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  • 1
    Publication Date: 2016-12-14
    Description: Terrestrial water isotope records preserve a history of hydrological cycling that is influenced by past climate and surface topography. δ18O and δD records from authigenic minerals of the western United States display a long-term increase during the Neogene in the vicinity of the Sierra Nevada and the central Rocky Mountains (Rockies), but a smaller increase or decrease in the northern Great Basin. Interpretations of these isotopic trends require quantitative estimates of the influence of climatic and environmental changes on δ18O and δD of soil water. Here we use a coupled atmosphere-land model with water-isotopologue tracking capabilities, ECHAM5-JSBACH-wiso, to simulate precipitation and δ18O responses to elevation-independent changes in Neogene geography, equator to pole temperature gradient (EPGRAD), grassland expansion, and tropical Pacific sea surface temperatures. Both precipitation and soil water δ18O (δ18Osw) respond strongly to Neogene strengthening of the EPGRAD, but weakly to other forcings. An increase in EPGRAD leads to significant drying and 18O enrichment (3‰–5‰) of soil water over the northern Sierra Nevada and central Rockies as a result of Hadley circulation strengthening and enhanced coastal subtropical subsidence. These large-scale circulation changes reduce inland moisture transport from the Pacific Ocean and Gulf of Mexico. Our simulated δ18Osw responses could explain 50%–100% of the proxy δ18O increases over the Sierra Nevada and central Rockies, suggesting that climate change rather than surface subsidence may have been the dominant climate signal in δ18O records in these regions. On the contrary, δ18O responses to climate changes are small in the Great Basin, indicating that the observed δ18O increase over this region was likely a direct response to surface subsidence with elevation losses of 1–1.5 km. Adding this elevation loss to current Great Basin elevations reveals the former existence of a uniformly high plateau extending from the Sierra Nevada to the central Rockies prior to Neogene extension. This revised elevation history brings Neogene δ18O and δD paleoaltimetry of the western United States in accordance with independent lines of structural evidence and early Cenozoic elevation reconstructions.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 2
    Publication Date: 2019-02-01
    Description: Past warm periods provide an opportunity to evaluate climate models under extreme forcing scenarios, in particular high ( 〉  800 ppmv) atmospheric CO2 concentrations. Although a post hoc intercomparison of Eocene ( ∼  50  Ma) climate model simulations and geological data has been carried out previously, models of past high-CO2 periods have never been evaluated in a consistent framework. Here, we present an experimental design for climate model simulations of three warm periods within the early Eocene and the latest Paleocene (the EECO, PETM, and pre-PETM). Together with the CMIP6 pre-industrial control and abrupt 4 ×  CO2 simulations, and additional sensitivity studies, these form the first phase of DeepMIP – the Deep-time Model Intercomparison Project, itself a group within the wider Paleoclimate Modelling Intercomparison Project (PMIP). The experimental design specifies and provides guidance on boundary conditions associated with palaeogeography, greenhouse gases, astronomical configuration, solar constant, land surface processes, and aerosols. Initial conditions, simulation length, and output variables are also specified. Finally, we explain how the geological data sets, which will be used to evaluate the simulations, will be developed.
    Type: Article , PeerReviewed
    Format: text
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  • 3
    Publication Date: 2016-12-14
    Description: Variations in oxygen isotope ratios (δ18O) measured from modern precipitation and geologic archives provide a promising tool for understanding modern and past climate dynamics and tracking elevation changes over geologic time. In areas of extreme topography, such as the Tibetan Plateau, the interpretation of δ18O has proven challenging. This study investigates the climate controls on temporal (daily and 6 h intervals) and spatial variations in present-day precipitation δ18O (δ18Op) across the Tibetan Plateau using a 30 year record produced from the European Centre/Hamburg ECHAM5-wiso global atmospheric general circulation model (GCM). Results indicate spatial and temporal agreement between model-predicted δ18Op and observations. Large daily δ18Op variations of 25 to +5‰ occur over the Tibetan Plateau throughout the 30 simulation years, along with interannual δ18Op variations of ~2‰. Analysis of extreme daily δ18Op indicates that extreme low values coincide with extreme highs in precipitation amount. During the summer, monsoon vapor transport from the north and southwest of the plateau generally corresponds with high δ18Op, whereas vapor transport from the Indian Ocean corresponds with average to low δ18Op. Thus, vapor source variations are one important cause of the spatial-temporal differences in δ18Op. Comparison of GCM and Rayleigh Distillation Model (RDM)-predicted δ18Op indicates a modest agreement for the Himalaya region (averaged over 86°–94°E), confirming application of the simpler RDM approach for estimating δ18Op lapse rates across Himalaya.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Format: application/pdf
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  • 4
    Publication Date: 2019-07-13
    Description: Past warm periods provide an opportunity to evaluate climate models under extreme forcing scenarios, in particular high ( greater than 800 ppmv) atmospheric CO2 concentrations. Although a post hoc intercomparison of Eocene (approximately 50 Ma) climate model simulations and geological data has been carried out previously, models of past high-CO2 periods have never been evaluated in a consistent framework. Here, we present an experimental design for climate model simulations of three warm periods within the early Eocene and the latest Paleocene (the EECO, PETM, and pre-PETM). Together with the CMIP6 pre-industrial control and abrupt 4(times) CO2 simulations, and additional sensitivity studies, these form the first phase of DeepMIP - the Deep-time Model Intercomparison Project, itself a group within the wider Paleoclimate Modeling Intercomparison Project (PMIP). The experimental design specifies and provides guidance on boundary conditions associated with palaeogeography, greenhouse gases, astronomical configuration, solar constant, land surface processes, and aerosols. Initial conditions, simulation length, and output variables are also specified. Finally, we explain how the geological data sets, which will be used to evaluate the simulations, will be developed.
    Keywords: Meteorology and Climatology
    Type: GSFC-E-DAA-TN39639 , Geoscientific Model Development (e-ISSN 1991-9603); 10; 2; 889-901
    Format: text
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  • 5
    Publication Date: 2019-07-17
    Description: Paleoelevation reconstructions of the North American Cordillera in- ferred from the oxygen (delta 18O) and hydrogen (delta D) isotope ratios of terrestrial paleoclimate proxy materials (soils, ashes, lake sediments) suggest rapid north-to- south migration of topography in the early Cenozoic (pre-49 Ma to 28 Ma). The validation of this reconstruction relies on an accurate understanding of the delta 18Op and the associated regional climate change in response to the uplift of the western North America. Here we study this response using a global climate model (GCM) with explicit delta 18Op diagnostics (ECHAM5-wiso) focusing on the isotopic effects of different types of precipitation, vapor mixing, recycling and moisture source and compare the response against estimates made using a Rayleigh distillation models of moist adiabatic condensation (RDM). Four experiments are performed with Eocene topography inferred from terrestrial stable isotope paleoaltimetry records to investigate how southward propagation of topography affects regional climate (temperature, precipitation and circulation pattern) and dela 18Op over North America. Our experiments predict delta 18Op patterns that are broadly consistent with maps of temporally binned proxy delta 18O and generally support an early Cenozoic north-to-south propagation of high topogra- phy in the North American Cordillera. They do not support the commonly made assumption that isotopic fractionation occurs primarily through rainout following Rayleigh distillation nor the application of modern empirical delta 18Op lapse rates to past environments. In our GCM simulations, precipitation processes and climate changes that are not captured by RDMs substantially affect delta 18Op. These processes include shifts in local precipitation type between convective and large-scale rain and between rain and snow; intensification of low-level vapor recycling particularly on leeward slopes; develop- ment of air mass mixing and changes in wind direction and moisture source. Each of these processes can have significant (〉2‰) influences on delta 18Op that are comparable in magnitude to surface uplift of hundreds or even thousands of meters. In many regions, these processes fortuitously compensate each other, explaining the apparent agreement between ECHAM5-wiso and proxy delta 18O and, more broadly, between RDM estimates and observed delta 18O-elevation relationships. In some regions, compensation is incomplete, and as a result, ECHAM5-wiso delta 18Op does not agree with estimates from the RDM. In these regions, including the interior of the northern cordillera and the eastern flank of the southern Cordillera, moderate adjustments of paleoelevations may be in order.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 6
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    PANGAEA
    In:  Supplement to: Tabor, Clay; Feng, Ran; Otto-Bliesner, Bette L (2019): Climate responses to the splitting of a supercontinent: Implications for the breakup of Pangea. Geophysical Research Letters
    Publication Date: 2019-08-17
    Description: Atmospheric data associated with "Climate responses to the splitting of a supercontinent: Implications for the breakup of Pangea" by Tabor et al. (2019; GRL). Files contain climatologies of FLNS, FLNSC, FLNT, FLNTC, FSNS, FSNSC, FSNT, FSNTC, LHFLX, LWCF, OMEGA, PRECC, PRECL, PS, SHFLX, SWCF, TS, U, and V variables for the One Continent and Two Continents geographic configurations discussed in the manuscript.
    Type: Dataset
    Format: text/tab-separated-values, 10 data points
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  • 7
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    PANGAEA
    In:  Supplement to: Tierney, Jessica E; Haywood, Alan M; Feng, Ran; Bhattacharya, Tripti; Otto-Bliesner, Bette L (accepted): Pliocene warmth consistent with greenhouse gas forcing. Geophysical Research Letters, 46, https://doi.org/10.1029/2019GL083802
    Publication Date: 2019-09-14
    Description: Collection of raw alkenone data spanning the Pliocene; calibrated SST anomalies for each site; calibrated SST anomalies for regional averages; SST field reconstruction.
    Type: Dataset
    Format: application/zip, 33 datasets
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  • 8
    Publication Date: 2019-09-14
    Type: Dataset
    Format: text/tab-separated-values, 1140 data points
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  • 9
    Publication Date: 2019-09-14
    Type: Dataset
    Format: text/tab-separated-values, 1376 data points
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  • 10
    Publication Date: 2019-09-14
    Type: Dataset
    Format: text/tab-separated-values, 4584 data points
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