23. Seasonal Changes in the Radium-226 Distribution on the Southeastern USA Continental Shelf; Implications for Changing Submarine Groundwater Discharge

Enrichments of radium isotopes in coastal waters have served as indicators of submarine groundwater discharge (SGD). Because coastal waters exchange with the open ocean on a time scale of weeks to months, seasonal patterns of radium isotope distribution may be used to indicate changes in SGD through the year. Here I report the seasonal distributions of 226 Ra measured in surface waters of the continental shelf of southern USA. The study area encompassed most of the South Atlantic Bight. Activities of 226 Ra were highest off the coast of Georgia. In summer, these high activities extended throughout the study area; but during the spring and winter they decreased markedly off the coast of South Carolina. The primary source of excess 226 Ra (that is activities in excess of open ocean values) is SGD. Because the activities of 226 Ra in SGD vary little with season, the lower excess activities off South Carolina imply lower rates of SGD during the spring and winter.