Ocean models of the paleooceanographic development of the Australian Antarctic Basin through the Oligocene

Ocean modelling results of "Southern Ocean biogenic blooms freezing-in Oligocene colder climates" by Hochmuth et al.

Manuscript Abstract

Crossing a key atmospheric CO₂ threshold triggered a fundamental global climate reorganisation ~34 million years ago (Ma) establishing permanent Antarctic ice sheets. Curiously, a more dramatic CO₂ decline (~800-400 ppm by the Early Oligocene(~27Ma)), postdates initial ice sheet expansion but the mechanisms driving this later, rapid drop in atmospheric carbon during the early Oligocene remains elusive and controversial. Here we use marine seismic reflection and borehole data to reveal an unprecedented accumulation of early Oligocene strata (up to 2.2 km thick over 1,500 x 500 km) with a major biogenic component in the Australian Southern Ocean. High-resolution ocean simulations demonstrate that a tectonically-driven, one-off reorganisation of ocean currents, caused a unique period where current instability coincided with high nutrient input from the Antarctic continent. This unrepeated and short-lived environment favoured extreme bioproductivity and enhanced sediment burial. The size and rapid accumulation of this sediment package potentially holds ~1.067 x 10¹⁵ kg of the ‘missing carbon’ sequestered during the decline from an Eocene high CO₂-world to a mid-Oligocene medium CO₂-world, highlighting the exceptional role of the Southern Ocean in modulating long-term climate.

Information on modelling results:

The model runs simulating the response of the ocean across the Eocene-Oligocene transition use the Massachusetts Institute of Technology general circulation model (MITgcm) in an ocean-only regional configuration with no sea-ice. The regional domain extends from 100°E to 165°E in zonal direction and from 65°S to 49°S in meridional direction. We used the method established by Sauermilch et al. 2021 to investigate the effect of a deepening Tasmanian Gateway (TG) on the regional circulation.

The uploaded dataset includes the mean modelling output describing oceancurrent velocity, sea surface temperature and salinity at different depth of the Tasmanian Gateway. The model configuration, including paleobathymetric reconstructions, are available as grids with the corresponding gateway depth.