Johnstone, Heather

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Johnstone, Heather
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Johnstone, Heather
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    Assessing dissolution in the tests of planktonic foraminifera using computed tomography (CT): potential for improving paleoceanographic reconstructions
    (2010-11-15)
    Johnstone, Heather
    ;
    Wefer, Gerold
    ;
    Schulz, Michael
    ;
    Schulz, Michael
    An empirical dissolution index for planktonic foraminifera, XDX, was established based on the appearance of tests in computed tomography (CT) scans (Chapter 4). Calibrations between XDX and Delta[CO32-], Delta-mass (mass lost to dissolution) and Delta Mg/Ca (reduction in Mg/Ca due to dissolution) allow estimates of deep ocean Delta[CO32-] and also dissolution-corrected test mass and Mg/Ca (Chapter 5). Delta[CO32-] reconstructed for the deep (4,157 m) tropical western Indian Ocean (WIND28K) increased by ~25 µmol/kg over Termination I and ~15 µmol/kg over Termination II while dissolution maxima coincided with transitions to colder stages (Chapter 6). XDX-corrected Mg/Ca-derived SSTs were coolest during MIS 3. Minimum test mass in the corrected record coincided with the lowest temperatures. Comparison of two methods of cleaning foraminiferal tests from a depth transect (Chapter 7) found no offset in Mg/Ca between methods for G. sacculifer and P. obliquiloculata. Mg/Ca was decreased by reductive cleaning by ~4% for G. ruber and ~10% for N. dutertrei. Offset in Mg/Ca between the two methods was insensitive to preservation state.
    Dissertation
      725  178