In the region around the Gulf of Carpentaria, northern Australia, significant seasonal mass changes take place both in land and sea. The land shows increasing hydrological mass during the austral summer. The ocean within the gulf also shows significant mass increase in summer due to seasonal winds, and the peak comes a few months earlier than on land. We study seasonal gravity changes in this region with satellite data. We also use ground GNSS stations around the gulf to study seasonal surface displacements. Insufficient spatial resolution of satellite gravimetry makes it difficult to discriminate the oceanic mass changes from those on land surrounding the ocean. Vertical surface movements are not useful for separating the two, either, because the coastal stations subside both by the oceanic and terrestrial mass increases. Here we demonstrate the importance of horizontal crustal movements, sensitive to the azimuth of the dominant load, by showing their direction reversals within summer as the dominant load switches from ocean to land. This study would serve as a model case for interpreting complicated seasonal surface deformation caused by multiple seasonal loads with phase shifts, often seen in coastal areas in the world.
 

GNSS,Gulf of Carpentaria,seasonal gravity changes,horizontal displacement