MEPS 384:69-82 (2009)  -  DOI: https://doi.org/10.3354/meps08013

ABSTRACT: We examined a 32 mo continuous record of the flux of diatoms, silicoflagellates and bulk components collected between November 2000 and July 2003 at the pelagic mooring site Java Mooring (JAM), off southern Java in the tropical southeastern Indian Ocean. Temporal variations in the flux mainly reflected the dynamics of monsoon-driven seasonality of oceanographic and atmospheric conditions. Highest diatom fluxes coincided with the SE monsoon season during La Niña in September 2001, with the NW monsoon season in February/March 2003 and with the early SE monsoon season in 2003. Enhanced fluxes of diatoms, opal and organic carbon toward the end of the NW monsoon season are related to riverine nutrient inputs and the subsequent development of diatom-dominated phytoplankton blooms. During the SE monsoon season, the entrainment of nutrients from the subsurface into surface waters, due to upwelling, enhanced flux. A highly diverse diatom community characterized the fluxes throughout the sampling period. Several pelagic, warm-water species of the genus Nitzschia, accompanied by Thalassionema nitzschioides var. parva and T. nitzschioides var. inflata, dominated during periods of strong stratification, high sea surface temperature and low surface water productivity. The simultaneous occurrence of the pelagic Azpeitia tabularis, Fragilariopsis doliolus and Planktoniella sol and the coastal planktonic diatoms Actinocyclus curvatulus and Thalassiosira oestrupii var. venrickae reveals the intermingling of water masses of moderate-to-low nutrient content. Coastal upwelling diatoms Thalassionema nitzschioides var. nitzschioides and resting spores of Chaetoceros spp. occur most abundantly during the NW monsoon season. The diatom assemblage at the JAM site responded, with slight changes, to El Niño/Southern Oscillation occurrence. The co-occurrence of diatom species with different ecological affinities mirrors the fact that the JAM site was located in a region with large hydrographic variability over short time intervals.

KEY WORDS: Diatoms · Particle fluxes · Monsoon · Upwelling · Indian Ocean · Indonesian Archipelago