Replacement times of a spectrum of elements in the North Atlantic based on thorium supply

The measurable supply of 232Th to the ocean can be used to derive the supply of other elements, which is more difficult to quantify directly. The measured inventory of an element divided by the derived supply yields a replacement time estimate, which in special circumstances is related to a residenc...

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Bibliographic Details
Published in:Global Biogeochemical Cycles
Main Authors: Hayes, Christopher T., Anderson, Robert F., Cheng, Hai, Conway, Tim, Edwards, R.L., Fleisher, Martin Q., Ho, Peng, Huang, Kuo Fang, John, Seth, Landing, William, Little, Susan, Lu, Yanbin, Morton, Peter, Moran, S. Bradley, Robinson, Laura, Shelley, Rachel, Shiller, Alan, Zheng, Xin-Yuan
Format: Article in Journal/Newspaper
Language:English
Published: 2018
Subjects:
North Atlantic
Online Access:https://hdl.handle.net/1983/b5dd5868-e003-43ce-93d1-052f18d91907
https://research-information.bris.ac.uk/en/publications/b5dd5868-e003-43ce-93d1-052f18d91907
https://doi.org/10.1029/2017GB005839
https://research-information.bris.ac.uk/ws/files/164253011/Hayes_et_al_2018_GBC_North_Atlantic_element_replacement_times_Submitted.pdf
https://research-information.bris.ac.uk/ws/files/167839304/Hayes_et_al_2018_Global_Biogeochemical_Cycles.pdf
Description
Summary:The measurable supply of 232Th to the ocean can be used to derive the supply of other elements, which is more difficult to quantify directly. The measured inventory of an element divided by the derived supply yields a replacement time estimate, which in special circumstances is related to a residence time. As a proof of concept, Th-based supply rates imply a range in the replacement times of the rare earth elements (REEs) in the North Atlantic that is consistent with the chemical reactivity of REEs related to their ionic charge density. Similar estimates of replacement times for the bioactive trace elements (Fe, Mn, Zn, Cd, Cu and Co), ranging from <5 years to >50,000 years, demonstrate the broad range of elemental reactivity in the ocean. Here, we discuss how variations in source composition, fractional solubility ratios or non continental sources such as hydrothermal vents lead to uncertainties in Th-based replacement time estimates. We show that the constraints on oceanic replacement time provided by the Th-based calculations are broadly applicable in predicting how elements are distributed in the ocean and for some elements, such as Fe, may inform us on how the carbon cycle may be impacted by trace element supply and removal.

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