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The 8.2 ka event has been extensively investigated as a remarkable single event but rarely considered as a part of multi-centennial climatic evolution. Here, we present absolutely dated speleothem multi-proxy records spanning 9.0–7.9 ka from Beijing in North China, near the northern limit of the East Asian summer monsoon (EASM) and thus sensitive to climate change, to provide evidence of the intensified multi-decadal climatic oscillations since 8.52 ka. Three extreme excursions characterized by inter-decadal consecutive δ18 O excursions exceeding ±1σ are identified from 8.52 ka in our speleothem record. The earlier two are characterized by enriched 18 O at ∼8.50 and 8.20 ka, respectively, suggesting a prolonged arid event, which is supported by the positive trend in δ13 C values, increased trace element ratios, and lower growth rate. Following the 8.2 ka event, an excessive rebound immediately emerges in our δ18 O and trace element records but moderate in the δ13 C, probably suggesting pluvial conditions and nonlinear response of the local ecosystem. Following two similar severe droughts at 8.50 and 8.20 ka, the different behavior of δ13 C suggests the recovering degree of resilient ecosystem responding to different rebounded rainfall intensity. A comparison with other high-resolution records suggests that the two droughts–one pluvial pattern between 8.52 and 8.0 ka is of global significance instead of being a regional phenomenon, and is causally linked to the slowdown and acceleration of the Atlantic Meridional Overturning Circulation that was further dominated by the freshwater injections in the North Atlantic. [ABSTRACT FROM AUTHOR]

As prominent abrupt climatic events during the last deglaciation and the early Holocene, the Younger Dryas (YD) and the 8.2 ka events have been intensely discussed to reveal the relationship between their phases and intensities, and their underlying mechanisms based on massive marine and terrestrial archives. However, the related paleoclimate records with sufficient resolution and/or precise age constraints from the Southern Hemisphere, especially East Africa, are relatively sparse, hindering our comprehensive understanding about the phases of these two events. Here, we provide a precisely dated record of an aragonite-calcite stalagmite covering 11.3–13.5 ka BP from northwest Madagascar to unravel the arid conditions during the YD, in contrast to the pluvial conditions in the 8.2 ka event that has been evidenced before. Changes in austral summer precipitation related to the Intertropical Convergence Zone (ITCZ) have always been interpreted to be the primary means of controlling regional rainfall amounts and thus the δ18O variations in stalagmite. However, ITCZ's meridional migration alone is not enough to interpret the opposite hydroclimatic conditions during the YD and the 8.2 ka events in northwest Madagascar. The variation in convection intensity within the ITCZ combined with the rainfall dipole mode in East Africa, and the redistribution of the duration of the ITCZ's presence at different latitudes might be responsible for this phenomenon. In addition, sea surface temperature could play a nonnegligible role. [ABSTRACT FROM AUTHOR]

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 640,00o 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'., The seasonal cycle of solar heating over Asia gives rise to the Asian monsoon (AM), a vast system of overturning atmospheric circulation that transports heat and moisture during boreal summer [...]

The 8.2 ka event has been extensively studied, whereas its structure is ambiguous in North China. Here we present a high‐resolution (∼1 year) δ18O record from annual laminated speleothem from Beijing to characterize the detailed variability across this event in North China. Our record indicates a dry 8.2 ka event spanning 8.254–8.107 ka BP with a two‐stage structure superimposed by three prominent high δ18O excursions. The identical structure of speleothem δ18O records between North and central China during the event suggests a common forcing/response in East China, whereas the progressively increased offset between their average values may reflect changes in moisture source or rainout effect. A close comparison with the Greenland ice core records suggests a strong linear response of the Asian summer monsoon to the North Atlantic climate changes across the early and middle stages of the event, but a different mechanism in the termination processes. Plain Language Summary: As the most pronounced abrupt climate event in the Holocene, the 8.2 ka event has been studied using various geological archives worldwide, but its detailed structure in North China and its link to other climate systems remain poorly understood. Since the Beijing speleothem δ18O, a proxy of the precipitation δ18O, is sensitive to the Asian summer monsoon (ASM) variations, it allows us to establish precise timing and structure of the 8.2 ka event and estimate the cause of it. Our new speleothem δ18O record from Beijing reveals a two‐stage structure superimposed by three "V‐shape" excursions during the event and almost exactly covaries with another published speleothem record from central China, suggesting coherent climate changes over the east ASM domain in response to the same forcing. The gradually increased offset between them probably results from the changed atmospheric circulations. Our results suggest a fast climatic signal propagation from the North Atlantic to the ASM domain during the early and middle 8.2 ka event, and another forcing mechanism in the termination processes. Key Points: Annual laminated speleothem δ18O record from North China manifests a two‐stage 8.2 ka event superimposed by three positive excursionsHigh consistency in speleothem records from North and central China on interdecadal to multidecadal timescales indicates a common driverThe climate forcing for the termination process is different from the early and middle stages of the 8.2 ka event [ABSTRACT FROM AUTHOR]

The expansion of plants using the [C.sub.4] photosynthetic pathway is one of the most prominent changes in the global ecosystem during the Cenozoic Era. A significant late Miocene expansion is well documented. However, the existence and cause of subsequent expansions are still not clear, owing in part to the lack of long, continuous climate-vegetation records. Here we present two high-resolution carbon isotope time series, covering the past 7 m.y., derived from eolian deposits on the Chinese Loess Plateau. The data indicate three intervals of significant [C.sub.4] plant expansions within the semiarid monsoonal region of East Asia (ca. 2.9-2.7 Ma, 1.3-0.9 Ma, and 0.6 Ma-present). These expansions covary with strengthened East Asian summer monsoon circulation. We conclude that in East Asia, large-scale late Miocene [C.sub.4]/[C.sub.3] vegetation changes in semiarid areas have been primarily driven by warm seasonal precipitation and temperature variations associated with changes in monsoon circulation. Keywords: [C.sub.4] plant expansion, carbon isotope, summer monsoon, Chinese Loess Plateau, Miocene.

The objective of this work is to propose a more effective way to prepare an in-house CO2 with known triple oxygen isotope compositions. The major experimental steps include: (1) the O2 is combusted to CO2 on a graphite rod at 750 °C with Pt-catalyst for 3–4 min; and (2) converted CO2 is subsequently purified by two cryogenic traps. The results show high reproducibility of δ13C and δ18O values of the converted CO2 within 0.010–0.020 ‰ and 0.006–0.010 ‰ (1σ, SD), and the identical δ18O value within error with that of the original O2. Additionally, we have measured the triple oxygen isotope compositions of converted CO2 using an O2–CO2 Pt-catalyzed oxygen-isotope equilibration method. The measured δ17O values of CO2 show high reproducibility within 0.006 ‰ (1σ, SD), and are identical within error with the original O2 as well. Notably, our experiments also found that the O2 with heavier oxygen isotope ratios (δ18O > 40 ‰, VSMOW) might have a lesser conversion efficiency, and this effect, combined with the lighter isotope preferential fractionations during the reaction processes of O2 to CO and CO to CO2, may explain the observed lower 17O/16O and 18O/16O ratios of the converted CO2 relative to the original O2. [ABSTRACT FROM AUTHOR]

The abrupt climate event Younger Dryas (YD) has been extensively studied; however, its structure is still poorly understood. Climate in northeastern Brazil is very sensitive to the latitudinal position of the intertropical convergence zone (ITCZ) associated with abrupt climate change in the Atlantic. Here, we report changes in the ITCZ position within the YD by using precise speleothem multiproxy records from northeastern Brazil. We provide evidence for a gradual northward migration of the ITCZ preceding poleward shifts of the westerlies and the polar front in northern high latitudes within the YD. This can be attributed to gradual increase in atmospheric CO2 concentration as a consequence of the weakening Atlantic Meridional Overturning Circulation (AMOC). We suggest that a persistent increase in atmospheric CO2 might have triggered a resumption of the AMOC and reorganization of the atmosphere circulation in the Atlantic during the mid‐YD. Plain Language Summary: The Younger Dryas (YD) is the most recent millennial‐scale abrupt climate event in Earth history. Although its origin has been extensively studied, its structure is still poorly understood. Climate in northeastern Brazil is very sensitive to the latitudinal position of the intertropical convergence zone (ITCZ) responds to abrupt climate change in the Atlantic (e.g., YD). By using stable isotope and trace element proxy records of speleothem from Toca da Boa Vista Cave, northeastern Brazil, together with other paleoclimatic records in the Atlantic realm, we provide evidence for a gradual northward migration of the ITCZ preceding poleward shifts of the westerlies and the polar front in northern high latitudes within the YD. This can be attributed to a gradual increase in atmospheric CO2 concentration under the situation of weakening Atlantic Meridional Overturning Circulation (AMOC). A persistent increase in atmospheric CO2 concentration might have triggered a resumption of the AMOC and reorganization of the atmosphere circulation in the Atlantic during the mid‐YD. Key Points: Speleothem and other paleoclimate records confirm a wet climate in tropical South America within the Younger DryasPrecise speleothem multiproxy records reflect a bipartition of the Younger Dryas precipitation in northeastern BrazilGradual South‐North climate transition in the Atlantic responded to a gradual increase in atmospheric CO2 within the YD [ABSTRACT FROM AUTHOR]

Gas hydrates represent a huge reservoir of methane in marine sediments, prone to dissociation in response to environmental changes. There is consensus that past events of gas hydrate dissociation in the marine environment mainly occurred during periods of low sea level. Here, we report geochemical data for 2‐m‐thick layers of seep carbonate collected from a hydrate‐bearing drill core from ~800‐m water depth in the northern South China Sea. The aragonite‐rich carbonates reveal positive δ18O values, confirming a genetic link with gas hydrate dissociation. Uranium‐thorium dating of seep carbonates indicates that gas hydrates at the study site dissociated between 133,300 and 112,700 years BP, hence coinciding with the Last Interglacial (MIS 5e) sea‐level highstand. We put forward the concept that a climate‐driven increase in temperature was responsible for a period of pronounced gas hydrate dissociation. Plain Language Summary: The gas hydrate reservoir is a dynamically changing system extremely susceptible to variations of seafloor temperature and pressure. Therefore, gas hydrate dissociation and subsequent methane seepage frequently occur during times of global climate change, especially during sea‐level lowstands with reduced seabed pressure. However, this conclusion was mainly based on dating of seep carbonates sampled from the seabed. As a consequence, one cannot exclude that previous results have been compromised by a sampling bias since seafloor samples are easier to collect. Authigenic seep carbonates from drill cores represent a continuous record of gas hydrate dynamics. Our uranium‐thorium dating of seep carbonate from drill cores provides a unique example of the effects of temperature and pressure on the stability of the hydrate system in the Dongsha area, northern South China Sea (SCS), during the last interglacial stage (MIS 5e, about 130,000 years BP). Representing the most similar and most contemporary analog to the current interglacial, the study of a methane release event in the SCS during MIS 5e will shed light on the expected trend of methane release events in the future, while providing insight into the response of low‐latitude oceans to climate change. Key Points: U/Th dating of seep carbonates from a gas hydrate‐bearing sediment drill core provides constraints on the timing of methane seepageCarbonates precipitated from 18O‐enriched pore fluids derived from methane hydrate dissociationMethane hydrate dissociation occurred during sea‐level highstand (MIS 5e) possibly induced by increasing bottom‐water temperatures [ABSTRACT FROM AUTHOR]

Stalagmite is one kind of secondary carbonates formed in limestone caves (speleothem). After cave water droplets containing Ca2+ and H C O 3 − drip onto floor, carbonate in the water might become supersaturated due to CO2 degassing under certain conditions, resulting in the formation of stalagmite in a process year after year. Stalagmite is one of important geological archives for paleoclimate research. The advantages include wide spatial distribution, suitable for U-Th and U-Pb dating, enriched in climate proxies, continuity, long time span, comparability and lower sampling cost etc. These factors have propelled stalagmite paleoclimate research to the forefront of global paleoclimatology with an irreplaceable role. The stalagmite paleoclimate study started in the western countries, mainly in Europe and America in 1960s–1970s, while the relevant research in China was progressively developed in the 1980s–1990s after the Reform and Opening up. Although there was a huge gap between the overall research level in China and western countries, a solid research foundation, as well as a number of talent teams were established during the period. In the 21st century, starting from the publication of stalagmite records from Hulu Cave in Nanjing in 2001, the stalagmite paleoclimate research in China has ushered in a flourishing development and a real leap on the basis of international cooperation, resulting in significant international impacts. The landmark achievements, including establishment of the world's longest (640000 years) East Asian monsoon stalagmite record, as well as the longest Indian monsoon (280000 years), South American monsoon (250000 years), North American westerly climate (330000 years), Central Asian westerly climate (135000 years), and northwestern China westerly climate (500000 years), have laid a milestone in the paleoclimate study in these climate domains. Importantly, these stalagmite records have revealed the relationship of Asian monsoon variations with solar insolation climate change in polar regions, and the South American monsoon changes on orbital-suborbital timescales, which have provided new geological observations for the development of orbital-suborbital climate theory; elaborated coupling and differentiation relationships between the Asian monsoon and the westerly climate; reconstructed the history of Asian monsoon changes in the Holocene in detail, and thus the hydrological and climate variances behind Chinese and Indian civilization-cultural evolutions. Furthermore, a large number of high-resolution stalagmite records over the past 2000 years have been reconstructed, which are important for understanding short-term climate variability and magnitude, events, cycles, and thus the future climate projection. The achievements have also involved the improvements of a number of important techniques, such as U-Th dating method, the establishments of various hydroclimatic proxies, as well as the contributions to the reconstruction of the atmosphere 14C variation history over the past ∼54000 years. On the perspective of the future, the Chinese stalagmite community should continue to develop key techniques, further clarify the hydroclimatic significance of stalagmite proxies, impel the integration of related disciplines, and concentrate on key scientific issues in global climate change and major social demands. [ABSTRACT FROM AUTHOR]

A full‐spectrum characterization of past interglacial climate is a necessary prerequisite for the detection and attribution of climate changes during the current interglacial. Here we present a speleothem record of Asian summer monsoon (ASM) during Marine Isotope Stage (MIS) 11 interglacial (MIS 11c), from Yongxing cave, China. The record's unprecedented chronologic constraints and decadal‐scale temporal resolution allow a precise and direct comparison of ASM between the MIS 11c and the Holocene. Our data suggest that orbital‐centennial patterns of ASM were remarkably similar during both interglacial, including their pacing and structure. Notably, a multi‐millennial stronger monsoon late in MIS 11c, the "Late‐MIS 11c shift," is similar to the Late Holocene strengthening of the ASM, the "2‐Kyr shift." Thus, the multicentennial ASM weakening at the end of the Late‐MIS 11c shift could imply that the current century‐long ASM waning trend may persist into the future, if only natural forcings are considered. Plain Language Summary: The interglacial of Marine Isotope Stage 11 (MIS 11c) is generally considered to be an appropriate natural climate analog to the current interglacial, the Holocene. A new speleothem oxygen‐isotope (δ18O) record is reconstructed to characterize Asian summer monsoon (ASM) variability across MIS 11c on a wide range of timescales. This new record has an unprecedented high resolution (~11 years) and precise chronology constrained by 230Th dating and annual band counting. It thus allows for the first time a precise comparison of ASM variability between MIS 11c and the Holocene. We find that the observed pattern of decreasing ASM strength during the late portion of MIS 11c was interrupted by a multi‐millennial period of stronger monsoon (the "Late‐MIS 11c shift"), which is similar to the Late Holocene increase in ASM strength (the "2‐Kyr shift"), which also occurred against a backdrop of long‐term decline in Northern Hemisphere summer insolation. Notably, the Late‐MIS 11c shift was terminated by a multicentennial ASM weakening trend, thus suggesting that the current century‐long ASM waning trend could persist into the future, provided that the anthropogenic forcing does not supersede the natural variability. Key Points: A new high‐resolution record of the Asian summer monsoon is reconstructed over Marine Isotope Stage 11 as a natural analog to the HoloceneThe Marine Isotope Stage 11 record with a chronology constrained by annual band counting shows climate variability similar to the HoloceneThe projection of the Marine Isotope Stage 11‐Holocene comparison into the future suggests a weakening trend for the Asian summer monsoon [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The "4.2 ka event" is frequently described as a major global climate anomaly between 4.2 and 3.9 ka, which defines the beginning of the current Meghalayan age in the Holocene epoch. The "event" has been disproportionately reported from proxy records from the Northern Hemisphere, but its climatic manifestation remains much less clear in the Southern Hemisphere. Here, we present highly resolved and chronologically well-constrained speleothem oxygen and carbon isotopes records between ∼6 and 3 ka from Rodrigues Island in the southwestern subtropical Indian Ocean, located ∼600 km east of Mauritius. Our records show that the 4.2 ka event did not manifest itself as a period of major climate change at Rodrigues Island in the context of our record's length. Instead, we find evidence for a multi-centennial drought that occurred near-continuously between 3.9 and 3.5 ka and temporally coincided with climate change throughout the Southern Hemisphere. [ABSTRACT FROM AUTHOR]

The carbon isotopic compositions of soil organic matter (SOM) and total carbonate (TC) in Xifeng loess-paleosol sequence have been studied. The δ13CSOM values vary from -23.8‰ to -20.2‰, which are higher in interglacial than in glacial stages. Contrary to δ13CSOM values, the δ13CTC values vary from -8.5‰ to -3.6‰ and are lower in interglacial than in glacial stages. The differences (Δδ13C) between the δ13CS0M and δ13CTC values vary from 14.1‰ to 19.4‰. Our results from the Xifeng loess-paleosol sequence indicate that the Δδ13C values represent the ratio of primary carbonate (PC) to secondary carbonate (SC). The Δδ13C values were high in the loess stages, and the maximal PC-to-SC ratio can reach 6:4. But in the paleosol stages, the Δδ13C values were low, with a small proportion of PC. The Δδ13C values in loess-paleosol sequence also indicate the contributions of the dust to the loess sediment in the Chinese Loess Plateau because the dust contains the PC. [ABSTRACT FROM AUTHOR]

We have investigated carbon isotopic compositions of four plant genus/species, Bothriochloa ischaemum (C4), Stipa bungeana (C3), Lespedeza sp. (C3) and Heteropappus less (C3), along a precipitation gradient in northwest China in order to assess the impact of water availability on the carbon isotopic discrimination against 13C during carbon assimilation in this area. This information is necessary for reconstruction of paleovegetation, particularly paleo-C3/C4 plant ratios using δ13C value of organic matter in loess and paleosols in the Chinese Loess Plateau. The δ13C of C3 plants, as a group, exhibits a negative correlation with the annual precipitation amount with a total change and sensitivity of 5‰ and −1.1‰/100 mm, respectively, for the precipitation range from 200 to 700 mm. The C4 grass, B. ischaemum responds to aridity by decreasing 1.7‰ for over the precipitation range from 350 to 700 mm; the plant δ13C is significantly correlated with annual precipitation with a slope −0.61‰/100 mm. This result implies that without considering the effect of water availability on the plant δ13C values, reconstruction of percent C4 vegetation during the last glaciation can be overestimated by about a factor of two. [ABSTRACT FROM AUTHOR]

• A speleothem record from Eastern North America spans three glacial/interglacial cycles. • The oxygen isotope record displays strong cyclicity in the precession band. • The record lags summer insolation at 65°N by ∼5000 yr. • The record is in phase with Northern Hemisphere fall insolation. • Our findings are consistent with North American climates being forced by global ice volumes. The nature and controls of orbital-scale climate variability in North America (NA) are subjects of ongoing debates. On the basis of previous cave records from Southwestern United States, two mutually incompatible hypotheses have been proposed. One links NA orbital-scale climate variability to Northern Hemisphere (NH) summer insolation forcing in a manner analogous to low-latitude monsoon systems, while the other suggests that it is not causally tied to either changes in global ice-volumes or NH summer insolation. Here we report new cave oxygen isotope (δ 18 O) records from Buckeye Creek Cave (BCC), West Virginia, east central North America, covering most of the past three glacial-interglacial periods (∼335 to 45 kyr ago). The BCC δ 18 O record exhibits a strong precession-band cycle, which is in-phase with changes in global ice-volumes (i.e., sea level), sea surface temperatures in the NE Gulf of Mexico and is consistent with the results from published cave records from Nevada and Devils Hole. As with global ice-volume, the BCC records lag summer insolation at 65°N by ∼5000 yr, which stands in contrast with records of low-latitude monsoon variability in South America and Asia, which are in phase and out-of-phase with changes in summer insolation and sea level, respectively. Provided the degree of lag to summer insolation provides a measure of competing forcing from global ice-volume and summer insolation, our data suggest that NA orbital-scale climate variability is dominantly driven by ice-volume forcing. In addition, the sea surface temperatures in the NE Gulf of Mexico and changes in northern high-latitude cryosphere may be also important in explaining the unusually low δ 18 O values at times of the intermediate ice-volume periods in BCC and other NA cave records. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Previous research has shown a strong persistence for direct teleconnections between the East Asian summer monsoon (EASM) and high northern latitude climate variability during the last glacial and deglaciation, in particular between monsoon weakening and a reduced Atlantic meridional overturning circulation (AMOC). However, less attention has been paid to EASM strengthening as the AMOC was reinvigorated following peak Northern Hemisphere (NH) cooling. Moreover, climate model simulations have suggested a strong role for Antarctic meltwater discharge in modulating northward heat transport and hence NH warming, yet the degree to which Southern Hemisphere (SH) climate anomalies impacted the Asian monsoon region is still unclear. Here we present a new stalagmite oxygen-isotope record from the EASM affected region of central China, which documents two prominent stages of increased 18 O-depleted moisture delivery to the region through the transition from Heinrich Stadial 1 (HS1) to the Bølling–Allerød (B–A) interstadial; this is in general agreement with the other monsoonal records from both NH and SH mid to low latitudes. Through novel comparisons with a recent iceberg-rafted debris (IRD) record from the Southern Ocean, we propose that the two-stage EASM intensification observed in our speleothem records were linked with two massive Antarctic icesheet discharge (AID) events at ∼16.0 ka and ∼14.7 ka, immediately following the peak HS1 stadial event. Notably, the large increase in EASM intensity at the beginning of the HS1/B–A transition (∼16 ka) is relatively muted in the NH higher latitudes, and better aligns with the changes observed in the SH, indicating the Antarctic and Southern Ocean perturbations could have an active role in driving the initial EASM strengthening at this time. Indeed, Antarctic freshwater input to the Southern Ocean during these AID events would have cooled the surrounding surface waters and caused an expansion of sea ice, restricting the southern extent of the SH westerlies. Moreover, increased meltwater flux during IRD events would have freshened Antarctic Intermediate Water, leading to the increased formation of North Atlantic Deep Water and enhanced North Atlantic subsurface heat release, and causing a strengthening of the AMOC during the HS1-Bølling transition. The result of this sequence-of-events would have been warming in the North Atlantic whilst at the same time cooling in the Antarctic. The ensuing interhemispheric temperature gradient would have acted to push the ITCZ northward, weakening the Australian–Indonesian summer monsoon (AISM) whilst intensifying the EASM. [ABSTRACT FROM AUTHOR]

The Sansha Yongle Blue Hole (SYBH) is the deepest (301.19 m) blue hole known in the world and is a water-filled karst opening in the intertidal reef flats of the eastern Yongle Atoll, Xisha Islands, South China Sea. It is differentiated from the surrounding environment by its deep blue colour as observed when viewed from above. The SYBH exhibits extremely rare karst networks and speleothems and differs from the blue holes of the Bahamas and Bermuda, indicating a different development process. Here, we present the morphology and U Th ages of the SYBH, which document the evolution of the coastal cave over time. Morphology and lithostratigraphy indicate that the hole resulted from dissolution via ascending acidic water/gas followed by subsequent collapse. The adjacent volcanoes surrounding the eastern Yongle Atoll are the most likely source of these ascending fluids. U Th ages of the cemented carbonate sand underlying the entrance constrain an upper limit of the opening time of the SYBH to be up to 111.7 ± 9.5 kyr BP. Deeply submerged speleothems at −116 m determine the lower collapse time of the SYBH to be 29.16 ± 0.17 kyr BP. The SYBH probably formed due to the upward release of volcanogenic acid water/gas through low-lying unconsolidated carbonate sediments, followed by buoyant collapses due to a 40-m fall in the sea level during 31–29 kyr BP. As the sea level rose to −15 m in the early Holocene, corals grew in the cave opening since 8.58 kyr BP and surrounded the entrance for the SYBH. • SYBH may be dissolved by volcanic related ascending acidified gases or waters. • SYBH could collapse at about 29 kyr BP due to a rapid sea-level fall. • Optical U Th dating suggests Pleistocene eolianites in the Xisha Islands deposited during MIS 5. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this study was to investigate the optimization and pathways of lignosulfonate biodegradation by a newly isolated lignin-degrading bacterial strain, Sphingobacterium sp. HY-H. The optimal conditions for lignosulfonate degradation capability were determined by Taguchi's orthogonal matrix method to be: initial pH, 7.0; temperature, 30 °C; and a lignosulfonate/nitrogen (as NH4Cl) mass ratio of 5. Under optimal conditions, the maximum lignosulfonate degradation capacity of strain HY-H was 31%. In order to characterize the changes in residual lignosulfonate and the metabolic products, FTIR spectra, functional groups, and elemental and GC–MS analysis were introduced. An examination of the data suggests a possible route of lignosulfonate degradation by strain HY-H was that lignosulfonate was first depolymerized to low-molecular-weight compounds; then the side chains of lignosulfonate were partially oxidized and further decarboxylated to produce carbon dioxide. If properly optimized and controlled, strain HY-H may play a role in the treatment of pulp and paper wastewater containing a high concentration of lignosulfonate, as well as in the lignocellulose breakdown for biofuel and chemicals production. [Copyright &y& Elsevier]