High-resolution Marine Heat Wave Mapping in Australasian waters using Himawari-8 SST and SSTAARS data

Marine heat waves (MHWs) have significant ecological and economic impact. Consequently, there is a pressing need to map the temporal and spatial patterns of MHWs, for both historical and near real-time events. Satellite remote sensing of Sea Surface Temperature (SST) provides fundamental data for the mapping of MHWs. This study used high-resolution Himarwari-8 SST and the Sea Surface Temperature Atlas of the Australian Regional Seas (SSTAARS) data, which have a spatial resolution of ~ 2 km, to map recent and near real-time MHW events in waters around Australasia. The high-resolution MHWs mapping has identified two broad areas of MHW hotspots between August 2015 and February 2019. Firstly, the Tropical Warm Pool region (including the GBR and part of the Coral Sea) between the maritime continent and the Australian continent was affected by strong and prolonged MHW conditions for the greater part of 2016. The unusually strong 2015-16 El Niño event was believed to be the primary driver for the MHWs, and the air-sea heat flux rather than the ocean advection was the main local process controlling the heat budget. Secondly, the south-east of the study area (including Australia’s south-east coast, the Tasman Sea and New Zealand’s east coast) suffered severe MHWs in 2015-16, 2017-18 and 2018-19. ENSO played little role in the generation of the MHWs in this region. Instead, the MHWs in the western part of this region were more likely due to the extensive heat transported by the East Australia Current; while in the eastern part, the MHWs were more likely due to more local climate modes such as SAM. This mapping has not only enhanced our understanding of the spatio-temporal characteristics of several previously documented MHWs but also identified and mapped several previously undocumented MHWs. The case study in the Beagle Marine Park proved the values of Himawari-8 SST and SSTAARS data in mapping fine details of MHWs in a small area, which are not possible for broad-scale SST data such as the Optimal Interpolated SST (OISST) which has a spatial resolution of ~ 25 km. The case study revealed much stronger MHW influence in the shallow waters east of the marine park where most of the important rocky reef habitats exist. The near-real time MHWs mapping shows that both the GBR and the Coral Sea marine parks were experiencing MHW conditions in early March 2020, with most affected areas having strong MHW class.