Reorganization of Pacific Deep Waters linked to middle Miocene Antarctic cryosphere expansion: A perspective from the South China Sea

Abstract

Changes in intermediate and deep ocean circulation likely played a significant role in global carbon cycling and meridional heat/moisture transport during the middle Miocene climate transition (∼ 14 Ma). High-resolution middle Miocene (16–13 Ma) benthic foraminifer stable isotope records from the South China Sea reveal a reorganization of regional bottom waters, which preceded the globally recognized middle Miocene ∼ 1‰ δ 18O increase (13.8 Ma) by 100,000 years. An observed reversal of the benthic foraminifera δ 13C gradient between ODP Sites 1146 (2092 m) and 1148 (3294 m; 13.9–13.5 Ma) is interpreted to reflect an increase in the southward flux of low δ 13C deep (> 2000 m) Pacific Ocean waters (Flower and Kennett, 1993; Shevenell and Kennett, 2004). Large-scale changes in Pacific intermediate and deep ocean circulation, coupled with enhanced global carbon cycling at the end of the Monterey Carbon Isotope excursion, likely acted as internal feedbacks to the Earth's climate system. These feedbacks reduced the sensitivity of Antarctica to lower latitude-derived heat/moisture and facilitated the transition of the Earth's climate system to a new, relatively stable glacial state.