Double Diffusion in the Arabian Sea during Winter and Spring

Abstract

Microstructure measurements from two cruises during winter and spring 2019 documented the importance of double-diffusion processes for small-scale mixing in the upper 400 m of the open-ocean region of the eastern Arabian Sea (EAS) below the mixed layer. The data indicated that shear-driven mixing rates are weak, contributing diapycnal diffusivity (Kρ) of not more than 5.4 × 10−6 m2 s−1 in the EAS. Instead, signatures of double diffusion were strong, with the water column favorable for salt fingers in 70% of the region and favorable for diffusive convection in 2%–3% of the region. Well-defined thermohaline staircases were present in all the profiles in these regions that occupied 20% of the water column. Strong diffusive convection favorable regime occurred in ∼45% of data in the barrier layer region of the southern EAS (SEAS). Comparison of different parameterizations of double diffusion with the measurements of vertical heat diffusivity (KT) found that the Radko and Smith salt fingering scheme and the Kelley diffusive convection scheme best match with the observations. The estimates based on flux law show that the combination of downward heat flux of approximately −3 W m−2 associated with salt fingering in the thermocline region of the EAS and the upward heat flux of ∼5 W m−2 due to diffusive convection in the barrier layer region of the SEAS cools the thermocline.

Amplified vertical salinity contrasts in the northwestern tropical Pacific under ocean warming

“…Tu ranges between −180° and 180°, and since Tu values within our study area were between 45° and 90°, the conditions were conducive to the development of double diffusion (Bebieva and Timmermans, 2016). Thus, we used the diapycnal mixing coefficient Γ (Oakey, 1982;Ashin et al, 2022) to measure the dissipation ratio under double-diffusion conditions induced by saline/thermal destabilizing effects:…”

On the wall-bounded model of fingering double diffusive convection

“…2019; Ashin et al. 2022). Experiments are also challenging in the sense that two scalar components must be controlled and measured simultaneously.…”