Skip to main content

Atmospheric and oceanic impacts of Antarctic glaciation across the Eocene–Oligocene transition

Composite satellite image of what the Earth may have looked like prior to Antarctic
glaciation during the late Eocene (image by Alan Kennedy).
The Eocene-Oligocene Transition occurred approx. 34 million years ago and was one of the biggest climatic shifts since the end of the Cretaceous (with the extinction of the dinosaurs). The Earth dramatically cooled and the Antarctic ice sheet first formed, but the cause and nature of the cooling remain uncertain. Using a climate model, HadCM3L, we looked at the effect of ice sheet growth and palaeogeographical change (i.e. continental reconfiguration as Australia separated from Antarctica) on the Earth’s steady-state climate. We utilised four simulations: a late Eocene palaeogeography with and without an ice sheet and an early Oligocene palaeogeography with and without an ice sheet.

The formation of the Antarctic ice sheet causes a similar atmospheric response for both palaeogeographies: cooling of the air over Antarctica, intensification of the polar atmospheric cell and increased winds over the Southern Ocean. The sea surface temperature response to the growth of ice is very different, however, between the two palaeogeographies. For the Eocene palaeogeography there is a 6°C warming in the South Pacific sector of the Southern Ocean in response to ice growth, but very little change (or even a slight cooling) for the Oligocene palaeogeography. Why, under the same forcing (the appearance of the ice sheet), do these different palaeogeographies have such different sea surface temperature responses?

The stronger winds over the Southern Ocean force more-saline water from the southern Indian Ocean into the less-saline southern Pacific Ocean. This is particularly important for the Eocene simulations, where the narrow gap between Australia and Antarctica limits flow from the Indian to the Pacific Ocean. As salinity in the southern Pacific Ocean increases the water becomes denser and sinks, releasing heat. This accounts for the increase in sea surface temperature in the Eocene simulations. In the Oligocene simulations, flow is already much greater between the Indian and Pacific Oceans, and so there is no marked increase in density, sinking or sea surface temperature following glaciation. There is only a mild cooling due to the presence of the large, cold ice sheet.

Whether in reality the dominant ocean response to glaciation was warming or cooling may have impacted the growth of the ice sheet at this major transition in the Earth’s history. However, more importantly, this research highlights that sensitivity to subtle changes in palaeogeography can potentially have very large effects on the modelled climatic response to an event such as Antarctic glaciation. This could be very important for understanding palaeoclimate records and interpreting climate model results.

This research, carried out by Alan Kennedy, Dr Alex Farnsworth and Prof Dan Lunt of the Cabot Institute and University of Bristol with others, is featured in a special issue of the Philosophical Transactions of the Royal Society A. The full special issue on the theme of ‘Feedbacks on climate in the Earth System’ and the paper can be accessed here.

Special issue cover (image from Royal Society).
Citation: Kennedy A.T., Farnsworth A., Lunt D.J., Lear C.H., & Markwick P.J. (2015) Atmospheric and oceanic impacts of Antarctic glaciation across the Eocene–Oligocene transition. Phil. Trans. R. Soc. A, 373, 20140419, doi:10.1098/rsta.2014.0419.
This blog is written by Alan Kennedy from the School of Geographical Sciences at the University of Bristol.  This blog post was edited from Alan's blog post at Ezekial Boom.
Alan Kennedy


Popular posts from this blog

A response to Trump's withdrawal from the Paris Agreement

The decision by President Trump to withdraw from the Paris Agreement on Climate Change puts the United States at odds with both science and global geopolitical norms.  The fundamentals of climate change remain unambiguous: greenhouse gas concentrations are increasing, they are increasing because of human action, the increase will cause warming, and that warming creates risks of extreme weather, food crises and sea level rise. That does not mean that scientists can predict all of the consequences of global warming, much work needs to be done, but the risks are both profound and clear. Nor do we know what the best solutions will be - there is need for a robust debate about the nature, fairness and efficacy of different decarbonisation policies and technologies as well as the balance of responsibility; the Paris Agreement, despite its faults with respect to obligation and enforcement, allowed great flexibility in that regard, which is why nearly every nation on Earth is a signatory.


The Diamond Battery – your ideas for future energy generation

On Friday 25th November, at the Cabot Institute Annual Lecture, a new energy technology was unveiled that uses diamonds to generate electricity from nuclear waste. Researchers at the University of Bristol, led by Prof. Tom Scott, have created a prototype battery that incorporates radioactive Nickel-63 into a diamond, which is then able to generate a small electrical current.
Details of this technology can be found in our official press release here:
Despite the low power of the batteries (relative to current technologies), they could have an exceptionally long lifespan, taking 5730 years to reach 50% battery power. Because of this, Professor Tom Scott explains:
“We envision these batteries to be used in situations where it is not feasible to charge or replace conventional batteries. Obvious applications would be in low-power electrical devices where long life of the energy source is needed, such as pacemakers, satellite…

Dadaism in Disaster Risk Reduction: Reflections against method

Reflections and introductions: A volta The volta is a poetic device, closely but not solely, associated with the Shakespearean sonnet, used to enact a dramatic change in thought or emotion. Concomitant with this theme is that March is a month with symbolic links to change and new life. The Romans famously preferred to initiate the most significant socio-political manoeuvres of the empire during the first month of their calendar, mensis Martius. A month that marked the oncoming of spring, the weakening of winter’s grip on the land and a time for new life.
The need for change Having very recently attended the March UKADR conference, organised by the Cabot Institute here in Bristol, I did so with some hope and anticipation. Hope and anticipation for displays and discussions that conscientiously touched upon this volta, this need for change in how we study the dynamics of natural hazards. The conference itself was very agreeable, it had great sandwiches, with much stimulating discussion …