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Precise characterization of hydroclimate variability in Amazonia on various timescales is critical to understanding the link between climate change and biodiversity. Here we present absolute-dated speleothem oxygen isotope records that characterize hydroclimate variation in western and eastern Amazonia over the past 250 and 20 ka, respectively. Although our records demonstrate the coherent millennial-scale precipitation variability across tropical-subtropical South America, the orbital-scale precipitation variability between western and eastern Amazonia exhibits a quasi-dipole pattern. During the last glacial period, our records imply a modest increase in precipitation amount in western Amazonia but a significant drying in eastern Amazonia, suggesting that higher biodiversity in western Amazonia, contrary to 'Refugia Hypothesis', is maintained under relatively stable climatic conditions. In contrast, the glacial-interglacial climatic perturbations might have been instances of loss rather than gain in biodiversity in eastern Amazonia, where forests may have been more susceptible to fragmentation in response to larger swings in hydroclimate.

The Kuroshio intrusion (KI) is a northwestward‐flowing branch of the Kuroshio Current, which enters the South China Sea (SCS) and regulates its temperature, salinity, and water mass exchanges. However, limited direct observations hinder our understanding of KI's mechanisms and responses to climate change. Here, we present a 60‐year bi‐monthly resolved coral oxygen isotope (δ18Oc) record from Dongsha Atoll, the northern SCS. The dry‐season (December–March) δ18Oc record reveals interannual to decadal variabilities of the KI. The impact of the East Asian winter monsoon (EAWM) on Dongsha δ18Oc was more pronounced during the 1970s and 1980s and after the early 2000s, while the influence of the El Niño‐Southern Oscillation (ENSO) on Dongsha δ18Oc was higher between the 1980s and 1990s. The Pacific Decadal Oscillation (PDO) may have a relatively minor effect on KI strength or may indirectly modulate KI strength through its influence on ENSO activities. Our Dongsha δ18Oc record highlight the importance of the EAWM, ENSO, and PDO in predicting future KI changes. Plain Language Summary: The Kuroshio intrusion is a branch of the Kuroshio Current. It flows into the South China Sea and affects its temperature, salinity, and water movement. We however know very little how the Kuroshio intrusion responds to climate changes. Here we present a study on the chemical composition of a coral core from Dongsha Atoll in the northern South China Sea. Our study shows that the intrusion varies markedly over the past 60 years and is connected to changes in sea surface salinity. Stronger intrusions align with stronger East Asian winter monsoon intensity and El Niño events. Understanding how the Kuroshio intrusion reacts to climate change is important for effectively managing the potential impacts of global warming on the marine ecosystem. Key Points: A 60‐year‐long coral oxygen isotope record from Dongsha Atoll, South China Sea reveals interannual to decadal variations in the Kuroshio intrusionStrong Kuroshio intrusion, corresponding to high sea surface salinity, is identifiable over the past 60 yearsThe Kuroshio intrusion variations are primarily driven by East Asian winter monsoon changes and also influenced by El Niño‐Southern Oscillation [ABSTRACT FROM AUTHOR]

The impacts of anthropogenic forcing on Indian summer monsoon (ISM) rainfall are obscure, partly due to limited availability of highly resolved hydroclimate proxy records as well as the highly regionalized nature of precipitation. Here, we report an annually‐resolved speleothem oxygen isotope record from Xianren Cave, southwestern China, which represents rainfall change over the broad ISM region. We find that the region has endured at least six decadal‐scale weak monsoon events in the past three hundred years. One of them, lasting from the early to mid 19th century, shares the similar gradual, persistent trend as the most recent decline in ISM rainfall and both have a magnitude substantially larger than the others dominated by natural variability. This early weak monsoon event occurred during a historical time of intensive deforestation in the region. We conclude that the ISM trend could have been altered by the changes in land‐use and land‐cover since the early 19th century. Plain Language Summary: It is difficult to determine when human activities started to have visible effects on precipitation change. Here, we present a well‐resolved Indian summer monsoon (ISM) rainfall record, based on stable isotope studies on speleothems collected from a cave in southwestern China. The oxygen isotope record shows that ISM rainfall has six multi‐decadal decreases in the past three hundred years. One of the corresponding monsoon weakening, lasting from the early to mid 19th century, cannot be simply explained by natural variations in the climate system. This prolonged weak monsoon event was likely caused by regional‐scale changes in land‐use and land‐cover, which can be supported by carbon isotope data in speleothems as well as increased deforestation in the region. We hereby propose that observable changes in the trend of ISM rainfall caused by human activities could have occurred as early as in the early 19th century. Key Points: A speleothem oxygen isotope record shows that the Indian summer monsoon (ISM) has endured six multi‐decadal weakening in the past 300 yearsThe monsoon weakening, from the early to mid 19th century, has a similar gradual, persistent trend as the most recent decline in monsoon rainfallRegional changes in land‐use and land‐cover may have altered the trend of the ISM since the early 19th century [ABSTRACT FROM AUTHOR]

Monthly precipitation samples from Singapore were collected between 2013 and 2019 for stable isotope analysis to further our understanding of the drivers of tropical precipitation isotopes, in particular, 17O‐excess. δ18O ranges from –11.34‰ to –2.34‰, with a low correlation to rainfall (r = –0.31, p = 0.014), suggesting a weak amount effect. d‐excess is relatively consistent and has an average value of 10.89‰ ± 3.45‰. Compared to high‐latitude regions, 17O‐excess in our samples generally falls in a narrower range from 2 to 47 per meg with an average of 21 ± 11 per meg. Moreover, 17O‐excess shows strong periodic variability; spectral analysis reveals 3‐month, 6‐month, and 2.7‐year periodicities, likely corresponding to intraseasonal oscillations, monsoons, and the El Niño–Southern Oscillation (ENSO), respectively. In contrast, d‐excess shows no clear periodicities. Although spectral analysis only identifies 6‐month periodicity in the δ18O time series, δ18O tracks the Nino3.4 sea surface temperature variability; the average δ18O value (–5.2‰) is higher during El Niño years than ENSO neutral years (–7.6‰). Therefore, regional convection associated with monsoons and ENSO has different impacts on δ18O, d‐excess, and 17O‐excess. 17O‐excess and d‐excess are anticorrelated and do not relate to the relative humidity in moisture source regions. Extremely low humidity and drought conditions in moisture source regions would be required to account for high 17O‐excess. Processes during transport and precipitation likely modify these two parameters, especially 17O‐excess, which no longer record humidity conditions of moisture source regions. Our findings will be useful for further modeling studies to identify physical processes during convection that alter d‐excess and 17O‐excess. Key Points: Monthly tropical precipitation in Singapore exhibits a weak amount effectRegional convection has different impacts on precipitation δ18O, d‐excess, and 17O‐excessProcesses during transport and precipitation have modified 17O‐excess, which no longer records the relative humidity in moisture source regions [ABSTRACT FROM AUTHOR]

Numerous studies have been conducted on the Holocene climatic evolution of arid central Asia (ACA) using various geological proxies. However, the quality of the age control and the temporal resolution of the proxy records used make it difficult to characterize hydroclimatic changes on centennial to multidecadal timescales. Here we present a stalagmite δ18O record from Baluk cave in Xinjiang, NW China, in ACA, which has an average 22.8‐year resolution and provides a record of inferred hydroclimatic changes from 8.4 to 2.7 ka. Abrupt hydroclimatic shifts are evident during the following intervals: 2.75–2.90, 3.25–3.35, 3.75–3.85, 4.45–4.55, 4.75–4.90, 5.05–5.15, 5.2–5.3, 5.4–5.5, 5.9–6.0, 6.2–6.3, 6.4–6.5, 6.8–6.9, 7.1–7.6, 7.85–7.95, and 8.05–8.25 ka. Notably, an overall in‐phase relationship is observed between the hydroclimatic variations and change in solar activity, and the results of spectral analysis suggest the presence of the Eddy (~1,080 years), de Vries (~205 years), and Gleissberg (~88–102 years) cycles. This indicates a linkage between solar activity and hydroclimatic changes in ACA on centennial to multidecadal scales during the Holocene. We suggest that the influence of solar activity on hydroclimatic changes in ACA occurs via its effects on North Atlantic sea surface temperature, North Atlantic Oscillation, northern high‐latitude regional temperatures, and via direct heating. The relationship suggests that solar activity may play an important role in determining future hydroclimatic changes in ACA. Key Points: A precisely‐dated stalagmite δ18O record, spanning 8.4‐2.7 ka was obtained from Baluk cave, Xinjiang, Northwest ChinaBaluk cave δ18O record is characterized by abrupt centennial‐to multidecadal‐scale variations, suggesting dramatic hydroclimate shiftsSolar activity‐induced northern high‐latitude climate variations could be responsible for rapid hydroclimatic changes in arid central Asia [ABSTRACT FROM AUTHOR]

ABSTRACT A speleothem record from south-western China characterizes in detail the millennial-scale changes in Asian Monsoon (AM) intensity from 39.3 to 28.7 ka. The calcite δ18O profile, with an average resolution of ∼8 years, shows several strong monsoon events concurrent with Greenland Interstadials (GIS) 8-4. To gain a systematic perspective of AM millennial-scale variability, the new and previously reported data from the same cave are combined, showing that AM variation exhibits a broad similarity with Greenland ice δ18O records and with Antarctica but in an opposite sense. For the interval that encompasses GIS 5 and GIS 4.1, however, our stalagmite δ18O record depicts a sustained strong monsoon with no distinctive oscillation between these interstadials. Another prominent characteristic in our record is a gradual transition into Chinese Interstadial (CIS) 8, which is well constrained by an annually laminated sequence. We find that an initial rise in monsoon intensity, lasting a few centuries, significantly precedes the abrupt onset of CIS 8 in the AM realm. This suggests that atmospheric moisture and heat transport are probably capable of inducing abrupt climate change when a rapid reorganization of ocean/atmosphere circulations passes a tipping point. [ABSTRACT FROM AUTHOR]

Abstract: Speleothem growth requires humid climates sufficiently warm to stimulate soil CO2 production by plants. We compile 283 U/Th dates on 21 stalagmites from six cave systems in the NW coast of Spain to evaluate if there are patterns in stalagmite growth that are evidence of climatic forcing. In the oldest stalagmites, from marine oxygen isotope stage (MIS) 7–5, growth persists through the glacial period. Hiatuses and major reductions in growth rate occur during extreme minima in summer insolation. Stalagmites active during the last interglaciation cease growth at the MIS 5–4 boundary (74ka), when regional sea-surface temperature cooled significantly. During MIS 3, only two stalagmites grew; rates were highest between 50 and 60ka during the maximum in summer insolation. One stalagmite grew briefly at 41ka, 36.5 and 28.6ka, all during warm phases of the Dansgaard–Oeschger cycles. A pronounced Holocene optimum in stalagmite growth occurs from 9 to 6ka. The cessation of most growth by 4.1ka, coincident with broad increases in aridity over the Mediterranean and areas influenced by the North African Monsoon, suggest that regions such as NW Spain, with dominant Atlantic moisture sources, also experienced increased aridity at this time. [Copyright &y& Elsevier]

The regional monsoons of the world have long been viewed as seasonal atmospheric circulation reversal-analogous to a thermally-driven land-sea breeze on a continental scale. This conventional view of monsoons is now being integrated at a global scale and accordingly, a new paradigm has emerged which considers regional monsoons to be manifestations of global-scale seasonal changes in response to overturning of atmospheric circulation in the tropics and subtropics, and henceforth, interactive components of a singular Global Monsoon (GM) system. The paleoclimate community, however, tends to view 'paleomonsoon' (PM), largely in terms of regional circulation phenomena. In the past decade, many high-quality speleothem oxygen isotope (δO) records have been established from the Asian Monsoon and the South American Monsoon regions that primarily reflect changes in the integrated intensities of monsoons on orbital-to-decadal timescales. With the emergence of these high-resolution and absolute-dated records from both sides of the Equator, it is now possible to test a concept of the 'Global-Paleo-Monsoon' (GPM) on a wide-range of timescales. Here we present a comprehensive synthesis of globally-distributed speleothem δO records and highlight three aspects of the GPM that are comparable to the modern GM: (1) the GPM intensity swings on different timescales; (2) their global extent; and (3) an anti-phased inter-hemispheric relationship between the Asian and South American monsoon systems on a wide range of timescales. [ABSTRACT FROM AUTHOR]

Abstract: We have obtained a high-resolution oxygen isotopic record of cave calcite from Caverna Botuverá (27°13′S, 49°09′W), southern Brazil, which covers most of the last 36 thousand years (ka), with an average resolution of a few to several decades. The chronology was determined with 46U/Th ages from two stalagmites. Tests for equilibrium conditions show that oxygen isotopic variations are primarily caused by climate change. We interpret our record in terms of meteoric precipitation changes, hence the variability of South American Monsoon (SAM) intensity. The oxygen isotopic profile broadly follows local insolation changes and shows clear millennial-scale variations during the last glacial period with amplitudes as large as 3‰ but with smaller centennial-scale shifts during the Holocene. The overall record is strikingly similar to, but strongly anti-correlated with, a number of records from the Northern Hemisphere. We compared our record to other precisely dated contemporaneous records from Hulu Cave eastern China. Minima in δ 18O (wet periods, intense SAM) at our site are synchronous with maxima in δ 18O (dry periods, weak East Asian Monsoon, EAM) in eastern China (within precise dating errors) and vice versa. This anti-phased precipitation relationship between two low-latitude locations may be interhemispheric in extent, based on comparison with records from other sites. Precipitation anti-phasing may be related to north–south shifts in the mean position of the intertropical convergence zone (ITCZ) and asymmetry in Hadley circulation in two hemispheres, associated not with seasonal changes as observed today, but with millennial-scale climate shifts. The millennial-scale atmospheric see-saw patterns that we observe could have important controls and feedbacks on climate within hemispheres because of water vapor''s greenhouse properties. [Copyright &y& Elsevier]

The Marine Isotope Stage (MIS) 4/3 boundary, the so-called unfinished or failed termination, is a time period during which climate shifted from glacial to near-interglacial conditions that is akin to the Termination I. Paleoclimate records on this boundary can provide insights into the mechanisms of abrupt climate change under the circumstances when the global climate system has not reached a full threshold state. However, investigations on this specific climate period are sparse largely due to limited geological records with high temporal resolution. Here, we present a new highly resolved stalagmite record from Wanxiang Cave in western China that provides a detailed evolution of the Asian summer monsoon (ASM) from its northern fringe region. Established with 7 high-precision U Th dates and 647 pairs of isotope data (δ18O and δ13C), this record spans from 59.99 kyr B.P. to 52.94 kyr B.P., and contains the whole MIS 4/3 boundary. Its δ18O reveals three Chinese Interstadials (CISs) on millennial scales, i.e., CISs A.16–17 and 14. Sub-millennial events CIS A.17a and 16a correspond to the Greenland Interstadials 17 and 16 (GISs 16 and 17). The CIS A.17b is related to the 'precursor events' (PE 17), while the PEs 14 and 16 events are not evident in our δ18O record, probably due to the gradual change of the CIS A.14b and the lower amplitude of the CIS A.16b. Compared with other climate records, particularly those from the high latitudes, our δ18O record strengthens the notion of the close teleconnection between the ASM and high-latitude climates. Gradual change in δ18O from the CIS A.17b to 17a and the smaller amplitude of the CIS A.16b and 14b are likely coupled to the gradual Antarctic temperature variations, suggesting a dominant role of southern climate process to modulate ASM variability in western China via reorganization of atmospheric circulation. In addition, the westerly jet position relative to the Qinghai-Tibet Plateau may also have suppressed the abrupt 18O-depletion during these periods. At the onset of the MIS 4/3 boundary (at ∼59.82 kyr B.P.), an increase in the Northern Hemisphere summer insolation resulted in rapid ocean-atmospheric reorganizations between the high and low latitudes. This process led to an abrupt increase in precipitation associated with strengthening of ASM circulation, which promoted soil microbial activity and the transition of vegetation type from C4 to C3 as indicated by the δ13C decreasing in the record. After that, centennial-scale variations in δ13C are mainly related to soil humidity change throughout the MIS 4/3 boundary. Our δ18O record further confirms that the MIS 4/3 deglaciation is dominated by a northern-residing forcing, but also involves climate change process from the south. On a regional scale, the δ18O record from Wanxiang Cave may be largely influenced by the Indian summer monsoon, and thus inherits signatures from the south characterized by slightly more negative δ18O than other Chinese stalagmite records on millennial timescales. • A precisely dated stalagmite from the northern edge of the ASM captures the CIS A.14-17 during the MIS 4/3 boundary. • The δ18O records correspond well to millennial-scale climatic oscillations in northern high latitudes. • The well relationship between δ18O and Antarctic climate change confirms the impact of the SH climate process on ASM. • Rapid ocean-atmospheric reorganizations act as a vital part to abrupt recovery of ASM at the onset of the MIS 4/3. • The ISM may be the dominant factor influencing variations in δ18O in western China on regional scale. [ABSTRACT FROM AUTHOR]

Multi-proxy analysis of abrupt climate change during Ice Age Termination III (T-III) is necessary to understand Asian summer monsoon (ASM) characteristics and mechanisms. We present 230Th dates and δ 18O, δ 13C, with equilibrium diameter, carbonate deposition amount and lithological characteristics from an annually laminated stalagmite (No. YXB) in Yongxing Cave, central China. Our multi-proxy records span 243.90 to 239.20 ka before present, falling within T-III/Marine Isotope Stage 7e. The changes in δ 18O, equilibrium diameter, carbonate deposition amount, and lithological characteristics suggest a weak ASM interval during T III. By comparing these results with records from Ice Age Termination I (T-I), we find that the weakened ASM event during T-III is similar to the Younger Dryas (YD) event in terms of duration and structure. This result suggests that the YD-like event could be an inherent feature of glacial-interglacial climate cycles in the middle and late Pleistocene. The YXB δ 13C sequence, without YD-like events, is broadly similar to the δ 18O record on orbital timescale, indicating that variations in local vegetation could be driven by rising CO 2 during ice age terminations. • Stalagmite records based on layer counting chronology from Southern China. • Stalagmite δ 18O, lithological characteristics indicate a weak Asian summer monsoon interval during Termination III. • Duration and structure of weak monsoon interval during Termination III is similar to Younger Dryas. • δ 13C indicates no YD-III but driven by greenhouse gases during ice age terminations. [ABSTRACT FROM AUTHOR]

A number of key paleoclimate records in the Southern Hemisphere midlatitudes exhibit climate changes synchronous with abrupt climate changes in the North Atlantic. We advance a hypothesis – argued from consideration of model evidence, observational climate diagnostics, and atmospheric dynamics – that attributes said climate changes in the Southern Hemisphere to a modulation in the strength of the South Pacific Split Jet, a pronounced zonally asymmetric feature of the wintertime Southern Hemisphere westerlies. North Atlantic cooling is associated with a weaker Split Jet, characterized by weaker South Pacific subtropical and subpolar jets and a strengthened midlatitude jet. It leads to climate impacts over the South Pacific sector that coincides with regions with observed paleoclimate changes timed to the North Atlantic. These circulation changes are envisioned to operate in addition to the climate impacts resulting from the oceanic bipolar seesaw. A proposed global atmospheric teleconnection links North Atlantic cooling to the weakening of the Split Jet. North Atlantic cooling induces a southward shift of the marine Intertropical Convergence Zone and weakening of the Asian monsoon. The resulting Hadley circulation change weakens the wintertime South Pacific subtropical jet, and which in turn leads to a weaker South Pacific Split Jet. A weaker Split Jet leads to a southward shift of the zero wind-stress curl line, implying a shift in the same sense for the South Pacific subtropical front. Over land, it leads to winter warming over New Zealand, winter cooling over subtropical South America, drying over Western Patagonia, and winter warming and wetting of southernmost Patagonia. Our hypothesis also predicts reduced storminess over West Antarctica. Similar changes but of opposite sign occur in the Northern Hemisphere, where a stronger wintertime North Pacific subtropical jet increases precipitation over the Western United States. [ABSTRACT FROM AUTHOR]

Abstract: Although the initiation and continuation of orbital and millennial climate transitions were reported to be roughly similar, little is yet known about the extent to which their sequences of climate events are linked together in the same physical processes. Here we present a stalagmite isotope record from Wulu Cave, southwestern China, based on 1200 oxygen isotope data and 15 230Th ages, registering a detailed history of the Asian Monsoon (AM) from 61.3 to 50.5 ka BP with an average resolution of 12 yr. Two replicated, high-resolution calcite δ18O profiles show four millennial-scale strong summer monsoon events, analogous in timing and structure to Chinese Interstadials A.17–A.14 (CIS A.17–A.14), as recorded elsewhere in China and Greenland Interstadials 17–14 (GIS 17–14). These events exhibit two distinct phases, consistent with multi-decadal/centennial shifts in Greenland temperature and storminess. This relationship reveals a tight coupling between high- and low-latitude climates at sub-millennial scales, implying a role for westerly winds in linking Greenland temperature and the AM. Around the Marine Isotope Stage (MIS) 4/3 boundary, successive AM events resemble, but in higher frequency, structure of the Bølling–Younger Dryas (YD) surrounding Termination I. Along with evidence from similar shifts in bipolar temperature and atmospheric CH4, we suggest that the recurrence of similar climate structure worldwide is likely caused by changes in Atlantic meridional overturning circulation (AMOC) at various timescales under thresholds of global ice volume boundaries, as predicted by the bipolar seesaw model. [Copyright &y& Elsevier]

Abstract: An annual layer-counted and 230Th-dated stalagmite oxygen isotope record from Qingtian Cave in Hubei province, central China, provides an Asian Monsoon (AM) history across the Allerød to Younger Dryas (YD) transition, with an average 2.5-year resolution. Seasonal δ 18O profiles indicate that the calcite δ 18O is a sensitive proxy for AM changes, and the close similarity between the Qingtian and other cave records from eastern China suggests a large-scale regional coherence of monsoonal precipitation δ 18O variations associated with the temperature changes in high-northern latitudes. The annually-resolved chronology with a U–Th age uncertainty of less than 100 yr defines the timing, duration and transition of the early Allerød, the intra-Allerød cold period (IACP), the late Allerød, and the start of the YD. The 160-yr-long IACP, with two brief reversals, is clearly shown in both δ 18O and lamina thickness records. The early and late Allerød, separated by the IACP, are characterized by several decadal to centennial cycles of δ 18O variations, each punctuated by sub-cycles. These decadal to centennial monsoon variations correlate with the Greenland temperature changes, supporting a model simulation that the decadal North Atlantic Oscillation (NAO) and North Pacific Oscillation (NPO) are coupled via atmospheric circulation under glacial boundary conditions, perhaps affecting tropical/subtropical monsoon changes. However, the monsoon transition between the late Allerød and YD lasted 380 yr, longer than the analogous Greenland temperature shift by at least 130 yr [Stuiver, M., Grootes, P.M., GISP2 oxygen isotope ratios. Quat. Res. 53 (2000) 277–284]. This implicates other links besides the direct link between Greenland and the AM, which is now well documented. One possibility is the influence by Southern Hemisphere climate via cross-equatorial air flow [An, Z.S., The history and variability of the East Asian paleomonsoon climate. Quat. Sci. Rev. 19 (2000) 171–187]. [Copyright &y& Elsevier]

Karst area located in northwestern Vietnam is geologically well-known as a tectonically extruded block apart from its counterpart: Permian limestone distributed in Yunnan, southern China. It has long been geographically stabilized since its early sinistral movement ceased in middle Miocene. Its distribution covers latitudes roughly from 21 to 23 degree north where is currently located within the summer ITCZ. Enormous karst caves are formed due to the sufficient groundwater replenishment and speleothems are consequently developed including stalactite or stalagmite. With the purpose of understanding the paleo-precipitation changes in respond to the evolution of the global climate change, we collected stalagmites and used geochemical analyses to conduct sequential isotopic values and corresponding ages. Two of them within the age range from 22ka to 33ka display continuous records of precipitation in this period. Global climate events: the Heinrich events II, III and Dansgaard-Oeschger events 3 and 4 can be recognized in our records, similar to other speleothems collected in low latitudes. However, the changing patterns including starting time, rate, and duration are different from place to place when comparing with other geographical records. Also, our high-resolution results obviously exhibit centennial-scale events. According to the previous studies the Oxygen isotope record of speleothem is mainly controlled by the precipitation changes in this latitude. We believe those explicit features found in northwestern Vietnam are related to the strength variation of Asia Summer Monsoon, which is governed by the global climate forcing in both scales of millennium and centennial. [ABSTRACT FROM AUTHOR]