Past levels of pH and pCO2 in the western Pacific
The atmospheric concentration of carbon dioxide (CO2) concentration has a major influence on the Earth's climate. Studies have revealed that atmospheric CO2 levels were lower during glaciations than in inter-glacial periods. Work by the 6C project demonstrated that the equatorial Pacific Ocean was an important source of CO2 to the atmosphere around 14,000 to 16,000 years ago. This was a time characterised by a rapid rise in atmospheric CO2 and the warming of the Earth's climate. The 6C project partners measured boron isotopes in the foraminifer Globigerinoides sacculifer a type of plankton, to determine the pH of the seawater. Once this information was known the level of CO2 in the water could be calculated. Researchers studied samples of G. sacculifer from between 400 to 23,200 years ago. The results indicated that the CO2 in surface waters for this area of the Pacific Ocean were usually in equilibrium with atmospheric CO2. However, between 13,800 and 15,600 years ago the level of CO2 in the surface water was around 100 parts per million higher than atmospheric levels. This suggested a period of more frequent upwelling, which brought nutrients and CO2-rich waters to the ocean's surface. These conditions were a result of intensifying conditions of the cold pool in the eastern Pacific and the strengthening of the trade winds. The results from the 6C project demonstrate that studies using planktonic foraminifers are an extremely useful tool for investigating variations in ocean-atmosphere CO2 exchanges. This technique was used to identify past sources and sinks of atmospheric CO2 and increases our understanding of the atmosphere's sensitivity to changes in CO2. This in turn helps scientists studying climate change to better understand the role the ocean plays in controlling atmospheric CO2.
