The growth of Tibetan Plateau is considered to have played a key role during the evolution of Asian climate. Our understanding of the relationship between the plateau growth and Asian climate changes ...is limited, however, due to the scarcity of well-dated sedimentary sequences that could provide parallel information of the evolution of elevation and climate. Here, we report a high-resolution time series record of the stable hydrogen isotopic composition of leaf-wax n-alkanes (δDn-alk) from a continuous Neogene stratigraphic sequence (15–1.8 Ma) from the Qaidam basin on the northern Tibetan Plateau. These data are used to reconstruct the isotopic composition of meteoric waters (δDm) and subsequently applied to interpret the history of paleotopography and climate in Qaidam.
Our results indicate four stages in the evolution of hydrology in the Qaidam basin. In Stage I (15 Ma to 10.4 Ma), δDm gradually decreases from −24.9‰ to −75.5‰, synchronous with a period of active tectonism. The estimated topographic growth of 2.1±0.3 km is comparable to the height of Qaidam basin relative to the foreland Hexi Corridor. We note that C3 plants were dominant in this region since the Miocene; we take this as independent evidence that this area was mountainous before the C4 expansion in late Miocene and Pliocene. δDm variability in subsequent stages appears to be related to shifts in dry and moist conditions and independent of topographical changes — a conclusion supported by other independent climatic records on the Tibetan Plateau. High δDm values in Stage II (10.4 Ma to 6.9 Ma) are related to severe aridity, and Stage III (6.9 Ma to 4.1 Ma) is marked by low δDm values, suggestive of moist conditions related to the strengthening East Asia Summer Monsoon. High δDm values in Stage IV (4.1 Ma to 1.8 Ma) reflect a climate, drier than the present.
•We explore the potential of compound-specific isotope analysis in paleoaltimetry.•We present a high-resolution reconstruction of paleometeoric waters (δDm).•The record from the northern Tibetan Plateau covers a period from 15 Ma to 1.8 Ma.•The decrease in δDm between 15 Ma and 10.4 Ma suggests a surface uplift of 2.1 km.•The record reflects a dynamic climate varying between dry and moist conditions.
There is a large range of future aerosol emissions scenarios explored in the Shared Socioeconomic Pathways (SSPs), with plausible pathways spanning a range of possibilities from large global ...reductions in emissions by 2050 to moderate global increases over the same period. Diversity in emissions across the pathways is particularly large over Asia. Rapid reductions in anthropogenic aerosol and precursor emissions between the present day and the 2050s lead to enhanced increases in global and Asian summer monsoon precipitation relative to scenarios with weak air quality policies. However, the effects of aerosol reductions do not persist to the end of the 21st century for precipitation, when instead the response to greenhouse gases dominates differences across the SSPs. The relative magnitude and spatial distribution of aerosol changes are particularly important for South Asian summer monsoon precipitation changes. Precipitation increases here are initially suppressed in SSPs 2-4.5, 3-7.0, and 5-8.5 relative to SSP1-1.9 when the impact of remote emission decreases is counteracted by continued increases in South Asian emissions.
Earth's modern climate, characterized by polar ice sheets and large equator-to-pole temperature gradients, is rooted in environmental changes that promoted Antarctic glaciation ~33.7 million years ...ago. Onset of Antarctic glaciation reflects a critical tipping point for Earth's climate and provides a framework for investigating the role of atmospheric carbon dioxide (CO₂) during major climatic change. Previously published records of alkenone-based CO₂ from high-and low-latitude ocean localities suggested that CO₂ increased during glaciation, in contradiction to theory. Here, we further investigate alkenone records and demonstrate that Antarctic and subantarctic data overestimate atmospheric CO₂ levels, biasing long-term trends. Our results show that CO₂ declined before and during Antarctic glaciation and support a substantial CO₂ decrease as the primary agent forcing Antarctic glaciation, consistent with model-derived CO₂ thresholds.
Temperatures in tropical regions are estimated to have increased by 3° to 5°C, compared with Late Paleocene values, during the Paleocene-Eocene Thermal Maximum (PETM, 56.3 million years ago) event. ...We investigated the tropical forest response to this rapid warming by evaluating the palynological record of three stratigraphic sections in eastern Colombia and western Venezuela. We observed a rapid and distinct increase in plant diversity and origination rates, with a set of new taxa, mostly angiosperms, added to the existing stock of low-diversity Paleocene flora. There is no evidence for enhanced aridity in the northern Neotropics. The tropical rainforest was able to persist under elevated temperatures and high levels of atmospheric carbon dioxide, in contrast to speculations that tropical ecosystems were severely compromised by heat stress.
Abstract
With increasing global interest in molecular hydrogen to replace fossil fuels, more attention is being paid to potential leakages of hydrogen into the atmosphere and its environmental ...consequences. Hydrogen is not directly a greenhouse gas, but its chemical reactions change the abundances of the greenhouse gases methane, ozone, and stratospheric water vapor, as well as aerosols. Here, we use a model ensemble of five global atmospheric chemistry models to estimate the 100-year time-horizon Global Warming Potential (GWP100) of hydrogen. We estimate a hydrogen GWP100 of 11.6 ± 2.8 (one standard deviation). The uncertainty range covers soil uptake, photochemical production of hydrogen, the lifetimes of hydrogen and methane, and the hydroxyl radical feedback on methane and hydrogen. The hydrogen-induced changes are robust across the different models. It will be important to keep hydrogen leakages at a minimum to accomplish the benefits of switching to a hydrogen economy.
High-resolution geochemical analyses of the Lower Eocene Contessa Road section (Italy) reveal orbitally controlled fluctuations in the percent concentration of calcium carbonate (wt.% CaCO
3) that ...include the ETM2 (Elmo) and ETM3 (“X”) hyperthermal events. Patterns of increased dissolution, negative carbon isotope excursions, and warmer global climates are intimately linked to maxima in insolation, through the global carbon cycle. Extraction of short- and long-eccentricity orbital periodicities of the wt.% CaCO
3 record provides a relative cyclochronology for the interval ranging from ∼
52 to ∼
55.5
Ma. The Contessa Road section is easily accessible and offers a continuous integrated stratigraphic record (stable isotopes, standard calcareous plankton biostratigraphy, magnetostratigraphy, and cyclostratigraphy), thus providing a potential type succession for the study of Early Eocene hyperthermals.
The Paleocene–Eocene Thermal Maximum is characterized by a massive perturbation of the global carbon cycle reflected in a large, negative carbon isotope excursion associated with rapid global warming ...and changes in the hydrologic system. The magnitude of the carbon isotope excursion from terrestrial carbonates and organic carbon is generally larger relative to marine carbonates. However, high-resolution marine and terrestrial isotopic records from the same locality for direct comparison are limited. Here we present coupled carbon isotope records from terrestrial biomarkers (δ
13C
n-alkane
), marine bulk carbonates (δ
13C
carbonate), and bulk organic carbon (δ
13C
organic) from the continuous sedimentary record of the Forada section in northern Italy in order to evaluate the magnitude and phase relationships between terrestrial and marine environments. Consistent with previous reports, we find that the carbon isotope excursion established from δ
13C
n-alkane
values is more negative than those established from δ
13C
carbonate and δ
13C
organic values. In contrast to the majority of PETM records, all Forada δ
13C records show a sharp
13C-enrichment immediately following the onset of the carbon isotope excursion. Further, the terrestrial δ
13C
n-alkane
record lags δ
13C
carbonate/δ
13C
organic trends by ~
4–5
kyr—offsets that reflect the long residence time of soil organic carbon.
Hydrogen isotope records from higher-plant leaf waxes (δD
n-alkane
) and sea-surface temperatures (TEX
86) were established to assess hydrologic and ocean temperature trends. We find δD
n-alkane
values trend more positive, associated with higher temperatures prior to the onset of the carbon isotope excursion, and conclude that regional changes in the hydrologic cycle likely occurred before the onset of the carbon isotope anomaly.
► Coupled terrestrial and marine δ
13C records were recovered across the PETM. ► Isotope records suggest the leaf wax CIE lagged the marine excursions by ~
5
kyr. ► δD and temperature records suggest climatic variations prior to the CIE.
The Eocene hyperthermals, including the Paleocene–Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM2), represent extreme global warming events ∼56 and 54 million years ago associated ...with rapid increases in atmospheric greenhouse gas concentrations. An initial study on PETM characteristics in the Arctic region argued for intensification of the hydrological cycle and a substantial increase in poleward moisture transport during global warming based on compound-specific carbon and hydrogen isotopic (2H/1H) records from sedimentary leaf-wax lipids. In this study, we apply this isotopic and hydrological approach on sediments deposited during ETM2 from the Lomonosov Ridge (Integrated Ocean Drilling Program Expedition 302). Our results show similar 2H/1H changes during ETM2 as during the PETM, with a period of 2H-enrichment (∼20‰) relative to “pre-event” values just prior to the negative carbon isotope shift (CIE) that is often taken as the onset of the hyperthermal, and more negative lipid δ2H values (∼−15‰) during peak warming. Notably, lipid 2H-enrichment at the base of the event is coeval with colder TEX86H temperatures.
If 2H/1H values of leaf waxes primarily reflect the hydrogen isotopic composition of precipitation, the observed local relationship between temperature and 2H/1H values for the body of ETM2 is precisely the opposite of what would be predicted using a simple Rayleigh isotope distillation model, assuming a meridional vapor trajectory and a reduction in equator-pole temperature gradients. Overall, a negative correlation exists between the average chain length of n-alkanes and 2H/1H suggesting that local changes in ecology could have impacted the hydrogen isotopic compositions of leaf waxes. The negative correlation falls across three separate intervals — the base of the event, the initial CIE, and during the H2 hyperthermal (of which the assignment is not fully certain). Three possible mechanisms potentially explain 2H-enriched signals at the base of the event, including (1) intense local drying and cooling leading to evaporative 2H-enrichment; (2) changes in frequency/intensity of storm events and its impact on high latitude amount effects; and (3) changes in low-latitude temperatures. Evidence for hydrological shifts at the base of both hyperthermals suggests that hydrological change or the factors promoting hydrological change played a role in triggering the release of greenhouse gases. Generation of similar high-resolution isotopic- and temperature records at other latitudes is crucial for understanding the causal links between temperature and hydrological changes and may help constrain the source and mechanism of carbon release that triggered the early Eocene hyperthermals.
•Two Eocene hyperthermals exhibit similar hydrological trends in the Arctic.•Reduced Equator-Pole temperature gradient cannot explain pre-event changes.•Pre-event shifts may indicate greater local evaporation or storm activity.
•Two PETM records from one basin in Northern Italy show similar hydrological trends.•Significant differences are observed in the magnitude of hydrogen isotope changes.•Changes during peak warming ...corroborate changes in global hydrology.
Paired assessments of carbon (δ13Clipids) and hydrogen isotopic compositions of leaf-wax lipids (δ2Hlipids) from warm intervals in Earth’s history have been used to investigate the relationship between greenhouse gases, hydrological cycle and global warming. Modern studies, however, show that δ2Hlipids can exhibit significant variability due to secondary factors including differences in biosynthetic fractionation and 2H enrichments in soil- and leaf-water. To evaluate the intrabasinal variability of sedimentary compound specific isotopic records, we generated new carbon and hydrogen isotopic compositions of leaf wax lipids for the Paleocene–Eocene Thermal Maximum (PETM; ∼55Ma) from Cicogna Creek (Belluno Basin, northern Italy), and compared results with published PETM records from the proximal Forada Creek section.
Similar isotopic trends are observed at both localities. The magnitude of the negative carbon isotope excursion at Cicogna is ∼2.5‰. Pre-event 2H enrichment recorded in the Forada section is missing at Cicogna, likely due to a disturbed interval at the Paleocene–Eocene boundary. A 2H depletion of ∼10–15‰ during the body of the PETM at Cicogna is observed in several PETM sections, implicating a primary change in the global hydrological cycle. Given the proximity of Cicogna and Forada, isotopic compositions of paleo-meteoric water are expected to be similar. However, a ∼15‰ offset between the records is apparent. Possible reasons include differences in vegetation, biomarker transport and precipitation altitude, underscoring the complexity of using a single record for zonal reconstructions and data model comparisons. Ultimately, this study shows that while 2H/1H trends can be applied for paleoclimate analysis with reasonable certainty, absolute magnitudes can be biased by secondary local factors.
Clean air policies can have significant impacts on climate in remote regions. Previous modeling studies have shown that the temperature response to European sulfate aerosol reductions is largest in ...the Arctic. Here we investigate the atmospheric and ocean roles in driving this enhanced Arctic warming using a set of fully coupled and slab‐ocean simulations (specified ocean heat convergence fluxes) with the Norwegian Earth system model (NorESM), under scenarios with high and low European aerosol emissions relative to year 2000. We show that atmospheric processes drive most of the Arctic response. The ocean pathway plays a secondary role inducing small temperature changes mostly in the opposite direction of the atmospheric response. Important modulators of the temperature response patterns are changes in sea ice extent and subsequent turbulent heat flux exchange, suggesting that a proper representation of Arctic sea ice and turbulent changes is key to predicting the Arctic response to midlatitude aerosol forcing.
Plain Language Summary
Aerosols are liquid or solid particles suspended in air, which may have adverse air quality and health impacts. Sulfate aerosols also have a cooling influence on climate and can mask some of the greenhouse gas‐induced global warming. While aerosol emissions are variable in space and time, their impacts are not limited to where they are emitted. In fact, studies using global climate models have shown that changing sulfur dioxide emissions in Europe can have significant impacts on Arctic climate. Here we investigate the roles of changes in atmospheric and ocean heat transport in driving these changes in the Arctic by conducting a series of climate model simulations with specified anthropogenic sulfur dioxide emissions and different ocean heat transport fluxes. We find that changes through the atmosphere play a primary role in affecting the Arctic climate. These changes are modulated by changes in sea ice extent and the energy exchange between ocean and atmosphere in the sub‐Arctic. Aerosol‐driven changes in ocean heat transport play a smaller, secondary role in the Arctic and tend to reduce the impacts. Our results show that the proper representation of Arctic sea ice is crucial for accurately modeling the Arctic response to changes in midlatitude aerosol forcing.
Key Points
Atmospheric processes drive the Arctic climate response to European aerosol emission changes
Changes in ocean heat transport play a smaller role and buffer the response
Accurate simulation of sea ice changes is critical for predicting the Arctic response to midlatitude aerosol changes
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