Heavy nickel isotope compositions in rivers and the oceans
Nickel is a biologically-active trace metal whose dissolved concentration depth profiles in the ocean show nutrient-like behaviour. If the pronounced removal of nickel from the dissolved phase in the surface ocean, and its return in the deep, is associated with an isotopic fractionation nickel isoto...
| Published in: | Geochimica et Cosmochimica Acta |
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| Main Authors: | , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
2014
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| Subjects: | |
| Online Access: | https://hdl.handle.net/1983/a2bd89bf-dfbf-4f24-946c-da33c2536d97 https://research-information.bris.ac.uk/en/publications/a2bd89bf-dfbf-4f24-946c-da33c2536d97 https://doi.org/10.1016/j.gca.2013.12.007 http://www.scopus.com/inward/record.url?scp=84892461924&partnerID=8YFLogxK |
| Summary: | Nickel is a biologically-active trace metal whose dissolved concentration depth profiles in the ocean show nutrient-like behaviour. If the pronounced removal of nickel from the dissolved phase in the surface ocean, and its return in the deep, is associated with an isotopic fractionation nickel isotopes may be able to yield constraints on the precise biogeochemical processes involved. Here we present the first nickel isotope data for seawater along with data for the dissolved phase of rivers, one of the principal sources of nickel to the oceans. The dissolved phase of rivers exhibits substantial variability in both Ni concentration and delta Ni-60: from 2.2 to 35 nmol kg(-1) and +0.29 to +1.34 parts per thousand, respectively. The most striking result from the nickel isotope analyses of rivers is that they are substantially heavier (by up to 1 parts per thousand for delta Ni-60) than the range for silicate rocks on the continents, a finding that is analogous to that for other transition metal isotope systems. If the data presented here are close to representative of the global riverine flux, they suggest an annual input of Ni to the oceans of 3.6 x 10(8) moles, and a discharge-and concentration-weighted delta Ni-60 average of +0.80 parts per thousand. The relationship between Ni isotopes and concentrations shows similarities with those for other transition metal isotope systems, where the main control has been suggested to be isotopic partitioning between the dissolved phase and particulates, either in the weathering environment or during transport. In stark contrast to the rivers, the dataset for seawater is very homogeneous, with 2SD of the entire dataset being only twice the analytical reproducibility. The second main feature is that seawater is distinctly heavier in Ni isotopes than rivers. The average delta Ni-60 is 1.44 +/- 0.15 parts per thousand (2SD), and only 2 of the 29 seawater analyses have a Ni isotopic composition that is lighter than the heaviest river. The lack of an isotopic shift associated ... |
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