Aragonite saturation state in a monsoonal upwelling system off Java, Indonesia

• Ωarag in a monsoonal eastern boundary upwelling system was presented.
• Effects on Ωarag from physical transport and biological production were separated.
• Influence from interannual upwelling variability modulated by IOD was estimated.

Aragonite saturation state (Ωarag) and its influence from upwelling along the southern coast of Java, Indonesia were examined using carbonate and hydrographic data collected from 22 September to 2 October 2013. Results showed that sea surface Ωarag was lower in the upwelling area (2.97–3.44) than in the nonupwelling area (3.45–3.57), with the lowest value in the eastern part of the study area. We used a two end-member mixing model to separate contributions on Ωarag from two processes associated with upwelling: physical transport vs. biological production. Results indicated that physical transport induced at least a Ωarag decrease of 0.8, whereas biological production caused Ωarag to increase by up to 0.6. Additionally, the influence on Ωarag of interannual upwelling variability modulated by the Indian Ocean Dipole (IOD), a unique climate phenomenon in the Indian Ocean, was roughly estimated. We argue that the effect of interannual upwelling variability modulated by IOD events was possibly larger than what was imposed on Ωarag by increasing atmospheric CO2 levels over the past decade.