[A-CG36] Satellite Earth Environment Observation

[ACG36-P01] Spatiotemporal Characteristics of Marine Heatwaves in Coral Reef Areas with Periodic Temperature Drops

*Po-Chun Hsu¹, Tzu-Ning Chen² (1.Center for Space and Remote Sensing Research, National Central University, Taiwan, 2.Department of Atmospheric Sciences, National Central University, Taiwan)

Keywords:Marine heatwave, Coral reef, Himawari-8/9, Taiwan

Marine heatwaves (MHWs) are one of the extreme oceanic environmental events that have gained significant attention in recent years. The occurrence of MHWs poses a severe threat to coral reef areas, as excessively warm seawater accelerates coral bleaching, thereby affecting the entire adjacent marine ecosystem. This study utilizes sea surface temperature (SST) and degree heating week (DHW) data from the NOAA Coral Reef Watch database and combines it with SST data from the geostationary Himawari satellite to assess the impact of MHWs on three important coral reef areas in Taiwan, namely Green Island, Nanwan, and Dongsha Atoll. The results show that from 2020 to 2022, MHW events had a very significant impact on these three islands. Dongsha experienced an average of 68 days of bleaching alert levels per year over these three years, while Green Island and Nanwan averaged 40 and 50 days of impact in 2020 and 2022, respectively. We attribute the marine heatwave events in the marginal seas adjacent to Taiwan to the negative phase of the Pacific Decadal Oscillation and to La Niña conditions. Additionally, we discovered that the Coral Reef Watch database's SST dataset might overlook nearshore and smaller-scale upwelling of cold water, particularly in the Green Island and Nanwan areas, where significant differences in daily SST data are observed between these two datasets. This discrepancy may be due to the periodic SST drops produced by topographic effects not being fully interpolated into the Coral Reef Watch database. Consequently, we also analyzed MHW events and coral bleaching alerts based on Himawari satellite SST data to compare with the findings from the Coral Reef Watch dataset.