Atmospheric Drivers of Tasman Sea Marine Heatwaves

Marine heatwaves (MHWs) can severely impact marine biodiversity, fisheries, and aquaculture. Consequently, there is an increasing desire to understand the drivers of these events to inform their predictability so that proactive decisions may be made to reduce potential impacts. In the Tasman Sea (TS), several relatively intense and broad-scale MHWs have caused significant damage to marine fisheries and aquaculture industries. To assess the potential predictability of these events, we first de-termined the main driver of each MHW event in the TS from 1993 to 2021. We found that those MHWs driven by ocean advection-approximately 45% of all events-are generally longer in duration and less intense and affected a smaller area com-pared with the remaining 55%, which are driven by air-sea heat fluxes, are shorter in duration, and are more surface intense. As ocean advection-driven events in the TS have been closely studied and reported previously, we focus here on atmospherically driven MHWs. The predictability of these events is assessed by identifying the patterns of atmospheric pressure, winds, and air- sea heat fluxes in the Southern Hemisphere that coincide with MHWs in the Tasman Sea. We found that atmospherically driven MHWs in this region are more likely to occur during the positive phase of the asymmetric Southern Annular Mode (A-SAM)-which presents as an atmospheric zonal wave-3 pattern and is more likely to occur during La Nina years. These A-SAM events are linked to low wind speeds and increased downward solar radiation in the TS, which lead to increased surface ocean tempera -tures through the reduction of mixing.

Automated summary

Marine heatwaves have significant impacts on marine biodiversity, fisheries, and aquaculture. By determining the main drivers of these events in the Tasman Sea, it was found that ocean advection and air-sea heat fluxes are the key drivers, with different characteristics in duration, intensity, and affected area. The predictability of atmospherically driven marine heatwaves is influenced by atmospheric pressure, winds, and air-sea heat fluxes, which are associated with the Southern Annular Mode and La Nina years.