Open AccessPleistocene vertical carbon isotope and carbonate gradients in the South Atlantic sector of the Southern Ocean
Author(s) -
Hodell David A.,
Venz Kathryn A.,
Charles Christopher D.,
Ninnemann Ulysses S.
Publication year - 2003
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2002gc000367
Subject(s) - geology , glacial period , north atlantic deep water , pleistocene , oceanography , deep sea , interglacial , circumpolar deep water , thermohaline circulation , benthic zone , paleontology , early pleistocene , isotopes of carbon , last glacial maximum , total organic carbon , ecology , biology
We demonstrate that the carbon isotopic signal of mid‐depth waters evolved differently from deep waters in the South Atlantic sector of the Southern Ocean during the Pleistocene. Deep sites (>3700 m) exhibit large glacial‐to‐interglacial variations in benthic δ 13 C, whereas the amplitude of the δ 13 C signal at Site 1088 (∼2100 m water depth) is small. Unlike the deep sites, at no time during the Pleistocene were benthic δ 13 C values at Site 1088 lower than those of the deep Pacific. Reconstruction of intermediate‐to‐deep δ 13 C gradients (Δ 13 C I‐D ) supports the existence of a sharp chemocline between 2100 and 2700 m during most glacial stages of the last 1.1 myr. This chemical divide in the glacial Southern Ocean separated well‐ventilated water above ∼2500 m from poorly ventilated water below. The Δ 13 C I‐D signal parallels the Vostok atmospheric pCO 2 record for the last 400 kyr, lending support to physical models that invoke changes in Southern Ocean deep water ventilation as a mechanism for changing atmospheric pCO 2 . The emergence of a strong 100‐kyr cycle in Δ 13 C I‐D during the mid‐Pleistocene supports a change in vertical fractionation and deep‐water ventilation rates in the Southern Ocean, and is consistent with possible CO 2 ‐forcing of this climate transition.