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  4. Persisting maximum Agulhas leakage during MIS 14 indicated by massive Ethmodiscus oozes in the subtropical South Atlantic
 
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Persisting maximum Agulhas leakage during MIS 14 indicated by massive Ethmodiscus oozes in the subtropical South Atlantic

Journal
Paleoceanography
Journal Volume
26
Journal Issue
3
Date Issued
2011
Author(s)
Rackebrandt N
Kuhnert H
JEROEN GROENEVELD  
Bickert T.
DOI
10.1029/2010PA001990
URI
https://www.scopus.com/inward/record.uri?eid=2-s2.0-79960757722&doi=10.1029%2f2010PA001990&partnerID=40&md5=28ee404aca969ced61216fb63e2866cd
https://scholars.lib.ntu.edu.tw/handle/123456789/624790
Abstract
The glacial marine isotope stage 14 (MIS 14) appears in many climate records as an unusually warm glacial. During this period an almost monospecific, up to 1.5 m thick, laminated layer of the giant diatom Ethmodiscus rex has been deposited below the South Atlantic Subtropical Gyre. This oligotrophic region is today less favorable for diatom growth with sediments typically consisting of calcareous nannofossil oozes. We have reconstructed temperatures and the stable oxygen isotopic compositions of sea surface and thermocline water (δ18Ow) from planktonic foraminiferal (Globigerinoides ruber and Globorotalia inflata) Mg/Ca and stable oxygen isotopes to test whether perturbations in surface ocean conditions contributed to the deposition of the diatom layer at ∼530 kyr B.P. Temperatures and δ18Ow values reconstructed from this diatom ooze interval are highly variable, with maxima similar to interglacial values. Since the area of the Ethmodiscus oozes resembles the region where Agulhas rings are present, we interpret these hydrographic changes to reflect the varying influence of warm and saline water of Indian Ocean origin that entered the Subtropical Gyre trapped in Agulhas rings. The formation of the Ethmodiscus oozes is associated with a period of maximum Agulhas leakage and a maximum frequency of Agulhas ring formation caused by a termination-type position of the Subtropical Front during the unusual warm MIS 14. The input of silica through the Agulhas rings enabled the shift in primary production from calcareous nannoplankton to diatoms, leading to the deposition of the massive diatom oozes. Copyright 2011 by the American Geophysical Union.
Other Subjects
deposition; fossil record; glacial environment; gyre; hydrography; isotopic analysis; leakage; oligotrophic environment; ooze; oxygen isotope; paleoenvironment; planktonic foraminifera; reconstruction; salinity; sea surface; sediment analysis; stable isotope; subtropical region; temperature effect; thermocline; Atlantic Ocean; Atlantic Ocean (South); Bacillariophyta; Ethmodiscus; Globigerinoides ruber; Globorotalia inflata
Type
journal article

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