EGU22-8018, updated on 22 May 2022
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Increased zonal δ13C gradient in the deep South Atlantic after the Mid-Brunhes Transition

João Ballalai1,2, Thiago Santos1, Rodrigo Nascimento1, Igor Venancio1,3, Patrícia Piacsek4, Bruna Dias5, André Belem6, Karen Costa7, Natalia Vázquez Riveiros2, and Ana Luiza Albuquerque1
João Ballalai et al.
  • 1Geochemistry Department, Fluminense Federal University, Niterói, Brazil
  • 2UMR Geo-Ocean, IFREMER, Brest, France
  • 3MARUM - Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany
  • 4Radioecology and Global Change Laboratory (LARAMG), Biophysics and Biometry Department, Rio de Janeiro State University, Rio de Janeiro, Brazil
  • 5School of Arts, Sciences and Humanities, University of São Paulo, São Paulo, Brazil
  • 6Oceanographic Observatory, Fluminense Federal University, Niterói, Brazil
  • 7South Atlantic Paleoceanography Laboratory, Oceanographic Institute, University of Sao Paulo, Sao Paulo, Brazil

The climate system experienced several periodic oscillations over the last ca. 800 ka known as glacial-interglacial (G-IG) cycles. Disruptions of the global carbon cycle were evident on this time scale, promoting fluctuations in the atmospheric CO2 concentration leading to global climate variability. In the more recent interglacials, both Antarctic temperatures and atmospheric CO2 concentrations are significantly higher than in the previous “lukewarm interglacials” (ca. 800 – 430 ka) before the Mid-Brunhes Transition (MBT). Changes in the Atlantic Meridional Overturning Circulation (AMOC) and deepwater formation rate around Antarctica have been invoked to explain a 30 ppm increase in the atmospheric CO2 ­during post-MBT interglacial periods. Deepwater variability is tightly coupled to the ventilation of CO2 in the Southern Ocean by atmospheric and oceanic connections, contributing to carbon storage in the deep ocean and the atmospheric CO2. Here, we present a new 770 ka benthic foraminifera δ13C record from sediment core GL-854 retrieved from the western South Atlantic (WSA) at 2200 m water depth. We compare our record with published δ13C data from the eastern margin to investigate the zonal gradient variability of the North Atlantic Deep Water (NADW) in the deep South Atlantic basin. WSA δ13C variability and absolute values strongly mimic the North Atlantic mid-depth record at the NADW formation region. This similarity is interpreted as NADW preferentially carrying a modified signal through the deep western boundary current towards the WSA (rather than towards the eastern margin) after the MBT. The δ13C gradient based on the difference between benthic foraminifera C. wuellerstorfi from both margins (Δδ13Cw-e) gradually increases after a transitional period between ca. 400 ka to 300 ka towards the Holocene. We suggest that the mechanism behind this long-term increasing trend on the Δδ13Cw-e record post-MBT is the result of enhanced production of North Component Water due to Agulhas Leakage intensification driven by reduced sea-ice extent after the MBT. Furthermore, reduced sea-ice extent decreases the Antarctic Bottom Water density and formation in the Southern Ocean, contributing to the deepening of the AMOC during post-MBT interglacial periods. Our interpretation proposes a framework connecting sea-ice and ocean-atmosphere dynamics to deepwater geometry within the South Atlantic basin, which ultimately contributed to the climate change observed across the MBT.

How to cite: Ballalai, J., Santos, T., Nascimento, R., Venancio, I., Piacsek, P., Dias, B., Belem, A., Costa, K., Vázquez Riveiros, N., and Albuquerque, A. L.: Increased zonal δ13C gradient in the deep South Atlantic after the Mid-Brunhes Transition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8018,, 2022.