High-resolution Paleoclimate Reconstructions Research Articles

Subsistence strategies and climate change as key factors in the vicinity of the Great Wall in northern China from 500 BCE

Whether, and in what ways, the association between changes in climate and the shifting of imperial frontiers (i.e. the Great Wall) could be mediated by the social responses of major ethnic groups is a question that remains unanswered. Ulanqab is a region in Inner Mongolia associated with a long history of Great Wall construction from the Warring States to the Ming dynasties (~500 BCE–1644 CE) and the Great Wall is often regarded as the boundary of the Central Plains dynasty. This paper uses Ulanqab as a case study to investigate the historical inter-relationship between changes in climate and subsistence strategies on the one hand, and the positioning of the Great Wall on the other. We determined the precise geographical coordinates of the Great Wall in this region during each dynastic period of Chinese history, and compared its location to (1) the empire’s boundaries in each dynasty, (2) evidence that is available on climate change from high-resolution paleo-climate reconstructions and (3) subsistence strategies (whether agriculture, pastoralism, or nomadism) that people adopted as recorded in historical documents. Geo-referenced information from associated archaeological sites was also used to determine the extent of habitation in different areas. We found that during the period of agriculturalist empires (the Han and Ming dynasties), the Great Wall was a frontier between farming and animal husbandry, and was located to the south of the Daqing Mountains. In contrast, during the period of pastoralist empires (the Zhao Kingdom [of the Warring States], Northern Wei and Jurched Jin periods), the Great Wall was the frontier between animal husbandry and nomadism, and was located to the north of the Daqing Mountains. These mountains (42.5°N) seem to have been the northern limit of human settlements that were based on animal husbandry and farming. We observed that, when precipitation and temperature increased, this resulted in an augmentation of agricultural production that most likely facilitated the northward expansion of the agriculturalist peoples. A decrease in precipitation, on the other hand, resulted in the shrinkage of pastures and food, triggering a southward expansion that was characteristic of the pastoralist peoples. This study attempts to provide new insights into the interrelationships among changes in climate, human societies and geopolitics in Chinese history.

A time window averaging method to mitigate the impact of shell growth trends on Tridacna δ18O records

Tridacna shells have become valuable archives for high-resolution paleoclimate reconstructions due to their daily-to-annual bands. The δ18O, influenced by temperature and salinity, serves as a key geochemical proxy for Tridacna. Traditionally, linear interpolation has been the go-to method for creating evenly spaced Tridacna δ18O timeseries. However, the accuracy of this method can be influenced by the prominent negative shell growth trends. Given that Tridacna shells exhibit significantly faster growth rates during the juvenile stage than in adulthood, constant sampling intervals may lead to overly dense sampling during the juvenile phase, which could potentially introduce errors in the linearly interpolated Tridacna δ18O record. In this study, we proposed a time window averaging method to mitigate the influence of growth trends in Tridacna δ18O records from the northern South China Sea (SCS). The time window averaging method calculates the average of measured Tridacna δ18O data within a time window, whose length is determined by the sampling resolution for each year and the expected temporal resolution. Pseudo-Tridacna experiments, using the newly developed proxy system model for Tridacna δ18O, were conducted to assess the accuracy of both interpolation and averaging methods. Results indicate that the averaging method outperforms the interpolation method, especially in seasonality estimation. The pseudo-Tridacna experiments recommend employing the averaging method for monthly Tridacna δ18O records when sampling density exceeds ∼20 samples/year. Two real Tridacna δ18O records from the northern SCS demonstrate consistency with pseudo-Tridacna experiments, supporting the efficacy of the averaging method in reducing bias in Tridacna δ18O records associated with growth trends. Our results show the potential of the time window averaging method to improve Tridacna-based paleoclimate reconstructions.

Tree ring oxygen isotope in Asia

Tree-ring oxygen isotope (δ18OTR) is a powerful proxy for paleoclimatology, ecology and archaeology, δ18OTR studies in Asia over the past ∼50 years have made significant achievements in improving our understanding of Asian climatic and ecological systems. Here, we review these developments in δ18OTR research in Asia. Most study sites are located within East Asia, Southeast Asia, South Asia, and North Asia, and δ18OTR records from conifers, broadleaf trees, and shrubs have been produced. Progress has been made in the following areas: (1) Experimental techniques. The novel plate method for cellulose extraction has been developed, which reduces experimental time and greatly improves efficiency. (2) Development of δ18OTR chronologies. Ninety-six chronologies exceeding 200 years in length have been produced. A 4354-year δ18OTR chronology with an annual-resolution has been produced in Japan, and a 6700-year δ18OTR chronology with a 1–5 year resolution has been produced in the northeastern Tibetan Plateau, which is the longest in Asia. (3) Biological influences on δ18OTR. Variations of intra- and inter-tree and inter-species δ18OTR have been investigated, and the relationship between tree age and δ18OTR has been explored. (4) Climatic implications. Seasonal δ18OTR records primarily reflect the variability of precipitation δ18O, facilitating high-resolution paleoclimate reconstructions, while interannual δ18OTR records mainly reflect summer moisture variability. (5) Climate reconstructions. Quantitative estimates have been produced for past precipitation, relative humidity, PDSI (Palmer Drought Severity Index), runoff, and other parameters from δ18OTR records. Since 1850, δ18OTR chronologies in monsoon regions show upward trends indicative of drying, while these from westerlies regions exhibit downward shifts implying wetting. (6) Dating. Intra- and inter-annual δ18OTR records help determine the annual growth of trees without rings and facilitate the cross-dating of trees with rings. Thus, the dating of archaeological and buried wood is feasible via comparisons with δ18OTR master chronologies. Promising areas of development include climatic implications (e.g., Position-specific isotope analysis, seasonal δ18OTR records on longer timescales and larger spatial scales), climate reconstructions (syntheses of multiple sites and records, development of long chronologies, deep time paleoclimate reconstructions) and ecological applications (e.g., the response of trees to climatic extremes, and the combinations with multiple tree-ring multiple proxies such as width and density).

Holocene Monsoonal Variations Over Southern India: Looking Into Its Antecedents

A proper understanding of the paleoclimatic variability in the Southern Peninsular India demands a high-resolution paleoclimate reconstruction record. Hence, in this paper, we compiled all the available paleoclimate records from various locations across the Southern India that receives the southwest and the northeast monsoon. We delineated the southwest monsoon (SWMR) and Northeast monsoon (NEMR) variations within the Holocene Period based on the existing paleoclimatic record from this region. Paleoclimate records are primarily based on various paleoclimate archives and proxies. A detailed study of these variations unravels, (i) that SWMR gradually intensified since the younger dryas during the Early Holocene period. On the contrary, NEMR records indicate a dry phase during the same period. (ii) During the mid-late Holocene, precipitation in SWMR-dominated regions decreased, whereas precipitation in NEMR-dominated regions shows an increasing trend. (iii) Then, in the late Holocene Period, SWMR exhibits an overall wet phase with a few drier periods, and NEMR shows an intense dry period with shorter wet phases, which can be correlated to the demise of Chola dynasty, in the Southern India.

A 23.7-year long daily growth rate record of a modern giant clam shell from South China Sea and its potential in high-resolution paleoclimate reconstruction

Tridacna spp. usually have annual and even daily growth bands, and thus provide great potential to be the high-resolution recorders of past climate and environmental changes of the ocean. However, current studies mainly focus on the geochemical records of Tridacna shells, the environmental and climatic implications of long time sequenced daily growth increments are relatively unexplored. In this study, based on the confocal microscopic line-scanning imaging, a 23.7-year long (from 5 June 1989 to 21 February 2013) daily growth rate (DGR) record of Tridacna gigas shell MD3 from southern South China Sea was established and its climatic implication was investigated. On seasonal scale, significant positive correlation was found between the DGR and sea surface temperature (SST). The main growing season of T. gigas MD3 was from March to August, when sufficient sunlight and warmer SST prevailed. While high rainfall (low sunlight) from September to December and low SST from December to March hindered the growth of the shell in autumn and winter. On an inter-annual scale, the DGR of the shell varied periodically on timescales of 2–3 years and 4–5 years, which possibly represented the impacts of the Tropospheric Biennial Oscillation and El Niño-Southern Oscillation activities respectively. Our result suggested that the daily growth lines of T. gigas can establish an extraordinarily high-resolution chronology and have high potential to explore daily to inter-annual paleoenvironmental changes in tropical ocean. Compared with the paleoclimate reconstructions of geochemical approaches, this method has the advantages of low cost and short experimental time. • A modern Tridacna shell from southern SCS has clear daily growth bands. • 23.7-year long daily growth rate (DGR) profile was obtained. • Seasonal variation of the DGR was positively correlated with local SST. • DGR has potential to reconstruct daily to inter-annual paleoclimate changes. • DGR analysis is simpler, faster and less cost compared to geochemical approaches.

A Late Pleistocene high-resolution paleoclimate reconstruction: insights from the archaeobotanical assemblage and the carbon isotope analysis of wild almond (Amygdalus sp.) from Raqefet Cave, Mount Carmel, Israel

Raqefet Cave is located in southeast Mount Carmel, Israel. It contains a long archaeological sequence with two major occupations: in the early Upper Paleolithic (Levantine Aurignacian culture, ca. 36,000–35,000 cal. BP) and the Late Epipaleolithic (Natufian culture, ca. 14,000–12,000 cal. BP). Abundant charred remains were found in the cave's deposits consisting of various species. Drawing on Δ13C values of dated Amygdalus sp. (almond) charcoal specimens, we sought to reconstruct Late Pleistocene precipitation patterns from a high-resolution archaeological record. The results produced the longest, single-site, plant-based paleoclimatic sequence in the southern Levant, and they generally correspond to other paleoclimatic proxies generated for the region. They indicate that the plant taxa and reconstructed precipitation levels were all in the range of modern eastMediterranean climate but with some notable fluctuations. Specifically, we highlight the rainfall differences between the dryer Levantine Aurignacian and the wetter Natufian cultures.

Rainfall-driven and hydrologically-controlled variations in cave CO2 sources and dynamics: Evidence from monitoring soil CO2, stream flow and cave CO2

Speleothems are used as a promising proxy for high-resolution paleoclimate reconstruction. Partial pressures of CO2 (pCO2) is one of the most important factors in the processes of speleothem formation in caves. The objective of our study was to monitor the CO2 variations in the overlying soil, the cave air and the stream, and distinguish its sources and processes based on stable carbon isotopes in the Xueyu Cave system from October 2014 to February 2017. Overlying soil CO2 was influenced by soil temperature and soil moisture. The cave air pCO2 and equilibrium pCO2 in the stream water during two years showed very similar seasonal variations, fluctuating with high values in wet seasons and low values in dry seasons. The average δ13Csoil air value was −19.3 ± 0.8‰ and δ13Ccave air value was −18.8 ± 0.4‰ in November; while the average δ13Csoil air value was −23.9 ± 1.4‰ and δ13Ccave air value was −23.3 ± 0.3‰ in June. Moreover, the contribution from soil during the transitional ventilation (in November) was calculated based on the two end-members model of stable carbon isotopes. On the contrary, in wet season, cave air CO2 were mainly controlled by soil CO2 inputs. The total amount of C from stream degassing was calculated, which was higher in June than in November. High-resolution monitoring of cave air CO2 and its sources reveals the highly sensitive nature of CO2 dynamics within cave environments, and highlights its sensitivity to hydrological conditions in the cave system.

Evidence from giant-clam <i>δ</i><sup>18</sup>O of intense El Ninõ–Southern Oscillation-related variability but reduced frequency 3700 years ago

Abstract. Giant clams (Tridacna) are the largest marine bivalves, and their carbonate shells can be used for high-resolution paleoclimate reconstructions. In this contribution, δ18Oshell was used to estimate climatic variation in the Xisha Islands of the South China Sea. We first evaluate sea surface temperature (SST) and sea surface salinity (SSS) influence on the modern resampled monthly (r-monthly) resolution of Tridacna gigas δ18Oshell. The results obtained reveal that δ18Oshell seasonal variation is mainly controlled by SST and appears to be insensitive to local SSS change. Thus, the δ18O of Tridacna shells can be roughly used as a proxy of local SST: a 1 ‰ δ18Oshell change is roughly equal to 4.41 ∘C of SST. The r-monthly δ18O of a 40-year-old Tridacna squamosa (3673±28 BP) from the North Reef of the Xisha Islands was analyzed and compared with the modern specimen. The difference between the average δ18O of the fossil Tridacna shell (δ18O =-1.34 ‰) and the modern Tridacna specimen (δ18O =-1.15 ‰) probably implies a warm climate, roughly 0.84 ∘C, 3700 years ago. The seasonal variation 3700 years ago was slightly lower than that suggested by modern instrumental data, and the transition between warm and cold seasons was rapid. Higher amplitudes of reconstructed r-monthly and r-annual SST anomalies imply an enhanced climate variability during this warm period. Investigation of the El Ninõ–Southern Oscillation (ENSO) variation (based on the reconstructed SST series) indicates reduced ENSO frequency but increased ENSO-related variability and extreme El Ninõ winter events 3700 years ago.

Morphological variations of crossed-lamellar ultrastructures of Glycymeris bimaculata (Bivalvia) serve as a marine temperature proxy

Bivalve shells are among the most promising archives for high-resolution seawater temperature reconstructions. However, despite major research advances in bivalve sclerochronology over the past decades, estimating water temperature from shells remains a challenging task. This is largely because the most frequently used and widely accepted temperature proxy in bivalves, i.e., the shell oxygen isotope (δ18Oshell) value, also requires knowledge of changes in δ18O of the water (δ18Owater) in which the bivalve lived, which is rarely available for ancient environments. According to a few recent studies, the size and shape of individual biomineral units (BMUs) of the shell ultrastructure may serve as an independent temperature proxy that is also less vulnerable to diagenetic changes than isotope chemical proxies. However, the crossed-lamellar ultrastructure, which occurs in ca. 90% of all mollusk species, has hitherto not been investigated. Here, we evaluate the potential use of morphological properties of the BMUs in Glycymeris bimaculata as a proxy for water temperature. For this purpose we introduce a suitable preparation technique (immersion for 2 m in 0.001 vol% formic acid followed by 20–30 m in 3.5 vol% H2O2) and an automated image processing technique that tremendously speed up ultrastructure analysis (5 s versus one to 2 h image processing time with automated and manual methods, respectively) and increase the robustness of BMU measurements. Glycymeris is a particularly useful target taxon, because it is a cosmopolitan genus with evolutionary roots in the Upper Cretaceous, and some species of Glycymeris can attain a lifespan of more than two hundred years, which allows for long-term, high-resolution paleoclimate reconstructions. As in other previously studied ultrastructures, larger and more elongated BMUs formed in warmer water permitting temperature estimates with an error of 2.3 °C (1 σ). Since the new temperature proxy is unaffected by other environmental variables, including salinity, it can potentially be applied to (modern and fossil) specimens from brackish environments.

Oxygen stable isotopes of a network of shrubs and trees as high-resolution plaeoclimatic proxies in Northwestern China

Tree rings play an important role in high-resolution paleoclimate reconstruction over large areas. Nevertheless, the sampling sites of most existing tree-ring networks are unevenly distributed due to the limitations of the availability of appropriate tree species and sampling conditions. In light of the good spatial representation provided by tree-ring stable oxygen isotope ratio (δ18O), we selected several shrubs (Hippophae rhamnoides L.) found in near-glacier valleys, conifer (Picea crassifolia Komarov) trees in alpine meadows, and broad-leaved (Populus euphratica Olivier) trees found in deserts. Although the three sampling sites were each 250–360 km apart, with varied site conditions and very distinct species, we observed coherent variations in the δ18O of the three species within a common time interval. The average correlation coefficient was found to be 0.674 (p < 0.001, n = 30) among annual-ring δ18O series of three species. All annual-ring δ18O of three species demonstrated significant negative correlations with relative humidity (RH) and precipitation, and significant positive correlations with temperature, in spring and summer. The correlation coefficient between the first principal component (PC1) of the δ18O variations in the three species and the regional summer (June to August) RH was found to be −0.855 (p < 0.001, n = 30). In addition, PC1 showed variations similar to those of δ18O in precipitation. Spatial correlation demonstrated that PC1 represents the hydroclimatic variability that occurs in most of central-western China. Significant correlations with sea-level pressure and several East Asian Summer Monsoon indices indicated that PC1 was affected by the large-scale atmospheric circulation pattern and could be used as an indicator of monsoon moisture. PC1 correlated significantly with ten annually resolved hydroclimatic series in central-western China, demonstrating the potential of establishing a tree-ring climate network with uniform spatial distribution using multi-species tree-ring δ18O. The results from these series suggest that an abrupt climate change occurred in 1979. After 1979, PC1 correlated significantly with the summer-season EI Nino Modoki index (r = 0.474, p < 0.02, n = 24). This implied that the effect of the central Pacific ENSO on the variability in monsoon moisture in China became more prominent after the abrupt climate change in 1979.

Southern Hemisphere Sediments Show Surprising Pliocene Cyclicity

New, high-resolution paleoclimate reconstructions with 100,000-year rhythms may offer insights into how Earth’s climate system operated during a time when the planet was warmer than it is today.

(In)coherent multiproxy signals in marine sediments: Implications for high-resolution paleoclimate reconstruction

Accurate chronologies are the backbone of paleoclimate research, yet for marine sedimentary records the same age model is often applied to co-eval components that may have experienced different pre-depositional histories, leading to aliasing in corresponding proxy signals. Here we demonstrate 14C age discrepancies among several proxy carriers and use them to highlight spatio-temporal disparities among different components of the sediment. Total organic carbon (TOC), alkenones, and alkanoic (fatty) acids have older ages than co-occurring planktonic foraminifera in corresponding depth intervals of a sediment core retrieved from the so-called ‘Shackleton Sites’ on the southwest Iberian margin off Portugal. Temporal differences are explained by the addition of pre-aged material that is transported to the site by lateral advection, rivers or wind. We then modeled the age structure and relative abundance of the different pools that might have contributed to the older ages of TOC and alkenones. Results suggest the addition of a moderate (15-20%) proportion of very old allochthonous material (18,500-49,900 yr). This information was used to deconvolve the alkenone-derived sea surface temperature (SST) record and assess the impact of allochthonous inputs on paleoclimate signals.

A preliminary study on teak tree ring cellulose δ18O from northwestern Thailand: the potential for developing multiproxy records of Thailand summer monsoon variability

Thailand monsoon is located in the transition zone between the Indian and western North Pacific monsoons. Assuredly, proxy climate data from this area could improve our understanding of the nature of Asian monsoon. Tree rings and stalagmites from this area are two potential materials for high-resolution paleoclimate reconstructions. However, a comprehensive understanding of these multiproxy records is still a challenge. In this study, a 76-year tree ring cellulose oxygen isotope value (δ18O) of a teak tree from northwestern Thailand was developed to test its climatic significance and potential for multiproxy climate reconstruction. The results indicate that the interannual variability of cellulose δ18O can be interpreted as a proxy of rainfall in the early monsoon season (May to July rainfall) as well as a proxy of relative humidity. Comparisons with speleothem proxies from the same locality and tree ring records from wider geographical areas provide a basis for developing a multiproxy approach. The results from a teleconnection analysis reveal that the El Nino-Southern Oscillation (ENSO) is an important climate mode that impacts monsoon rainfall in Thailand. High-quality proxy records covering recent decades are critically important not only to improve proxy data calibrations but also to provide a better understanding of teleconnections within the modern atmosphere. Preliminary findings demonstrated the potential of tree ring stable isotopes from Thai teak to develop multiproxy climate reconstruction.

Unsaturated zone hydrology and cave drip discharge water response: Implications for speleothem paleoclimate record variability

Summary High-frequency, spatially-dense discharge monitoring was conducted over fifteen months to characterise unsaturated zone flow at Harrie Wood Cave (HWC), in the Snowy Mountains, Yarrangobilly (SE Australia). The cave was formed in the Late Silurian Yarrangobilly Limestone, a fractured rock associated with very low primary porosity due to past diagenesis. Over our monitoring period we simultaneously measured rainfall, soil moisture saturation and drip discharge rate at fourteen sites to characterise infiltration–discharge relationships. All drip discharge sites exhibited non-Gaussian distributions, indicating long periods where low discharge predominates, punctuated by short infrequent periods of high discharge. However, there was significant variability in discharge between sites and consequently no spatial correlation in the cave. We investigated the depth–discharge relationship at HWC and found a moderate relationship between depth and drip discharge lag (response) times to soil moisture content, but only weak relationships between depth and mean and maximum discharge. This highlights that the karst architecture plays an important role in controlling drip discharge dynamics. Principal Component Analysis (PCA) and Agglomerative Hierarchal Clustering (AHC) were used to classify similar drip types, revealing five unique drip regimes. Two-phase flow and non-linear response to recharge behaviour were observed, suggesting secondary porosity is controlling unsaturated zone flow in mature limestone environments with low primary porosity. Using the data presented here, the first coupled conceptual and box hydrological flow model was developed. This study highlights the heterogeneous nature of hydrological flow in karst and the need to understand unsaturated zone hydrology at the individual drip discharge level, to inform speleothem studies for high-resolution paleoclimate reconstruction.

A novel geochemical approach to paleorecords of dust deposition and effective humidity: 8500 years of peat accumulation at Store Mosse (the “Great Bog”), Sweden

Both bog surface wetness and atmospheric dust deposition are intricately linked to changes in the hydrological cycle and pairing these types of records at the same site provides complementary information. Here a peat core from Store Mosse in southern Sweden covering the last 8500 years was used to make a high-resolution paleoclimate reconstruction based on a combination of bog development, colourimetric humification and inorganic geochemistry data. The coupling of Principal Component Analysis with changepoint modelling allowed for precise linking of changes in bog surface wetness and dust deposition records.A long-term trend towards warm (and possibly wet) conditions starts ca 8150 cal yr BP and culminates with the most pronounced conditions from 6900 to 6600 cal yr BP. The most significant arid period at Store Mosse occurred between 6500 and 5600 cal yr BP during which dust deposition was significantly higher. Wetter conditions dominate from 5500 to 4980 cal yr BP as the transition from the Hypsithermal and into the Neoglacial is made. After a shift to drier conditions, humification enters a more stable period that lasts from 4525 until 3200 cal yr BP. It is during this time that the first possible anthropogenic dust signals occur at ca 4200 cal yr BP. From 3200 cal yr BP to present humification generally shows a long-term decline moving towards wetter conditions. The main exceptions are during the transition from the Neoglacial to Roman Warm Period which is registered as a significantly wetter period and two dry periods recorded 2365 to 2155 cal yr BP and 1275–1105 cal yr BP. In general, the observed changes agree well with regional records of effective humidity and temperature. The high temporal resolution of the Store Mosse record reveals that palaeoclimatic change over the last 8500 years in southern Sweden has had a complex and variable structure.

Proxy-to-proxy calibration: Increasing the temporal resolution of quantitative climate reconstructions

High-resolution paleoclimate reconstructions are often restricted by the difficulties of sampling geologic archives in great detail and the analytical costs of processing large numbers of samples. Using sediments from Lake Braya Sø, Greenland, we introduce a new method that provides a quantitative high-resolution paleoclimate record by combining measurements of the alkenone unsaturation index () with non-destructive scanning reflectance spectroscopic measurements in the visible range (VIS-RS). The proxy-to-proxy (PTP) method exploits two distinct calibrations: the in situ calibration of to lake water temperature and the calibration of scanning VIS-RS data to down core data. Using this approach, we produced a quantitative temperature record that is longer and has 5 times higher sampling resolution than the original time series, thereby allowing detection of temperature variability in frequency bands characteristic of the AMO over the past 7,000 years.

Pleistocene climate, phylogeny, and climate envelope models: an integrative approach to better understand species' response to climate change.

Mean annual temperature reported by the Intergovernmental Panel on Climate Change increases at least 1.1°C to 6.4°C over the next 90 years. In context, a change in climate of 6°C is approximately the difference between the mean annual temperature of the Last Glacial Maximum (LGM) and our current warm interglacial. Species have been responding to changing climate throughout Earth's history and their previous biological responses can inform our expectations for future climate change. Here we synthesize geological evidence in the form of stable oxygen isotopes, general circulation paleoclimate models, species' evolutionary relatedness, and species' geographic distributions. We use the stable oxygen isotope record to develop a series of temporally high-resolution paleoclimate reconstructions spanning the Middle Pleistocene to Recent, which we use to map ancestral climatic envelope reconstructions for North American rattlesnakes. A simple linear interpolation between current climate and a general circulation paleoclimate model of the LGM using stable oxygen isotope ratios provides good estimates of paleoclimate at other time periods. We use geologically informed rates of change derived from these reconstructions to predict magnitudes and rates of change in species' suitable habitat over the next century. Our approach to modeling the past suitable habitat of species is general and can be adopted by others. We use multiple lines of evidence of past climate (isotopes and climate models), phylogenetic topology (to correct the models for long-term changes in the suitable habitat of a species), and the fossil record, however sparse, to cross check the models. Our models indicate the annual rate of displacement in a clade of rattlesnakes over the next century will be 2 to 3 orders of magnitude greater (430-2,420 m/yr) than it has been on average for the past 320 ky (2.3 m/yr).

On linking climate to Chinese dynastic change: Spatial and temporal variations of monsoonal rain

The causal correlation or linkage between the East Asian Monsoon (EAM) intensity and rise/fall of Chinese dynasties recently proposed by high-resolution paleoclimate reconstructions is examined in detail. Aside from many exceptions to the correlation, both instrumental and historical climate records show strong spatial variations of rainfall on annual-to-decadal scales over eastern China. The relationship between rainfall and EAM intensity also exhibits regional disparity. These observations suggest: (1) Taking paleo-proxy records from a single locality in eastern China to imply changes in drought/wetness as to affect the cultural and political history of China is fraught with uncertainty. (2) On annual-to-decadal scales, the thesis that δ18O in speleothems can be used as a proxy for the EAM strength lacks empirical underpinnings.