Satellite observations of anomalous winter cooling in Shark Bay, Western Australia

In Shark Bay, a large inverse estuary in Western Australia, recent well-documented, warm temperature extremes had devastating effects on some of the largest seagrass beds in the southern hemisphere and caused a near collapse of important crab and scallop fisheries. Here, we provide evidence that recent extreme summer ocean temperatures have been accompanied by
previously unreported colder winter temperatures linked to anomalous synoptic conditions, and highlight the sensitivity of the Shark Bay system to shifts in the position and intensity of the subtropical high pressure ridge (STR). An analysis of Integrated Marine Observing System (IMOS) satellite sea surface temperature data and atmospheric reanalysis (ERA-Interim) indicated that in years when the STR was further south winds were stronger and more easterly in the Shark Bay region with high pressure and clear skies dominating. These conditions caused cold, dry air from the continent to blow (stronger) over the bay, cooling the shallow (<20 m depth) areas of the bay that were isolated from the ocean during winter. The converse was also true: a northward shift was related to (weaker) onshore flow with cloudier conditions resulting in warmer winter SST. Climate
models predict southward shifts of the STR, suggesting that winds may intensify and drier conditions and colder SSTs may become more common during winter months, with unknown ecological consequences.