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  • 1
    Electronic Resource
    Electronic Resource
    Palaeoclimate A balmy Arctic (2004)
    [s.l.] : Nature Publishing Group
    Nature 432 (2004), S. 814-815 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Various lines of evidence show that Earth's climate was much warmer during the Cretaceous period than it is today. Yet that evidence — fossil plants and animals, sedimentary features and geochemical indicators — is sparse, spotty and often inexact, making the magnitude and distribution ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/432814a
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    Paper (German National Licenses)
    Fulltext
  • 2
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    Stable hydrogen isotope record of C30-Alkanoic acid from sediment core MD98-2152 for 450 kyr (2020)
    PANGAEA
    Details
    Publication Date: 2023-06-27
    Description: The stable hydrogen isotopes of C30-Alkanoic acids were measured from marine sediment core MD98-2152, collected off the southern coast of Sumatra, likely reflecting rainfall over southern Sumatra and western Java. The record extends to ~450,000 years before present and includes the five most recent glacial periods. To purify the leaf wax fatty acids for analysis, organic material was extracted from the sediment using an Accelerated Solvent Extractor, leaf waxes were isolated from each total lipid extract using column chromatography then methylated with methanol of a known isotopic composition to form fatty acid methyl esters, and purified with a final column. Hydrogen isotopes were measured using a gas chromatography-isotope ratio-monitoring mass spectrometer against Vienna Standard Mean Ocean Water (VSMOW). The hydrogen isotopes of the leaf wax fatty acids were then used in tandem with previously measured carbon isotopes of the same samples to calculate the hydrogen isotope values of precipitation, accounting for vegetation changes, through time following the methods in Tierney et al. (2017). This data was collected with the purpose of examining rainfall variability in the southern Indo-Pacific Warm Pool during glacial climates and to improve the spatial coverage of precipitation isotope records in the region. The age model and leaf wax carbon isotopes for MD98-2152 are available in Windler et al. (2019).
    Keywords: AGE; CALYPSO; Calypso Corer; DEPTH, sediment/rock; Gas chromatography - Isotope ratio mass spectrometer (GC-IRMS); IMAGES IV-IPHIS III; Indo-Pacific Warm Pool; Leaf wax; Marion Dufresne (1995); MD111; MD982152; MD98-2152; n-Alkanoic acid C30, δD; precipitation; δ Deuterium, precipitation
    Type: Dataset
    Format: text/tab-separated-values, 724 data points
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    DATA PANGAEA
  • 3
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    Last Glacial Maximum SST proxy collection and data assimilation (2020)
    PANGAEA
    Details
    Publication Date: 2024-04-20
    Description: A collection of geochemical SST proxy from the Last Glacial Maximum (23-19 ka) and the Late Holocene (4-0 ka) and results from data assimilation with iCESM 1.2. Includes raw proxy data from the LGM (Tierney2020_LGMProxyData.csv) and LH (Tierney2020_LHProxyData.csv) time slices, with calibrated absolute SSTs; "paired" (data in the same location) proxies with calibrated SST anomalies (Tierney2020_ProxyDataPaired.csv); a 5˚ x 5˚ gridded product of the paired proxies in netCDF format (Tierney2020_ProxyData_5x5_deltaSST.nc); and the results from the DA in netCDF format. The DA results are split into atmospheric variables (SAT, d18O of precipitation; Tierney2020_DA_atm.nc) and oceanic variables (SST, SSS, and d18O of seawater; Tierney2020_DA_ocn.nc). The ocean data are provided on their native tripolar grid (Tierney2020_DA_ocn.nc) as well as a 1 x 1 regridded version (Tierney2020_DA_ocn_regrid.nc).
    Keywords: Binary Object; Binary Object (File Size); Binary Object (Media Type); d18O; Data Assimilation; File content; Last Glacial Maximum; Mg/Ca; SST; TEX86; UK37
    Type: Dataset
    Format: text/tab-separated-values, 14 data points
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    DATA PANGAEA
  • 4
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    The PMIP4 Last Glacial Maximum experiments: preliminary results and comparison with the PMIP3 simulations (2021)
    COPERNICUS GESELLSCHAFT MBH
    In:  EPIC3Climate of the Past, COPERNICUS GESELLSCHAFT MBH, 17(3), pp. 1065-1089, ISSN: 1814-9324
    Details
    Publication Date: 2021-06-07
    Description: The Last Glacial Maximum (LGM, ∼ 21 000 years ago) has been a major focus for evaluating how well state-of-the-art climate models simulate climate changes as large as those expected in the future using paleoclimate reconstructions. A new generation of climate models has been used to generate LGM simulations as part of the Paleoclimate Modelling Intercomparison Project (PMIP) contribution to the Coupled Model Intercomparison Project (CMIP). Here, we provide a preliminary analysis and evaluation of the results of these LGM experiments (PMIP4, most of which are PMIP4-CMIP6) and compare them with the previous generation of simulations (PMIP3, most of which are PMIP3-CMIP5). We show that the global averages of the PMIP4 simulations span a larger range in terms of mean annual surface air temperature and mean annual precipitation compared to the PMIP3-CMIP5 simulations, with some PMIP4 simulations reaching a globally colder and drier state. However, the multi-model global cooling average is similar for the PMIP4 and PMIP3 ensembles, while the multi-model PMIP4 mean annual precipitation average is drier than the PMIP3 one. There are important differences in both atmospheric and oceanic circulations between the two sets of experiments, with the northern and southern jet streams being more poleward and the changes in the Atlantic Meridional Overturning Circulation being less pronounced in the PMIP4-CMIP6 simulations than in the PMIP3-CMIP5 simulations. Changes in simulated precipitation patterns are influenced by both temperature and circulation changes. Differences in simulated climate between individual models remain large. Therefore, although there are differences in the average behaviour across the two ensembles, the new simulation results are not fundamentally different from the PMIP3-CMIP5 results. Evaluation of large-scale climate features, such as land–sea contrast and polar amplification, confirms that the models capture these well and within the uncertainty of the paleoclimate reconstructions. Nevertheless, regional climate changes are less well simulated: the models underestimate extratropical cooling, particularly in winter, and precipitation changes. These results point to the utility of using paleoclimate simulations to understand the mechanisms of climate change and evaluate model performance.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 5
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    DeepMIP: Model intercomparison of early Eocene climatic optimum (EECO) large-scale climate features and comparison with proxy data (2021)
    COPERNICUS GESELLSCHAFT MBH
    In:  EPIC3Climate of the Past, COPERNICUS GESELLSCHAFT MBH, 17(1), pp. 203-227, ISSN: 1814-9324
    Details
    Publication Date: 2021-07-26
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    Tropical circulation intensification and tectonic extension recorded by Neogene terrestrial δ18O records of the western United States (2016)
    In:  EPIC3Geology, 44(11), pp. 971-974, ISSN: 0091-7613
    Details
    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 , isiRev
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  • 7
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    Modern precipitation δ18O and trajectory analysis over the Himalaya-Tibet Orogen from ECHAM5-wiso simulations (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Atmospheres, Wiley, 121(18), pp. 10,432-10,452, ISSN: 0148-0227
    Details
    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 , isiRev
    Format: application/pdf
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  • 8
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    Precipitation δ18O over the Himalaya-Tibet orogen from ECHAM5-wiso simulations: Statistical analysis of temperature, topography and precipitation (2016)
    AGU Publications
    In:  EPIC3Journal of Geophysical Research: Atmospheres, AGU Publications, 121(16), pp. 9278-9300, ISSN: 2169897X
    Details
    Publication Date: 2016-09-19
    Description: Variations in oxygen isotope compositions (δ18O) provide insight into modern climate and past changes in climate and topography. In addition, in regions such as Tibet, geologic archives of isotope ratios record climate change driven by plateau uplift and therefore also provide information about the surface uplift history. A good understanding of modern-day controls on δ18O is crucial for interpreting geologic δ18O in this context. We use the ECHAM5-wiso global atmospheric general circulation model to calculate δ18O in precipitation (δ18Op) for the present-day climate. In the region of the Tibetan Plateau, spatial variations of monthly means of δ18Op are statistically related to spatial variations of 2 m air temperature and precipitation rate, as well as to topography. The size and location of investigated regions are varied in our study to capture regional differences in these relationships and the processes governing the modern δ18Op. In addition to correlation analyses, a cross-validated stepwise multiple regression is carried out using δ18Op as the predictand, and topography and atmospheric variables (temperature and precipitation amount) as predictors. The 2 m air temperature and topography yield the highest spatial correlation coefficients of 〉0.9 and 〈 0.9, respectively, throughout most of the year. Particularly high correlation coefficients are calculated for the region along the Himalayan orogeny and parts of western China. The predictors explain 〉90% of the δ18Op spatial variance in the same regions. The 2 m air temperature is the dominant predictor and contributes 93.6% to the total explained spatial variance on average. The results demonstrate that most of the δ18Op pattern on and around the Tibetan Plateau can be explained by variation in 2 m air temperature and altitude. Correlation of the dependent predictors indicate that in low-altitude regions where topography does not determine temperature variability, the high correlation of temperature and δ18Op may partially be explained by variations in precipitation rates.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 9
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    Drilling the Agulhas Plateau and Transkei Basin to reconstruct the Cretaceous - Paleocene Tectonic and Climatic evolution of the Southern Ocean Basin (2016)
    In:  EPIC3IODP Kollqouium der DFG, Heidelberg, Germany, 2016-03-14-2016-03-16
    Details
    Publication Date: 2016-03-17
    Description: The transition from the Cretaceous “Supergreenhouse” to the Oligocene icehouse provides an opportunity to study changes in Earth system dynamics from a time when climate models suggest CO2 levels may have been as high as 3500 ppmv (parts per million by volume) and then declined to less than 560 ppmv. During the Supergreenhouse interval meridional temperature gradients were very low and oceanic deposition was punctuated by episodes of widespread anoxia, termed Oceanic Anoxic Events (OAEs) resulting in large scale burial of organic carbon reflected in positive delta 13C excursions. High CO2, greenhouse climate conditions are envisioned for the near future calling for action to get a better understanding of their potential impacts and dynamics. Climate models have identified significant geography-related Cenozoic cooling arising from the opening of Southern Ocean gateways, pointing towards a progressive strengthening of the Antarctic Circumpolar Current as the major cause for cooler deep ocean temperatures. Analogous arguments point to an important role for deep circulation in explaining Late Cretaceous climate evolution. The Agulhas Plateau is located in a key area for retrieving high-quality geochemical records to test competing models, e.g. to what extent and exactly when the opening of Drake Passage contributed to cooling of the deep ocean. The proposed drill sites on Agulhas Plateau and Transkei Basin are at high latitudes (65°S-58°S from 100 to 65 Ma) and within a gateway between the newly opening South Atlantic, Southern Ocean and southern Indian Ocean basins. Recovery of expanded and stratigraphically complete pelagic carbonate sequences from this region, and comparison with drilling results from Naturaliste Plateau (760-Full), will provide a wealth of new data to significantly advance the understanding of how Cretaceous temperatures, ocean circulation, and sedimentation patterns evolved as CO2 level rose and fell, and the breakup of Gondwana progressed.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 10
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    Early Cenozoic evolution of topography, climate, and stable isotopes in precipitation in the North American Cordillera (2013)
    AMER JOURNAL SCIENCE
    In:  EPIC3American Journal of Science, AMER JOURNAL SCIENCE, 313, pp. 613-648, ISSN: 0002-9599
    Details
    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 , isiRev
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