Spatial variation of the annual cycle of temperature in the Patagonian shelf between 40 and 50° of south latitude

Abstract

This paper analyses the geographic and seasonal variation of depth-integrated water temperature in the region of the Argentinian shelf extending between 40 and 50°S. The data used were taken from more than 1300 oceanographic stations; they were averaged in a network of 1° × 1° and fitted by least squares to a mean value plus a co-sinusoidal signal. The main characteristics of amplitude and phase of the annual signal are explained with a one-dimensional model which shows that the seasonal cycle depends basically on local conditions (water depth and seasonal variation of surface heat flux), and that horizontal advection and diffusion play only a secondary role. On the other hand, the annual mean value of temperature depends on the mean heat flux through the surface and on horizontal advection, which is what prevents temperature from increasing as a consequence of a net gain of heat in the air-sea interface. From the observed data of mean temperature a geostrophic field of velocities was calculated and then modified so as to satisfy the equation of heat conservation. The obtained circulation coincides acceptably with other estimates and observations carried out in the area. It consists of a flux in the N-NE direction, with a mean velocity of the order of 2 cm s −1, which enters the area under study with a temperature 4°C lower than when it leaves the northern frontier.