Silicon isotopes reveal the different Arctic endmembers contributing to the deep water formed in the North Atlantic Ocean

20 April 2020

Combining a multiparametric analysis, biogenic and dissolved silicon (Si) isotope data (³⁰Si-bSiO₂ and δ³⁰Si-DSi, respectively) in the Arctic Ocean, Liguori and co-workers (2020, see reference below) could unravel the influence of water masses on the δ³⁰Si-DSi distribution within the Arctic Ocean. Any deviation of the δ³⁰Si-DSi signature from pure mixing was attributed to the contribution of biogenic particle dissolution. This is particularly true for the Dense Arctic Atlantic Waters which are dominating from 200 to 500 m water depth and are marked by the highest δ³⁰Si-DSi, indicating a strong lateral influence of waters from the shelves, especially the Barents Sea shelf, due to its high productivity. Contrastingly, the deepest waters are not influenced by the dissolution of sinking bSiO₂, probably due to the low concentration of bSiO₂. The authors could thus establish that the Arctic Ocean potentially presents several isotopically different endmembers that contribute to the deep water formed in the North Atlantic Ocean.

**Figure:** Isosurface plots for δ³⁰Si-DSi for different water depths in the Arctic Ocean. (A) Blue dots – this study, purple stars – Varela et al. (2016), pink diamonds – de Souza et al. (2012) and black squares – Sutton et al. (2018b). Black arrows mark the outflowing waters: 1 – Labrador Sea Water, 2 – Denmark Strait Overflow Water, and 3 – Iceland Scotland Overflow Water. Waters from the Canadian Arctic Ocean leaving predominantly through the shallow Canadian Archipelago and the Labrador Sea contribute higher δ³⁰Si-DSi (Varela et al., 2016) to the Labrador Sea Water (1) and therefore to North Atlantic Deep Water (NADW). In contrast, waters from the Central Arctic Ocean/Eurasian Basin leaving through the much deeper Fram Strait contribute lower δ³⁰Si-DSi to the Denmark Strait Overflow Water (2) and Iceland Scotland Overflow Water (3) and their respective precursor water masses revealing that the Arctic Ocean export different endmember signals contributing to the NADW.

References:

Liguori, B. T. P., Ehlert, C., & Pahnke, K. (2020). The Influence of Water Mass Mixing and Particle Dissolution on the Silicon Cycle in the Central Arctic Ocean. Frontiers in Marine Science, 7. DOI: https://doi.org/10.3389/fmars.2020.00202

de Souza, G. F., Reynolds, B. C., Rickli, J., Frank, M., Saito, M. A., Gerringa, L. J., et al. (2012). Southern Ocean control of silicon stable isotope distribution in the deep Atlantic Ocean. Glob. Biogeochem. Cycles 9, 4199-4213. DOI: https://doi.org/10.5194/bg-9-4199-2012

Sutton, J. N., Souza, G. F. D., Garcia-Ibiliez, M. I., and De La Rocha, C. L. (2018b). The silicon stable isotope distribution along the GEOVIDE section (GEOTRACES GA-01) of the North Atlantic Ocean. Biogeosciences 15, 5663–5676. DOI: https://doi.org/10.5194/bg-15-5663-2018

Varela, D. E., Brzezinski, M. A., Beucher, C. P., Jones, J. L., Giesbrecht, K. E., Lansard, B., et al. (2016). Heavy silicon isotopic composition of silicic acid and biogenic silica in Arctic waters over the Beaufort shelf and the Canada Basin. Glob. Biogeochem. Cycles 30, 804–824. DOI: https://doi.org/10.1002/2015gb005277

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