Vertical Structure of the Seasonal Cycle in the Central Equatorial Atlantic Ocean: XBT Sections from 1980 to 1988

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  • 1 LODYC, Paris, France
  • 2 Lamont-Doherty Geological Observatory, Palisades, New York
  • 3 ORSTOM, B.P. A5, Nouméa, Nouvelle-Calédonie
  • 4 Centre ORSTOM, IFREMER, Plouzané France
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Abstract

A set of temperature profiles from expendable bathythermographs collected from 1980 to April 1988 along two ship routes transecting the equatorial Atlantic from 11°N to 11°S is analyzed to inter the vertical structure of the annual variability of the temperature and the currents in the upper ocean.

During the average seasonal cycle, the vertical isotherm displacements occur earlier below 300 meters than near the surface at most locations within 4 degrees of the equator. At the equator the amplitude of the displacements does not decrease with depth in the upper 500 meters. This still holds down to 700 meters, but there are less data at these depths. The lead of the deeper isotherm displacements with respect to those in the upper thermocline implies that there is a contribution to the pressure forces from these layers that is not in phase with the contribution of the upper thermocline. This also suggests that the energy source of the seasonal variability is close to the surface. Dynamic height and geostrophic currents relative to 400 db are also estimated. A seasonal cycle is found on the subsurface currents, which vary by up to a factor two during the cycle.

Abstract

A set of temperature profiles from expendable bathythermographs collected from 1980 to April 1988 along two ship routes transecting the equatorial Atlantic from 11°N to 11°S is analyzed to inter the vertical structure of the annual variability of the temperature and the currents in the upper ocean.

During the average seasonal cycle, the vertical isotherm displacements occur earlier below 300 meters than near the surface at most locations within 4 degrees of the equator. At the equator the amplitude of the displacements does not decrease with depth in the upper 500 meters. This still holds down to 700 meters, but there are less data at these depths. The lead of the deeper isotherm displacements with respect to those in the upper thermocline implies that there is a contribution to the pressure forces from these layers that is not in phase with the contribution of the upper thermocline. This also suggests that the energy source of the seasonal variability is close to the surface. Dynamic height and geostrophic currents relative to 400 db are also estimated. A seasonal cycle is found on the subsurface currents, which vary by up to a factor two during the cycle.

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