Short Term Variability Of Hydrogen-Peroxide In Surface Oceans

This study reports on several of the factors affecting the short term variability of hydrogen peroxide in surface oceans. A major pathway in the formation of H$\sb{2}$O$\sb{2}$ in surface waters is thought to be the in situ photochemical formation of H$\sb{2}$O$\sb{2}$ via humic substances. The photochemical rate of formation of H$\sb{2}$O$\sb{2}$ was studied in several waters with varying concentrations of natural organic carbon, 0.2 to 17 mg C L$\sp{-1}$. The results of this study indicated that the rate of formation of hydrogen peroxide is related to the concentration of humic substances as measured by dissolved organic carbon and absorbance at wavelengths $\u3e295$ nm.To quantitatively describe the photochemical formation of hydrogen peroxide, it was also necessary to obtain the quantum yield at various wavelengths. The apparent quantum yield was determined at individual wavelengths and over spectral regions. All of the waters studied showed the same general trend, i.e. a gradually decreasing apparent quantum yield with increasing wavelength.The impact of marine rain on surface ocean H$\sb{2}$O$\sb{2}$ concentration was studied in several oceanic environments. It was found that the concentration of H$\sb{2}$O$\sb{2}$ is higher in marine rain than rain collected over land. It was also found that the concentration of H$\sb{2}$O$\sb{2}$ in marine rain was about two orders of magnitude higher, approximately 10-80 uM, than surface ocean concentrations, 0.05-0.1 uM. Therefore, rain may have a substantial impact on the surface ocean H$\sb{2}$O$\sb{2}$ concentration, the magnitude of the affect largely dependent on the extent of mixing in the area of the rain.A continuous analyzer for determining H$\sb{2}$O$\sb{2}$, fluorescence and chlorophyll was developed and used, and the three variables measure in coastal, shelf-break and open ocean environments. Wide fluctuations occurred in all three variables in the coastal waters studied. As expected, open ocean environments did not show the wide variations in any of the variables. Decomposition rates of H$\sb{2}$O$\sb{2}$ were measured in several coastal environments and were very fast when compared to open ocean environments. Although the processes leading to the decomposition of H$\sb{2}$O$\sb{2}$ were not studied, it is clear that these processes control the concentration of H$\sb{2}$O$\sb{2}$ in coastal environments. (Abstract shortened with permission of author.