Calculating sedimentation rates of oxic pelagic clays using core top thorium isotopes

Costa, Kassandra M., Ossa Ossa, Frantz, Dunlea, Ann, Pavia, Frank J., Tegler, Logan, Auro, Maureen, Andersen, Morten ORCID: https://orcid.org/0000-0002-3130-9794 and Nielsen, Sune G. 2025. Calculating sedimentation rates of oxic pelagic clays using core top thorium isotopes. Geochemistry, Geophysics, Geosystems 26 (1) , e2024GC011717. 10.1029/2024gc011717

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Abstract

AbstractOxic pelagic clays are an important component of seafloor sediment that may hold valuable information about past ocean chemistry due to their affinity for and accumulation of biogeochemically important metals. We present a new approach to calculating site‐specific sedimentation rates (SRs) by comparing authigenic sediment thorium isotope compositions (230Th/232Th) to seawater dissolved 230Th/232Th in a suite of deep (>3,000 m) pelagic core sites. We extracted the authigenic sediment fraction using an HHAc leach protocol, which major element chemistry (Al, Mn, Fe, Ti) suggested was less affected by lithogenic contamination than the HCl leach. Four different methods were tested for extracting the appropriate initial 230Th/232Th from seawater: using either the nearest water column station (methods 1 and 2) or a regionally averaged profile (methods 3 and 4) and using either the bottommost profile measurement (methods 1 and 3) or linear regression of the profile and extrapolation to the seafloor (methods 2 and 4). Method 3 outperformed the other methods in reconstructing previously published SRs from pelagic clays in the North Pacific. The new thorium‐based SRs were then combined with estimates from the total sediment thickness on ocean crust and non‐lithogenic cobalt accumulation to determine the best estimates for SRs of oxic pelagic clays. The Pacific has the lowest SR (median 0.28 cm/kyr), while the Atlantic is higher (median 0.46 cm/kyr) and the Indian Ocean is highest (median 0.75 cm/kyr). These new estimates are consistent with the expected spatial patterns of sedimentation, but they revise the absolute SR values downward from available gridded SR maps.

Item Type:	Article
Date Type:	Published Online
Status:	Published
Schools:	Earth and Environmental Sciences
Additional Information:	License information from Publisher: LICENSE 1: URL: http://creativecommons.org/licenses/by/4.0/, Start Date: 2025-01-25
Publisher:	Wiley
ISSN:	1525-2027
Date of First Compliant Deposit:	6 February 2025
Date of Acceptance:	20 December 2024
Last Modified:	06 Feb 2025 11:00
URI:	https://orca.cardiff.ac.uk/id/eprint/176001

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