Effects of Mixed Layer Depth on Phytoplankton Biomass in a Tropical Marginal Ocean: A Multiple Timescale Analysis

In open oceans, changes in mixed layer depth (MLD) may affect phytoplankton growth and biomass variations via the regulation of nutrient supply from deep waters. Estimates relationships between variability dynamics MLD remain limited, especially at different time scales. We compiled analyzed averaged euphotic-depth-integrated chlorophyll-a (IChl-a) surface (SChl-a) concentrations collected 27 cruises during period 1999–2019 tropical northern South China Sea (SCS). Seasonal differences existed both IChl-a SChl-a concentrations, with significantly high cold season. Inconsistent seasons implied that use concentration as a common indicator should be performed caution. Over past decades SCS, IChl-a, SChl-a, decreased to greater extent season than warm season, while sea temperature (SST) rose rapidly dramatically seasons. The was observed have better correlations SST time-series data. Our results highlight importance concentration, which is an overall measure responses euphotic zone conditions, could used good index for under climate change.