226Ra in phosphate nodules from the Peru/Chile seafloor

226Ra and other uranium-series radionuclides have been measured in a suite of marine phosphorite samples from the upwelling area off Peru/Chile by gamma-ray spectrometry and radiochemical techniques. Our results lead to the following conclusions: (1) phosphorite nodules typically show unidirectional growth at rates of 1 to 10 mm/Kyr; (2) very young samples (less than a few thousand years) contain slight excess amounts of 226Ra probably derived from pore fluids; and (3) slow but persistent leakage of 226Ra out of phosphate nodules occurs resulting in systematically lower 226Ra ages compared to 230Th ages for samples older than about twenty thousand years. Radium fluxes from these phosphate nodules appear to be 1 to 3 orders of magnitude less than those calculated for deep-sea sediments and ferromanganese nodules. (author)