Monsoon Proxies Research Articles

North Atlantic Influence on the Glacial Amplitude of East Asian Millennial-Scale Monsoon Variability

Abstract Millennial-scale climate change is thought to be synchronous throughout the Northern Hemisphere and has been demonstrated to be strongly modulated by longer-term glacial–interglacial and orbital-scale processes. However, processes that modulate the magnitude of millennial-scale variability (MMV) at the glacial–interglacial time scale remain unclear. We present multiproxy evidence showing out-of-phase relationships between the MMV of East Asian and North Atlantic climate proxies at the eccentricity band. During most late Pleistocene glacial intervals, the MMV in North Atlantic SST and East Asian monsoon (EAM) proxies shows a gradual weakening trend from glacial inceptions into glacial maxima, inversely proportional to that of the North Atlantic ice-rafted detritus record. The inverse glacial age trends apply to both summer and winter monsoon proxies across the loess, speleothem, and marine archives, indicating fundamental linkages between MMV records of the North Atlantic and East Asia. We infer that intensified glacial age iceberg discharge is accompanied by weakened Atlantic meridional overturning circulation via changes in freshwater input and water column stability, leading to a reduction in North Atlantic SST and wind anomalies, subsequently propagating dampened millennial-scale variability into the midlatitude East Asian monsoon region via the westerlies. Our results indicate that the impact of North Atlantic iceberg discharge and the associated variability in water column stability at the millennial scale is a primary influence on hydroclimate instability in East Asia.

Obliquity-paced summer monsoon from the Shilou red clay section on the eastern Chinese Loess Plateau

Abstract The red clay of the Chinese Loess Plateau (CLP) is an important geological archive for understanding the variability in the late Neogene East Asian monsoon. The periodicity of the summer monsoon of the red clay on the eastern CLP is dominated by eccentricity cycles within the constraints of the palaeomagnetic chronological framework, whereas global climate change characteristics represented by the deep-sea oxygen isotope record at that time show a dominating obliquity cycle. Here, we analyzed the East Asian summer monsoon proxies from the Shilou red clay section with the cyclostratigraphy method. The results show that the summer monsoon variation was dominated by obliquity, the optimum deposition rate was 4.451 cm/kyr, and the floating age of the Shilou red clay section was ca. 1.7 Ma. The late Neogene East Asian summer monsoon inferred from the eastern CLP was thus paced by the obliquity cycle, which is consistent with global change.

High‐Resolution, Multiproxy Speleothem Record of the 8.2 ka Event From Mainland Southeast Asia

AbstractThe 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.

Variability of indian monsoon and its forcing mechanisms since late quaternary

The Indian monsoon is an important part of the global monsoon system, allowing important transfers of moisture at a large geographical scale and deeply affecting human populations and economic prosperity of regions. The tropical summer monsoon in the Northern Hemisphere is generally considered to be driven by low latitude solar radiation. Therefore, the summer monsoon strength is near zero-phase to the maximum of Northern Hemisphere Summer Insolation (NHSI). However, records from the Arabian Sea and some other parts of the Indian Ocean (e.g., Andaman Sea) show that a ∼8 kyr phase difference exists between the Indian summer monsoon (ISM) strength and the northern Hemisphere Summer Insolation maxima, which is obviously different from the records of stalagmites in the East Asia and other marine sediments (e.g., Bay of Bengal). This leads to the “sea-land precession phase paradox” in indian summer monsoon research. This paper systematically summarizes the Indian monsoon variability on orbital scale indicated by various records from the Indian monsoon regions (including oceans and continents) since the late Quaternary. The orbital forcing of Indian monsoon, the potential phase difference between indian summer monsoon and northern Hemisphere Summer Insolation and its possible forcing mechanism(s) are further discussed. The observed phase lag between indian summer monsoon and northern Hemisphere Summer Insolation may be controlled by the Atlantic Meridional Overturning Circulation (AMOC), latent heat transfer between the southern Indian Ocean and the Asian continent, or caused by the lack of tightly coupling between the Arabian Sea summer monsoon proxies and the monsoon intensity. In addition, it is still unclear whether previous monsoon proxies can provide a strong constraint on the intensity of summer monsoon. Environmental magnetism has been widely used in high-resolution dating and the analysis of paleoclimate variabilities in marine and terrestrial sediments, due to its high sensitivity on the rainfall and temperature. Therefore, in order to solve these issues, it is necessary to combine magnetic parameters with geochemical and paleontological parameters for more systematic work in the future.

Indian monsoon wind variability since ~11 kyr in the northwestern and northeastern Arabian Sea

• We studied varying monsoon wind stress in the Arabian Sea during the Holocene . • Surface productivity was high during the early Holocene . • Summer monsoon was weak and winter monsoon was strong in the middle Holocene. • Monsoon winds show high spatial variability in strength in the Arabian Sea. In this paper, we use planktic foraminifera and mixed-layer species from cores SK-240/327, SK-243/I- and ABP-25/03, northeastern Arabian Sea to investigate monsoon wind variability. Planktic foraminifera include Globigerina bulloides, a monsoon proxy and mixed-layer species Globigerinoides ruber, Gs. sacculifer, Gs. obliquus and Gs. extremus from cores SK-240/327, SK-243/I-1 and ABP-25/03 encompassing last ~11 calibrated kilo years before the Present (~11 cal kyr BP). The population abundances of Globigerina bulloides and mixed-layer species were compared with published Globigerina bulloides percentages from the western Arabian Sea Ocean Drilling Program Holes 723A, 724B and 727B, and eastern Arabian Sea core ABP-25, 02 to understand variations in Indian monsoon winds during the Holocene. In the eastern Arabian Sea, upwelling induced productivity was higher during 10–6.5 cal kyr BP which decreased during 6.5–3 cal kyr BP. In the northwestern Arabian Sea, we observe a similar scenario but not every site captured this change owing to spatial diverseness in monsoon wind stress. The productivity increased since 3 cal kyr BP due to intense summer monsoon winds in the northeastern Arabian Sea, whereas productivity began to increase at ~1.5 cal kyr BP in the northwestern Arabian Sea. The upwelling intensity shows large spatial and temporal variations in the eastern and western Arabian Sea, indicating varying monsoon wind strength across the Arabian Sea during the Holocene. The spectral analysis performed on Globigerina bulloides shows cyclicity which is associated with solar variability during the past 11 kyr record in the northeastern Arabian Sea.

Chinese loess and the Asian monsoon: What we know and what remains unknown

The variability and dynamics of the Asian monsoon (AM, hereafter indicates both of the summer and winter monsoons.) at orbital and millennial timescales has attracted wide interest. Chinese loess deposits, covering an area of ~500 × 103 km2 and with a thickness of several tens to more than three hundred meters, is an ideal continental archive to reconstruct AM variations during the Quaternary epoch. Over the past thirty years, since the earliest paper published in an international journal that linked the Asian monsoon and Chinese loess deposits, many studies have been undertaken focusing on this research topic. These results have greatly deepened our understanding of the variations of the AM climate and their driving mechanisms during the past ~2.6 Myr. In this paper, we emphasize recent progress on the AM variability and dynamics revealed by Chinese loess records; in particular, we discuss the reliability and precision of the timescale and the monsoon proxy indicators for the loess-paleosol sequences, which are two fundamental aspects for understanding AM behavior. We analyze what we know and discuss what we do not know about the AM. We refine the timescale for the typical loess-paleosol sequence in the central Chinese Loess Plateau (CLP), which can be used as a new timescale to study palaeoclimate and palaeoenvironmental changes in the monsoonal Asia. We conclude that low-latitude insolation changes induced by precession, and global ice volume, temperature at high-latitudes, as well as sea-level changes forced variations of the AM at orbital time scales. High-latitude cooling events and low-latitude hydroclimate process at millennial time scales, such as climate changes associated with Heinrich events and Dansgaard-Oeschger cycles in Northern Atlantic and Greenland, have also modulated AM variability. We suggest that high-latitude forcing of AM variations occurs through ocean and atmospheric circulation linkages, although the roles of atmospheric CO2, ocean and vegetation feedbacks need further investigation. In future study, high-resolution independent dating, novel proxy indices and transient numerical simulations are still basic tools to understand the loess deposition and AM variations that require considerably more work. Issues such as reliable spatial comparison and regional linkages of records (dependent on precise and accurate numerical chronologies), and quantitative reconstruction of the AM variations, should be given priority in the study the past climate change in Asia, and low-latitude hydroclimate process.

Vegetation feedback causes delayed ecosystem response to East Asian Summer Monsoon Rainfall during the Holocene

One long-standing issue in the paleoclimate records is whether East Asian Summer Monsoon peaked in the early Holocene or mid-Holocene. Here, combining a set of transient earth system model simulations with proxy records, we propose that, over northern China, monsoon rainfall peaked in the early Holocene, while soil moisture and tree cover peaked in the mid-Holocene. The delayed ecosystem (soil moisture and tree cover) response to rainfall is caused by the vegetation response to winter warming and the subsequent feedback with soil moisture. Our study provides a mechanism for reconciling different evolution behaviors of monsoon proxy records; it sheds light on the driving mechanism of the monsoon evolution and monsoon-ecosystem feedback over northern China, with implications to climate changes in other high climate sensitivity regions over the globe.

A 5000-Year Sedimentary Record of East Asian Winter Monsoon from the Northern Muddy Area of the East China Sea

The variability of the winter monsoon is one of the key components of the Asian monsoon, significantly influencing paleoenvironmental evolution in East Asia. However, whether the winter or the summer monsoon is the dominated factor controlling sedimentary dynamics of the muddy areas of the continental shelves of the East China Sea is debated, due to lack of consistency between various winter monsoon proxies in previous studies. In this work, the sediments of the upper part of core ECS-DZ1 with several marine surface samples were studied in terms of sediment grain size and radiocarbon dating, and changes in sedimentary dynamics of the northern muddy area of the ECS over the past 5000 years were documented. The main findings are as follows: (1) regional sedimentary dynamics were low and did not significantly change since the middle Holocene; (2) coarse particles are the dominated component in the sediments; (3) a proxy can be derived to indicate changes in winter monsoon. Based on this reconstructed winter monsoon record, we found that this record was generally negatively correlated to the stalagmite-based summer monsoon variability over the past 3500 years, but positively correlated before that. Moreover, this record can be well correlated to changes in the Kuroshio Current and the Bond ice-rafting debris events in the North Atlantic on millennial timescales, inferring large-scale and common atmospheric dynamics across the Asian continent over the past 5000 years. Therefore, we concluded that the winter monsoon is the predominant factor controlling sedimentary dynamics in the northern part of the ECS and proposed that the contribution of coarse particles may be one of potential indices to identify the role of the winter and the summer monsoons in sedimentary evolution.

Different precipitation response over land and ocean to orbital and greenhouse gas forcing

Various proxies suggest a nearly in-phase variation of monsoons with local summer insolation. Oceanic proxies of monsoons document a more complex response. Climate model simulations also indicate that the response is different over land and ocean. Here using a transient simulation by a climate model over the last 22,000 years we have unraveled the factors that lead to these differences within the Indian subcontinent. We show that during the deglacial (22–12 ka) precipitation over India and the Bay of Bengal (BoB) are in phase, whereas they are out of phase across the Holocene (sim 12 ka to 0 ka). During the deglacial, water vapor amplifies the effect of solar forcing on precipitation over both the regions, whereas contributions from surface latent heat fluxes over the BoB drive an opposite response across the Holocene. We find that greenhouse gas forcing drives similar precipitation response over land and ocean, whereas orbital forcing produces a different response over land and ocean. We have further demonstrated that during periods of abrupt climate change [such as the Bølling–Allerød (sim 14 ka)], water vapor affects precipitation mainly through its influence on the vertical stability of the atmosphere. These results highlight the complex nature of precipitation over the BoB and thus has implications for the interpretation of monsoon proxies.

Decadal‐ to Centennial‐Scale East Asian Summer Monsoon Variability Over the Past Millennium: An Oceanic Perspective

AbstractThe East Asian summer monsoon (EASM) is a key component of the Asian Monsoon system affecting regional precipitation in East Asia and thus human culture, society, and development. Despite this, decadal‐ to centennial‐scale EASM dynamics remain poorly understood over the last millennium. Here we used high‐resolution benthic microfossil proxies to reconstruct EASM variability for the last 1,000 years from a brackish lake in South Korea. We compared this EASM record with Asian Monsoon proxy records from East China (i.e., continental proxy) and East Asian coasts (i.e., oceanic setting), and identified four pervasive EASM strengthening events at 1250, 1450, 1550, and 1900 CE and their deviation, likely related to land‐ocean temperature gradients. Our results indicate that data from the oceanic setting under the direct influence of the Pacific High are important in understanding the EASM dynamics over the last millennium. It is also noteworthy that EASM variability shows striking similarity to changes in the Atlantic meridional overturning circulation, implying the causal relationship.

Mineralogical evidence of reduced East Asian summer monsoon rainfall on the Chinese loess plateau during the early Pleistocene interglacials

The East Asian summer monsoon (EASM) is an important component of the global climate system. A better understanding of EASM rainfall variability in the past can help constrain climate models and better predict the response of EASM to ongoing global warming. The warm early Pleistocene, a potential analog of future climate, is an important period to study EASM dynamics. However, existing monsoon proxies for reconstruction of EASM rainfall during the early Pleistocene fail to disentangle monsoon rainfall changes from temperature variations, complicating the comparison of these monsoon records with climate models. Here, we present three 2.6 million-year-long EASM rainfall records from the Chinese Loess Plateau (CLP) based on carbonate dissolution, a novel proxy for rainfall intensity. These records show that the interglacial rainfall on the CLP was lower during the early Pleistocene and then gradually increased with global cooling during the middle and late Pleistocene. These results are contrary to previous suggestions that a warmer climate leads to higher monsoon rainfall on tectonic timescales. We propose that the lower interglacial EASM rainfall during the early Pleistocene was caused by reduced sea surface temperature gradients across the equatorial Pacific, providing a testable hypothesis for climate models.

Microcodium in Chinese loess as a recorder for the oxygen isotopic composition of monsoonal rainwater

Records of Asia Summer Monsoon (ASM) from the Chinese loess and the speleothem display distinct features. The very different proxies that were applied to the two archives may be responsible for this discrepancy. A direct comparison between the speleothem and the loess records under the same proxy system of rainwater δ18O may help to resolve this puzzle. Here we show that the calcified microcodium in the loess deposits may record the oxygen isotopic composition of the summer rainwater. A microcodium based δ18O record covering the past 140 kyrs was generated, which shows similar magnitude of the overall variation to that of the speleothem records. However, much weaker precession variability was registered in the microcodium record during the last interglacial period. Instead, the microcodium δ18O record is more consistent with the widely used summer monsoon proxy of magnetic susceptibility in the loess deposits with clear glacial-interglacial pattern. This similarity may originate from the low sedimentation rate of the interglacial paleosol layer that preferentially record the peak ASM signals on the precession band. It is also possible that the orbital variability of ASM between the North China and South China is inherently different with more ice-volume related influence in the north. A longer microcodium δ18O record in sequences of higher sedimentation rate and a reliable record of summer rainfall may help to resolve these possibilities.

Increased chemical weathering during the deglacial to mid-Holocene summer monsoon intensification

Chemical weathering and the ensuing atmospheric carbon dioxide consumption has long been considered to work on geological time periods until recently when some modelling and natural records have shown that the weathering-related CO2 consumption can change at century to glacial-interglacial time scale. Last glacial to interglacial transition period is a best test case to understand the interplay between Pco2-temperature-chemical weathering when a pulse of rapid chemical weathering was initiated. Here we show, from a high resolution 54 ka record from the Andaman Sea in the northern Indian Ocean, that the chemical weathering responds to deglacial to mid-Holocene summer monsoon intensification in the Myanmar watersheds. The multi-proxy data (Al/K, CIA, Rb/Sr, 87Sr/86Sr for degree of weathering and 143Nd/144Nd for provenance) reveal an increase in silicate weathering with initiation of interglacial warm climate at ~17.7 ka followed by a major change at 15.5 ka. Inferred changes in chemical weathering have varied in tandem with the regional monsoonal proxies (δ18Osw-salinity changes of Northern Indian Ocean, effective Asian moisture content and δ18O records of Chinese caves) and are synchronous with changes in summer insolation at 30°N and δ18O of GISP2 implying that chemical weathering was not a later amplifier but worked in tandem with global climate change.

The influence of obliquity in the early Holocene Asian summer monsoon

AbstractThe early Holocene climatic optimum is associated with perihelion precession and high obliquity, though most studies emphasize the former over the latter. Asian monsoon proxy records only decisively show the precessional impact. To explore the obliquity effect, four climate simulations are conducted by fixing orbital parameters of present‐day (0K), early Holocene (11K), the lowest obliquity (31K), and 11K's precession and eccentricity with 31K's obliquity (11Kp31Ko). We show that high obliquity significantly augments the precessional impact by shifting the Asian monsoon farther north than present. By contrast, the present‐day monsoon seasonality can still be identified in the simulations with low obliquity. We argue that the upper tropospheric (South Asian) and lower tropospheric (North Pacific) high‐pressure systems are affected by the subtropical atmospheric heating changes responding to obliquity. As a consequence, associated with the changes in meridional gradients of geopotential height and temperature made by the heating, midlatitude transient eddies and monsoon‐midlatitude interactions are modulated.

Mass accumulation rate and monsoon records from Xifeng, Chinese Loess Plateau, based on a luminescence age model

ABSTRACTLuminescence dating of loess accumulation in China has raised questions over disturbance and gaps in the record, the magnitude of mass accumulation rates (MARs), and monsoon forcing mechanisms. Here we present a detailed quartz optically stimulated luminescence (OSL) chronology from the Xifeng Chinese Loess Plateau site. We reconstruct MARs and construct an age model for monsoon proxies at the site. The luminescence ages show significant pedogenic and anthropogenic disturbance in material deposited after ca. 20–22 ka. Analysis of other published data suggests that this disturbance may be more common than previously realized. MARs from undisturbed portions of Xifeng vary dramatically, with peaks potentially matching the timing of Heinrich events. The last glacial maximum peak MAR (22–27 ka) matches the Pacific and Greenland dust flux records, although appears earlier than peak MARs seen in many other OSL‐dated Loess Plateau sites. East Asian monsoon grain‐size and magnetic susceptibility records also show several differences between independently dated loess sites. This complicates our understanding of any lag between insolation forcing and monsoon response. Nevertheless, the Xifeng climate proxy changes show apparent broad agreement with the timing of Heinrich events in the North Atlantic, supporting assertions of a climatic teleconnection between the two areas.

Asian summer monsoon variability during the late glacial and Holocene inferred from the stable carbon isotope record of black carbon in the sediments of Muge Co, southeastern Tibetan Plateau, China

A sediment core from an alpine lake (Muge Co) from the southeastern margin of the Tibetan Plateau was analyzed for sediment grain size distribution and the carbon isotopic composition of black carbon in order to reconstruct Asian summer monsoon variability over the last 12 ka. Five major climatic stages were identified: (1) From 12 to 10.5 cal. ka BP, a cold and dry climate prevailed, corresponding to the Younger Dryas in the North Atlantic; (2) from 10.5 to 9.2 cal. ka BP, precipitation increased rapidly but was interrupted by a pronounced cold and dry phase at about 10 cal. ka BP; (3) from 9.2 to 6.2 cal. ka BP, the Holocene climatic optimum was reached and maintained; (4) from 6.2 to 2.5 cal. ka BP, the climate gradually became cooler and drier; (5) from 2.5 cal. ka BP to the present, a climatic reversal toward wetter conditions occurred. The trend of our reconstructed Asian summer monsoon precipitation record is similar on orbital and millennium timescales to that of other records from the Asian monsoon region. Although the maximum monsoon intensity recorded in the Muge Co sediments lagged the peak of Northern Hemisphere insolation by ~3.0 ka, the strengthening trend was in phase with the rise in the Western Pacific Warm Pool sea surface temperature. Therefore, we suggest that the tropical ocean temperatures may have been the major driver of Asian summer monsoon precipitation in the southeastern Tibetan Plateau. In addition, other factors such as sea-level rise and temperature in the North Atlantic region may have played an important role in the evolution of the Asian summer monsoon since the last deglaciation. However, human activity may have affected the monsoon proxies during the last 2.5 ka, and further studies are needed to distinguish the effects of climate and human disturbance.

Astronomical and glacial forcing of East Asian summer monsoon variability

The dynamics of glacial–interglacial monsoon variability can be attributed to orbitally induced changes in summer insolation and internal boundary conditions. However, the relative impacts of astronomical and internal factors on East Asian summer monsoon variability remain controversial. Here we combine proxy data and model results to evaluate the response of East Asian summer monsoon change to these forcings. δ13C of loess carbonate, a sensitive summer monsoon proxy from the western Chinese Loess Plateau, demonstrates coexistence of distinct 100-, 41- and 23-ka periods, in contrast to precession-dominated speleothem δ18O records in South China. Model results indicate that insolation, ice and CO2 have distinct impacts on summer precipitation changes in East Asia, whereas their relative impacts are spatially different, with a relatively stronger insolation effect in south China and a more dominant ice/CO2 influence in north China. Combined proxy data and model results indicate that East Asian summer monsoon variability was induced by integrated effects of summer insolation and changing boundary conditions (e.g., ice sheets and CO2 concentration). Our proxy-model comparison further suggests that gradual weakening of the summer monsoon related to slowly decreasing summer insolation at astronomical timescales will be likely overwhelmed by the projected ongoing anthropogenic CO2 emissions.

Dynamics of the Australian–Indonesian monsoon across Termination II: Implications of molecular-biomarker reconstructions from the Timor Sea

Abstract Molecular biomarker-derived proxies in a marine sediment core from the eastern Timor Sea have been employed to track changes in the Australian–Indonesian monsoon system over the time period from the penultimate glacial to the last interglacial. The average chain length of n-alkanes originating from terrestrial higher plants reveals an expansion of woody plants during both Termination II and the last interglacial with respect to the penultimate glacial. This is consistent with previous reconstructions for the last glacial–interglacial cycle, indicating that water-stress conditions during dry seasons of southern Indonesia should have been relieved during interglacials and deglacials relative to glacials. However, in contrast to an only muted response during Heinrich Stadial 1, the vegetation composition showed a dramatic and prominent change during Heinrich Stadial 11. This was probably caused by a much more significant and longer duration iceberg discharge event to the northern North Atlantic during Heinrich Stadial 11 relative to Heinrich Stadial 1, which exerted a significant influence on the tropical hydrological cycle and monsoon rainfall seasonality. In addition, marine algae-derived biomarkers are used to reconstruct primary productivity variations, which are in agreement with previous studies from the same area. The precessional cyclicity of paleo-productivity variations is possibly induced by changes in the Australian–Indonesian winter monsoon intensity, showing a correlation with boreal winter insolation. However, this phase relationship is in contrast to the inference based on other lines of evidence, which suggests strong winter monsoon strength during boreal summer insolation maxima. New winter monsoon proxies are therefore required to clarify this discrepancy.

Temperature and leaf wax δ2H records demonstrate seasonal and regional controls on Asian monsoon proxies

Orbital-scale precipitation isotope records can elucidate climate forcing mechanisms and provide benchmarks for climate model validation. The ability to differentiate the influence of temperature, seasonality, and vapor transport history on precipitation isotope proxies is critical to both objectives. We present a 300 k.y. leaf wax hydrogen isotope record from the South China Sea with the effects of local condensation temperature removed (δ 2 H wax– T ). δ 2 H wax– T reflects annually integrated precipitation δ 2 H in the Pearl River catchment of southeast China. Depleted δ 2 H wax– T lags minimum precession (P min ) by 1.0 ± 0.7 k.y., reflecting the influence of maximum summer insolation and minimum winter insolation, with a minor influence of global ice volume, which lags P min by 3.3 ± 0.4 k.y. In contrast, annually integrated cave δ 18 O minima in central China, 1000 km north of our site, lag P min by 2.7 ± 0.3 k.y., in phase with ice volume minima. This phase indicates that precipitation δ 18 O in central China is more strongly influenced by ice volume forcing at the precession band, with a lesser influence of Northern Hemisphere insolation. Our new δ 2 H wax– T data demonstrate that precipitation isotopes in Asia have strong regional variability. Interpreting water isotope records within the context of regionally varying temperature, seasonality, and sensitivity to changing glacial boundary conditions is imperative to understanding Asian hydroclimatic change.

The global monsoon across timescales: coherent variability of regional monsoons

Abstract. Monsoon has earned increasing attention from the climate community since the last century, yet only recently have regional monsoons been recognized as a global system. It remains a debated issue, however, as to what extent and at which timescales the global monsoon can be viewed as a major mode of climate variability. For this purpose, a PAGES (Past Global Changes) working group (WG) was set up to investigate the concept of the global monsoon and its future research directions. The WG's synthesis is presented here. On the basis of observation and proxy data, the WG found that the regional monsoons can vary coherently, although not perfectly, at various timescales, varying between interannual, interdecadal, centennial, millennial, orbital and tectonic timescales, conforming to the global monsoon concept across timescales. Within the global monsoon system, each subsystem has its own features, depending on its geographic and topographic conditions. Discrimination between global and regional components in the monsoon system is a key to revealing the driving factors in monsoon variations; hence, the global monsoon concept helps to enhance our understanding and to improve future projections of the regional monsoons. This paper starts with a historical review of the global monsoon concept in both modern and paleo-climatology, and an assessment of monsoon proxies used in regional and global scales. The main body of the paper is devoted to a summary of observation data at various timescales, providing evidence of the coherent global monsoon system. The paper concludes with a projection of future monsoon shifts in a warming world. The synthesis will be followed by a companion paper addressing driving mechanisms and outstanding issues in global monsoon studies.