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.
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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
24 citations
Ritsumeikan University1, University of Newcastle2, Free University of Berlin3, University of Oxford4, University of Glasgow5, University of Derby6, Aberystwyth University7, Trinity College, Dublin8, Osaka City University9, Chiba University of Commerce10, Nagoya University11, University of Groningen12, Naruto University of Education13, University of Tokyo14
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
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
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
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TL;DR: In this paper, high-resolution oxygen and hydrogen isotope measurements were made on pore fluids from deep-sea sediments from sites in the North and South Atlantic to provide direct measurements of changes in the isotopic composition of bottom waters during the Last Glacial Maximum (LGM).
358 citations
TL;DR: The thorium-230-dated records reveal that between 75 and 55 ka, the midcontinental climate oscillated on millennial time scales between cold and warm, and vegetation alternated among forest, savanna, and prairie.
Abstract: Four Missouri stalagmites yield consistent overlapping records of oxygen and carbon isotopic changes and provide a climate and vegetation history with submillennial resolution from 75 to 25 thousand years ago (ka). The thorium-230-dated records reveal that between 75 and 55 ka, the midcontinental climate oscillated on millennial time scales between cold and warm, and vegetation alternated among forest, savanna, and prairie. Temperatures were highest and prairie vegetation peaked between 59 and 55 ka. Climate cooled and forest replaced grassland at 55 ka, when global ice sheets began to build during the early part of Marine Oxygen Isotope Stage 3.
337 citations
TL;DR: In this article, the authors show that the timing of light cave δ18O peaks cannot be interpreted as reflecting strong summer monsoons alone, and that the combined influence of summer monsoon forcing with a phase lag of 8 kyrs relative to precession minima and winter temperature forcing that is in phase with precess minima is inconsistent with a direct response to northern hemisphere summer insolation.
Abstract: [1] Southeast China cave δ18O, often interpreted as a pure East Asian summer monsoon proxy, lags maximum northern hemisphere summer insolation by 2.9 ± 0.3 kyrs at the precession cycle. The Arabian Sea summer monsoon stack lags by 8 ± 1 kyr, consistent with 13 other Indian and East Asian summer monsoon proxies from marine, lake, and terrestrial archives. This 5 kyr phase difference cannot be attributed to age control inadequacies in the marine chronology; it requires reconciliation in the context of proxy interpretation. Both of these lags are incompatible with a direct response to northern hemisphere summer insolation, implicating additional forcing mechanisms. Analysis of heterodynes in the cave δ18O spectrum demonstrates that variance contained in the Arabian Sea summer monsoon proxies also resides in the cave δ18O record. This variance is subtracted from the cave δ18O record yielding a residual that is highly coherent and in phase with precession minima, reflecting the impact of winter temperature change on cave δ18O (meteorological precipitation under cold conditions). Thus, we argue that the timing of light cave δ18O peaks cannot be interpreted as reflecting the timing of strong summer monsoons alone. The 2.9 kyr precession band phase lag of cave δ18O reflects the combined influence of summer monsoon forcing with a phase lag of 8 kyrs relative to precession minima and winter temperature forcing that is in phase with precession minima. This interpretation is consistent with modern seasonality in the amount and isotopic composition of rainfall in southeast China.
314 citations
TL;DR: StalAge as discussed by the authors uses stratigraphic information in order to further constrain and improve the age model, which is applicable to problematic datasets that include outliers, age inversions, hiatuses and large changes in growth rate.
288 citations
"On the glacial-interglacial variabi..." refers methods in this paper
...We used the StalAge method (54) to establish the chronology for samples with large errors in their age dating due to low U and high Th contents (e....
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TL;DR: In this paper, the authors postulate that the summer monsoon initiates, amplifies, and terminates the Dansgaard-Oeschger cycles in the Northern Hemisphere.
Abstract: High-frequency suborbital variations (Dansgaard-Oeschger cycles) characterize the climatic history of the Northern Hemisphere as observed in Greenland ice cores, deep-sea sediments of the North Atlantic, the Californian borderland, the Arabian Sea, the South China Sea, and the Chinese loess area. Paleoceanographic data from core KL126 from the Bay of Bengal in combination with data from the other Asian monsoonal areas indicate that the feedback processes involving snow and dust of the Tibetan Plateau vary the summer monsoon capacity to transport moisture into central South Asia and into the atmosphere. We postulate that the summer monsoon initiates, amplifies, and terminates these cycles in the Northern Hemisphere.
281 citations
"On the glacial-interglacial variabi..." refers background in this paper
...S1), which is also interpreted as fluvial input or ISM intensity (27)....
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...The stars mark the Mawmluh (21, 26), Hulu (60), Dongge (2, 61, 62), and Sanbao (1, 2) caves; and squares mark marine sediment cores SO93-126KL (27) and SO189-39KL (39) for reference....
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...For example, during the LGM, the temperature likely dropped between 2° and 4°C at CBoB (5, 20, 27, 29, 34) and between 4° and 8°C at SEY (20, 24, 57)....
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...ruber 18O record, retrieved from sediment core SO93-126KL, as a proxy for ISM intensity (27)....
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