominate glacial–interglacial hydroclimate over the MC, whereas latitudinal shifts in the mean location of the InterTropical Convergence Zone control rainfall patterns during abrupt climate changes. Highlights • We present new speleothem results from Sulawesi, Indonesia for the past 40,000 yr. • Atmospheric convection over the Maritime Continent was reduced from ∼40 to 12 kyr. • Convection strengthened following the inundation of shallow continental shelves. • Convection dominates glacial–interglacial hydroclimate over the Maritime Continent. • Latitudinal shifts in the ITCZ control rainfall patterns during abrupt climate events. [ABSTRACT FROM AUTHOR]

Highlights • Kinetics of thorium (Th) scavenging are quantified in a SE Pacific hydrothermal plume. • Calculated adsorption and desorption rates of Th in hydrothermal plume to determine that scavenging may be irreversible. • Greater hydrothermal depletion of total 230Th relative to 228Th and 234Th. • Removal signature of 230Th is likely integrated across many scavenging events as waters flow northward above the EPR ridge axis. Abstract Hydrothermal activity in the deep ocean generates plumes of metal-rich particles capable of removing certain trace elements from seawater by adsorption and sedimentation. This removal process, known as scavenging, can be probed using the insoluble radiogenic isotopes of thorium (Th), which are produced at a known rate in the water column via the decay of soluble uranium (234Th, 230Th) and radium (228Th) isotopes. We present dissolved and particulate measurements of these three thorium isotopes in a hydrothermal plume observed in the southeast Pacific Ocean on the GEOTRACES GP16 section. Since their half-lives vary from days (234Th) to years (228Th) to tens of thousands of years (230Th), the combination of their signals can be used to understand scavenging processes occurring on a wide range of timescales. Scavenging is a multi-step process involving adsorption and desorption onto particles, followed by particle aggregation, sinking, and eventual sedimentation. We use thorium isotopes to study how hydrothermal activity affects these steps. The rate constants for net adsorption of 234Th determined here are comparable to previous estimates from hydrothermal plumes in the Atlantic and North Pacific Oceans. The partitioning of 234Th and 230Th between large and small particles is more similar in the hydrothermal plume than above it, indicating faster aggregation of particles within the hydrothermal plume at stations nearby the East Pacific Rise than in waters outside the plume. In addition to rapid scavenging and aggregation near the ridge axis, we also infer continuous off-axis scavenging from observations and modeling of 228Th/228Ra activity ratios. The degree of depletion of the three thorium isotopes increases in order of half-life, with total 234Th activity close to that of its parent 238U, but 230Th showing nearly 70% depletion compared to expected values from reversible scavenging. By modeling the variations in depletion for the different isotopes, we show that much of the 230Th removal is inherited from scavenging events happening long before the most recent hydrothermal inputs. [ABSTRACT FROM AUTHOR]

Here we present the results of a first application of a “Combined Vacuum Crushing and Sieving (CVCS)” system to determine past (cave/soil) temperatures from dissolved noble gas concentrations in stalagmite samples grown under ‘cold’ climatic conditions (e.g. close to freezing point of water) during the last glacial–interglacial transition. To establish noble gas temperatures (NGTs) also for stalagmites grown in cold regions, we applied the CVCS system to samples from stalagmite M2 precipitated in the Milandre Cave, located in the Swiss Jura Mountains. The investigated stalagmite M2 covers the Allerød–Younger Dryas–Holocene transitions. Noble gas temperatures are determined by using a new algorithm based on noble gas and water abundances and not from concentrations. Noble gas results indicate annual mean temperatures in the Milandre Cave were 2.2 ± 1.8  °C during the late stages of the Allerød, then dropping to 0 ( − ) + 2.6 ° C at the onset of the Younger Dryas. Such temperatures indicate conditions near to the freezing point of water during the first part of the Younger Dryas. During the last part of the Younger Dryas, the temperature increased to 6.3 ± 2.3  °C. No early Holocene temperature could be determined due the non-detectable water abundances in these samples, however one late Holocene sample indicates a cave temperature of 8.7 ± 2.7  °C which is close to the present day annual mean temperature. NGTs estimated for the Allerød–Younger Dryas–Holocene are in good agreement with paleo-temperature reconstructions from geochemical and biological proxies in lake sediments. The observed deviations between the different paleo-temperature reconstructions are minor if the according temperatures are rescaled to annual mean temperatures and are primarily attributed to the chronological tuning of the different records. As in other stalagmites, NGT reconstructions of the recently precipitated stalagmite (‘young’) samples again are biased, most likely due to diffusive gas loss during sample processing. We speculate that a reduced retentivity of noble gases during experimental sample processing is a general feature of recently precipitated stalagmite fabrics. Therefore, the recently precipitated stalagmite samples do not allow the reliable NGT determination given the currently available experimental methods. Nevertheless, this study makes the case that noble gas thermometry can be applied to stalagmites for paleo-temperature reconstruction based on a physical method including stalagmites that grew during cold climatic conditions. [ABSTRACT FROM AUTHOR]

Here we present high-resolution δ 18 O records obtained from speleothems collected in the eastern Bolivian Andes. The stable isotope records are related to the regional- to large-scale atmospheric circulation over South America and allow interpreting changes in δ 18 O during the last 1400 yr as a function of changes in precipitation regimes over the southern tropical Andes. Two distinct phases with more negative δ 18 O values, interpreted as periods of increased convective activity over the eastern Andean Cordillera in Bolivia are observed concomitantly with periods of global climate anomalies during the last millennium, such as the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) respectively. Changes in the Bolivian δ 18 O record during the LIA are apparently related to a southward displacement of the Intertropical Convergence Zone (ITCZ), which acts as a main moisture driver to intensify convection over the tropical continent. During the MCA, however, the increased convective activity observed in the Bolivian record is likely the result of a different mechanism, which implies moisture sourced mainly from the southern tropical Atlantic. This interpretation is consistent with paleoclimate records further to the north in the tropical Andes that show progressively drier conditions during this time period, indicating a more northerly position of the ITCZ. The transition period between the MCA and the LIA shows a slight tendency toward increased δ 18 O values, indicating weakened convective activity. Our results also reveal a non-stationary anti-phased behavior between the δ 18 O reconstructions from Bolivia and northeastern Brazil that confirms a continental-scale east–west teleconnection across South America during the LIA. [ABSTRACT FROM AUTHOR]

Paleoclimate reconstructions based on speleothems require a robust interpretation of their proxies. Detailed transfer functions of external signals to the speleothem can be obtained using models supported by monitoring data. However, the transferred signal may not be stationary due to complexity of karst processes. Therefore, robust interpretations require the calibration of speleothem records with instrumental time series lasting no less than a decade. We present the calibration of a speleothem δ 18 O record from Postojna Cave (Slovenia) with the regional record of δ 18 O composition of precipitation during the last decades. Using local meteorological data and a regional δ 18 O record of precipitation, we developed a model that reproduces the cave drip water δ 18 O signal measured during a two-year period. The model suggests that the average water mixing and transit time in the studied aquifer is 11 months. Additionally, we used an ion microprobe to study the δ 18 O record of the top 500 μm of a speleothem from the studied cave gallery. According to U–Th dates and 14 C analyses, the uppermost section of the speleothem was formed during the last decades. The δ 18 O record of the top 500 μm of the speleothem has a significant correlation ( r 2 = 0.64 ; p -value <0.001) with the modelled δ 18 O record of cave drip water. Therefore, we confirm that the top 500 μm of the speleothem grew between the years 1984 and 2003 and that the speleothem accurately recorded the variability of the δ 18 O values of regional precipitation filtered by the aquifer. We show that the recorded speleothem δ 18 O signal is not seasonally biased and that the hydrological dynamics described during monitoring period were stationary during recent decades. This research demonstrates that speleothems with growth rates <50 μm/yr can also be used for calibration studies. Additionally, we show that the fit of measured and modelled proxy data can be used to achieve annually resolved chronologies in speleothems that were not actively growing at the time of collection and/or that do not record annual laminae. [ABSTRACT FROM AUTHOR]

Previous research has shown a strong persistence for direct teleconnections between the East Asian summer monsoon (EASM) and high northern latitude climate variability during the last glacial and deglaciation, in particular between monsoon weakening and a reduced Atlantic meridional overturning circulation (AMOC). However, less attention has been paid to EASM strengthening as the AMOC was reinvigorated following peak Northern Hemisphere (NH) cooling. Moreover, climate model simulations have suggested a strong role for Antarctic meltwater discharge in modulating northward heat transport and hence NH warming, yet the degree to which Southern Hemisphere (SH) climate anomalies impacted the Asian monsoon region is still unclear. Here we present a new stalagmite oxygen-isotope record from the EASM affected region of central China, which documents two prominent stages of increased 18 O-depleted moisture delivery to the region through the transition from Heinrich Stadial 1 (HS1) to the Bølling–Allerød (B–A) interstadial; this is in general agreement with the other monsoonal records from both NH and SH mid to low latitudes. Through novel comparisons with a recent iceberg-rafted debris (IRD) record from the Southern Ocean, we propose that the two-stage EASM intensification observed in our speleothem records were linked with two massive Antarctic icesheet discharge (AID) events at ∼16.0 ka and ∼14.7 ka, immediately following the peak HS1 stadial event. Notably, the large increase in EASM intensity at the beginning of the HS1/B–A transition (∼16 ka) is relatively muted in the NH higher latitudes, and better aligns with the changes observed in the SH, indicating the Antarctic and Southern Ocean perturbations could have an active role in driving the initial EASM strengthening at this time. Indeed, Antarctic freshwater input to the Southern Ocean during these AID events would have cooled the surrounding surface waters and caused an expansion of sea ice, restricting the southern extent of the SH westerlies. Moreover, increased meltwater flux during IRD events would have freshened Antarctic Intermediate Water, leading to the increased formation of North Atlantic Deep Water and enhanced North Atlantic subsurface heat release, and causing a strengthening of the AMOC during the HS1-Bølling transition. The result of this sequence-of-events would have been warming in the North Atlantic whilst at the same time cooling in the Antarctic. The ensuing interhemispheric temperature gradient would have acted to push the ITCZ northward, weakening the Australian–Indonesian summer monsoon (AISM) whilst intensifying the EASM. [ABSTRACT FROM AUTHOR]

An increasing number of studies have recognized the crucial impact of upstream convective activities and rainout processes on the stable isotopic composition of precipitation (δ 18 O p) and water vapor (δ 18 O v) at mid and low latitudes. However, it is difficult to precisely identify the upstream convection and rainout zones using the common method based on the spatial distribution of time-lagged temporal correlation. Using a 10-year continuous high-resolution δ 18 O v and δ 18 O p dataset at Nanjing (southeast China), the longest record of this kind, we develop an improved time-lagged correlation method for Key Upstream Convection Zones Identification (KUCZI). Utilizing this method, we find that summer δ 18 O v and δ 18 O p at Nanjing are primarily controlled by the convective activities and rainout processes along the moisture transport pathway from the Maritime Continent (MC), via the Indo-China Peninsula and South China Sea (ICP_SCS), to Southeast China (SEC), particularly over SEC. Contrary to the conclusion of many existing studies, there is a possibility that the Indian Ocean is not a major convection zone affecting δ 18 O p and δ 18 O v at Nanjing. Our results indicate that we may need to reconsider the role of the Indian Ocean on the paleoclimate interpretation of stalagmite δ 18 O records in the East Asian Monsoon (EAM) region. • A 10-year isotopic observation of δ 18 O v and δ 18 O p was performed at Nanjing. • A method was developed to identify the key upstream convection zones affecting δ 18 O. • Convection and rainout effect along the moisture transport pathway control the δ 18 O. • Convection processes over the Indian Ocean have little impact on δ 18 O at Nanjing. [ABSTRACT FROM AUTHOR]

A Holocene stalagmite from Botuverá Cave, southeastern Brazil was analyzed by LA-ICPMS for Mg/Ca, Sr/Ca, Ba/Ca. The observed variability in the record was demonstrated to be modulated by prior calcite precipitation, and, thus, is interpreted to reflect monsoon intensity. We find that the calcite δ 18 O is strongly correlated with Sr/Ca, indicating that atmospheric circulation over South America and monsoon intensity have been tightly correlated throughout most of the Holocene, both directly responding to solar precession. Comparison with other contemporaneous high-resolution hydroclimate records reveals that SAMS has shown a degree of complexity during the Holocene not previously detected, with periods where the South American Convergence Zone (SACZ) expanded to cover most of the South American sub-continent, and coincident with periods of low-SST in the north Atlantic. We also detect periods where rainfall amount in northeastern and southeastern Brazil are markedly anti-phased, suggesting a north-south migration of SACZ, which it appears to be mediated by solar irradiance. The high-resolution nature of our record allow us to examine the effect that Holocene climate anomalies had upon SAMS dynamics and hydroclimate in southeastern Brazil, in particular the 8.2 ka event and the Little Ice Age. In addition to confirm the internal structure of the events, we also detect the possible consequences of the climatic anomalies upon ocean–atmosphere interactions through its effects upon SAMS. [ABSTRACT FROM AUTHOR]

Abstract: Records of past changes in lake levels and lake water isotopic composition in closed basins provide key insights into past variations in the hydrological cycle; however, these records are often limited by dating precision and temporal resolution. Here we present data from lacustrine cave carbonates, a previously unexplored class of carbonates that comprise a promising new archive of past hydrologic changes in the Bonneville Basin of the northeastern Great Basin (USA). These dense carbonates precipitated within caves, crevices, and other protected spaces flooded by Lake Bonneville during its highstand in the last glacial period. We report on deposits in Cathedral and Craners caves, located ∼50km apart at similar elevations approximately 100m above the modern Great Salt Lake and almost 200m below Lake Bonneville’s highstand shoreline. Carbonates from the two caves show similar chronologies, mineralogical transitions, isotopic compositions, and uranium concentrations. These findings suggest that lacustrine cave carbonates record changes in lake level and in the isotopic composition and chemistry of lake water. Importantly, the deposits can be precisely dated by U–Th methods, providing the first records of Lake Bonneville’s water balance changes tied to precise U–Th ages. Close agreement between paired U–Th and calibrated 14C ages in the deposits suggests a minimal (<200a) carbon reservoir effect in the lake and allows 14C dating to be used for age control in portions of the deposits less suitable for U–Th dating. We use ages for the onset and cessation of lacustrine cave carbonate deposition to offer new constraints on past changes in lake level and the carbonate saturation state of lake water. We also present precisely dated, high-resolution oxygen and uranium isotope records from the deposits. Within a first phase of deposition reflecting the lake’s transgression between 26 and 18ka, our isotopic data suggest a large influx of freshwater during Heinrich Stadial 2. A hiatus in deposition beginning at 18.2±0.3ka may be the result of freshening related to the lake’s overflow. Calcite deposition resumes at Cathedral Cave at 16.4±0.2ka, suggesting that basin overflow had ceased by this time and that the lake’s calcite saturation state had increased, and δ18O values increase markedly after 15.9ka, consistent with drying at this time. These data imply that the lake’s deglacial regression began well before the Bølling warming. Cessation of this second phase of deposition at 14.7±0.2ka, coincident with the Bølling warming, may reflect the lake’s drop below Cathedral Cave’s elevation. A final stage of aragonite deposition between 13.8 and 13.6ka differs from the underlying facies and may not reflect deposition from lake waters filling the cave. [Copyright &y& Elsevier]

Abstract: The long-term behavior of the tropical Atlantic ocean/atmospheric system prior to the 20th century is not well characterized due to a lack of high-resolution proxy records to extend the short instrumental record. Here we present the first reconstruction of rainfall variability for the western tropical Atlantic that spans the past 8 centuries and is derived from the δ18O of speleothem calcite. The δ18O of speleothem calcite at this Puerto Rican location varies primarily in response to changes in the amount of summer-time precipitation. The speleothem documents multi-decadal to centennial length oscillations in δ18O that point to large variations in rainfall that have not been manifest in the short instrumental period. Since AD 1850, variations in δ18O have tracked shifts in the Atlantic Multidecadal Oscillation (AMO). We tentatively suggest that the speleothem δ18O-based rainfall record from Puerto Rico extends the history of the AMO to the 12th century. [Copyright &y& Elsevier]

Abstract: Annual layer analysis in two stalagmites collected from Spring Valley Caverns, southeastern Minnesota, reveals hydrological response of the cave to extreme rainfall events in the Midwest, USA. Cave-flooding events are identified within the two samples by the presence of detrital layers composed of clay sized particles. Comparison with instrumental records of precipitation demonstrates a strong correlation between these cave-flood events and extreme rainfall observed in the Upper Mississippi Valley. A simple model is developed to assess the nature of rainfall capable of flooding the cave. The model is first calibrated to the last 50-yr (1950–1998 A.D.) instrumental record of daily precipitation data for the town of Spring Valley and verified with the first 50yr of record from 1900 to 1949 A.D. Frequency analysis shows that these extreme flood events have increased from the last half of the nineteenth century. Comparison with other paleohydrological records shows increased occurrence of extreme rain events during periods of higher moisture availability. Our study implies that increased moisture availability in the Midwestern region, due to rise in temperature from global warming could lead to an increase in the occurrence of extreme rainfall events. [ABSTRACT FROM AUTHOR]

Abstract: High-resolution oxygen isotope records of three stalagmites from Sanbao (central China), Wulu (southern China) and Dashibao (southern China) Caves, based on 876 oxygen isotope measurements and 25 precise 230Th dates, provide a detailed Asian monsoon (AM) history from 32.5 to 20.8kaB.P., spanning the shift between Marine Isotope Stages 3 and 2. The calcite δ18O records, although geographically widespread (about 1000km between them), including the previously-reported Hulu record, are similar in timing, shape, and amplitude. These observations support the idea that changes in speleothem δ18O largely represent variations of precipitation isotopic composition associated with large-scale summer monsoon circulation over a large portion of China. These profiles show four centennial to millennial scale strong summer monsoon events, analogous in timing and structure to Greenland Interstadials 5 through 3 (GIS 5–3). Chronology of the events refines the Hulu record and broadly supports the NGRIP GICC05 timescale. Five weak monsoon events are identified at 31.2, 30.1, 28.1, 25.7 and 24.2kaB.P., all of which correspond to stadial events in Greenland. The 30.1 and 24.2ka events correlate with Heinrich stadials 3 and 2. Furthermore, these events correlate to warm episodes in Antarctic ice cores, indicating that the climatic response to North Atlantic cooling is similar in China and in Antarctica, but in an opposite sense. These observations are consistent with the bi-polar seesaw hypothesis. The strong coupling between AM circulation and climate at both high latitudes at the centennial scale indicates that atmospheric circulation changes are important in transmitting abrupt climate signals globally. [ABSTRACT FROM AUTHOR]

Abstract: We present a replicated record of Holocene climate change from a cave in West Virginia, USA. Based on analysis of stable isotopes in precipitation (δ 18Ow) from the closest Global Network of Isotopes in Precipitation (GNIP) station in Coshocton, OH, we interpret enriched oxygen isotopes in calcite (δ 18Oc) as representing an increase in the relative contribution of summer precipitation to annual totals. Significant coherence between local summer (July and August) precipitation and the Summer North Atlantic Oscillation (SNAO) index on multi-decadal timescales suggests that summer precipitation in our study area is strongly influenced by changes in the Bermuda High. A strengthened Bermuda High circulation would increase summer precipitation amounts in the region and lead to enriched δ 18Oc of speleothem calcite. Our δ 18Oc record achieves maximum values during the mid-Holocene, consistent with previous studies indicating an intensified Bermuda High circulation at that time. At 4.2ka, δ 18Oc transitions to lower values at a time when numerous records around the globe document significant changes in the hydrologic budget. Over the last 2000years, there are intervals of substantially decreased δ 18Oc, coincident with aridity in the Yucatan, Alpine glacial advances, and a weakened Asian summer monsoon. [Copyright &y& Elsevier]

Abstract: The instrumental record of Indian Summer Monsoon (ISM) precipitation displays two complete manifestations of an inferred multidecadal cycle. Hitherto, no precipitation-sensitive proxy record from the Indian subcontinent has had the necessary resolution and length to adequately assess whether this observed feature is an inherent aspect of the ISM system on longer timescales. Here we present compelling evidence for persistence of this cycle using a millennial length (AD 600–1550) and sub-annually resolved speleothem oxygen isotope record (δ18O) from Dandak Cave in east-central India. The record displays a high degree of correlation with a speleothem-based Asian monsoon reconstruction from Wanxiang Cave in north-central China on annual to decadal timescales showing the regional significance of these findings. The observed period in our monsoon reconstruction is similar to that associated with the Gleissberg solar cycle and multidecadal sea surface temperature variability in the north Atlantic (AMO), both of which are often cited as the prominent pacemakers of ISM variability on multidecadal timescales. We document transient coherence between ISM precipitation amount and solar variability that persists exclusively in the century prior to and during the Medieval Climate Anomaly (nominally, AD 950–1300). The non-stationary nature of the SFV–monsoon relationship presented here may be evidence of the time-varying influence of tropical ocean–atmosphere dynamics on the solar–monsoon link; however, it is not possible to show with significance that this period of coherence is anything more than an artifact of two timeseries with similar spectra. We therefore, are inclined to interpret our record as evidence of a minimal role of solar variability in driving persistent multidecadal variability of the ISM. Multidecadal SST variability in the North Atlantic remains as the likely alternative driver for persistence of this cycle. Regardless of the causative mechanism(s), the amplitude and regional signature of the observed cycle in ISM precipitation highlight its societal importance with respect to forecasting ISM precipitation on multidecadal timescales. [Copyright &y& Elsevier]

• A composite high-resolution monsoon precipitation record over the mid-YRV. • Centennial-scale oscillations in EASM rainfall related to solar activity and ENSO. • An anti-phase relationship of monsoon rainfall between the mid-YRV and tropical WNP. • A new EAP index calculated as the difference between monsoon rainfall in the mid-YRV and WNP. • A strong correlation between the EAP and SOI index. Meteorological observations reveal an inverse relationship of summer monsoon rainfall between the tropical western North Pacific (WNP) and middle Yangtze River Valley (mid-YRV) on interannual and intraseasonal timescales. This seesaw-like pattern, named the East Asian-Pacific (EAP) pattern, is one of the major teleconnections that affect summer precipitation in the mid-YRV. However, due to the scarcity of long and continuous instrumental data, the behavior and mechanism of the EAP pattern on a long timescale are poorly understood. Here, we present a composite high-resolution summer monsoon rainfall record from 230 BC to 1810 AD, based on 1221 δ 18 O measurements and 22 230Th dates from two stalagmites (EB1 and EB5) in Shenqi Cave over the mid-YRV. Our new record shows that monsoon rainfall in the mid-YRV varies at a dominant periodicity of ∼100 years, probably linked to solar activity and ENSO variability. The multi-centennial fluctuations in the EB record, broadly consistent with the North Hemisphere temperature reconstruction, display strong similarities to two stalagmite δ 18 O records from nearby Heshang and Luoshui caves. To represent the integrated hydroclimate variations over the mid-YRV, we extracted the first principal component (PC1) of these three cave δ 18 O records by using the principal component analysis. We reveal a striking inverse relationship of wet/dry conditions between the mid-YRV and tropical WNP, suggesting that changes in the EAP pattern have an important impact on centennial-scale monsoon precipitation changes. Furthermore, we compile monsoon rainfall records from the mid-YRV and WNP to reconstruct a new EAP index. This EAP index exhibits a strong correlation with the ENSO proxy, confirming that the ENSO variability may play a key role in modulating the monsoon rainfall in the mid-YRV through the EAP teleconnection. [ABSTRACT FROM AUTHOR]

Abstract: Paleoclimatic conditions associated with the East Asian monsoon are reconstructed for the Mid- to Late-Holocene using δ 18O values (819 measurements) from a precisely dated (10 230Th dates) aragonite stalagmite from Lianhua Cave, Hunan Province, China. δ 18O values (−1.6‰ to −7.0‰) are interpreted to reflect the precipitation amount effect related to the strength of summer monsoonal circulation. Throughout this period, the intensity of East Asian summer monsoonal circulation declined in response to changes in insolation and a southward shift in the Intertropical Convergence Zone (ITCZ). Punctuating this first-order trend are abrupt millennial- to decadal-scale fluctuations, the most prominent of which occurred around 3337±5 yr BP and records a dramatic weakening in summer monsoonal circulation that coincides with the beginning of Neoglacial conditions. Comparisons between the δ 18O values of stalagmite A1 and previously published data from stalagmite HS-4 from Heshang Cave and stalagmites D4 and DA from Dongge Cave, China, demonstrate a similar regional response to changes in East Asian monsoonal circulation. Several spectral analysis techniques and wavelet analysis were applied to these stalagmite records to evaluate the nature and character of cyclicity in the East Asian monsoon during the Holocene. Multi-Taper Method (MTM), Lomb–Scargle, and Single Spectrum Analysis (SSA) results reveal common periodicities that are unlikely to be artifacts of any single technique. The periodicities expressed in the stalagmite δ 18O records occur at both solar and non-solar frequencies and support previous interpretations that variability in monsoonal circulation responds to both solar forcing and internal climatic mechanisms. Wavelet analysis demonstrates that some of these frequencies are intermittent and recur at semi-regular intervals, which may indicate long-term cyclicity that is unconstrained by the chronology of the record. [Copyright &y& Elsevier]

• Paleovegetation seesaw in Brazil is a result of different transition timings since the late Pleistocene. • Stalagmites record soil and vegetation change coupled with atmospheric CO 2 and temperature in Cerrado. • Distinct forcings modulate the δ 13 C and 87Sr/86Sr values in stalagmites from different biomes. Paleovegetation studies in Brazil have been mostly based on pollen analysis and geochemical proxies in lacustrine and soil records. These records, however, are sparsely located in the continent and, in most of the cases, centered over the Holocene, giving a minor picture of past vegetation since the Last Glacial Maximum. Stalagmites have been long used as recorders of paleoprecipitation and monsoon activity over time in tropical and subtropical South America by using δ 18 O analyses, but recently they also showed the potential to record past vegetation and soil changes through the combined use of δ 13 C and 87Sr/86Sr. We utilize this new approach to determine the periods of paleovegetation transition and soil development in the Cerrado (Brazilian savanna) biome from central Brazil. Our results show a coherent period of transition from sparser vegetation and shallower soil above the cave to denser vegetation and thicker soil since the last deglaciation circa 15 ka BP. The timing of this transition is different from the multiproxy evidence found in the Caatinga (dry forest) biome, in northeastern Brazil, circa 4.2 ka BP, resulting in a period of paleovegetation seesaw pattern between central and northeastern regions of Brazil. Additionally, atmospheric pCO 2 and temperature variations may have played a major role on the paleovegetation transition in the Cerrado region whereas precipitation linked to the Intertropical Convergence Zone was the major modulator of paleovegetation in the Caatinga. [ABSTRACT FROM AUTHOR]

• A ∼4-yrs resolution Holocene stalagmite δ 18 O record from central China was studied. • The variability of 100-500- and 500-3000-yrs were diminished from 8.5 to 4.9 ka BP. • Changes in tropical SST likely caused the mid-Holocene weak monsoon events. • Climate change has impacts on the evolution of ancient cultures in central China. Monsoon precipitation in East China shows distinct spatial distribution and its variability is closely linked with the changes of the East Asian summer monsoon (EASM). Located in the transition zone between the southern subtropical humid climate and the northern warm temperate semi-humid climate, central China is a core region for recognizing and understanding the spatio-temporal variability of the EASM. Using U-series dating and stable isotope analysis on five stalagmites (MG-1, MG-2, MG-7, MG-40 and MG-64) from Magou Cave, Henan Province, Central China, we construct a high-resolution and precisely dated composite stalagmite δ 18 O time series covering most of the Holocene. This composite record reveals variations in precipitation δ 18 O between 11.7 and 1.1 ka BP with average resolution of ∼4 yrs. The Magou composite record demonstrates that EASM intensity dominates long-term changes in precipitation δ 18 O, which generally follows the northern hemisphere summer insolation (NHSI) trend. Both, Ensemble Empirical Mode Decomposition (EEMD) and wavelet filtering analyses real that the amplitudes of long-term (100-500 and 500-3000 yrs) components were slightly reduced between 8.5 and 4.9 ka BP, implying a weakened influence of climatic forcings on centennial and even millennial timescales during this warm period. Variance on 1-30-yr timescales is relatively low and ascribed to sampling resolution. Fourteen weak EASM intervals, including the 8.2 ka event, were identified within the period corresponding broadly with the Holocene Megathermal. Since no cold excursions other than the 8.2 ka event are found in the Greenland ice core records, we tentatively propose that oscillations in tropical sea surface temperature (SST) likely play an important role in steering other weak monsoon events. Aligning the Magou composite record and other moisture records with archaeological records from the study region, it seems that climate change influenced both the spatial distribution and agricultural practices of ancient cultures. However, overall moderate climatic changes in this region, most likely characterized by shifts between subtropical humid climate and warm temperate semi-humid climate, supported a generally consecutive development of ancient cultures without major hiatuses. [ABSTRACT FROM AUTHOR]

Experimental reconstruction of temperature - altitude in the past remain often elusive. With the development of a combined vacuum crushing and sieving system (CVCS), it is now possible to determine paleotemperatures from the noble gases dissolved in minute amounts of water from inclusions in speleothems that have grown under a broad range of climatic conditions. Here we present noble gas temperature (NGT) estimates during the last deglaciation, which are based on two stalagmites from Milandre Cave (stalagmite M6) and Grotte aux Fées de Vallorbe (stalagmite GEF1), Jura Mountains, Switzerland. The caves are located at different geographical altitudes (Milandre Cave: 373 m a.s.l. and Grotte aux Fées de Vallorbe: 895 m a.s.l.) and thus allow for a reconstruction of the respective temperature – altitude gradients within Switzerland during the last deglaciation. Our reconstruction shows that the past temperature – altitude gradients are within 1 σ error in agreement with the modern temperature – altitude gradient, suggesting that the local temperature – altitude gradient was rather stable over time. In addition to the noble gas analysis, we complemented our study with deuterium (δ D FI) and oxygen isotope (δ 18 O FI) measurements of fluid inclusion water. In combination with NGTs, this allows us to reconstruct the past δ 18 O FI – δ D FI / temperature relation. These reconstructions show that the temporal temperature sensitivity of δ 18 O FI and δ D FI (Δ(δ 18 O FI) / Δ(T) and Δ(δ D FI) / Δ(T)) seems to be stable over time and therefore support the use of water isotopes for temperature reconstructions in Switzerland. • Determining paleotemperatures from stalagmites at different geographical altitudes. • Local temperature – altitude gradient remains rather stable over time. • The temperature sensitivity of δ 18 O FI and δ D FI are stable for Switzerland. [ABSTRACT FROM AUTHOR]

• Stalagmite δ 18 O and δ 13 C records from north China spanning the last 130 ka. • δ 18 O and δ 13 C co-vary on multi-millennial to orbital timescales. • The different trends and amplitudes of δ 18 O and δ 13 C among MIS 5e, 5c, 5a, 3 and 1. • δ 13 C is a sensitive and reliable indicator of EASM rainfall amount. • δ 18 O is an indicator of changes in the phase of the EASM but not its intensity. There is a vigorous and ongoing debate about the interpretation of the stalagmite δ 18 O record from east China as an indicator of East Asian summer monsoon (EASM) intensity. This is mainly because of the inconsistent spatial variation of precipitation amount in east China, but the generally consistent variation of precipitation δ 18 O, on various timescales. However, a direct comparison of a proxy record of precipitation amount with the δ 18 O record from the same stalagmite has rarely been reported, especially in north China. Here, we present precisely-dated high-resolution stalagmite δ 13 C and δ 18 O records for the past 130 ka (1 ka =1000 years) from Zhenzhu (ZZ) Cave in north China. On multi-millennial to orbital timescales, the δ 13 C and δ 18 O records exhibit a high degree of in-phase co-variation; however, there are differences in the trend and amplitude of change between various marine isotopic stages (MIS): specifically, MIS5e, MIS5c, MIS5a, MIS3 and MIS1. Modern monitoring results of two years from ZZ Cave, together with a comparison of the δ 13 C record from the cave with a pedogenic carbonate δ 13 C record from the western Chinese Loess Plateau (CLP), demonstrate that the δ 13 C record is a sensitive and reliable indicator of EASM rainfall amount. Considering that variations in both the amount and δ 18 O of precipitation can be modulated by the atmospheric circulation system, we conclude that the amplitude and trend of the stalagmite δ 18 O variations from north China are not an absolute indicator of EASM intensity, but rather an indicator of changes in the phase of the EASM. We suggest that stalagmite δ 18 O records combined with other unambiguous proxy indicators from stalagmites can provide a more comprehensive history of changes of the EASM. [ABSTRACT FROM AUTHOR]

δ 18 O values in speleothems have been utilized to document past changes in South American monsoon intensity. However, changes in regional vegetation and ecosystems have not been part of this discussion, and other cave proxies such as speleothem δ 13 C values, a useful proxy for vegetation reconstruction, have been neglected due to interpretive complexities. Here we report δ 13 C values and 87Sr/86Sr ratios in stalagmites, together with XRF-derived elemental chemistry, δ 13 C org values and carbon content from a sedimentary profile from the same cave where the stalagmites were collected. In combination with a previously published δ 18 O record, this enables us to clarify climate and environmental shifts that occurred between the Last Glacial Maximum and the Holocene in central South America. We show that vegetation was sparse during the last glacial period in spite of a previously inferred strong monsoon, and that changes in atmospheric p CO 2 combined with local hydrological and temperature feedbacks may have determined vegetation development during this time. • Multiple cave sediment proxies for vegetation and environmental reconstructions. • Vegetation was sparse during the last glacial period in Southern Amazon. • Climate and environmental transformation occurred between the LGM and the Holocene. • Atmospheric CO 2 have determined vegetation evolution. [ABSTRACT FROM AUTHOR]