Final answer:
A message in a bottle dropped on the western side of Australia would most likely be carried by the West Australian Current and the South Equatorial Current, potentially making landfall on the African coast or Indian Ocean islands.
Step-by-step explanation:
If you dropped a message in a bottle into the ocean on the western side of Australia, it is likely that the bottle would end up on the coast of Africa, or potentially carried towards the Indian Ocean islands, such as Madagascar or the Seychelles. This is due to the ocean currents that exist in the region.
The Indian Ocean is dominated by a current known as the South Equatorial Current that flows from east to west, pushing water towards the African continent. Furthermore, the presence of the West Australian Current would initially carry the bottle northwards, before it potentially gets caught in the broader flow of the South Equatorial Current.
The Indian Ocean Gyre, a system of circulating currents, would facilitate the bottle's journey across the ocean. As the gyre circulates clockwise, the South Equatorial Current could sweep the bottle westward towards Africa or the Indian Ocean Islands. Additionally, if the bottle reaches the southern part of the gyre, it might get caught in the Antarctic Circumpolar Current and taken further south, potentially reaching the eastern coast of Africa or even caught in a loop within the gyre, circulating for an extended period before making landfall.