| 1. |
- Gutiérrez Loza, Lucia, et al.
(author)
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Air–sea CO2 exchange in the Baltic Sea—A sensitivity analysis of the gas transfer velocity
- 2021
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In: Journal of Marine Systems. - : Elsevier. - 0924-7963 .- 1879-1573. ; 222
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Journal article (peer-reviewed)abstract
- Air–sea gas fluxes are commonly estimated using wind-based parametrizations of the gas transfer velocity. However, neglecting gas exchange forcing mechanisms – other than wind speed – may lead to large uncertainties in the flux estimates and the carbon budgets, in particular, in heterogeneous environments such as marginal seas and coastal areas. In this study we investigated the impact of including relevant processes to the air–sea CO2 flux parametrization for the Baltic Sea. We used six parametrizations of the gas transfer velocity to evaluate the effect of precipitation, water-side convection, and surfactants on the net CO2 flux at regional and sub-regional scale. The differences both in the mean CO2 fluxes and the integrated net fluxes were small between the different cases. However, the implications on the seasonal variability were shown to be significant. The inter-annual and spatial variability were also found to be associated with the forcing mechanisms evaluated in the study. In addition to wind, water-side convection was the most relevant parameter controlling the air–sea gas exchange at seasonal and inter-annual scales. The effect of precipitation and surfactants seemed negligible in terms of the inter-annual variability. The effect of water-side convection and surfactants resulted in a reduction of the downward fluxes, while precipitation was the only parameter that resulted in an enhancement of the net uptake in the Baltic Sea.
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| 2. |
- Gutiérrez-Loza, Lucía, 1989-, et al.
(author)
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Evaluating the effect of precipitation on air-sea CO2 exchange using eddy covariance measurements
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Other publication (other academic/artistic)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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| 3. |
- Gutiérrez Loza, Lucia, et al.
(author)
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Measurement of air-sea methane fluxes in the Baltic Sea using the eddy covariance method
- 2019
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In: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 7
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Journal article (peer-reviewed)abstract
- Methane (CH4) is the second-most important greenhouse gas in the atmosphere having a significant effect on global climate. The ocean-particularly the coastal regions-have been recognized to be a net source of CH4, however, the constraints on temporal and spatial resolution of CH4 measurements have been the limiting factor to estimate the total oceanic contributions. In this study, the viability of micrometeorological methods for the analysis of CH4 fluxes in the marine environment was evaluated. We present 1 year of semi-continuous eddy covariance measurements of CH4 atmospheric dry mole fractions and air-sea CH4 flux densities at the Ostergarnsholm station at the east coast of the Gotland Island in the central Baltic Sea. The mean annual CH4 flux density was positive, indicating that the region off Gotland is a net source of CH4 to the atmosphere with monthly mean flux densities ranging between -0.1 and 36 nmol m(-2)s(-1). Both the air-water concentration gradient and the wind speed were found to be crucial parameters controlling the flux. The results were in good agreement with other measurements in the Baltic Sea reported in the MEMENTO database. Our results suggest that the eddy covariance technique is a useful tool for studying CH4 fluxes and improving the understanding of air-sea gas exchange processes with high-temporal resolution. Potentially, the high resolution of micrometeorological data can increase the understanding of the temporal variability and forcing processes of CH4 flux.
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| 4. |
- Gutiérrez-Loza, Lucía
(author)
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Mechanisms controlling air-sea gas exchange in the Baltic Sea
- 2020
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Licentiate thesis (other academic/artistic)abstract
- Carbon plays a major role in physical and biogeochemical processes in the atmosphere, the biosphere, and the ocean. CO2 and CH4 are two of the most common carbon-containing compounds in the atmosphere, also recognized as major greenhouse gases. The exchange of CO2 and CH4 between the ocean and the atmosphere is an essential part of the global carbon cycle. The exchange is controlled by the air–sea concentration gradient and by the efficiency of the transfer processes. The lack of knowledge about the forcing mechanisms affecting the exchange of these climate-relevant gases is a major source of uncertainty in the estimation of the global oceanic contributions. Quantifying and understanding the air–sea exchange processes is essential to constrain the estimates and to improve our knowledge about the current and future climate. In this thesis, the mechanisms controlling the air–sea gas exchange in the Baltic Sea are investigated.The viability of micrometeorological techniques for CH4 monitoring in a coastal environment is evaluated. One year of semi-continuous measurements of air–sea CH4 fluxes using eddy covariance measurements suggests that the method is useful for CH4 flux estimations in marine environments. The measurements allow long-term monitoring at high frequency rates, thus, capturing the temporal variability of the flux. The region off Gotland is a net source of CH4, with both the air–sea concentration gradient and the wind as controlling mechanisms.A sensitivity analysis of the gas transfer velocity is performed to evaluate the effect of the forcing mechanisms controlling the air–sea CO2 exchange in the Baltic Sea. This analysis shows that the spatio-temporal variability of CO2 fluxes is strongly modulated by water-side convection, precipitation, and surfactants. The effect of these factors is relevant both at regional and global scales, as they are not included in the current budget estimates.
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| 5. |
- Gutiérrez-Loza, Lucía, 1989-
(author)
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On mechanisms controlling air-sea gas exchange
- 2022
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Doctoral thesis (other academic/artistic)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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| 6. |
- Gutiérrez Loza, Lucia, et al.
(author)
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On physical mechanisms enhancing air-sea CO2 exchange
- 2022
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In: Biogeosciences. - : European Geosciences Union (EGU). - 1726-4170 .- 1726-4189. ; 19:24, s. 5645-5665
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Journal article (peer-reviewed)abstract
- Reducing uncertainties in the air–sea CO2 flux calculations is one of the major challenges when addressing the oceanic contribution in the global carbon balance. In traditional models, the air–sea CO2 flux is estimated using expressions of the gas transfer velocity as a function of wind speed. However, other mechanisms affecting the variability in the flux at local and regional scales are still poorly understood. The uncertainties associated with the flux estimates become particularly large in heterogeneous environments such as coastal and marginal seas. Here, we investigated the air–sea CO2 exchange at a coastal site in the central Baltic Sea using nine years of eddy covariance measurements. Based on these observations we were able to capture the temporal variability of the air–sea CO2 flux and other parameters relevant for the gas exchange. Our results show that a wind-based model with similar pattern to those developed for larger basins and open sea condition can, on average, be a good approximation for k. However, in order to reduce the uncertainty associated to these averages and produce reliable short-term k estimates, additional physical processes must be considered. Using a normalized gas transfer velocity, we identified conditions associated to enhanced exchange (large k values). During high and intermediate wind speeds (above 6–8 m s−1),conditions on both sides of the air–water interface were found to be relevant for the gas exchange. Our findings further suggest that at such relatively high wind speeds, sea spray is an efficient mechanisms for air–sea CO2 exchange. During low wind speeds (<6 m s−1), water-side convection was found to be a relevant control mechanism. The effect of both sea spray and water-side convection on the gas exchange showed a clear seasonality with positive fluxes (winter conditions) being the most affected.
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| 7. |
- Gutierrez-Loza, Lucia, et al.
(author)
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The Effect of Breaking Waves on Air-Sea Fluxes in the Coastal Zone
- 2018
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In: Boundary-layer Meteorology. - : SPRINGER. - 0006-8314 .- 1573-1472. ; 168:2, s. 343-360
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Journal article (peer-reviewed)abstract
- The influence of wave-associated parameters controlling turbulent fluxes through the air-sea interface is investigated in a coastal region. A full year of high-quality data of direct estimates of air-sea fluxes based on eddy-covariance measurements is presented. The study area located in Todos Santos Bay, Baja California, Mexico, is a net sink of with a mean flux of (). The results of a quantile-regression analysis computed between the flux and, (1) wind speed, (2) significant wave height, (3) wave steepness, and (4) water temperature, suggest that the significant wave height is the most correlated parameter with the magnitude of the flux but the behaviour of the relation varies along the probability distribution function, with the slopes of the regression lines presenting both positive and negative values. These results imply that the presence of surface waves in coastal areas is the key factor that promotes the increase of the flux from and into the ocean. Further analysis suggests that the local characteristics of the aqueous and atmospheric layers might determine the direction of the flux.
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| 8. |
- Martinez-Osuna, Juan F., et al.
(author)
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Coastal buoy data acquisition and telemetry system for monitoring oceanographic and meteorological variables in the Gulf of Mexico
- 2021
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In: Measurement. - : Elsevier. - 0263-2241 .- 1873-412X. ; 183
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Journal article (peer-reviewed)abstract
- This paper presents a data acquisition and telemetry system designed and built to monitor oceanographic and meteorological parameters. A voltage regulator and readout module was designed for the reading of data from a set of dedicated commercial sensors and to continuously monitor the voltage level of the power supply. In order to monitor the measured parameters and the status of the buoy remotely, a data string was transmitted every hour using an Iridium satellite transceiver. The described system was implemented and tested in four coastal oceanographic buoys that were deployed and operated in remote sites in the Gulf of Mexico (GoM) for several months in 2016. The data recorded by the buoys is used to describe the oceanographic and meteorological conditions at each site. The system proved to be reliable for long-term monitoring at offshore sites, requiring only minor corrective maintenance during their operation in the field.
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| 9. |
- Van Dam, Bryce, et al.
(author)
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Global Trends in Air-Water CO2 Exchange Over Seagrass Meadows Revealed by Atmospheric Eddy Covariance
- 2021
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In: Global Biogeochemical Cycles. - : American Geophysical Union (AGU). - 0886-6236 .- 1944-9224. ; 35:4
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Journal article (peer-reviewed)abstract
- Coastal vegetated habitats like seagrass meadows can mitigate anthropogenic carbon emissions by sequestering CO2 as “blue carbon” (BC). Already, some coastal ecosystems are actively managed to enhance BC storage, with associated BC stocks included in national greenhouse gas inventories. However, the extent to which BC burial fluxes are enhanced or counteracted by other carbon fluxes, especially air-water CO2 flux (FCO2) remains poorly understood. In this study, we synthesized all available direct FCO2 measurements over seagrass meadows made using atmospheric Eddy Covariance, across a globally representative range of ecotypes. Of the four sites with seasonal data coverage, two were net CO2 sources, with average FCO2 equivalent to 44%–115% of the global average BC burial rate. At the remaining sites, net CO2 uptake was 101%–888% of average BC burial. A wavelet coherence analysis demonstrated that FCO2 was most strongly related to physical factors like temperature, wind, and tides. In particular, tidal forcing was a key driver of global-scale patterns in FCO2, likely due to a combination of lateral carbon exchange, bottom-driven turbulence, and pore-water pumping. Lastly, sea-surface drag coefficients were always greater than the prediction for the open ocean, supporting a universal enhancement of gas-transfer in shallow coastal waters. Our study points to the need for a more comprehensive approach to BC assessments, considering not only organic carbon storage, but also air-water CO2 exchange, and its complex biogeochemical and physical drivers.
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