Computer Science
Scientific paper
Apr 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996e%26psl.139..365t&link_type=abstract
Earth and Planetary Science Letters, vol. 139, Issue 3-4, pp.365-377
Computer Science
14
Armorican Seamount Atlantic Ocean, Geochemistry, Oxidation Zone, Glacial Environment, Sediments, Elsevier: Armorican Seamount Atlantic Ocean, Geochemistry, Oxidation Zone, Glacial Environment, Sediments
Scientific paper
The Armorican Seamount lies in the deep northeast Atlantic, southwest of the British Isles. Here, sediments laid down in the latter part of the last glacial period exhibit enhanced concentrations of several elements. Peaks in the ratio reveal the presence of Heinrich events H1, H2 and H4, while the remainder of the ratio peaks are arranged in a diagenetic redox succession. The known times of the Heinrich events provide a chronology and indicate a considerably slower sediment accumulation rate (2.2 cm ky -1 ) during and after the last glacial/interglacial (oxygen isotope stage ) transition than in earlier glacial times (5.6 cm ky -1 ). Between Heinrich events H1 and H2 ([14-21] conventional radiocarbon ky B.P.), diagenetic enrichments of the redox-sensitive elements are arranged in the following sequence with depth: Mn and Mo; Fe, As and P; Se and V; Cd; and U. The peak depths and shapes are different because of the different directions of movement and the efficiencies of the immobilisation mechanisms. These enrichments are not syngenetic with the sediments which host them. Rather, the peak sequence is caused by a sustained localisation of the oxic/post-oxic boundary at a particular level in the sediments, and peak formation is still active. This is a consequence of the decrease in accumulation fluxes from glacial time into the Holocene. In a piston core from the same site, a modification of this set of elements is also present as separated peaks in the sediments of the previous full glacial just below the oxygen isotope transition (~ 125 ky). By comparison with the active case in the sediments of the oxygen isotope transition, only those elements which form peaks in post-oxic conditions (Se, V, Cd and U) are still in place. Following passage into reducing conditions on burial, further diagenesis has affected Mn and Fe and those elements which sorb to Mn oxyhydroxides (Mo) and Fe oxyhydroxides (As and P) in the active case. A large amount of extra Cu of uncertain origin is also observed in this latter core section.
Colley Stephen
Higgs N. C.
Thomson J. J.
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