Sunda Shelf Seas: flushing rates and residence times

Abstract. The region of the Sunda Shelf has an average depth of approx. 48 m and is subject to many physical and biogeochemical processes with a strong impact from human activities. For the investigation of marine environmental water properties and quality, it is helpful to have an idea about exchange rates of water masses in the different parts of this region. Four numerical models, the global hydrodynamical model MPI-OM, the global hydrological model MPI-HM, the regional hydrodynamical model HAMSOM and a Lagrangian tracer model have been utilized to estimate the flushing rates and residence times in different seas on the Sunda Shelf. Using decadal averaged monthly transports, the commonly used flushing rate formula gives rates for the different months of approximately 40 to 70 days for the entire Sunda Shelf. For most parts of it (Malacca Strait, southern South China Sea, Java Sea), the results are similar, while for the Gulf of Thailand, the flushing rates amount to 80 to 170 days. The tracer model provides quite different but very detailed 3-D pictures with residence times of below 30 days to more than two years, depending on the location within the region, on the starting layer and on the season.