A General Circulation Model of the Indian Ocean at 9000 Years B.P.

Abstract

A general circulation model of the Indian Ocean was run using monthly average wind and thermal forcing from an atmospheric model for conditions appropriate for today and 9000 years B.P. The present‐day forcing is poor during the equinoxes but representative of actual conditions during the summer and winter. We therefore concentrate on discussing the simulated ocean circulation during these seasons. It is shown that the upper ocean circulation of the entire northern Indian Ocean was strengthened by 15–30% at 9000 years B.P. relative to today, with the largest effect in the Arabian Sea and south of India. The surface equatorial flow is weaker in the boreal summer, but the stronger easterly winds through much of the year lead to a bigger thermocline slope along the equator. This, in turn, leads to a stronger undercurrent but weaker equatorial upwelling than at present. The sea surface temperatures during the boreal winter are found to be generally 1°–2°C cooler over the Indian Ocean but mostly 1°C warmer in the summer. The Arabian Sea was, however, cooler at 9000 years B.P. The simulation supports quantitatively the palaeoclimate record.