Ra and Rn isotopes as natural tracers of submarine groundwater discharge in the patagonian coastal zone (Argentina): an initial assessment

Submarine groundwater discharge (SGD) is herein recognized as a significant pathway of material transport from land to the coastal SW Atlantic Ocean and thus, it can be a relevant factor affecting the marine biogeochemical cycles in the region. This paper focuses on the initial measurements of Ra-226, Ra-228 and Rn-222 made in Patagonia's coastal zone of Chubut and Santa Cruz provinces (42 degrees S-48 degrees S, Argentina). Ra-226 activity ranged from 2.9 to 73.5 dpm 100 L-1, and Ra-228 activity ranged from 11.9 to 311.0 dpm 100 L-1 in groundwater wells. The radium activities found in Patagonia's marine coastal regions and adjacent shelf indicate significant enrichment throughout the coastal waters. Groundwater samples presented the largest Rn-222 activity and ranged from 2.66 to 1083 dpm L-1. Conversely, in the coastal marine environment, the Rn-222 activity ranged from 1.03 to 6.23 dpm L-1. The Patagonian coastal aquifer showed a larger enrichment in Ra-228 than in Ra-226, which is a typical feature for sites where SGD is dominant, probably playing a significant role in the biogeochemistry of these coastal waters.