Oxygen isotope records from Chinese caves characterize changes in both the Asian monsoon and global climate. Here, using our new speleothem data, we extend the Chinese record to cover the full ...uranium/thorium dating range, that is, the past 640,000 years. The record's length and temporal precision allow us to test the idea that insolation changes caused by the Earth's precession drove the terminations of each of the last seven ice ages as well as the millennia-long intervals of reduced monsoon rainfall associated with each of the terminations. On the basis of our record's timing, the terminations are separated by four or five precession cycles, supporting the idea that the '100,000-year' ice age cycle is an average of discrete numbers of precession cycles. Furthermore, the suborbital component of monsoon rainfall variability exhibits power in both the precession and obliquity bands, and is nearly in anti-phase with summer boreal insolation. These observations indicate that insolation, in part, sets the pace of the occurrence of millennial-scale events, including those associated with terminations and 'unfinished terminations'.
Observations show that summer rainfall over large parts of South Asia has declined over the past five to six decades. It remains unclear, however, whether this trend is due to natural variability or ...increased anthropogenic aerosol loading over South Asia. Here we use stable oxygen isotopes in speleothems from northern India to reconstruct variations in Indian monsoon rainfall over the last two millennia. We find that within the long-term context of our record, the current drying trend is not outside the envelope of monsoon's oscillatory variability, albeit at the lower edge of this variance. Furthermore, the magnitude of multi-decadal oscillatory variability in monsoon rainfall inferred from our proxy record is comparable to model estimates of anthropogenic-forced trends of mean monsoon rainfall in the 21st century under various emission scenarios. Our results suggest that anthropogenic-forced changes in monsoon rainfall will remain difficult to detect against a backdrop of large natural variability.
The Younger Dryas (YD), arguably the most widely studied millennial-scale extreme climate event, was characterized by diverse hydroclimate shifts globally and severe cooling at high northern ...latitudes that abruptly punctuated the warming trend from the last glacial to the present interglacial. To date, a precise understanding of its trigger, propagation, and termination remains elusive. Here, we present speleothem oxygen-isotope data that, in concert with other proxy records, allow us to quantify the timing of the YD onset and termination at an unprecedented subcentennial temporal precision across the North Atlantic, Asian Monsoon-Westerlies, and South American Monsoon regions. Our analysis suggests that the onsets of YD in the North Atlantic (12,870 ± 30 B.P.) and the Asian Monsoon-Westerlies region are essentially synchronous within a few decades and lead the onset in Antarctica, implying a north-to-south climate signal propagation via both atmospheric (decadal-time scale) and oceanic (centennial-time scale) processes, similar to the Dansgaard–Oeschger events during the last glacial period. In contrast, the YD termination may have started first in Antarctica at ∼11,900 B.P., or perhaps even earlier in the western tropical Pacific, followed by the North Atlantic between ∼11,700 ± 40 and 11,610 ± 40 B.P. These observations suggest that the initial YD termination might have originated in the Southern Hemisphere and/or the tropical Pacific, indicating a Southern Hemisphere/tropics to North Atlantic–Asian Monsoon-Westerlies directionality of climatic recovery.
The Indian summer monsoon (ISM) monsoon is critical to billions of people living in the region. Yet, significant debates remain on primary ISM drivers on millennial-orbital timescales. Here, we use ...speleothem oxygen isotope (δ(18)O) data from Bittoo cave, Northern India to reconstruct ISM variability over the past 280,000 years. We find strong coherence between North Indian and Chinese speleothem δ(18)O records from the East Asian monsoon domain, suggesting that both Asian monsoon subsystems exhibit a coupled response to changes in Northern Hemisphere summer insolation (NHSI) without significant temporal lags, supporting the view that the tropical-subtropical monsoon variability is driven directly by precession-induced changes in NHSI. Comparisons of the North Indian record with both Antarctic ice core and sea-surface temperature records from the southern Indian Ocean over the last glacial period do not suggest a dominant role of Southern Hemisphere climate processes in regulating the ISM variability on millennial-orbital timescales.
The vast Indo-Gangetic Plain in South Asia has been home to some of the world's oldest civilizations, whose fortunes ebbed and flowed with time-plausibly driven in part by shifts in the ...spatiotemporal patterns of the Indian summer monsoon rainfall. We use speleothem oxygen isotope records from North India to reconstruct the monsoon's variability on socially relevant time scales, allowing us to examine the history of civilization changes in the context of varying hydroclimatic conditions over the past 5700 years. Our data suggest that significant shifts in monsoon rainfall have occurred in concert with changes in the Northern Hemisphere temperatures and the discharges of the Himalayan rivers. The close temporal relationship between these large-scale hydroclimatic changes and the intervals marking the significant sociopolitical developments of the Indus Valley and Vedic civilizations suggests a plausible role of climate change in shaping the important chapters of the history of human civilization in the Indian subcontinent.
The extent to which climate variability in Central Asia is causally linked to large-scale changes in the Asian monsoon on varying timescales remains a longstanding question. Here we present precisely ...dated high-resolution speleothem oxygen-carbon isotope and trace element records of Central Asia's hydroclimate variability from Tonnel'naya cave, Uzbekistan, and Kesang cave, western China. On orbital timescales, the supra-regional climate variance, inferred from our oxygen isotope records, exhibits a precessional rhythm, punctuated by millennial-scale abrupt climate events, suggesting a close coupling with the Asian monsoon. However, the local hydroclimatic variability at both cave sites, inferred from carbon isotope and trace element records, shows climate variations that are distinctly different from their supra-regional modes. Particularly, hydroclimatic changes in both Tonnel'naya and Kesang areas during the Holocene lag behind the supra-regional climate variability by several thousand years. These observations may reconcile the apparent out-of-phase hydroclimatic variability, inferred from the Holocene lake proxy records, between Westerly Central Asia and Monsoon Asia.
In southeastern China (SEC), the precipitation amount produced by the East Asian summer monsoon (EASM) is almost equivalent to that during the non-summer monsoon (NSM) period, both of them ...significantly affecting agriculture and socioeconomy. Here, we present a seasonally-resolved stalagmite δ
O record (δ
O
) for the interval 1810-2009 AD from E'mei cave, Jiangxi Province, SEC. The comparison between δ
O
and instrumental data indicates that the δ
O
variability is primarily controlled by the precipitation seasonality (i.e., the ratio of EASM/NSM precipitation) modulated by the El Niño/Southern Oscillation (ENSO) on interannual to interdecadal timescales. Higher (lower) δ
O
values thereby correspond to lower (higher) EASM/NSM ratios associated with El Niño (La Niña) events. Significant correlations with ENSO and the Pacific Decadal Oscillation (PDO) indicate that the precipitation seasonality in SEC is remarkably influenced by ocean-atmosphere interactions, with lower (higher) EASM/NSM ratios during warm (cold) phases of ENSO/PDO. The progressive increase in δ
O
since 2005 AD may reflect a strengthening of the central Pacific El Niño under continued anthropogenic global warming. The relationship between seasonal precipitation and δ
O
with ENSO/PDO requires further studies.
A large array of proxy records
suggests that the “4.2 ka event” marks an approximately
300-year long period (∼3.9 to 4.2 ka) of
major climate change across the globe. However, the climatic ...manifestation of
this event, including its onset, duration, and termination, remains less
clear in the Indian summer monsoon (ISM) domain. Here, we present new oxygen
isotope (δ18O) data from a pair of speleothems (ML.1 and ML.2)
from Mawmluh Cave, Meghalaya, India, that provide a high-resolution record of
ISM variability during a period (∼3.78 and 4.44 ka) that fully
encompasses the 4.2 ka event. The sub-annually to annually resolved ML.1
δ18O record is constrained by 18 230Th dates with an
average dating error of ±13 years (2σ) and a resolution of ∼40 years, which allows us to characterize the ISM variability with
unprecedented detail. The inferred pattern of ISM variability during the
period contemporaneous with the 4.2 ka event shares broad similarities and
key differences with the previous reconstructions of ISM from the Mawmluh
Cave and other proxy records from the region. Our data suggest that the ISM
intensity, in the context of the length of our record, abruptly decreased at
∼4.0 ka (∼±13 years), marking the onset of a multi-centennial
period of relatively reduced ISM, which was punctuated by at least two
multi-decadal droughts between ∼3.9 and 4.0 ka. The latter stands out
in contrast with some previous proxy reconstructions of the ISM, in which the
4.2 ka event has been depicted as a singular multi-centennial drought.
The precipitation variability associated with the East Asian summer monsoon (EASM) has profound societal implications. Here, we use precisely dated and seasonally-resolved stalagmite oxygen isotope ...(δ
O) records from Shihua Cave, North China to reconstruct the EASM variability over the last 145 years. Our record shows a remarkable weakening of the EASM strength since the 1880s, which may be causally linked to the warming of the tropical Pacific and Indian Oceans. The δ
O record also exhibits a significant ~30-year periodicity, consistent with the instrumental, historical and proxy-based rainfall records from North China, plausibly driven by the Pacific Decadal Oscillation (PDO). Together, these observations imply that ~30-year periodicity is a persistent feature of the EASM, which remains significant with or without anthropogenic forcing. If indeed, the EASM rainfall in North China might decline significantly in the near future, which may affect millions of people in this region.
The Liangzhu culture in the Yangtze River Delta (YRD) was among the world’s most advanced Neolithic cultures. Archeological evidence suggests that the Liangzhu ancient city was abandoned, and the ...culture collapsed at ~4300 years ago. Here, we present speleothem records from southeastern China in conjunction with other paleoclimatic and archeological data to show that the Liangzhu culture collapsed within a short and anomalously wet period between 4345 ± 32 and 4324 ± 30 years ago, supporting the hypothesis that the city was abandoned after large-scale flooding and inundation. We further show that the demise of Neolithic cultures in the YRD occurred within an extended period of aridity that started at ~4000 ± 45 years ago. We suggest that the major hydroclimatic changes between 4300 and 3000 years ago may have resulted from an increasing frequency of the El Niño–Southern Oscillation in the context of weakened Northern Hemisphere summer insolation.
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