Self-organising maps reveal distinct spatial and temporal patterns in the build-up of marine heatwaves in the Tasman Sea

Abstract Marine heatwaves (MHWs) pose a significant threat to marine ecosystems and economies. Predicting MHWs is essential for mitigating their impact, but remains a challenge. Despite considerable progress having been made in understanding the regional-scale drivers of MHWs, a significant knowledge gap remains when it comes to understanding the synoptic-scale processes associated with these events. In this study, we used self-organising maps to identify the synoptic-scale atmospheric and oceanic patterns associated with MHWs identified in four sub-regions of the Tasman Sea between 1985 and 2014. Our results reveal patterns associated with recurring, as well as distinct extreme warming events. We show that anomalous atmospheric influence is consistently present during MHWs and that the two most recurring patterns are linked to a La Niña climate phase. Distinct synoptic air-sea patterns are also identified in the 1997/98 El Niño event. Furthermore, we identify a ‘reservoir’ of warm subsurface temperatures from 2000-2014, during which MHW frequency increased two-fold. Importantly, we have identified patterns of persistent anomalous conditions before the onset of MHWs with timescales on the order of days for atmospheric conditions and weeks to months for oceanic conditions, providing valuable insight into MHW predictors. These findings highlight the importance of understanding synoptic-scale drivers of MHWs and timescales of recurring patterns for MHW prediction. The temporal variability observed in the lead-up to MHWs underscores the potential significance of factors such as surface-layer temperature and sea-level anomalies in capturing longer-term warming trends, likely influenced by sustained atmospheric stress and oceanic dynamics, whilst atmospheric conditions at onset precipitate the transition to the extreme warming thresholds.