A comparison of sediment accumulation chronologies by the radiocarbon and 230Th excess methods

Abstract

Four Northeast Atlantic cores which exhibited well-correlated linear progressions of conventional radiocarbon age with depth were analysed to provide 230Th excess profiling data. The current evaluation of marine radiocarbon data suggests that conventional radiocarbon ages consistently underestimate true time. This deficit progressively increases from 4 to 22 ky BP. As a result, steady-state sediment accumulation rate models based on conventional radiocarbon ages are expected to be in error by up to 17%, dependent on the period over which the estimates are made. When proxy timescales from the radiocarbon and 230Th excess data for the four cores are compared over periods between 0–11.5 and 0–18.2 ky BP, the trend of cumulative time derived from the 230Th excess profiling data is shown to be consistent with the expected trend of conventional radiocarbon age vs the best current estimate of true time. This agreement supports the use of 230Th excess as a tracer for detailed estimates of changing deep-sea sediment accumulation fluxes.