Coupled 230Th/ 234U–ESR analyses for corals: A new method to assess sealevel change

Abstract

Although coupled 230Th/ 234U–ESR analyses have become routine for dating teeth, they have never been used for corals. While the ESR age depends on, and requires assumptions about, the time-averaged cosmic dose rate, D ¯ cos ( t ) , 230Th/ 234U dates do not. Since D ¯ cos ( t ) received by corals depends on the attenuation by any intervening material, D ¯ cos ( t ) response reflects changing water depths and sediment cover. By coupling the two methods, one can determine the age and a unique D ¯ cos , coupled ( t ) simultaneously. From a coral's water depth and sedimentary history as predicted by a given sealevel curve, one can predict D ¯ cos , sealevel ( t ) . If D ¯ cos , coupled ( t ) agrees well with D ¯ cos , sealevel ( t ) , this provides independent validation for the curve used to build D ¯ cos , sealevel ( t ) . For six corals dated at 7–128 ka from Florida Platform reef crests, the sealevel curve by Waelbroeck et al. [2002. Sea-level and deep water temperature changes derived from benthonic foraminifera isotopic records. Quat. Sci. Rev. 21, 295–305] predicted their D ¯ cos , coupled ( t ) values as well as, or better than, the SPECMAP sealevel curve. Where a whole reef can be sampled over a transect, a precise test for sealevel curves could be developed.