¹⁰Be, ¹⁴C and U-Th decay series nuclides and δ¹⁸O in a box core from the Central North Atlantic

Abstract

The stratigraphy of several radioisotopes has been determined in an undisturbed core from the central north Atlantic (¹⁴C, ²³⁸U, ²³⁰Th, ²³²Th, ²²⁶Ra, ²¹⁰Pb, ¹⁰Be). Carbon-14 indicates a sedimentation rate of 1 cm 1000 yrs⁻¹. The core represents about 30,000 years. The oxygen isotope signal agrees with this scale. The δ¹⁸O range is about 1.5%., from glacial to Holocene. The maximum change is near 11,000 years B.P. Mixing effects are minor because of the low fertility of the overlying waters. Excess lead-210 shows a minimum between 1 and 2 cm depth, and a maximum immediately below. It does not yield a diffusion coefficient for the Goldberg and Koide (1962) mixing model. The ¹⁰Be concentration in the Holocene sediment (on a CaCO₃-free basis) is somewhat higher than that deposited during the previous cold period. However, both clay and ¹⁰Be deposition rates are lower by a factor of over two during the Holocene. The source of the excess ¹⁰Be in the glacial section could be a continental reservoir or increased cosmic ray production. The U and Th concentrations as well as the excess ²³⁰Th/²³²Th activity ratios of the sediment deposited during the Holocene are higher (by 30-100%) than in glacial sediments. Again, this is in contrast to the deposition rates of U and Th, which are lower in the Holocene by a factor of about two. The most reliable signals are the radiocarbon and the oxygen isotope stratigraphy.