Distribution of 226Ra Radionuclide in Upwelling Event Off Ulsan, Gampo and Pohang, Korea

Abstract

Upwelling is an important event in the sea for it makes the area to become more productive. The objective of this study is to determine the distribution of radium-226 as radiotoxic in the upwelling area in the summer season. Measurements of the horizontal and vertical activities of ²²⁶Ra in the Ulsan, Gampo and Pohang waters were conducted in June, August 1999 and June 2000 when the upwelling event was expected to occur. Water temperature, salinity and dissolved oxygen (DO) were also measured concurrently. The thermocline layer or the layer where the temperature decreased drastically occurred at a depth between 30 m to 100 m for samples dated June 1999 and 30 m to more than 100 m for samples dated August 1999 and June 2000. The salinity decreased with depth but the DO concentration increased in this layer. The condition affected the vertical distribution of ²²⁶Ra in the study area, where the ²²⁶Ra activities showed to be relatively homogeneous vertically in each station. This indicates that the upwelling which occurred in the study area was capable to distribute the ²²⁶Ra activities from the bottom to the surface. Thus, the ²²⁶Ra distribution at that time did not increase with depth, opposite to what usually occurs in the ocean at normal condition. The ²²⁶Ra activities also did not decrease after elapsed time of one year, in fact, it increased. However, horizontally the ²²⁶Ra activities decreased with increasing distance from the coastal zone. Based on these results, it can be concluded that the upwelling event in the Ulsan, Gampo and Pohang was effective for increasing the ²²⁶Ra activities and was capable to create homogeneous ²²⁶Ra activities from the bottom to the surface in the water column, and the source of ²²⁶Ra was likely to originate from outside area (i.e. coastal zone) and bottom area.

Received: 25 March 2009; Revised: 24 August 2009; Accepted: 30 September 2009