Using <sup>226</sup>Ra and <sup>228</sup>Ra isotopes to distinguish water mass distribution in the Canadian Arctic Archipelago
<p>As a shelf-dominated basin, the Arctic Ocean and its biogeochemistry are heavily influenced by continental and riverine sources. Radium isotopes (<span class="inline-formula"><sup>226</sup>Ra</span>, <span class="inline-formula"><sup>2...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-10-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/17/4937/2020/bg-17-4937-2020.pdf |
| Summary: | <p>As a shelf-dominated basin, the Arctic Ocean and its biogeochemistry are
heavily influenced by continental and riverine sources. Radium isotopes
(<span class="inline-formula"><sup>226</sup>Ra</span>, <span class="inline-formula"><sup>228</sup>Ra</span>, <span class="inline-formula"><sup>224</sup>Ra</span>, and <span class="inline-formula"><sup>223</sup>Ra</span>), are transferred from the
sediments to seawater, making them ideal tracers of sediment–water exchange
processes and ocean mixing. As the two long-lived isotopes of the radium
quartet, <span class="inline-formula"><sup>226</sup>Ra</span> and <span class="inline-formula"><sup>228</sup>Ra</span> (<span class="inline-formula"><sup>226</sup>Ra</span> with a <span class="inline-formula"><i>t</i><sub>1∕2</sub></span> of 1600 years and <span class="inline-formula"><sup>228</sup>Ra</span> with a <span class="inline-formula"><i>t</i><sub>1∕2</sub></span> of 5.8 years) can provide insight into the water mass
compositions, distribution patterns, as well as mixing processes and their
associated timescales throughout the Canadian Arctic Archipelago (CAA). The
wide range of <span class="inline-formula"><sup>226</sup>Ra</span> and <span class="inline-formula"><sup>228</sup>Ra</span> activities, as well as of the
<span class="inline-formula"><sup>228</sup>Ra∕<sup>226</sup>Ra</span>, measured in water samples collected during the
2015 GEOTRACES cruise, complemented by additional chemical tracers –
dissolved inorganic carbon (DIC), total alkalinity (AT), barium (Ba), and
the stable oxygen isotope composition of water (<span class="inline-formula"><i>δ</i><sup>18</sup>O</span>) –
highlight the dominant biogeochemical, hydrographic, and bathymetric features
of the CAA. Bathymetric features, such as the continental shelf and shallow
coastal sills, are critical in modulating circulation patterns within the
CAA, including the bulk flow of Pacific waters and the inhibited eastward
flow of denser Atlantic waters through the CAA. Using a principal component
analysis, we unravel the dominant mechanisms and apparent water mass
end-members that shape the tracer distributions. We identify two distinct
water masses located above and below the upper halocline layer throughout
the CAA and distinctly differentiate surface waters in the eastern
and western CAA. Furthermore, we highlight water exchange across
80<span class="inline-formula"><sup>∘</sup></span> W, inferring a draw of Atlantic water (originating from Baffin
Bay) into the CAA. This underscores the presence of an Atlantic water “U-turn”
located at Barrow Strait, where the same water mass is seen along the
northernmost edge at 80<span class="inline-formula"><sup>∘</sup></span> W as well as along the southeasternmost
confines of Lancaster Sound. Overall, this study provides a stepping stone
for future research initiatives within the Canadian Arctic Archipelago,
revealing how quantifying disparities in the distributions of radioactive
tracers can provide valuable information on water mass distributions, flow
patterns, and mixing within vulnerable areas such as the CAA.</p> |
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| ISSN: | 1726-4170 1726-4189 |