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Modern, Preindustrial, and Past (Last 25 ka) Carbon Isotopic (δ13C) Variability in the Surface Waters of the Southwest Pacific

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jats:titleAbstract</jats:title>jats:pCarbon stable isotopes (δjats:sup13</jats:sup>C) in modern seawater samples and planktic foraminifera <jats:styled-content style="fixed-case">jats:italicGlobigerina bulloides</jats:italic></jats:styled-content> from core top and downcore sediments are used to estimate the distribution of δjats:sup13</jats:sup>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 δjats:sup13</jats:sup>C distribution in the modern (δjats:sup13</jats:sup>Cjats:subDIC</jats:sub>), PI (δjats:sup13</jats:sup>Cjats:subPI</jats:sub>), and late Holocene (from planktic foraminifera <jats:styled-content style="fixed-case">jats:italicGlobigerina bulloides</jats:italic></jats:styled-content> [temperature corrected δjats:sup13</jats:sup>Cjats:subjats:italicG</jats:italic>.jats:italicbulloides</jats:italic>TC</jats:sub>] 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 COjats:sub2</jats:sub> in this region. The estimated δjats:sup13</jats:sup>Cjats:subPI</jats:sub> values and measured δjats:sup13</jats:sup>Cjats:subjats:italicG</jats:italic>.jats:italicbulloides</jats:italic>TC</jats:sub> values from the core tops are higher than the modern values due to the Suess Effect. However, there is poor agreement between the δjats:sup13</jats:sup>Cjats:subPI</jats:sub> values and core top δjats:sup13</jats:sup>Cjats:subjats:italicG</jats:italic>.jats:italicbulloides</jats:italic>TC</jats:sub> values south of 40°S as the back‐calculation approach using chlorofluorocarbon‐11 (CFC‐11) method for removing the anthropogenic δjats:sup13</jats:sup>C is not effective at these higher southern latitudes. The δjats:sup13</jats:sup>Cjats:subjats:italicG</jats:italic>.jats:italicbulloides</jats:italic>TC</jats:sub> 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 δjats:sup13</jats:sup>C over the last 25 kyr. Glacial subantarctic δjats:sup13</jats:sup>Cjats:subjats:italicG</jats:italic>.jats:italicbulloides</jats:italic>TC</jats:sub> values are low, while subtropical δjats:sup13</jats:sup>C jats:subjats:italicG</jats:italic>.jats:italicbulloides</jats:italic>TC</jats:sub> are high. The peak in δjats:sup13</jats:sup>Cjats:subjats:italicG</jats:italic>.jats:italicbulloides</jats:italic>TC</jats:sub> values shifts south in the early Holocene. These latitudinal variations in δjats:sup13</jats:sup>C jats:subjats:italicG</jats:italic>.jats:italicbulloides</jats:italic>TC</jats:sub> are linked to changes in ocean circulation, biological productivity (associated with the shifts in the subtropical front), and air‐sea COjats:sub2</jats:sub> exchange, likely related to the structure and position of the Southern Hemisphere Westerly Wind in the South Pacific region.</jats:p>



37 Earth Sciences, 3709 Physical Geography and Environmental Geoscience, 3705 Geology

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Paleoceanography and Paleoclimatology

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American Geophysical Union (AGU)


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