Coastal upwelling events, salinity stratification, and barrier layer observed along the southern coasts of Sumatra and Java

Abstract:

Coastal upwelling occurs along the southwestern coasts of Sumatra and Java due to southeasterly wind during the boreal summer monsoon. It plays an important role in the ocean surface heat balance, biogeochemical balance, coastal ecosystem and fisheries in the eastern tropical Indian Ocean. To understand the coastal upwelling system, we investigated ocean temperature and salinity variations obtained from Argo floats. During 2005-2017, several Argo floats successfully observed vertical structure of temperature and salinity near the coasts of Sumatra and Java. During the 2008 positive Indian Ocean Dipole (IOD) event, an Argo float approached Java and observed two intraseasonal-scale temperature cooling events in July and August, with significant upward movements of thermocline. During 2013-2017, two Argo floats observed temperature and salinity variations within 100 km from the southwestern coast of Sumatra. These data indicate that the Argo floats observed coastal upwelling signals along the southern coasts of Sumatra and Java. On the observational data south of Java, we found that the coastal upwelling signal can be quantitatively explained by local southwesterly alongshore wind forcing. In case southwest of Sumatra, the upwelling signals were frequently accompanied by surface low salinity and subsurface density stratification associated with local precipitation. The relationship of the local precipitation, surface-to-subsurface salinity stratification, barrier layer thickness, and mixed layer temperature variation observed during the coastal upwelling events are further presented.