INTRIGUED: INvestigating The Role of the North Pacific In Glacial and Deglacial CO2 and Climate

The geological record offers an invaluable window into the different ways earth's climate can operate. The most recent major changes in earth's climate, prior to modern climate change, were the Pleistocene ice ages. These feature growth and collapse of massive ice sheets, rapid shifts in rain belts, and abrupt changes in ocean circulation. Changes in atmospheric CO2 are intimately linked with these ice age climate changes, but despite decades of effort, we still don't fully understand their driving mechanisms.

The aim of the newly NERC-funded research by Dr James Rae of the Department of Earth and Environmental Sciences is to transform our understanding of ice age CO2 and climate change, by investigating how the deep Pacific stored CO2 during ice ages, and released it back to the atmosphere during deglaciation. Although all leading hypotheses for ice age CO2 change involve CO2 storage in the deep ocean, the role of the Pacific remains unknown. As the Pacific contains half of global ocean volume, and ~30 times more CO2 than the atmosphells, whichere, its behaviour will have global impact. Our work will involve making geochemical measurements on fossil shells taken from sediment cores from the deep Pacific Ocean. These shells - called foraminifera - record the chemistry of the surrounding water at the time they grow, so by making measurements on them down the length of a sediment core, we can read back through the history of ocean circulation and CO2. A particular focus of our grant is the boron isotope composition of these sh reflects ocean pH and CO2. The new St Andrews Isotope Geochemistry labs at the University of St Andrews are among the first in the world to have be built fully boron-free, allowing us to be at the forefront of this cutting-edge technique.

The research is based at St Andrews, but features a team of leading scientists from around the world, including the Universities of Bristol, Kiel, Oregon, McGill, and ETH Zurich, the Woods Hole Oceanographic Institute and Scripps Institute of Oceanography USA, the Alfred Wegner Institute for Polar Research Germany, and radiocarbon facilities in Glasgow and California.

The project will ultimately improve understanding of CO2 exchange between the ocean and the atmosphere, which is an important factor for predicting the path of future climate change.

The Southern CO2 that helped end the ice age

Scientists have long puzzled over the processes that caused CO2 to rise and help end the last ice age. Leading theories have involved increased CO2 release from the deep ocean around Antarctica, but there has been no direct evidence to prove this happened.

Our study used the geochemistry of tiny planktonic fossil shells to reconstruct the amount of CO2 in waters around Antarctica during the end of the last ice age.  We were able to show, for the first time, that CO2 was indeed released from the Southern Ocean to the atmosphere, helping warm the planet and melt back the ice sheets that would have covered Scotland and much of the rest of Northern Europe and America.

Dr James Rae, of the Department of Earth and Environmental Sciences, who co-authored the study, said “intervals of CO2 and climate change in the past offer a fantastic opportunity for us to better understand the path of future climate.  As the ocean currently takes up about a third of the CO2 emitted by humans, it’s important to understand the controls on CO2 exchange between the ocean and the atmosphere so we can predict how ocean CO2 uptake may change in the future.  It’s also striking to think that CO2 change has contributed to climate changes in the past as dramatic as melting back a mile of ice on top of Scotland, and you’ve got to wonder what adding the same amount of CO2 to the atmosphere, but 100 times faster, will do to climate in the years to come.” [Nature 518, 219–222 (12 February 2015) DOI: 10.1038/nature14155, "Boron isotope evidence for oceanic carbon dioxide leakage during the last deglaciation"] [press release]