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- Gutiérrez-Loza, Lucía, 1989-, et al.
(författare)
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Evaluating the effect of precipitation on air-sea CO2 exchange using eddy covariance measurements
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The air-sea exchange of carbon dioxide (CO2) is modulated by processes controlling the physical and biogeochemical characteristics of the upper layer of the ocean. One such process is precipitation, which is known to alter the surface layer of the ocean via rain-induced turbulence, deposition of dissolved CO2, and through changes of the temperature, salinity, and chemical composition of the surface waters (i.e. dilution effects). Even though great advances have been made in the understanding of these mechanisms, and their impact on the regional and global air-sea CO2 fluxes from laboratory experiments and numerical models, the effect of rain and other types of precipitation has seldom been studied using field data. In this study, we use eddy covariance based measurements of air-sea CO2 flux along with in-situ precipitation data from the Östergarnsholm station in the central Baltic Sea, to evaluate the effect of precipitation on the gas exchange. The results show that most types of precipitation enhance the CO2 transport when the flux is positive, i.e. from the ocean to the atmosphere, in particular during high wind-speed conditions. Negative fluxes, on the other hand, are less affected by precipitation. Snow, and mixed precipitation of rain with snow, induce the greatest increase on the exchange rate, while smaller droplets like drizzle cause smaller enhancement. According to the results presented here, not only the impact of rain, but all types of precipitation, should be accounted for in the air-sea CO2 flux estimates, even in regions where precipitation rates are low. At high latitudes, accounting for these effects, in particular the effect of snow and other solid types of precipitations, might be essential to constrain regional CO2 flux estimates.
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| 2. |
- Gutiérrez-Loza, Lucía, 1989-
(författare)
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On mechanisms controlling air-sea gas exchange
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Carbon is essential to the Earth’s system functioning, playing a major role in physical and biogeochemical processes in the atmosphere, the terrestrial biosphere, and the oceans. The concentration of carbon-based greenhouse gases in the atmosphere, such as carbon dioxide (CO2) and methane (CH4), has been increasing since the industrial era. Therefore, assessing the redistribution of these greenhouse gases between the Earth’s reservoirs has become essential for understanding the current climate system and modelling future climate scenarios.The oceans are a component of the global carbon cycle, and their role as sinks and sources of greenhouse gases has significant implications for the Earth’s climate. The gas exchange between the atmosphere and the ocean is driven by the concentration difference in these two reservoirs. However, the turbulent processes in the layers adjacent to the ocean surface control the efficiency of the transport.This thesis investigates mechanisms controlling the air–sea gas exchange using direct measurements of CO2 and CH4 fluxes from the Östergarnsholm station in the Central Baltic Sea. The gas exchange of both gases is found to have a strong variability at time scales from sub-hourly to inter-annual. The region is found to be a net source of CH4, with both the concentration gradient and wind as controlling mechanisms. In the case of the CO2 fluxes, the variability is strongly modulated by local processes such as sea spray and water-side convection, as well as precipitation. Interestingly, an asymmetric effect is observed, with these processes enhancing the upward transport of CO2 but not the downward flux. Furthermore, a model-based sensitivity analysis of the gas transfer velocity is performed to evaluate the effect of the forcing mechanisms on the air-sea gas exchange at a regional scale. The results show that water-side convection, precipitation, and surfactants strongly modulate the spatio-temporal variability of the CO2 fluxes in the Baltic Sea.
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