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

Type Article
Acceptance Date 2021-01 IN PRESS
Language English
Author(s) Olivier Léa1, Boutin JacquelineORCID1, Reverdin Gilles1, Lefèvre Nathalie1, Landschützer PeterORCID2, Speich Sabrina3, Karstensen JohannesORCID4, Ritschel MarkusORCID2, Wanninkhof Rik5
Affiliation(s) 1 : LOCEAN-IPSL, Sorbonne Université-CNRS-IRD-MNHN, Paris, France
2 : Max Planck Institute for Meteorology, Hamburg, Germany
3 : Laboratoire de Météorologie Dynamique, ENS-Ecole Polytechnique-CNRS-Sorbonne Université, Paris, France
4 : GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany
5 : Atlantic Oceanographic & Meteorological Laboratory of NOAA, Miami, USA
Source Biogeosciences (1726-4189) (Copernicus GmbH) In Press
DOI 10.5194/bg-2021-269
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.

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Olivier Léa, Boutin Jacqueline, Reverdin Gilles, Lefèvre Nathalie, Landschützer Peter, Speich Sabrina, Karstensen Johannes, Ritschel Markus, Wanninkhof Rik Impact of North Brazil Current rings on air-sea CO2 flux variability in winter 2020. Biogeosciences IN PRESS. Publisher's official version : https://doi.org/10.5194/bg-2021-269 , Open Access version : https://archimer.ifremer.fr/doc/00738/85015/