Thermodynamic air-sea equilibration controls carbon isotopic composition of the South Atlantic thermocline during the last glacial period

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Pinho, Taina M. L. ; Chiessi, Cristiano M. ; Campos, Marilia C. ; Portilho-Ramos, Rodrigo C. ; Martinez-Mendez, Gema ; Venancio, Igor M. ; Nascimento, Rodrigo A. ; Crivellari, Stefano ; Albuquerque, Ana L. S. ; Arz, Helge W. ; Tiedemann, Ralf ; Bahr, Andre ; Mulitza, Stefan

• Document type: Journal article
• Source: GLOBAL AND PLANETARY CHANGE; v. 229, p. 12-pg., 2023-09-06.

Abstract

Negative stable carbon isotope (813C) excursions in the marine upper water column have been related to the release of aged oceanic CO2 to the atmosphere during millennial-scale events of the last glacial called Heinrich Stadials (HS). Different driving mechanisms have been proposed to explain upper water column 813C variations. In order to fully capture the 813C inventory of the South Atlantic Central Water (SACW) we utilized high temporal-resolution thermocline-dwelling foraminiferal 813C data from three marine sediment cores located at the NW, SW, and SE portions of the South Atlantic. Our data allows a basin-wide assessment of SACW 813C millennial-scale variability. The SE- and NW-South Atlantic thermocline 813C records reveal concurrent negative excursions during most HS, which contrasts with the lack of negative excursions in the SW-South Atlantic thermocline 813C record. Considering the marked similarity between these 813C records and the local predicted dissolved inorganic carbon (813Cpred), we attribute the SACW 813C variability during HS to the local thermodynamic air-sea isotopic equilibration. Such resemblance was also observed on the long-term timescale, which suggests that thermodynamic air-sea isotopic equilibration was the main factor controlling the 813C of SACW as well. However two exceptions were observed. First, in the SW-South Atlantic, a decoupling between 813C and 813Cpred between 50 and 45 ka B.P. that we attributed to an enhanced primary productivity. Second, in the SESouth Atlantic, a decoupling between 813C and 813Cpred between 35 and 20 ka B.P. that we attributed to a northward shift of the Subtropical Front. (AU)

• FAPESP's process: 16/10242-0 - Occurrence and impact of the mega-South Atlantic Convergence Zone over the eastern South America during the last glacial period: a paleoceanographic approach
• Grantee: Marília de Carvalho Campos Garcia
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 19/10642-6 - Response of the upper water column at the origin of the Brazil Current to slowdown events of the Atlantic Meridional Ocean Circulation during the last 80 ka
• Grantee: Tainã Marcos Lima Pinho
• Support Opportunities: Scholarships in Brazil - Master
• FAPESP's process: 22/09822-2 - Improvement of analytical routines and software development for analysis of carbon and oxygen stable isotopes by gas isotope ratio mass spectrometry in single specimens
• Grantee: Stefano Crivellari
• Support Opportunities: Scholarships in Brazil - Technical Training Program - Technical Training
• FAPESP's process: 23/05764-0 - The South Atlantic on a 2°C warmer planet
• Grantee: Marília de Carvalho Campos Garcia
• Support Opportunities: Scholarships in Brazil - Generation Project
• FAPESP's process: 20/06534-0 - Abrupt changes in the deep Western Tropical Atlantic Ocean during the last two glacial periods
• Grantee: Stefano Crivellari
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 18/06790-7 - Variability of the Brazil Current and South American climate during the last glacial cycle: assessing sea-surface temperatures via Mg/Ca analyses and pulses of terrigenous sediments via X-ray fluorescence analyses
• Grantee: Marília de Carvalho Campos Garcia
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• FAPESP's process: 19/24349-9 - Assessing the effects of past and future climate change on Amazonian biodiversity (CLAMBIO)
• Grantee: Cristiano Mazur Chiessi
• Support Opportunities: BIOTA-FAPESP Program - Regular Research Grants
• FAPESP's process: 18/15123-4 - Past perspectives on tipping elements of the climate system: the Amazon Rainforest and the Atlantic Meridional Overturning Circulation (PPTEAM)
• Grantee: Cristiano Mazur Chiessi
• Support Opportunities: Research Grants - Research Program on Global Climate Change - Young Investigators - Phase 2