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<p>The central Arctic Ocean (CAO) plays an important role in the global carbon cycle, but the current and future exchange of the climate-forcing trace gases methane (<span class="inline-formula">CH₄</span>) and carbon dioxide (<span class="inline-formula">CO₂</span>) between the CAO and the atmosphere is highly uncertain. In particular, there are very few observations of near-surface gas concentrations or direct air–sea <span class="inline-formula">CO₂</span> flux estimates and no previously reported direct air–sea <span class="inline-formula">CH₄</span> flux estimates from the CAO. Furthermore, the effect of sea ice on the exchange is not well understood. We present direct measurements of the air–sea flux of <span class="inline-formula">CH₄</span> and <span class="inline-formula">CO₂</span>, as well as air–snow fluxes of <span class="inline-formula">CO₂</span> in the summertime CAO north of 82.5<span class="inline-formula">^∘</span> N from the Synoptic Arctic Survey (SAS) expedition carried out on the Swedish icebreaker <i>Oden</i> in 2021.</p> <p>Measurements of air–sea <span class="inline-formula">CH₄</span> and <span class="inline-formula">CO₂</span> flux were made using floating chambers deployed in leads accessed from sea ice and from the side of <i>Oden</i>, and air–snow fluxes were determined from chambers deployed on sea ice. Gas transfer velocities determined from fluxes and surface-water-dissolved gas concentrations exhibited a weaker wind speed dependence than existing parameterisations, with a median sea-ice lead gas transfer rate of 2.5 <span class="inline-formula">cm h⁻¹</span> applicable over the observed 10 <span class="inline-formula">m</span> wind speed range (1–11 <span class="inline-formula">m s⁻¹</span>). The average observed air–sea <span class="inline-formula">CO₂</span> flux was <span class="inline-formula">−</span>7.6 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M20" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">mmol</mi><mspace linebreak="nobreak" width="0.125em"/><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">d</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="67pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="6add7475d1c0615a24800106f13ac773"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-671-2024-ie00001.svg" width="67pt" height="13pt" src="bg-21-671-2024-ie00001.png"/></svg:svg></span></span>, and the average air–snow <span class="inline-formula">CO₂</span> flux was <span class="inline-formula">−</span>1.1 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M23" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">mmol</mi><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">d</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="67pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="8c4b3213a0a8ab1c445432263e63f72b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-671-2024-ie00002.svg" width="67pt" height="13pt" src="bg-21-671-2024-ie00002.png"/></svg:svg></span></span>. Extrapolating these fluxes and the corresponding sea-ice concentrations gives an August and September flux for the CAO of <span class="inline-formula">−</span>1.75 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M25" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">mmol</mi><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">d</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="67pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="7577e0735720859b6cef6768466f7d08"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-671-2024-ie00003.svg" width="67pt" height="13pt" src="bg-21-671-2024-ie00003.png"/></svg:svg></span></span>, within the range of previous indirect estimates.</p> <p>The average observed air–sea <span class="inline-formula">CH₄</span> flux of 3.5 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M27" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">µ</mi><mi mathvariant="normal">mol</mi><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">d</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="64pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="d4b681ee9159c6466a531df63bb9f062"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-671-2024-ie00004.svg" width="64pt" height="15pt" src="bg-21-671-2024-ie00004.png"/></svg:svg></span></span>, accounting for sea-ice concentration, equates to an August and September CAO flux of 0.35 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M28" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">µ</mi><mi mathvariant="normal">mol</mi><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">d</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="64pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="f92bc3adeb03ab641b77d252d5bbc101"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-671-2024-ie00005.svg" width="64pt" height="15pt" src="bg-21-671-2024-ie00005.png"/></svg:svg></span></span>, lower than previous estimates and implying that the CAO is a very small (<span class="inline-formula">≪</span> 1 %) contributor to the Arctic flux of <span class="inline-formula">CH₄</span> to the atmosphere.</p>