Southern Ocean bottom-water cooling and ice sheet expansion during the middle Miocene climate transition

The middle Miocene climate transition (MMCT), around 14 Ma, was associated with a significant climatic shift, but the mechanisms triggering the event remain enigmatic. We present a clumped isotope ( Δ 47 ) bottom-water temperature (BWT) record from 16.0 to 12.2 Ma from Ocean Drilling Program (ODP) S...

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Bibliographic Details
Published in:Climate of the Past
Main Authors: T. J. Leutert, S. Modestou, S. M. Bernasconi, A. N. Meckler
Format: Article in Journal/Newspaper
Language:English
Published: Copernicus Publications 2021
Subjects:
Environmental pollution
TD172-193.5
Environmental protection
TD169-171.8
Environmental sciences
GE1-350
Southern Ocean
Ice Sheet
Online Access:https://doi.org/10.5194/cp-17-2255-2021
https://doaj.org/article/2922e7c628d14838a1e8c53180e96ffc
Description
Summary:The middle Miocene climate transition (MMCT), around 14 Ma, was associated with a significant climatic shift, but the mechanisms triggering the event remain enigmatic. We present a clumped isotope ( Δ 47 ) bottom-water temperature (BWT) record from 16.0 to 12.2 Ma from Ocean Drilling Program (ODP) Site 747 in the Southern Ocean and compare it to existing BWT records from different latitudes. We show that BWTs in the Southern Ocean reached 8–10 ∘ C during the Miocene climatic optimum. These high BWT values indicate considerably warmer bottom-water conditions than today. Nonetheless, bottom-water δ 18 O (calculated from foraminiferal δ 18 O and Δ 47 ) suggests substantial amounts of land ice throughout the interval of the study. Our dataset further demonstrates that BWTs at Site 747 were variable with an overall cooling trend across the MMCT. Notably, a cooling of around 3–5 ∘ C preceded the stepped main increase in benthic δ 18 O , interpreted as global ice volume expansion, and appears to have been followed by a transient bottom-water warming starting during or slightly after the main ice volume increase. We speculate that a regional freshening of the upper water column at this time may have increased stratification and reduced bottom-water heat loss to the atmosphere, counteracting global cooling in the bottom waters of the Southern Ocean and possibly even at larger scales. Feedbacks required for substantial ice growth and/or tectonic processes may have contributed to the observed decoupling of global ice volume and Southern Ocean BWT.

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