Assessing the variability in chlorophyll-a and covariates in Arabian Sea using ARIMAX model and wavelet coherence approaches

The Arabian Sea is one of the most productive regions in the global ocean. In the present study, relationship of Chl-a with environmental parameters have been studied in the Arabian Sea. The Autoregressive Integrated Moving Average with explanatory variable (ARIMAX) models namely ARIMAX (1,0,1), ARIMAX (2,0,3), ARIMAX (5,0,4), ARIMAX (7,0,6), ARIMAX (8,0,8), ARIMAX (11,0,9) and ARIMAX (12,0,11) were tested. After evaluation, ARIMAX (2,0,3) and ARIMAX (12,0,11) were identified as the best fit models and can be used to model Chl-a in the Arabian Sea. Wavelet coherence approach was applied to understand the relationship of Chl-a with rainfall, sensible heat flux, remote sensing at 443 nm, aerosol optical depth, black carbon deposition and calcite concentration. Two strips of high correlation in the frequency bands of 4–8 and 8–16 significant at 95% level were observed in each wavelet coherence diagram except for remote sensing reflectance at 443 nm and sensible heat flux.