| Abstrakt: |
We present a dating method for deep‐sea sediments that uses the natural radionuclide 230Th (half‐life 75,380 years) in analogy to 210Pb with the constant rate of supply (CRS) model. Using an example from the western Indian sector of the Southern Ocean, we demonstrate how sets of values of 230Th, 232Th, and U isotopes activities can supply absolute age information for the last ~450,000 years, given a sufficient precision, resolution, and depth coverage of the analytical data in a suitable core. An assessment of age uncertainties resulting from analytical errors using a Monte Carlo approach and an analytical solution for error propagation shows good agreement. We also investigate errors due to a violation of model assumptions by variable focusing of deep‐sea sediments by means of a simulated core. Finally, we use real examples from independently dated sediment cores containing carbonate, using previously existing 230Th data, to test the approach. The consideration of the systematic errors and the examples suggests that the uncertainties are smallest in the central part of the record and that the variability of focusing conditions controls the accuracy of the 230Th CRS dates. Our own example demonstrates an excellent agreement of the 230Th CRS method with independent age constraints, adding an important tool for dating marine records that does not depend on the presence of carbonate. The obtained values are also suitable to calculate 230Th‐normalized preserved vertical rain rates of various sedimentary compounds, permitting an improved quantitative comparison of marine paleorecords with other archives like ice cores. Plain Language Summary: This study explores a new way of determining the age of sediments at the seafloor. It exploits the fact that a rare variety of the element thorium (230Th) that occurs naturally in the ocean is supplied to the seafloor at a constant rate. Due to its natural radioactivity with a half‐life of 75,380 years, it can be used to determine the age of sediments back to approximately 450,000 years. The mathematical approach is very similar to a well‐established method for 210Pb (22‐year half‐life) that reaches back about 100–150 years. In this study, we present this method based on an example from the Southern Ocean, introducing the measurement techniques used, the calculations, and the results and discussing the agreement with alternative methods. The importance of the method lies in the fact that it can be used to date a very abundant type of seafloor sediments that do not contain carbonate microfossils and that therefore cannot be dated or only with a larger uncertainty. Key Points: The excess of thorium‐230 can be used to date deep‐sea sediments in analogy to lead‐210In an example from the Indian Sector of the Southern Ocean, 230Th CRS‐dates agree very well with expected glacial‐interglacial cyclesThe dating method, which also yields vertical mass fluxes, works best in an age range of 50,000–450,000 years, depending on local conditions [ABSTRACT FROM AUTHOR] |
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