Climate changes on Southeastern Tibetan Plateau have important impacts on social and economic development, as well as the ecosystem of southwestern China and Indo-China Peninsula. Here, we collected ...two stalagmites from Shenqi (Miraculous) cave in southern Sichuan, China. The stalagmite δ18O record shows good coherence with local instrumental rainfall record, as well as tree ring- and pollen-based moisture reconstructions from southeastern Tibetan Plateau during overlapped time periods. As a result, we reconstructed high-resolution (∼4.9 yrs) monsoon precipitation variations on southeastern Tibetan Plateau over the past 2300 years by using the combined stalagmite δ18O record.
The result reveals an overall decreasing precipitation trend, with two most notable wet periods occurred in 60–280 AD and 370–510 AD. The most remarkably dry period is the recent 200 years. Some decadal scale wet and dry intervals were also identified. The abnormal drought during 1160–1245 AD might have accelerated Dali kingdom's demise at 1253 AD. Power spectrum analysis indicated significant 373-, 187-, 22-, 12- and 11- yr cycles in our stalagmite record, suggesting the impact of solar activity. Increased monsoon precipitation on southeastern TP was observed in solar activity minima during the last millennium. We further synthesized an integrated precipitation record for southwestern China and discussed spatial patterns of precipitation over China during the last two millennia. The comparisons confirm a "dry southern and wet northern" pattern in monsoonal China during the Medieval Warm Period and a "wet southern and dry northern" pattern during the Little Ice Age and Dark Age Cold Period. Solar activity, the strength of westerly jet and summer monsoon, as well as the SST of tropical Indo-Pacific might play important roles on the rainfall spatial patterns over monsoonal China during the last 2000 years.
•An overall decreasing rainfall trend on SE TP during the past 2300 years.•Increased rainfall during solar activity minima.•A ″dry southern and wet northern" pattern in monsoonal China during the MWP.•A "wet southern and dry northern" pattern during the LIA and DACP.
Hydroclimatic variations of arid central Asia (ACA) significantly impact regional ecosystems and human civilizations. Here we present a lake water salinity record of the last 3,000 years from Lake ...Sayram in the core area of ACA using a new alkenone isomer‐based RIK37 index. Our record shows an abrupt decrease in salinity by more than 5‰ since the “early” Little Ice Age (LIA) (about CE 1150), which can be attributed to the combined effect of regional wetting, cooling, and topographic features. Combined with other moisture records in the region, we find two periods of relatively wet conditions during CE 1150–1550 and 1850 to present, which may be linked to Arctic sea ice expansion due to natural variability and, from CE 1950, anthropogenically induced warming. The wet conditions during CE 1206–1260 may have favored the spread of the Mongol Empire across the entire core area of ACA.
Plain Language Summary
Arid central Asia (ACA), one of the largest arid zones in the world, suffers from water resource scarcity, which impacts the regional ecosystems and human civilizations. Reconstructions of lake water salinity in ACA can provide valuable information on past overall hydroclimatic changes, which is of crucial importance for our understanding of past and future climates. Here we apply a new salinity proxy, based on the lipid biomarkers of haptophyte algae, to quantitatively reconstruct salinity changes of the last 3,000 years from Lake Sayram in the core area of ACA and find an abrupt freshening of lake water since the early Little Ice Age (LIA). Our reconstruction, together with other moisture records in the region, indicate relatively wet conditions at two intervals during CE 1150–1550 and 1850 to present, which are associated with natural and anthropogenic forcing. During the period of CE 1206–1260, the favorable wet conditions may have aided the spread of the Mongol Empire across the entire core area of ACA.
Key Points
We present the first application of an alkenone isomer‐based RIK37 index as salinity proxy in Lake Sayram
Lake water freshened abruptly since the early Little Ice Age
Wet conditions during CE 1150–1550 and 1850 to present may be related to Arctic sea ice expansion and anthropogenically induced warming
Rain‐belt migration, and in particular monsoon migration, are a cardinal, yet under‐constrained aspect of climate change. Here, we present a new lake‐level record from a closed‐basin lake in northern ...China and a compilation of available lake level records from closed‐basin lakes located at the northern margins of East Asian and Indian monsoon regions. These data show that ca. 6 ka ago, changes in water availability, as recorded by the surface areas of the closed‐basin lakes, shrunk dramatically, within a few decades, and have not been restored to their pre‐6 ka sizes since. These data imply that the Indo‐East Asian monsoon systems underwent a large coeval southward contraction, which preceded the gradual decline in insolation forcing, and abruptly ended the Holocene Humid Period (HHP). This new compilation enables to constrain potential feedback mechanisms involved in the early termination of the HHP at the monsoon fringes.
Plain Language Summary
A cardinal question in climate research is how and why rain‐belts shift under different climatic conditions. Here we show, that ∼6,000 years ago the surface areas of nine closed‐basin lakes located at the northern margins of the East Asian and Indian monsoon regions shrunk dramatically, within a few decades, and have not been restored to their pre‐6 ka sizes since. These data suggest that an abrupt, large scale, southward contraction of the Asian monsoons ended the Holocene Humid Period, and caused large scale desertification at the monsoonal fringes.
Key Points
Lake‐levels of closed‐basin lakes at Asian monsoon margins were high during the early‐middle Holocene and dried out abruptly ∼6 ka ago
A lake‐level record from north China provides unprecedented age and rate resolution of monsoon decline at Holocene Humid Period termination
Asian monsoon margin lakes dried out earlier then vegetation change thus, “vegetation feedback” was not a leading factor of monsoon decline
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 andmiddle 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.
Knowledge of peatland dynamics and its response to the intensity of the Indian summer monsoon (ISM) is crucial to predict the future fate of the peatlands in the southwestern China under climate ...warming scenarios. In this study, we obtained a sediment core from the Napahai wetland in southwestern China and analyzed geochemical indices, including loss on ignition at 550 °C, carbonate content, as well as magnetic susceptibility, and ash-free bulk density, to investigate the peatland development since the last deglaciation. Results show that peat formation at ca. 13.3 cal. kyr BP in the Napahai wetland was likely attributed to climate warming during the Bølling-Allerød period. The results clearly suggest the peat continuously accumulated from 13.3 to 7.2 cal. kyr BP and weakened from the Middle to Late Holocene (7.2–1.5 cal. kyr BP), indicating notably wet conditions during the Early to Middle Holocene (11.8–7.2 cal. kyr BP) and a clear long-term drying trend in the Middle to Late Holocene. A comparison of the Napahai records with other monsoon intensity and related hydroclimatic records in areas dominated by the ISM suggests that the development of the Napahai peatland at orbital–suborbital timescales corresponded to the variations in the ISM intensity and the summer insolation.
•Napahai peatland initiated at ~13.3 cal kyr BP.•Napahai peat evolution at orbital timescale corresponded to Holocene ISM variations.•Records suggest a humid Early Holocene and a drying trend during Mid- to Late Holocene.
The long half‐life of 129I makes it useful for dating marine sediments aged 2–90 Ma. However, the lack of initial value dating hinders its application for dating terrestrial sediments. A large ...scatter of 129I/127I in prenuclear terrestrial samples has been reported; however, the key influencing factors remain unclear. This study presented iodine isotope data from three Argentine Entisol profiles and developed an iodine‐source model to determine the influence of the source on iodine isotopic composition. The temporal patterns demonstrated clear climate modulations in natural terrestrial iodine isotopes over the last ∼15 Kyr. The model identified rock weathering as a major source of iodine in continental sediments. Higher 129I/127I ratios at mid‐high latitudes arise from weak geomagnetic shielding of cosmic rays and thus a high production rate, implying limited meridional diffusion of atmospheric iodine. These findings reveal that environmental factors are significant for constraining the initial value of terrestrial 129I.
Plain Language Summary
In terrestrial sediments, the absence of a specific initial value poses a challenge for 129I dating. Through examination of three profiles of Argentine Entisols, this study investigated how changes in the environment over the past 15 Kyr affected iodine isotopic composition. The climate modulations of iodine isotopes were indicated by comparing them with climatic proxies. A simple multi‐source model of iodine suggested that “old” iodine from catchment rock weathering was a major iodine provider, and decreased 129I/127I with the enhanced South American Summer Monsoon and South Westerly Wind indicated a low‐129I iodine input. The deviant 129I/127I of the most southern site was hypothesized to be caused by a greater cosmogenic 129I production rate at high latitudes than at mid‐low latitudes.
Key Points
Natural 129I/127I was for the first time found to co‐vary with the summer monsoon and westerlies in South America
Rock weathering contributes more iodine to terrestrial sediments than oceanic emissions
High 129I/127I values at mid‐high latitudes imply low geomagnetic shielding and limited meridional diffusion of atmospheric iodine
The arid region of Central Asia is one of the world's major sources of dust and exerts a significant influence on marine ecosystems, atmospheric carbon dioxide concentrations, the global radiation ...budget, and thus global climate change. Recent global warming has considerably reduced mid-latitude net precipitation by decreasing the latitudinal temperature gradient between the Equator and the Arctic; however, the influence of ice sheet and solar insolation on moisture evolution in Central Asia during the Holocene remains uncertain. Here we show that the relative wet conditions during the early Holocene in northern Central Asia (NCA) were controlled principally by the southern position of the mid-latitude Westerlies under the negative phase of the North Atlantic Oscillation (NAO), a pattern that was influenced by the substantial remnants of the Laurentide and Fennoscandian ice sheets. Subsequent northward migration of the mid-latitude Westerlies under a positive NAO phase resulted in persistent drought conditions during the middle Holocene thermal maximum, due to the combined effects of relatively higher summer insolation and Arctic amplification as well as sea ice loss. In contrast, southward migration of the mid-latitude Westerlies since approximately 3.6 cal kyr BP, driven by declining summer insolation and coincident with the negative NAO phase, increased regional precipitation towards to persistent relatively wet conditions in Central Asia. This reconstructed pattern of Holocene moisture availability contrasts markedly with the increase in precipitation over Central Asia under the current anthropogenically forced warming, thereby justifying further investigation into the multiple forcing mechanisms driving natural and anthropogenic climate change.
The variations in Indian summer monsoon (ISM) precipitation during the last millennium are key to understanding ISM dynamics and predicting extreme hydroclimatic changes under global warming ...scenarios. Here, we reconstructed the history of ISM precipitation during the past ca. 800 yr based on multiple proxies, including sediment grain size, organic matter content, biogenic silica content, magnetic susceptibility, and major element data (e.g., Fe, Ti, and Ca), obtained for a core from Lake Mahu in southwestern China. Relatively humid climate conditions prevailed during the Little Ice Age (LIA; 1400–1700 CE), whereas a relatively dry climate has characterized the Current Warm Period (CWP; 1800 CE–present). A significant dry event occurred during the transition from the LIA to CWP. The hydroclimatic record for the last millennium from Lake Mahu is generally similar to those of other areas affected by the ISM, including southwestern China, South China, the South China Sea, and northern India. We propose that southward migration of the Intertropical Convergence Zone may have been responsible for the abrupt hydroclimatic change during the transition from the LIA to CWP.
•Humid LIA and dry CWP climates occurred in southern China and adjacent areas.•A notably drying event occurred during the LIA-CWP transition in southern China.•A rapidly southward shifted ITCZ may be responsible for such a hydroclimatic shift.
Understanding hydroclimatic patterns and their possible driving mechanisms during distinct climate periods over the last 1500 years—such as the Medieval Warm Period (MWP), the Little Ice Age (LIA), ...and the Current Warm Period—is crucial for predicting future changes to monsoon precipitation in southwest China under global warming scenarios. In this study, based on
210
Pb and
137
Cs dating of surface sediments and AMS
14
C dating of terrestrial plant residues, we establish a robust age model that covers the last ∼1500 years (AD 439–2012) at Lake Yihai in southwest China. We use analyses of multiple geochemical proxy indices, including loss on ignition at 550°C, total organic carbon, total nitrogen, C/N ratios, and stable carbon isotopes of organic matter to reconstruct changes in summer monsoon precipitation at Lake Yihai during the last ∼1500 years. The results show that, over southwest China, warm and dry climate conditions prevailed during the MWP (AD 1000–1400) and the past 200 years, whereas conditions during the LIA (AD 1400–1800) were cold and wet. This is consistent with evidence from other geological records over southwest China, such as stalagmite and lake sediment data. Similar hydroclimatic patterns have occurred over the last 1500 years in adjacent tropical/subtropical monsoon regions where the climate is similarly dominated by the Indian summer monsoon (e.g., South China, the South China Sea, Southeast Asia, Northeast India). We suggest that the meridional migration of the mean position of the Inter-tropical Convergence Zone, and El Niño/Southern Oscillation conditions which are linked to tropical Pacific sea surface temperature, are responsible for centennial-scale hydroclimatic patterns over southwest China and adjacent areas during the last 1500 years.
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