Item

Abstract

The frequent occurrence of intense marine heat waves (MHWs) in recent decades, which is thought to be driven by climate change, is a big concern for the sustainability of marine biodiversity and our well-being. MHWs associated with Benguela Nino and Ningaloo Nino are studied extensively for their large impacts on the marine ecosystems in those upwelling regions. On the western Indian Ocean, the Arabian Sea has experienced a number of MHWs, including a particularly severe event in 2019 that lasted for several months and had significant impacts on the marine ecosystems in the region. In this study, we investigated the MHWs in the Agulhas retroflection region of the southwestern Arabian Sea off the coast of South Africa. In 2021, unusual fish mortality was reported in the Eastern Cape coastal regions of South Africa. Preliminary investigations pointed to a large deviation in ocean temperature (~12C) in those coastal regions, leading to fish mortality and fish washing up ashore. Based on a sea surface temperature index from that region, six strong events are identified post-1982. The 2021 event was found to be one of the strongest in the record, second only to the 2015-16 event in terms of cumulative intensity, maximum intensity, and duration of the heatwave. The remote influence from the tropical Pacific seems to play a role in the development of MHWs in the Agulhas retroflection region through modulation of the local processes.