Abstract
A considerable amount of the Amazon River water that is discharged into the equatorial Atlantic is then advected northward along the shelf by the strong North Brazil Current (NBC). Being relatively fresh, this water remains in the near-surface layer and can serve as an excellent tracer for the complex and variable flow of the offshore mesoscale eddies. Both surface salinity observations and CZCS (Coastal Zone Color Scanner) imagery can be mapped to estimate the circulation patterns of the eddies. Presented here are two sets of XBT (expendable bathythermograph) sections that give the thermal structure of eddies off the Demerara Rise (6–9°N). They were occupied nearly contemporaneously with CZCS imagery obtained during October 1980 and November 1981. Several studies have shown from ship drift data, from CZCS observations, and from Geosat altimetry that, particularly during late summer and fall, the NBC is found to retroflect offshore to the east, supplying the North Equatorial Counter Current (NECC) and is associated with eddies along the coast. Good agreement is shown between the CZCS and a NAVOCEANO AXBT (airborne bathythermograph) survey during this period as well as observations of surface phytoplankton and geopotential anomaly from an earlier 1964 survey. Estimates of volume transport within the eddy structure indicate that at times the offshore retroflection during spring as well as autumn can amount to 10 × 106 m3 s−1. The pronounced eddy variability off South America is shown by comparing a number of past hydrographic surveys. These suggest that considerable spatial variability can occur as can seasonal changes in volume transport of the NBC and the associated eddy circulation.
Similar content being viewed by others
References
Boyd JD (1986) AXBT Measurements off the northeast coast of South America, fall 1985. Naval Ocean Research and Development Activity, NSTL, Mississippi (USA) Report 171. 347 pp
Boyd JD and Perkins HT (1986) AXBT Measurements off the Northeast coast of South America, spring 1985. Naval Ocean Research and Development Activity, NSTL, Mississippi (USA) Report 112. 260 pp
Bruce JG (1984) Comparison of eddies off the north Brazilian and Somali coasts. Journal of Physical Oceanography 14:825–832
Bruce JG and Kerling JL (1984) Near equatorial eddies in the North Atlantic. Geophysical Research Letters 11:779–782
Csanady GT (1985) A zero potential vorticity model of the North Brazilian Coastal Current. Journal of Marine Research 43:553–579
Didden N and Schott F (1993) Eddies in the North Brazil current retroflection region observed by Geosat altimetry. Journal of Geophysical Research 98:20,121–20,131
Gordon HR, Clark DK, Brown JW, Brown OB, Evans RH, and Broenkow WW (1983) Phytoplankton pigment concentrations in the Middle Atlantic Bight: Comparison of ship determinations and CZCS estimates. Applied Optics 22:20–36
Johns WE, Lee TN, Schott FA, Zantopp RJ, and Evans RH (1990) The North Brazil Current retroflection: Seasonal structure and eddy variability. Journal of Geophysical Research 95:22,103–22,120
Muller-Karger FE, McClain CR, and Richardson PL (1988) The dispersal of the Amazon's water. Nature 333:56–59
Richardson PL (1993) North Brazil Current retroflection eddies. Journal of Geophysical Research 99:5081–5093
Richardson PL and Walsh D (1986) Mapping climatological seasonal variations of surface currents in the tropical Atlantic using ship drifts. Journal of Geophysical Research 91:10,537–10,550
Ryther JH, Menzel DW, and Corwin N (1967) Influence of Amazon River outflow on the ecology of the western tropical Atlantic. Journal of Marine Research 25:69–83
Wilson WD, Johns E, and Molinari RL (1994) Upper layer circulation in the western tropical North Atlantic Ocean during August 1989. Journal of Geophysical Research 99:22,513–22,523
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Bruce, J.G. Near-equatorial eddies off South America. Geo-Marine Letters 15, 185–194 (1995). https://doi.org/10.1007/BF01204462
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF01204462