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

Charles R. Maxson, Helen C. Bostock, Andrew Mackintosh, Sara Mikaloff-Fletcher, Nick McCave, Helen L. Neil

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Carbon stable isotopes (δ 13 C) in modern seawater samples and planktic foraminifera Globigerina bulloides from core top and downcore sediments are used to estimate the distribution of δ 13 C 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 δ 13 C distribution in the modern (δ 13 C DIC ), PI (δ 13 C PI ), and late Holocene (from planktic foraminifera Globigerina bulloides [temperature corrected δ 13 C G.bulloidesTC ] 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 2 in this region. The estimated δ 13 C PI values and measured δ 13 C G.bulloidesTC values from the core tops are higher than the modern values due to the Suess Effect. However, there is poor agreement between the δ 13 C PI values and core top δ 13 C G.bulloidesTC values south of 40°S as the back-calculation approach using chlorofluorocarbon-11 (CFC-11) method for removing the anthropogenic δ 13 C is not effective at these higher southern latitudes. The δ 13 C G.bulloidesTC 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 δ 13 C over the last 25 kyr. Glacial subantarctic δ 13 C G.bulloidesTC values are low, while subtropical δ 13 C G.bulloidesTC are high. The peak in δ 13 C G.bulloidesTC values shifts south in the early Holocene. These latitudinal variations in δ 13 C G.bulloidesTC are linked to changes in ocean circulation, biological productivity (associated with the shifts in the subtropical front), and air-sea CO 2 exchange, likely related to the structure and position of the Southern Hemisphere Westerly Wind in the South Pacific region.

Original languageEnglish
Pages (from-to)692-714
Number of pages23
JournalPaleoceanography and Paleoclimatology
Issue number4
Publication statusPublished - 30 Apr 2019
Externally publishedYes


  • carbon isotopes
  • planktic foraminifera
  • southwest Pacific
  • ocean circulation
  • biological productivity
  • Southern Hemisphere Westerly Winds

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