Air–sea fluxes of greenhouse gases and oxygen in the northern Benguela Current region during upwelling events

Morgan, Eric J.; Lavric, Jost V.; Arévalo-Martínez, Damian L.; Bange, Hermann W.; Steinhoff, Tobias; Seifert, Thomas; Heimann, Martin

Ground-based atmospheric observations of inline-formulaCO2, inline-formulaδ(O2∕N2), inline-formulaN2O, and inline-formulaCH4 were used to make estimates of the air–sea fluxes of these species from the Lüderitz and Walvis Bay upwelling cells in the northern Benguela region, during upwelling events. Average flux densities (inline-formula±1σ) were inline-formula0.65±0.4inline-formulaµmol minline-formula−2 sinline-formula−1 for inline-formulaCO2, inline-formula M11inlinescrollmathml - normal 5.1 ± normal 2.5 52pt10ptsvg-formulamathimg933c0c0eac7ae5c810ff7be83feadc95 bg-16-4065-2019-ie00001.svg52pt10ptbg-16-4065-2019-ie00001.png inline-formulaµmol minline-formula−2 sinline-formula−1 for inline-formulaO2 (as APO), inline-formula0.61±0.5 nmol minline-formula−2 sinline-formula−1 for inline-formulaN2O, and inline-formula4.8±6.3 nmol minline-formula−2 sinline-formula−1 for inline-formulaCH4. A comparison of our top-down (i.e., inferred from atmospheric anomalies) flux estimates with shipboard-based measurements showed that the two approaches agreed within inline-formula±55 % on average, though the degree of agreement varied by species and was best for inline-formulaCO2. Since the top-down method overestimated the flux density relative to the shipboard-based approach for all species, we also present flux density estimates that have been tuned to best match the shipboard fluxes. During the study, upwelling events were sources of inline-formulaCO2, inline-formulaN2O, and inline-formulaCH4 to the atmosphere. inline-formulaN2O fluxes were fairly low, in accordance with previous work suggesting that the evasion of this gas from the Benguela is smaller than for other eastern boundary upwelling systems (EBUS). Conversely, inline-formulaCH4 release was quite high for the marine environment, a result that supports studies that indicated a large sedimentary source of inline-formulaCH4 in the Walvis Bay area. These results demonstrate the suitability of atmospheric time series for characterizing the temporal variability of upwelling events and their influence on the overall marine greenhouse gas (GHG) emissions from the northern Benguela region.

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Morgan, Eric J. / Lavric, Jost V. / Arévalo-Martínez, Damian L. / et al: Air–sea fluxes of greenhouse gases and oxygen in the northern Benguela Current region during upwelling events. 2019. Copernicus Publications.

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