Spatial distribution of turbulent diapycnal mixing along the Mindanao current inferred from rapid-sampling Argo floats

Abstract

The Mindanao Current (MC) bridges the North Pacific low-latitude western boundary current system region and the Indonesian Seas by supplying the North Pacific waters to the Indonesian Throughflow. Although the previous study speculated that the diapycnal mixing along the MC might be strong on the basis of the water mass analysis of the gridded climatologic dataset, the real spatial distribution of diapycnal mixing along the MC has remained to be clarified. We tackle this question here by applying a finescale parameterization to temperature and salinity profiles obtained using two rapid-sampling profiling Argo floats that drifted along the MC. The western boundary (WB) region close to the Mindanao Islands and the Sangihe Strait are the two mixing hotspots along the MC, with energy dissipation rate ε and diapycnal diffusivity Kρ enhanced up to ~ 10–6 W kg−1 and ~ 10–3 m2 s−1, respectively. Except for the above two mixing hotspots, the turbulent mixing along the MC is mostly weak, with ε and Kρ to be 10–11–10–9 W kg−1 and 10–6–10–5 m2 s−1, respectively. Strong mixing in the Sangihe Strait can be basically attributed to the existence of internal tides, whereas strong mixing in the WB region suggests the existence of internal lee waves. We also find that water mass transformation along the MC mainly occurs in the Sangihe Strait where the water masses are subjected to strong turbulent mixing during a long residence time.

Modern technologies and integrated observing systems are “instrumental” to fisheries oceanography: A brief history of ocean data collection

“…By staying submerged throughout their deployment, reporting their position and data every 10‐days, the path of these floats can resolve the dynamic and time‐evolving structure of mesoscale features such as boundary currents and subsurface eddies (Armi et al, 1989; Collins et al, 2013). They are integral to studying physical process such as diapycnal mixing (He et al, 2022). The Argo Program's global scope and long record has been key to quantifying the accumulation of heat in the deep ocean due to climate change (Hansen et al, 2011).…”

Spatial and Temporal Variability of Turbulent Mixing in the Deep Northwestern Pacific

“…Concomitantly, the long‐range radiation and interference of multisource internal tides result in complex dissipation distribution (Y. Wang et al., 2018, 2021). Besides the internal tides, previous studies have indicated other dynamic factors contributing to the inhomogeneous spatial distribution of mixing in the Northwestern Pacific, including parametric subharmonic instability (PSI; Qiu et al., 2012), wind‐induced near inertial motions (Jing & Wu, 2010; Jing et al., 2011; Whalen et al., 2012), mesoscale eddies (Jing et al., 2011; Whalen et al., 2018; You et al., 2021), and large‐scale currents (He et al., 2022; Liu et al., 2017; Yang et al., 2014). However, most of these results focus primarily on the upper layer, with insufficient attention given to abyssal mixing due to the lack of deep‐sea observations.…”