Warm Water Paths in the Equatorial Atlantic as Diagnosed with a General Circulation Model

Abstract

Monthly mean velocity fields from a global ocean general circulation model are used to study the main circulation patterns within the upper 1200 m of the equatorial Atlantic. Some recently developed Lagrangian techniques are used to picture and quantify the routes followed in the model by distinct water mass classes, defined by their initial temperature on model transatlantic sections at 10°S and 10°N. The qualitative description in terms of equatorial pathways of this warm component of the so-called global “conveyor belt” is found coherent with the most recent circulation schemes inferred from direct measurements. Diagnostics emphasize the crucial role of the western boundary current system and that of the equatorial subsurface jets in distributing the flow in the equatorial domain, both for northward-flowing and southward-recirculating warm water masses. As the model tracer fields are constrained to remain close to the observed climatology outside the equatorial strip, the circulation calculated by the model is also shown to fairly reproduce the intensity of the net northward interhemispheric warm water exchange as inferred from direct measurements, as well as known conversions of warm water masses within the tropical Atlantic.