How can we reconstruct the long-term ‘greenhouse-icehouse’ transition?

In order to understand the long-term greenhouse-icehouse transition, the project has been split into five main work packages (WP):

 WP 1. The evolution of the oceanic carbonate system and atmospheric pCO₂ during the early Cenozoic

We aim to generate more accurate and higher resolution records of whole water column pH using boron isotopes from multiple sites providing vital new constraints on atmospheric pCO₂ and oceanic carbon storage in the early Cenozoic. We can also use the δ¹³C values of alkenones(organic molecules derived from haptophyte algae) to determine pCO₂ however the applicability of this method is somewhat limited by low alkenone abundance during the early Cenozoic

Figure 1: Dr. Gavin Foster and MP Caroline Nokes in the University of Southampton boron isotope geochemistry laboratory

 WP 2. Spatial patterns of oceanic cooling in the early Cenozoic

The spatial patterns of cooling during the early Cenozoic will largely reflect the mechanisms responsible – e.g. pCO₂ decline should be evident as cooling at all latitudes with some high latitude amplification, whereas ocean circulation changes will involve a redistribution of heat from low to high latitudes. Using a combination of organic and inorganic temperature proxies we aim to reconstruct the temperature of the ocean throughout the Eocene.

 WP 3. The physical effects of ocean gate way closure during the early Cenozoic

The relative importance of changes in gateway configuration versus pCO₂ change in driving Cenozoic climate change has never been systematically investigated in a model framework. Here we will carry out a number of simulations with a fully coupled general circulation model developed by the UK Met Office (HadCM3L), incorporating various gateway configurations and at several pCO₂ levels. These sensitivity tests will identify the relative roles of gateway reorganisation and pCO₂ in driving the reconstructed cooling.

 WP 4. Biological consequences and causes of Cenozoic climate change

Biological change in the early Cenozoic has the potential to amplify climate change in several ways.

Figure 2: Scanning electron micrographs of planktonic foraminifera, contrasting well preserved (a±f) and poorly preserved (g±i) shell textures[1].

In order to better understand the processes responsible for driving biological change, and the subsequent impact of these changes on the organic carbon pump, we therefore need to have an understanding of water column thermal and nutrient structure during this time interval.  This will be achieved here using δ¹³C depth profiles of foraminifera from a number of open ocean sites while changes in the upper water column nutrient characteristics will be examined using nannofossil assemblage studies.

 WP 5. Modelling non-linear Earth System dynamics during the early Cenozoic

The only practical way to quantitatively address feedbacks and thresholds in the Earth system is through Earth system modelling. Experiments will be carried out using the EMIC GENIE (http://www.genie.ac.uk/) and the 3 box model Jmodel. At all stages model output will be tested against new and existing data derived from the aforementioned work packages.

 Figure 3: exhibits the different environmental parameters incorporated into the GENIE model[2]