137CS ACTIVITY IN USVI COASTAL SEDIMENTS: FALLOUT OR RESEDIMENTATION?

A series of sediment cores were collected from coastal, marine, and salt pond environments surrounding St. John, USVI. Cores were analyzed using ²¹⁰Pb, ¹³⁷Cs, and ⁷Be radioisotopes in order to develop a high resolution age model for the past 100 years. ¹³⁷Cs is bomb derived and should exhibit a major peak (activity) around the mid 1960's. This peak was consistently observed in cores from the USVI; however, additional ¹³⁷Cs peaks were observed as well. The Constant Rate of Supply (CRS) model was applied to the ²¹⁰Pb data in an effort to determine precise dates for these additional ¹³⁷Cs peaks. The major peak observed around the mid 1960's indicates that ¹³⁷Cs is bomb derived and helps to validate the use of the CRS model as a precise dating technique. Based on this age model, the additional peaks were dated around the mid-late 1980's and late 1990's. Peaks observed around the mid-late 1980's may represent the Chernobyl event of 1986. Additional peaks observed after the 1960's may be explained by redeposition, as they correlate to significant increases in mass accumulation rates. Further research will help to better understand these processes and potentially strengthen these correlations.