Modern, Preindustrial, and Past (Last 25 ka) Carbon Isotopic (δ 13 C) Variability in the Surface Waters of the Southwest Pacific

Carbon stable isotopes (δC) in modern seawater samples and planktic foraminifera Globigerina bulloides from core top and downcore sediments are used to estimate the distribution of δC of dissolved inorganic carbon (DIC) in the surface waters of the southwest Pacific in the modern, preindustrial (PI), and over the last 25 kyr. The predicted δC distribution in the modern (δC), PI (δC), and late Holocene (from planktic foraminifera Globigerina bulloides [temperature corrected δC] from core tops) displays a broad peak at the subtropical front) and subantarctic surface waters due to the combination of high biological productivity and thermodynamic air-sea gas exchange of CO in this region. The estimated δC values and measured δC values from the core tops are higher than the modern values due to the Suess Effect. However, there is poor agreement between the δC values and core top δC values south of 40°S as the back-calculation approach using chlorofluorocarbon-11 (CFC-11) method for removing the anthropogenic δC is not effective at these higher southern latitudes. The δC from a latitudinal transect of cores in the southwest Pacific were compiled by region using a Monte Carlo approach to determine the long-term trends in δC over the last 25 kyr. Glacial subantarctic δC values are low, while subtropical δC are high. The peak in δC values shifts south in the early Holocene. These latitudinal variations in δC are linked to changes in ocean circulation, biological productivity (associated with the shifts in the subtropical front), and air-sea CO exchange, likely related to the structure and position of the Southern Hemisphere Westerly Wind in the South Pacific region.