Preprints
https://doi.org/10.5194/bg-2021-269
https://doi.org/10.5194/bg-2021-269

  30 Nov 2021

30 Nov 2021

Review status: this preprint is currently under review for the journal BG.

Impact of North Brazil Current rings on air-sea CO2 flux variability in winter 2020

Léa Olivier1, Jacqueline Boutin1, Gilles Reverdin1, Nathalie Lefèvre1, Peter Landschützer2, Sabrina Speich3, Johannes Karstensen4, Markus Ritschel2, and Rik Wanninkhof5 Léa Olivier et al.
  • 1LOCEAN-IPSL, Sorbonne Université-CNRS-IRD-MNHN, Paris, France
  • 2Max Planck Institute for Meteorology, Hamburg, Germany
  • 3Laboratoire de Météorologie Dynamique, ENS-Ecole Polytechnique-CNRS-Sorbonne Université, Paris, France
  • 4GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany
  • 5Atlantic Oceanographic & Meteorological Laboratory of NOAA, Miami, USA

Abstract. The North Brazil Current (NBC) flows northward across the Equator, passes the mouth of the Amazon River, and forms large oceanic eddies near 8° N. We investigate the processes driving the variability of air-sea CO2 fluxes at different scales in early 2020 in the region [50° W–59° W–5° N–16° N]. This region is a pathway between the equatorial and North Atlantic Ocean and was surveyed during the EUREC4A-OA/ATOMIC campaign. In-situ surface fugacity of CO2 (fCO2), salinity and temperature combined with maps of satellite salinity, chlorophyll-a and temperature highlight contrasting properties in the region. In February 2020, the area is a CO2 sink (−1.7 TgC.month−1), previously underestimated by a factor 10. The NBC rings transport saline and high fCO2 water indicative of their equatorial origins and are a small source of CO2 at regional scale. Their main impact on the variability of biogeochemical parameters is through the filaments they entrain into the open ocean. During the campaign, a nutrient-rich freshwater plume from the Amazon River is entrained from the shelf up to 12° N and caused a phytoplankton bloom leading to a significant carbon drawdown (~20 % of the total sink). On the other hand, saltier filaments of shelf water rich in detrital material act as strong local sources of CO2. Spatial distribution of fCO2 is therefore strongly influenced by ocean dynamics south of 12° N. The less variable North Atlantic subtropical water extends from Barbados northward. They represent ~60 % of the total sink due to their lower temperature associated with winter cooling and strong winds.

Léa Olivier et al.

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Léa Olivier et al.

Léa Olivier et al.

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Short summary
We investigate the impact of the eddies and of the Amazon River water on the CO2 air-sea fluxes to better characterize the ocean carbon sink in winter 2020. The region is a strong CO2 sink, underestimated in climatology by a factor 10 due to a lack of data and understanding of the processes responsible for the variability of ocean carbon parameters. The CO2 absorption is mainly driven by freshwater from the amazon entrained away from the coast by eddies, and by the winter seasonal cooling.
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