Chuanyu Liu, Dan Huo, Zhiyu Liu, Xiaowei Wang, Cong Guan, Jifeng Qi, Fan Wang

Published in Geophysical Research Letters, FEB 2022

The barrier layer (BL) is an expansive halocline layer commonly found in the western equatorial Pacific, long been thought to inhibit entrainment of colder thermocline water into the surface mixed layer (ML), consequently facilitating the development of El Niño. But here we find frequent turbulent mixing in the BL from both direct turbulence measurements and indirect mixing estimates within an 11-year-long Argo profile data set. The observed BL mixing is as strong as in the ML, yielding effective heat transfers across the isothermal layer (IL) base. The estimated BL mixing is ubiquitous, with occurrence ranging 20%–60% spatially and peaking at around 160°W, 0°N; it occurs more frequently in La Niña than El Niño years. The BL mixing is associated with thicker ML, BL, and IL, weaker BL stratification, and lower temperature and higher salinity in the IL. How the BL mixing may impact the El Niño development deserves further exploration.

Fig. Argo-based estimates of (a) and (b) calculated over 2° × 2° boxes. (c) and calculated over 2° (longitude) × 10° (5°S–5°N) boxes, (d) monthly climatology of and , (e) monthly (black dashed) with its 13-month running mean (red), and (f) monthly for El Niño, La Niña and all years. In (d)–(f), and are calculated over 140°E−180°, 5°S–5°N (box in a) and 180°–140°W, 5°S–5°N (box in b), respectively; shading denotes 95% bootstrap confidence levels. The interannual variation-associated stds for the mean values in f are within 5%–20% (not shown).

Liu, C., Huo, D., Liu, Z., Wang, X., Guan, C., Qi, J., & Wang, F. (2022). Turbulent mixing in the barrier layer of the equatorial Pacific Ocean. Geophysical Research Letters, 49, e2021GL097690. https://doi.org/10.1029/2021GL097690