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Journal ArticleDOI

On the glacial-interglacial variability of the Asian monsoon in speleothem δ18O records.

TL;DR: It is found that the records close to the monsoon moisture source show large glacial-interglacial variability, which then decreases landward, the moisture transport pathway effect, which counteracts the forcing of glacial boundary conditions.
Abstract: While Asian monsoon (AM) changes have been clearly captured in Chinese speleothem oxygen isotope (δ18O) records, the lack of glacial-interglacial variability in the records remains puzzling. Here, we report speleothem δ18O records from three locations along the trajectory of the Indian summer monsoon (ISM), a major branch of the AM, and characterize AM rainfall over the past 180,000 years. We have found that the records close to the monsoon moisture source show large glacial-interglacial variability, which then decreases landward. These changes likely reflect a stronger oxygen isotope fractionation associated with progressive rainout of AM moisture during glacial periods, possibly due to a larger temperature gradient and suppressed plant transpiration. We term this effect, which counteracts the forcing of glacial boundary conditions, the moisture transport pathway effect.
Citations
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Journal ArticleDOI
TL;DR: In this article, Wang et al. reconcile the Chinese 100 kyr problem and the sea-land precession phase paradox by comparing the results of different hydroclimatic proxies.
Abstract: The Asian summer monsoon (ASM) is a vast climate system, whose variability is critical to the livelihoods of billions of people across the Asian continent. During the past half-century, much progress has been made in understanding variations on a wide range of timescales, yet several significant issues remain unresolved. Of note are two long-standing problems concerning orbital-scale variations of the ASM. (1) Chinese loess magnetic susceptibility records show a persistent glacial-interglacial dominated ~100 kyr (thousand years) periodicity, while the cave oxygen-isotope (δ18O) records reveal periodicity in an almost pure precession band (~20 kyr periodicity)—the “Chinese 100 kyr problem”. (2) ASM records from the Arabian Sea and other oceans surrounding the Asian continent show a significant lag of 8–10 kyr to Northern Hemisphere summer insolation (NHSI), whereas the Asian cave δ18O records follow NHSI without a significant lag—a discrepancy termed the “sea-land precession-phase paradox”. How can we reconcile these differences? Recent and more refined model simulations now provide spatial patterns of rainfall and wind across the precession cycle, revealing distinct regional divergences in the ASM domain, which can well explain a large portion of the disparities between the loess, marine, and cave proxy records. Overall, we also find that the loess, marine, and cave records are indeed complementary rather than incompatible, with each record preferentially describing a certain aspect of ASM dynamics. Our study provides new insight into the understanding of different hydroclimatic proxies and largely reconciles the “Chinese 100 kyr problem“ and “sea-land precession-phase paradox”.

50 citations

Journal ArticleDOI
TL;DR: In this article, the authors present new pollen data and mean annual temperature reconstruction from the annually laminated sediments of Lake Suigetsu, Japan, which is an integral component of the IntCal20 radiocarbon calibration model, in which the absolute age scale is established to the highest standard.

18 citations

Journal ArticleDOI
01 Feb 2021-Catena
TL;DR: In this paper, the authors presented a high-resolution EASM precipitation record reconstructed from the loess redness in North China over the past 720 kyr, showing that the average precipitation for interglacials is 420mm/yr, higher than present (~280 mm/yr).
Abstract: The periodicity and forcing mechanism of the past East Asian summer monsoon (EASM) precipitation are the natural background for predicting future precipitation changes, but they are controversial and intensely debated. Here, we present a high-resolution EASM precipitation record reconstructed from the loess redness in North China over the past 720 kyr. The average precipitation for interglacials is 420 mm/yr, higher than present (~280 mm/yr). Combing through our EASM records and previously published data exhibits a dominated periodicity of 100 kyr on the orbital timescale, and thus supports the hypothesis of high-latitude climate forcing. More importantly, we found the precession cycle appears only after the Mid-Brunhes Transition (MBT, ~430 ka) in the EASM records and it follows the global ice volume prior to the MBT in the interglacials interiors. We argue that during the post-MBT interglacials, abruptly appearing Arctic perennial sea ice resulted southward shift of the Northern Hemisphere Westerlies jet, thereby decreasing the EASM precipitation in North China. This suggests that the precession rhythm in the EASM possibly is a result of Arctic perennial sea ice or Northern Hemisphere ice sheets changes. In the warm Marine Isotope Stages (MIS) 5e and 11e, the strongest EASM precipitation may be related to the strengthening of the moisture transport from the warming tropical ocean. Therefore, the variation of the mid-latitude EASM precipitation intensity during the interglacial interiors is the integrated effect between the North Hemisphere high latitude ice volume and low latitude climate changes.

15 citations

Journal ArticleDOI
TL;DR: In this article, the authors quantitatively deconvolve these parameters affecting δ18OCc by applying three geochemical techniques in speleothems covering the penultimate glacial termination, and reveal that the different modes of the AMOC produced distinct impacts on the monsoon system.
Abstract: During glacial terminations, massive iceberg discharges and meltwater pulses in the North Atlantic triggered a shutdown of the Atlantic Meridional Overturning Circulation (AMOC). Speleothem calcium carbonate oxygen isotope records (δ18OCc) indicate that the collapse of the AMOC caused dramatic changes in the distribution and variability of the East Asian and Indian monsoon rainfall. However, the mechanisms linking changes in the intensity of the AMOC and Asian monsoon δ18OCc are not fully understood. Part of the challenge arises from the fact that speleothem δ18OCc depends on not only the δ18O of precipitation but also temperature and kinetic isotope effects. Here we quantitatively deconvolve these parameters affecting δ18OCc by applying three geochemical techniques in speleothems covering the penultimate glacial termination. Our data suggest that the weakening of the AMOC during meltwater pulse 2A caused substantial cooling in East Asia and a shortening of the summer monsoon season, whereas the collapse of the AMOC during meltwater pulse 2B (133,000 years ago) also caused a dramatic decrease in the intensity of the Indian summer monsoon. These results reveal that the different modes of the AMOC produced distinct impacts on the monsoon system. The influence of meltwater pulse events on Asian monsoon systems varied in line with the degree of AMOC weakening, according to a multi-proxy analysis of speleothems from China covering the penultimate glacial termination.

11 citations

References
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Journal ArticleDOI
TL;DR: Evidence of two mechanisms explaining key patterns of ocean cooling and rainfall change interpreted from proxy data are found, demonstrating the importance of air-sea interactions in the Indian Ocean, amplifying externally forced climate changes over a large part of the tropics.
Abstract: The mechanisms driving glacial-interglacial changes in the climate of the Indo-Pacific warm pool are poorly understood. Here, we address this question by combining paleoclimate proxies with model simulations of the Last Glacial Maximum climate. We find evidence of two mechanisms explaining key patterns of ocean cooling and rainfall change interpreted from proxy data. Exposure of the Sahul shelf excites a positive ocean-atmosphere feedback involving a stronger surface temperature gradient along the equatorial Indian Ocean and a weaker Walker circulation-a response explaining the drier/wetter dipole across the basin. Northern Hemisphere cooling by ice sheet albedo drives a monsoonal retreat across Africa and the Arabian Peninsula-a response that triggers a weakening of the Indian monsoon via cooling of the Arabian Sea and associated reductions in moisture supply. These results demonstrate the importance of air-sea interactions in the Indian Ocean, amplifying externally forced climate changes over a large part of the tropics.

76 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used the isotopic general circulation model (GCM) LMDZ to better understand what controls 17O-excess in precipitation at present-day (PD) and during the last glacial maximum (LGM).
Abstract: . Combined measurements of the H218O and HDO isotopic ratios in precipitation, leading to second-order parameter D-excess, have provided additional constraints on past climates compared to the H218O isotopic ratio alone. More recently, measurements of H217O have led to another second-order parameter: 17O-excess. Recent studies suggest that 17O-excess in polar ice may provide information on evaporative conditions at the moisture source. However, the processes controlling the spatio-temporal distribution of 17O-excess are still far from being fully understood. We use the isotopic general circulation model (GCM) LMDZ to better understand what controls d-excess and 17O-excess in precipitation at present-day (PD) and during the last glacial maximum (LGM). The simulation of D-excess and 17O-excess is evaluated against measurements in meteoric water, water vapor and polar ice cores. A set of sensitivity tests and diagnostics are used to quantify the relative effects of evaporative conditions (sea surface temperature and relative humidity), Rayleigh distillation, mixing between vapors from different origins, precipitation re-evaporation and supersaturation during condensation at low temperature. In LMDZ, simulations suggest that in the tropics convective processes and rain re-evaporation are important controls on precipitation D-excess and 17O-excess. In higher latitudes, the effect of distillation, mixing between vapors from different origins and supersaturation are the most important controls. For example, the lower d-excess and 17O-excess at LGM simulated at LGM are mainly due to the supersaturation effect. The effect of supersaturation is however very sensitive to a parameter whose tuning would require more measurements and laboratory experiments. Evaporative conditions had previously been suggested to be key controlling factors of d-excess and 17O-excess, but LMDZ underestimates their role. More generally, some shortcomings in the simulation of 17O-excess by LMDZ suggest that general circulation models are not yet the perfect tool to quantify with confidence all processes controlling 17O-excess.

74 citations

Journal ArticleDOI
TL;DR: In this article, the authors present the first results of a new isotope-enabled general circulation model set-up, consisting of the fully coupled ECHAM5/MPI-OM atmosphere-ocean model, enhanced by the JSBACH interactive land surface scheme and an explicit hydrological discharge scheme to close the global water budget.
Abstract: . In this study we present the first results of a new isotope-enabled general circulation model set-up. The model consists of the fully coupled ECHAM5/MPI-OM atmosphere–ocean model, enhanced by the JSBACH interactive land surface scheme and an explicit hydrological discharge scheme to close the global water budget. Stable water isotopes H218O and HDO have been incorporated into all relevant model components. Results of two equilibrium simulations under pre-industrial and Last Glacial Maximum conditions are analysed and compared to observational data and paleoclimate records for evaluating the model's performance in simulating spatial and temporal variations in the isotopic composition of the Earth's water cycle. For the pre-industrial climate, many aspects of the simulation results of meteoric waters are in good to very good agreement with both observations and earlier atmosphere-only simulations. The model is capable of adequately simulating the large spread in the isotopic composition of precipitation between low and high latitudes. A comparison to available ocean data also shows a good model–data agreement; however, a strong bias of overly depleted ocean surface waters is detected for the Arctic region. Simulation results under Last Glacial Maximum boundary conditions also fit to the wealth of available isotope records from polar ice cores, speleothems, as well as marine calcite data. Data–model evaluation of the isotopic composition in precipitation reveals a good match of the model results and indicates that the temporal glacial–interglacial isotope–temperature relation was substantially lower than the present spatial gradient for most mid- to high-latitudinal regions. As compared to older atmosphere-only simulations, a remarkable improvement is achieved for the modelling of the deuterium excess signal in Antarctic ice cores. Our simulation results indicate that cool sub-tropical and mid-latitudinal sea surface temperatures are key for this progress. A recently discussed revised interpretation of the deuterium excess record of Antarctic ice cores in terms of marine relative humidity changes on glacial–interglacial timescales is not supported by our model results.

67 citations

Journal ArticleDOI
TL;DR: The authors show that the long held view that precession drove changes in monsoon strength is wrong, and that obliquity and eccentricity played a stronger role.
Abstract: The orbital-scale timing of South Asian monsoon (SAM) precipitation is poorly understood. Here we present new SST and seawater δ18O (δ18Osw) records from the Bay of Bengal, the core convective region of the South Asian monsoon, over the past 1 million years. Our records reveal that SAM precipitation peaked in the precession band ~9 kyrs after Northern Hemisphere summer insolation maxima, in phase with records of SAM winds in the Arabian Sea and eastern Indian Ocean. Precession-band variance, however, accounts for ~30% of the total variance of SAM precipitation while it was either absent or dominant in records of the East Asian monsoon (EAM). This and the observation that SAM precipitation was phase locked with obliquity minima and was sensitive to Southern Hemisphere warming provides clear evidence that SAM and EAM precipitation responded differently to orbital forcing and highlights the importance of internal processes forcing monsoon variability.

64 citations

Journal ArticleDOI
TL;DR: In this paper, a 6.35-m core was retrieved from Lake Shudu, Yunnan Province, China and analyzed using a combination of variables including pollen, charcoal, particle size, magnetic susceptibility and loss-on-ignition.

63 citations


"On the glacial-interglacial variabi..." refers background in this paper

  • ...With an initial rainfall δ18Opi of -2.6‰ (Table S3), rainfall δ18Op would have decreased to -9.2‰ at the SEY site if temperature gradient was similar to today, but would have further dropped to -10.3‰ if the temperature gradient increased modestly by ~2 °C/1,000 km (i.e., to 9 °C at SEY)....

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  • ...SEY samples: A14 and A15 are from an unnamed cave in SEY; BF2 is from Baifen cave; SY10 is from Shuiyuan cave; JJ03 and JJ06 are from Jiangjun cave; SL08 and SL10 are from Shuanglong cave; and XR05 is from Xianren cave....

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  • ...Note that for the SEY record, the smoothed record was slightly biased to its high resolution portion (e.g., ~7 ka). b)....

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  • ...Dark blue: the atmospheric molecular oxygen δ18O record from Vostok ice core, Antarctica (86); purple: speleothem δ18O records from SEY caves; dark brown: speleothem δ18O records Xiaobailong cave (20); green-brown-blue: combined speleothem δ18O records from southern China’s Hulu cave, HL (2, 60), Dongge cave, DG (61, 62), and Sanbao cave, SB, in which the Sanbao record was shifted positively by 1.6‰ to align it with the other two cave records (1)....

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  • ...Scatter plot of δ18O versus δ13C. a). for the CBoB stalagmites; b). for the CM stalagmites; and c). for the SEY stalagmites....

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