title: Deep-sea coral evidence for lower Southern Ocean surface nitrate concentrations during the last ice age.
abstract: The Southern Ocean regulates the ocean's biological sequestration of CO2and is widely suspected to underpin much of the ice age decline in atmospheric CO2concentration, but the specific changes in the region are debated. Although more complete drawdown of surface nutrients by phytoplankton during the ice ages is supported by some sediment core-based measurements, the use of different proxies in different regions has precluded a unified view of Southern Ocean biogeochemical change. Here, we report measurements of the15N/14N of fossil-bound organic matter in the stony deep-sea coralDesmophyllum dianthus, a tool for reconstructing surface ocean nutrient conditions. The central robust observation is of higher15N/14N across the Southern Ocean during the Last Glacial Maximum (LGM), 18-25 thousand years ago. These data suggest a reduced summer surface nitrate concentration in both the Antarctic and Subantarctic Zones during the LGM, with little surface nitrate transport between them. After the ice age, the increase in Antarctic surface nitrate occurred through the deglaciation and continued in the Holocene. The rise in Subantarctic surface nitrate appears to have had both early deglacial and late deglacial/Holocene components, preliminarily attributed to the end of Subantarctic iron fertilization and increasing nitrate input from the surface Antarctic Zone, respectively.
authors.affiliation: Department of Geosciences, Princeton University, Princeton, NJ 08544; xingchen@caltech.edu.|Climate Geochemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany.
authors.forename: Xingchen Tony
authors.identifier: 0000-0001-5316-789X
authors.initials: XT
authors.lastname: Wang
authors.affiliation: Department of Geosciences, Princeton University, Princeton, NJ 08544.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Sigman
authors.affiliation: Department of Geology, Pomona College, Claremont, CA 91711.
authors.forename: Maria G
authors.initials: MG
authors.lastname: Prokopenko
authors.affiliation: Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125.
authors.forename: Jess F
authors.initials: JF
authors.lastname: Adkins
authors.affiliation: Bristol Isotope Group, School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom.
authors.forename: Laura F
authors.initials: LF
authors.lastname: Robinson
authors.affiliation: Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125.
authors.forename: Sophia K
authors.initials: SK
authors.lastname: Hines
authors.affiliation: Atmospheric and Oceanic Sciences Program, Princeton University, NJ 08544.
authors.forename: Junyi
authors.initials: J
authors.lastname: Chai
authors.affiliation: Climate Geochemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany.
authors.forename: Anja S
authors.initials: AS
authors.lastname: Studer
authors.affiliation: Climate Geochemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany.
authors.forename: Alfredo
authors.initials: A
authors.lastname: Martínez-García
authors.affiliation: Bristol Isotope Group, School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom.
authors.forename: Tianyu
authors.initials: T
authors.lastname: Chen
authors.affiliation: Climate Geochemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany.|Geological Institute, ETH Zürich, 8092 Zurich, Switzerland.
authors.forename: Gerald H
authors.initials: GH
authors.lastname: Haug
mesh_terms: D000818:Animals; D000864:Antarctic Regions; D037421:Anthozoa / Q000737:chemistry* / Q000378:metabolism; D001272:Atmosphere; D002245:Carbon Dioxide / Q000032:analysis* / Q000378:metabolism; D009566:Nitrates / Q000032:analysis; D009792:Oceans and Seas; D010839:Phytoplankton / Q000737:chemistry / Q000378:metabolism; D012623:Seawater / Q000737:chemistry
chemical_list: D009566:Nitrates; D002245:Carbon Dioxide
keywords: Southern Ocean; atmospheric CO2; ice ages; nutrient consumption