High-frequency, year-round time series of the carbonate chemistry in a high-Arctic fjord (Svalbard)

<p>The Arctic Ocean is subject to high rates of ocean warming and acidification, with critical implications for marine organisms as well as ecosystems and the services they provide. Carbonate system data in the Arctic realm are spotty in space and time, and, until recently, there was no time-series station measuring the carbonate chemistry at high frequency in this region, particularly in coastal waters. We report here on the first high-frequency (1 <span class="inline-formula">h</span>), multi-year (5 years) dataset of salinity, temperature, <span class="inline-formula">CO₂</span> partial pressure (<span class="inline-formula">pCO₂</span>) and pH at a coastal site (bottom depth of 12 <span class="inline-formula">m</span>) in a high-Arctic fjord (Kongsfjorden, Svalbard). Discrete measurements of dissolved inorganic carbon and total alkalinity were also performed. We show that (1) the choice of formulations for calculating the dissociation constants of the carbonic acid remains unsettled for polar waters, (2) the water column is generally somewhat stratified despite the shallow depth, (3) the saturation state of calcium carbonate is subject to large seasonal changes but never reaches undersaturation (<span class="inline-formula">Ω_a</span> ranges between 1.4 and 3.0) and (4) <span class="inline-formula">pCO₂</span> is lower than atmospheric <span class="inline-formula">CO₂</span> at all seasons, making this site a sink for atmospheric <span class="inline-formula">CO₂</span> (<span class="inline-formula">−</span>9 to <span class="inline-formula">−</span>16.8 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">mol</mi><mspace width="0.125em" linebreak="nobreak"/><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">2</mn></msub><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">yr</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="84pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="4e5889a0777e270956ecfd34b4695b60"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="essd-15-2809-2023-ie00001.svg" width="84pt" height="16pt" src="essd-15-2809-2023-ie00001.png"/></svg:svg></span></span>, depending on the parameterisation of the gas transfer velocity). Data are available on PANGAEA: <a href="https://doi.org/10.1594/PANGAEA.960131">https://doi.org/10.1594/PANGAEA.960131</a> <span class="cit" id="xref_paren.1">(<a href="#bib1.bibx32">Gattuso et al.</a>, <a href="#bib1.bibx32">2023</a><a href="#bib1.bibx32">a</a>)</span>.</p>