Contribution of seasonal sub-Antarctic surface water variability to millennial-scale changes in atmospheric CO 2 over the last deglaciation and Marine Isotope Stage 3

• Published in: Earth and Planetary Science Letters
• Main Authors: Gottschalk, Julia, Skinner, Luke C., Waelbroeck, Claire
• Other Authors: University of Cambridge UK (CAM), Paléocéanographie (PALEOCEAN), Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: South Atlantic; planktonic foraminifera; stable oxygen and carbon isotopes; atmospheric CO2; last glacial period; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology; Antarctic; Southern Ocean; Antarc*; Neogloboquadrina pachyderma; Planktonic foraminifera; Sea ice
• Online Access: https://hal.archives-ouvertes.fr/hal-01806679; https://hal.archives-ouvertes.fr/hal-01806679/document; https://hal.archives-ouvertes.fr/hal-01806679/file/1-s2.0-S0012821X14007511-main.pdf; https://doi.org/10.1016/j.epsl.2014.11.051

International audience The Southern Ocean is thought to have played a key role in past atmospheric carbon dioxide (CO2,atm) changes. Three main factors are understood to control the Southern Ocean's influence on CO2,atm, via their impact on surface ocean pCO2 and therefore regional ocean–atmosphere CO2 fluxes: 1) the efficiency of air–sea gas exchange, which may be attenuated by seasonal- or annual sea-ice coverage or the development of a shallow pycnocline; 2) the supply of CO2-rich water masses from the sub-surface and the deep ocean, which is associated with turbulent mixing and surface buoyancy- and/or wind forcing; and 3) biological carbon fixation, which depends on nutrient availability and is therefore influenced by dust deposition and/or upwelling. In order to investigate the possible contributions of these processes to millennial-scale CO2,atm variations during the last glacial and deglacial periods, we make use of planktonic foraminifer census counts and stable oxygen- and carbon isotope measurements in the planktonic foraminifera Globigerina bulloides and Neogloboquadrina pachyderma (sinistral) from marine sediment core MD07-3076Q in the sub-Antarctic Atlantic. These data are interpreted on the basis of a comparison of core-top and modern seawater isotope data, which permits an assessment of the seasonal biases and geochemical controls on the stable isotopic compositions of G. bulloides and N. pachyderma (s.). Based on a comparison of our down-core results with similar data from the Southeast Atlantic (Cape Basin) we infer past basin-wide changes in the surface hydrography of the sub-Antarctic Atlantic. We find that millennial-scale rises in CO2,atm over the last 70 ka are consistently linked with evidence for increased spring upwelling, and enhanced summer air–sea exchange in the sub-Antarctic Atlantic. Parallel evidence for increased summer export production would suggest that seasonal changes in upwelling and air–sea exchange exerted a dominant influence on surface pCO2 in the sub-Antarctic ...