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Life on Earth has been capitalizing on the C3 photosynthetic pathway for 2.8 billion years. However, in the world's grasslands that emerged since the Paleogene, C4 vegetation expanded dramatically between 8 and 3 Ma in response to climatic changes. Here we present the first comprehensive Late Miocene to Holocene δ13C soil carbonate record from the Eastern Mediterranean region (Anatolia) to reconstruct long-term geographic distributions of C3 and C4 plants, a region with patchy records compared to parts of Africa and Asia. Our results show a colonization of Anatolian floodplains by C4 biomass by 9.9 Ma, similar to regions in NW and E Africa, followed by a transition from this mixed C3-C4vegetation to C4 dominance between ca. 7.1 Ma and 4.9 Ma. The transition coincides with a similar shift from C3 to C4 vegetation in southern Asia and is generally attributed to the Late Miocene Cooling in response to decreasing atmospheric pCO2. However, the Anatolian paleoecosystem patterns are unique due to a rapid and permanent return to C3 dominance in the Early Pliocene, which is not observed elsewhere and occurs simultaneously with the disappearance of the open environment-adapted large mammal Pikermian chronofauna. We propose that this return to C3 vegetation was caused by paleoclimatic processes that regionally shifted precipitation from the warm to the cool season, resembling the modern Mediterranean climate. In conclusion, changes in rainfall seasonality under subhumid climate, rather than increased aridity, drove the demise of C4-dominated floodplains and the open-environment adapted Pikermian chronofauna at the Eurasian-African crossroads. [ABSTRACT FROM AUTHOR]

Conservation of species and ecosystems is increasingly difficult because anthropogenic impacts are pervasive and accelerating. Under this rapid global change, maximizing conservation success requires a paradigm shift from maintaining ecosystems in idealized past states toward facilitating their adaptive and functional capacities, even as species ebb and flow individually. Developing effective strategies under this new paradigm will require deeper understanding of the long-term dynamics that govern ecosystem persistence and reconciliation of conflicts among approaches to conserving historical versus novel ecosystems. Integrating emerging information from conservation biology, paleobiology, and the Earth sciences is an important step forward on the path to success. Maintaining nature in all its aspects will also entail immediately addressing the overarching threats of growing human population, overconsumption, pollution, and climate change.

Capturing the mechanisms leading to the local extirpation of a species in deep time is a challenge. Here, by combining stable oxygen and carbon isotopic analyses on benthic and planktonic foraminifera and the otoliths of pelagic and benthic fish species, we reveal the paleoceanographic regime shifts that took place in the eastern Mediterranean from 7.2 to 6.5 Ma, in the precursor phase to the Messinian salinity crisis, and discuss the fish response to these events. The stepwise restriction of the Mediterranean–Atlantic gateway impacted the metabolism of fishes in the Mediterranean, particularly those dwelling in the lower, deeper part of the water column. An important shift in the Mediterranean paleoceanographic conditions took place between 6.951 and 6.882 Ma, from predominantly temperature to salinity control, which was probably related to stratification of the water column. A regime shift at 6.814 Ma, due to changes in the influx, source and/or preservation of organic matter, led to pelagic–benthic decoupling of the fish fauna. At that time, the oxygen isotopic composition of benthic fish otoliths reflects higher salinity in the lower part of the water column that is accompanied by a rapid fluctuation in the carbon isotopic composition (a proxy for the metabolic rate), ultimately leading to the local extirpation of the benthic species. Overall, our results confirm that otolith stable oxygen and carbon isotope ratios are reliable proxies for paleoceanographic studies and, when combined with those of foraminifera, can reveal life history changes and migration patterns of teleost fishes in deep time. [ABSTRACT FROM AUTHOR]

Isotopic and elemental records of authigenic calcite from lacustrine deposits in the intraforeland basins of Utah were analyzed in an effort to reconstruct the regional paleoclimate, paleohydrology, and paleotopography of the early Cenozoic central North American Cordillera. Isotopic profiles for Paleogene Lakes Uinta, Flagstaff, and Claron show relatively large oxygen isotopic shifts that are diachronous among basins with an ∼7% decrease in δ18 Ocalcite values at ca. 45 Ma in Lake Flagstaff, an ∼5% decrease in δ18Ocalcite values between ca. 42 and 35 Ma in Lake Claron, and an ∼6% decrease in δ18Ocalcite values between ca. 44 and 43 Ma in Lake Uinta. We interpret these negative oxygen isotopic shifts to be the combined result of increased hypsometric mean elevation of basin catchments and related freshening associated with basin infilling. The basins studied also have undergone periods of intense evaporation during periods of hydrologic closure, which, for example, produced an ∼7% increase in δ18Ocalcite values in Lake Uinta beginning at ca. 51 Ma. Hydrologic closure in the Uinta Basin probably resulted from growth of local topography that diverted previously substantial inflows from low elevation regions within the foreland. This study adds to the growing body of evidence that suggests a pattern of along-strike variations in the timing of topographic development and dissection of the Cordilleran landscape during the early Cenozoic. We favor an interpretation that calls for the middle Eocene rearrangement of regional drainage patterns such that intraforeland basins that once received waters from far-flung foreland river systems became dominated by inflows of low δ18O waters from catchments with higher hypsometric mean elevations that drained the adjacent hinterland and/or basin-bounding uplifts. This drainage reorganization is analogous but subsequent to the large-scale integration of catchments in the northern Cordillera that has been recognized on the basis of isotopic and sedimentological evidence in Montana and Idaho at ca. 50-47 Ma, with rivers flowing southeast into Lake Gosiute at ca. 49 Ma and then for a time reaching Lake Uinta, causing a prominent highstand in that lake at 48.6 Ma. The negative oxygen isotopic shifts presented herein, which occurred between ca. 45 and ca. 35 Ma in the intraforeland basins of Utah, may reflect the north-to-south progression of drainage integration in the Cordillera as magmatism and related topography swept southward through the hinterland and increased the hypsometric mean of catchments that fed subjacent intraforeland basins. © 2008 Geological Society of America.

Many continental paleoclimate archives originate from wetland sedimentary sequences. While several studies have investigated biomarkers derived from peat-generating vegetation typical of temperate/boreal bogs (e.g., Sphagnum), only scant information is available on emergent plants predominant in temperate/subtropical coastal marshlands, peri-lacustrine and fen environments. Here, we address this gap, focusing on two wetlands in the Mediterranean (Nisí fen and Tenaghi Philippon, Greece). We examined the concentration, homologue distribution, and hydrogen stable isotopic composition (δ[sup 2]H) of leaf wax n-alkanes in 13 fen plant species, their surrounding soil, and surface water during the wet growing season (spring) and the declining water table period (summer). Our findings indicate that local graminoid species primarily contribute to the soil n-alkane signal, with a lesser influence from forbs, likely owing to differences in morphology and vegetation structure. The δ[sup 2]H values of surface and soil water align with local average annual precipitation δ[sup 2]H, reflecting winter-spring precipitation. Consistently, the average δ[sup 2]H of local surface, soil, and lower stem water showed negligible evaporative enrichment, confirming minimal [sup 2]H-fractionation during water uptake. We find that δ[sup 2]H values of source water for wax compound synthesis in local fen plants accurately mirror local annual precipitation. Furthermore, despite differences between leaves and lower stems in n-alkane production rates, their δ[sup 2]H values exhibit remarkable similarity, indicating a shared metabolic substrate, likely originating in leaves. Our net [sup 2]H-fractionation values (i.e., precipitation to leaf n-alkanes) align with those in Chinese highlands and other similar environments, suggesting consistency across diverse climatic zones. Notably, our data reveal a seasonal decrease in the carbon preference index (CPI) in plant samples, indicating wax lipid synthesis changes associated with increased aridity. Additionally, we introduce a new parity isotopic difference index (PID) based on the consistent δ[sup 2]H difference between odd and even n-alkane homologues. The PID demonstrates a strong anticorrelation with plant CPI, suggesting a potential avenue to trace long-term aridity shifts through δ[sup 2]H analysis of odd and even n-alkane homologues in sedimentary archives. While further development of the PID is necessary for broad application, these findings highlight the intricate interplay between plant physiology, environmental parameters, and sedimentary n-alkanes in unravelling past climatic conditions. [ABSTRACT FROM AUTHOR]

This study presents the simulated response of regional climate and the oxygen isotopic composition of precipitation (δ18 O p) to different along-strike topographic evolution scenarios. These simulations are conducted to determine if the previously hypothesized diachronous surface uplift in the Western and Eastern Alps would produce δ18 O p signals in the geologic record that are sufficiently large and distinct to be detected using stable isotope paleoaltimetry. We present a series of topographic sensitivity experiments conducted with the water-isotope-tracking atmospheric general circulation model (GCM) ECHAM5-wiso. The topographic scenarios are created from the variation of two free parameters, (1) the elevation of the Western–Central Alps and (2) the elevation of the Eastern Alps. The results indicate Δδ18 O p values (i.e., the difference between δ18 O p values at the low- and high-elevation sites) of up to -8 ‰ along the strike of the Alps for the diachronous uplift scenarios, primarily due to changes in orographic precipitation and adiabatic lapse rate driven localized changes in near-surface variables. These simulated magnitudes of Δδ18 O p values suggest that the expected isotopic signal would be significant enough to be preserved and measured in geologic archives. Moreover, the simulated slight δ18 O p differences of 1 ‰–2 ‰ across the low-elevation sites support the use of the δ – δ paleoaltimetry approach and highlight the importance of sampling far-field low-elevation sites to differentiate between the different surface uplift scenarios. The elevation-dependent rate of change in δ18 O p ("isotopic lapse rate") varies depending on the topographic configuration and the extent of the surface uplift. Most of the changes are significant (e.g., -1.04 ‰ km -1 change with slope error of ±0.09 ‰ km -1), while others were within the range of the statistical uncertainties (e.g., -0.15 ‰ km -1 change with slope error of ±0.13 ‰ km -1). The results also highlight the plausible changes in atmospheric circulation patterns and associated changes in moisture transport pathways in response to changes in the topography of the Alps. These large-scale atmospheric dynamics changes can complicate the underlying assumption of stable isotope paleoaltimetry and therefore require integration with paleoclimate modeling to ensure accurate reconstruction of the paleoelevation of the Alps. [ABSTRACT FROM AUTHOR]