Barium in the Arctic Ocean

Barium? Why would you want to measure barium in seawater?

Barium is a metal, and is dissolved in seawater in very low concentrations – for every litre of seawater there’s only about 0.00001g of barium. This amount isn’t fixed and varies around the ocean. Scientists have noticed that barium seems to correlate with other things in the ocean, for example the nutrient silicic acid (dissolved silicon) and alkalinity (which is basically the amount of ions in the water). Linked to this, barium has been thought to be useful in the Arctic as a tracer of river input (especially in winter when there’s not much biological activity that can also take up barium). However, this use of dissolved barium hasn’t been explored fully, and there haven’t been any studies to look at how dissolved barium behaves from one season to the next.

In a new paper, published in the Journal of Geophysical Research Oceans, we investigated barium in seawater and sea-ice from the Arctic. We collected samples during the Norwegian funded N-ICE2015 project, which was set up to study the physics, chemistry and biology of sea-ice in a changing Arctic. The Norwegian Polar Institute led the expedition, freezing their ship – the R/V Lance – into sea-ice north of Svalbard and taking a lot of measurements and samples as it drifted through the Arctic.

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Sampling sea-ice during the N-ICE2015 expedition. Photo from https://www.flickr.com/photos/worldmeteorologicalorganization/

The barium measurements showed that there was no simple relationship with freshwater input, even in winter when biological activity was very low. This points towards an important process – likely within sea-ice – that is controlling barium distribution. Whilst this observation puts a question mark over using barium as a river tracer, our results do highlight the importance of understanding the chemical reactions that go on within sea-ice: in a changing world where sea-ice is diminishing, not only are we fundamentally changing the physics of the ocean but also the chemistry, with knock-on effects on marine biological production.

Read the full paper here.

Hendry, Katharine R., Kimberley M. Pyle, G. Barney Butler, Adam Cooper, Agneta Fransson, Melissa Chierici, Melanie J. Leng, Amelie Meyer, and Paul A. Dodd. “Spatiotemporal Variability of Barium in Arctic Sea‐Ice and Seawater.” Journal of Geophysical Research: Oceans (2018).

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