the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Sep 2024
Aerosol trace element solubility and deposition fluxes over the polluted, dusty Mediterranean and Black Sea basins
Abstract. Aerosol samples collected during summer 2013 on GEOTRACES cruise GA04 in the Mediterranean and Black seas were analysed for their soluble and total metal and major ion composition. The fractional solubilities (soluble / total concentrations) of the lithogenic elements (Al, Ti, Mn, Fe, Co, Th) varied strongly with atmospheric dust loading. Solubilities of these elements in samples that contained high concentrations of mineral dust were noticeably lower than at equivalent dust concentrations over the Atlantic Ocean. This behaviour probably reflects the distinct transport and pollutant regimes of the Mediterranean basin. Elements with more intense anthropogenic sources (P, V, Ni, Cu, Zn, Cd, Pb) had a variety of largely independent sources in the region and generally displayed higher fractional solubilities than the lithogenic elements. Calculated dry deposition fluxes showed a west to east decline in the N/P ratio in deposition over the Mediterranean, a factor that contributes to the P-limited status of the eastern basin. Atmospheric deposition may make a significant contribution to the surface water budgets of Mn and Zn in the western Mediterranean.
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RC1: 'Comment on egusphere-2024-2667', Anonymous Referee #1, 02 Oct 2024
This manuscript by Shelley et al. investigates aerosol trace element solubility and deposition fluxes over the polluted and dusty Mediterranean and Black Sea regions. The study provides valuable insights into the interplay between natural mineral dust and anthropogenic pollutants by analyzing aerosol samples to quantify the soluble and total concentrations of various lithogenic and anthropogenic elements. The authors explore how different air mass origins, such as North African dust and European pollution, influence these concentrations and examine the impact of atmospheric deposition on nutrient ratios and element budgets in the Mediterranean Sea.
While the observations are limited to a specific period, the paper nonetheless contributes significantly to understanding aerosol trace element solubility and its implications for marine nutrient cycling. Additionally, the manuscript is well-organized and clearly written. Below, I offer some minor suggestions for the authors consideration:
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Section 2.3.3: Some ions mentioned in this section are not discussed in subsequent sections, such as Br⁻ and K⁺. I suggest removing these ions unless they are addressed later. Furthermore, is there data on NH₄⁺ recovery that could be included?
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Section 2.5: As the authors acknowledge, there are substantial uncertainties in the estimation of deposition velocities (Vd). If this section is to remain in the main body of the text, I recommend providing a more detailed uncertainty analysis. For instance, could the authors incorporate model results to assess the impact of these uncertainties?
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Section 2.6: The manuscript states that “samples were assigned to one of five air mass types, indicative of likely aerosol source characteristics as described below.” Was this classification based on a subjective assessment, or was an algorithm or objective method used? Were there any ambiguous cases that the authors had to resolve, and if so, how?
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Section 3.1: In Figure 2, rather than showing an example trajectory for each air mass type, would it be possible to display the mean trajectory for each class? Additionally, the colors used for the borders of the LE and LAN areas are too similar to the trajectory colors, which makes the figure somewhat confusing. I suggest modifying the color scheme. Lastly, the text mentions 'LAM,' but the figure is labeled as 'LA'—this inconsistency should be corrected.
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Section 3.2: In Figure 3 (and in similar figures later on), it would be clearer to differentiate air mass types by using distinct colors for each type rather than using different colors for the various elements, which does not seem to add much clarity to the interpretation.
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Section 3.6: The authors list several factors that influence element solubility. While they appropriately acknowledge that some mechanisms cannot be fully explored due to missing data, I believe that the discussion of acidity effects could be strengthened. Specifically, when discussing the role of acidic species concentrations, the authors should clarify to readers that while these concentrations provide useful insights, they do not directly represent aerosol pH. It would be helpful to explicitly state the limitations of using these parameters as proxies for aerosol acidity.
Citation: https://doi.org/10.5194/egusphere-2024-2667-RC1 -
AC1: 'Reply on RC1', Alex Baker, 01 Nov 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2667/egusphere-2024-2667-AC1-supplement.pdf
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RC2: 'Comment on egusphere-2024-2667', Karine Desboeufs, 06 Oct 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2667/egusphere-2024-2667-RC2-supplement.pdf
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AC2: 'Reply on RC2', Alex Baker, 01 Nov 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2667/egusphere-2024-2667-AC2-supplement.pdf
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AC2: 'Reply on RC2', Alex Baker, 01 Nov 2024
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RC3: 'Comment on egusphere-2024-2667', Anonymous Referee #3, 22 Oct 2024
Review of “Aerosol trace element solubility and deposition fluxes over the polluted, dusty Mediterranean and Black Sea basins” by R. Shelley et al.
An interesting work reporting trace metals, their solubility and dry atmospheric fluxes during GA04 cruise in Mediterranean (Med) and Black seas. The manuscript is well-written and deserves publication after addressing the following points:
General comments:
- Since the campaign covers a period during summer, as title I would suggest: Aerosol trace element solubility and deposition fluxes over the Mediterranean and Black Sea basins during summer time (or warm period if they wish).
- There is a good amount of works based on either long-term or annual basis sampling and reported fluxes of nutrients and elements in the Mediterranean and Black Sea which are missing. Please compare with them. Below a non-exhaustive list:
Theodosi C., Markaki Z., Pantazoglou F., Tselepides A., Mihalopoulos N., Chemical composition of downward fluxes in the Cretan Sea (Eastern Mediterranean) and possible link to atmospheric deposition: A 7 year survey, Deep-Sea Research Part II, 164, 89-99, 2019.
Desboeufs, K., Bon Nguyen, E., Chevaillier, S., Triquet, S., and Dulac, F.: Fluxes and sources of nutrient and trace metal atmospheric deposition in the northwestern Mediterranean, Atmos. Chem. Phys., 18, 14477–14492, doi.org/10.5194/acp-18-14477-2018, 2018.
Im U., S. Christodoulaki, K. Violaki, P. Zarbas, M. Kocak, N. Daskalakis, N. Mihalopoulos and M. Kanakidou, Atmospheric deposition of nitrogen and sulfur over Europe with focus on the Mediterranean and the Black Sea, Atmospheric Environment, 81, 660-670, 2013.
Markaki Z., M.D. Loye-Pilot, K. Violaki, L. Benyahya, N. Mihalopoulos, Variability of atmospheric deposition of dissolved nitrogen and phosphorus in the Mediterranean and possible link to the anomalous seawater N/P ratio, Marine Chemistry, Volume 120, Issues 1-4, Pages 187-194, 2010.
Theodosi C., Z. Markaki, A. Tselepides, N. Mihalopoulos, The significance of atmospheric inputs of soluble and particulate major and trace metals to the eastern Mediterranean seawater, Marine Chemistry, Volume 120, Issues 1-4, 20, 154-163, 2010.
Guerzoni, S., Molinaroli, E., Rossini, P., Rampazzo, G., Quarantotto, G., and Cristini, S.: Role of desert aerosol in metal fluxes in the Mediterranean area, Chemosphere, 39, 229–246, https://doi.org/10.1016/S0045-6535(99)00105-8, 1999.
For Black Sea, Kocak et al., 2014 and references therein: Atmospheric deposition of macronutrients (dissolved inorganic nitrogen and phosphorous) onto the Black Sea and implications on marine productivity, Journal of the Atmospheric Sciences 73 (4), 1727-1739, 2014. There total deposition measurements performed in Black Sea (Varna, Bulgaria) during similar period (2013-2014) were reported
Other comments:
- Few words on meteorological conditions are missing. For instance, any rain event occurred during the cruise? Wind speed variability? This information is valuable for the reader.
- Figure 4: How the authors explain the increased soluble levels and the extremely high solubility for terrigenic elements such as Al, Fe and especially Mn (almost up to 100% for the last) under the influence of EEU air masses (pink color). A short comment would be very useful.
- Figure 7: Solubility as a function of aerosol load. Similar figure and results were reported by Theodosi et al., 2010 at Finokalia Crete for both wet and dry deposition. Please compare your findings with this work.
- For solubility: Did the authors calculate ionic balance as a better index of acidity or even better (SO4+NO3/NH4) ratio (in equivalent)? Any relation of (SO4+NO3/NH4) ratio with solubility?
- N/P ratio in the Mediterranean: Your finding about N/P variability across Mediterranean is in very good agreement with the study of Markaki et al 2010 and I think it is worth mentioning. “Markaki Z., M.D. Loye-Pilot, K. Violaki, L. Benyahya, N. Mihalopoulos, Variability of atmospheric deposition of dissolved nitrogen and phosphorus in the Mediterranean and possible link to the anomalous seawater N/P ratio, Marine Chemistry, Volume 120, Issues 1-4, Pages 187-194, 2010”
- For Black sea fluxes compare with the work of Kocak et al., 2014 and references therein.
Citation: https://doi.org/10.5194/egusphere-2024-2667-RC3 -
AC3: 'Reply on RC3', Alex Baker, 01 Nov 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2667/egusphere-2024-2667-AC3-supplement.pdf
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