The rate of photoreductive dissolution of manganese oxide in eastern Caribbean waters appears to be relatively rapid with an approximate linear dependency of dissolution rate on organic content of these waters. From the magnitude of derived absolute dissolution rates it would appear that reductive rather than oxidative processes should dominate transformations of manganese in surface waters though further insight into the reactivity of ''naturally occurring'' oxides is needed. Oxidation of Mn(II) added to surface water samples is observed and occurs at rates between those observed for coastal and open ocean surface waters by other investigators. Obvious correlations between oxidation rates and water column characteristics such as total bacterial numbers, dissolved (or particulate) manganese concentrations or organic content of surface waters are not evident. Transformations of manganese in the surface waters of the eastern Caribbean appear to be masked by the supply of fresh particulate material presumably, in part at least, from the Orinoco River. ¿ American Geophysical Union 1993