Articles | Volume 20, issue 24
https://doi.org/10.5194/bg-20-5003-2023
https://doi.org/10.5194/bg-20-5003-2023
Research article
 | 
19 Dec 2023
Research article |  | 19 Dec 2023

Revisiting the applicability and constraints of molybdenum- and uranium-based paleo redox proxies: comparing two contrasting sill fjords

K. Mareike Paul, Martijn Hermans, Sami A. Jokinen, Inda Brinkmann, Helena L. Filipsson, and Tom Jilbert

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Cited articles

Adelson, J. M., Helz, G. R., and Miller, C. V.: Reconstructing the rise of recent coastal anoxia; molybdenum in Chesapeake Bay sediments, Geochim. Cosmochim. Ac., 65, 237–252, https://doi.org/10.1016/S0016-7037(00)00539-1, 2001. 
Aksnes, D. L., Aure, J., Johansen, P. O., Johnsen, G. H., and Salvanes, A. G. V.: Multi-decadal warming of Atlantic water and associated decline of dissolved oxygen in a deep fjord, Estuar. Coast. Shelf. S., 228, 106392, https://doi.org/10.1016/j.ecss.2019.106392, 2019. 
Alessi, D. S., Lezama-Pacheco, J. S., Stubbs, J. E., Janousch, M., Bargar, J. R., Persson, P., and Bernier-Latmani, R.: The product of microbial uranium reduction includes multiple species with U(IV)-phosphate coordination, Geochim. Cosmochim. Ac., 131, 115–127, https://doi.org/10.1016/j.gca.2014.01.005, 2014. 
Alessi, D. S., Uster, B., Veeramani, H., Suvorova, E. I., Lezama-Pacheco, J. S., Stubbs, J. E., Bargar, J. R., and Bernier-Latmani, R.: Quantitative separation of monomeric U(IV) from UO2 in products of U(VI) reduction, Environ. Sci. Technol., 46, 6150–6157, https://doi.org/10.1021/es204123z, 2012. 
Algeo, T. J. and Li, C.: Redox classification and calibration of redox thresholds in sedimentary systems, Geochim. Cosmochim. Ac., 287, 8–26, https://doi.org/10.1016/j.gca.2020.01.055, 2020. 
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Short summary
Seawater naturally contains trace metals such as Mo and U, which accumulate under low oxygen conditions on the seafloor. Previous studies have used sediment Mo and U contents as an archive of changing oxygen concentrations in coastal waters. Here we show that in fjords the use of Mo and U for this purpose may be impaired by additional processes. Our findings have implications for the reliable use of Mo and U to reconstruct oxygen changes in fjords.
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