Search

Cave carbonate minerals are an important terrestrial paleoclimate archive. A few studies have explored the potential for applying carbonate clumped isotope thermometry to speleothems as a tool for constraining past temperatures. To date, most papers utilizing this method have focused on mass-47 clumped isotope values (Δ47) at a single location and reported that cave carbonate minerals rarely achieve isotopic equilibrium, with kinetic isotope effects (KIEs) attributed to CO2 degassing. More recently, studies have shown that mass-47 and mass-48 CO2 from acid digested carbonate minerals (Δ47 and Δ48) can be used together to assess equilibrium and probe KIEs. Here, we examined 44 natural and synthetic modern cave carbonate mineral samples from 13 localities with varying environmental conditions (ventilation, water level, pCO2, temperature) for (dis)equilibrium using Δ47-Δ48 values, in concert with traditional stable carbon (δ13C) and oxygen (δ18O) isotope ratios. Data showed that 19 of 44 samples exhibited Δ47-Δ48 values indistinguishable from isotopic equilibrium, and 18 (95 %) of these samples yield Δ47-predicted temperatures within error of measured modern temperatures. Conversely, 25 samples exhibited isotopic disequilibria, 13 of which yield erroneous temperature estimates. Within some speleothem samples, we find Δ47-Δ48 values consistent with CO2 degassing effects, however, the majority of samples with KIEs are consistent with other processes being dominant. We hypothesize that these values reflect isotopic buffering effects on clumped isotopes that can be considerable and cannot be overlooked. Using a Raleigh Distillation Model, we examined carbon and oxygen isotope exchange trajectories and their relationships with dual clumped isotope disequilibria. Carbon isotope exchange is associated with depletion of both Δ47 and Δ48 relative to equilibrium, while oxygen isotope exchange is associated with enrichment of both Δ47 and Δ48 relative to equilibrium. Cave rafts collected from proximate locations in Mexico exhibit the largest average departures from equilibrium (ΔΔ47¯ = −0.032 ± 0.007, ΔΔ48¯ = −0.104 ± 0.035, where ΔΔi is the measured value – the equilibrium value). This study shows how the Δ47-Δ48 dual carbonate clumped isotope framework can be applied to a variety of tcave carbonate mineral samples, enabling identification of isotopic equilibria and therefore quantitative application of clumped isotope thermometry for paleoclimate reconstruction, or alternatively, constraining the mechanisms of kinetic effects.

Most paleoclimate studies of Mainland Southeast Asia hydroclimate focus on the summer monsoon, with few studies investigating rainfall in other seasons. Here, we present a multiproxy stalagmite record (45,000 to 4,000 years) from central Vietnam, a region that receives most of its annual rainfall in autumn (September-November). We find evidence of a prolonged dry period spanning the last glacial maximum that is punctuated by an abrupt shift to wetter conditions during the deglaciation at ~14 ka. Paired with climate model simulations, we show that sea-level change drives autumn monsoon rainfall variability on glacial-orbital timescales. Consistent with the dry signal in the stalagmite record, climate model simulations reveal that lower glacial sea level exposes land in the Gulf of Tonkin and along the South China Shelf, reducing convection and moisture delivery to central Vietnam. When sea level rises and these landmasses flood at ~14 ka, moisture delivery to central Vietnam increases, causing an abrupt shift from dry to wet conditions. On millennial timescales, we find signatures of well-known Heinrich Stadials (HS) (dry conditions) and Dansgaard-Oeschger Events (wet conditions). Model simulations show that during the dry HS, changes in sea surface temperature related to meltwater forcing cause the formation of an anomalous anticyclone in the Western Pacific, which advects dry air across central Vietnam, decreasing autumn rainfall. Notably, sea level modulates the magnitude of millennial-scale dry and wet phases by muting dry events and enhancing wet events during periods of low sea level, highlighting the importance of this mechanism to autumn monsoon variability.

The timing and mechanisms of past hydroclimate change in northeast Mexico are poorly constrained, limiting our ability to evaluate climate model performance. To address this, we present a multiproxy speleothem record of past hydroclimate variability spanning 62.5 to 5.1 ka from Tamaulipas, Mexico. Here we show a strong influence of Atlantic and Pacific sea surface temperatures on orbital and millennial scale precipitation changes in the region. Multiple proxies show no clear response to insolation forcing, but strong evidence for dry conditions during Heinrich Stadials. While these trends are consistent with other records from across Mesoamerica and the Caribbean, the relative importance of thermodynamic and dynamic controls in driving this response is debated. An isotope-enabled climate model shows that cool Atlantic SSTs and stronger easterlies drive a strong inter-basin sea surface temperature gradient and a southward shift in moisture convergence, causing drying in this region.

Reconstructing hydroclimate over the Common Era is essential for understanding the dominant mechanisms of precipitation change and improving climate model projections, which currently suggest Northeast Mexico will become drier in the future. Tree-ring reconstructions have suggested regional rainfall is primarily controlled by Pacific sea-surface temperatures (SSTs). However, tree ring records tend to reflect winter-spring rainfall, and thus may not accurately record total annual precipitation. Using the first multiproxy speleothem record spanning the last millennium, combined with results from an atmospheric general circulation model, we demonstrate mean annual rainfall in Northeast Mexico is highly sensitive to Atlantic SST variability. Our findings suggest future precipitation in Northeast Mexico is more dependent upon the warming of Tropical Atlantic SSTs relative to the Tropical Pacific.

The interpretation of palaeoclimate archives based on oxygen isotopes depends critically on a detailed understanding of processes controlling the isotopic composition of precipitation. In the summer monsoonal realm, like Southeast Asia, seasonally and interannually depleted oxygen isotope ratios in precipitation have been linked to the summer monsoon strength. However, in some regions, such as central Vietnam, the majority of precipitation falls outside the summer monsoon period. We investigate processes controlling stable isotopes in precipitation from central Vietnam by combining moisture uptake calculations with monthly stable isotope data observed over five years. We find that the isotopic seasonal cycle in this region is driven by a shift in moisture source from the Indian Ocean to the South China Sea. This shift is reflected in oxygen isotope ratios with low values (- 8 to - 10‰) during summer and high values during spring/winter (0 to - 3‰), while 70% of the annual rainfall occurs during autumn. Interannual changes in precipitation isotopes in central Vietnam are governed by the timing of the seasonal onset and withdrawal of the Intertropical Convergence Zone, which controls the amount of vapour contributed from each source.

Between 5 and 4 thousand years ago, crippling megadroughts led to the disruption of ancient civilizations across parts of Africa and Asia, yet the extent of these climate extremes in mainland Southeast Asia (MSEA) has never been defined. This is despite archeological evidence showing a shift in human settlement patterns across the region during this period. We report evidence from stalagmite climate records indicating a major decrease of monsoon rainfall in MSEA during the mid- to late Holocene, coincident with African monsoon failure during the end of the Green Sahara. Through a set of modeling experiments, we show that reduced vegetation and increased dust loads during the Green Sahara termination shifted the Walker circulation eastward and cooled the Indian Ocean, causing a reduction in monsoon rainfall in MSEA. Our results indicate that vegetation-dust climate feedbacks from Sahara drying may have been the catalyst for societal shifts in MSEA via ocean-atmospheric teleconnections.

Introduction: Encrustation of implanted urinary tract devices is associated with significant morbidity. Pellethane® is a polyether-based compound noted for its strength, porosity, and resistance to solvents. We assessed Pellethane thermoplastic polyurethane (TPU) with and without surface coatings 2-hydroxyethyl methacrylate (HEMA) and tetraethylene glycol dimethyl ether (TETRA) for the potential to resist encrustation in an artificial urine environment. Materials and Methods: Samples of Pellethane TPU, HEMA Pellethane TPU, TETRA Pellethane TPU, and hydrogel-coated ureteral stent (Cook®) were suspended in a batch-flow model with an artificial urine solution (AUS). Every 48 hours for 90 days, 40% of the solution was replaced with fresh AUS. All samples were stored in a 37°C incubator. Subsequently, the samples were thoroughly dried for 48 hours before weighing. Scanning electron microscopy was used to assess the degree of encrustation. Nu-Attom Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used to determine the precise compositions of the encrustation specifically with regard to calcium, magnesium, and phosphate. Results: At the conclusion of the 90-day trial, the samples were analyzed, and the average mass changes were as follows: stent 63.78%, uncoated Pellethane TPU 11.50%, HEMA-coated Pellethane TPU 2.90%, and TETRA-coated Pellethane TPU 0.60%. Pellethane TPU products, and specifically those coated with HEMA and TETRA, exhibited less average mass increase and a lesser propensity to form encrustation than the traditional urinary tract stent. The mass increases noted on coated Pellethane devices were primarily ionic, whereas that of the stent was not. Conclusion: Pellethane, particularly with an HEMA-based preventative coating, may serve as a favorable alternative to traditional urinary stent material, providing its improved resistance to encrustation.

The Asian monsoon region is highly dependent on boreal summer rainfall, which directly impacts the socio-economic stability and welfare of billions of people each year. Precipitation variability over East China has been extensively studied and is known to be characterized by meridional tripole and dipole precipitation structures. In contrast, few studies have focused on precipitation variability over Mainland Southeast Asia (MSEA) and the possible relationship with the variability over East China. Here we focus on how interannual precipitation variability across MSEA during 1983–2017 may be associated with the tripole or dipole patterns using an empirical orthogonal function (EOF) analysis. The first EOF shows a meridional tripole pattern in East China summer precipitation and an in-phase relationship between MSEA and South China precipitation. In contrast, the second EOF shows a meridional dipole pattern in East China precipitation and an out-of-phase relationship between MSEA and South China precipitation. We show that the first EOF mode is a delayed precipitation response to the El Niño-Southern Oscillation (ENSO), while the second EOF mode is a simultaneous precipitation response to the remote influence of the North Atlantic Oscillation (NAO). Therefore, the in-phase or out-of-phase variations in precipitation between MSEA and South China may be used to gauge the relative importance of local Pacific and remote Atlantic influences on Asian monsoon climate.

Extreme precipitation events, commonly associated with “Atmospheric Rivers,” are projected to increase in frequency and severity in western North America; however, the intensity and landfall position are difficult to forecast accurately. As the isotopic signature of precipitation has been widely utilized as a tracer of the hydrologic cycle and could potentially provide information about key physical processes, we utilize both climate and precipitation isotope data to investigate these events in California from 2001 to 2011. Although individual events have extreme isotopic signatures linked to associated circulation anomalies, the composite across all events unexpectedly resembles the weighted mean for the entire study period, reflecting diverse moisture trajectories and associated teleconnection phases. We document that 90% of events reaching this location occurred during the negative Arctic Oscillation, suggesting a possible link with higher-latitude warming. We also utilize precipitation data of extreme precipitation events across the entire western U.S. to investigate the relationships between key tropical and Arctic climate modes known to influence precipitation in this region. Results indicate that the wettest conditions occur when the negative Arctic Oscillation, negative Pacific/North American pattern, and positive Southern Oscillation are in sync and that precipitation has increased in the southwestern U.S. and decreased in the northwestern U.S. relative to this phase combination’s 1979-2011 climatology. Furthermore, the type of El Niño-Southern Oscillation event, Central Pacific or Eastern Pacific, influences the occurrence, landfall location, and isotopic composition of precipitation.

Interdecadal modes of tropical Pacific ocean-atmosphere circulation have a strong influence on global temperature, yet the extent to which these phenomena influence global climate on multicentury timescales is still poorly known. Here we present a 2,000-year, multiproxy reconstruction of western Pacific hydroclimate from two speleothem records for southeastern Indonesia. The composite record shows pronounced shifts in monsoon rainfall that are antiphased with precipitation records for East Asia and the central-eastern equatorial Pacific. These meridional and zonal patterns are best explained by a poleward expansion of the Australasian Intertropical Convergence Zone and weakening of the Pacific Walker circulation (PWC) between ∼1000 and 1500 CE Conversely, an equatorward contraction of the Intertropical Convergence Zone and strengthened PWC occurred between ∼1500 and 1900 CE. Our findings, together with climate model simulations, highlight the likelihood that century-scale variations in tropical Pacific climate modes can significantly modulate radiatively forced shifts in global temperature.

© 2015 Elsevier Ltd. Several recent studies have used records of the radiocarbon (14C) bomb peak in speleothems to inversely model the soil a 14CO2 and the age distribution of soil organic material (SOM) above caves, in part to investigate the potential of speleothems as sensitive records of past SOM dynamics. The results of these modeling studies have suggested that soil CO2 at karst sites is derived primarily from the decomposition of SOM with turnover times on the order of decades to centuries. This result is in stark contrast with observations of soil a 14CO2 at non-karst sites, which indicate that soil CO2 is derived primarily from root respiration and decomposition of SOM with much shorter turnover times. This discrepancy suggests that SOM in karst settings may have a very different age distribution than sites that have been studied previously and/or that soil CO2 is not the main source of speleothem carbon. To help resolve this discrepancy, we present an improved inverse model which we use to estimate the age of CO2 above several caves. We also present results from a detailed case study of soil carbon dynamics at Heshang Cave, China. This work demonstrates that SOM in karst sites may be much older than SOM in non-karst soils that have been studied previously, but that CO2 produced in the shallow soil zone is unlikely to be the main source of speleothem carbon. A review of the literature suggests that the most likely explanation for the aforementioned discrepancy is that decomposition of down-washed SOM in the vadose zone is the dominant source of speleothem carbon.

East Asian summer monsoon (EASM) rainfall impacts the world’s most populous regions. Accurate EASM rainfall prediction necessitates robust paleoclimate reconstructions from proxy data and quantitative linkage to modern climatic conditions. Many precisely dated oxygen isotope records from Chinese stalagmites have been interpreted as directly reflecting past EASM rainfall amount variability, but recent research suggests that such records instead integrate multiple hydroclimatic processes. Using a Lagrangian precipitation moisture source diagnostic, we demonstrate that EASM rainfall is primarily derived from the Indian Ocean. Conversely, Pacific Ocean moisture export peaks during winter, and the moisture uptake area does not differ significantly between summer and winter and is thus a minor contributor to monsoonal precipitation. Our results are substantiated by an accurate reproduction of summer and winter spatial rainfall distributions across China. We also correlate modern EASM rainfall oxygen isotope ratios with instrumental rainfall amount and our moisture source data. This analysis reveals that the strength of the source effect is geographically variable, and differences in atmospheric moisture transport may significantly impact the isotopic signature of EASM rainfall at the Hulu, Dongge, and Wanxiang Cave sites. These results improve our ability to isolate the rainfall amount signal in paleomonsoon reconstructions and indicate that precipitation across central and eastern China will directly respond to variability in Indian Ocean moisture supply.

Recently, it has been shown that U-Th dated speleothems may provide a valuable archive of atmospheric radiocarbon (14C), but the reliability of these records is dependent upon the stability of the dead carbon proportion (DCP) derived from the soil and bedrock. In order to assess climatic influences on speleothem DCP, we have investigated DCP variability over the Holocene interval where atmospheric 14C is well known based on dendrochronologically dated tree rings by conducting 14C measurements on a U-Th dated stalagmite (HS4) from Heshang Cave, Hubei Province, China (30°27 'N, 110°25 'E; 294 m) spanning 0.5-9.6 ka. We investigated climatic controls on DCP, and found that DCP in HS4 has an average value over the Holocene of 10.3 ± 1.5%, with an average age offset from atmospheric radiocarbon of 875 ± 130 years, and displays a response to both precipitation increases and decreases. HS4 DCP increases during the wetter mid-Holocene interval (~5.5-7.1 ka), likely reflecting a shift to more closed-system dissolution in response to increased soil moisture. DCP decreases during the 8.2 ka event, a time period of dry conditions at Heshang Cave, though the lower amplitude of this shift indicates that DCP may be less sensitive to dry events. Speleothems are potentially valuable archives of atmospheric radiocarbon, especially in older portions of the 14C calibration curve where knowledge of atmospheric 14C is limited, however minor climatic influences on DCP could introduce uncertainties of several hundred years to calibrated ages. © 2014 Elsevier B.V.

Precipitation in southwestern North America has exhibited significant natural variability over the past few thousand years. This variability has been attributed to sea surface temperature regimes in the Pacific and Atlantic oceans, and to the attendant shifts in atmospheric circulation patterns. In particular, decadal variability in the North Pacific has influenced precipitation in this region during the twentieth century, but links to earlier droughts and pluvials are unclear. Here we assess these links using δ 18 O data from a speleothem from southern California that spans AD 854-2007. We show that variations in the oxygen isotopes of the speleothem correlate to sea surface temperatures in the Kuroshio Extension region of the North Pacific, which affect the atmospheric trajectory and isotopic composition of moisture reaching the study site. Interpreting our speleothem data as a record of sea surface temperatures in the Kuroshio Extension, we find a strong 22-year periodicity, suggesting a persistent solar influence on North Pacific decadal variability. A comparison with tree-ring records of precipitation during the past millennium shows that some droughts occurred during periods of warmth in the Kuroshio Extension, similar to the instrumental record. However, other droughts did not and instead must have been influenced by other factors. Finally, we find a significant increase in sea surface temperature variability over the past 150 years, which may reflect an influence of greenhouse gas concentrations on variability in the North Pacific.

Extractive electrospray ionization mass spectrometry (EESI-MS) has been shown, in other laboratories, to be a useful technique for the analysis of aerosols from a variety of sources.EESI-MS is applied here, for the first time, to the analysis of secondary organic aerosol (SOA) formed from the reaction of ozone and α-pinene. The results are compared to those obtained using atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The SOA was generated in the laboratory and merged with electrospray droplets. The recovered ions were directed towards the inlet of a triple quadrupole mass spectrometer. Through the use of a denuder to remove gas phase compounds, the EESI-MS technique was found to be effective for measuring the major ozonolysis products either in particles alone or in a combination of vapor phase and particulate products. Due to its relatively simple setup and the avoidance of sample collection and work-up, EESI-MS shows promise as an excellent tool for the characterization of atmospherically relevant particles.

Marine radiocarbon (14C) is a widely used tracer of past ocean circulation, but very few high-resolution records have been obtained. Here, we report a time series of carbon isotope abundances of dissolved inorganic carbon (DIC) in surface seawater collected from the Newport Beach pier in Orange County, within the Southern California Bight, from 2005 to 2010. Surface seawater was collected bimonthly and analyzed for Δ14C, δ13C, and salinity. Results from May 2005 to November 2010 show no long-term changes in δ13C DIC values and no consistent variability that can be attributed to upwelling. Δ14C DIC values have lowered from ~34‰ to about ~16‰, an 18‰ decrease from the beginning of this project in 2005, and is consistent with the overall 14C depletion from the atmospheric thermonuclear bomb pulse at the end of the 1950s. Δ14C DIC values, paired with salinity, do appear to be suitable indicators of upwelling strength with periods of upwelling characterized by more saline and lower DIC Δ14C values. However, a similar signal was not observed during the strong upwelling event of 2010. These results were obtained in the Southern California Bight where upwelling is fairly weak and there is a complex oceanographic circulation in comparison with the remaining western USA coastline. It is therefore likely that the link between DIC Δ14C, salinity, and upwelling would be even stronger at other sites. These data represent the longest time series of Δ14C data from a coastal Southern California site performed to date.

A record from Wanxiang Cave, China, characterizes Asian Monsoon (AM) history over the past 1810 years. The summer monsoon correlates with solar variability, Northern Hemisphere and Chinese temperature, Alpine glacial retreat, and Chinese cultural changes. It was generally strong during Europe's Medieval Warm Period and weak during Europe's Little Ice Age, as well as during the final decades of the Tang, Yuan, and Ming Dynasties, all times that were characterized by popular unrest. It was strong during the first several decades of the Northern Song Dynasty, a period of increased rice cultivation and dramatic population increase. The sign of the correlation between the AM and temperature switches around 1960, suggesting that anthropogenic forcing superseded natural forcing as the major driver of AM changes in the late 20th century.

Based on 5 high-precision 230Th dates and 103 stable oxygen isotope ratios (δ18O) obtained from the top 16 mm of a stalagmite collected from Wanxiang Cave, Wudu, Gansu, variation of monsoonal precipitation in the modern Asian Monsoon (AM) marginal zone over the past 100 years was reconstructed. Comparison of the speleothem δ18O record with instrumental precipitation data at Wudu in the past 50 years indicates a high parallelism between the two curves, suggesting that the speleothem δ18O is a good proxy for the AM strength and associated precipitation, controlled by “amount effect” of the precipitation. Variation of the monsoonal precipitation during the past 100 years can be divided into three stages, increasing from AD 1875 to 1900, then decreasing from AD 1901 to 1946, and increasing again thereafter. This variation is quite similar to that of the Drought/Flooding index archived from Chinese historical documents. This speleothem-derived AM record shows a close association with the Pacific Decadal Oscillation (PDO) between AD 1875 and 1977, with higher monsoonal precipitation corresponding to cold PDO phase and vice versa at decadal timescale. The monsoonal precipitation variation is out of phase with the PDO after AD 1977, probably resulting from the decadal climate jump in the north Pacific occurring at around AD 1976/77. These results demonstrate a strong linkage between the AM and associated precipitation and the Pacific Ocean via ocean/atmosphere interaction. This relationship will aid to forecast future hydrological cycle for the AM monsoon region, and to improve forecasting potential of climatic model with observation data from cave.

A reconstruction of Holocene rainfall is presented for southwest China - an area prone to drought and flooding due to variability in the East Asian monsoon. The reconstruction is derived by comparing a new high-resolution stalagmite δ18O record with an existing record from the same moisture transport pathway. The new record is from Heshang Cave (30°27′N, 110°25′E; 294 m) and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature. Heshang lies 600 km downwind from Dongge Cave which has a published high-resolution δ18O record (Wang, Y.J., Cheng, H., Edwards, R.L., He, Y.Q., Kong, X.G., An, Z.S., Wu, J.Y., Kelly, M.J., Dykoski, C.A., Li, X.D., 2005. The Holocene Asian monsoon: links to solar changes and North Atlantic climate. Science 308, 854-857). By differencing co-eval δ18O values for the two caves, secondary controls on δ18O (e.g. moisture source, moisture transport, non-local rainfall, temperature) are circumvented and the resulting Δδ18O signal is controlled directly by the amount of rain falling between the two sites. This is confirmed by comparison with rainfall data from the instrumental record, which also allows a calibration of the Δδ18O proxy. The calibrated Δδ18O record provides a quantitative history of rainfall in southwest China which demonstrates that rainfall was 8% higher than today during the Holocene climatic optimum (≈ 6 ka), but only 3% higher during the early Holocene. Significant multi-centennial variability also occurred, with notable dry periods at 8.2 ka, 4.8-4.1 ka, 3.7-3.1 ka, 1.4-1.0 ka and during the Little Ice Age. This Holocene rainfall record provides a good target with which to test climate models. The approach used here, of combining stalagmite records from more than one location, will also allow quantification of rainfall patterns for past times in other regions. © 2008.

The 8.2 ka event is the most significant global climate anomaly of the Holocene epoch, but a lack of records from Mainland Southeast Asia (MSEA) currently limits our understanding of the spatial and temporal extent of the climate response. A newly developed speleothem record from Tham Doun Mai Cave, Northern Laos provides the first high‐resolution record of this event in MSEA. Our multiproxy record (δ18O, δ13C, Mg/Ca, Sr/Ca, and petrographic data), anchored in time by 9 U‐Th ages, reveals a significant reduction in local rainfall amount and weakening of the monsoon at the event onset at ∼8.29 ± 0.03 ka BP. This response lasts for a minimum of ∼170 years, similar to event length estimates from other speleothem δ18O monsoon records. Interestingly, however, our δ13C and Mg/Ca data, proxies for local hydrology, show that abrupt changes to local rainfall amounts began decades earlier (∼70 years) than registered in the δ18O. Moreover, the δ13C and Mg/Ca also show that reductions in rainfall continued for at least ∼200 years longer than the weakening of the monsoon inferred from the δ18O. Our interpretations suggest that drier conditions brought on by the 8.2 ka event in MSEA were felt beyond the temporal boundaries defined by δ18O‐inferred monsoon intensity, and an initial wet period (or precursor event) may have preceded the local drying. Most existing Asian Monsoon proxy records of the 8.2 ka event may lack the resolution and/or multiproxy information necessary to establish local and regional hydrological sensitivity to abrupt climate change. Plain Language Summary: The most significant global climate event in the last ∼11,000 years occurred ∼8,200 years ago (the "8.2 ka event"). Many globally distributed records of past climate (paleoclimate) document significant changes during the event, but there are few from Mainland Southeast Asia available to reconstruct the climate impacts in this region. We present a new speleothem (cave sample) record from Tham Doun Mai Cave, Northern Laos that uses multiple geochemical and physical signals (proxies) to document local and regional climate effects of the 8.2 ka event at a high resolution. Using oxygen isotopes, we find that the 8.2 ka event weakened regional monsoon intensity for at least ∼170 years, which resembles findings from other studies. However, other proxies suggest local rainfall changed abruptly decades before the signal of monsoon weakening. Additionally, local drying may have lasted much longer than current estimates of 8.2 ka event responses. Most proxy records of the 8.2 ka event in monsoon regions lack similar multiproxy information and/or do not have high enough resolution to fully capture the climatic response. Additional records like ours from monsoon regions may assist in establishing how sensitive local and regional rainfall is to abrupt climate change. Key Points: High‐resolution speleothem record of the 8.2 ka event in northern Laos shows weakened monsoon intensity and reduced local rainfall amountsMultiproxy data suggest the disruption to local rainfall amounts started decades before the weakened monsoon intensity inferred from δ18OPrevious monsoon records of the event lack the resolution and/or multiproxy dimensions needed to reconstruct local hydrologic changes [ABSTRACT FROM AUTHOR]

Speleothems from Wanxiang Cave, China (33°19′ N, 105°00′ E), located near the northern limit of the East Asian summer monsoon, provide high-resolution records of paleomonsoon variability. We present a simple model for interpreting δ18O shifts in speleothems from this region in which the δ18O of speleothem calcite is inversely related to monsoon intensity. In contrast to observations at higher latitudes, atmospheric temperature has little effect on δ18O of precipitation near Wanxiang Cave. Furthermore, the temperature dependence of calcite-water δ18O fractionation acts in the opposite sense, most likely canceling out the effect of local temperature variations on speleothem δ18O. Given this, the maximum δ18O shift that could occur due only to changes in the composition of the oceanic source region, the amount of rainfall, and the amount of evaporation between full glacial conditions with a weak summer monsoon and full interglacial conditions with a strong summer monsoon is 5.5‰. Accordingly, it is necessary to invoke changes in past atmospheric circulation patterns and in the ratio of summer to winter precipitation to explain the nearly 7‰ range observed in fossil Wanxiang Cave speleothems. Two stalagmites, WXSM 51 and WXSM 52, exhibit more positive δ18O during stadial periods (marine isotope stages [MIS] 8, 6, 5d, 5b, and 2) than during interstadial periods (MIS 9, 5a, 5c, 5e). Thus, East Asian summer monsoon intensity is generally decreased during globally cooler periods and increased during globally warmer periods. We present detailed δ18O records from MIS 5a-5b and 5c-5d. During the MIS 5d-5c transition, summer monsoon intensity increased steadily from 117.6 ka, with a peak in intensity occurring at 106.8 ka, concurrent with Greenland Interstadial 24. During the MIS 5b-5a transition, monsoon intensity increased abruptly at about 85.7 ka, when δ18O decreased by approximately 4‰ in 200 years. Monsoon variability, inferred from the MIS 5c-5d and MIS 5a-5b records, closely coincides with global climate changes observed in the GISP2, Vostok, and SPECMAP records, and with the Northern Hemisphere insolation curve. This suggests that East Asian summer monsoon intensity varies in phase with global climate fluctuations and is largely controlled by variations in Northern Hemisphere incident solar radiation. The MIS 5a-5b and 5c-5d paleomonsoon records from Wanxiang Cave also agree well with other records of Asian monsoon variability indicating that δ18O of speleothems from Wanxiang Cave is a valid proxy for past changes in monsoon intensity. © 2006 Elsevier B.V. All rights reserved.

We report the presence of clear annual cycles in trace-element (Mg/Ca, Sr/Ca, Ba/Ca, and U/Ca) and stable-isotope (δ18O and δ13C) composition in an annually banded stalagmite from Heshang Cave, Hubei Province, China (30.44°N, 110.42°E). Through a combination of micromilling and in situ analysis (LA-MC-CPMS), we measured geochemical variations across 16 annual growth bands, to assess their potential as seasonal resolution paleomonsoon proxies. To facilitate comparison with modern climatic and environmental data we created composite annual cycles for each proxy by stacking 6 well-defined years. Speleothem δ18O variations (- 10.8‰ to - 8.5‰) are controlled by seasonal variations in temperature and drip-water δ18O which lead to maximum values during May, around the time of summer monsoon onset. This provides a chronological marker which can be used to constrain the timing of the other geochemical cycles. The composite cycles reveal a strong positive correlation between Mg/Ca, Sr/Ca, Ba/Ca, and δ13C values in the micromilled section (R2 = 0.65-0.98), with minimum values occurring around May. Maximum U/Ca values occur at the same time. We present simple models which show that these correlations, as well as the observed ranges of Mg/Ca (14.1 to 22.4 mmol/mol), Sr/Ca (0.2 to 0.4 mmol/mol), and δ13C (- 12.5 ‰ to - 10.7-), may be fully explained by progressive CO2 degassing and calcite precipitation from an initially saturated solution. Using realistic initial conditions for Heshang Cave (T = 18 °C, Mg/Casolution = 0.84 mol/mol, Sr/Casolution = 0.69 mmol/mol, δ13CTDIC = - 16.75‰), we find that the observed relationships can be produced by using DMg = 0.016 and DSr = 0.30, within the range of expected values. The model suggests that the fraction of Ca removed from the solution ranges from 0 to 30% to produce the observed seasonal cycles. This variation may be due to two related processes which occur during drier periods: (1) increased prior precipitation of calcite in the epikarst or on the cave ceiling, and/or (2) a greater degree of CO2 degassing and calcite precipitation on stalagmite surfaces when drip-rates are lower. Both mechanisms would have the effect of enriching speleothem Mg/Ca, Sr/Ca, Ba/Ca, and δ13C values during drier periods. Past variations in Heshang carbonate chemistry may therefore be useful as seasonal resolution proxies for past rainfall. © 2006 Elsevier B.V. All rights reserved.

The stable isotopic composition of materials such as glacial ice, tree rings, lake sediments, and speleothems from low-to-mid latitudes contains information about past changes in temperature (T) and precipitation amount (P). However, the transfer functions which link δ18Op to changes in T or P, dδ18Op/d T and dδ18Op/d P , can exhibit significant temporal and spatial variability in these regions. In areas affected by the Southeast Asian monsoon, past variations in δ18O and δD of precipitation have been attributed to variations in monsoon intensity, storm tracks, and/or variations in temperature. Proper interpretation of past δ18Op variations here requires an understanding of these complicated stable isotope systematics. Since temperature and precipitation are positively correlated in China and have opposite effects on δ18Op, it is necessary to determine which of these effects is dominant for a specific region in order to perform even qualitative paleoclimate reconstructions. Here, we evaluate the value of the transfer functions in modern precipitation to more accurately interpret the paleorecord. The strength of these transfer functions in China is investigated using multiple regression analysis of data from 10 sites within the Global Network for Isotopes in Precipitation (GNIP). δ18Op is modeled as a function of both temperature and precipitation. The magnitude and signs of the transfer functions at any given site are closely related to the degree of summer monsoon influence. δ18Op values at sites with intense summer monsoon precipitation are more dependent on the amount of precipitation than on temperature, and therefore exhibit more negative values in the summer. In contrast, δ18Op values at sites that are unaffected by summer monsoon precipitation exhibit strong relationships between δ18Op and temperature. The sites that are near the northern limit of the summer monsoon exhibit dependence on both temperature and amount of precipitation. Comparison with simple linear models (δ18Op as a function of T or P) and a geographic model (δ18Op as a function of latitude and altitude) shows that the multiple regression model is more successful at reproducing δ18Op values at sites that are strongly influenced by the summer monsoon. The fact that the transfer function values are highly spatially variable and closely related to the degree of summer monsoon influence suggests that these values may also vary temporally. Since the Southeast Asian monsoon intensity is known to exhibit large variations on a number of timescales (annual to glacial-interglacial), and the magnitude and sign of the transfer functions is related to monsoon intensity, we suggest that as monsoon intensity changes, the magnitude and possibly even the sign of the transfer functions may vary. Therefore, quantitative paleoclimate reconstructions based on δ18Op variations may not be valid. © 2004 Elsevier B.V. All rights reserved.

This paper presents the stable isotopic compositions from the cave dripwater and actively forming soda straw stalactites collected from Wanxiang Cave, Wudu, Gansu, located on the Qinghai-Tibetan Plateau and Loess Plateau transition zone, China. The δ18Odw and δDdw of dripwater samples in the cave plot directly on the local MWL, constructed by using GNIP data from 3 sites surrounding the cave regions (Lanzhou, Xi’an, and Chengdu), the nearest site to the cave, suggesting that there is a close relationship between the δ18Odw of the cave water and the δ18O of the precipitations. Using the measured δ18Odw and δ18Omc values from the mid-farthest parts from the cave entrance and the carbonate paleotemperature equation, the calculated tem peratures range from 8.9 to 12.4°C, with the mean value of 10.7°C and the temperature calculated at 8 locations in the farthest part of the cave is in the range of 10.1–12.4°C with the mean value of 11.5°C, being consistent with the survey value(10.99°C)in the cave, slightly lower than the mean annual temperature (14.4°C) in Wudu. This suggests that modern speleothems are forming under isotopic equilibrium and their isotopic composition accurately reflects the mean annual temperature at the surface, indicating that the isotopic composition of the modern speleothems records local temperature change with credibility.

Three alternate China-wide temperature composites covering the last 2000 years were established by combining multiple paleoclimate proxy records obtained from ice cores, tree rings, lake sediments and historical documents. Five periods of temperature variation can be identified: a warm stage in AD 0–240, a cold interval between AD 240 and 800, a return to warm conditions from AD 800–1400, including the Medieval Warm Period between AD 800–1100, the cool Little Ice Age period between 1400–1920, and the present warm stage since 1920. Regional temperature variation is found during AD 800–1100, when warm conditions occurred in Eastern China and in the northeastern Tibetan Plateau and in AD 1150–1380, when the southern Tibetan Plateau experienced a warm interval. In contrast, evidence for cool conditions during the LIA is more consistent among the proxy records. The temperature reconstructions for China and the Northern Hemisphere show good agreement over the past millennium.

Chinese speleothem oxygen isotope (δ18O) variations have been widely interpreted as recording the evolution of the Asian Monsoon. However, calibration of δ18O to monsoon intensity has not yet been carried out in a quantitative way. To understand the climatic significance of δ18O, we measured monthly precipitation δ18O data at Heshang Cave, China, where speleothem δ18O records were previously obtained. We examined the influence of local climate and large‐scale atmospheric circulation on the δ18O by correlating to local meteorological data and various monsoon indices. We find neither a significant amount effect nor temperature effect, and therefore suggest that local climate is not the primary driver of δ18O variability. On seasonal timescales, monthly δ18O is significantly correlated to all monsoon indices, especially the Indian Monsoon (IM) and Western North Pacific Monsoon (WNPM) indices, proving δ18O responds dominantly to the tropical monsoon circulation. On interannual timescales, there are significant negative correlations between annual δ18O and the WNPM and IM monsoon indices defined by zonal winds, reflecting the impact of the El Niño‐Southern Oscillation on δ18O. Similar correlations between δ18O and precipitation amount in these monsoon regions lend further support to this finding. As the driving force of seasonal and interannual monsoon changes can be compared to variations on orbital and suborbital scales, respectively, we argue that speleothem δ18O in southern China is influenced by both external forcing and internal variability. Solar radiation plays an indispensable role on the orbital and seasonal scale δ18O variations, whereas ocean–atmosphere interactions are dominant on suborbital timescales. Key Points: Local climate conditions are not the main factor determining the precipitation oxygen isotopes in east ChinaEast Asian precipitation δ18O reflects tropical monsoons on seasonal timescales and links to air–sea interactions on interannual timescalesSolar insolation dominates speleothem δ18O on orbital timescales, and internal variability influences speleothem δ18O on suborbital timescales [ABSTRACT FROM AUTHOR]

This study involves an analysis of the web content of 30 award winning companies regarding diversity and perceived company openness to employing people with disabilities. The results are mixed: some websites appear designed with disabilities in mind while others reveal constraints to website job access which in turn can result in underemployment and talent underutilization of people with disabilities. Based upon these findings, the authors discuss and make recommendations to optimize website designs that welcome people with disabilities. [ABSTRACT FROM AUTHOR]

Marine radiocarbon (14C) is a widely used tracer of past ocean circulation, but very few high-resolution records have been obtained. Here, we report a time series of carbon isotope abundances of dissolved inorganic carbon (DIC) in surface seawater collected from the Newport Beach pier in Orange County, within the Southern California Bight, from 2005 to 2010. Surface seawater was collected bimonthly and analyzed for Δ14C, δ13C, and salinity. Results from May 2005 to November 2010 show no long-term changes in δ13C DIC values and no consistent variability that can be attributed to upwelling. Δ14C DIC values have lowered from ~34‰ to about ~16‰, an 18‰ decrease from the beginning of this project in 2005, and is consistent with the overall 14C depletion from the atmospheric thermonuclear bomb pulse at the end of the 1950s. &dELTA;14C DIC values, paired with salinity, do appear to be suitable indicators of upwelling strength with periods of upwelling characterized by more saline and lower DIC Δ14C values. However, a similar signal was not observed during the strong upwelling event of 2010. These results were obtained in the Southern California Bight where upwelling is fairly weak and there is a complex oceanographic circulation in comparison with the remaining western USA coastline. It is therefore likely that the link between DIC Δ14C, salinity, and upwelling would be even stronger at other sites. These data represent the longest time series of Δ14C data from a coastal Southern California site performed to date. [ABSTRACT FROM AUTHOR]

Numerous studies have found that feminine characteristics of the mother stereotype interact with masculine characteristics of the ideal worker stereotype with the result that mothers are perceived more negatively than are fathers and nonparents when the job is male-typed. Our research investigated potential biases in evaluations of mothers performing a gender-neutral job. Our choice of a gender-neutral job was intended to reduce lack of fit perceptions between "mother" and "ideal worker." We assigned participants to one of four experimental conditions crossing target gender (male, female) and parental status (nonparent, prospective parent requesting parental leave). After reviewing performance information, participants evaluated the targets on job-related traits and predicted future behavior. Results indicated that mothers were judged significantly more negatively than were fathers, while male and female nonparents were judged similarly. We argue that sex-based stereotypes persist in the context of gender-neutral jobs and serve to disadvantage working mothers. [ABSTRACT FROM AUTHOR]

Abstract: Speleothems from Wanxiang Cave, China (33°19′ N, 105°00′ E), located near the northern limit of the East Asian summer monsoon, provide high-resolution records of paleomonsoon variability. We present a simple model for interpreting δ 18O shifts in speleothems from this region in which the δ 18O of speleothem calcite is inversely related to monsoon intensity. In contrast to observations at higher latitudes, atmospheric temperature has little effect on δ 18O of precipitation near Wanxiang Cave. Furthermore, the temperature dependence of calcite–water δ 18O fractionation acts in the opposite sense, most likely canceling out the effect of local temperature variations on speleothem δ 18O. Given this, the maximum δ 18O shift that could occur due only to changes in the composition of the oceanic source region, the amount of rainfall, and the amount of evaporation between full glacial conditions with a weak summer monsoon and full interglacial conditions with a strong summer monsoon is 5.5‰. Accordingly, it is necessary to invoke changes in past atmospheric circulation patterns and in the ratio of summer to winter precipitation to explain the nearly 7‰ range observed in fossil Wanxiang Cave speleothems. Two stalagmites, WXSM 51 and WXSM 52, exhibit more positive δ 18O during stadial periods (marine isotope stages [MIS] 8, 6, 5d, 5b, and 2) than during interstadial periods (MIS 9, 5a, 5c, 5e). Thus, East Asian summer monsoon intensity is generally decreased during globally cooler periods and increased during globally warmer periods. We present detailed δ 18O records from MIS 5a–5b and 5c–5d. During the MIS 5d–5c transition, summer monsoon intensity increased steadily from 117.6 ka, with a peak in intensity occurring at 106.8 ka, concurrent with Greenland Interstadial 24. During the MIS 5b–5a transition, monsoon intensity increased abruptly at about 85.7 ka, when δ 18O decreased by approximately 4‰ in 200 years. Monsoon variability, inferred from the MIS 5c–5d and MIS 5a–5b records, closely coincides with global climate changes observed in the GISP2, Vostok, and SPECMAP records, and with the Northern Hemisphere insolation curve. This suggests that East Asian summer monsoon intensity varies in phase with global climate fluctuations and is largely controlled by variations in Northern Hemisphere incident solar radiation. The MIS 5a–5b and 5c–5d paleomonsoon records from Wanxiang Cave also agree well with other records of Asian monsoon variability indicating that δ 18O of speleothems from Wanxiang Cave is a valid proxy for past changes in monsoon intensity. [Copyright &y& Elsevier]

The following review provides a summary of and comment on Timothy M. Devinney's article entitled “Is the Socially Responsible Corporation a Myth? The Good, the Bad, and the Ugly of Corporate Social Responsibility.” I argue that Devinney provides a convincing explanation for the failure of corporate social responsibility (CSR) in current predatory, oligopolistic business practices. His exposition provides an initial and necessary first step towards addressing the inequitable systems of organization that contribute to our social and environmental problems. [ABSTRACT FROM AUTHOR]

The spatiotemporal variability of the Asian Monsoon (AM) over the last two millennia has been attributed to a combination of external solar and volcanic forcing and/or internal coupled atmosphere-ocean dynamics, but the relative importance of these mechanisms remains unresolved. The present knowledge of multidecadal to centennial-scale AM variability over Mainland Southeast Asia is not well-constrained, despite substantial progress in understanding seasonal to decadal variability from tree ring records. Here we present the first high-resolution stable isotope (δ 13 C and δ 18 O) speleothem record from northern Laos spanning the Common Era (∼50 BCE to 1880 CE). The δ 13 C record reveals substantial centennial-scale fluctuations primarily driven by local water balance. Notably, the driest period at our site occurred from ∼1280 to 1430 CE, during the time of the Angkor droughts, supporting previous findings that this megadrought likely impacted much of Mainland Southeast Asia. In contrast, variations in stalagmite δ 18 O reflect changes in rainfall upstream from our study site. Interestingly, the δ 18 O record exhibits a positive correlation with solar activity that persists after 1200 CE, contrary to the findings in previous studies. Solar-forced climate model simulations reveal that these δ 18 O variations may be driven by solar-forced changes in upstream rainout over the tropical Indian Ocean, which modify the δ 18 O of moisture transported to our study site without necessarily affecting local rainfall amount. We conclude that future rainfall changes in Mainland Southeast Asia are likely to be superimposed on multidecadal to centennial-scale variations in background climate driven primarily by internal climate variability, whereas solar forcing may impact upstream rainout over the Indian Ocean. • New high-resolution speleothem record from northern Laos spanning ∼50 BCE to 1880 CE. • δ 13 C reflects local water balance and records centennial-length dry periods during the Little Ice Age. • δ 18 O reflects upstream rainout over the Indian Ocean and may be influenced by solar forcing. [ABSTRACT FROM AUTHOR]

Canonical models for speleothem formation and the subsurface carbon cycle invoke soil respiration as the dominant carbon source. However, evidence from some karst regions suggests that belowground CO 2 originates from a deeper, older source. We therefore investigated the carbon sources to central Texas caves. Drip-water chemistry of two caves in central Texas implies equilibration with calcite at CO 2 concentrations (P CO2_sat ) higher than the maximum CO 2 concentrations observed in overlying soils. This observation suggests that CO 2 is added to waters after they percolate through the soils, which requires a subsoil carbon source. We directly evaluate the carbon isotope composition of the subsoil carbon source using δ 13 C measurements on cave-air CO 2 , which we independently demonstrate has little to no contribution from host rock carbon. We do so using the oxidative ratio, OR, defined as the number of moles of O 2 consumed per mole of CO 2 produced during respiration. However, additional belowground processes that affect O 2 and CO 2 concentrations, such as gas-water exchange and/or diffusion, may also influence the measured oxidative ratio, yielding an apparent OR (OR apparent ). Cave air in Natural Bridge South Cavern has OR apparent values (1.09 ± 0.06) indistinguishable from those expected for respiration alone (1.08 ± 0.06). Pore space gases from soils above the cave have lower values (OR apparent = 0.67 ± 0.05) consistent with respiration and gas transport by diffusion. The simplest explanation for these observations is that cave air in NB South is influenced by respiration in open-system bedrock fractures such that neither diffusion nor exchange with water influence the composition of the cave air. The radiocarbon activities of NB South cave-air CO 2 suggest the subsoil carbon source is hundreds of years old. The calculated δ 13 C values of the subsoil carbon source are consistent with tree-sourced carbon (perhaps decomposing root matter), the δ 13 C values of which have shifted during industrialization due to changes in the δ 13 C values and concentrations of atmospheric CO 2 . Seasonal variations in P CO2_sat in most of the drip waters suggest that these waters exchange with ventilated bedrock fractures in the epikarst, implying that the subsoil CO 2 source contributes carbon to speleothems. [ABSTRACT FROM AUTHOR]

• A palaeohydrological shift documented in early Pliocene in the North China. • A tectonic-scaled 'tripole-like' rainfall pattern existed in Pliocene over East Asia. • Simulated dynamics of Pacific zonal and meridional SST proposed. Considerable uncertainty remains over the nature and causes(s) of East Asian monsoon evolution since the Late Miocene, a significantly warmer period characterized by substantially weaker meridional and zonal Pacific sea surface temperature (SST) gradients than today and therefore regarded as a potential analog for current and future global warming. However, the extent to which these temperature gradients impacted rainfall patterns across East Asia, and particularly the northern extent of the monsoon domain, remains controversial. Here we present the first hydrological record extending back eight million years (Ma) for North China Plain derived from organic biomarkers preserved in a terrestrial sediment sequence. Our record shows a significant increase in monsoon rainfall during the Early Pliocene (∼4.2-4.5 Ma), coincident with strengthening of Pacific meridional and zonal SST gradients, and the eastern equatorial Pacific cold tongue. This marked intensification of the monsoon rainfall in northern China is also observed in paleoclimate archives from southern Asia, but anti-phased with those from central-eastern China (including southern China), indicating a 'tripole-like' rainfall pattern over East Asia. Through a set of climate model experiments, we show that this redistribution of monsoon rainfall across East Asia during the Early Pliocene (5.33-3.6 Ma) was likely due to an equatorward contraction of the western Pacific warm pool, reduced summer convection in the western subtropical Pacific, and the strengthening of the Hadley and Walker circulations. Our study thus highlights the strong influence of Pacific Ocean temperature gradients on East Asian hydroclimate. [ABSTRACT FROM AUTHOR]

A record from Wanxiang Cave, China, characterizes Asian Monsoon (AM) history over the past 1810 years. The summer monsoon correlates with solar variability, Northern Hemisphere and Chinese temperature, Alpine glacial retreat, and Chinese cultural changes. It was generally strong during Europe's Medieval Warm Period and weak during Europe's Little Ice Age, as well as during the final decades of the Tang, Yuan, and Ming Dynasties, all times that were characterized by popular unrest. It was strong during the first several decades of the Northern Song Dynasty, a period of increased rice cultivation and dramatic population increase. The sign of the correlation between the AM and temperature switches around 1960, suggesting that anthropogenic forcing superseded natural forcing as the major driver of AM changes in the late 20th century. [ABSTRACT FROM AUTHOR]