Ocean Cores May Give Clues On Climate Change

Core samples taken from far below the ocean floor are helping a University of Edinburgh geologist to form a picture of dramatic climate changes which took place 30 to 40 million years ago. Dr Bridget Wade is part of an international team of scientists studying climate shifts between the Eocene period – the warmest cycle in the last 65 million years – and the cooler Oligocene period, which saw the first major build-up of Antarctic ice. The study could shed new light on present climate trends as the Eocene climatic regime appears to have established itself rapidly – at a rate comparable to modern global warming – before ending almost as abruptly.

The team of 28 scientists from eight nations is analysing drill cores taken from eight sites near the equator in the Pacific Ocean in October. The cores are the first to be recovered which contain continuous geological records of the Eocene and Oligocene periods. Dr Wade is studying sediment which records the transition 33.7million years ago from the Eocene period – when London was covered by tropical rainforest and crocodiles swam in the River Thames – to the Oligocene period, a time about which scientists know relatively little.

The start of the Oligocene period coincides not only with huge climate shifts, but also with marked changes in the Earth’s oceanography. Scientists detect a shift towards patterns more like those today where wind systems from the northern and southern hemispheres come together and stir the ocean near the equator so that deep, nutrient-rich waters come to the surface and support a diverse, thriving community of plankton. In the Eocene period, the oceanic biological system had been broad and diffuse with low plankton productivity.

Dr Wade is completing a detailed study of plankton fossils, which will help to build the most accurate picture so far of how the Oligocene climate changed over time. And, because the core sample holds a unique, unbroken geological record over a 10m year period, it can help the scientists to date Oligocene rocks more accurately than ever before. The current margin for error is 1m years, but the new study could help to cut that figure to about 50,000 years.

Dr Wade said: “It’s exciting being part of an international team working on a single grand problem. The Oligocene period remains something of a mystery because, until now, there have been no good cores. This study will help us create a more accurate picture of that time. People used to think big climate changes had only occurred during the last million years, but research suggests that dramatic change has always taken place as a result of natural processes.”