Dried, closed-path eddy covariance method for measuring carbon dioxide flux over sea ice

Brian J. Butterworth, Brent G. T. Else
2018 Atmospheric Measurement Techniques  
<p><strong>Abstract.</strong> The Arctic marine environment plays an important role in the global carbon cycle. However, there remain large uncertainties in how sea ice affects air–sea fluxes of carbon dioxide (<span class="inline-formula">CO<sub>2</sub></span>), partially due to disagreement between the two main methods (enclosure and eddy covariance) for measuring <span class="inline-formula">CO<sub>2</sub></span> flux (<span class="inline-formula"><math
more » ... 3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>F</mi><mrow><mi mathvariant="normal">CO</mi><msub><mi/><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="6b8cbfd9be1fe094f1cc39ba3389da73"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-11-6075-2018-ie00001.svg" width="23pt" height="14pt" src="amt-11-6075-2018-ie00001.png"/></svg:svg></span></span>). The enclosure method has appeared to produce more credible <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>F</mi><mrow><mi mathvariant="normal">CO</mi><msub><mi/><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="647cda4c1184e3ee1e2e34e33689234d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-11-6075-2018-ie00002.svg" width="23pt" height="14pt" src="amt-11-6075-2018-ie00002.png"/></svg:svg></span></span> than eddy covariance (EC), but is not suited for collecting long-term, ecosystem-scale flux datasets in such remote regions. Here we describe the design and performance of an EC system to measure <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>F</mi><mrow><mi mathvariant="normal">CO</mi><msub><mi/><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="0632e7a6a53d08c3ed8efc4956b7f74c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-11-6075-2018-ie00003.svg" width="23pt" height="14pt" src="amt-11-6075-2018-ie00003.png"/></svg:svg></span></span> over landfast sea ice that addresses the shortcomings of previous EC systems. The system was installed on a 10<span class="thinspace"></span>m tower on Qikirtaarjuk Island – a small rock outcrop in Dease Strait located roughly 35<span class="thinspace"></span>km west of Cambridge Bay, Nunavut, in the Canadian Arctic Archipelago. The system incorporates recent developments in the field of air–sea gas exchange by measuring atmospheric <span class="inline-formula">CO<sub>2</sub></span> using a closed-path infrared gas analyzer (IRGA) with a dried sample airstream, thus avoiding the known water vapor issues associated with using open-path IRGAs in low-flux environments. A description of the methods and the results from 4 months of continuous flux measurements from May through August 2017 are presented, highlighting the winter to summer transition from ice cover to open water. We show that the dried, closed-path EC system greatly reduces the magnitude of measured <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>F</mi><mrow><mi mathvariant="normal">CO</mi><msub><mi/><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="201812cb0124c03de581e702a3f1399b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-11-6075-2018-ie00004.svg" width="23pt" height="14pt" src="amt-11-6075-2018-ie00004.png"/></svg:svg></span></span> compared to simultaneous open-path EC measurements, and for the first time reconciles EC and enclosure flux measurements over sea ice. This novel EC installation is capable of operating year-round on solar and wind power, and therefore promises to deliver new insights into the magnitude of <span class="inline-formula">CO<sub>2</sub></span> fluxes and their driving processes through the annual sea ice cycle.</p>
doi:10.5194/amt-11-6075-2018 fatcat:wdz7umfvfnaa3nxn376gmqru3i