Paleoclimatic Changes Research Articles

Petroleum generation modelling of the Middle‐Late Cretaceous sediments in the Abu Gharadig Field, Northwestern Desert, Egypt

The present work introduces an integral study concerning the Middle‐Late Cretaceous source rocks in Abu Gharadig (AG) Field utilizing source rock evaluation techniques and hydrocarbon generation modelling. The used methods include TOC%, Rock‐Eval pyrolysis, vitrinite reflectance (Ro%), and 1D basin modelling data. Our results show that most of the studied marine Middle‐Late Cretaceous intervals in AG Field are considerable as source rocks, excluding the Abu Roash A‐D members. The Kharita, Bahariya, and Abu Roash E & G intervals have mainly gas‐prone kerogen. The Abu Roash F and Khoman B members contain mixed kerogen type II/III with oil/gas‐prone generative potential. Khoman A member has marine type II kerogen with mainly oil‐ and minor gas‐prone generative potential. Among the Middle‐Late Cretaceous rock units, the Khoman Formation is either immature or early mature, whereas others are mature enough to generate hydrocarbons. The burial history models typify a high subsidence rate during the deposition of Kharita, Bahariya, and Abu Roash formations in response to the Tethyan rifting phase. The timing of the peak of oil generation window for the Abu Roash G interval is ranged as Late Oligocene‐Early Pliocene time. Moreover, the timing of the peak of oil generation for the Abu Roash F interval is ranged as Early Miocene‐Latest Miocene. Based on transformation ratios (TR), the Abu Roash F member demonstrates a limited hydrocarbon expulsion (25% > TR <50), whereas both Abu Roash G and Khoman B members can generate in‐situ hydrocarbon (TR ≤10%). Compiling data along the AG basin from previous works infers that there are spatial and temporal discrepancies in organics composition and thermal maturity of the Middle‐Late Cretaceous intervals. Changes in paleoclimate, eustatic, and basin tectonics can be considered as the primary drivers that triggered such spatiotemporal variation. Integrated approaches are needed to constrain the multi‐geospheric interactions of major Cretaceous anoxic events in the Northwestern Desert of Egypt, and to explore the driving forces on these organics‐accumulating events.

Climatic and environmental changes in the Baidunzi wetland, Northwest China, over the last 800 years inferred from glycerol dialkyl glycerol tetraethers

To help understand the temperature and moisture variations in the semiarid and semi-humid regions of China that lie a transitional zone between the Westerlies and the East Asian monsoon, reconstruction of the regional climatic changes over the last millennium is useful. However, high-resolution time-series data related to the histories of climatic changes in these areas are limited. Therefore, this multiproxy analysis of a sediment core from the Baidunzi wetland, northwest China, was conducted using grain size, total organic carbon, glycerol dialkyl glycerol tetraethers (GDGTs), and molecular biomarkers. The results show that GDGTs can reliably reconstruct paleoclimate changes recorded in sediments in salt marsh environments. The climate and environment history of the past 800 years can be divided into the three stages: the end of the dry Medieval Warm Period (MWP) (1278–1366 CE), a humid Little Ice Age (LIA) (1366–1896 CE), and the humid Current Warm Period (CWP) (1896–1999 CE). The Baidunzi setting during the end of the MWP was a warm and dry wetland with high salinity, low water levels, and emersed aquatic plants, and the depositional environment transitioned from fluvial facies to shore lake facies. In contrast, the local climate during the LIA was cold and humid, and the era was characterized by the appearance of vascular flora and two short-term flooding events, that caused a rise in water levels. The lowest temperatures and highest salinities of the period were correlated, which was likely caused by seasonal freeze-thaw cycles. During the CWP, the local climate was warm and humid, with a higher water level than during the LIA, and emersed plants again developed in shallow lagoon facies. Generally, salinity was positively correlated with temperature, except for freezing and thawing salinization resulting from episodes of extremely low temperatures. The warm–dry to cold–humid climate changes of the area were like those of arid Central Asia, which indicates that the Baidunzi region was affected mainly by the Westerlies and was impacted by southward intrusions of that system. The area was also affected by the North Atlantic Oscillation and experienced diminished evaporation during periods of cold climate.

Flood activity revealed millennial-scale climatic changes during the late Holocene in the Qaidam Basin, northeastern Tibetan Plateau

Flood activity in arid region is not only crucial process for evolution of rivers and terminal salt lakes, but also sensitive indicator of paleoclimatic changes. Here, slackwater paleoflood sediments of the Nalinggele River, the largest river in the Qaidam Basin, were studied with optically stimulated luminescence dating and grain size analysis to reconstruct flood events, mechanisms and their climatic implications. Seven slackwater deposit layers which show a weak hydrodynamic sedimentary environment, were dated to three main flood stages at ca. 3.6–3.4 ka, 2.2 ka and 1.0 ka. These stages correspond to similar millennial-scale flood activities in the basin bordering Kunlun Mountains, millennial-scale humid intervals in the eastern Qaidam Basin, glacial melting events on the Tibetan Plateau, and as well warm intervals between cold ice-rafted debris events in the North Atlantic, which may triggered by and the intensified solar activities. These flood stages were attributed to increased precipitation from the enhanced Asian Summer Monsoon and increased glacial meltwater delivery during the late Holocene. The findings suggest that a climate on the northeastern Tibtean Plateau that was fluctuant and with humid periods during the late Holocene, and not undergoing a constant drying trend as previously understood.

Phylogeny of Strombidae (Gastropoda) Based on Mitochondrial Genomes

The marine gastropod Strombidae is widely distributed in tropical and subtropical regions all over the world and possesses high morphological diversity. In order to better understand how morphological characteristics evolved within Strombidae, a robust phylogenetic framework is needed. In the present study, the complete mitochondrial genomes ofLentigo lentiginosus,Euprotomus aratrum, andCanarium labiatumwere sequenced. The three newly sequenced mt genomes contained 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, two ribosomal RNA (rRNA) genes, and several non-coding regions, indicating a similar pattern with respect to genome size, gene order, and nucleotide composition compared with those of other strombids reported before. Two different datasets derived from mitochondrial genes were constructed to resolve the internal phylogenetic relationships of Stromboidea and Strombidae. Within Stromboidea, the sister group formed by Clade I [Rostellariidae + (Seraphsidae + Strombidae)] and Clade II [Xenophoridae + (Struthiolariidae + Aporrhaidae)] were fully recovered and supported by morphological synapomorphies as previously suggested. The phylogenetic positions ofL. lentiginosus,E. aratrum, andC. labiatumwere confirmed within Strombidae, and several morphological similarities were observed corresponding to the present phylogeny. A correlation between strombids speciation events and paleoclimate change was presumed. Our results indicate that complete mt genomes would be a promising tool to reconstruct a robust phylogeny of Strombidae with an increased taxon sampling in the future.

Sedimentary Characteristics of the Neogene in the Eastern Liaodong Area, Bohai Sea, China

The sedimentary characteristics of the Neogene in the eastern Liaodong area are poorly studied, which restricts the oil and gas exploration in this area. Based on the current seismic, logging, drilling, and core data, we have studied the sequence stratigraphy and sedimentary characteristics of the Neogene in the eastern Liaodong area. Ultimately, we identified the controlling factors of sedimentation and established the depositional model. In this study, six sequence boundaries of the Neogene were identified and can be divided into five third-order sequences. The sedimentary evolution can be divided into four stages: braided river delta, meandering river delta with a low sand-stratum ratio, meandering river delta with a high sand-stratum ratio, and meandering river delta. Both the palaeotectonic movements and paleoclimate changes of the Neogene influence the periodical fluctuation of the lake level and then control the vertical evolution of the sedimentary types. The paleogeomorphology controls the macroscopic distribution of the sedimentary facies zone, the paleo-valleys that are associated with the strike-slip faults control the channel strike, and the fault slopes at the edge of the lacustrine basins control the sand redistribution of the delta front.

Eruptive tempo of Emeishan large igneous province, southwestern China and northern Vietnam: Relations to biotic crises and paleoclimate changes around the Guadalupian-Lopingian boundary

Abstract The Emeishan large igneous province (LIP), southwestern China and northern Vietnam, is thought to have been a potential driver for the biotic crises and paleoclimate changes around the Guadalupian-Lopingian boundary (GLB; Permian), but the lack of high-precision radiometric dates to constrain the duration and eruption rates of the volcanism has limited the assessment of their relationship. We present new chemical abrasion–isotope dilution–isotope ratio mass spectrometry U-Pb zircon geochronology of three samples from the lowermost and uppermost parts of the volcanic succession in the central portion of the Emeishan LIP. The results demonstrate that Emeishan volcanism began by 260.55 ± 0.07 Ma and persisted until at least 257.22 ± 0.37 Ma. Combined with a previously published age of 259.1 ± 0.5 Ma for silicic ignimbrites, we estimate that ~85% of Emeishan LIP volume erupted within 1.45 ± 0.50 m.y. Our new results confirm that the Emeishan volcanism began slightly prior to the initiation of the associated mass extinction event and was contemporaneous with the associated warming interval. The new data support the hypothesis that the Emeishan LIP likely triggered the biotic crises and paleoclimate changes around the GLB.

Holocene vegetation history and responses to climate and sea-level change in the Liaohe Delta, northeast China

To reconstruct the Holocene vegetation history from Liaohe Delta in northeast (NE) China, a high-resolution palynological study on a well-dated sediment core ZK2 was conducted. The pollen record of ZK2 suggests that during the early Holocene, the regional vegetation in the plain was meadow-dominated by Artemisia. And forest with cool-temperate conifers and temperate broad-leaved trees were present in the nearby hills, which is coincident with the gradual climate warming and delta transgression. From mid-Holocene to early late Holocene, meadow vegetation with Artemisia was relatively stable, while the forest vegetation with broadleaved trees reached the maximum expansion in the nearby hills. The large expansion of broadleaved trees indicates warm and humid regional environmental conditions and this is coincidental with the relatively high regional sea-level stand during this period. Since ca. 1470 cal yr BP, with the continuous delta progradation, a large coastal region was colonized by Suaeda spp., which suggests that the formation of unique red beach wetlands along the coastal region of the Liaohe Delta. By analysis of pollen dispersal and transportation mechanism in surface sediments of Liaodong Bay, it is indicated that the percentage changes of arboreal pollen dominated by Pinus and Quercus and the non-arboreal pollen dominated by Amaranthaceae and Artemisia in core ZK2 may as an index refers to the local sea level oscillation and paleoclimate change. Then by comparison with previous multi-proxy records together with the surface sediment record from Liaodong Bay, it is suggested that the Holocene vegetation changes of the Liaohe Delta are mainly driven by the intensity changes of East Asia monsoon and regional sea-level oscillation.

Paleoenvironmental Changes Since the Late Pleistocene Revealed by Ostracodes Record in Changmu Co., Western Tibet

A 4.9-m profile (BG-1) in Changmu Co., western Tibet, provides a continuous climate record from the Late Pleistocene to mid-Holocene on the basis of ostracode assemblages and shell trace elements. The results show six distinct climate change zones from 23.4 to 4.9 ka BP based on U-Th dating. The climate remained extremely cold until 13 ka BP because of the influence of the Last Glacial Maximum, which was indicated by the rare ostracodes occurring in this period. After that, the temperature rose gradually and the paleolake (Changmu Co.) enlarged. The ostracode assemblage during this period had high abundance and diversity, although the dominance of cold-water species and low Mg/Ca ratios indicate that the climate was still cold. More runoff water from a relatively warm climate entering into the lake, suggested by the increased U/Ca and Mn/Ca, led to a high lake level of 13–10.5 ka BP; this trend was also verified by the decreasing Sr/Ca values. The climate changed from humid to drought between 10.5 and 7.9 ka BP, which was inferred from the decreased abundance of ostracodes; however, there was a short humid period from 9.5 to 9.2 ka BP suggested by increased U/Ca and Mn/Ca ratios. A gradual transition to a humid environment began at 7.9 ka BP and ended at 5.3 ka BP. After this period, an extremely arid climate occurred after rising temperature and increasing evaporation, indicated by sharply increased Mg/Ca and Sr/Ca ratios. Eventually, the Changmu Co. paleolake shrank and dried up at some time after 4.9 ka BP. The changes in paleoclimate in Changmu Co. since the Late Pleistocene corresponded well to changes that occurred in the Westerlies-dominated Central Asia, suggesting that the climate in this region was mainly controlled by Westerlies circulation.

Paleoenvironmental and Biotic Changes in the Late Triassic of Argentina: Testing Hypotheses of Abiotic Forcing at the Basin Scale

Paleoenvironmental factors such as climate change are often hypothesized as critical for ecosystem changes over evolutionary time scales. Theoretically, these changes should be observable in the fossil record, but the robust linkage of biotic shifts to climate events remains difficult. The Late Triassic Period is an ideal interval for testing such hypotheses within terrestrial ecosystems because of a number of large-scale climate events, such as the Carnian Pluvial Episode (CPE), and a rich, well-studied fossil record. Nonetheless, at regional to global scales, few linkages have been identified during most of the Late Triassic. Here, we synthesize a multi-proxy basin-scale dataset of paleoenvironmental data, including new information from clay mineralogy and paleosol major- and trace-element geochemistry, to understand paleoclimate changes in the Ischigualasto-Villa Unión Basin of northwestern Argentina. In combination with diversity and relative abundance information from the well-sampled plant and tetrapod fossil record in the basin, we then use accepted evolutionary models of abiotic forcing of changes in ecosystems to test previously proposed hypotheses of floral and faunal variations at a basin scale. We find that although many patterns are best explained by sampling issues and taphonomy, pseudosuchian archosaur diversity and rhynchosaur relative abundance conform to predictions of paleoenvironmental forcing as the climate changed from warmer, drier conditions to more temperate humid conditions. These data demonstrate how high-resolution multi-proxy data and a well-sampled fossil record at a basin-scale can be used to test hypotheses of abiotic forcing of ecosystems in deep time, and highlights where future efforts should be directed in terms of filling data gaps and testing new hypotheses.

A fossil diatom-based reconstruction of sea-level changes for the Late Pleistocene and Holocene period in the NW South China Sea

Marine transgressions-regressions have profoundly shaped marginal seas following global sea-level fluctuations driven by climate change. This study on a sedimentary core profile SO219/31-4 from the Beibu Gulf, northwestern South China Sea (SCS), reveals information about paleoenvironment, paleoceanography and paleoclimate changes through fossil diatom assemblages and grain size distributions during the last ca. 12900 cal. yr. BP. Eight local diatom assemblage zones were distinguished and assigned to paleoenvironmental fluctuations recording sea-level and depositional environment changes in eight stages, ca. 12900–11700 (stage 1), ca. 11700–9500 (stage 2), ca. 9500–7200 (stage 3), ca. 7200–5800 (stage 4), ca. 5800–3800 (stage 5), ca. 3800–2400 (stage 6), ca. 2400–800 (stage 7) and ca. 800–0 (stage 8), cal. yr. BP. After the low sea level of stage 1 within the last deglaciation, rapid increases in sea level in stages 2 and 3 were recorded as meltwater events pulse-1B and pulse-1C resulting in marine transgression rates of ca. 16 m/kyr and 8 m/kyr, respectively. The high sea level, above the present level, in stages 4 and 5, in the Middle Holocene Climatic Optimum period, was clearly documented by more significant open sea/tropical diatom species and coastal planktonic species percentages, respectively. The late Holocene regression of sea levels was marked by a pronounced reversion of diatom taphocoenosis, responding to neoglacial climate. Fossil diatom assemblages outlined responded to paleoclimate of global warming in the deglacial and early Holocene. This study provides additional insights into the late Pleistocene and Post-glacial history of a tropical-subtropical shallow water gulf, in the NW-SCS.

Sedimentary characteristics and implications for hydrocarbon exploration in a retrograding shallow-water delta: An example from the fourth member of the Cretaceous Quantou Formation in the Sanzhao depression, Songliao Basin, NE China

Based on the analysis of core, logging, and testing data, the fourth member of the Cretaceous Quantou Formation (K2q4) in the Sanzhao depression, Songliao Basin, is investigated in order to understand the sedimentary characteristics and hydrocarbon exploration significance of a retrograding shallow-water delta. The results show that during the sedimentary period of K2q4, the Sanzhao depression with a gentle basement experienced stable tectonic subsidence and suffered a long-term lake level rise caused by paleoclimate changes (from semiarid to semihumid), the K2q4 in the study area were dominated by a fining-upward deltaic succession and had relatively stable thickness. From the bottom to the top, the color of mudstone gradually changes from purplish-red to gray and grayish-green, the contents of caliche nodules decrease gradually, while the presence of pyrite in sediments becomes frequent. Channel sandstones mainly composed of siltstone and fine sandstone with developed high-energy sedimentary structures constitute the main sand bodies of deltaic deposits, but the scale of channel sandstones decrease upward. Despite the long-term lake level rise and fining-upward sedimentary succession, purplish-red mudstone, caliche nodules and thin channel sandstones are still broadly distributed in the study area, and thin channel sandstones can be found at the top of K2q4 covered by the black oil shale of Qingshankou Formation. These assertations suggest that the study area was dominated by retrograding shallow-water delta deposits during the sedimentary period of K2q4. In comparison with modern Poyang Lake, we infer that during the sedimentary period of K2q4, the study area experienced frequent lake level fluctuations triggered by paleoclimate changes despite the long-term lake level rise, and the lake level fluctuations control the deposition of retrograding shallow-water delta. In addition, most of the thin channel sandstones distributed at the top of K2q4 and covered by black oil shale are generally immersed in oil, indicating that the thin channel sandstones formed at the top of a retrograding shallow-water delta sedimentary succession are favorable targets for lithological reservoir exploration.

The Guttenberg δ13C excursion (GICE) and paleoclimate change recorded in the early Late Ordovician carbonate succession of the Ordos Basin, Northern Chinas

The well-known Guttenberg isotopic carbon excursion (GICE) is a global palaeoceanographic event in the early Katian, Late Ordovician. Here, based on analysis of the carbon oxygen isotopes and K-bentonite characteristics, we documented the evidence of the GICE from the Upper Ordovician carbonate succession in the Ordos Basin, Northern China. The results revealed a positive δ13C excursion occurred in the Jinsushan Formation. Based on SHRIMP U-Pb dating of the K-bentonites and biostratigraphic constraints, the carbon isotope excursion of X1 (in Xilingggou section) and Z1 (in Zhaolaoyu section) identified in the area can be regarded as local expressions of the GICE. It is the first time that the GICE was identified in the Ordos Basin. Compared with the GICE profiles from the Dolly Ridge, North America and the Mehikoorma Drill Core from Europe, the X1 profile exhibits a similar feature with a positive δ13C excursion of 2.11‰. While the Z1 profile shows a two-peaks curve with a positive shift up to 5.61‰, representing one of the largest shifts in δ13C for the GICE so far. Considering that the X1 and Z1 profiles started immediately above the K-bentonites, and the GICE in North America and Europe were also in close association with marked bentonites, we argued that the carbon cycle perturbation depicted by the GICE and its equivalents were genetically related to increased volcanic eruptions in the early Late Ordovician, which may have led to a climate cooling and enhanced organic burial, thus resulted in the positive δ13C excursion.

Polycyclic aromatic hydrocarbons in the Upper Cretaceous lacustrine deposits from the Songliao Basin (NE China): Implications for wildfires and paleoclimate

Changes in wildfires and paleoclimate during the Late Cretaceous have been widely discussed in the literature, yet terrestrial evidence for these changes is temporally limited. This study presents biomarker evidence for wildfires and paleoclimate using polycyclic aromatic hydrocarbons (PAHs) from drill core J79 of the Nenjiang Formation (K2n1+2, boundary at about 83.3 Ma) deposited during the Late Santonian in the Songliao Basin, NE China. A variety of di-ring to hepta-ring aromatic hydrocarbons, including pyrogenic-derived, petrogenic-derived and mixed PAHs, was identified in the lacustrine deposits using gas-chromatography mass-spectrometry. According to fluorene and its derivates, the PAHs in the K2n1 were dominantly preserved under an anoxic water column, with a shift to preservation under a weakly oxidizing water column (around 83.3 Ma) in the lower part of K2n2. The occurrence of higher-plant-derived PAHs (e.g., retene, simonellite, cadalene, perylene and 6-isopropy-1-isohexyl-2-methylnaphthalene) is as probable plant fingerprint, representing a relatively humid condition and a semi-humid to arid paleoclimate condition during the lower part of K2n1 and lower part of K2n2 and during the upper part of K2n1, respectively. Sharp increases in the abundance of pyrogenic PAHs compounds (e.g., benzo[h]fluoranthenes, benzo[e]pyrene, and coronene) are interpreted as indicators of intense wildfires in the K2n. The scale of fire events in the lower part of K2n1 and lower part of K2n2 was larger than that in the upper part of K2n1. This change in wildfire extent may have been caused by the wetter climate stimulating the growth of sufficient biomass to fuel large wildfires. Therefore, the availability of fuel likely played an important role in controlling fire frequency during the Late Cretaceous.

Paleoclimate-induced stress on polar forested ecosystems prior to the Permian–Triassic mass extinction

The end-Permian extinction (EPE) has been considered to be contemporaneous on land and in the oceans. However, re-examined floristic records and new radiometric ages from Gondwana indicate a nuanced terrestrial ecosystem response to EPE global change. Paleosol geochemistry and climate simulations indicate paleoclimate change likely caused the demise of the widespread glossopterid ecosystems in Gondwana. Here, we evaluate the climate response of plants to the EPE via dendrochronology snapshots to produce annual-resolution records of tree-ring growth for a succession of late Permian and early Middle Triassic fossil forests from Antarctica. Paleosol geochemistry indicates a shift in paleoclimate towards more humid conditions in the Early and early Middle Triassic relative to the late Permian. Paleosol morphology, however, supports inferences of a lack of forested ecosystems in the Early Triassic. The plant responses to this paleoclimate change were accompanied by enhanced stress during the latest Permian as determined by high-resolution paleoclimate analysis of wood growth intervals. These results suggest that paleoclimate change during the late Permian exerted significant stress on high-latitude forests, consistent with the hypothesis that climate change was likely the primary driver of the extinction of the glossopterid ecosystems.

Dunefield expansion and paleoclimate during MIS 3 in the Qaidam Basin, Northeastern Tibetan Plateau: Evidence from Aeolian-Fluvial processes and revised luminescence chronologies

It is proposed that an extremely warm, humid climate existed in the Tibetan Plateau (TP), including the currently hyper-arid Qaidam Basin (QB), during Marine isotope stage 3 (MIS 3). A detailed luminescence study of aeolian, fluvial and aeolian-fluvial records from the Tiekui Dunefield (TKD) and its margins in the eastern QB reveals paleoenvironmental and paleoclimatic changes during the MIS 3 (ca. 60–32 ka). The records, dated by post-Infrared Infrared Stimulated Luminescence (pIRIR), provide the first aeolian MIS 3 ages in the QB thanks to preservation by overlaying fluvial deposition in the dunefield margins and demonstrate the aeolian expansion of the TKD compared to its modern extent. Complemented by aeolian records in nearby regions, these deposits reflect intensified dune activity in an arid and windy climate and with adequate glacier-derived alluvial-dominated sand supply. These results do not support a significant increase in precipitation from the Asian Summer Monsoon (ASM). Comparisons of new ages derived from pIRIR and Optically Stimulated Luminescence (OSL) of quartz in this study suggest that some published quartz OSL ages of the QB may be underestimated, even below 90 Gy (ca. 30 ka, with normal dose rates of 2.8 Gy/ka). The revised chronology questions previously suggested hypotheses of the existence of a mega Qaidam Lake in the upwind reaches of the basin, under an extremely strong ASM during the MIS 3. We propose a conceptual aeolian-fluvial geomorphic model that demonstrates the paleoclimatic value of aeolian-fluvial records and where and how fluvial process can erode or preserve ancient and previously untapped aeolian records.

High-frequency modification of the central Mediterranean seafloor environment over the last 74 ka

Here we present a high-resolution record of benthic foraminiferal assemblages for the last 74 kyr from the Sicily Channel Ocean Drilling Program Leg 160 Site 963. Benthic foraminiferal results are compared with geochemical (benthic and planktic δ 18 O and δ 13 C) and calcareous plankton data, previously acquired on the same marine core sediments. Within the succession, three benthic foraminifera compositional zones were defined. Temporal changes in the assemblages are interpreted in the context of the modification of subtropical and temperate climate systems that affected the Mediterranean thermohaline circulation. A close connection between bottom conditions in the Sicily Channel and eastern Mediterranean Sea is evident in two intervals, characterized in the ODP Site 963 by reduced oxygen conditions. The first one, around 53–51 ka, is tentatively attributed to the ‘missing’ sapropel S2 while the second, between 35 and 29 ka, is marked by short and recurrent episodes of bottom-water oxygen decrease. Both are related to a weakening of the intermediate circulation in the Sicily Channel connected with relatively high northern hemisphere summer insolation and increase in Nile River discharge, which inhibited vertical mixing and intermediate water ventilation in Eastern Mediterranean Sea. Over the last deglaciation, the African humid period (AHP) and the sea level rise, also influenced the water mass structure in the Sicily Channel and a reduction of the bottom ventilation is suggested by a strong reduction of deep-water Miliolids. Decreased bottom oxygen levels, which testifies for a weakening of intermediate circulation in Sicily Strait, also characterized the interval corresponding to S1 deposition. Yet, the strong decrease of benthic foraminiferal abundance related to a low surface water trophic level, appears to be conditioned by the reduction of trophic levels in the western Mediterranean. The very high relative abundance of U. mediterranea recorded during this interval is explained by the availability of organic matter during a limited short year period and/or the availability of more degraded organic matter from river runoff. In general, compositional data analysis highlighted a quite complex response of benthic foraminifera to paleoclimatic changes. However, changes in the benthic foraminiferal assemblages recorded during the last glacial are coherent with surface paleoproductivity dynamics connected with D-O oscillation, and support oligotrophic, meso-eutrophic and oligo-mesotrophic conditions during the early interstadials, late interstadials and stadials, respectively. • High-resolution ODP963 (Sicily Channel) Last Glacial to Holocene benthic record. • Dansgaard-Oeschger imprints in bottom environments. • Connection between western and eastern Mediterranean dynamics. • Relationships between Levantine Intermediate Water flow and bottom ventilation.

Global Changes in Terrestrial Vegetation and Continental Climate During the Paleocene‐Eocene Thermal Maximum

AbstractMost studies of the response of terrestrial vegetation to climate change during the Paleocene‐Eocene Thermal Maximum (PETM) have focused on individual sites and sections. To get a broader perspective we compiled published records of terrestrial pollen and spores across the Paleocene‐Eocene transition at 38 sites around the globe. For the 10 sites with quantitative data PETM palynofloras were largely distinct in composition from those in the latest Paleocene or post‐PETM early Eocene. We also inferred paleoclimatic conditions at each site from the distributions of nearest living relatives (NLRs) of fossil pollen taxa among present‐day Köppen climate types. The NLRs of Paleocene high‐paleolatitude palynotaxa are most diverse in cooler climates, whereas the NLRs of PETM taxa are more diverse in warmer, wetter climates. At middle‐paleolatitudes NLRs of Paleocene palynotaxa are most diverse in warm, wet climates, whereas NLRs of PETM palynotaxa are most diverse in warm, seasonally dry climates. In the tropics there is little change from Paleocene to PETM in the climate distributions of NLRs. We compared changes in paleoclimate reconstructed from the Köppen distributions of the NLRs with those simulated from the Community Earth System Model (version CESM1.2). Paleoclimatic changes during the PETM inferred from palynological proxies are mostly consistent with modeled climate changes, including the expansion of temperate climates at the expense of cold climate types at high‐paleolatitudes and the expansion of temperate and tropical climates in middle‐paleolatitudes. Despite this concordance, modeled winter temperatures in continental interiors and high‐paleolatitudes remain colder than those reconstructed from NLR distributions.

Review of modern trends and historical stages of development of lake research in Mongolia

There is the need to divide Mongolia's lake research into trends of development stages and to provide a detailed analysis of modern lake research. The aim of this study is to identify the development stages of lake research in Mongolia and to analyse lake research development. This study provides a comparative analysis of the development trends of lake research carried out in the country. The historical development of lake research in Mongolia was divided into 4 stages in chronological order, highlighting the current research direction, scope, and contribution to geography. Since 1990, researchers from many countries have been able to conduct extensive research in Mongolia, and especially since the 2000s, lake research intensified owing to global warming and environmental change. Studies, in particular, focus on paleogeography, paleoclimate changes, lake water regimes and water level fluctuation. Mongolian lake-based studies have tended to identify environmental evolution from the Pleistocene to the Holocene. The investigated areas were primarily Khuvsgul Lake and Darkhad Basin, Lakes Valley and Gobi Lakes, the Great Lake Depression, Mongolian Altai and Khangai Mountain lakes. Since 1990, scientists from Russia, Mongolia, Germany, China, Japan, USA and South Korea have been increasingly focusing on research into lakes in Mongolia. Paleogeographic and paleoclimatic reconstruction, based on the lakes of Central Asia, is being conducted in an innovative manner. Dividing Mongolia's lake research into development stages and identifying research trends will help determine which areas of research can be developed in the future.

Multi-proxy records of paleoclimatic changes in sediment core ST2 from the southern Zhejiang-Fujian muddy coastal area since 1650 yr BP

Sediment core ‘ST2’ collected from southern Zhejiang-Fujian muddy coastal area (ZFMA) was analyzed for grain size, bulk elemental composition (TOC and TN), stable carbon isotopes (δ13C), and lignin-derived phenols. The C/N ratios (6.2–10.1) and δ13C values (−21.7‰ to −23.0‰) demonstrated the predominance of marine organic matter. This was supported by a three end-member mixing model generated based on N/C ratio, δ13C, and Ʌ (total lignin in mg/100 mg of TOC). The results showed that marine and soil-derived organic matter accounted for 68.0% and 29.7%, respectively, of the total organic matter. The syringyl/vanillyl (S/V; 0.32 to 1.07) and cinnamyl/vanillyl (C/V; 0.13 to 0.91) ratios, together with the estimated range of lignin phenol vegetation index (LPVI) from 22.39 to 1451.91, indicated the predominance of non-woody angiosperms. The high vanillic acid/vanillin and syringic acid/syringaldehyde ratios suggested that the sediments were degraded prior to deposition. Our results showed that the variation of soil-derived organic matter along the core was affected by the East Asian monsoons, suggesting an anti-phase relationship between East Asian Winter Monsoon and East Asian Summer Monsoon. On the other hand, the temperature variations affected the abundance and type of vegetation. In addition, the variation of soil-derived organic matter showed remarkable consistency with other climate factors, such as solar irradiance, El Niño Southern Oscillation, North Atlantic Oscillation and North Atlantic ice drift. Meanwhile, the coherency relationship between the soil-derived organic matter and paleotyphoon activity indicates a possible linkage with paleotyphoon activity. Thus, the southern ZFMA was affected by both regional and global climatic factors, as well as extreme events-typhoon activity.

Impact of Climate Change on Hunter‐Fisher‐Gatherer Cultures in Northern Japan Over the Past 4,400 Years

AbstractIn Hokkaido, northern Japan, densely populated societies of hunter‐fisher‐gatherer cultures persisted over the Holocene until the 19th century. We used the cellulose δ18O values of Sphagnum and vascular plants in peat cores from Rishiri Island to understand paleoclimate changes in Hokkaido over the past 4,400 years and discuss the impacts of climate changes on the development of the cultures. The cellulose δ18O values showed multi‐centennial and millennial variations, reflecting the intensity of the Tsushima Warm Current and the summer position of the westerly jet. The marine hunter‐fisher cultures responded to changes in the strength of Tsushima Warm Current and coastal primary production. In contrast, the inland cultures responded to changes in the latitudinal position of the summer westerlies. This implies that human societies of different lifestyles responded differently to climate changes.