Marine Heatwaves in the Arabian Sea

Abstract

Abstract. Marine heatwaves (MHWs) are prolonged warm sea condition events that cause a destructive impact on marine ecosystems. The documentation of MHWs and assessment of their impacts are largely confined to a few regional seas or in global mean studies. The Indian Ocean received almost no attention in this regard despite the fact that this ocean basin, particularly the Arabian Sea, is warming at the most rapid pace among the other tropical basins in recent decades. This study shows the characteristics MHWs for the Arabian Sea during 1982–2019. Our analysis shows that the duration of MHWs exhibit a rapidly increasing trend of ~20 days/decade (1.5–2 count/decade) in the northern Arabian Sea and in the southeastern Arabian Sea close to the west coast of India; which is more than 15 fold increase in the MHW days from the early 80s'. At the same time increase in MHW frequency is ~1.5–2 count/decade i.e an increase of ~6 fold, indicating more frequent and much longer heatwave events in the recent decade. Notably, since the beginning of the satellite record, the year 2010 and 2016 saw the maximum number of heatwave days with more than 75 % of days of the pre-monsoon and summer monsoon season experienced heatwaves. The accelerated trend of the heatwave days is found to be driven by the rapid rise of the mean SST of the Arabian Sea in the recent decade. Moreover, longer heatwave days are also associated with the dominant climate modes and among them, Indian Ocean Basin mode via the decaying phase of the El-Niño is found to be the most influencing mode contributing in more than 70–80 % of observed heatwave days in this basin. Mixed layer heat budget analysis suggests significant heterogeneity in the dominant processes across the years; however, weakening of latent heat loss is in general one of the key mechanism in the genesis of most of the MHWs.

Seasonal Diversity of El Niño‐Induced Marine Heatwave Increases in the Bay of Bengal

“…The largest increase in MHW days at a rate of ～1 day per year occurred in the southern bay during winter and in the northern bay during summer (Figure S3 in Supporting Information ). Similar changes were also reported in the coastal Arabian Sea (Chatterjee et al., 2022) and tropical Indian Ocean (Saranya et al., 2022), and they were linked to the rapid increase in the mean SST in recent decades and the Indian Ocean basin‐wide warming associated with El Niño events during their decaying phase. In the BOB, the rapidly increasing MHWs are obviously caused by the frequent occurrence of El Niño events after 2010 (Figure 1d).…”

“…On a local scale, MHWs can be induced by processes such as anomalous heating at the ocean surface (Chatterjee et al., 2022; Saranya et al., 2022; Schlegel et al., 2021) or as a result of oceanic advection, mixing and vertical entrainment (Oliver et al., 2017). On the regional and global scales, large‐scale climate modes can contribute to the build‐up of MHWs through teleconnection processes, including atmospheric bridges or oceanic planetary waves, that make up the physical connection between the remote forcing of the climate modes and the local MHW‐driving processes (Holbrook et al., 2019).…”

Genesis and Trends in Marine Heatwaves Over the Tropical Indian Ocean and Their Interaction With the Indian Summer Monsoon

“…Chatterjee et al. (2022) links these coastal Arabian Sea MHWs to the increase in the mean SST in the recent decades and the Indian Ocean basin‐wide warming in response to El‐Niño events during their decaying phase.…”