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  • 1
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    Using paleoclimate proxy-data to select an optimal realisation in an ensemble of simulations of the climate of the past millenium (2006)
    Springer
    In:  Climate Dynamics, 27 . pp. 165-184.
    Details
    Publikationsdatum: 2016-09-13
    Beschreibung: We present and describe in detail the advantages and limitations of a technique that combines in an optimal way model results and proxy-data time series in order to obtain states of the climate system consistent with model physics, reconstruction of past radiative forcing and proxy records. To achieve this goal, we select among an ensemble of simulations covering the last millennium performed with a low-resolution 3-D climate model the ones that minimise a cost function. This cost function measures the misfit between model results and proxy records. In the framework of the tests performed here, an ensemble of 30 to 40 simulations appears sufficient to reach reasonable correlations between model results and reconstructions, in configurations for which a small amount of data is available as well as in data-rich areas. Preliminary applications of the technique show that it can be used to provide reconstructions of past large-scale temperature changes, complementary to the ones obtained by statistical methods. Furthermore, as model results include a representation of atmospheric and oceanic circulations, it can be used to provide insights into some amplification mechanisms responsible for past temperature changes. On the other hand, if the number of proxy records is too low, it could not be used to provide reconstructions of past changes at a regional scale.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00382-006-0128-6
    Standort Signatur Einschränkungen Verfügbarkeit
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    OceanRep: Artikel in einer Fachzeitschrift - begutachtet
  • 2
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    Surface temperature control in the North and tropical Pacific during the last glacial maximum (2004)
    Springer
    Details
    Publikationsdatum: 2022-03-01
    Beschreibung: Based on coupled modelling evidence we argue that topographically-induced modifications of the large-scale atmospheric circulation during the last glacial maximum may have led to a reduction of the westerlies, and a slowdown of the Pacific subtropical gyre as well as to an intensification of the Pacific subtropical cell. These oceanic circulation changes generate an eastern North Pacific warming, an associated cooling in the Kuroshio area, as well as a cooling of the tropical oceans, respectively. The tropical cooling pattern resembles a permanent La Niña state which in turn forces atmospheric teleconnection patterns that lead to an enhancement of the subtropical warming by reduced latent and sensible cooling of the ocean. In addition, the radiative cooling due to atmospheric CO2 and water vapor reductions imposes a cooling tendency in the tropics and subtropics, thereby intensifying the permanent La Niña conditions. The remote North Pacific response results in a warming tendency of the eastern North Pacific which may level off the effect of the local radiative cooling. Hence, a delicate balance between oceanic circulation changes, remotely induced atmospheric flux anomalies as well local radiative cooling is established which controls the tropical and North Pacific temperature anomalies during the last glacial maximum. Furthermore, we discuss how the aftermath of a Heinrich event may have affected glacial temperatures in the Pacific Ocean.
    Materialart: Article , PeerReviewed
    Format: text
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
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    Early Pliocene increase in thermohaline overturning : a precondition for the development of the modern equatorial Pacific cold tongue (2010)
    American Geophysical Union
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 25 (2010): PA2202, doi:10.1029/2008PA001645.
    Beschreibung: Unraveling the processes responsible for Earth's climate transition from an “El Niño–like state” during the warm early Pliocene into a modern-like “La Niña–dominated state” currently challenges the scientific community. Recently, the Pliocene climate switch has been linked to oceanic thermocline shoaling at ∼3 million years ago along with Earth's final transition into a bipolar icehouse world. Here we present Pliocene proxy data and climate model results, which suggest an earlier timing of the Pliocene climate switch and a different chain of forcing mechanisms. We show that the increase in North Atlantic meridional overturning circulation between 4.8 and 4.0 million years ago, initiated by the progressive closure of the Central American Seaway, triggered overall shoaling of the tropical thermocline. This preconditioned the turnaround from a warm eastern equatorial Pacific to the modern equatorial cold tongue state about 1 million years earlier than previously assumed. Since ∼3.6–3.5 million years ago, the intensification of Northern Hemisphere glaciation resulted in a strengthening of the trade winds, thereby amplifying upwelling and biogenic productivity at low latitudes.
    Beschreibung: Funding for this research was provided by the Deutsche Forschungsgemeinschaft (DFG) through projects Ti 240/7, Ti 240/12 (being part of the DFG Research Unit, FOR 451: Impact of Gateways on Ocean Circulation, Climate, and Evolution at Kiel University), and Ti 240/17 and through the DFG Research Center/Excellence Cluster “The Ocean in the Earth System” at the University of Bremen. A. Timmermann is supported by the Japan Agency for Marine-Earth Science and Technology through its sponsorship of the International Pacific Research Center.
    Schlagwort(e): Pliocene ; Thermohaline circulation ; East Pacific cold tongue
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: application/pdf
    Format: text/plain
    Standort Signatur Einschränkungen Verfügbarkeit
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    ARTIKEL (OA)
  • 4
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    Eastern tropical Pacific hydrologic changes during the past 27,000 years from D/H ratios in alkenones (2010)
    American Geophysical Union
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 22 (2007): PA4214, doi:10.1029/2007PA001468.
    Beschreibung: The tropical Pacific plays a central role in the climate system by providing large diabatic heating that drives the global atmospheric circulation. Quantifying the role of the tropics in late Pleistocene climate change has been hampered by the paucity of paleoclimate records from this region and the lack of realistic transient climate model simulations covering this period. Here we present records of hydrogen isotope ratios (δD) of alkenones from the Panama Basin off the Colombian coast that document hydrologic changes in equatorial South America and the eastern tropical Pacific over the past 27,000 years (a) and the past 3 centuries in detail. Comparison of alkenone δD values with instrumental records of precipitation over the past ∼100 a suggests that δD can be used as a hydrologic proxy. On long timescales our records indicate reduced rainfall during the last glacial period that can be explained by a southward shift of the mean position of the Intertropical Convergence Zone and an associated reduction of Pacific moisture transport into Colombia. Precipitation increases at ∼17 ka in concert with sea surface temperature (SST) cooling in the North Atlantic and the eastern tropical Pacific. A regional coupled model, forced by negative SST anomalies in the Caribbean, simulates an intensification of northeasterly trade winds across Central America, increased evaporative cooling, and a band of increased rainfall in the northeastern tropical Pacific. These results are consistent with the alkenone SST and δD reconstructions that suggest increasing precipitation and SST cooling at the time of Heinrich event 1.
    Beschreibung: K. P. and J. P. S. thank the Comer Science and Education Foundation for financial support. J. P. S. acknowledges support by the National Science Foundation (grant NSF-ESH-0639640). NSF grant OCE-0317702 funded cruise KNR176 to the Panama Basin and L. D. K.’s results presented here. A. T. is supported by the Japan Agency for Marine-Earth Science and Technology. S. P. X. is supported by the National Oceanic and Atmospheric Administration CLIVAR Program, the Japan Ministry of Education, Culture, Science and Technology through the Kyosei-7 Project, and the Japan Agency for Marine-Earth Science and Technology.
    Schlagwort(e): Past hydrologic changes ; Eastern tropical Pacific ; Compound-specific hydrogen isotope ratios
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: application/pdf
    Standort Signatur Einschränkungen Verfügbarkeit
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    ARTIKEL (OA)
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