Search

The Indo-Pacific Warm Pool (IPWP) is the primary supplier of heat and moisture to the global atmosphere, and exerts a significant impact on tropical and worldwide climate variability. This special issue expands our understanding of the paleoceanographic and paleoclimatic evolution of the IPWP since Neogene times with implications for understanding future change. It contains fifteen research articles addressing two primary themes: (1) Ocean-atmosphere coupled processes via the ocean water-column, sea surface, atmospheric evaporation/precipitation; and (2) Sediment source-to-sink and biogeochemical carbon-cycles, and their interactions with oceanographic, hydrological, tectonic and other factors. These contributions improve our understanding of thermocline temperature, salinity, oxygenation, hydrography, carbon cycle, biological productivity, and sedimentary response in the IPWP across Neogene and Quaternary time scales, as well as aiding in the forecast of future climate responses in the context of current global warming. The special issue will capture the attention of geologists, climatologists, and anybody else interested in global climate change. • This is the editorial preface for the VSI on Indo-Pacific Warm Pool. • 15 papers are included and shortly introduced. • Two themes are included. • The 15 papers provide new views on paleoceanographic and paleoclimatic changes in the Indo-Pacific Warm Pool. [ABSTRACT FROM AUTHOR]

The Arctic Ocean is rapidly warming. In this paper, we document changes in the source, distribution, and accumulation rate of organic matter (OM) for three sediment cores in the Bering and Chukchi seas to investigate changes to the oceanic carbon cycle over the past ∼75 years. Analyses were undertaken using bulk properties, such as total organic carbon (OC), total nitrogen (TN), stable carbon isotope (δ13C), OC to TN molar ratio (C/N), and biomarkers (lignin phenols). The OC, TN, and lignin (Σ8, in mg (g sediment)−1) contents were found to be significantly related to the fraction of sand (Sand%) as a result of sediment sorting and/or different sediment sources. Using an end-member mixing model, we estimated marine OM accounted for ∼67% of all organic matter in all cores, being the dominant source. Moreover, terrestrial OM mainly originated from angiosperm non-woody tissue, while moss contribution was negligible. In the Bering Sea shelf, OC% has not changed over time, but there have been some extreme peaks around the 1960s–1970s and in 2005, which correspond to increased terrestrial input from North American rivers. In the southern core from the Chukchi Sea, the OC% showed an apparent decrease after 2000, accompanied by an increase in sand content, likely due to enhanced delivery of volcanic rocks by the Pacific Inflow from the Bering Sea. In contrast, in the northern core from the Chukchi Sea, the OC% showed a significant increasing trend, with some peaks occurring at the same time as in the Bering Sea core. The mean increase rate was compared to the increase in Siberian riverine discharge, which both could be caused by long-term climate changes. The results highlight the regional differences in the response of OC preservation to climate change and other controlling factors. Further studies with higher spatial resolution are required to better understand the preservation of OC in response to climate change. [Display omitted] • The main vegetation source was vascular plant, contribution from moss was limited. • Marine source accounted for ∼67% of the sedimentary OC in the (sub)Arctic cores. • OC preservation changed differently in the (sub)Arctic Ocean in past decades. [ABSTRACT FROM AUTHOR]

Despite the importance of pastoralism, as an alternative or adjunct to farming in China's long history, a clear understanding of the spreading routes and mechanisms of pastoralism in China is lacking. Fungal spores can be a useful addition to zooarchaeological evidence and have been widely used to explore the origins and development of pastoralism in different regions of the globe. The northern Loess Plateau is one of the most important areas for the emergence and development of pastoralism in early China. The aim of this paper was to take the fungal spores in the Baihemiao (BHM) core that we extracted from a site in the Yulin region, combine them with the zooarchaeological records to explore their relationship with climate and environmental changes, and reconstruct the evolution of animal husbandry in the northern Loess Plateau since the mid-Holocene. The results indicate that the climatic conditions in the northern Loess Plateau during the first period of 6–4.2 ka were relatively humid, the number of domesticated herbivores was small, animal husbandry was not developed, and the spores of coprophilous fungi in the sediments mainly originated from wild herbivores. Fungal spores as well as zooarchaeological evidence reveal that cattle and sheep grazing developed rapidly in the region during the second period, c. 4.2–3 ka. We suggest that the arid climatic conditions during this period facilitated the development of pastoral activities in the northern Loess Plateau. However, this pastoral economy gradually weakened after 1.2 ka. • Sporormiella suggests a high volume of herbivore activities in the Baihemiao area in 6–4.2 ka. • Fungal spores and zooarchaeological record from the archaeological sites indicate that grazing activity was strong in 4.2-3 ka. • Arid climatic conditions facilitated the development of pastoral activities in the northern Loess Plateau in 4.2–3 ka. • Pastoralism weakened and declined during the period from 3 ka to 1.2 ka. [ABSTRACT FROM AUTHOR]

The combined effects of climate change and human disturbance has degraded lake ecosystems worldwide in recent times, but there are few studies that explore the relative impact of these factors over long timescales. In this paper, we use sedimentary pigment data to reveal variations in algal abundance and the lake ecological environment of a typical subalpine lake (Beilianchi Lake) in the southwestern Chinese Loess Plateau, to distinguish the relative effects of natural climate change and human disturbance over the past 5000 years. Our data show that between 5000 and 1400 cal yr BP, algal abundance exhibited a slow decline without obvious fluctuations, mainly driven by a gradually drying and cooling climate. After 1400 cal yr BP, algal abundance showed large and rapid fluctuations characterized by a pattern of a decline, then increase, and then decline again. During this period, human activities began to affect lake ecology and gradually overshadowed the role of climatic changes as the main driving factor. Enhanced human disturbances caused a rapid and synchronous decline in algal abundance due to increases in soil erosion and reductions in water transparency. Algal biomass levels recovered when the soil erosion intensity decreased during 800–500 cal yr BP corresponding to the period from Southern Song to Yuan Dynasties. Thereafter (during the period of Ming and Qing Dynasties), as human activities became further enhanced and the soil erosion intensity became very high, the lake ecosystem rapidly transitioned to a stable state of low algal growth. This indicates that the lake ecosystem may have had the capacity to recover from moderate external disturbances in the early stages of human activity, but the resilience of the lake ecosystem began to decrease under stronger human disturbances. Our findings provide important empirical evidence for evaluating the current state of lakes and for sound lake management in the future. • High-resolution sedimentary pigment data reveal the lake ecological evolution of an alpine lake since 5000 yr BP. • Human activities began to exceed climate in driving lake ecological changes since 1400 yr BP. • The effect of human activities on lake ecological changes is more dramatic. • Lake ecosystem may have the capacity to recover from moderate human disturbances. [ABSTRACT FROM AUTHOR]

The sedimentary sequences of the Yangtze River delta comprise important Quaternary records of tectonics, sea-level oscillation, and climatic change; however, analysis is hampered by a lack of a reliable chronological framework. In this paper, we present an integrated chronology for two sedimentary sequences (core ZKW2 and ZKW4) on the southern side of the Yangtze River delta, based on magnetostratigraphy and absolute methods (OSL, 14C, and ESR dating). The basal ages of the core ZKW2 and ZKW4 are ca. 2.25 Ma and 2.96 Ma, respectively. The integrated chronology indicates significant increases in the sedimentary accumulation rate at ∼0.15 Ma, rather than the Matuyama-Brunhes boundary as indicated by magnetostratigraphy alone. The observed sedimentary transition is possibly controlled by regional subsidence of the Zhe-Min Uplift, and climate evolution during the last interglacial period. • High-quality magnetostratigraphy is obtained for the Quaternary sediments in the YRD. • The SARs of the YRD sediments significantly enhanced since ∼0.15 Ma. • Tectonics and climate factors jointly control the sedimentary evolution in the YRD. [ABSTRACT FROM AUTHOR]

Coastal wetlands provide valuable ecosystem services and understanding their response to past climatic changes may help predict their possible future responses. In this paper, we obtained records of pollen, algae, sediment grain-size, and other environmental proxies, from a late Holocene sediment core (CFD-E) from the Caofeidian area, on the northwest coast of the Bay of Bohai, China. Our results indicate three major stages of environmental change. During Stage I (3500–2800 cal yr BP), arboreal pollen content was high (mostly >60%), especially for Pinus and Quercus , and the PCA sample scores on Axis 1 were negative indicating that regional vegetation was temperate broadleaved forest and the climate was wet. During Stage II (2800–2350 cal yr BP), the arboreal pollen content decreased substantially (mostly <40%), and the PCA Axis 1 sample scores were positive indicating a decrease in forest vegetation, grassland expansion, and a drier climate. During Stage III (2350–1400 cal yr BP), the arboreal pollen content increased again (mostly >40%), although it remained lower than during Stage I, indicating that forests expanded under a relatively humid climate while the wetland area decreased slightly. Our results also record the 2.8 ka and 2.4 ka events of monsoon weakening, which were characterized by increases in herbaceous pollen (indicating grassland expansion) and the drying of the regional climate. There are several differences in the regional expression of these two climatic events. During the 2.4 ka event, Chenopodiaceae pollen increased substantially (average of 42.0%), indicating the expansion of halophytes; whereas during the 2.8 ka event, an increase in Artemisia indicates the occurrence of a dry climate throughout the region. We suggest that the aridity during the 2.8 ka event was triggered by decreased solar activity and the resulting changes in the El Niño-Southern Oscillation, which weakened the East Asian summer monsoon. However, we suggest that the 2.4 ka event was driven by the weakening of the Atlantic Meridional Overturning Circulation. • Significant increase in halophytic vegetation during 3500–1400 cal yr BP • The 2.8 ka and 2.4 ka events were characterized by climate drying lasting ∼150 years. • During these two events the area of forest decreased and grassland expanded. [ABSTRACT FROM AUTHOR]

The distribution pattern of arid–humid climate in the modern northwest–southeast confrontation in Asia evolved from the zonal distribution pattern of the Paleogene. However, this evolutionary process remains poorly constrained by geological evidence. In this paper, we analyze the characteristics of sporopollen assemblages recorded in Late Eocene strata of the Jianchuan Basin in southwest China. We show that vegetation patterns exhibited a remarkable shift from tropical–subtropical sparse forest to subtropical–temperate mixed broad-leaved–coniferous forest at ∼40.6 Ma; this shift is further indicated by the rapid decrease in drought-tolerant plants, mostly Ephedra and Chenopodiaceae, evidence that the previous hot–dry climate was replaced by a warm–humid climate at this time. This evidence suggests that the Asian monsoon began to affect the study area at ∼40.6 Ma. We then comprehensively integrated sporopollen results from several basins across East Asia, revealing that the frontal edge of the humid monsoon climate moved intermittently to the northwest after the Late Eocene, and may have advanced to the Lunpola–Lanzhou line by the early Late Oligocene, this being similar to the position of the leading edge of the modern monsoon. Moreover, the frontal edge of the humid monsoon climate may have extended as far as the Qaidam Basin during the Middle Miocene, but then gradually retreated to the position of the modern monsoon front. The uplift of the Tibetan Plateau and global climate change may have played dominant roles in this evolution. • A Late Eocene sporopollen record was obtained from the subtropical Yunnan region. • The Asian monsoon extended from tropical to subtropical regions around 40.6 Ma. • The Asian monsoon reached the modern monsoon front in the early Late Oligocene. • The Asian monsoon advanced on one occasion to the Qaidam Basin in the Mid-Miocene. [ABSTRACT FROM AUTHOR]

Mountain glaciers are one of the most sensitive indicators of climate change. Reconstructing past glacier extents provides valuable insights into the climate change for specific regions where instrumental records are not enough and even absent. In the paper we mapped the outlines for 691 Little Ice Age (LIA) glaciers in terms of prominent moraines beyond contemporary glaciers in the Tanggula Mountains, central Tibetan Plateau (TP). Based on these glacier outlines, we reconstructed the ice thicknesses and surfaces for the LIA glaciers in the region. Accordingly, we calculated the equilibrium-line altitudes (ELAs) for contemporary and LIA glaciers. By comparing the ELAs between the contemporary and LIA glaciers, we estimated the LIA summer temperature decreases in different subregions of the Tanggula Mountains. Since the LIA, the ELA have risen by 35.6 ± 18.8 m, 26.1 ± 17.6 m, and 63.1 ± 38.6 m in the respective western, central, and eastern subregions of the Tanggula Mountains. Assuming no change in precipitation, the LIA summer temperature would decrease by 0.22 ± 0.12 °C, 0.14 ± 0.09 °C, and 0.34 ± 0.21 °C in the three subregions, respectively. Moreover, glaciers in the western, central, and eastern subregions have lost 13.3%, 23.9%, and 42.8% of their area, 15.4%, 25.3%, and 39.6% of their length, and 20.8%, 39.0%, and 61.0% of their volume, respectively. By compiling the LIA ELA data from previous studies, we also estimated the LIA summer temperature changes for other regions of the TP. The LIA ELA and summer temperature changes relative to the present showed a decreasing trend from the edges towards the interior on the TP. • LIA glaciers and summer climate were reconstructed at the Tanggula Mountains. • LIA summers were 0.22 ± 0.12 °C, 0.14 ± 0.09 °C, and 0.34 ± 0.21 °C cooler than present in three subregions. • Summer temperature change had a decreasing trend from the edges towards the interior on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The Carnian Pluvial Event (CPE) induced an intense carbon-cycle disturbance and biological crisis at a global scale. The eruption of the Wrangellia Large Igneous Province (W-LIP) is considered a possible triggering mechanism; however, this cannot fully explain the significant differences in environmental perturbations across different regions. In this paper, we present detailed records of petrography, mercury geochemistry, carbon and sulfur isotopes, trace elements, and provenance data for the Triassic lacustrine facies of the Ordos Basin in the North China Plate, which provide insights into the important effects of volcanic activities, other than the W-LIP, on palaeoenvironment during the CPE interval. Massive emissions of SO 2 , CO 2 , and pyroclastic deposits resulting from these volcanic activities triggered four humid episodes, each characterized by lake-level rise, negative δ13C org excursion, a transition from mudstones to organic-rich shales facies, as well as algal bloom within a time span of 180 kyrs. The establishment of an age framework in the Ordos Basin enables comparative analyses of environmental evolution during the Carnian age across the North China Plate, the western Tethys domain, and the South China Plate. During the period of global climate perturbation driven by the W-LIP eruption, we conclude that short-term localized volcanic activities may have further induced high frequentcy environmental perturbations, which influenced biological shifts and increase organic carbon burial. These short-term volcanic activities with different occurrence times and frequencies complicate local-scale palaeoenvironmental evolutions, which may be an important reason contributing to significant differences in environmental perturbations during the CPE interval across different regions of the globe. • Four humid episodes and sedimentary changes occurred within 0.18Ma in the Ordos Basin during Carnian age. • Environmental changes in the Ordos Basin was related to the local volcanisms in its nearby Qinling orogenic belts. • Short-term local volcanisms can complicate the environmental evolutions in different parts of globe during the CPE interval. • Local volcanic processes may cause inconsistent environment perturbation in different parts of globe during the CPE interval. [ABSTRACT FROM AUTHOR]

Climate modelling and palaeotemperature reconstructions derived from several proxies (TEX 86 , δ18O) suggest that the Late Cretaceous was one of the warmest intervals in Earth history. The greenhouse climate reached its acme near the Cenomanian-Turonian boundary (CTB) interval with sea surface temperatures over 35 °C in low and mid- palaeolatitudes, coinciding with the highest sea level stands of the Phanerozoic. Following this warming phase, a general cooling trend punctuated by short-term hot snaps characterized the rest of the Cretaceous. Palaeotemperature and palaeoenvironmental changes are well documented in deep-water carbonate deposits based on variations in geochemical proxies and distribution patterns of macro- and microfauna. However, such climatic and environmental fluctuations severely impacted carbonate platforms, sedimentary environments that are particularly sensitive to external perturbations. Palaeontological data show major changes within the main carbonate platform producers (rudists and benthic foraminifera) during the early Late Cretaceous. Both groups experienced major taxonomic turnovers at the CTB, followed by a further re-radiation in the middle/late Turonian. The lack of detailed palaeoclimatic reconstructions in shallow water carbonate succession hampers the possibility to investigate a possible causal relationship between temperature changes and faunal evolution. In this paper, we report integrated geochemical, sedimentological, and palaeontological data from the Adriatic Carbonate Platform (Friuli, north-east Italy). Benthic foraminifera biostratigraphy and isotope stratigraphy (δ13C and 87Sr/86Sr) were used to precisely constrain the stratigraphy of the late Cenomanian-middle Turonian interval. δ18O analysis on both well-preserved rudist shells and bulk rock samples enabled the construction of high-resolution palaeotemperature curves. The resulting temperature trends are comparable with those from the deep-water record across the late Cenomanian-Turonian interval. The warmest phase was in the Early Turonian with sea surface palaeotemperatures as high as 41–45 °C recorded in rudist shells. Data show temperature fluctuation from the late Cenomanian to the Early Turonian with a magnitude >7 °C. Benthic foraminifera and rudist evolution responded to these palaeotemperature fluctuations, and their decline in the late Cenomanian and full recovery in the Turonian suggest a strong link with temperature changes. • Reconstructed temperatures from carbonate platforms during the Cenomanian -Turonian interval are missing • High resolution paleotemperatures reconstruction and biota evolution (rudists and benthic foraminifera) from Friuli Carbonate Platform is presented • Paleotemperatures estimated using δ18O analyses on bulk rock and well preserved bivalve samples (rudists and Chondrodonta) • δ18O analyses in bivalve shells suggest warmest Temperatures °>40°C in the Early Turonian • Rudists and benthic foraminifera distribution/abundance strongly modulated by temperature changes [ABSTRACT FROM AUTHOR]

Southwestern China, a biodiversity hotspot, underwent dramatic climate change following the Last Glacial Maximum and intensive human activity also exerted a major impact since the late Holocene. In this paper, we report a pollen record from Yilong Lake in Yunnan Province, southwestern China, to understand vegetation response to long-term climatic variation and human activities at a regional-level over the last 27,000 years. Findings show that temperate and coniferous taxa were dominant before 18 cal kyr BP reflecting the glacial climate. Between 18 and 14 cal kyr BP, thermophilic taxa increased in response to global deglaciation. A notable shift from deciduous to evergreen forests occurred at approximately 14 cal kyr BP, after which pollen concentration increased but pollen diversity decreased. Pollen assemblages indicated dense forests, primarily composed of evergreen oaks developed under warm and strong summer monsoon conditions from 13 to 8 cal kyr BP. High rates of vegetation change occurred during the middle Holocene before vegetation diversity gradually increased during the Holocene Thermal Optimum, with high variability of precipitation in the Yilong Lake region. Anthropogenic forcing progressively became the main factor affecting vegetation composition and vegetation change rates over the past three millennia. • We reported a pollen record from Yilong Lake in Yunnan province, China. • Cold-tolerant taxa dominated before 18 cal kaBP after which thermal-like taxa increased. • Evergreen forests replaced deciduous forests around 14 cal kaBP. • Vegetation change rates peaked in mid-Holocene with mega-thermal but frequent droughts. • Departure of vegetation and potential climax occurred in late-Holocene due to human activities. [ABSTRACT FROM AUTHOR]