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  • 1
    Online Resource
    Online Resource
    Ocean circulation and atmospheric CO 2 changes: Coupled use of models and paleoceanographic data
    American Geophysical Union (AGU) ; 1990
    In:  Paleoceanography Vol. 5, No. 1 ( 1990-02), p. 15-41
    Details
    In: Paleoceanography, American Geophysical Union (AGU), Vol. 5, No. 1 ( 1990-02), p. 15-41
    Abstract: We have perturbed a simple model of oceanic circulation in a series of sensitivity tests to determine how circulation changes associated with the last glacial maximum could affect observable or potentially observable paleoceanographic parameters. Ultimately, we want to use such paleoceanographic data to construct models of glacial ocean circulation. We have found that the different circulation patterns that we imposed in our sensitivity tests have dramatically different responses for the distribution of PO 4 , O 2 , and ∂ 13 C contents of the oceans. They also produce different levels of low‐latitude productivity. By comparing the coupled responses of several of these paleoceanographic parameters to the responses from the sensitivity tests it is possible to constrain the possible glacial circulation scenarios to a relatively small number. We give, as one example, a case where intermediate turnover is significantly higher than the present and deep ocean turnover has dropped. In addition, exchange of waters between the intermediate‐ and high‐latitude surface ocean is much lower. The result of this scenario is an atmosphere with 60 ppm lower atmospheric CO 2 , low latitudes with about 40% higher productivity, and a change in the planktic/benthic ∂ 13 C contrast of about 0.3‰. When we compare our model to other independent paleoceanographic data, we find that the major point of disagreement is in the distribution of surface water ∂ 13 C in the Antarctic region. We believe that somewhat more complex box models which take open system effects into account will resolve this discrepancy.
    Type of Medium: Online Resource
    ISSN: 0883-8305 , 1944-9186
    URL: Article
    DOI: 10.1029/PA005i001p00015
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1990
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  • 2
    Online Resource
    Online Resource
    Carbonate Variations in the Northeast Pacific during the Late Quaternary
    American Geophysical Union (AGU) ; 1992
    In:  Paleoceanography Vol. 7, No. 1 ( 1992-02), p. 43-61
    Details
    In: Paleoceanography, American Geophysical Union (AGU), Vol. 7, No. 1 ( 1992-02), p. 43-61
    Abstract: Quaternary glacial/interglacial changes in the carbonate compensation depth (CCD) have been determined from core suites in three regions of the NE Pacific. The cores have sedimentation rates ranging from 1.6 to 16 cm/kyr, based on oxygen isotope, radiocarbon, and/or carbonate stratigraphies. Carbonate values are higher in glacial than interglacial times and generally follow a pattern similar to that of the central equatorial Pacific. The sediment's carbonate profiles can be readily intercorrelated, allowing the construction of a regional carbonate stratigraphy. The extent of carbonate preservation is very sensitive to small changes in water depth but does not depend on geographic location. A depth transect of cores off northern California and Oregon provides a detailed record of glacial/interglacial shifts in the CCD through time. During the late Holocene, intensified carbonate dissolution at ∼7 ka is coincident with shifts in continental climatic indicators and may suggest the onset of the modern upwelling regime along the NW U.S. margin. During the last 45 ka the CCD has migrated more than 1800 m between glacial and interglacial times. Although carbonate patterns are similar to those in the equatorial Pacific, the amplitude of the carbonate fluctuations is much greater in the northeast Pacific. This suggests that regional mechanisms, such as glacial deepwater formation or enhanced dissolution due to interglacial noncarbonate productivity related to coastal upwelling, may modulate carbon cycling.
    Type of Medium: Online Resource
    ISSN: 0883-8305 , 1944-9186
    URL: Article
    DOI: 10.1029/91PA03077
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1992
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  • 3
    Online Resource
    Online Resource
    Geochemical logging in the Cajon Pass Drill Hole and its application to a new, oxide, igneous rock classification scheme
    American Geophysical Union (AGU) ; 1992
    In:  Journal of Geophysical Research: Solid Earth Vol. 97, No. B4 ( 1992-04-10), p. 5167-5180
    Details
    In: Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 97, No. B4 ( 1992-04-10), p. 5167-5180
    Abstract: A new elemental oxide classification scheme for crystalline rocks is developed and applied to geochemical well logs from the Cajon Pass drill hole. This classification scheme takes advantage of measurements of elements taken by a geochemical logging tool string. It uses K 2 O versus SiO 2 /Al 2 O 3 to distinguish between granites, granodiorites, tonalites, syenites, monzonites, diorites, and gabbros. Oxide measurements from cores are used to calibrate the elemental abundances determined from the well logs. From these logs, a detailed lithologic column of the core is generated. The lithologic column derived from the well log classification scheme is compared with a lithologic column constructed from core samples and well cuttings. In the upper 1295 m of the well, agreement between the two columns is good. Discrepancies occur from 1295 to 2073 m and are believed to be caused by the occurrence of rock types not distinguished by the classification scheme and/or the occurrence of secondary minerals. Despite these discrepancies, the well log‐based classification scheme helps to distinguish changes in rock type and shows potential as an aid to the construction of lithologic columns in boreholes of crystalline rocks.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/91JB02643
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1992
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  • 4
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    Online Resource
    Paleoproductivity and carbon burial across the California Current: The multitracers transect, 42°N
    American Geophysical Union (AGU) ; 1992
    In:  Paleoceanography Vol. 7, No. 3 ( 1992-06), p. 251-272
    Details
    In: Paleoceanography, American Geophysical Union (AGU), Vol. 7, No. 3 ( 1992-06), p. 251-272
    Abstract: The Multitracers Experiment studied a transect of water column, sediment trap, and sediment data taken across the California Current to develop quantitative methods for hindcasting paleoproductivity. The experiment used three sediment trap moorings located 120 km, 270 km, and 630 km from shore at the Oregon/California border in North America. We report here about the sedimentation and burial of particulate organic carbon (C org ) and CaCO 3 . In order to observe how the integrated CaCO 3 and C org burial across the transect has changed since the last glacial maximum, we have correlated core from the three sites using time scales constrained by both radiocarbon and oxygen isotopes. By comparing surface sediments to a two‐and‐a‐half year sediment trap record, we have also defined the modern preservation rates for many of the labile sedimentary materials. Our analysis of the C org data indicates that significant amounts (20–40%) of the total C org being buried today in surface sediments is terrestrial. At the last glacial maximum, the terrestrial C org fraction within 300 km of the coast was about twice as large. Such large fluxes of terrestrial C org obscure the marine C org record, which can be interpreted as productivity. When we corrected for the terrestrial organic matter, we found that the mass accumulation rate of marine C org roughly doubled from the glacial maximum to the present. Because preservation rates of organic carbon are high in the high sedimentation rate cores, corrections for degradation are straightforward and we can be confident that organic carbon rain rate (new productivity) also doubled. As confirmation, the highest burial fluxes of other biogenic components (opal and Ba) also occur in the Holocene. Productivity off Oregon has thus increased dramatically since the last glacial maximum. CaCO 3 fluxes also changed radically through the deglaciation; however, they are linked not to CaCO 3 production but rather to changes in deepwater carbonate chemistry between 18 Ka and now.
    Type of Medium: Online Resource
    ISSN: 0883-8305 , 1944-9186
    URL: Article
    DOI: 10.1029/92PA00696
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1992
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  • 5
    Online Resource
    Online Resource
    Molecules record sea change
    Springer Science and Business Media LLC ; 1992
    In:  Nature Vol. 356, No. 6368 ( 1992-4), p. 385-386
    Details
    In: Nature, Springer Science and Business Media LLC, Vol. 356, No. 6368 ( 1992-4), p. 385-386
    Type of Medium: Online Resource
    ISSN: 0028-0836 , 1476-4687
    URL: Article
    DOI: 10.1038/356385a0
    RVK:
    TA 1000
    RVK:
    UA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 1992
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    detail.hit.zdb_id: 1413423-8
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  • 6
    Online Resource
    Online Resource
    Downhole Logging as a Paeoceanographic Tool on Ocean Drilling Program Leg 138: Interface Between High‐Resolution Stratigraphy and Regional Syntheses
    American Geophysical Union (AGU) ; 1992
    In:  Paleoceanography Vol. 7, No. 6 ( 1992-12), p. 691-700
    Details
    In: Paleoceanography, American Geophysical Union (AGU), Vol. 7, No. 6 ( 1992-12), p. 691-700
    Abstract: On Ocean Drilling Program (ODP) Leg 138, standard shipboard procedures were modified to allow for the real‐time monitoring of several laboratory core‐scanning systems that provide centimeter‐scale measurements of saturated bulk density, magnetic susceptibility and digital color reflectance. These continuous, high‐resolution data sets were used to ensure the proper offset of multiple holes and to splice together complete sedimentary sections. Typically, the spliced, continuous sediment sections were found to be about 10% longer than the section drilled, as measured by the length of the drill string. While the source of this elongation is not yet fully understood, it must be compensated for in order to property determine sediment fluxes and mass accumulation rates. Downhole logging, in conjunction with inverse correlation techniques provided a means to determine where the distortion occurred and to correct back to true in situ depths. Downhole logging also provides a means, through the generation of synthetic seismograms, of precisely relating the paleoceanographic events found in the core record to the high‐resolution seismic record. Once correlated to the seismic record, the spatial and temporal extent of paleoceanographic events can be traced well beyond the borehole. Most seismic events in the equatorial Pacific are related to rapid changes in carbonate content that, in turn, are related to both productivity events (often expressed as monospecific laminated diatom oozes) and times of enhanced dissolution. While many of these events may have oceanwide extent, others, like the absence of carbonate in the late‐Miocene to Recent in the Guatemala Basin have been shown to be regional and confined to only the deeper portions of the Guatemala Basin. As we identify and trace specific paleoceanographic events in the seismic record, we can begin to explore the response of the ocean through gradients of latitude, productivity, and depth.
    Type of Medium: Online Resource
    ISSN: 0883-8305 , 1944-9186
    URL: Article
    DOI: 10.1029/92PA02073
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1992
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