Numerical simulations of seasonal changes of plankton and minerals in the north of Oman Sea using the ROMS-NPZD paired model

In this study, the seasonal changes of plankton in the north of Oman Sea have been investigated using the three-dimensional Regional Ocean Modeling System (ROMS) model. The initial conditions of the model follow the preliminary conditions as in WOA5 data with a horizontal resolution of 0.25 degrees and a time step of 300 seconds for one year. Vertical coordinate data were for 30 layers sigma levels by interpolations in the vertical direction of temperature and salinity. Due to the greater sub-model compatibility, ROMS model is coupled with Nutrient-Phytoplankton-Zooplankton-Detritus (NPZD) model. The simulation results showed that: (1) Temperature change is one of the main factors in the frequency of phytoplankton and zooplankton blooms; (2) Clock and counterclockwise Eddies, which represent the phenomenon of extra down or upwells in the Sea of Oman and the Strait of Hormuz, causes the transfer of chlorophyll from the south to the north; (3) The amount of chlorophyll is higher during winter compared to summer. It can be due to the presence of seasonal thermocline layer which prevents blooming despite the availability of nutrients; (4) The phytoplankton cncenteration changes in a period of one year shows that their maximum value is in late March and early spring, and April is the peak of zooplankton due to the increase in phytoplankton population. Moreover, the density of plankton depends mainly on mineral nutrients, therefore, the availability of minerals is often considered as a key factor in their growth and metabolism; (5) Chlorophyll content shows a positive correlation with water surface temperature in winter (r = 0.965), while a negative one in summer (r = -0.549). There is a significant difference between chlorophyll density in winter and summer (p <0.05). There was a positive correlation between amount of chlorophyll and nitrate in winter (r = 0.268) and summer (r = 0.794), which suggests a significant difference between winter and summer (for p <0.05); (6) There were good agreements between satellite observations of temperature and chlorophyll and the values measured in numerical modeling in majority of the cases.