Bo Qiu, Patrick L. Colin, Shuiming Chen

Published in Geophysical Research Letter, July 2021

The western tropical Pacific Ocean (WTPO) features complicated ocean circulation systems and has the warmest world open-ocean waters. Small upper ocean temperature change there can exert significant impact on the regional coral reef ecosystems. In the past three decades, moderate to severe coral bleaching events have been observed in the WTPO surrounding Palau in 1998, 2010, 2016, 2017, and 2020. Reflecting the diversity of El Niño-Southern Oscillation (ENSO) variability, the observed coral bleaching severity does not correspond simply to the amplitude of an ENSO index, such as Niño-3.4. By conducting an upper ocean temperature budget, we found the time-varying upper ocean circulation advection acted to damp the anomalous surface heat flux forcing and played critical roles in controlling the surface ocean thermal conditions around Palau. This happened either directly via the advective temperature flux convergence, or indirectly through the pre-conditioning of upper ocean thermal structures.

Fig. (a) Upper ocean circulation schematic in the western tropical Pacific Ocean. Currents shown are: Subtropical Countercurrent (STCC); North Equatorial Current (NEC); Mindanao Current (MC); Mindanao Eddy (ME); North Equatorial Countercurrent (NECC); Halmahera Eddy (HE); Indonesian Throughflow (ITF); Equatorial Undercurrent (EUC); New Guinea Coastal Undercurrent (NGCUC); South Equatorial Current (SEC); and North Queensland Current (NQC). (b) Sea surface height standard deviation map based on AVISO merged satellite altimeter data of 1993–2019. (c) Mean SST map of 1993–2019 based on OI-SST dataset of Reynolds et al. (2007). Solid thick contours denote the 28°C isotherms. (d) Correlation coefficient map of upper ocean (0–60 m) temperature variability relative to that at Palau based on ECCOv4r4 state estimate

Qiu, B., Colin, P. L., & Chen, S. (2021). Time-varying upper ocean circulation and control of coral bleaching in the western tropical Pacific. Geophysical Research Letters, 48, e2021GL093632. https://doi.org/10.1029/2021GL093632