137Cs and excess 210Pb deposition patterns in estuarine and marine sediment in the central region of the Great Barrier Reef Lagoon, north-eastern Australia

This paper focuses on the distribution of Cs-137 and Pb-210(xs),, in 51 estuarine and marine sediment cores collected between the Upstart Bay and Rockingham Bay in the Great Barrier Reef Lagoon, north-eastern Australia. Historical records of Pb-210(xs) and Cs-137 atmospheric deposition and present day terrestrial inventories in north-eastern Australia are presented. Pb-210(xs) and Cs-137 fluxes measured on suspended sediments in the Burdekin River are considered to be a source of recent inputs of these nuclides to the nearshore region of this part of the Great Barrier Reef. Direct correlations between sediment nuclide inventories, maximum detectable depths, and sediment mass accumulation rates (MARs), calculated using both Cs-137 and Pb-210(xs) are explored. In relation to inventories of Pb-210(xs) 60% of atmospheric fallout Cs-137 appears to be missing from the sediments. The reasons for these differences in two tracers, primarily of atmospheric origin, are discussed in terms of the geo-chemical properties of these two nuclides. Evidence is presented to support the hypothesis that the 137Cs distribution in these cores can be a useful independent tracer which provides confirmation of MARs calculated from the decay of Pb-210(xs). Crown Copyright (C) 2004 Published by Elsevier Ltd. All rights reserved.