Preprints
https://doi.org/10.5194/cp-2021-131
https://doi.org/10.5194/cp-2021-131

  18 Oct 2021

18 Oct 2021

Review status: this preprint is currently under review for the journal CP.

Eocene to Oligocene vegetation and climate in the Tasmanian Gateway region controlled by changes in ocean currents and pCO2

Michael Amoo1, Ulrich Salzmann1, Matthew J. Pound1, Nick Thompson1, and Peter K. Bijl2 Michael Amoo et al.
  • 1Department of Geography and Environmental Sciences, Northumbria University, Newcastle upon Tyne, UK
  • 2Marine Palynology and Palaeoceanography, Utrecht University, Princetonlaan 8A, Utrecht, The Netherlands

Abstract. Considered as one of the most significant climate reorganisations of the Cenozoic period, the Eocene-Oligocene Transition (EOT; ca. 34.44–33.65) is characterised by global cooling and the first major glacial advance on Antarctica. While in the southern high-latitudes, the EOT cooling is primarily recorded in the marine realm, the extent and effect on terrestrial climate and vegetation is poorly documented. Here, we present a new, well-dated, continuous, high-resolution palynological (sporomorph) data and quantitative sporomorph-based climate estimates recovered from the East Tasman Plateau (ODP Site 1172) to reconstruct climate and vegetation dynamics from the late Eocene (37.97 Ma) to early Oligocene (33.06 Ma). Our results indicate three major climate transitions and four vegetation communities occupying Tasmania under different precipitation and temperature regimes: (i) a warm-temperate Nothofagus-Podocarpaceae dominated rainforest with paratropical elements from 37.97–37.52 Ma; (ii) cool-temperate Nothofagus dominated rainforest with secondary Podocarpaceae rapidly expanding and taking over regions previously occupied by the warmer taxa between 37.306–35.60 Ma; (iii) fluctuation between warm temperate – paratropical taxa and cool temperate forest from 35.50–34.49 Ma, followed by a cool phase across the EOT (34.30–33.82 Ma); (iv) post-EOT (earliest Oligocene) recovery characterised by a warm-temperate forest association from 33.55–33.06 Ma. Coincident with changes in stratification of water masses and sequestration of carbon from surface water in the Southern Ocean, our sporomorph-based temperature estimates between 37.52 Ma and 35.60 Ma (phase ii) showed 2–3 °C terrestrial cooling. The unusual fluctuation between warm and cold temperate forest between 35.50 to 34.59 Ma is suggested to be linked to the initial deepening of the Tasmanian Gateway allowing eastern Tasmania to come under the influence of warm water associated with the proto-Leeuwin Current (PLC). Further to the above, our terrestrial data show mean annual temperature declining by about 2 °C across the EOT before recovering in the earliest Oligocene. This phenomenon is synchronous with regional and global cooling during the EOT and linked to declining pCO2. However, the earliest Oligocene climate rebound along eastern Tasmania is linked to transient recovery of atmospheric pCO2 and sustained deepening of the Tasmanian Gateway, promoting PLC throughflow. The three main climate transitional events across the studied interval (late Eocene–earliest Oligocene) in the Tasmanian Gateway region suggest that changes in ocean circulation due to accelerated deepening of the Tasmanian Gateway may not have been solely responsible for the changes in terrestrial climate and vegetation dynamics, but a series of regional and global events, including a change in stratification of water masses, sequestration of carbon from surface waters, and changes in pCO2 may have played vital roles.

Michael Amoo et al.

Status: open (until 13 Dec 2021)

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  • EC1: 'Comments on Amoo et al', Alberto Reyes, 04 Nov 2021 reply

Michael Amoo et al.

Michael Amoo et al.

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Short summary
Late Eocene to earliest Oligocene (37.97–33.06 Ma) climate and vegetation dynamics around the Tasmanian Gateway region reveal that, changes in ocean circulation due to accelerated deepening of the Tasmanian Gateway may not have been solely responsible for the changes in terrestrial climate and vegetation, but a series of regional and global events, including a change in stratification of water masses and changes in pCO2 may have played significant roles.