Quantifying thermohaline circulations: seawater isotopic compositions and salinity as proxies of the ratio between advection time and evaporation time

Abstract. Uncertainties in quantitative estimates of the thermohaline circulation in any particular basin are ‎large, partly due to large uncertainties in quantifying excess evaporation over precipitation and ‎surface velocities. A single nondimensional parameter, ‎γ ≡ ^q⁄_h ^x⁄_u is proposed to characterize the ‎‎strength of the thermohaline circulation by combining the physical parameters of surface ‎velocity (u), evaporation rate (q), mixed layer depth (h) and trajectory length (x). Values of γ can ‎be estimated directly from cross-sections of salinity or seawater isotopic composition (δ¹⁸O and δD). Estimates of ‎γ in the Red Sea and the South-West Indian Ocean are 0.1 and 0.02, ‎respectively, which implies that the thermohaline contribution to the circulation in the former is ‎higher than in the latter. Once the value of ‎γ has been determined in a particular basin, either q ‎or u can be estimated from known values of the remaining parameters. In the studied basins ‎such estimates are consistent with previous studies. ‎