Absorption coefficients of colored dissolved organic matter in the surface waters of the East China Sea

Abstract

Seasonal and spatial variations in the sea surface absorption coefficients of colored dissolved organic matter in the entire shelf of the East China Sea were studied extensively. The absorption coefficients generally showed a decreasing trend from the inner shelf near the China coast toward the offshore direction in all four seasons. The results indicate that more than 75% of the shelf waters belong to the Case 2 water category. It was ascertained that the entire absorption spectra in the UV ( lambda = 250 nm) to the Visible (lambda = 500 nm) range could not be well-described when only one single exponential decay function was employed. Four discontinuity points at wavelengths of around 250, 275, 325 and 400 nm in the log-transformed absorption spectra were noted. Based on the regressive analysis of a total of 137 absorption spectra, the mean slopes of the exponential decay constant at 250, 275, 325 and 400 nm were 0.018 +/- 0.004, 0.025 +/- 0.004, 0.015 +/- 0.002 and 0.012 +/- 0.002 nm(-1), respectively. In addition, it was found that the values of the absorption coefficients had a high linear correlation with salinity. This suggests that in terms of mixing, the concentrations of colored dissolved organic matter were mostly conservative. The finding of such a relationship provides researchers with the opportunity to obtain remotely obtain the absorption coefficients of colored dissolved organic matter by using the newly-developed Scanning Low-Frequency Microwave Radiometer (SLFMR) technique.