C3 Vegetation Research Articles

Cross shelf transport of terrigenous organic matter in surface sediments from outer shelf to Okinawa Trough in East China Sea

Identification of sources and distribution of terrigenous organic matter (TOM) are significant to understand the carbon transport in East China Sea (ECS). However, sources of TOM buried in the ECS are diverse and complex, which are likely derived from the Changjiang River, Yellow River and/or small rivers from China mainland and Taiwan. In order to evaluate the fate of TOM offshore in the ECS, the study sampled 80 surface sediments from outer shelf-slope-Okinawa Trough (OT) region in the ECS. Both terrigenous and marine organic biomarkers were detected. The concentration (ng/g dry weight sediment) of terrigenous biomarkers including ƩC27 + C29 + C31 n-alkanes ranged from 12.2 to 990.9; while the content of marine biomarkers varied from 1.3 to 3891.2 for C37 alkenones, 2.6 to 922.6 for brassicasterol and 7.1 to 1535.8 for dinosterol. Bulk organic carbon and TOM distributions were controlled by the hydrodynamic conditions. The terrigenous and marine biomarker ratio (TMBR) (ƩC27 + C29 + C31 n-alkanes)/(ƩC27 + C29 + C31 n-alkanes + (brassicasterol + dinosterol +alkenones)) increased first and decreased from the outer shelf to OT spatially, showing the distribution pattern of relative proportion of TOM. Hotspots of significant deposition of TOM were observed in the ECS by δ13C and TMBR proxies that the mechanism was unclear yet. Binary model revealed higher percentage of TOM based on TMBR than δ13C for both slope (32.1% vs. 20.0%) and trough (23.1% vs. 15.2%) region. An underestimation of C4 vegetation contribution likely biased the bulk carbon model. Carbon preference index suggested a zonation distribution of TOM that outer shelf had different sources from the slope and OT attributed to cross shelf transport of terrigenous organic matter.

Comparison of climate and environment on the edge of the Palaeo-Agulhas Plain to the Little Karoo (South Africa) in Marine Isotope Stages 5–3 as indicated by speleothems

Given the steep present-day climatic gradients in southern South Africa, comparative studies of its coastal and inland paleoclimate provide important insight into the region's spatial climate dynamics. We present a comparative study of new speleothem stable oxygen (δ18O) and carbon (δ13C) isotopic composition from Efflux Cave (EC; 113–19 ka, hiatus between 105 and 94 ka) in the Little Karoo inland basin and Herolds Bay Cave (HBC; 93–62 ka) at the boundary between the Cape coastal lowlands and the Palaeo-Agulhas Plain. Gaussian kernel based cross-correlation analyses against palaeoclimate proxy records show that rainfall seasonality at EC is related to rainfall amount in the South African interior, whereas HBC is similar to the South African east coast. Our new proxy records, corroborated by archaeological evidence from the Cape coastal lowlands and the Little Karoo, suggest that in both regions, surface water was readily available and grassland ecosystems with variable amounts of C4 and C3 grasses as well as fynbos communities could be found nearby. Cross-correlation analyses of the new records from EC and HBC compared to previously published speleothem records from southern South Africa show only limited statistical correlation. However, there are some similarities in overall trends of palaeoclimate change in the Cape coastal lowlands and the Little Karoo whereby Marine Isotope Stage (MIS) 5b (mainly Greenland Interstadial 22) and 4 generally have more summer rainfall and higher abundances of C4 vegetation than MIS 5a and MIS 3.

Past and present distributions and community evolution of Muridae and Soricidae from MIS 9 to MIS 1 on the edge of the Palaeo-Agulhas Plain (south coast, South Africa)

This paper reviews past and present distributions of murid (mice and rats) and soricid (shrew) species from the Pinnacle Point fossil sites PP5-6N, PP9C, PP13B, and PP30, as well as the coastal site of Knysna Eastern Heads Cave 1. The positioning of these sites on the edge of the Palaeo-Agulhas Plain resulted in the micromammal communities being exposed to rapid landmass changes through sea-level regressions and transgressions, as well as climatic and environmental fluctuations during glacial-interglacial cycling. Together, Pinnacle Point and Knysna preserve a composite coastal sequence from MIS 9 to MIS 1, and provide an opportunity to assess the long term sensitivity of micromammals to environmental change. Modern distributional information for the south coast region was obtained from owl pellet and small-carnivore scat assemblages, and extended the known current distributions of six murids. A uniform suite of micromammals was pervasive throughout all the fossil sites, during both glacial and inter-glacial cycling, and the composition of the majority of fossil micromammal assemblages remained unchanged, despite fluctuations in rainfall amount, seasonality, and the proportion of C3 versus C4 vegetation. This suggests an ability to adapt to, and cope with, climatic and environmental changes with relative ease. The fact that the fossil evidence indicates that many murid taxa occupied different ranges in the past, and, in some cases, had considerably more extensive ranges, and lived in a greater variety of habitats, raises a note of caution regarding using current biogeographies to elucidate palaeoenvironmental and climatic change, and for biogeographic and species distribution modelling.

Iron Age landscape changes in the Benoué River Valley, Cameroon

AbstractThe introduction of agriculture is known to have profoundly affected the ecological complexion of landscapes. In this study, a rapid transition from C3 to C4 vegetation is inferred from a shift to higher stable carbon (13C/12C) isotope ratios of soils and sediments in the Benoué River Valley and upland Fali Mountains in northern Cameroon. Landscape change is viewed from the perspective of two settlement mounds and adjacent floodplains, as well as a rock terrace agricultural field dating from 1100 cal yr BP to the recent past (<400 cal yr BP). Nitrogen (15N/14N) isotope ratios and soil micromorphology demonstrate variable uses of land adjacent to the mound sites. These results indicate that Early Iron Age settlement practices involved exploitation of C3 plants on soils with low δ15N values, indicating wetter soils. Conversely, from the Late Iron Age (>700 cal yr BP) until recent times, high soil and sediment δ13C and δ15N values reflect more C4 biomass and anthropogenic organic matter in open, dry environments. The results suggest that Iron Age settlement practices profoundly changed landscapes in this part of West Africa through land clearance and/or utilization of C4 plants.

Caribbean hydroclimate and vegetation history across the last glacial period

We present a new speleothem trace element and stable isotope record, which extends previous paleoclimate evidence from Cuban speleothems to the last 96 ka. Multiple proxies were used to reconstruct Caribbean hydroclimate and vegetation variability on orbital to millennial timescales. In particular, our proxies indicate a shift to more abundant C4 (compared to C3) vegetation and/or reduced soil activity during the Last Glacial Maximum. Our results confirm the close link of Caribbean precipitation to North Atlantic climate variability, insolation and the strength of the AMOC. The associated variations in Caribbean SSTs and the shift of the ITCZ led to substantial changes of the hydrological cycle. During Heinrich stadials and the Younger Dryas, climatic conditions in Cuba were comparably cool and/or dry. In contrast, warm Dansgaard/Oeschger cycles were accompanied by wetter conditions. This is in agreement with previous evidence for the Holocene, when North Atlantic cold (warm) events coincided with drier (wetter) conditions in Cuba. However, our record suggests that this connection was less dominant during MIS 4 to 2, displayed by a weaker response of Cuban precipitation proxies to North Atlantic climatic shifts than during MIS 5 in particular. We hypothesize that this weaker connection was mediated by the southerly shifted ITCZ inducing a weakening of the northern branch of the Caribbean Low Level Jet which usually transports moisture into the northern Caribbean. This is strikingly evident during the deglacial, when driest and/or coolest conditions prevailed in western Cuba from HS 1 into the Younger Dryas, including the Bølling/Allerød interstadial.

Climatic and environmental conditions in the Western Galilee, during Late Middle and Upper Paleolithic periods, based on speleothems from Manot Cave, Israel

Early Ahmarian, Levantine Aurignacian and Post-Levantine Aurignacian archeological assemblages show that the karstic Manot Cave, located 5 km east of the Mediterranean coast in the Western Galilee region of Israel, was intensively occupied during the Early Upper Paleolithic. The coexistence of these rich archaeological layers with speleothems in Manot Cave provides a window of opportunity for determining the relationships between climatic conditions and the nature of human activity and mobility patterns in the Western Galilee region during the Early Upper Paleolithic period. This study, based on four stalagmites that grew almost continuously from ∼75 to 26.5 ka, covers most of the last glacial, and overlaps with the human occupation of the cave. The speleothems oxygen (δ18O) and carbon (δ13C) isotopic records indicate that climate and environmental conditions fluctuated during the last glacial, some of which correspond with Dansgaard–Oeschger (D-O) cycles 12, 10, 7 and Heinrich (H) events VI and V. Consistent with independent evidence from botanic and faunal remains, these climatic shifts brought about significant environmental changes in the region, ranging from dominant thick Mediterranean forest to more open landscape. A good correlation with less negative δ13C values is most pronounced during the Early Ahmarian time period, but there was also a change to less negative δ13C values during the Levantine Aurignacian and Post-Levantine Aurignacian industries in the Levant. These positive δ13C shifts suggest that environmental transformation towards a more open grassy landscape dominated by C4 vegetation might have played an important role in the development of these cultural entities (mainly the Early Ahmarian) in Manot Cave region.

The last glacial cycle of the southern Levant: Paleoenvironment and chronology of modern humans

The spectrum of glacial-interglacial environmental shifts in the southern Levant Mediterranean zone is evaluated based upon carbon isotopic records of speleothems from several caves, faunal records of Middle Paleolithic and Upper Paleolithic layers in caves, together with additional evidence from the base levels of the region. The studied evidence suggests that food resources were commonly abundant, but some water scarcity and increase in summer rains occurred during MIS 5e, when soils and C3 vegetation were eliminated, causing soil erosion. This was followed by penetration of summer rainfall and lightning storms from the south, and associated C4 vegetation and fires. Faunal resources remained abundant, and humans using the southern Levant corridor enjoyed also a favorable passage through the greening Sahara Desert during MIS 5e, which was crucial for human and faunal dispersion. Qafzeh and Rantis caves’ environmental records indicate xeric grassland-type ecosystem with Afro–Arabian elements that can be attributed to MIS 5e. As the environmental conditions of MIS 5e were unique, faunal and isotopic records within this region can be used in the future as chronologic markers for MIS 5e. During the last glacial period, conditions became gradually cooler and wetter, and C3 vegetation dominated the Mediterranean zone. Lower temperatures promoted the entry of Palearctic mammals. Fluctuations of speleothem δ13C increased during the latest Pleistocene – early Holocene, indicating environmental instability through the deglaciation. Significantly, the δ13C records indicate that vegetation did not change from the last glacial period to the Holocene in spite of the observed fluctuations. The extreme environmental event of MIS 5e was not repeated during the Holocene in terms of natural vegetation and fauna. Anthropogenic environmental change, accelerating towards the present, is overriding the natural trend.

Holocene changes in biome size and tropical cyclone activity around the Northern South China Sea

The South China Sea (SCS), characterized by a large continental shelf, is located at the edge of the Asian monsoon domain. In this study, two marine sediment cores from the northern SCS (NSCS) continental slope were investigated to construct composite vegetation and precipitation isotopic composition records based on the δ13C and δD values of plant-wax n-alkanes throughout the Holocene (last 11,200 years; i.e. 11.2 ka). The composite δ13Cwax record indicates an overall predominance of C3 vegetation over the last 11.2 ka. Before 8 ka BP, higher δ13Cwax values are attributed to preferential wax input from grassland and wetland biomes on the exposed continental shelf. After the inundation of the shelf by eustatic sea level rise until ca. 8 ka BP grassland and wetland biomes suffered a major size reduction and arboreal vegetation became better represented in the δ13Cwax record. The composite temperature corrected δDwax-T record suggests that moisture source variability drove precipitation isotopic composition changes during the Holocene. Lower δDwax-T values before 8.3 ka BP are interpreted as a larger moisture contribution by Pacific Ocean tropical cyclones, whereas higher δDwax-T values after 8.5 ka BP are interpreted as a larger moisture contribution from the Indian Ocean summer monsoon. Higher incidence of tropical cyclones in the NSCS during the Early Holocene was related to a temporary westward shift of the Western Pacific Warm Pool and enhanced insolation over the Northern Hemisphere. Both external and internal forcing mechanisms regulated moisture source changes in East Asia during the Holocene.

Early Miocene expansion of C4 vegetation on the northern Tibetan Plateau

Abstract The proliferation of C4 photosynthesis in land plants marks the most important ecological shift in tropical and subtropical terrestrial ecosystems during the Cenozoic. Despite the wealth of geochemical data indicating an increased C4 biomass in the paleovegetation since the Late Miocene spatial and temporal variations of C4 plants abundance are not well known. The driving force for their expansion such as CO2 starvation, aridification and fire frequency are controversially discussed. Here we present an integrated review of the stable isotope stratigraphy, trace elements, palynology, lithological and phytolith record from early-middle Miocene lacustrine sediments in the Hoh Xil Basin. We report the first known silicified wood fossils from the genus Picea and indicate the Hoh Xil region might have already reached an elevation above 2500 m at least in the early Miocene, representing the early uplift stage of northern Tibetan Plateau. Our results show that the expansion of C4 vegetation and the appearance of Picea in the interior of the Tibet during the early Miocene may be related to early uplift of the northern Tibetan Plateau and the consequent cooling event, PCO2 decrease, and aridification. We suggest that the C4 signal in vertebrate faunas predating the early Miocene is due to the ecology of the herbivores (who preferred plants with C3 metabolism) rather than the lack of C4 plants in the vegetation.

Ecological flexibility and differential survival of Pleistocene Stegodon orientalis and Elephas maximus in mainland southeast Asia revealed by stable isotope (C, O) analysis

Elephas maximus and Stegodon orientalis were two keystone proboscideans in southern Asia that coexisted mainly after the Middle Pleistocene in many regions. The long-term paleoecology and possible foraging competition of these two species have not been intensively investigated yet. Here, we applied stable isotope (C, O) analysis to the tooth enamel of coexisting Elephas maximus, Stegodon orientalis, and other associated mammalian species in Quzai Cave, southern China, dated to the early Late Pleistocene, to explore their paleoenvironmental context and foraging ecology. The δ13C values of Elephas maximus were widely distributed between −17.9‰ and −11.9‰ (n = 10), while Stegodon orientalis δ13C values ranged from −16.7‰ to −14.7‰ (n = 7). These results suggest that Elephas maximus was possibly a mixed feeder with a broader range of dietary resources than Stegodon orientalis, which probably browsed on a narrower range of plant resources in more densely forested landscape. A chronological comparison (from 8 Ma to recent) of published δ13C data for these two species from Asia showed that none of them were dietary specialists. However, Elephas had a more flexible foraging ecology and a stronger ability to exploit abrasive grasses than Stegodon. The niche partitioning and perceived different foraging behaviors of Stegodon and Elephas might have reduced the level of interspecific competition and allowed them to coexist during the Pleistocene. Moreover, the high-level of ecological flexibility of Elephas might have helped them to survive until the present day, while Stegodon eventually went extinct by the terminal Pleistocene ∼12 ka. An extensive comparison and evaluation of the δ13C data from fossil mammals in mainland southeast Asia during the Early to Late Pleistocene suggests that southern China was dominated by C3 vegetation throughout the Pleistocene, in contrast with the evidence of C4 biomes in neighboring Laos, Cambodia, and Thailand. Southern China experienced relatively stable environments during the Pleistocene, which can be attributed to the wide range of mountainous regions that acted as ecological refugia from human interference and climatic fluctuations, and allowed the preservation of high biodiversity. The isotopic data we present here provides new evidence about the ecological complexity of mainland southeast Asia and elucidates the need for more systematic research to investigate extinction models and ecological conservation in this region.

Biomarkers reveal abrupt switches in hydroclimate during the last glacial in southern California

Reconstructions of past hydroclimate provide a means to understand precipitation responses to global ocean-atmosphere climate dynamics beyond the scope of that in the instrumental record. Late glacial climate was characterized by abrupt variability in ice and ocean dynamics, however the implications for hydroclimate are not as well known. Here we present organic geochemical proxy evidence for precipitation isotopes based on plant leaf wax hydrogen isotopic compositions (δDwax) and temperature proxy evidence based upon the branched glycerol dialkyl glycerol tetraethers (brGDGTs), that derive from the membrane lipids of bacteria, each extracted from a sedimentary archive in Lake Elsinore, California spanning 32–9 ka. We add proxy evidence for vegetation and salinity from additional biomarker analyses and compare to prior pollen and sedimentological evidence from the same core. Our record indicates a strong deglacial warming of 10°C in Lake Elsinore (beginning at 14.5 ka) that accompanied a D-enrichment of precipitation of +90‰ and more C4 vegetation (12–10 ka), after a cold, wet and C3-dominated phase (20–14.5 ka), indicating winter-dominated precipitation during the Last Glacial Maximum and Heinrich Stadial 1. During the late glacial (32–20 ka) we find abrupt variability, with precipitation isotopic shifts (∼70‰) that are independent of temperature swings implicating changes in storm track, rather than local temperature as drivers of the precipitation isotope signal. Temperature is however not irrelevant for hydroclimate: we find extreme warmth at 29.4 ka and 26.8 ka, the latter coincident with existing reports of an extended dry period (27.5–25.5 ka), suggesting a long hot and dry interlude during the generally cooler glacial period. We compare δDwax with speleothem δ18O from Nevada, also within the winter-dominated precipitation region. Our results corroborate the Last Glacial Maximum and deglacial signals, and fill gaps revealing storm-track instability from 32–20 ka, however the pacing and magnitude of the biomarker signals merit cautious interpretation.

Speleothem evidence for C3 dominated vegetation during the Late Miocene (Messinian) of South Africa

During the Late Miocene, Africa experienced a number of ecological transitions including the spread of C4 grasslands, the expansion of the Sahara Desert, the Messinian Salinity Crisis and a number of mammalian migrations and expansions, including the origin of the hominin clade. A detailed understanding of the relationship between environmental change and hominin evolution is hampered by the paucity of data available from terrestrial localities, especially in southern Africa. Here, we present a stable isotope and trace element record from a speleothem from the South African cave site of Hoogland. Uranium-lead dating and magnetostratigraphy places the speleothem within the Messinian Age (7.25–5.33 Ma) of the Late Miocene, making it the oldest known cave deposit from the region near the UNESCO Fossil Hominids of South Africa World Heritage Site (locally known as the “Cradle of Humankind”). Low carbon isotope values indicate a predominantly C3 vegetation in the vicinity of the cave throughout the period of speleothem growth. It is not possible to determine if this represents a C3 grassland or a C3 woodland, but it is clear that an equivalent C3-rich environment has yet to be found during the Messinian of east Africa. We conclude that the C4 grass expansion occurred millions of years later in South Africa than it did in eastern Africa, and that this vegetation shift should be considered when comparing African vegetation change with the late Miocene hominin fossil record.

Multi-Scale Phenology of Temperate Grasslands: Improving Monitoring and Management With Near-Surface Phenocams

Grasslands of the Australian Southern Tablelands represent a patchwork of native and exotic systems, occupying a continuum of C3-dominated to C4-dominated grasslands where composition depends on disturbance factors (e.g. grazing) and climate. Managing these complex landscapes is both challenging and critical for maintaining the security of Australia’s pasture industries, and for protecting the biodiversity of native remnants. Differentiating C3 from C4 vegetation has been a prominent theme in remote sensing research due to distinct C3/C4 seasonal productivity patterns (phenology) and high uncertainty about how C3/C4 vegetation will respond to a changing climate. Phenology is used in northern hemisphere ecosystems for a range of purposes but has not been widely adopted in Australia, where dynamic climate often results in non-repetitive seasonal vegetation patterns. We employed time-lapse cameras (phenocams) to study the phenology of twelve grassland areas dominated by cool season (C3) and warm season (C4), native or exotic grasses near Canberra, Australia. Our aims were to assess phenological characteristics of the functional types and to determine the drivers of phenological variability. We compared the fine-scale phenocam seasonal profiles with field sampling and MODIS/Landsat satellite products to assess paddock-to-landscape functioning. We found C3/C4 species dominance to be the primary driver of phenological differences among grassland types, with C3 grasslands demonstrating peak greenness in spring, and senescing rapidly in response to high summer temperatures. In contrast, C4 grasslands showed peak activity in Austral summer and autumn (January-March). Some sites displayed primary and secondary peaks dependent on rainfall and species composition. We found that the proportion of dead vegetation is an important biophysical driver of grassland phenology, as were grazing pressures and species-dependent responses to rainfall and temperature. The satellite and field datasets were in general agreement with the phenocam results. However, the higher temporal fidelity of the cameras captured changes in vegetation not observed in the coarser satellite or field results. Our phenocam data shows consistent periods of increasing and decreasing greenness over as little as five days. Applications for management of grasslands in temperate Australia include the identification of remnant native grasslands, tracking biosecurity issues, and assessing productivity responses to climate variability.

Late Quaternary Biomass Burning in Northwest Africa and Interactions With Climate, Vegetation, and Humans

AbstractBiomass burning on the African continent is widespread, and interactions with climate, vegetation dynamics, and biogeochemical cycling are complex. To obtain a better understanding of these complex relationships, African fire history has been widely studied, although mostly on relatively short timescales (i.e., years to kiloyears) and less commonly on long‐term scales. Here we present a 192‐kyr, continuous biomass‐burning record from sub‐Saharan Northwest Africa based on the fire biomarker levoglucosan in a marine sediment core offshore Guinea. Notable features of our record include an increase in levoglucosan accumulation at 80 ka and two peaks at 50–60 ka. The event at 80 ka is likely related to an overall increase in sedimentation rates rather than an increase in biomass burning in the Northwest African savanna region. Our record indicates that glacial/interglacial changes in regional climate and vegetation composition (C3 vs. C4 plants) were not a major influence on biomass burning over the last 192 kyr. However, we suggest that the burning events at 50–60 ka might be caused by increased occurrence of C3 vegetation and human settlement in this region. At this time, the savanna region became wetter and fuel loads likely increased. Therefore, the region was more hospitable for humans, who likely used fire for hunting activities. Collectively, we hypothesize that on longer (glacial/interglacial) timescales, biomass burning, regional climate, and African vegetation are not necessarily coupled, while around 50–60 ka, higher fuel loads and human fire use may have influenced fire occurrence in sub‐Saharan Northwest Africa.

Reconstruction of Late Quaternary Climate From a Paleo-Lacustrine Profile in the Central (Kumaun) Himalaya: Viewing the Results in a Regional Context

In this paper, we reconstruct the climatic changes starting from late Pleistocene to the early Holocene as recorded from a fluvio-lacustrine section located within the Kumaun Central Himalaya. The results suggest two major climatic events corresponding with the Last Glacial Maximum (LGM) and Older Dryas (OD). The values of carbon isotopes vary between -23‰ to -14‰, along with a shift in vegetation pattern. The lower part of the section shows prevalence of C3 type vegetation, indicating warm and moist conditions at around 25,000 yr BP, possibly coinciding with the intensification of the Indian Summer Monsoon. The onset of cold and arid phase is evident in the gradual shift in vegetation pattern from C3 to C4 plants, which is prominently observed in the middle part of the paleolake profile. Eventually, as the value of δ13C during this time interval confirms, a prolonged phase of cold and arid climate sets in, coinciding with the strengthening of winter westerlies. This cold phase is dated at ~19,000 yr BP and the extended phase of cold interval observed at Dwarahat profile correlates well with previous results elsewhere from the Himalaya. The profile also shows that the LGM phase gradually transforms into a warm and moist climate. This transition registered at 200 cm above the base of the profile, marks the end of glacial period. The short, yet a clear warm spike could be related to the oscillation of Bolling-Allerod interstadial at ~15,000 yr BP. A significant negative excursion marked by an abrupt increase in δ13C values from -20‰ to -14‰ observed towards the top part of the profile, however, is reflective of the reduced monsoon precipitation, corresponding possibly with Older Dryas (OD). The topmost part of the profile that registers a depleted trend in δ13C values with dominance of C3 vegetation marks the return of the warm and moist climate.

Geochemical characteristics of newly discovered Elongatoolithidae eggs from the Upper Cretaceous of Jiangxi Province, southern China: Palaeoenvironmental and palaeoclimatic inferences

We analyzed identified oospecies and associated geochemical characteristics of newly discovered dinosaur eggs from the Cretaceous Hekou Formation in Yudu District, Jiangxi Province, China. Results reveal that the Yudu eggs can be identified as representatives of the known oospecies Macroolithus rugustus within Elongatoolithidae based on external shape, size, ornamentation, and internal microstructure between the columnar and cone layers. The major element found in Macroolithus rugustus shells is Ca, while trace elements mainly include Sr, Ba, As, Cr, Mn, Pb, Cd, La, and Ir, characterised by Ir and Sr abnormalities, as well as the toxic elements As and Pb. Enrichment of trace elements in shells might be due to the diet of dinosaurs and subsequent deposition in eggs, consistent with global Ir anomalies and the regional enrichment of trace elements. δ13C values for Macroolithus rugustus ranging between −8.81‰ and −7.65‰ are indicative of C3 plants with relatively high CO2 concentration and low mean annual precipitation (MAP), while δ18O values ranging between −8.51‰ and 3.14‰ indicate relatively low humidity and the alteration of water sources of female dinosaur. The Sr and Ca contents as well as δ18O values of eggshells could be associated with the drinking water and food materials together with dissolved bone apatite. In light of the red-brown colour of surrounding rocks, high Fe composition revealed by macroelement analysis, and the presence of a C3 vegetation with low MAP, the palaeoenvironment of Yudu dinosaur nesting area was most likely to be fluvial and the palaeoclimate was semi-arid to arid, which is conducive to the preservation of eggs.

Climatic significance of the stable carbon isotopic composition of surface soils in northern Iran and its application to an Early Pleistocene loess section

The stable carbon isotopic composition of bulk organic matter (δ13Corg) in paleosols has been widely used as a proxy indicator for reconstructing past vegetation and climate. Previous studies generally show a negative correlation between the δ13Corg values of modern C3 plants and surface soils under C3 plant-dominated ecosystems and mean annual precipitation (MAP). However, the relationship between δ13Corg and MAP varies among different climatic regimes, resulting in uncertainties in paleo-precipitation reconstructions. In this study, we analyzed the δ13Corg values of surface soil samples collected along a north-south climatic gradient in northern Iran, in the western part of arid central Asia (ACA). Our aims were to explore the relationship between surface soil δ13Corg values and climatic factors; to use it to develop a transfer function for ACA; and then to apply the transfer function to a well-dated loess-paleosol sequence (AB1) to reconstruct early Pleistocene (2.4–1.8 Ma) MAP in northern Iran. The results show that: (1) the δ13Corg values of 44 surface soil samples range from −27.56‰ to −23.61‰, with an average of −25.77‰, indicating that the modern natural ecosystem in northern Iran is dominated by C3 vegetation; (2) The δ13Corg values of the surface soil samples are strongly negatively correlated with MAP (y = −0.0079x − 22.8418, R2 = 0.4419, p < 0.001), with a coefficient of −0.79‰/100 mm. We infer that the effects of mean annual temperature (MAT) and elevation on the relationship are minimal; (3) Reconstructed early Pleistocene MAP in northern Iran was ∼649 mm, much wetter than the present day (∼331 mm); (4) The loess δ13Corg values from ACA exhibit similar trends to records from monsoonal Asia, suggesting a similar history of Quaternary climate change between ACA and monsoonal Asia, which is likely related to the growth and decay of Northern Hemisphere ice sheets.

Linkage between C4 vegetation expansion and dune stabilization in the deserts of NE China during the late Quaternary

Knowledge of the role of C4 vegetation expansion in regulating dune stabilization during the late Quaternary is important for understanding the evolution of the environment and climate in the climatically-sensitive margin of the East Asian summer monsoon. However, due to the lack of both reliable vegetation records and chronological control during episodes of dune activity, the relationship between C4 vegetation expansion and dune stabilization in the deserts of NE China during the late Quaternary remains unclear. Here, we present a new regional compilation of late Quaternary stable carbon isotopic data from organic matter, together with dated records from sub-aerial sedimentary deposits in the region. Our compilation of vegetation development and dune activity in these deserts suggests that C4 vegetation expansion, with a main contribution from Chenopodiaceae, and a secondary contribution from Poaceae and Cyperaceae, may have played a critical role in dune semi-stabilization with a northwestward trend, from ∼13 to 9 ka; and dune stabilization throughout the entire study region, from ∼9 to 5 ka. In addition, during the late Holocene, intensified millet cultivation (or overgrazing) and/or climatic deterioration at ∼1.5 ka likely caused an increase in C4 vegetation abundance in the deserts of NE China, which is associated with a dune mobilization episode. In contrast, after ∼2.5 ka, decreased vegetation cover and dune mobilization in the Mu Us and Hobq deserts were likely caused by poor land-use practices and historically documented droughts. Overall, C4 vegetation expansion was the main cause of dune stabilization in these deserts during the late Quaternary.

N-Alkanes as indicators of climate and vegetation variations since the last glacial period recorded in a sediment core from the northeastern South China Sea (SCS)

Variations in n-alkanes proxies (L/H, C31/C27 and ACL), molecular abundances of n-alkanes and stable carbon isotopic compositions of n-alkanes (δ13Calk) from the core STD235 (20°21.15′N, 118°22.56′E) have been used to trace characterize the climatic changes that occurred in the northern South China Sea (SCS) during the last glacial period. The ratio of low to high molecular-weight n-alkanes (L/H) and the concentration of n-alkanes indicated that organic matters in the sediments were derived from the mixture of both marine and terrestrial sources, but dominated by marine autochthonous input over the past 20 ka. Total n-alkanes were higher during the last glacial stage relative to the interglacial stage, implying the low sea level and the strengthened East Asian winter monsoon (EAWM) during the glacial time. The δ13Calk data indicated that the terrestrial plants on the adjacent continent of the present study area were dominated by C3 plants during the Holocene and experienced the expansion of C4 plants during the last glacial period. This similar result can be proved by the chain length parameter of n-alkanes (C31/C27, ACL) and the content of the herb pollen. In addition, n-alkanes distributions and C4 vegetation proportion calculated by δ13C of long-chain n-alkanes in the core STD235 recorded a short arid duration paralleled by the Heinrich event 1. Thereby we deduced that the occurrence of the dry event and the variation of regional vegetation community at the adjacent lands of the northern SCS were likely under the influence of the climate change emanated from the boreal high-latitudes.

Foraging connections: Patterns of prey use linked to invasive predator diel movement.

Invasive predators can profoundly impact native communities, especially in insular ecosystems where functionally equivalent predators were evolutionarily absent. Beyond direct consumption, predators can affect communities indirectly by creating or altering food web linkages among existing species. Where invasive predators consume prey from multiple distinct resource channels, novel links may couple the dynamics of disjunct modules and create indirect interactions between them. Our study focuses on invasive populations of Eleutherodactylus coqui (Anura: Leptodactylidae) on Hawaii Island. Coqui actively forage in the understory and lower canopy at night but return to the forest floor and belowground retreats by day. Recent dietary studies using gut contents and naturally occurring stable isotopes indicate higher than expected consumption of litter arthropods, which in these Hawaiian forests are primarily non-native species. We used laboratory studies to observe diurnal and nocturnal foraging behavior, and experimental field additions of C4 vegetation as a litter tracer to distinguish epigaeic sources from food web pools in the C3 canopy. Lab trials revealed that prey consumption during diurnal foraging was half that consumed during nocturnal foraging. Analysis of δ13C isotopes showed incorporation of C4 carbon into litter arthropods within one month, and Bayesian mixing models estimated that 15–25% of the carbon in coqui tissue was derived from litter sources. These results support recent findings that E. coqui are not quiescent diurnally but instead actively forage. Such activity by a mobile invasive predator may introduce a novel linkage that integrates detrital and foliar resource pools, potentially distributing influences of invasive litter arthropods through the broader system to amplify impacts on native species.