Intellectual merit: Because changes in ocean circulation have profoundly influenced climate in the past, this project addresses the fundamental role that ocean circulation plays in the regulation of CO2. The work uses radiocarbon in foraminifera tests deposited in sediments off New Zealand to examine how global ocean circulation affects the partitioning of the greenhouse gas CO2 between the ocean and atmosphere. The work has two primary goals: (1) to reconstruct the radiocarbon signature of the glacial Southern Pacific to confirm or refute the presence of a deep water mass old enough to account for the glacial-interglacial changes in atmospheric CO2 and (2) to produce a high resolution record of radiocarbon at various intervals the time of deglaciation to provide a Southern Hemisphere perspective, which is missing from global CO2 and radiocarbon budgets. Ocean circulation can be traced with radiocarbon (14C) because there is a quantifiable difference between the 14C content of atmospheric CO2 gas and that in the ocean where it exists in the form of dissolved carbonate and bicarbonate. In addition, this project takes advantage of the precise stratigraphic control afforded by volcanic ash layers in cored, off-shore sediments from different water depths. Planktonic and benthic foraminiferal pairs will be used to construct vertical profiles of radiocarbon at different depths in the ocean and a time series of oxygen isotope data will be collected to track the evolution of changes in shallow waters (600-2500 m) and deep waters (600-4300m) through the time of the last period of deglaciation (17,500 to 9,500 years ago).
Broader impacts: The project includes collaboration between US and New Zealand scientists, student training, and the support of an early career investigator whose gender is under-represented in the sciences.
