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Dating Deep‐Sea Sediments With 230 Th Excess Using a Constant Rate of Supply Model
Author(s) -
Geibert W.,
Stimac I.,
Rutgers van der Loeff M. M.,
Kuhn G.
Publication year - 2019
Publication title -
paleoceanography and paleoclimatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.927
H-Index - 127
eISSN - 2572-4525
pISSN - 2572-4517
DOI - 10.1029/2019pa003663
Subject(s) - carbonate , monte carlo method , sediment , sedimentary rock , deep sea , geology , seawater , environmental science , statistics , paleontology , oceanography , mathematics , chemistry , organic chemistry
We present a dating method for deep‐sea sediments that uses the natural radionuclide 230 Th (half‐life 75,380 years) in analogy to 210 Pb 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 230 Th, 232 Th, 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 230 Th 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 230 Th CRS dates. Our own example demonstrates an excellent agreement of the 230 Th 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 230 Th‐normalized preserved vertical rain rates of various sedimentary compounds, permitting an improved quantitative comparison of marine paleorecords with other archives like ice cores.