Data-based estimates of interannual sea–air CO<sub>2</sub> flux variations 1957–2020 and their relation to environmental drivers
<p>This study considers year-to-year and decadal variations in as well as secular trends of the sea–air <span class="inline-formula">CO<sub>2</sub></span> flux over the 1957–2020 period, as constrained by the <span class="inline-formula"><i...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-05-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/19/2627/2022/bg-19-2627-2022.pdf |
| Summary: | <p>This study considers
year-to-year and decadal variations in as well as secular trends
of the sea–air <span class="inline-formula">CO<sub>2</sub></span> flux over the 1957–2020 period,
as constrained by the <span class="inline-formula"><i>p</i></span><span class="inline-formula">CO<sub>2</sub></span> measurements from the SOCATv2021 database.
In a first step,
we relate interannual anomalies in ocean-internal carbon sources and sinks
to local interannual anomalies in
sea surface temperature (SST), the temporal changes in SST (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi mathvariant="normal">dSST</mi><mo>/</mo><mi mathvariant="normal">d</mi><mi>t</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="46pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="1a0163aad574aca97b29c36bb85b047f"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-19-2627-2022-ie00001.svg" width="46pt" height="14pt" src="bg-19-2627-2022-ie00001.png"/></svg:svg></span></span>),
and squared wind speed (<span class="inline-formula"><i>u</i><sup>2</sup></span>),
employing a multi-linear regression.
In the tropical Pacific, we find interannual variability to be dominated by <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi mathvariant="normal">dSST</mi><mo>/</mo><mi mathvariant="normal">d</mi><mi>t</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="46pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="fb5dd6eff66c05c246f188eb3bc63eab"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-19-2627-2022-ie00002.svg" width="46pt" height="14pt" src="bg-19-2627-2022-ie00002.png"/></svg:svg></span></span>,
as arising from variations in the upwelling of colder and more carbon-rich waters into the mixed layer.
In the eastern upwelling zones as well as in circumpolar bands in the high latitudes of both hemispheres,
we find sensitivity to wind speed,
compatible with the entrainment of carbon-rich water during wind-driven deepening of the mixed layer
and wind-driven upwelling.
In the Southern Ocean,
the secular increase in wind speed leads to a secular increase in the carbon source into the mixed layer,
with an estimated reduction in the sink trend in the range of <span class="inline-formula">17</span> % to <span class="inline-formula">42 <i>%</i></span>.
In a second step,
we combined the result of the multi-linear regression and
an explicitly interannual <span class="inline-formula"><i>p</i></span><span class="inline-formula">CO<sub>2</sub></span>-based additive correction
into a “hybrid” estimate of the sea–air <span class="inline-formula">CO<sub>2</sub></span> flux over the period 1957–2020.
As a <span class="inline-formula"><i>p</i></span><span class="inline-formula">CO<sub>2</sub></span> mapping method,
it combines (a) the ability of a regression to bridge data gaps and extrapolate into
the early decades almost void of <span class="inline-formula"><i>p</i></span><span class="inline-formula">CO<sub>2</sub></span> data
based on process-related observables
and (b) the ability of an auto-regressive interpolation to follow signals
even if not represented in the chosen set of explanatory variables.
The “hybrid” estimate can be applied as an ocean flux prior for
atmospheric <span class="inline-formula">CO<sub>2</sub></span> inversions covering the whole period of atmospheric <span class="inline-formula">CO<sub>2</sub></span> data since 1957.</p> |
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| ISSN: | 1726-4170 1726-4189 |