Interannual variability of the lower trophic ecosystem in the Ulleung Basin, East Sea: an ERSEM box model study

Abstract

An ERSEM box model was modified and applied to study the dynamics of the lower trophic ecosystem in the Ulleung Basin, East Sea. A simple 2-layer structure was forced by the changing mixed layer and insolation. Nutrients were supplied to the upper box by two processes: entrainment and diffusive mixing across the interface. Observational data were used to run 13-years long simulations from 2000 to 2012. The model results were in a reasonable agreement with the temporal variability of SeaWiFS-MODIS/Aqua-merged chlorophyll-a data. However, the timing of spring and fall bloom was earlier and chlorophyll-a concentration in winter was lower than the observed data. We compared the interannual variability of mixed layer depth and that of chlorophyll-a contrasting two years, 2008 and 2010, which had the deepest and shallowest winter mixing respectively during the period. A sensitivity analysis with varying mixed layer depth has also been performed to understand the role of winter mixing associated with nutrient and light availability of phytoplankton. Diatoms and dinoflagellates were more sensitive to the winter mixing than other groups.e upper box by two processes: entrainment and diffusive mixing across the interface. Observational data were used to run 13-years long simulations from 2000 to 2012. The model results were in a reasonable agreement with the temporal variability of SeaWiFS-MODIS/Aqua-merged chlorophyll-a data. However, the timing of spring and fall bloom was earlier and chlorophyll-a concentration in winter was lower than the observed data. We compared the interannual variability of mixed layer depth and that of chlorophyll-a contrasting two years, 2008 and 2010, which had the deepest and shallowest winter mixing respectively during the period. A sensitivity analysis with varying mixed layer depth has also been performed to understand the role of winter mixing associated with nutrient and light availability of phytoplankton. Diatoms and dinoflagellates were more sensitive to the winter mixing than other groups.