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  • 2000-2004  (63)
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  • 1
    Online Resource
    Online Resource
    GEOTRACES: studying the global marine biogeochemistry of trace elements and isotopes (2003)
    Details Availability
    Keywords: marine sciences ; biogeochemistry ; isotopes ; trace elements
    In: (2003)
    In: year:2003
    Type of Medium: Online Resource
    URL: http://www.ldeo.columbia.edu/res/poj/geotraces
    Language: Undetermined
    Note: EOS : transactions / American Geophysical Union
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  • 2
    Electronic Resource
    Electronic Resource
    Multiple mantle sources during island arc magmatism: U–Pb and Hf isotopic evidence from the Kohistan arc complex, Pakistan (2002)
    Oxford, UK : Blackwell Science Ltd
    Terra nova 14 (2002), S. 0 
    Details
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: This paper presents high-precision U–Pb ages and initial Hf isotopic compositions of zircon from mafic to felsic rocks of the Kohistan Arc Complex, Pakistan. Three magmatic pulses tapping geochemically different reservoirs are distinguished. Partial melting of mantle with MORB-type isotopic characteristics generated 99–92-Ma-old magmas. Plutonism around 85 Ma tapped a more fertile mantle source, most likely consisting of a 〉600-Ma-old metasomatically enriched mantle, or of mantle contaminated by an old sedimentary component; 82-Ma-old felsic peraluminous dykes have MORB-type isotopic compositions considered to be inherited from remelting earlier magmas in the deep base of the arc. The isotopic results demonstrate several and rather rapid changes in melt source region during arc development. They also show that there was subordinate continental influence and negligible importance of slab components for the Hf budget during the generation of the Kohistan Arc Complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3121.2002.00432.x
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    The transition from rifting to sea-floor spreading within a magma-poor rifted margin: field and isotopic constraints (2002)
    Oxford UK : Blackwell Science Ltd
    Terra nova 14 (2002), S. 0 
    Details
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: We provide new geological and isotope geochemical constraints on the evolution from continental rifting to sea-floor spreading along a segment of the Jurassic Tethyan margin exposed in the Platta and Err nappes (eastern Central Alps). Field observations show that the ocean–continent transition zone is characterized by oceanward-dipping detachment faults leading to the exhumation of subcontinental mantle rocks subsequently intruded by gabbro bodies and dolerite dikes, and covered by pillow basalts and radiolarites. Zircons extracted from gabbros and albitite yield concordant U–Pb ages of 161 ± 1 Ma; their initial ɛHf (+ 14.4 to + 14.9) as well as bulk rock ɛNd values of from gabbros and basalts (+ 7.3 to + 9.5) point to a MORB-type depleted mantle source. These data suggest that the onset of magmatic activity coincides with the latest phase of mantle exhumation along low-angle detachment faults and may be controlled by upwelling asthenosphere beneath a zone of exhumed continental mantle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3121.2002.00406.x
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    Paper (German National Licenses)
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  • 4
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    North Atlantic Deep Water export to the Southern Ocean over the past 14 Myr: Evidence from Nd and Pb isotopes in ferromanganese crusts (2002)
    AGU (American Geophysical Union)
    In:  Paleoceanography, 17 (2). 12-1-12-9.
    Details
    Publication Date: 2017-01-18
    Description: The intensity of North Atlantic Deep Water (NADW) production has been one of the most important parameters controlling the global thermohaline ocean circulation system and climate. Here we present a new approach to reconstruct the overall strength of NADW export from the North Atlantic to the Southern Ocean over the past 14 Myr applying the deep water Nd and Pb isotope composition as recorded by ferromanganese crusts and nodules. We present the first long-term Nd and Pb isotope time series for deep Southern Ocean water masses, which are compared with previously published time series for NADW from the NW Atlantic Ocean. These data suggest a continuous and strong export of NADW, or a precursor of it, into the Southern Ocean between 14 and 3 Ma. An increasing difference in Nd and Pb isotope compositions between the NW Atlantic and the Southern Ocean over the past 3 Myr gives evidence for a progressive overall reduction of NADW export since the onset of Northern Hemisphere glaciation (NHG). The Nd isotope data allow us to assess at least semiquantitatively that the amount of this reduction has been in the range between 14 and 37% depending on location.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2000PA000606
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  • 5
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    The Hf isotope composition of global seawater and the evolution of Hf isotopes in the deep Pacific Ocean from Fe-Mn crusts (2001)
    Elsevier
    In:  Chemical Geology, 178 . pp. 23-42.
    Details
    Publication Date: 2017-12-06
    Description: This paper presents a revised chemical purification method of Hf for the measurement of Hf isotope ratios of Fe–Mn crusts on a new generation of double focusing multiple collector plasma source mass spectrometer (MC-ICP-MS). By measuring surface scrapings of hydrogenetic Fe–Mn crusts distributed over the three major ocean basins, the present-day Hf isotope distribution of oceanic deep water is assessed in detail. The results show an εHf provinciality correlated with those of other radiogenic isotope tracers such as Nd and Pb in agreement with previous studies. This supports the use of Hf isotopes as tracer of element source provenance and water masses. Fe–Mn crusts display the same present-day Hf–Nd isotope array as given before for Mn nodules. The smaller isotopic variability of Hf compared with Nd may either be caused by a more efficient mixing of Hf than Nd in the ocean due to a longer residence time or may be a consequence of a systematically more radiogenic Hf than Nd isotope signature delivered to the oceans by weathering of continental crust. A Hf isotope time series was measured on crust VA13/2 to assess the Hf isotope compositions of the Central Pacific deep water over the past 26 Ma. No consistency is observed between the Hf and Pb isotope time series. In contrast, Hf and Nd isotope time series display similar patterns which are, however, apparently offset by 2 Ma prior to 14 Ma. Differential diffusion of Hf and Nd does not explain this offset. The smaller amplitude in the Hf isotope variations compared with the Nd isotopes rather argues for more efficient mixing of Hf in the ocean. We suggest that both isotope systems have responded in a similar way to the processes affecting the dissolved radiogenic isotope composition of Pacific deep water during this time interval. The parallel increase in εHf and εNd observed between 14 and 3 Ma may probably be attributed to the increased inputs of Hf and Nd into the Central Pacific Ocean derived from the weathering of the Pacific Islands Arcs. Over the past 3 Ma an increased aeolian continental input derived from Asia most likely caused negative shifts in εNd and εHf recorded by VA13/2. The fact that Hf and Nd isotope compositions plot along the present-day array for Fe–Mn crusts and Mn nodules over the entire past 26 Ma suggests that aeolian supply of Hf to the Pacific Ocean has been a long-term important feature.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0009-2541(00)00427-7
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Radiogene Isotopensysteme in Eisen/Mangankrusten: Tracer für Zirkulation und Verwitterungseintrag in den Ozean (2003)
    In:  Vierteljahresschrift der Naturforschenden Gesellschaft in Zürich . pp. 89-96.
    Details
    Publication Date: 2016-04-26
    Description: Die radiogene Isotopenzusammensetzung bestimmter gelöster Metalle im Meerwasser (Neodym, Blei, Hafnium) kann als Tracer in der Ozeanographie und Paläo- Ozeanographie genutzt werden. Diese Metalle haben Verweilzeiten im Ozean, die vergleichbar sind mit der Zeit, die das Wasser der Weltozeane braucht, um einmal komplett ausgetauscht zu werden (ca. 1500 Jahre). Die typischen Isotopensignaturen bestimmter Wassermassen bleiben daher über lange Distanzen erhalten (Tausende von Kilometern). Änderungen der isotopischen Zusammensetzung dieser Metalle im Meerwasser geschehen auf Zeitskalen von wenigen 10er Jahren bis hin zu Millionen von Jahren als Funktion von Veränderungen der Zlrkulation und der Mischung von Wassermassen, der Eintragsquellen von erodiertem kontinentalem Material, von VerwitteIungsprozessen oder geographischen VerändeIungen wie der Öffnung oder Schliessung von Verbindungen zwischen Meeresbecken oder Gebirgsbildungen. Die Effekte dieser Prozesse überlagern sich und müssen voneinander getrennt werden, um aus den Zeilserien der radiogenen Isotopensignale verlässliche Angaben über Paläozirkulation oder Verwitterungseintrag in der Vergangenheit abzuleiten. Tiefsee-Eisen-/Mangankrusten, die chemische MeeIwasser-Präzipilate daIstellen und die bei ihrem sehr langsamen Wachstum (wenige mm pro Million Jahre) die radiogenen Isotopensignaturen des Tiefenwassers einbauen, stellen ideale Archive dar, um die Evolution der radiogenen Isotopensignaturen im Ozean der letzten 60 Millionen Jahre zu rekonstIuieren.
    Type: Article , NonPeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - without review
  • 7
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    Timing and magma evolution of the Chelopech volcanic complex (Bulgaria) (2004)
    In:  Schweizerische Mineralogische und Petrographische Mitteilungen, 84 . pp. 101-117.
    Details
    Publication Date: 2016-09-13
    Type: Article , NonPeerReviewed
    Format: text
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  • 8
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    The global variation in the iron isotope composition of marine hydrogenetic ferromanganese deposits: implications for seawater chemistry? (2004)
    Elsevier
    In:  Earth and Planetary Science Letters, 224 . pp. 91-105.
    Details
    Publication Date: 2016-11-15
    Description: The iron (Fe) isotope compositions of 37 hydrogenetic ferromanganese deposits from various oceans have been analysed by MC-ICPMS; they permit the construction of a global map of Fe isotopic values. The isotopic compositions range between −1.2 and −0.1‰ in δ57FeIRMM14. Averages for the Atlantic and the Pacific are −0.41 and −0.88‰, but their standard deviations are identical (0.27, 1σ) and the data very largely overlap. No correlation is found with Pb or Nd isotope compositions and there is no evidence that the observed oceanic Fe isotopic heterogeneity is directly controlled by variations in continental sources. The small quantities of Fe that can be introduced from hydrothermal sources render as unlikely the possibility that the isotopic variations reflect variable proportions of continental and hydrothermal Fe, as recently proposed. The more likely explanation is that the variations are induced locally within the ocean. The exact sources of fractionation remain unclear. Likely possibilities are the dissolution and reprecipitation processes that liberate Fe from sediments during anoxic events, dissolution in surface waters or processes occurring during growth of the crusts
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.epsl.2004.05.010
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  • 9
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    Cenozoic marine geochemistry of thallium deduced from isotopic studies of ferromanganese crusts and pelagic sediments (2004)
    Elsevier
    In:  Earth and Planetary Science Letters, 219 . pp. 77-91.
    Details
    Publication Date: 2016-12-06
    Description: Cenozoic records of Tl isotope compositions recorded by ferromanganese (Fe–Mn) crusts have been obtained. Such records are of interest because recent growth surfaces of Fe–Mn crusts display a nearly constant Tl isotope fractionation relative to seawater. The time-series data are complemented by results for bulk samples and leachates of various marine sediments. Oxic pelagic sediments and anoxic marine deposits can be distinguished by their Tl isotope compositions. Both pelagic clays and biogenic oozes are typically characterized by ϵ205Tl greater than +2.5, whereas anoxic sediments have ϵ205Tl of less than −1.5 (ϵ205Tl is the deviation of the 205Tl/203Tl isotope ratio of a sample from NIST SRM 997 Tl in parts per 104). Leaching experiments indicate that the high ϵ205Tl values of oxic sediments probably reflect authigenic Fe–Mn oxyhydroxides. Time-resolved Tl isotope compositions were obtained from six Fe–Mn crusts from the Atlantic, Indian, and Pacific oceans and a number of observations indicate that these records were not biased by diagenetic alteration. Over the last 25 Myr, the data do not show isotopic variations that significantly exceed the range of Tl isotope compositions observed for surface layers of Fe–Mn crusts distributed globally (ϵ205Tl=+12.8±1.2). This indicates that variations in deep-ocean temperature were not recorded by Tl isotopes. The results most likely reflect a constant Tl isotope composition for seawater. The growth layers of three Fe–Mn crusts that are older than 25 Ma show a systematic increase of ϵ205Tl with decreasing age, from about +6 at 60–50 Ma to about +12 at 25 Ma. These trends are thought to be due to variations in the Tl isotope composition of seawater, which requires that the oceans of the early Cenozoic either had smaller output fluxes or received larger input fluxes of Tl with low ϵ205Tl. Larger inputs of isotopically light Tl may have been supplied by benthic fluxes from reducing sediments, rivers, and/or volcanic emanations. Alternatively, the Tl isotope trends may reflect the increasing importance of Tl fluxes to altered ocean crust through time.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0012-821X(03)00703-9
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  • 10
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    Radiogenic isotopes: New tools help reconstruct paleocean circulation and erosional input (2001)
    AGU (American Geophysical Union)
    In:  Eos, Transactions American Geophysical Union, 82 (6). pp. 66-71.
    Details
    Publication Date: 2017-02-10
    Description: Ocean and atmosphere circulation and continental weathering regimes have undergone great changes over thousands of years as well as tens of millions of years. During the glacial stages of the Pleistocene, ocean circulation was generally more sluggish and deep water circulation in the Atlantic had a shallower flow. At the same time, weathering on the continents was enhanced by glacial erosion, particularly in high northern latitudes, which increased the input of erosional detritus into the ocean. In addition, atmospheric pressure gradients were larger, leading to higher wind speeds and increased supply of aeolian dust to the ocean. Prior to the onset of Northern Hemisphere glaciation and pronounced glacial/interglacial cyclicity at ∼3 m.ya., global climate was warmer than at present. There is also evidence for a more vigorous thermohaline circulation during the early Pliocene.
    Type: Article , NonPeerReviewed
    Format: text
    DOI: 10.1029/01EO00040
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    OceanRep: Article in a Scientific Journal - without review
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