The Middle Miocene represents a crucial interval to reconstruct the paleoceanographic evolution of the Eastern Mediterranean, marked by different events such as the closure of the seaways, or intense tectonic and volcanic activity. In this study, we present new foraminiferal Sr–Nd isotopic and elemental ratio data from four Burdigalian–Langhian sections in south-eastern Türkiye (Adana and Adıyaman basins). Elevated Fe/Ca, Al/Ca, Mn/Ca and Mg/Ca ratios indicate substantial non-carbonate admixture, with an additional Mg contribution that cannot be attributed to aluminosilicate detritus alone. The systematic offset between foraminiferal and detrital εNd nevertheless indicates that primary water mass signals are partially preserved. The εNd foraminiferal data reveal section-dependent paleoceanographic conditions. The Adıyaman Basin record is dominated by anomalously radiogenic values expressing important admixture of volcanic material and therefore carries limited value as a water mass tracer. Within the Adana Basin, the late Burdigalian record suggests opening of Eastern Mediterranean connectivity, while Langhian sections record spatial heterogeneity between sub-basins, indicating both Paratethyan and Mediterranean influences. This pattern may reflect the position of the Adana Basin as an inner foredeep position inboard of the Cyprus Arc, distinct from open Mediterranean waters. These results highlight how tectonics, volcanism, and global climatic forcing are linked to marine connectivity in the Eastern Mediterranean during the Middle Miocene.
Under ongoing global warming, the impacts of heat stress are intensifying worldwide. Quantifying the role of human activities in driving historical changes in heat stress and generating reliable future projections, especially at continental and subcontinental scales, holds scientific value for the development of targeted climate adaptation and mitigation strategies. This study uses the Wet-Bulb Globe Temperature (WBGT) as a key heat stress index and conducts a comprehensive detection and attribution analysis of summer WBGT changes over global land areas from 1961 to 2014 at both continental and subcontinental scales, using ERA5 reanalysis and CMIP6 model simulations under different external forcings. Based on the attribution results, we constrain future WBGT projections under the SSP2–4.5 and SSP5–8.5 scenarios. Results show that anthropogenic forcing, dominated by greenhouse gas (GHG) forcing, is the primary driver of the observed increase in WBGT over the past 54 years across all six continents and most of the 21 subcontinental regions. The aerosol (AER) forcing exerts a modest offsetting effect in some regions, while natural (NAT) forcing signals are generally undetectable. CMIP6 models tend to overestimate the response of WBGT to external forcings. After applying attribution constraints, projected increases in WBGT are substantially reduced compared to raw projections. The strongest enhancements are expected in the mid- to high-latitudes of the Northern Hemisphere, while tropical regions show relatively moderate changes. These findings highlight the dominant role of anthropogenic GHG in driving WBGT and demonstrate that emission mitigation can substantially lower future heat stress risks.
Vegetation greening, suggested by increasing leaf area index (LAI), has enhanced ecosystem photosynthesis (gross primary productivity, GPP) and the terrestrial carbon sink since the 1980s. However, multiple lines of evidence show a decoupling between LAI and GPP under droughts, raising questions about how this relationship varies across timescales, particularly at the subseasonal scale under increasing flash droughts. Here we combined observations from 95 FLUXNET flux towers, satellite-derived vegetation products (LAI and solar-induced chlorophyll fluorescence), nine terrestrial biosphere models, and 1927 documented flash drought events to investigate LAI-GPP coupling across subseasonal, seasonal, and multi-annual timescales during 1982–2023. Results show that LAI-GPP coupling is strongest at seasonal scales but has declined markedly at subseasonal timescales over the past four decades. This decoupling is primarily driven by rising CO2, increasing vapor pressure deficit, and evapotranspiration, with models highlighting a dominant role of CO2 fertilization. Field evidence from global-distributed flash drought events identified the role of ecosystem physiology (light use efficiency) in explaining the enhanced decoupling of ecosystem structure (LAI) and photosynthesis. Our findings provide a mechanistic understanding of relationship between vegetation structure and photosynthetic carbon uptake under the future increase of flash droughts, and underscore that the impact of canopy greening on global carbon cycle might be more complicated than ever expected.
The Piacenzian–Gelasian transition represents a key phase in the intensification of Northern Hemisphere glaciation and the reorganisation of Mediterranean hydroclimate. Here we present a high-resolution terrestrial palynological record from the Monte San Nicola Gelasian Global boundary Stratotype Section and Point (GSSP), southern Italy, integrated with astrochronology and marine multiproxy records between ~2.7 and 2.5 Ma. The record indicates that vegetation change culminated in a threshold-like reorganisation at MIS 104 following earlier precursor fluctuations. Prior to this transition, ecosystems remained relatively buffered, with variability expressed mainly through changes in forest composition. After MIS 104, vegetation responses became increasingly state-dependent, with recurrent landscape opening, steppe expansion and enhanced hydroclimatic seasonality. Spectral analyses reveal a hierarchical organisation of orbital forcing, with obliquity pacing vegetation structure, while precession primarily modulated hydroclimatic variability. However, precession-driven forcing was only intermittently translated into ecological change, indicating that vegetation response depended on background climate conditions. At shorter timescales, suborbital variability became increasingly expressed after MIS 104, with strong amplification during MIS 100, consistent with the increasing climate instability documented in coeval marine records. Comparison of terrestrial and marine variability reveals a coupled but non-equivalent land–sea response, indicating that vegetation dynamics were governed primarily by effective moisture and its seasonal distribution rather than temperature. The palynological record also provides the first high-resolution terrestrial characterisation of the Gelasian GSSP section, linking the formal chronostratigraphic boundary to orbitally paced vegetation reorganisation and documenting the increasing sensitivity of Mediterranean ecosystems to hydroclimatic instability during the intensification of Northern Hemisphere glaciation.
Lithium isotopes are widely applied to trace silicate weathering processes and their linkages to climate. Elevated riverine Li isotopic composition (δ7Li) is commonly interpreted to reflect incongruent weathering associated with extensive secondary mineral formation. However, rivers draining cold and arid environments with relatively weak weathering intensity can exhibit riverine δ7Li comparable to those observed in more intensely weathered regions. The controls on riverine δ7Li under cold and arid environments remain incompletely understood. Here we investigate δ7Li of river waters, fine sediments, salts extracted from sediments, lake waters, and groundwater in small catchments of the northern Tibetan Plateau. River waters exhibit exceptionally high variable Li concentrations (1.4 to 173 μmol/L), primarily derived from evaporite dissolution and silicate weathering. Their δ7Li values systematically exceed those of silicates, evaporites, lake waters, and groundwater, arguing against simple source mixing. Moreover, riverine δ7Li values are higher than those of coexisting fine sediments, consistent with the preferential incorporation of isotopically light Li into secondary minerals. The positive covariations between river water and fine sediment δ7Li suggest a Rayleigh-type fractionation, likely driven by Li adsorbing onto exchangeable sites of secondary minerals. This behavior contrasts with the negative river-sediment δ7Li relationships and weathering-intensity-controlled δ7Li systematics observed in large Tibetan Plateau rivers. δ7Li values of fine sediments and river waters correlate strongly with aridity index and evaporation-related geochemical indices, and salts extracted from sediments carry relatively high δ7Li values (12.9‰ to 28.5‰). Therefore, we propose that evaporative concentration of soil and riparian pore waters elevates dissolved Li concentrations and promotes preferential adsorption of isotopically light Li onto secondary minerals, progressively elevating δ7Li in residual waters. The subsequent transfer of this isotopically heavy Li to rivers via shallow hydrological flow paths plays a dominant role in shaping riverine δ7Li signatures. These results highlight evaporation-driven isotope fractionation as a previously underappreciated control on riverine δ7Li, with implications for interpreting chemical weathering and the variation of riverine δ7Li under changing climate conditions.
