Multi-year marine cold-spells off the west coast of Australia and effects on fisheries

Ocean temperature variability off the west coast of Australia is affected by the El Nino Southern Oscillation from the Pacific, the Indian Ocean Dipole, the Southern Annular Mode, and the regional air-sea coupling mode - the Ningaloo Nino. The modes of climate variability affect the strength of the Leeuwin Current, a warm, polewardflowing eastern boundary current, and air-sea heat exchanges off the coast, impacting on the upper ocean heat balance and sea surface temperature (SST) variability. After the unprecedented 2010-2011 Ningaloo Nino (extreme marine heatwave) event, the region experienced more marine heatwaves in the following two austral summers, before SST off the coast eventually switched to a multi-year cold phase. This marine cold-spell (MCS) commenced with the 2015-16 El Nino and continued to 2019, when the Nino-4 W region SST was warmed up and Leeuwin Current was weakened. The upper ocean heat content in the southeast Indian Ocean was lowered (thermocline being elevated), due to the reduction of the Indonesian Throughflow transport, and alongshore northward winds strengthened during this period, which allowed thermocline waters to be more efficiently entrained into the surface layer to cool the SST. Thus, several factors might have contributed in the multi-year MCSs. The MCSs was associated with increased primary production in the Leeuwin Current and helped the recovery of benthic species of local fisheries such as Roe's abalone, saucer scallops and Shark Bay's blue swimmer crabs that were significantly affected by the damaging heat stress during the 2011-2013 marine heatwave period.

Automated summary

Ocean temperature variability off the west coast of Australia is influenced by various climate variability modes, with a shift to a multi-year cold phase following the unprecedented Ningaloo Nino event. This marine cold-spell has facilitated the recovery of local fisheries species impacted by previous marine heatwaves.