21-12 Climatic forcing of the Southern Ocean deep-sea ecosystem

Session: Insights from Microfossils and Their Modern Analogs: From Traditional to Emerging Approaches

Presenting Author:

Moriaki Yasuhara

Authors:

Yasuhara, Moriaki¹, Huang, Huai-Hsuan May², Chong, Raine Wing Ki³, Hong, Yuanyuan⁴, Iwatani, Hokuto⁵, Zhang, Jingwen⁶, Kimoto, Katsunori⁷, Ikehara, Minoru⁸

(1) School of Energy and Environment, City University of Hong Kong, Kowloon, Hong Kong SAR, China, (2) Department of Geosciences, Princeton University, Princeton, NJ, USA, (3) School of Biological Sciences, The University of Hong Kong, Hong Kong, Hong Kong SAR, China, (4) School of Biological Sciences, The University of Hong Kong, Hong Kong, Hong Kong SAR, China, (5) Yamaguchi University, Yamaguchi, Japan, (6) Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA, (7) Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan, (8) Kochi University, Kochi, Japan,

Abstract:

The deep-time development of the Southern Ocean’s deep-sea ecosystem remains poorly understood, despite being a key region in global ecological, climatological, and oceanographic systems, where deep water forms and biodiversity is unexpectedly high. Here, we present an 500,000-year fossil record of the deep-sea Southern Ocean ecosystem in the subantarctic zone, using microfossil ostracods as a proxy. The results indicate that changes in surface productivity and the resulting food supply to the deep sea, driven by eolian dust input and iron fertilization, along with changes in bottom-water temperature influenced by deep-water circulation, have controlled the deep-sea ecosystem in the Southern Ocean on orbital (10⁴–10⁵ years) timescales following the Mid-Brunhes event (MBE), a major climatic transition 430,000 years ago. However, before the MBE, the deep-sea Southern Ocean ecosystem was distinct from the present-day, post-MBE one. The present-day form of the deep-sea Southern Ocean ecosystem was established following the MBE, likely because of a stronger incursion of the warm North Atlantic deep water into the Southern Ocean after the MBE. Before that, the deep-sea Southern Ocean ecosystem lacked typical deep-sea faunal components and resembled deep, marginal sea fauna, likely because of the stronger thermal isolation of the Southern Ocean from the Atlantic Ocean. This result suggests that if future human-induced climatic warming weakens global deep-water circulation from the Atlantic through the Southern Ocean to the Pacific, a deep-sea biodiversity hotspot in the Southern Ocean may diminish or even vanish.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8292

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