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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1 Citation (Scopus)

Abstract

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
Volume34
Issue number4
DOIs
Publication statusPublished - 30 Apr 2019
Externally publishedYes

Keywords

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

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