STC Marcus was the strongest tropical cyclone anywhere within the Australian region since STC Monica in April 2006 according to the BoM. It struck Darwin at only category 2 intensity, causing widespread damage, but went on to reach category 5 on 22 March 2018 well away from land. This MODIS ocean colour image (click to expand) shows that Marcus left a distinct trail in the ocean as it tracked west near latitude 15S and turned south near longitude 108E. It appears that the winds (estimated to have reached 325km/h) and waves caused a lot of vertical mixing, bringing nutrients and the deep layer of phytoplankton up to the surface. Apart from coastal storm surge and a slight reduction of sea surface temperature along the path of the cyclone, however, other ocean impacts are not obvious. Weaker, but slower-moving cyclones have had more impact on the ocean.
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