Cross-gyre transport by North Brazil Current rings

William E. Johns, Rainer J. Zantopp, Gustavo J. Goni

Research output: Contribution to journalArticle

47 Scopus citations

Abstract

Recent observations collected as part of the North Brazil Current Rings Experiment are used to assess the role played by NBC rings in tropical to subtropical cross-gyre transport in the Atlantic Ocean. During the course of the 20 month experiment, four different NBC Rings were surveyed by ships and twelve additional rings were identified by moored current meters and temperature/salinity recorders. Of the total of 16 rings observed, four were subsurface-intensified rings with little or no surface signal. Except for these subsurface rings, generally good agreement was found in the identification of NBC rings during the experiment by various techniques including satellite altimetry, ocean color, and inverted echo sounders. The observations of water properties in the ring cores provided by the in-situ temperature and salinity measurements are used to estimate the trapped core volumes of South Atlantic water in the rings. Based on these new measurements we estimate a ring formation rate of 8-9 rings per year, with no apparent seasonal variation in the formation rate. However, the surface rings show a seasonal cycle in their vertical penetration and associated trapped core volumes. Deeper rings tend to occur in fall and early winter, while shallower rings occur in spring and summer. The subsurface rings are usually smaller in diameter than the surface rings (average radius of maximum velocity 100 km versus 130 km), but have a thicker layer of trapped South Atlantic water and consequently a larger transport per ring. The average ring-induced transport including all ring types is about 1.1 Sv per ring, leading to an estimate of 9.3 Sv for the total annualized ring transport. This value is nearly twice that of most previous estimates, and suggests that NBC rings could account for more than half of the northward transport in the warm limb of the Atlantic meridional overturning cell.

Original languageEnglish (US)
Pages (from-to)411-441
Number of pages31
JournalElsevier Oceanography Series
Volume68
Issue numberC
DOIs
StatePublished - Dec 1 2003

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ASJC Scopus subject areas

  • Oceanography

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