Two atmospheric circulation systems, the mid-latitude Westerlies and the Asian summer monsoon (ASM), play key roles in northern-hemisphere climatic changes. However, the variability of the Westerlies in Asia and their relationship to the ASM remain unclear. Here, we present the longest and highest-resolution drill core from Lake Qinghai on the northeastern Tibetan Plateau (TP), which uniquely records the variability of both the Westerlies and the ASM since 32 ka, reflecting the interplay of these two systems. These records document the anti-phase relationship of the Westerlies and the ASM for both glacial-interglacial and glacial millennial timescales. During the last glaciation, the influence of the Westerlies dominated; prominent dust-rich intervals, correlated with Heinrich events, reflect intensified Westerlies linked to northern high-latitude climate. During the Holocene, the dominant ASM circulation, punctuated by weak events, indicates linkages of the ASM to orbital forcing, North Atlantic abrupt events, and perhaps solar activity changes.
The magnitude, rate, and extent of past and future East Asian monsoon (EAM) rainfall fluctuations remain unresolved. Here, late Pleistocene-Holocene EAM rainfall intensity is reconstructed using a well-dated northeastern China closed-basin lake area record located at the modern northwestern fringe of the EAM. The EAM intensity and northern extent alternated rapidly between wet and dry periods on time scales of centuries. Lake levels were 60 m higher than present during the early and middle Holocene, requiring a twofold increase in annual rainfall, which, based on modern rainfall distribution, requires a ∼400 km northward expansion/migration of the EAM. The lake record is highly correlated with both northern and southern Chinese cave deposit isotope records, supporting rainfall "intensity based" interpretations of these deposits as opposed to an alternative "water vapor sourcing" interpretation. These results indicate that EAM intensity and the northward extent covary on orbital and millennial timescales. The termination of wet conditions at 5.5 ka BP (∼35 m lake drop) triggered a large cultural collapse of Early Neolithic cultures in north China, and possibly promoted the emergence of complex societies of the Late Neolithic.East Asian monsoon | closed-basin lake | paleo-rainfall | Chinese cave record | northward expansion T he East Asian monsoon (EAM) is a major component of the global climate system (1), and its variability directly impacts the lives of over a billion people. Understanding EAM sensitivity to past climate changes and its future variability are essential for determining the EAM response to different climate forcings and for constraining future climate projections. Two competing interpretations of existing paleoclimate records frame our current understanding of the response of the EAM to orbital-scale and high-latitude millennial-scale forcing during the late PleistoceneHolocene. The first interpretation suggests that oxygen isotopic records from Chinese cave deposits reflect real rainfall changes, indicating a direct response of EAM rains to external climate forcings (2-4). The competing view holds that these isotopic records reflect changes in moisture sourcing and depend on the Indian Monsoon intensity (5-10), suggesting that the cave deposit isotopic values are decoupled from actual rainfall amounts, and thus question the validity of oxygen isotope-based EAM intensity reconstructions. Missing from this debate has been an independent quantitative record of past rainfall variability in the EAM region.Here, we present a detailed, well-dated lake-level history for Lake Dali (43.15°N, 116.29°E), a closed-basin lake in Inner Mongolia (1,220 m above sea level, 220 km 2 lake area and maximum depth of 11 m), presently located near the northwestern limit of EAM domain (e.g., ref. 11; Fig. 1). The peripheral location of Lake Dali with respect to the monsoon region provides an excellent opportunity to examine the magnitude of spatial expansion of the EAM and whether the millennial-and orbital-scale change...
Atmospheric methane concentrations decreased during the early to middle Holocene; however, the governing mechanisms remain controversial. Although it has been suggested that the mid-Holocene minimum methane emissions are associated with hydrological change, direct evidence is lacking. Here we report a new independent approach, linking hydrological change in peat sediments from the Tibetan Plateau to changes in archaeal diether concentrations and diploptene δ13C values as tracers for methanogenesis and methanotrophy, respectively. A minimum in inferred methanogenesis occurred during the mid-Holocene, which, locally, corresponds with the driest conditions of the Holocene, reflecting a minimum in Asian monsoon precipitation. The close coupling between precipitation and methanogenesis is validated by climate simulations, which also suggest a regionally widespread impact. Importantly, the minimum in methanogenesis is associated with a maximum in methanotrophy. Therefore, methane emissions in the Tibetan Plateau region were apparently lower during the mid-Holocene and partially controlled by interactions of large-scale atmospheric circulation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.