Tests for size and shape dependency in deep-sea mixing |
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| Authors: | WF Ruddiman GA Jones T-H Peng LK Glover BP Glass PJ Liebertz |
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| Institution: | 1. Lamont-Doherty Geological Observatory of Columbia University, Palisades, N.Y. 10964 U.S.A.;2. U.S. Department of Commerce, N.O.A.A., Rockville, Md. 20852 U.S.A.;3. Department of Geology, University of Delaware, Newark, Del. 19711 U.S.A.;4. Computer Sciences Corp., Silver Springs, Md. 20910 U.S.A. |
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| Abstract: | Bioturbation is generally not a strongly size-dependent or shape-dependent process in deep-sea sediments. Different sizes of ash (11–250 μm) deposited during a single eruption are usually mixed about equally, although in a few cores we found minor tendencies toward greater mixing of finer ash. Platey volcanic ash and spherical microtektites initially deposited within a few centimeters of each other in the sediment column are mixed with roughly comparable intensity. Radiocarbon dating of three sizes of CaCO3 near the top of one box core produced ages within the analytical error; this also suggests no size dependency in the mixing process. Another core showed age differences opposite in sense to those that would be predicted if the finer fractions were more intensely mixed than the coarser fractions.The sizes examined (11–250 μm) encompass most of the sedimentary components used in paleoclimatic analyses of deep-sea cores. From these findings, we infer that significant artificial lead/lag offsets in paleoclimatic signals will not be created by size-selective or shape-selective mixing. Mixing models calibrated on one sediment size fraction should be generally applicable to other sizes and kinds of material. |
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