Contrasting Heat Budget Dynamics During Two La Niña Marine Heat Wave Events Along Northwestern Australia

Abstract

Two marine heat wave events along Western Australia (WA) during the alternate austral summer periods of 2010/2011 and 2012/2013, both linked to La Niña conditions, severely impacted marine ecosystems over more than 12° of latitude, which included the unprecedented bleaching of many coral reefs. Although these two heat waves were forced by similar large‐scale climate drivers, the warming patterns differed substantially between events. The central coast of WA (south of 22°S) experienced greater warming in 2010/2011, whereas the northwestern coast of WA experienced greater warming in 2012/2013. To investigate how oceanic and atmospheric heat exchange processes drove these different spatial patterns, an analysis of the ocean heat budget was conducted by integrating remote sensing observations, in situ mooring data, and a high‐resolution (∼1 km) ocean circulation model (Regional Ocean Modeling System). The results revealed substantial spatial differences in the relative contributions made by heat advection and air‐sea heat exchange between the two heat wave events. During 2010/2011, anomalous warming driven by heat advection was present throughout the region but was much stronger south of 22°S where the poleward‐flowing Leeuwin Current strengthens. During 2012/2013, air‐sea heat exchange had a much more positive (warming) influence on sea surface temperatures (especially in the northwest), and when combined with a more positive contribution of heat advection in the north, this can explain the regional differences in warming between these two La Niña‐associated marine heat wave events.

Insights into projected changes in marine heatwaves from a high-resolution ocean circulation model

“…MHWs can also increase the likelihood of ecosystem changes through mechanisms other than thermal stress. Reported ecological and economic impacts of recent MHW events include local extinction of mangrove and kelp forests 2 , coral bleaching [3][4][5] , elevated mortalities of invertebrates 6 , fishes, seabirds 7 , and marine mammals, and invasions of non-native species 8 . These changes have altered global biodiversity and caused societal impacts 9 .…”

Advancing the theory and applications of Lagrangian Coherent Structures methods for oceanic surface flows

“…furthermore, the resilience of these ecosystems [Botsford et al, 2009;Kool et al, 2011]. In Western Australia, for example, strong recent coral reef bleaching events is in part due to the horizontal advective transport of heat [Xu et al, 2018].…”

Air-Sea Heat Flux Variability in the Southeast Indian Ocean and Its Relation With Ningaloo Niño

“…Recently, Kataoka et al (2017) calculated the mixed layer temperature balance associated with Ningaloo Niño events and found that shortwave radiation contributes to the coastal warming in both locally and non-locally amplified modes due to the warming produced by the climatological surface heat flux enhanced by the shallow mixed-layer depth (MLD) anomaly during the onset. Moreover, Xu et al (2018) compared the difference in SST warming patterns between the 2012/2013 event with the 2010/2011 event and found that the difference in the relative importance of surface heat fluxes and heat advection between the two events is mostly responsible for the different spatial distribution of the warming.…”