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The relationship between zinc, its isotopes, and the major nutrients in the North-East Pacific

The relationship between zinc, its isotopes, and the major nutrients in the North-East Pacific
The relationship between zinc, its isotopes, and the major nutrients in the North-East Pacific

Trace metal micronutrients play key roles in photosynthesis by oceanic phytoplankton. Though they are required in much smaller amounts than the major nutrients (P, N, Si), their bioavailable forms are also present in the seawater solution at much lower levels. Relationships between the dissolved chemistry of the nutrient-type trace metals, their stable isotope variations, as well those of the major nutrients, have highlighted the importance of biological and physical processes in the Southern Ocean in controlling their oceanic biogeochemistry. However, the first-order Southern Ocean processes are overprinted by vertical cycling in other parts of the ocean, particularly upwelling regions remote from the Southern Ocean, with the North Pacific standing out in particular. Here we present new zinc (Zn) concentration and isotope, as well as major nutrient data for the NE Pacific, and couple these new data with a compilation of published data from across the region, with the objective of better understanding the impact of this important region on oceanic biogeochemical cycles. The new Zn isotope data for two stations along Line P (P04 and P26) show a large range in δ66Zn in the upper ocean (−0.4‰ up to >1‰), associated with a very small isotope fractionation but extreme depletion of the dissolved pool during photic zone biological uptake, and the regeneration of this cellular Zn at very shallow depths (50 m). Beneath this, the two profiles approach the δ66Zn value of +0.5‰, seen throughout the deep ocean, by about 500 m. The minimum δ66Zn resulting from regeneration is associated with very high Zn concentrations, particularly at the marginal P04 station where diatoms dominate the phytoplankton ecology. Combining the new data with published Zn and major nutrient concentrations from across the North Pacific emphasises the role of vertical biological cycling in controlling regional biogeochemistry in the North Pacific, resulting in the partial overprinting of biogeochemical signatures transported out of the Southern Ocean by the ocean circulation. Zinc isotope data document the uptake of this metal into diatoms and the co-regeneration of Zn with phosphate in the upper water column. Silica in contrast is regenerated at greater depth, resulting in a decoupling of the Zn–Si correlation that is set in the Southern Ocean and that dominates the Atlantic. Previous work has suggested that the decoupling of Zn and Si in the subarctic North Pacific results from removal of Zn (and other metals) to water column particulate sulphide. In our dataset, and in the compilation of data documenting relationships between Zn and the major nutrients across the North Pacific, this decoupling is clearly due to the different lengthscales of regeneration for organic matter (Zn and P) and diatom opal (Si).

isotopes, North Pacific, ocean biogeochemistry, trace metals, zinc
0012-821X
Vance, D.
2cc02d9f-ca79-457f-b1fa-ca1e5e2a4d0e
de Souza, Gregory F.
7eb06867-ccc4-49d7-81ba-a23f85e82c79
Zhao, Ye
642efe8e-b1b3-474b-a6bf-a9fb4b4eb3d8
Cullen, J. T.
ab503137-0428-41aa-8232-c6f748c54bcf
Lohan, Maeve C.
6ca10597-2d0f-40e8-8e4f-7619dfac5088
Vance, D.
2cc02d9f-ca79-457f-b1fa-ca1e5e2a4d0e
de Souza, Gregory F.
7eb06867-ccc4-49d7-81ba-a23f85e82c79
Zhao, Ye
642efe8e-b1b3-474b-a6bf-a9fb4b4eb3d8
Cullen, J. T.
ab503137-0428-41aa-8232-c6f748c54bcf
Lohan, Maeve C.
6ca10597-2d0f-40e8-8e4f-7619dfac5088

Vance, D., de Souza, Gregory F., Zhao, Ye, Cullen, J. T. and Lohan, Maeve C. (2019) The relationship between zinc, its isotopes, and the major nutrients in the North-East Pacific. Earth and Planetary Science Letters, 525. (doi:10.1016/j.epsl.2019.115748).

Record type: Article

Abstract

Trace metal micronutrients play key roles in photosynthesis by oceanic phytoplankton. Though they are required in much smaller amounts than the major nutrients (P, N, Si), their bioavailable forms are also present in the seawater solution at much lower levels. Relationships between the dissolved chemistry of the nutrient-type trace metals, their stable isotope variations, as well those of the major nutrients, have highlighted the importance of biological and physical processes in the Southern Ocean in controlling their oceanic biogeochemistry. However, the first-order Southern Ocean processes are overprinted by vertical cycling in other parts of the ocean, particularly upwelling regions remote from the Southern Ocean, with the North Pacific standing out in particular. Here we present new zinc (Zn) concentration and isotope, as well as major nutrient data for the NE Pacific, and couple these new data with a compilation of published data from across the region, with the objective of better understanding the impact of this important region on oceanic biogeochemical cycles. The new Zn isotope data for two stations along Line P (P04 and P26) show a large range in δ66Zn in the upper ocean (−0.4‰ up to >1‰), associated with a very small isotope fractionation but extreme depletion of the dissolved pool during photic zone biological uptake, and the regeneration of this cellular Zn at very shallow depths (50 m). Beneath this, the two profiles approach the δ66Zn value of +0.5‰, seen throughout the deep ocean, by about 500 m. The minimum δ66Zn resulting from regeneration is associated with very high Zn concentrations, particularly at the marginal P04 station where diatoms dominate the phytoplankton ecology. Combining the new data with published Zn and major nutrient concentrations from across the North Pacific emphasises the role of vertical biological cycling in controlling regional biogeochemistry in the North Pacific, resulting in the partial overprinting of biogeochemical signatures transported out of the Southern Ocean by the ocean circulation. Zinc isotope data document the uptake of this metal into diatoms and the co-regeneration of Zn with phosphate in the upper water column. Silica in contrast is regenerated at greater depth, resulting in a decoupling of the Zn–Si correlation that is set in the Southern Ocean and that dominates the Atlantic. Previous work has suggested that the decoupling of Zn and Si in the subarctic North Pacific results from removal of Zn (and other metals) to water column particulate sulphide. In our dataset, and in the compilation of data documenting relationships between Zn and the major nutrients across the North Pacific, this decoupling is clearly due to the different lengthscales of regeneration for organic matter (Zn and P) and diatom opal (Si).

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NEPacificPaperRevised (1) - Accepted Manuscript
Restricted to Repository staff only until 9 August 2020.
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More information

Accepted/In Press date: 30 July 2019
e-pub ahead of print date: 9 August 2019
Published date: 1 November 2019
Keywords: isotopes, North Pacific, ocean biogeochemistry, trace metals, zinc

Identifiers

Local EPrints ID: 433722
URI: https://eprints.soton.ac.uk/id/eprint/433722
ISSN: 0012-821X
PURE UUID: 6cbb7a4c-4a60-4cf8-9294-815a9290c9a9

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Date deposited: 02 Sep 2019 16:30
Last modified: 09 Dec 2019 17:32

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Contributors

Author: D. Vance
Author: Gregory F. de Souza
Author: Ye Zhao
Author: J. T. Cullen
Author: Maeve C. Lohan

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