The 318-m long sediment record from Lake El'gygytgyn, NE Russia situated in the present-day herb tundra zone, provides a unique archive of high Arctic environmental changes since ca 3.6 million years ...ago (Ma). This paper focuses on pollen-derived vegetation change during the mid-Pliocene Warm Period (mPWP) and in particular during Marine Isotope Stage (MIS) M2, which is known to represent the coldest interval of the Pliocene. Building on initial pollen studies, we provide a more complete record and a more detailed discussion of climatically-driven vegetation and environmental changes in the northeastern Russian Arctic, spanning the 203-thousand-year interval between 3.383 and 3.180 Ma ago. Pine-spruce-fir-larch-Douglas fir forests dominated the area around Lake El'gygytgyn between 3.383 and 3.330 Ma (MIS MG4 - MIS MG2). Colder and drier climate caused a decrease of coniferous forests and widespread Sphagnum habitats around the lake between 3.370 and 3.357 Ma. After 3.3 Ma, the presence of spruce, fir and Douglas fir decreased again. A very pronounced cooling took place at the first half of MIS M2 (3.312–3.283 Ma), when treeless tundra- and steppe-like habitats became common in the regional vegetation. Climate conditions were similar or only slightly warmer and wetter to those of the Holocene. Numerous coprophilous fungi spores identified in the MIS M2 pollen samples suggest the presence of grazing mammals around the lake. Larch-pine forests with some spruce started to dominate the area again after ca. 3.282 Ma, thus pointing to a significant climate amelioration during the mPWP. However, the forested area decreased, while herb- and shrub-dominated vegetation spread again during MIS KM6 (especially 3.235–3.223 Ma), suggesting a noticeable climatic deterioration and relatively cold and dry conditions.
•Insight into the mid-Pliocene Warm Period (mPWP) interval from 3.383 to 3.180 Ma ago.•Detailed reconstruction of climate and vegetation changes in north-eastern Eurasia during the mPWP.•Heterogeneous environments during the 203-thousand-year mPWP interval in the high Arctic.•Pine-spruce-fir-larch-Douglas fir forests dominated in the present-day herb tundra zone.•Pronounced cooling during the MIS M2 led to the spread of tundra and steppe-like vegetation.
Although the development of Gobi Desert in central and eastern Asia has greatly affected the regional and even the global climate, its precise origin and evolution have yet to be determined. The ...three preconditions for the formation of Gobi Desert are: i) a dry climate, ii) basin landforms and iii) abundant sediment production. In this study, we present a synthesis of both new and published data on the formation and evolution of Gobi Desert in central and eastern Asia. We conclude that the combined effects of mountain building, the mid-latitude westerly circulation and changes in the Asian monsoon, accompanied by global cooling, were principally responsible for the formation of modern Gobi Desert landscapes in central and eastern Asia during the late Pliocene. The arid climate in central and parts of eastern Asia probably developed in the early Cenozoic, from ~50 Ma. Related events included the collision of the Indian and Asian plates, the closure and complete retreat of the Paratethys Ocean from central Asia, and the growth of the Himalayas and the Tibetan Plateau in the Eocene through late Miocene, which blocked the water vapor supply and intensified the aridification of the Asian interior. Superimposed on the topographic changes was the process of stepwise global cooling since the early Oligocene, and in particular since the late Miocene, which controlled the formation and evolution of the Gobi Desert landscape. Global cooling weakened the Asian monsoon circulation, strengthened the westerly circulation and enhanced physical weathering processes in mountain areas, which together promoted both the aridification of the Asian interior and sediment production. These processes finally resulted in the establishment of the modern Gobi Desert landscape in the late Pliocene. We estimate that the modern Gobi Desert landscape was formed at ~2.6 Ma and was the result of the stepwise evolution of Asian topography and climate during the Cenozoic, dominated by Asian tectonic deformation and uplift, and the evolution of Asian monsoon climate and the westerly circulation, forced by global temperature change.
•High arsenic in groundwater was generally related to high Na+ and low Ca2+.•The middle-Pliocene aquifer sediments had low contents of water-soluble Ca and SIC.•Endogenic CO2 was responsible for ...silicate weathering in middle-Pliocene aquifer.•Silicates weathering in middle-Pliocene aquifer released arsenic into groundwater.•High temperature promoted arsenic desorption and weathering of silicates.
High arsenic (As) groundwater in reduced shallow Holocene and Pleistocene aquifers has been intensively investigated, but the occurrence and the genesis mechanisms of high As groundwater in deep Pliocene aquifers affected by geothermal activity still remain unclear. To address these issues, geochemical characteristics of groundwater and aquifer sediments in both middle-Pliocene aquifers and Quaternary aquifers of the Guide basin were investigated to clarify groundwater-sediments interaction and the causes of As enrichment in groundwater from middle-Pliocene aquifer. Higher As and Na+ concentrations were observed in groundwater from middle-Pliocene aquifer (GPA) than those in groundwater from Quaternary aquifer (GQA), while GPA had lower Ca2+ concentrations than GQA. Results showed that middle-Pliocene aquifer sediments had low contents of carbonate minerals, and water-soluble Ca-bearing minerals relative to Quaternary aquifer sediments, which explain higher concentration of Ca2+ in GQA than in GPA. Na+ from weathering of silicates (i.e. (Na+)*), being calculated based on mass balance, accounted for high proportion of dissolved Na+ (up to 68%) in GPA. Weathering of silicates was related to As accumulation in GPA, which was proved by a positive correlation between As and (Na+)* in GPA, and high proportion of As bound to unweathered silicates (up to 65.7%) in middle-Pliocene aquifer sediments. The weathering of silicate minerals directly released As bound to silicates into GPA, and indirectly led to As desorption from solid surfaces by increasing pH, HCO3– and CO32–. Both (Na+)* and As in groundwater increased with the increasing groundwater temperature, showing that high temperature was conducive to weathering of silicates and As enrichment. This paper establishes a bridge between high groundwater temperature and high As concentration with weathering of silicates in aquifers.
•The hypothesis “Atlantification of Arctic” is tested for mid-Pliocene warm period.•Near complete “Atlantification” of Eurasian sector of Arctic Ocean was observed.•Orbital forcing was dominant ...factor for north Atlantic volume transport to Arctic.•Atlantification caused ∼30–35% reduction in Arctic spring sea ice.•Our results provide important input for improving Arctic climate modeling.
Quantifying the contribution of poleward oceanic heat transport to the Arctic Ocean is important for making future sea ice and climate predictions. To highlight its potential importance in a warmer world, we present a new record of water-mass exchange between the Atlantic and the Arctic Oceans using the authigenic neodymium isotopic composition of marine sediments from the Fram Strait during the past ∼3.4 to 2.6 Ma. In this study, we target the mid-Pliocene Warm Period (mPWP: 3.264–3.025 Ma) of the Pliocene epoch, the most recent geological analogue for future climate change. We complement our semi-quantitative water mass exchange reconstruction with estimates of spring sea ice concentration based on source-specific biomarkers. Our estimates of volume transport of warm waters into the Arctic Ocean suggest long-term secular changes from the lowest during the Marine Isotope Stage M2 “glacial” (3.312–3.264 Ma), to near complete “Atlantification” of the Eurasian sector of the Arctic Ocean during the mPWP. Orbital forcing is found to be the dominant controlling factor for modulating northward volume transport of Atlantic-derived water masses, with an associated reduction in Arctic spring sea ice concentration of ∼30–35%. Current generation models often produce diverging results, however, and have not yet been validated against proxy data in northern high latitude settings during the mPWP. Our new results of northward volume transport and sea ice extent therefore provide much needed input for validation of current generation models aimed at improving the robustness of future climate modeling in the Arctic.
Planktonic Foraminifera assemblages from cores of a borehole are studied. Depth interval is from 380 m to 2300 m. The drill site is located in the continental shelf of "Golfo de Cadiz" (SW Spain). ...The distribution of planktonic foraminiferal species is in agreement with Blow's zonation (1969) extending in age from the Messinian to the Pleistocene.
Environmental conditions in one of Earth's most densely populated regions, East Asia, are dominated by the monsoon. While Quaternary monsoon variability is reasonably well understood, pre-Quaternary ...monsoon variability and dynamics remain enigmatic. In particular, little is known about potential relationships between northern hemispheric monsoon response and major Cenozoic changes in Antarctic ice cover. Here we document long-term East Asian summer monsoon (EASM) intensification through the Late Miocene–Pliocene (∼8.2 to 2.6 Ma), and attribute this to progressive Antarctic glaciation. Our new high-resolution magnetic records of long-term EASM intensification come from the Late Miocene–Pliocene Red Clay sequence on the Chinese Loess Plateau; we identify underlying mechanisms using a numerical climate-model simulation of EASM response to an idealized stepwise increase in Antarctic ice volume. We infer that progressive Antarctic glaciation caused intensification of the cross-equatorial pressure gradient between an atmospheric high-pressure cell over Australia and a low-pressure cell over mid-latitude East Asia, as well as intensification of the cross-equatorial sea-surface temperature (SST) gradient. These combined atmospheric and oceanic adjustments led to EASM intensification. Our findings offer a new and more global perspective on the controls behind long-term Asian monsoon evolution.
•Improved magnetochronology for the Shilou Red Clay on the Chinese Loess Plateau.•New magnetic records of the Late Miocene–Pliocene East Asian Summer monsoon.•East Asian Summer monsoon intensity increases progressively from ∼8 to 2.6 Ma.•Asian monsoon intensification is attributed to increased Antarctic glaciation.
•More negative δ2Hwax values from Gyirong paleosediments than from modern soils.•Higher GDGT-based paleotemperatures in the Gyirong Basin than at present.•Similar differences between basin floor and ...mountain altitudes using isotopic and GDGT altimeters.•Better applicability of GDGT altimeters under warmer and wetter environments.•A lower-altitude Himalayas (basin floor at ∼2.5 km asl) before the Mid-Pliocene.
Contradictory paleoaltitudinal histories of the Himalayas arrived at using isotopic paleoaltimeters and ecological evidences have constrained our further exploration of the geodynamic mechanisms driving the India-Eurasia collision and the resultant interaction between tectonic uplift and climate change. In this study, based on evidence derived from glycerol dialkyl glycerol tetraethers (GDGTs), the hydrogen isotopes of leaf wax n-alkanes (δ2Halk), we estimated the paleoaltitude of the Gyirong Basin (GB), central Himalayas, for the 7.0∼3.2 Ma period. The paleoaltitudinal reconstruction based on δ2Halk values (∼6.3 km above sea level (asl)) was consistent with that of the revised δ18Oc values (∼5.6 km asl), and higher than the present-day altitude (∼4 km asl). The reconstructed paleotemperatures based on brGDGTs (14.2 ± 4.5°C for the lake surface; 7.5 ± 3.3°C for terrestrial organic matter source areas) were consistent with the ecological evidences, indicating a low-altitude paleoenvironment. This proves that a systemic bias exists between the isotopic paleoaltimeters and the ecological evidence, rather than a problem with specific indicators. The reconstructed paleoaltitudinal differences between the δ2Halk and δ18Oc values are similar to those of brGDGT reconstructions, seemingly representing the paleoaltitudinal differences between the source areas of terrestrial organic matter inputs and the lake surface, and suggesting that the isotopic palaeoaltimeters do not specifically record the higher-altitude parts of the basinal topography. Further paleoenvironmental analysis indicated that the warmer and wetter environment present during the Late Miocene to Mid-Pliocene would, on the face of it, be better suited to the application of brGDGT paleothermometers, and this in turn would potentially lead to a systemic overestimation by isotopic paleoaltimeters. We therefore adopted the paleoaltitudinal reconstructions which used brGDGTs and concluded that the lake surface of the GB during the Late Miocene to Mid-Pliocene was 2.5 ± 0.8 km asl, and that the surrounding mountains exceeded 3.6 km asl in height, implying that the central Himalayas underwent a rapid uplift of ∼1.5 km after the Mid-Pliocene.
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