Impact of Chondrites on trace metal distribution in the sapropel S7 (ODP Site 966): Implications for paleoenvironmental and paleoceanographic reconstructions
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Show full item recordEditorial
Elsevier
Materia
Trace metal Redox conditions Chondrites
Date
2024-02-15Referencia bibliográfica
Monedero-Contreras, Ricardo D., Francisco J. Rodríguez-Tovar, and Francisca Martínez-Ruiz. Impact of Chondrites on trace metal distribution in the sapropel S7 (ODP Site 966): Implications for paleoenvironmental and paleoceanographic reconstructions. Global and Planetary Change 234 (2024) 104387 [10.1016/j.gloplacha.2024.104387]
Sponsorship
Grants PID2019-104625RB-100, PID2019-104624RB-I00 and TED2021-131697B-C22 through MCIN/AEI/ 10.13039/501100011033; Grants FEDER/Junta de Andalucía P18-RT-3804 and P18-RT-4074; Research Groups RNM-179 and RNM-178 by Junta de AndalucíaAbstract
Organic-rich deposits are valuable paleo-archives, recording significant paleoceanographic changes linked to
past climate variations and marine deoxygenation events. The deposition of organic-rich sediments stops when
bottom-water reventilation/oxygenation occurs. This impedes organic matter preservation, enabling macro and
micro burrowing-organisms to recover and bioturbate the seafloor. In this sense, highly bioturbated sediments
require particular attention when sampling is done for geochemical analyses, as sediments can be considerably
mixed. While avoiding trace fossils during sampling for geochemical analyses is easy for large traces (e.g. Planolites,
Thallasinoides, and Zoophycos), it becomes challenging for smaller and complex traces (< 0.5 cm), as is the
case with Chondrites. Chondrites-producers have an opportunistic behavior, being one of the first organisms to
colonize the seafloor after an anoxic event. As a result, Chondrites are commonly and sometimes abundantly
found in the upper layers of organic-rich sediments, including sapropels and black shales.
This study focuses on sapropel S7, which was deposited between ~198.5 and 191.9 ka at the top of Eratosthenes
Seamount and exhibits abundant Chondrites. For this sapropel, we demonstrated that Chondrites-producers
can bioturbate significant volumes of organic-rich sediments (over 35%), introducing oxic/dysoxic material
downward into anoxic sediments enriched in redox-sensitive trace metals and organic matter. This process can
dilute up to 18% the original concentration of redox-sensitive trace metals (e.g. Mo, U and V). This dilution is
especially important to consider when calculating trace metals and organic matter burial flux from bulk sediment
data. Therefore, Chondrites-producers can play a crucial role in altering the sediment texture and distribution of
minerals and organic matter at sub-cm scale, and may thus impact paleoenvironmental and paleoceanographic
reconstructions based on geochemical signals. Furthermore, the subsequent redistribution of organic matter and
redox-sensitive trace metals (including oligoelements) within the sediment can affect carbon and nutrient
cycling, microbial activity, organic matter degradation in deep-marine sediments, and the overall sedimentary
biogeochemistry.