CLIMATE CHANGE OF THE SOUTHERN OCEAN IN RESPONSE TO TOPOGRAPHIC FORCING DURING THE PALEOCENE-EOCENE THERMAL MAXIMUM

The Paleocene-Eocene thermal maximum (PETM), which occurred approximately 56 Ma, is marked by an estimated global temperature increase of 5-6 ˚C, a large negative carbon isotope excursion, and deep-sea carbonate dissolution. Determining the factors that contributed to and amplified this short-term global warming episode is essential to better understand rapid responses of the climate system to perturbations in the carbon cycle. In this study, we utilize the fully coupled Community Earth System Model version 1.2 to assess the role of global topography on the climate of the Southern Ocean during the PETM. When comparing the present-day topography (including ice sheets) to the topography of the PETM, the model shows a significant increase of both surface air temperature and sea surface temperature which is in agreeance with previous studies. Increase in PETM precipitation over the Southern Ocean relative to present is linked to this warming and thus higher vapor concentration. Ventilation of water masses inferred from an idealized age tracer in the PETM polar Pacific and Atlantic Ocean suggests an increased pole ward heat transport, that is also supported by strengthening of the western boundary currents (approximately to 40 Sv in the subtropical South Atlantic Ocean). However, a reduced meridional temperature gradient near Antarctica and closure of seaways lead a decrease barotropic stream function by nearly 160 Sv around Antarctica. Ekman-induced equatorial upwelling at 100 meters in the Pacific Ocean during the PETM slightly increases compared to present-day by rise in wind stress thus influences surface temperature pattern across the Pacific equatorial region. In summary, Eocene to present changes in the topography leads to significant changes in ocean circulation, heat transport, and impacts climatic responses globally.