Impact of internal tides on distributions and variability of Chlorophyll-a and Nutrients in the Indonesian Seas

Abstract

Internal tides (ITs) in the Indonesian seas were largely investigated and hotspots of intensified mixing identified in the straits in regional models and observations. Both of them indicate strong mixing up to 10-4cm/s even close to the surface and show that tides at spring-neap cycle cool by 0.2°C the surface water at ITs' generation sites.These findings supported the idea of strong and surfaced mixing capable of providing cold and nutrient-rich water favorable for the whole ecosystem. However, it has never been assessed through an ad-hoc study.Our aim is to provide a quantification of ITs impact on chlorophyll-a through a coupled model, whose physical part was validated against the INDOMIX data in precedent studies and the biogeochemical part is compared to in-situ samples and satellite products. In particular, explicit tides' inclusion within the model improves the representation of chlorophyll and of the analyzed nutrients.Results from harmonic analysis of chlorophyll-a demonstrate that tidal forcing modify spring/neap tides' variability on the regions of maximum concentration in correspondence to ITs' génération areas and to plateau sites where barotropic tides produce large friction reaching the surface. The adoption of measured vertical diffusivities explains the biogéochemical tracers' transformation within the Halmahera Sea and used to estimate the nutrients' turbulent flux, with an associated increase in new production of ˜25% of the total and a growth in mean chlorophyll of ˜30%. Hence, we confirm the key role of ITs in shaping vertical distribution and variability of chlorophyll as well as nutrients in the maritime continent.