Late Cenozoic Climate Change Research Articles

Accretion of the NW Himalayan foreland pre‐dates Late Cenozoic climate change

AbstractConceptual models demonstrate that climate can control the structural evolution of mountain belts and that Pliocene–Quaternary global climate change modulated Himalayan wedge behaviour. A key test of this hypothesis is the timing of foreland accretion. If foreland accretion pre‐dates climate change, then climate is not the primary driver of mountain building. New apatite (U–Th)/He data from NW Himalaya foreland thrust sheets suggest that accretion had occurred by the latest 4 Ma, prior to the Pliocene–Quaternary global climate change. Climate cannot, therefore, be invoked as the principal driver of Himalayan tectonics in the late Cenozoic.Statement of significanceThis paper presents 66 new, single grain apatite (U–Th)/He (AHe) dates from the foreland basin that constrain NW Himalayan evolution through the late Cenozoic. We show that accretion of the NW sub‐Himalayan foreland was underway by 4 Ma at the latest, several million years earlier than previous estimates, and was followed by distributed, wedge‐internal deformation by 2 Ma. These and other published data present a consistent pattern and timing of deformation observed over nearly 600 km of the NW sub‐Himalaya. Our new constraints on orogen evolution provide key insights into the relative importance of climate and tectonics in driving orogenic systems.

The effects of late Cenozoic climate change on the global distribution of frost cracking

Abstract. Frost cracking is a dominant mechanical weathering phenomenon facilitating the breakdown of bedrock in periglacial regions. Despite recent advances in understanding frost cracking processes, few studies have addressed how global climate change over the late Cenozoic may have impacted spatial variations in frost cracking intensity. In this study, we estimate global changes in frost cracking intensity (FCI) by segregation ice growth. Existing process-based models of FCI are applied in combination with soil thickness data from the Harmonized World Soil Database. Temporal and spatial variations in FCI are predicted using surface temperature changes obtained from ECHAM5 general circulation model simulations conducted for four different paleoclimate time slices. Time slices considered include pre-industrial (∼ 1850 CE, PI), mid-Holocene (∼ 6 ka, MH), Last Glacial Maximum (∼ 21 ka, LGM), and Pliocene (∼ 3 Ma, PLIO) times. Results indicate for all paleoclimate time slices that frost cracking was most prevalent (relative to PI times) in the middle- to high-latitude regions, as well as high-elevation lower-latitude areas such the Himalayas, Tibet, the European Alps, the Japanese Alps, the US Rocky Mountains, and the Andes Mountains. The smallest deviations in frost cracking (relative to PI conditions) were observed in the MH simulation, which yielded slightly higher FCI values in most of the areas. In contrast, larger deviations were observed in the simulations of the colder climate (LGM) and warmer climate (PLIO). Our results indicate that the impact of climate change on frost cracking was most severe during the PI–LGM period due to higher differences in temperatures and glaciation at higher latitudes. The PLIO results indicate low FCI in the Andes and higher values of FCI in Greenland and Canada due to the diminished extent of glaciation in the warmer PLIO climate.

Rapid diversification of the Australian Amitermes group during late Cenozoic climate change

Late Cenozoic climate change led to the progressive aridification of Australia over the past 15 million years. This gradual biome turnover fundamentally changed Australia's ecosystems, opening new niches and prompting diversification of plants and animals. One example are termites of the Australian Amitermes group (AAG), consisting of the Australian Amitermes and affiliated genera. Although the most speciose and diverse higher termite group in Australia, little is known about its evolutionary history. We used ancestral range reconstruction and diversification analyses to illuminate 1) phylogenetic relationships of the AAG, 2) biogeographical processes leading to the current continent‐wide distribution and 3) timing and pattern of diversification in the context of late Cenozoic climate change. By estimating the largest time‐calibrated phylogeny for this group to date, we demonstrate monophyly of the AAG and confirm that their ancestor arrived in Australia ~11–10 million years ago (Mya) from Southeast Asia. Ancestral range reconstruction indicates that Australia's monsoon region was the launching point for a continental radiation shaped by dispersal and within‐biome speciation rather than vicariance. We found that multiple arid‐zone species diversified from mesic and tropical ancestors in the Plio‐Pleistocene, but also observed diversification in the opposite direction. Finally, we show that diversification steadily increased from ~8 to 9 Mya during the ‘Hill Gap' and accelerated from ~4 Mya in concert with major ecological change during the Pliocene. Consistent with rapid diversification, species accumulation then slowed down into the present, likely caused by progressive niche saturation. This study provides a stepping stone for predicting future responses of Australia's termite fauna in the face of human‐mediated climate change.

Fingerprints of climatic changes through the late Cenozoic in southern Asian flora: Magnolia section Michelia (Magnoliaceae).

Ongoing global warming is a challenge for humankind. A series of drastic climatic changes have been proven to have occurred throughout the Cenozoic based on a variety of geological evidence, which helps to better understand our planet's future climate. Notably, extant biomes have recorded drastic environmental shifts. The climate in southern Asia, which hosts high biodiversity, is deeply impacted by the Asian monsoon. The origins and evolutionary dynamics of biomes occurring between the tropics and sub-tropics in southern Asia have probably been deeply impacted by climatic changes; however, these aspects remain poorly studied. We tested whether the evolutionary dynamics of the above biomes have recorded the drastic, late Cenozoic environmental shifts, by focusing on Magnolia section Michelia of the family Magnoliaceae. We established a fine time-calibrated phylogeny of M. section Michelia based on complete plastid genomes and inferred its ancestral ranges. Finally, we estimated the evolutionary dynamics of this section through time, determining its diversification rate and the dispersal events that occurred between tropical and sub-tropical areas. The tropical origin of M. section Michelia was dated to the late Oligocene; however, the diversification of its core group (i.e. M. section Michelia subsection Michelia) has occurred mainly from the late Miocene onward. Two key evolutionary shifts (dated approx. 8 and approx. 3 million years ago, respectively) were identified, each of them probably in response to drastic climatic changes. Here, we inferred the underlying evolutionary dynamics of biomes in southern Asia, which probably reflect late Cenozoic climatic changes. The occurrence of modern Asian monsoons was probably fundamental for the origin of M. section Michelia; moreover, the occurrence of asymmetric dispersal events between the tropics and sub-tropics hint at an adaptation strategy of M. section Michelia to global cooling, in agreement with the tropical conservatism hypothesis.

Late Cenozoic climate change paces landscape adjustments to Yukon River capture

Late Cenozoic cooling and changes in glacial–interglacial cycle tempo are thought to increase global rates of erosion starting ~3 million years ago (Ma). Bedrock rivers set rates and patterns of erosion in most landscapes, but constraints on river response to late Cenozoic climate change remain elusive. Here, we determine cosmogenic isotope and luminescence ages of well-preserved bedrock terraces along the Fortymile River (Yukon River basin) to reconstruct an ~5 Myr history of fluvial adjustment to late Cenozoic climate and Yukon River headwater capture at 2.6 Ma. Post-capture Yukon River downcutting lowered the Fortymile River outlet, forcing subsequent bedrock incision throughout the Fortymile basin in two pulses, from 2.4 to 1.8 Ma and at ~1 Ma. These pulses of incision disrupted longer intervals of slow river channel sedimentation under near-consistent climate forcing from 4.8 to 2.4 Ma and from 1.8 to ~1 Ma. The Fortymile River delivers sediment to the Bering Sea, where provenance and accumulation rate changes since 4.3 Ma match observed variations in incision. Our results link alluviation and incision to late Cenozoic climate steadiness and change, respectively, and support the hypothesis that climate-forced changes in precipitation and runoff fundamentally control the pace of river incision and landscape erosion. Increased river incision and landscape erosion can be attributed to late Cenozoic cooling/changes in hydroclimate, according to cosmogenic isotope and luminescence ages of a sequence of bedrock terraces in the Yukon River basin.

A Late Miocene to Late Pleistocene Reconstruction of Precipitation Isotopes and Climate From Hydrated Volcanic Glass Shards and Biomarkers in Central Alaska and Yukon

AbstractThe Pliocene (5.3–2.6 Ma), an epoch with periods of climatic warmth and possible analogue for the future, has been well‐characterized globally by marine geochemical proxies. However, far less is known about Pliocene warmth at continental high latitudes, where the greatest impacts of warming are expected. This study seeks to better characterize the Pliocene climate of central Alaska and Yukon based on a reconstruction of the stable hydrogen isotope composition of precipitation relative to modern (ΔδDprecip) preserved in volcanic glass shards, a proxy for mean air temperature. The studied tephras are from a regional suite of outcrops that, when assembled into a composite record of ΔδDprecip, can be used to resolve broad trends during the late Miocene (6.7–5.86 Ma, n = 5), Pliocene (5.08–2.81 Ma, n = 7), and late Pleistocene (0.74–0.03 Ma, n = 3). These trends indicate that Pliocene ΔδDprecip estimates were generally more enriched in heavy isotopes than the latest Miocene, Pleistocene, and modern intervals. ΔδDprecip is likely influenced by changes in regional boundary conditions including orographic barriers, depositional environments, and ocean‐atmospheric circulation, but ΔδDprecip trends are most consistent with reconstructed temperatures from Yukon‐Alaska and North Pacific marine records. As such, this record appears predominantly sensitive to regional climate. Furthermore, qualitative temperature inferences from branched‐chain glycerol dialkyl glycerol tetraethers (brGDGTs) from four of our sites dating between 2.91 and 6.17 Ma corroborate elevated temperatures during the early Pliocene. Overall, this study demonstrates the viability of volcanic glass δD as a proxy for ΔδDprecip and late Cenozoic climate change in this region.

Steady erosion rates in the Himalayas through late Cenozoic climatic changes

Sediment accumulation rates and thermal trackers suggest a substantial and global increase in erosion rates over the past few million years. That increase is commonly associated with the impact of the Northern Hemisphere glaciation, but methodological biases have led researchers to debate this hypothesis. Here, we test whether Himalayan erosion rates increased by measuring beryllium-10 (10Be) in the sediment of the Bengal Bay seabed. Sediment originated from rocks that produced 10Be under the impact of cosmic rays during erosion near surface. Thus, the 10Be concentrations indicate erosion rates. The 10Be concentration of the Bengal Bay sediment depends on the contributions of the Ganga and Brahmaputra rivers. Their sediments have distinct 10Be concentrations because of distinct elevations and erosion in their drainage basins. Variable contributions could thus complicate erosion-rate calculation. We traced these contributions by a provenance study using the strontium (Sr) and neodymium (Nd) isotopic sediment compositions. Within uncertainties of ±30%, our reconstructed past erosion rates show no long-term increase for the past six million years. This stability suggests that climatic changes during the late Cenozoic have an undetectable impact on the erosion patterns in the Himalayas, at least on the ten thousand to million year timescales accounted for by our dataset. Long-term Himalayan erosion rates remained stable through the global climatic changes of the past six million years, according to the cosmogenic nuclide composition of terrestrial sediments recovered from the Bay of Bengal.

Spatial correlation bias in late-Cenozoic erosion histories derived from thermochronology.

The potential link between erosion rates at the Earth's surface and changes in global climate has intrigued geoscientists for decades1,2 because such a coupling has implications for the influence of silicate weathering3,4 and organic-carbon burial5 on climate and for the role of Quaternary glaciations in landscape evolution1,6. A global increase in late-Cenozoic erosion rates in response to a cooling, more variable climate has been proposed on the basis of worldwide sedimentation rates7. Other studies have indicated, however, that global erosion rates may have remained steady, suggesting that the reported increases in sediment-accumulation rates are due to preservation biases, depositional hiatuses and varying measurement intervals8-10. More recently, a global compilation of thermochronology data has been used to infer a nearly twofold increase in the erosion rate in mountainous landscapes over late-Cenozoic times6. It has been contended that this result is free of the biases that affect sedimentary records11, although others have argued that it contains biases related to how thermochronological data are averaged12 and to erosion hiatuses in glaciated landscapes13. Here we investigate the 30 locations with reported accelerated erosion during the late Cenozoic6. Our analysis shows that in 23 of these locations, the reported increases are a result of a spatial correlation bias-that is, combining data with disparate exhumation histories, thereby converting spatial erosion-rate variations into temporal increases. In four locations, the increases can be explained by changes in tectonic boundary conditions. In three cases, climatically induced accelerations are recorded, driven by localized glacial valley incision. Our findings suggest that thermochronology data currently have insufficient resolution to assess whether late-Cenozoic climate change affected erosion rates on a global scale. We suggest that a synthesis of local findings that include location-specific information may help to further investigate drivers of global erosion rates.

Estimates of late Cenozoic climate change relevant to Earth surface processes in tectonically active orogens

Abstract. The denudation history of active orogens is often interpreted in the context of modern climate gradients. Here we address the validity of this approach and ask what are the spatial and temporal variations in palaeoclimate for a latitudinally diverse range of active orogens? We do this using high-resolution (T159, ca. 80 × 80 km at the Equator) palaeoclimate simulations from the ECHAM5 global atmospheric general circulation model and a statistical cluster analysis of climate over different orogens (Andes, Himalayas, SE Alaska, Pacific NW USA). Time periods and boundary conditions considered include the Pliocene (PLIO, ∼ 3 Ma), the Last Glacial Maximum (LGM, ∼ 21 ka), mid-Holocene (MH, ∼ 6 ka), and pre-industrial (PI, reference year 1850). The regional simulated climates of each orogen are described by means of cluster analyses based on the variability in precipitation, 2 m air temperature, the intra-annual amplitude of these values, and monsoonal wind speeds where appropriate. Results indicate the largest differences in the PI climate existed for the LGM and PLIO climates in the form of widespread cooling and reduced precipitation in the LGM and warming and enhanced precipitation during the PLIO. The LGM climate shows the largest deviation in annual precipitation from the PI climate and shows enhanced precipitation in the temperate Andes and coastal regions for both SE Alaska and the US Pacific Northwest. Furthermore, LGM precipitation is reduced in the western Himalayas and enhanced in the eastern Himalayas, resulting in a shift of the wettest regional climates eastward along the orogen. The cluster-analysis results also suggest more climatic variability across latitudes east of the Andes in the PLIO climate than in other time slice experiments conducted here. Taken together, these results highlight significant changes in late Cenozoic regional climatology over the last ∼ 3 Myr. Comparison of simulated climate with proxy-based reconstructions for the MH and LGM reveal satisfactory to good performance of the model in reproducing precipitation changes, although in some cases discrepancies between neighbouring proxy observations highlight contradictions between proxy observations themselves. Finally, we document regions where the largest magnitudes of late Cenozoic changes in precipitation and temperature occur and offer the highest potential for future observational studies that quantify the impact of climate change on denudation and weathering rates.

The Sawqirah contourite drift system in the Arabian Sea (NW Indian Ocean): A case study of interactions between margin reactivation and contouritic processes

The relationships between oceanic circulation in the Arabian Sea and Late Cenozoic climate changes, including variations in monsoon intensity at the million year time-scale, remain poorly investigated. Using multibeam and seismic data, we provide the first description of a contourite drift in the Arabian Sea, along the south-eastern Oman margin. This contourite drift is referred as the “Sawqirah Contourite Drift System”. Late Miocene reactivation of the south-eastern Oman margin resulted in the formation of a complex anticline system, which shaped the seafloor topography above which the Sawqirah Drift subsequently developed. The drift resulted from the circulation of bottom currents within the North Intermediate Indian Water. Major seismic unconformities identified within the Sawqirah Drift were tied to Ocean Drilling Program (ODP) drill holes, and allowed defining distinct episodes of drift construction. At least two of these unconformities record reorganizations of the oceanic circulation at ~4.5–4.8Ma and ~2.4Ma. The 4.5–4.8Ma-old unconformity is coeval with the onset of upwelling of deep and cold waters in the Owen Basin. The 2.4Ma-old unconformity records a major episode of Indian monsoon intensification (at the million year time scale) over the Arabian Sea, indicating strong coupling between oceanic and atmospheric circulation processes.

Late Cenozoic climate and the phylogenetic structure of regional conifer floras world‐wide

AbstractAimUsing conifers as a model system, we aim to test four hypotheses. H1: the processes that shape the phylogenetic structure of regional species assemblages depend on climate. H2: apparent effects of current climate can be equally well explained by past climate. H3: strong Quaternary climate oscillations have led to phylogenetically non‐random assemblages, either with few closely related species because isolated populations do not persist long enough to become new species or with many close relatives due to increased allopatric speciation. H4: strong late Cenozoic aridification has led to assemblages with many close relatives due to extinction and adaptive radiation.LocationGlobal.MethodsWe used boosted regression trees to relate the net relatedness index (NRI) of regional conifer assemblages to current climate, past climate (0.021, 3 and 7.3–11.6 Ma), and gradual and cyclic late Cenozoic climate change while simultaneously accounting for habitat and biogeographic covariates.ResultsClimate was the most important predictor of NRI, supporting H1. Current and past climate showed similar relationships with NRI, supporting H2. Conifer NRI was further related to Quaternary climate oscillations and gradual late Cenozoic climate trends, but the shape of the relationships supported neither H3 nor H4.Main conclusionsThe climate–NRI relationships suggest that late Cenozoic climate consistently influenced the dynamics of conifer speciation, extinction and dispersal, leading to global patterns of phylogenetic assemblage structure. We deduce from the phylogenetic structure that diversification has been highest in warm or dry climates over the last ≥11.6 Myr. The fact that phylogenetic structure is related to climate trends and oscillations indicates that climate change plays an important role in addition to climate per se, but the exact underlying mechanisms remain unclear. Our results suggest that past climate needs to be taken into account when aiming to explain the phylogenetic structure of regional assemblages and other related aspects of biodiversity.

Climate-driven extinctions shape the phylogenetic structure of temperate tree floras.

When taxa go extinct, unique evolutionary history is lost. If extinction is selective, and the intrinsic vulnerabilities of taxa show phylogenetic signal, more evolutionary history may be lost than expected under random extinction. Under what conditions this occurs is insufficiently known. We show that late Cenozoic climate change induced phylogenetically selective regional extinction of northern temperate trees because of phylogenetic signal in cold tolerance, leading to significantly and substantially larger than random losses of phylogenetic diversity (PD). The surviving floras in regions that experienced stronger extinction are phylogenetically more clustered, indicating that non-random losses of PD are of increasing concern with increasing extinction severity. Using simulations, we show that a simple threshold model of survival given a physiological trait with phylogenetic signal reproduces our findings. Our results send a strong warning that we may expect future assemblages to be phylogenetically and possibly functionally depauperate if anthropogenic climate change affects taxa similarly.

Holocene book review: Late Cenozoic Climate Change in Asia: Loess, Monsoon and Monsoon-Arid Environment Evolution

Holocene book review: Late Cenozoic Climate Change in Asia: Loess, Monsoon and Monsoon-Arid Environment Evolution

Plio-Pleistocene evolution of the north Alpine drainage system: new constraints from detrital thermochronology of foreland deposits

The evolution of drainage systems in and around active orogens may be strongly affected by climatic or tectonic processes. Information on the drainage evolution is stored in the sediments of the foreland depocentres. We investigated the provenance of two key deposits adjacent to the Central Alps, the Pliocene Sundgau gravels and the Pleistocene Hohere Deckenschotter by applying detrital thermochronology. Combined with provenance information from Rhine Graben deposits, we propose a reconstruction of the north Alpine drainage system since the middle Pliocene and discuss potential controlling mechanisms. Our data show that the Rhine Graben received detritus from the Alpine realm already during the Pliocene, indicating two different river systems—the proto-Rhine and the Aare–Doubs—draining the Alpine realm toward the North Sea and Mediterranean Sea. The investigated sediments contain detritus from two central Alpine sources, one showing a regional exhumational equilibrium and the other characterized by increasing exhumation rates. Discharge of the latter source ceased after ~2 Ma, reflecting a northward shift of the main Alpine drainage divide. Between ~2.0 and 1.2 Ma, the drainage system was affected by a major change, which we explain as resulting from a change in the Alpine stress field leading to tectonic exhumation and topography reduction in the area of the southern Aar massif. Generally, it seems that between ~4 and 1.2 Ma, the drainage system was mainly controlled by tectonic processes, despite first glaciations that already affected the north-Alpine foreland by ~2 Ma. The drainage system only seems to have reacted to the late Cenozoic climate changes after ~1.2 Ma, i.e., at the time of the most intense Alpine glaciation. At that time, the course of the Rhine River shifted toward the area of the Hegau volcanics, and the size of the Rhine River catchment became strongly reduced.

Plio-Pleistocene fossil record of large predators in Iberia: Diversity, home range and climatic change

We investigated the patterns of change in diversity and home range-size structure of the latest Miocene–Pleistocene Iberian carnivores to recognize the tempo and mode of the major shifts, and place them in the context of late Cenozoic climatic changes. The database consists of 36 selected and taxonomically revised faunal lists. A general pattern of carnivore diversity from Iberia shows three maxima in diversity that can be correlated with major global changes. The first coincides with the glacial trend during Pliocene, starting at 2.7–2.6Ma, with the onset of glacial cycles of 41ka; second maximum happened at the beginning of the Middle Pleistocene and can be correlated with the switch at 1Ma; third maximum in diversity occurs at the end of Middle Pleistocene, when the amplitude of interglacials shifted from cooler to warmer interglacials. The most significant shifts in Carnivora diversity and home range-size patterns were linked to dispersal phases that were tracked by a renovation of the carnivore guild. From the patterns in home range-size structure it seems that some multifaceted, and not always straight, interactions exist between ecological and climatic change and shifts in home range-size. The onset of the Holocene home range-size structure in Iberian carnivores traces back to a high diversity pulse at the end of the Middle Pleistocene.

Late Miocene erosion and evolution of topography along the western slope of the Colorado Rockies

In the Colorado Rocky Mountains, the association of high topography and low seismic velocity in the underlying mantle suggests that recent changes in lithospheric buoyancy may have been associated with surface uplift of the range. This paper examines the relationships among late Cenozoic fluvial incision, channel steepness, and mantle velocity domains along the western slope of the northern Colorado Rockies. New 40 Ar/ 39 Ar ages on basalts capping the Tertiary Browns Park Formation range from ca. 11 to 6 Ma and provide markers from which we reconstruct incision along the White, Yampa, and Little Snake rivers. The magnitude of post–10 Ma incision varies systematically from north to south, increasing from ∼500 m along the Little Snake River to ∼1500 m along the Colorado River. Spatial variations in the amount of late Cenozoic incision are matched by metrics of channel steepness; the upper Colorado River and its tributaries (e.g., Gunnison and Dolores rivers) are two to three times steeper than the Yampa and White rivers, and these variations are independent of both discharge and lithologic substrate. The coincidence of steep river profiles with deep incision suggests that the fluvial systems are dynamically adjusting to an external forcing but is not readily explained by a putative increase in erosivity associated with late Cenozoic climate change. Rather, channel steepness correlates with the position of the channels relative to low-velocity mantle. We suggest that the history of late Miocene–present incision and channel adjustment reflects long-wavelength tilting across the western slope of the Rocky Mountains.

Desert landscape processes on a timescale of millions of years, probed by cosmogenic nuclides

Abstract Since their inception, cosmogenic nuclide methods have enhanced our understanding of Earth’s surface processes by providing a basis for directly determining surface exposure times and erosion rates of landscape elements. The ability to measure exposure ages up to several million years and erosion rates as low as a decimetre per million years means that the method is particularly useful for environments where landscapes change very slowly, such as deserts in tectonically stable regions. In this paper, we review cosmogenic nuclide studies of various aspects of desert landscapes, including regional to continental-scale landscape evolution in arid–semiarid Australia and the hyper-arid Namib, Atacama and Negev Deserts, together with mechanisms and timescales of formation of desert pavements and dune fields that have been difficult to be evaluated by other methods. The timescales revealed by these studies range beyond the Quaternary into the Miocene, and provide links between desert landscapes and late Cenozoic climate changes.

Active crustal deformation beyond the SE margin of the Tibetan Plateau: Constraints from the evolution of fluvial systems

An integrated explanation is proposed for the Late Cenozoic crustal deformation in Yunnan, SW China, using sedimentary and geomorphological evidence from the Yangtze and Red River systems. The observed fluvial incision indicates up to ~ 15 km of crustal thickening, associated with ~ 3 km of uplift, apparently triggered at ~ 8 Ma by monsoon-induced erosion drawing mobile lower crust from beneath Tibet to the northwest. The mobile lower-crustal layer beneath Yunnan was initially very thin, but a positive feedback loop developed, whereby each incremental influx of lower-crust widened and heated this layer, facilitating the next increment. At ~ 5 Ma, the shear tractions exerted on the brittle upper-crust by this flowing lower crust became sufficient to reactivate pre-existing lines of weakness, dragging blocks of the brittle layer southward and creating the region′s modern active fault systems. This region thus provides a dramatic example of crustal deformation induced by Late Cenozoic climate change, notwithstanding its location adjoining the India–Eurasia plate boundary.

Optical dating of abrupt shifts in the late Pleistocene East Asian monsoon

Chinese loess is regarded as one of the most detailed and complete terrestrial archives of late Cenozoic climate change. However, high-resolution optically stimulated luminescence (OSL) dates presented here reveal that the suborbital chronological framework of Chinese loess used in many previous climate reconstructions requires reassessment. Chronological uncertainty of as much as 10–15 k.y. for the late Pleistocene is largely a result of the widespread use of nonradiometric dating techniques that fail to account for site-specific depositional conditions associated with loess emplacement and diagenesis. OSL-based age models that account for these processes are used to examine detailed records of past sedimentation, as well as grain size and magnetic susceptibility proxies for late Pleistocene East Asian monsoon variation. Abrupt shifts in monsoon proxies occur over 10 2 –10 3 yr time scales, potentially forced by a variety of factors and influenced by site location and site-specific changes in sedimentation.

Late Cenozoic climate changes in China's western interior: a review of research on Lake Qinghai and comparison with other records

We review Late Cenozoic climate and environment changes in the western interior of China with an emphasis on lacustrine records from Lake Qinghai. Widespread deposition of red clay in the marginal basins of the Tibetan Plateau indicates that the Asian monsoon system was initially established by ∼8 Ma, when the plateau reached a threshold altitude. Subsequent strengthening of the winter monsoon, along with the establishment of the Northern Hemisphere ice sheets, reflects a long-term trend of global cooling. The few cores from the Tibetan Plateau that reach back a million years suggest that they record the mid-Pleistocene transition from glacial cycles dominated by 41 ka cycles to those dominated by 100 ka cycles. During Terminations I and II, strengthening of the summer monsoon in China's interior was delayed compared with sea level and insolation records, and it did not reach the western Tibetan Plateau and the Tarim Basin. Lacustrine carbonate δ 18O records reveal no climatic anomaly during MIS3, so that high terraces interpreted as evidence for extremely high lake levels during MIS3 remain an enigma. Following the Last Glacial Maximum (LSM), several lines of evidence from Lake Qinghai and elsewhere point to an initial warming of regional climate about 14 500 cal yr BP, which was followed by a brief cold reversal, possibly corresponding to the Younger Dryas event in the North Atlantic region. Maximum warming occurred about 10 000 cal yr BP, accompanied by increased monsoon precipitation in the eastern Tibetan Plateau. Superimposed on this general pattern are small-amplitude, centennial-scale oscillations during the Holocene. Warmer than present climate conditions terminated about 4000 cal yr BP. Progressive lowering of the water level in Lake Qinghai during the last half century is mainly a result of negative precipitation–evaporation balance within the context of global warming.