Intra‐ and Inter‐Annual Variability of North Brazil Current Rings Using Angular Momentum Eddy Detection and Tracking Algorithm: Observations From 1993 to 2016

Abstract

The North Brazil Current (NBC) is an intense western boundary current, which is the dominant feature of the surface circulation in the Western Tropical North Atlantic (WTNA). It flows predominantly northwestward along Brazilian northern coast and, around 6°N-8°N and 45°W, the current separates from the coast and retroflects to the east, feeding the North Equatorial Countercurrent (NECC; Garzoli et al., 2003; Johns

Volume and Heat Transports by North Brazil Current Rings

“…This value agrees with previous estimates based on satellite data, but is derived from a much longer dataset comprising 24 years of altimetry data, as opposed to the 6 and 10 years analyzed by Johns (2001 and2003, respectively). More recent studies (Meĺice andArnault, 2017, andAroucha et al, 2020), also based on longer time series of satellite data, find average formation rates similar to that of the present study.…”

“…Meĺice and Arnault (2017) provided an updated census based on almost 23 years of altimeter data and found from 2 to 7 NBC rings formed at different years, with an average of 5 rings per year. Recently, Aroucha et al (2020) applied an eddy detection algorithm based on dynamical and geometrical constraints in the NBC region for 24 years of altimetry data found an averaged shedding rate of 5 rings per year.…”

Impact of North Brazil Current rings on air-sea CO<sub>2</sub> flux variability in winter 2020

“…Freshwater from the Amazon is not just located on the shelf, but it can spread northward advected by the strong currents variability associated to the NBC rings (Reverdin et al, 2021). These rings are the largest, faster rotating and are the most energetic during boreal winter compared to other seasons (Aroucha et al, 2020).…”

“…Two of the main mechanisms driving the occurrence of the plume are the winds near the Amazon estuary that can induce along shelf transport to the Guyana plateau and the presence of NBC rings. This region is commonly crossed by several NBC rings during winter (Jochumsen et al, 2010;Johns et al, 2003;Mélice & Arnault, 2017) but it also is subject to a strong year to year variability that has linkages with the variability of the Amazon River outflow (Aroucha et al, 2020). Therefore, identifying and understanding the processes happening in 2020 should contribute to better assess the interannual variability of fCO2 as well as air-sea CO2 fluxes in the northwestern tropical Atlantic during winter.…”

“…When they reach the Lesser Antilles, they start to coalesce and disintegrate, partly due to interactions with the topography (Fratantoni & Richardson, 2006;Jochumsen et al, 2010). There is substantial variability in the number of rings shed per year, ranging from 5 (Aroucha et al, 2020;Fratantoni & Glickson, 2002;Mélice & Arnault, 2017, Goni & Johns, 2001 to 9 (Johns et al, 2003). NBC rings play a crucial role in the interhemispheric transport of salt and heat in the Atlantic Ocean and are an important part of the meridional overturning circulation (Johns et al, 2003).…”