Paleoclimatic Changes Research Articles

Developmental constraint shaped genome evolution and erythrocyte loss in Antarctic fishes following paleoclimate change

In the frigid, oxygen-rich Southern Ocean (SO), Antarctic icefishes (Channichthyidae; Notothenioidei) evolved the ability to survive without producing erythrocytes and hemoglobin, the oxygen-transport system of virtually all vertebrates. Here, we integrate paleoclimate records with an extensive phylogenomic dataset of notothenioid fishes to understand the evolution of trait loss associated with climate change. In contrast to buoyancy adaptations in this clade, we find relaxed selection on the genetic regions controlling erythropoiesis evolved only after sustained cooling in the SO. This pattern is seen not only within icefishes but also occurred independently in other high-latitude notothenioids. We show that one species of the red-blooded dragonfish clade evolved a spherocytic anemia that phenocopies human patients with this disease via orthologous mutations. The genomic imprint of SO climate change is biased toward erythrocyte-associated conserved noncoding elements (CNEs) rather than to coding regions, which are largely preserved through pleiotropy. The drift in CNEs is specifically enriched near genes that are preferentially expressed late in erythropoiesis. Furthermore, we find that the hematopoietic marrow of icefish species retained proerythroblasts, which indicates that early erythroid development remains intact. Our results provide a framework for understanding the interactions between development and the genome in shaping the response of species to climate change.

The differential genetic signatures related to climatic landscapes for jaguars and pumas on a continental scale

Modern and paleoclimate changes may have altered species dynamics by shifting species' niche suitability over space and time. We analyze whether the current genetic structure and isolation of the two large American felids, jaguar (Panthera onca) and puma (Puma concolor), are mediated by changes in climatic suitability and connection routes over modern and paleoclimatic landscapes. We estimate species distribution under 5 climatic landscapes (modern, Holocene, last maximum glaciations [LMG], average suitability, and climatic instability) and correlate them with individuals' genetic isolation through causal modeling on a resemblance matrix. Both species exhibit genetic isolation patterns correlated with LMG climatic suitability, suggesting that these areas may have worked as "allele refuges." However, the jaguar showed higher vulnerability to climate changes, responding to modern climatic suitability and connection routes, whereas the puma showed a continuous and gradual transition of genetic variation. Despite differential responsiveness to climate change, both species are subjected to the climatic effects on genetic configuration, which may make them susceptible to future climatic changes, since these are progressing faster and with higher intensity than changes in the paleoclimate. Thus, the effects of climatic changes should be considered in the design of conservation strategies to ensure evolutionary and demographic processes mediated by gene flow for both species.

Integrated Pliocene-Pleistocene magnetostratigraphy and tephrostratigraphy of deep-sea sediments at IODP Site U1424 (Yamato Basin, Japan Sea)

Sediments from the semi-enclosed Japan Sea are sensitive to paleoclimatic perturbations and they offer great opportunities for many regional and global paleoceanographic and paleoclimatic studies. These studies often require a robust chronology. However, due to rare preservation of calcareous microfossils and drastic changes in surface water salinity during glacial lowstands, the construction of a traditional oxygen isotope stratigraphy for Japan Sea sediments is often difficult. Here, we use sediments recovered at Integrated Ocean Drilling Program (IODP) Expedition 346 Site U1424 to build an integrated Pliocene-Pleistocene reference magnetostratigraphy and tephrostratigraphy for sedimentary sequences from the region. Rock magnetic experiments indicate that magnetic remanence of Site U1424 sediments are carried primarily by (titano)magnetite with small contributions from high coercivity minerals (e.g., hematite) and possibly iron sulphides (pyrrhotite and/or greigite). Dark-colored sediments appear to contain less (titano)magnetite probably due to reductive diagenesis under euxinic conditions. Natural remanent magnetization (NRM) of u-channel samples covering a continuous ~ 167.6 m sediment sequence at Site U1424 was repeatedly measured at 1 cm intervals before and after stepwise demagnetization. Despite lower NRM intensity in dark-colored sediments, NRM directional data from both dark- and light-colored sediments are considered suitable for the construction of magnetostratigraphy. Site U1424 sediments clearly recorded the majority of the polarity chrons and subchrons within the last ~ 4.89 Myr, with the Cobb Mountain subchron, the end of Kaena subchron, and the onset of Nunivak subchron less well preserved. Sixteen tephra layers from the site were sampled for chemical composition analyses and the results were correlated to reference tephrostratigraphy of the region. Ages of the identified tephras are consistent with and can be well integrated with the magnetostratigraphy. The resulting age model suggests that sedimentation rates at Site U1424 range between ~ 1.7 and 7.6 cm/kyr with an average of ~ 3.3 cm/kyr. The acquired magnetostratigraphy and tephrostratigraphy at Site U1424 provide a reference chronology that can be correlated with and transferred to other sediment sequences in the region to study paleoceanographic and paleoclimatic changes of the region as well as their links to other regional and global changes.Graphical abstract

Ostracods as a proxy for paleoclimatic change: An essential role of bioculture experiment taking Limnocythere inopinata (Crustacea: Ostracoda) as an example

Ostracods are favorable research materials for paleoclimatic reconstruction. Limnocythere inopinata, a commonly Holarctic species, is used frequently in paleoclimatic research. However, few ostracods bioculture data and its applications for paleoclimatic reconstruction have largely hindered deep understanding of the relationship between ostracods proxy and paleoclimatic change. Here we present the specific bioculture experiments on L. inopinata for the first time and statistically analyzed the survival curves of the experimental groups. The living specimens were collected from Lake Jiang co in northern Tibetan Plateau. Our results show that L. inopinata population living in Lake Jiang co prefers a narrow temperature range of 11–14 °C and a narrow salinity range of 3.50–6.50‰, respectively. The tolerance range is 11–17 °C for temperature and 0.50–9.50‰ for salinity. The results are apparently different from previous studies that this species has a very wide temperature (0.5–35.0 °C) and salinity range (0.18–18‰). Coupling with the records of other L. inopinata populations, it should be noted that L. inopinata populations living in different regions have adapted local aquatic environment, thus developed specific preference. This finding suggests that it is necessary to reassess the interpretation of L. inopinata valves in lacustrine sediments. As this example demonstrates, bioculture experiments on ostracods play an essential role in further realizing the relationship between ostracods proxy and paleoclimatic change.

Evolution pattern of Early Permian carbonate buildups: With reference to the carbonate mounds in eastern Inner Mongolia, North China

The Sakmarian–Kungurian (Early Permian) carbonate mounds of the Amushan Formation of the Deyanqimiao section in eastern Inner Mongolia, North China comprise phylloid algae-echinoderm mound, fusulinid-echinoderm mound and echinoderm mound. They were constructed by repeating the following steps in the mid-ramp and outer ramp environments: 1) skeletal grains accumulated in situ, or after short-distance transportation; 2) tubiform microbes eroded skeletal grains, induced the formation of CaCO3 crystallites near the cell surface, and trapped and bound suspended lime mud from ambient water; 3) some positive topographies slightly higher than adjacent sediments were formed.Data from North China, as well as the tropical Tethyan domain and the subtropical Pangean domain show a three-phase development pattern of Early Permian carbonate buildups. The first phase (Asselian-Sakmarian) is marked by carbonate buildups rich in organisms, such as phylloid algae, Palaeoaplysina, Shamovella, sponges and bryozoans. The second phase (Artinskian) is represented by the disappearance of phylloid algae and Palaeoaplysina from carbonate buildups resulted from the paleoclimatic change from an icehouse to a greenhouse. The third phase (Kungurian) is characterized by the sharp contrast between drastic decline of carbonate buildups in the subtropical Pangean domain and their successful development in North China and the tropical Tethyan domain.

Carbon and oxygen isotopes of calcified root cells, carbonate nodules and total inorganic carbon in the Chinese loess–paleosol sequence: The application of paleoenvironmental studies

Abstract The continuous loess-paleosol sequence on the Chinese Loess Plateau (CLP) is a major terrestrial archive of paleoclimate changes. The carbon and oxygen isotopes of soil carbonate in the sequence have long been applied to reconstruct Quaternary climate changes, yet which soil carbonates has the integrity to signify the climate variability still remains a controversy. Hence, in this study, we compared carbon and oxygen isotopic compositions of soil inorganic carbon (TIC), carbonate nodules, and calcified root cells (CRCs) found in the Xifeng loess profile on the CLP to test their significance as paleoclimate indicators. The X-ray diffraction and scanning electron microscope analysis performed on CRCs prove that they are pure micro-scale calcite minerals with distinct epidermal cell structures of plant rootlets. The results of 14C dating show that CRCs and nodules have evident translocation of younger carbon while the TIC appears more or less consistent with the model ages. The δ13CCRC values vary from −18.2‰ to −11.6‰, while the δ18OCRC values range from −13.7‰ to −9.2‰ on the V-PDB scale, spanning 6.6‰ and 4.5‰, respectively. The contrast shows that δ13CCRC values are more negative than those of nodules and TIC, and the δ13CCRC values disperse within a large spectrum, which reflects a rapid germination of root cell calcification with little or even no time for diffusion process within individual C3 plant roots. We argue that pure secondary micro carbonates like CRCs are closely associated with the plant-genic carbon. Their isotope values carry seasonal or even single event-based climate signals. Our study also suggests that stable isotope compositions of carbonate nodules and TIC are interfered by primary carbonate minerals. Thus, it should be used with caution when applying those materials for researches of paleoclimate changes.

Distribution, origin and speciation of soil selenium in the black soil region of Northeast China.

Selenium (Se) is an essential trace element within human beings that hold with crucial biological functions. Investigating the complex origin of soil Se is of great importance to scientifically approach the land use of Se-rich land use, and the respective promotion of regional economic development. In this study, 160 soil samples from 10 profiles in farmland and woodland were collected in Hailun city, which is a typical black soil region in Northeast China, in order to characterize the distribution and speciation of Se in the black soil, and to identify the origin of soil Se. The total selenium content in the soil ranges from 0.045 to 0.444μgg-1, with an average selenium content in black soil (0.318μgg-1) of three times greater than that found in the yellow-brown soil (0.114μgg-1). The land-use type has a significant influence on the distribution of selenium in the black soil. Moreover, Se and heavy metals have a significant (positive or negative) correlation, in which TOC plays an important role. The black soil presents a consistent REE distribution pattern with underlying yellow-brown soil indicating black soil originates from yellow-brown soil. REE geostatistical analysis suggests that the soil Se partly originates from shale weathering and enriches in black soil. Moreover, elemental geochemical analysis and XRD results show that the paleoclimate change from humid and warm to dry and cold is favorable for organic matter accumulation, resulting in less leaching and enhanced adsorption of selenium into the black soil.

Leaf Wax Lipid Extraction for Archaeological Applications.

Plant wax lipid molecules, chiefly normal (n-) alkanes and n-alkanoic acids, are frequently used as proxies for understanding paleoenvironmental and paleoclimatic change. These are regularly analyzed from marine and lake sediments and even more frequently in archaeological contexts, enabling the reconstruction of past environments in direct association with records of past human behavior. Carbon and hydrogen isotope measurements of these compounds are used to trace plant type and water-use efficiency, relative paleotemperature, precipitation, evapotranspiration of leaf and soil moisture, and other physiological and ecological parameters. Plant wax lipids have great potential for answering questions related to human-environment interactions, being for the most part chemically inert and easily recoverable in terrestrial sediments, including those dating back millions of years. The growing use of this technique, and comparison of such data with other paleoenvironmental proxies such as pollen and phytolith analysis and soil carbonate and tooth enamel isotope records, make it essential to establish consistent, best-practice protocols for extracting n-alkanes and n-alkanoic acids from archaeological sediments to provide comparable information for interpreting past climatic, ecosystem, and hydrological changes and their interaction with human societies. © 2020 The Authors. Basic Protocol 1: Total lipid extraction Support Protocol 1: Weighing the total lipid extract Support Protocol 2: Cleaning the PSE extraction cells Alternate Protocol 1: Soxhlet total lipid extraction Alternate Protocol 2: Ultrasonic total lipid extraction Basic Protocol 2: Separation of lipids by aminopropyl column chromatography Basic Protocol 3: Separation of lipids by silver-nitrate-infused silica gel column chromatography Support Protocol 3: Preparation of silica gel infused with 10% silver nitrate Basic Protocol 4: Methylation of n-alkanoic acids Basic Protocol 5: Gas chromatography mass spectrometry (GC-MS) Basic Protocol 6: Gas chromatography isotope ratio mass spectrometry (GC-IRMS).

Sharp changes in plant diversity and plant-herbivore interactions during the Eocene–Oligocene transition on the southeastern Qinghai-Tibetan Plateau

Herbivore damage patterns on fossil leaves are essential to explore the evolution of plant-herbivore interactions under paleoenvironmental changes and to better understand the evolutionary history of terrestrial ecosystems. The Eocene–Oligocene transition (EOT) is a period of dramatic paleoclimate changes that significantly impacted global ecosystems; however, the influences on plant-herbivore interactions during this period are largely unknown. We identified taxonomic composition of the flora, and investigated well-preserved herbivore damage on fossil leaves from two layers of the Lawula Formation in Markam County, southeastern Qinghai-Tibetan Plateau (QTP), China. Besides, paleoclimate conditions were reconstructed using fossil plant assemblages. The plant assemblage from the latest Eocene layer (MK-3, ~34.6 Ma) was dominated by Fagaceae and Betulaceae, whereas Rosaceae and Salicaceae were the most abundant in the earliest Oligocene layer (MK-1, ~33.4 Ma). In MK-3, 932 out of 2428 fossil leaves were damaged and presented 41 damage types (DTs). The richest functional feeding groups (FFGs) in this layer were hole feeding, margin feeding, and galling. In MK-1, 144 out of 599 leaves were damaged and presented 20 DTs, with the major FFGs being hole feeding, margin feeding, and skeletonization. Generally, MK-3 had a significantly higher damage frequency (DF) and more DTs compared to MK-1. The decline in temperature, accompanied by the mountain uplift during the EOT on the QTP margin, led to changes in plant composition, with a consequent decrease in herbivory quantity and diversity. Our results shed new light on the influence of paleoenvironmental changes in shaping the evolution of biodiversity as well as the ecosystem on the plateau.

The Eocene‐Oligocene Transition in the South‐Western Neo‐Tethys (Tunisia): Astronomical Calibration and Paleoenvironmental Changes

AbstractA detailed biostratigraphic, chemostratigraphic, and chronostratigraphic study was carried out in the South‐Western margin of the Neo‐Tethys ocean (Tunisia) covering the Eocene‐Oligocene interval to report potential paleoenvironmental and paleoclimatic changes associated with the growth of the Antarctic ice sheet (AIS). The studied section consists of marls and limestones extending from the Helicosphaera compacta nannofossil Zone (CNE21) to the Reticulofenestra umbilicus Zone (CNO2). The Bc of Clausicoccus subdistichus coincides in northeastern Tunisia with the extinction of hantkeninids and is thus used here to define the Eocene/Oligocene boundary (EOB) at 34.03 Ma. Calcareous nannofossil assemblages suggest a significant change from oligotrophic/warm surface waters during the late Eocene to eutrophic/cool waters during the early Oligocene. The observed changes in trophic conditions are synchronous with a shallowing trend testified by an increase in nearshore species and enhanced terrigenous input. Major environmental changes occurred at the EOB and across glaciation event Oi‐1a whereas we record a poor imprint of glaciation event Oi‐1. Three orbital configurations have been distinguished: (1) The late Eocene is characterized by a prominent 405‐kyr cycle and a weak obliquity component; (2) the onset of cooling at 34.35 Ma coincides with the rosette‐shaped discoaster extinction and is reflected by a shift toward enhanced obliquity and short‐eccentricity cycles. The installation of a fully developed AIS (event Oi‐1a, 32.75 Ma) shows the most pronounced obliquity imprint reflecting an increased influence of high‐latitude climate processes; (3) after 31.75 Ma, the obliquity decreases in coincidence with the return to a dominant long‐eccentricity cycle.

Evidence of Abrupt Climate Change during the Mid‐ to Late‐Holocene Recorded in a Tropical Lake, Southern China

AbstractResearch on abrupt paleoclimatic and paleoenvironmental change provides a scientific basis for evaluating future climate. Because of spatial variability in monsoonal rainfall, our knowledge about climate change during the mid‐ to late‐Holocene in southern China is still limited. We present a multi‐proxy record of paleoclimatic change in a crater lake, Lake Shuangchi. Based on the age‐depth model from 210Pb, 137Cs and AMS14C data, high‐resolution mid‐ to late‐ Holocene climatic and environmental records were reconstructed using multiple indices (TOC, TN, C/N, δ13C and grain size). Shuangchi underwent a marked change from a peat bog to a lake around 1.4 kaBP. The C3 plants likely dominated during 7.0–5.9 ka and 2.5–1.4 kaBP, while C4 plants dominated between 5.9–3.2 and 3.0–2.5 kaBP. Algae were dominant sources of organic matter in the lake sediments after 1.4 kaBP. Several intervals with high concentrations of coarser grain sizes might be due to flood events. These results reveal that several abrupt paleoclimatic events occurred around 6.6 ka, 6.1 ka, 5.9 ka, 3.0 ka, 2.5 ka and 1.4 kaBP. The paleoclimatic change recorded in the lake may be related to the migration of the Intertropical Convergence Zone (ITCZ) and El Niño ‐ Southern Oscillation (ENSO) activity.

Paleoclimatic evolution as the main driver of current genomic diversity in the widespread and polymorphic Neotropical songbird Arremon taciturnus.

Several factors have been proposed as drivers of species diversification in the Neotropics, including environmental heterogeneity, the development of drainage systems and historical changes in forest distribution due to climatic oscillations. Here, we investigate which drivers contributed to the evolutionary history and current patterns of diversity of a polymorphic songbird (Arremon taciturnus) that is widely distributed in Amazonian and Atlantic forests as well as in Cerrado gallery and seasonally-dry forests. We use genomic, phenotypic and habitat heterogeneity data coupled with climatic niche modelling. Results suggest the evolutionary history of the species is mainly related to paleoclimatic changes, although changes in the strength of the Amazon river as a barrier to dispersal, current habitat heterogeneity and geographic distance were also relevant. We propose an ancestral distribution in the Guyana Shield, and recent colonization of areas south of the Amazon river at ~380 to 166kya, and expansion of the distribution to southern Amazonia, Cerrado and the Atlantic Forest. Since then, populations south of the Amazon River have been subjected to cycles of isolation and possibly secondary contact due to climatic changes that affected habitat heterogeneity and population connectivity. Most Amazonian rivers are not associated with long lasting isolation of populations, but some might act as secondary barriers, susceptible to crossing under specific climatic conditions. Morphological variation, while stable in some parts of the distribution, is not a reliable indicator of genetic structure or phylogenetic relationships.

A 23000 year old record of paleoclimatic and environmental changes from the eastern Arabian Sea

Abstract Climate of the eastern Arabian Sea is highly influenced by both global climate and Indian monsoon. We produced multi-proxy records of benthic foraminiferal biofacies and stable isotope ratio (δ13C and δ18O), planktic foraminifera and total organic carbon (wt%) content of sediments from core SK291/GC11 in the upper continental shelf off Mangalore, off eastern Arabian Sea (EAS) to decipher paleoenvironmental and paleoclimatic changes during the past ~23,000 years. The monsoon was weak during the Last Glacial Maximum ~23,000–18,000 calibrated years before Present (cal yr BP) when sea level was lower. Globigerinoides ruber populations fluctuate from 30 to 60% in the studied interval with a maximum during ~6000–5000 cal yr BP and a minimum during 19,000–17,000 cal yr BP. The δ18O values of benthic foraminifer Ammonia gaimardii suggest pronounced cooling phases during ~23,000–18,000 cal yr BP, and a short-term cooling at ~6000 cal yr BP. Several intervals of high organic productivity and low oxygen conditions were identified based on benthic foraminiferal biofacies during 23,247–682 cal yr BP. Wind-induced surface mixing was intense during 3200–530 cal yr BP as evidenced by high Globigerina bulloides abundances. The core was affected by moderate chemical weathering and solar variability appears to have been an important forcing factor in shaping climate of the region.

Paleoenvironmental evolution of Central Paratethys Sea and Lake Pannon during the Cenozoic

Deep wells penetrated Cenozoic sedimentary record of two different basins: 1) Oligocene retro-arc basin which is buried under the 2) Miocene back-arc Danube Basin. This study is focused on biotic and abiotic proxies discussed in terms of existing biostratigraphical, paleoenvironmental and sedimentological data. Biotic proxies are represented by palynofacies and biomarkers (palynomorphs, AOM, phytoclasts, TOC, Pr/Ph ratio, steranes). Abiotic proxies are represented by inorganic geochemistry (e.g., CIA, Sr/Ba, Ga/Rb, Th/U, SiO2/Al2O3, Corg/P and enrichment factors). The biotic and abiotic proxies helped to refine the knowledge about the changes in redox conditions, salinity, depositional system, and paleoclimate. In the study area five temporally different environments are observed: 1) Sedimentation in the Oligocene fragment of the retro-arc Hungarian Paleogene Basin that took place on a highly proximal part of the shelf. A major dysoxic event connected with humid marsh environment is documented within (last Rupelian transgression; Ru4/Ch1–Ch2). 2) After a hiatus the Danube Basin initiated with early Badenian (Langhian) stable oxic to slightly dysoxic shelf with minor salinity changes (Lan2/Ser1-Ser2 transgression). 3) Late Badenian (early Serravallian) dysoxic deposition, similar in all basins of the Central Paratethys, was influenced by upwelling connected with the Ser2-Ser3 transgression. 4) Sarmatian (late Serravallian) dysoxic event associated with subsequent flooding (Ser3-Ser4/Tor1), which created shallow marginal marine environment. 5) Pannonian (Tortonian-Messinian) sedimentation took place on an oxic shelf of the Lake Pannon near a fluvio-deltaic source, most likely represented by the paleo-Danube delta system.

Terrestrial mollusk records in the loess sequences from eastern Central Asia since the last deglaciation and their paleoenvironmental significance

A variety of proxies has been studied to document paleoclimatic changes in arid Central Asia (ACA). However, biological archives, which can be directly related to climatic conditions, are still scarce in this region. Here we report records of the total count fossils (TCF) of terrestrial mollusks, organic carbon isotopes (δ13Corg) and loss on ignition (LOI), since the last deglaciation in the Talede and XRBLK loess sections in Xinjiang, eastern Central Asia. Prior to the Holocene, the records show rare fossils with relatively low LOI and more positive δ13Corg, indicating low biomass/organic carbon content under dry conditions which were unfavorable for the survival of snails. In contrast, TCF increased abruptly at the beginning of Holocene, coincident with a prominent increase in LOI and a marked negative shift in δ13Corg. Furthermore, TCF increased gradually to its maximum and δ13Corg became progressively negative with constant high LOI from the early to late Holocene. The variations imply a trend towards wetter environment, with optimal moisture (precipitation/relative humidity) conditions occurring in the late Holocene. Overall, this Holocene moisture evolution history could be attributed to the variations of Westerlies strength modulated by the latitudinal temperature gradient and the insolation-related evaporation should also be concerned.

Time marker of 137Cs fallout maximum in lake sediments of Northwest China

Caesium-137 (137Cs) has no natural source and is commonly employed in establishing the chronology of recent lake sediments in the Anthropocene epoch. Because of their location in the northern mid-latitude Westerlies circulation region, downwind of the Chernobyl accident and their proximity to the Lop Nur Chinese Nuclear Testing (CNT) site, lake sediments in NW China record a137Cs fallout maximum of global atmospheric thermonuclear weapon tests (GTWT) in 1963–1964 Common Era (CE), with probably local fallout subpeaks due to the Chernobyl accident in 1986 CE and CNT in 1976 CE. This complexity means that the use of 137Cs fallout maximum in lake sediments as a time marker in NW China is thus far not well constrained, impeding assessment of recent and future changes in paleoclimate and human activities. To identify the 137Cs time marker and provide a reliable chronology of surface lake sediments for investigating paleoclimatic changes and for defining the Anthropocene epoch in NW China during the last 50–100 years, here we describe chronologies of 6 near-surface sediment cores from NW China based on 137Cs and 210Pb activities, and review the chronology of 23 lake sediments and 10 ice cores from NW China and central Asia based on 137Cs, 210Pb, 239+240Pu, 3H, 241Am, and beta-activity dating methods, and annual layer counting, as well as 240Pu/239Pu isotopic ratios. Based on the potential influence of radioactivity transport from the Chernobyl accident and CNT, and the comparison with deposition records of 26 European lake sediments and 5 Alpine ice cores, we propose that the 137Cs fallout maximum of lake sediments in NW China and central Asia is primarily attributable to GTWT and that there is no unambiguous evidence to confirm the Chernobyl- and CNT-derived 137Cs local-fallout subpeaks. Taking into account the approximately one-year delay between injection of 137Cs into the atmosphere and its incorporation in lake sediment records, we conclude that the 137Cs fallout maximum in lake sediments of NW China provides a reliable GTWT time marker for 1964 CE.

Phylogenomics, biogeography, and evolution of morphology and ecological niche of the eastern Asian–eastern North AmericanNyssa(Nyssaceae)

AbstractNyssa(Nyssaceae, Cornales) represents a classical example of the well‐known eastern Asian–eastern North American floristic disjunction. The genus consists of three species in eastern Asia, four species in eastern North America, and one species in Central America. Species of the genus are ecologically important trees in eastern North American and eastern Asian forests. The distribution of living species and a rich fossil record of the genus make it an excellent model for understanding the origin and evolution of the eastern Asian–eastern North American floristic disjunction. However, despite the small number of species, relationships within the genus have remained unclear and have not been elucidated using a molecular approach. Here, we integrate data from 48 nuclear genes, fossils, morphology, and ecological niche to resolve species relationships, elucidate its biogeographical history, and investigate the evolution of morphology and ecological niches, aiming at a better understanding of the well‐known EA–ENA floristic disjunction. Results showed that the Central American (CAM)Nyssa talamancanawas sister to the remaining species, which were divided among three, rapidly diversified subclades. Estimated divergence times and biogeographical history suggested thatNyssahad an ancestral range in Eurasia and western North America in the late Paleocene. The rapid diversification occurred in the early Eocene, followed by multiple dispersals between and within the Erasian and North American continents. The genus experienced two major episodes of extinction in the early Oligocene and end of Neogene, respectively. The Central AmericanN. talamancanarepresents a relic lineage of the boreotropical flora in the Paleocene/Eocene boundary that once diversified in western North America. The results supported the importance of both the North Atlantic land bridge and the Bering land bridge (BLB) for the Paleogene dispersals ofNyssaand the Neogene dispersals, respectively, as well as the role of Central America as refugia of the Paleogene flora. The total‐evidence‐based dated phylogeny suggested that the pattern of macroevolution ofNyssacoincided with paleoclimatic changes. We found a number of evolutionary changes in morphology (including wood anatomy and leaf traits) and ecological niches (precipitation and temperature) between the EA–ENA disjunct, supporting the ecological selection driving trait evolutions after geographic isolation. We also demonstrated challenges in phylogenomic studies of lineages with rapid diversification histories. The concatenation of gene data can lead to inference of strongly supported relationships incongruent with the species tree. However, conflicts in gene genealogies did not seem to impose a strong effect on divergence time dating in our case. Furthermore, we demonstrated that rapid diversification events may not be recovered in the divergence time dating analysis using BEAST if critical fossil constraints of the relevant nodes are not available. Our study provides an example of complex bidirectional exchanges of plants between Eurasia and North America in the Paleogene, but “out of Asia” migrations in the Neogene, to explain the present disjunct distribution ofNyssain EA and ENA.

Enriched East Asian oxygen isotope of precipitation indicates reduced summer seasonality in regional climate and westerlies

Speleothem oxygen isotope records over East Asia reveal apparently large and rapid paleoclimate changes over the last several hundred thousand years. However, what the isotopic variation actually represent in terms of the regional climate and circulation is debated. We present an answer that emerges from an analysis of the interannual variation in amount-weighted annual δ18O of precipitation over East Asia as simulated by an isotope-enabled model constrained by large-scale atmospheric reanalysis fields. 18O-enriched years have reduced summer seasonality both in terms of precipitation isotopes and in the large-scale circulation. Changes occur between June and October, where the δ18O of precipitation (δ18Op) transitions from the isotopically heavier winter to the lighter summer regime. For 18O-enriched years, this transition is less pronounced. Variations in precipitation amount alone are insufficient to explain the amount-weighted annual δ18Op between 18O-enriched and 18O-depleted years. Reduced summer seasonality is also expressed in the low-level monsoonal southerlies and upper-level westerlies; for the latter, the northward migration across the Tibetan Plateau in the summer is less pronounced. Our result thus implicates the westerlies across the plateau as the proximate cause of East Asian paleomonsoon changes, manifested as a modulation of its summer peak.

First record of Pterophyllum propinquum and its epidermal structures in Yaojie Formation of Middle Jurassic in Gansu Province, Northwestern China

ABSTRACT The leaf morphology and epidermal anatomy of a species of Pterophyllum, a morphological genus of Bennettitales, were studied in detail based on leaf fossil collected from the Middle Jurassic Yaojie Formation in the Baojishan Basin, Gansu Province, northwestern China. The fossil lamia is large; the segments are broadly linear to rectangular, opposite, each segment containing ca. 20 thin veins. The leaf cuticle is thin, hypostomatic, possessing of syndetocheilic stomatal complex. According to a detailed comparison on the basis of leaf morphology and cuticle features to other similar fossil plants, the fossil material was attributed to Pterophyllum propinquum Goeppert, which add to the details of the rachis, leaf cuticles of the species. Combined with the characteristics of paleoclimate change during the Mesozoic in China, the responses of the palaeogeographical distribution of Pterophyllum to paleoclimate change in different periods of Mesozoic in China are discussed. Moreover, based on the fossil floral assemblage and the cuticle features of P. propinquum, we presumed that it is a warm and humid climate in the Middle Jurassic in Baojishan basin, where the P. propinquum is a typical plant member.

Phylogenomic insights into the temporal-spatial divergence history, evolution of leaf habit and hybridization in Stachyurus (Stachyuraceae)

Stachyuraceae, an East Asian endemic family of shrubs or small trees, comprises a single genus, Stachyurus (c. 11 spp.). Despite previous extensive studies based on both morphology and molecular data, species relationships within Stachyurus are still unresolved. Here, we employed transcriptome data aiming to elucidate the evolutionary history of Stachyurus and investigate possible causes of phylogenetic incongruence among individual gene trees in this genus. Our transcriptome phylogeny strongly supports four major clades of Stachyurus, with S. praecox from Japan being resolved as sister to the remainder of the genus on the Asian mainland. The deciduous S. praecox in Japan appears to have originated in the late Miocene, while the remainder diversified and expanded on the mainland over late Miocene to Pliocene/early Pleistocene times. These latter episodes of diversification and expansion were likely promoted by changes in paleoclimate and orogeny (e.g., late Miocene uplift of the Hengduan Mts. and/or enforcement of the East Asian summer monsoon). Species of this genus evolved from a deciduous ancestor, followed by multiple and independent transitions in leaf habit, possibly reflecting climate-related adaptations. Phylogenetic incongruence observed among individual gene trees may be attributable to incomplete lineage sorting following ancient rapid diversification and frequent interspecific gene flow caused by hybridization events. In sum, this study demonstrates the potential usefulness of genome-wide phylogenetic incongruence and network analyses for reconstructing complex evolutionary histories in rapidly diversifying and naturally hybridizing species groups.