A deep 226Ra maximum in the northeast Pacific

Seven vertical profiles of 226Ra have been measured along an east-west traverse at about 300N from San Diego to northwest of Hawaii. These profiles show that there is a distinct core of Ra maximum spreading westward as a tongue in the northeast Pacific deep water. This core starts in the east with 21.1 Ra units (1 Ra unit=10-14g/kg) at 3.9 km depth at about 1300W, and deepens westward to 4.1 km with its Ra reduced to 18.3 units at 1500W. A similar core with some uncertainty due to possible sampling errors extends westward near the bottom at 5.2 km depth from 19.4 Ra units at 1500W to 15.9 units at about 1800 longitude. In addition, these profiles appear to be correlated with each other in structure above the cores of Ra maximum. These cores indicate that the Ra input depends locally on the type and composition of sediments and so the flux varies over the ocean bottom. On the basis of a one-dimensional diffusion-decay model, a horizontal diffusion coefficient of 106cm2/sec has been computed along these cores. Although this value appears to be slightly lower, it is not inconsistent with those derived from other physical methods. (Auth.)