Increasing Earth temperatures and rising sea levels. Both of these are effects of climate change. The current concern is that human activity is changing our climate at a rate well above the natural climate cycling. Understanding how the Earth's climate system works and responds to human impact is therefore of uttermost importance.
"To predict future climate change we must first go back in the archives to understand a bit more about the natural cycles. This will enable us to decipher between natural changes and what's out of the ordinary," explained Gilbert Camoin, Centre National de la Recherche Scientifique (CNRS), at the European Geosciences Union (EGU) General Assembly in Vienna in April 2007.
The last deglaciation (23,000 - 6,000 years ago) is generally seen as a potential recent analogue for today's environmental changes. This period was characterised by abrupt climatic change and rapid sea-level rise due to polar ice sheets melting, similar conditions to what we see the Earth facing now and which are predicted for the future. Reconstructing past environments may lead to a better estimate of the climate sensitivity and hence of future climate change.
Fossil coral reefs can be used to accurately reconstruct past sea level variations, climate change and environmental perturbations. According to Camoin, they provide the most precise records of sea-level changes. This is because corals always live within very strict ecological requirements. They need clear and oxygenated water, only live in the first 50m of the sea column, at temperatures ranging from 18-35 C and within the very narrow salinity range of 35-36 per ml.
Any ecological changes affecting the narrow requirements of the coral reef environment will lead to changes in coral reef growth and composition. Thus, a fossil coral reef drill sample gives accurate information about the sea level, salinity and temperature at different times in history. Interpreting this information provides a way to reconstruct past climate change.
Using coral reefs as climatic archives started about 20 years ago. Initially, due to technical constraints, it was only possible to capture the last 10,000 years through coral reef drilling. To get datasets covering the entire period of the last deglaciation, it was crucial to find another technique. This became possible during a project where the Integrated Ocean Drilling Program (IODP) provided Camoin with the technology to drill down to 1100m recovering more than 600m of reef cores from 37 holes at depths ranging from 40 - 117m from the area around the island of Tahiti.
Source: European Science Foundation