Low <i>p</i>CO<sub>2</sub> under sea-ice melt in the Canada Basin of the western Arctic Ocean
In September 2013, we observed an expanse of surface water with low CO<sub>2</sub> partial pressure (<i>p</i>CO<sub>2</sub><sup>sea</sup>) (< 200 µatm) in the Chukchi Sea of the western Arctic Ocean. The large undersaturation of CO<sub>...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-12-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/14/5727/2017/bg-14-5727-2017.pdf |
| Summary: | In September 2013, we observed an expanse of surface water with low CO<sub>2</sub>
partial pressure (<i>p</i>CO<sub>2</sub><sup>sea</sup>) (< 200 µatm)
in the Chukchi Sea of the western Arctic Ocean. The large undersaturation of
CO<sub>2</sub> in this region was the result of massive primary production after
the sea-ice retreat in June and July. In the surface of the Canada Basin,
salinity was low (< 27) and <i>p</i>CO<sub>2</sub><sup>sea</sup> was closer to
the air–sea CO<sub>2</sub> equilibrium (∼ 360 µatm). From the
relationships between salinity and total alkalinity, we confirmed that the
low salinity in the Canada Basin was due to the larger fraction of meltwater
input (∼ 0.16) rather than the riverine discharge (∼ 0.1). Such
an increase in <i>p</i>CO<sub>2</sub><sup>sea</sup> was not so clear in the coastal
region near Point Barrow, where the fraction of riverine discharge was larger
than that of sea-ice melt. We also identified low <i>p</i>CO<sub>2</sub><sup>sea</sup>
(< 250 µatm) in the depth of 30–50 m under the halocline
of the Canada Basin. This subsurface low <i>p</i>CO<sub>2</sub><sup>sea</sup> was
attributed to the advection of Pacific-origin water, in which dissolved inorganic carbon is
relatively low, through the Chukchi Sea where net primary production is high.
Oxygen supersaturation (> 20 µmol kg<sup>−1</sup>) in the
subsurface low <i>p</i>CO<sub>2</sub><sup>sea</sup> layer in the Canada Basin indicated
significant net primary production undersea and/or in preformed condition. If
these low <i>p</i>CO<sub>2</sub><sup>sea</sup> layers surface by wind mixing, they will
act as additional CO<sub>2</sub> sinks; however, this is unlikely because
intensification of stratification by sea-ice melt inhibits mixing across the
halocline. |
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| ISSN: | 1726-4170 1726-4189 |