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80 million years of climate change

15 July 2005

Sediments from Tanzania are being used to evaluate 80 million years of climate change as part of a NERC-funded project conducted by Dr Rich Pancost and colleagues.

So far, ten sites in coastal Tanzania have been drilled in order to recover sediments from which climate change over the past 80 million years could be evaluated.  This time interval is of immense interest to scientists because it defines the transition from a warm, ice-free 'greenhouse' world to our current 'icehouse' world with extensive polar ice. 

The sites have been drilled by the Tanzania Drilling Project (TDP), primarily funded by the UK Natural Environment Research Council (NERC), but supported by numerous collaborators from across the UK as well as Tanzania, Ireland, the Netherlands and the United States. 

This represents the first scientific coring in this part of the world and has allowed us to develop geological maps of great value for the Tanzanian people.  Hopefully, insights gained from these efforts will contribute to the careful exploitation of Tanzania's natural resources. 

The cores span some of the most important events of the past 80 million years

The recovered cores also contain some of the best preserved sediments of this age; the organic compounds, rather than having been altered to petroleum-like structures, are similar to those that you could find in your garden, and the fossil shells look similar to those of living organisms.  

The cores also span some of the most important events of the past 80 million years, including the Late Palaeocene Thermal Maximum, when it is thought that massive methane release caused dramatic climate change and major extinctions on land and in the sea.  Thus, the TDP cores offer exciting new opportunities to reconstruct the tropical environment during this time of dramatic climate change.  

In particular, we are using a combination of geochemical tracers - from molecular 'fossils' to the elemental composition of tiny planktonic carbonate shells -to reconstruct the co-occurring change in atmospheric greenhouse gas levels and tropical sea surface temperature.  Determining carbon dioxide concentrations through these intervals has been challenging, but our results generally suggest that concentrations were much higher in the past. 

Tropical sea surface temperatures in the greenhouse world were significantly higher than today

We have developed some of the first Cenozoic tropical sea surface temperature records, using a combination of approaches.  The first is the application of a new proxy based on the distribution of the membrane constituents of archaea, single-celled organisms that live in almost all environments.  These compounds' structures vary with sea surface temperature to maintain the membrane fluidity - similar to how fats in oil are liquid at room temperature but fats in butter are not.   The second approach is using the distributions of different elements and isotopes in the calcareous fossil remains of microscopic animals called foraminifera.

Our results have yet to be published, but they clearly show that tropical sea surface temperatures in the greenhouse world were significantly higher than today. This is in contrast to much previous work and our dual-proxy results were made possible by the excellent preservation of these microbial membrane lipids and calcareous fossil shells. 

In the future, we still have a great amount of core material to exploit.  We will focus our analyses on specific horizons of interest, again utilising a multi-proxy approach in order to evaluate how the tropics responded to rapid geochemical changes similar to those induced by human activity today.

Dr Richard Pancost/School of Chemistry

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