Glacial δ13C decreases in the western South Atlantic forced by millennial changes in Southern Ocean ventilation
Marília C. Campos1, Cristiano M. Chiessi1, Ines Voigt2, Alberto R. Piola3,4, Henning Kuhnert2, and Stefan Mulitza21School of Arts, Sciences and Humanities, University of São Paulo, São Paulo, 03828-000, Brazil 2MARUM – Center for Marine Environmental Sciences, University of Bremen, Bremen, 28359, Germany 3Servicio de Hidrografia Naval (SHN), Buenos Aires, C1270ABV, Argentina 4Dept. Ciencias de la Atmósfera y los Océanos, FCEN, Universidad de Buenos Aires, C1428 EHA, and Instituto Franco–Argentino sobre Estudios de Clima y sus Impactos, CNRS/CONICET, C1428EGA, Argentina
Received: 01 Jun 2016 – Accepted for review: 14 Jun 2016 – Discussion started: 20 Jun 2016
Abstract. Abrupt millennial–scale climate change events of the last deglaciation (i.e., Heinrich Stadial 1 and the Younger Dryas) were accompanied by marked increases in atmospheric CO2 presumably originated by outgassing from the Southern Ocean. However, information on the preceding Heinrich Stadials during the last glacial period is scarce. Here we present stable carbon isotopic data (δ13C) from two species of planktonic foraminifera from the western South Atlantic that reveal major decreases (up to 1 ‰) during Heinrich Stadials 3 and 2. These δ13C decreases are most likely related to millennial–scale periods of intensification in Southern Ocean deep water ventilation presumably associated with a weak Atlantic meridional overturning circulation. After reaching the upper water column of the Southern Ocean, the δ13C depletion would be transferred equatorward via central and thermocline waters. Together with other lines of evidence, our data are consistent with the hypothesis that the CO2 added to the atmosphere during abrupt millennial–scale climate change events during the last glacial period also originated in the ocean and reached the atmosphere by outgassing from the Southern Ocean. The temporal evolution of δ13C during Heinrich Stadials in our records is characterized by two relative minima separated by a relative maximum. This “w–structure” is also found in North Atlantic and South American records, giving us confidence that such structure is a pervasive feature of Heinrich Stadial 2 and, possibly, also Heinrich Stadial 3.
Campos, M. C., Chiessi, C. M., Voigt, I., Piola, A. R., Kuhnert, H., and Mulitza, S.: Glacial δ13C decreases in the western South Atlantic forced by millennial changes in Southern Ocean ventilation, Clim. Past Discuss., doi:10.5194/cp-2016-59, in review, 2016.