Planktonic Foraminiferal Response to Middle Miocene Cooling in the Southern Ocean (ODP Site 747, Kerguelen Plateau)

Wojciech Majewski

doi:10.4202/app.2009.0088

Abstract

The response of planktonic foraminifera to changing oceanographic conditions during Middle Miocene Climate Transition (MMCT) ∼14 million years ago (Ma) at ODP Site 747 (Kergeulen Plateau) is investigated. Faunal changes are presented in the background of sea surface temperature (SST) estimates and multi-taxon δ18O and δ13C data presented in other studies. Four faunal transitions are distinguished between 15.0 and 12.2 Ma. The first two affected only a limited number of taxa, and do not lead to large-scale assemblage reorganizations. They are only minor assemblage changes within the pre-MMCT fauna. The first (14.5–14.4 Ma) is marked by a reduction in the Globorotalia zealandica plexus in favor of the Globorotalia praescitula plexus, coupled with the first signs of increased seasonality. The second (14.3–14.2 Ma) is characterized by recovery and diversification of the G. zealandica plexus and an increase in Turborotalita quinqueloba in response to further enhanced seasonality. The third faunal transition ac...

Highlights

Faunal changes are presented in the background of sea surface temperature (SST) estimates and multi−taxon δ O and °13C data presented in other studies
The third faunal transition across the Middle Miocene Shift (MMS) in δ O (13.9–13.8Ma) affects almost all planktonic foraminifera, leading to dismembering of the pre−Middle Miocene Climate Transition (MMCT) assemblage. These changes were triggered by the SST drop by ~7° C, followed by reduced sea−surface salinity following the MMS, which favored the opportunistic Neogloboquadrina continuosa
The fourth faunal threshold took place during the hiatus in the ODP Hole 747A record spanning 13.2–12.5Ma. It is expressed by the establishment of an assemblage dominated by Globorotalia praescitula and Globigerina bulloides in association with diminishing of the low−salinity surface layer

Summary

Introduction

The response of planktonic foraminifera to changing oceanographic conditions during Middle Miocene Climate Transition (MMCT) ~14 million years ago (Ma) at ODP Site 747 (Kergeulen Plateau) is investigated. Faunal changes are presented in the background of sea surface temperature (SST) estimates and multi−taxon δ O and °13C data presented in other studies. Four faunal transitions are distinguished between 15.0 and 12.2 Ma. The first two affected only a limited number of taxa, and do not lead to large−scale assemblage reorganizations.

Results

Conclusion