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1
In: Paleoceanography, Hoboken, NJ : Wiley, 1986, 19(2004), 1944-9186
In: volume:19
In: year:2004
In: extent:14
Type of Medium: Online Resource
Pages: 14 , graph. Darst
ISSN: 1944-9186
Language: English
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  • 2
    In: Paleoceanography, Hoboken, NJ : Wiley, 1986, 24(2009), 1944-9186
    In: volume:24
    In: year:2009
    In: extent:15
    Type of Medium: Online Resource
    Pages: 15 , graph. Darst
    ISSN: 1944-9186
    Language: English
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  • 3
    In: Paleoceanography, Hoboken, NJ : Wiley, 1986, 24(2009), 1944-9186
    In: volume:24
    In: year:2009
    In: extent:15
    Description / Table of Contents: Diagenetic processes are known to modify sedimentary records, but they can also reveal important paleoenvironmental changes. Here we investigate variations in sedimentary iron diagenesis and depositional environments for the last 35 ka by analyzing the rock magnetic and geochemical properties of two sediment cores collected in the Santa Barbara Basin (California). In organic-rich sediments, early diagenesis often leads to partial dissolution of detrital iron oxides and stepwise formation of authigenic pyrite (FeS2). The pyritization process takes place following several geochemical pathways, sometimes involving intermediate iron sulfide species such as greigite (Fe3S4). Sedimentary conditions in the basin appear to have recurrently favored preservation of greigite (identified by its magnetic properties) and inhibited its complete transformation into pyrite. The Holocene interval contains a series of centimeter-thick greigite-bearing layers that are associated with large flood deposits, which are known in the basin as gray layers.ʺ We propose that greigite preservation was enabled in these sediments by their relative enrichment in reactive iron over organic matter and/or hydrogen sulfide (because of their high ratio of terrigenous over organic material), which limited pyritization reactions. Within the glacial deposits, formation and preservation of meter-thick greigite layers occurred in terrigenous-rich and organic-poor sedimentary layers and is proposed to result from a similar diagenetic process to that in the Holocene greigite-bearing layers (dominance of reactive iron over organic matter and/or HS-). The terrigenous enrichments in the glacial greigite-bearing layers are probably related to climatic or sea level changes because they occur at times of massive iceberg releases in the North Atlantic, the so-called Heinrich events.
    Type of Medium: Online Resource
    Pages: 15 , graph. Darst
    ISSN: 1944-9186
    Language: English
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  • 4
    In: Paleoceanography, Hoboken, NJ : Wiley, 1986, 24(2009), 1944-9186
    In: volume:24
    In: year:2009
    In: extent:14
    Description / Table of Contents: The intratest variation in the chemical composition of Globorotalia scitula and G. inflata recovered from a sediment trap sample collected at 3000 m in the North Atlantic in early spring has been investigated using laser ablation inductively coupled plasmamass spectrometry and electron microprobe. Mg/Ca, Li/Ca, B/Ca, Mn/Ca, and Ba/Ca vary by up to a factor of 10 through the test walls. Water column properties, including temperature and salinity, are well documented at the trap site, and the observed variations are too large to be explained by vertical migration of the foraminifera. However, changes in calcite precipitation rate, crystal structure, or the chemical composition of the internal calcification reservoir also cannot, by themselves, fully account for the pattern of intratest variability. Nevertheless, the average Mg/Ca for each chamber generally produces a Mg/Ca temperature that matches that measured in the water column. The exception is small, morphologically distinct G. inflata tests that have anomalously high Mg/Ca.
    Type of Medium: Online Resource
    Pages: 14 , Ill., graph. Darst
    ISSN: 1944-9186
    Language: English
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  • 5
    In: Paleoceanography, Hoboken, NJ : Wiley, 1986, 23(2008), 1944-9186
    In: volume:23
    In: year:2008
    In: extent:15
    Description / Table of Contents: Cenozoic biostratigraphic, cosmogenic isotope, magnetostratigraphic, and cyclostratigraphic data derived from Integrated Ocean Drilling Program Expedition 302, the Arctic Coring Expedition (ACEX), are merged into a coherent age model. This age model has low resolution because of poor core recovery, limited availability of biostratigraphic information, and the complex nature of the magnetostratigraphic record. One 2.2 Ma long hiatus occurs in the late Miocene; another spans 26 Ma (18.244.4 Ma). The average sedimentation rate in the recovered Cenozoic sediments is about 15 m/Ma. Core-seismic correlation links the ACEX sediments to the reflection seismic stratigraphy of line AWI-91090, on which the ACEX sites were drilled. This seismostratigraphy can be correlated over wide geographic areas in the central Arctic Ocean, implying that the ACEX age model can be extended well beyond the drill sites.
    Type of Medium: Electronic Resource
    Pages: 15
    ISSN: 1944-9186
    Language: English
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  • 6
    In: Paleoceanography, Hoboken, NJ : Wiley, 1986, 23(2008), 1944-9186
    In: volume:23
    In: year:2008
    In: extent:16
    Description / Table of Contents: Lead (Pb), neodymium (Nd), and strontium (Sr) isotopic analyses were carried out on sediment leachates (reflecting the isotope composition of past seawater) and digests of the bulk residues (reflecting detrital continental inputs) of Integrated Ocean Drilling Program (IODP) Leg 302 and core PS2185 from the Lomonosov Ridge (Arctic Ocean). Our records are interpreted to reflect changes in continental erosion and oceanic circulation, driven predominantly by tectonic forcing on million-year timescales in the older (pre-2 Ma) part of the record and by climatic forcing of weathering and erosion of the Eurasian continental margin on thousand-year timescales in the younger (post-2 Ma) part. These data, covering the past 15 Ma, show that continental inputs to the central Arctic Ocean have been more closely linked to glacial and hydrological processes occurring on the Eurasian margin than on continental North America and Greenland. The constancy of the detrital input signatures supports the early existence of an Arctic sea ice cover, whereas the major initiation of Northern Hemisphere glaciation at 2.7 Ma appears to have had little impact on the weathering regime of the Eurasian continental margin.
    Type of Medium: Online Resource
    Pages: 16
    ISSN: 1944-9186
    Language: English
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  • 7
    In: Paleoceanography, Hoboken, NJ : Wiley, 1986, 23(2008), 1944-9186
    In: volume:23
    In: year:2008
    In: extent:12
    Description / Table of Contents: The upper 200 m of the sediments recovered during IODP Leg 302, the Arctic Coring Expedition (ACEX), to the Lomonosov Ridge in the central Arctic Ocean consist almost exclusively of detrital material. The scarcity of biostratigraphic markers severely complicates the establishment of a reliable chronostratigraphic framework for these sediments, which contain the first continuous record of the Neogene environmental and climatic evolution of the Arctic region. Here we present profiles of cosmogenic 10Be together with the seawater-derived fraction of stable 9Be obtained from the ACEX cores. The down-core decrease of 10Be/9Be provides an average sedimentation rate of 14.5 ± 1 m/Ma for the uppermost 151 m of the ACEX record and allows the establishment of a chronostratigraphy for the past 12.3 Ma. The age-corrected 10Be concentrations and 10Be/9Be ratios suggest the existence of an essentially continuous sea ice cover over the past 12.3 Ma.
    Type of Medium: Online Resource
    Pages: 12
    ISSN: 1944-9186
    Language: English
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  • 8
    In: Paleoceanography, Hoboken, NJ : Wiley, 1986, 19(2004), 1944-9186
    In: volume:19
    In: year:2004
    In: extent:17
    Description / Table of Contents: An 8 million year record of subtropical and midlatitude shelf-sea temperatures, derived from oxygen isotopes of well-preserved brachiopods from a variety of European sections, demonstrates a long-term Cenomanian temperature rise (16-20°C, midlatitudes) that reached its maximum early in the late Turonian (23°C, midlatitudes). Superimposed on the long-term trend, shelf-sea temperatures vary at shorter timescales in relation to global carbon cycle perturbations. In the mid-Cenomanian and the late Turonian, two minor shelf-sea cooling events (2-3°C) coincide with carbon cycle perturbations and times of high-amplitude sea level falls. Although this evidence supports the hypothesis of potential glacioeustatic effects on Cretaceous sea level, the occurrence of minimum shelf-sea temperatures within transgressive beds argues for regional changes in shelf-sea circulation as the most plausible mechanism. The major carbon cycle event in the latest Cenomanian (oceanic anoxic event 2) is accompanied by a substantial increase in shelf-sea temperatures (4-5°C) that occurred ~150 kyr after the commencement of the Delta 13 C excursion and is related to the spread of oceanic conditions in western European shelf-sea basins. Our oxygen isotope record and published Delta 18 O data of pristinely preserved foraminifera allow the consideration of North Atlantic surface water properties in the Cenomanian along a transect from the tropics to the midlatitudes. On the basis of fossil-derived Delta 18 O, estimated Delta w ranges, and modeled salinities, temperature-salinity-density ranges were estimated for tropical, subtropical, and midlatitude surface waters. Accordingly, the Cenomanian temperate shelf-seas waters have potentially the highest surface water density and could have contributed to North Atlantic intermediate to deep waters in the preopening stage of the equatorial Atlantic gateway.
    Type of Medium: Online Resource
    Pages: 17 , graph. Darst
    ISSN: 1944-9186
    Language: English
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  • 9
    In: Paleoceanography, Hoboken, NJ : Wiley, 1986, 24(2009), 1944-9186
    In: volume:24
    In: year:2009
    In: extent:18
    Type of Medium: Online Resource
    Pages: 18 , Ill., graph. Darst
    ISSN: 1944-9186
    Language: English
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  • 10
    In: Paleoceanography, Hoboken, NJ : Wiley, 1986, 25(2010), 1944-9186
    In: volume:25
    In: year:2010
    In: extent:17
    Type of Medium: Online Resource
    Pages: 17 , graph. Darst
    ISSN: 1944-9186
    Language: English
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