Controlling factors of latitudinal distribution of dissolved organic matter in the upper layers of the Indian Ocean

We studied chromophoric (CDOM) and fluorescent (FDOM) dissolved organic matter (DOM) and dissolved organic carbon in surface waters to determine the factors controlling the geographical distribution of DOM along two meridional transects in the Indian Ocean. For CDOM, we calculated the absorption coefficients, spectral slope, and absorption coefficient ratio from the observed absorption spectra. For FDOM, we calculated the biological (BIX) and humification (HIX) indices from the excitation emission matrices (EEMs); parallel factor analysis of the EEMs identified three fluorescent components, i.e., two humic-like and one protein-like. Using these DOM parameters, a factor analysis extracted fewer latent variables than the observed variables to account for the geographical distributions. We obtained three factors (F1, F2, and F3), which explained 84