Hydrography, transport and mixing of the West Spitsbergen Current: the Svalbard Branch in summer 2015
<p>Measurements of ocean currents, stratification and microstructure were made in August 2015, northwest of Svalbard, downstream of the Atlantic inflow in Fram Strait in the Arctic Ocean. Observations in three sections are used to characterize the evolution of the West Spitsbergen Current (WSC...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-12-01
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| Series: | Ocean Science |
| Online Access: | https://www.ocean-sci.net/14/1603/2018/os-14-1603-2018.pdf |
| Summary: | <p>Measurements of ocean currents, stratification and microstructure were made in August 2015,
northwest of Svalbard, downstream of the Atlantic inflow in Fram Strait in
the Arctic Ocean. Observations in three sections are used to characterize the
evolution of the West Spitsbergen Current (WSC) along a 170 km downstream
distance. Two alternative calculations imply 1.5 to 2 Sv
(1 Sv <span class="inline-formula">=</span> 10<span class="inline-formula"><sup>6</sup></span> m<span class="inline-formula"><sup>3</sup></span> s<span class="inline-formula"><sup>−1</sup></span>) is routed to recirculation and Yermak
branch in Fram Strait, whereas 0.6 to 1.3 Sv is carried by the Svalbard
branch. The WSC cools at a rate of 0.20 <span class="inline-formula"><sup>∘</sup></span>C per 100 km, with
associated bulk heat loss per along-path meter of
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>(</mo><mn mathvariant="normal">1.1</mn><mo>-</mo><mn mathvariant="normal">1.4</mn><mo>)</mo><mo>×</mo><msup><mn mathvariant="normal">10</mn><mn mathvariant="normal">7</mn></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="79pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="22f92739fae766779ce14d58986af1e6"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="os-14-1603-2018-ie00001.svg" width="79pt" height="15pt" src="os-14-1603-2018-ie00001.png"/></svg:svg></span></span> W m<span class="inline-formula"><sup>−1</sup></span>, corresponding to a surface heat loss of
380–550 W m<span class="inline-formula"><sup>−2</sup></span>. The measured turbulent heat flux is too small to
account for this cooling rate. Estimates using a plausible range of
parameters suggest that the contribution of diffusion by eddies could be
limited to one half of the observed heat loss. In addition to shear-driven
mixing beneath the WSC core, we observe energetic convective mixing of an
unstable bottom boundary layer on the slope, driven by Ekman advection of
buoyant water across the slope. The estimated lateral buoyancy flux is
<span class="inline-formula"><i>O</i>(10<sup>−8</sup>)</span> W kg<span class="inline-formula"><sup>−1</sup></span>, sufficient to maintain a large fraction of the
observed dissipation rates, and corresponds to a heat flux of approximately
40 W m<span class="inline-formula"><sup>−2</sup></span>. We conclude that – at least in summer – convectively
driven bottom mixing followed by the detachment of the mixed fluid and its
transfer into the ocean interior can lead to substantial cooling and
freshening of the WSC.</p> |
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| ISSN: | 1812-0784 1812-0792 |