the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Spatial distributions of iron and manganese in surface waters in the Arctic’s Laptev and East Siberian seas
Abstract. The Arctic’s Laptev and East Siberian Seas (LESS) is a region with high biogeochemical activity. Nutrient inputs associated with river runoff and shelf sediment-water exchange processes are vital for supporting primary production in the LESS. However, the dynamics of trace metals such as iron (Fe) and manganese (Mn), which are essential micronutrients for primary producers, remain unknown in the LESS. Here, we present data on Fe and Mn in surface waters in the late summer of 2021 and discuss the factors controlling their concentrations and distributions on the surface of the LESS continental margins. Property of surface waters in the East Siberian Sea and Chukchi Abyssal Plain differed significantly from the Makarov and Amundsen Basins. Nutrient-rich Pacific-sourced water exists in the East Siberian Shelf with a high dissolved Mn (dMn) concentration. Pacific-sourced water also receives a large sedimentary flux that releases dMn onto the continental shelf. Dissolved Fe (dFe) could have been released on the shelf as well; however, dFe remained low in the Pacific-sourced water. This is because dFe re-precipitated more rapidly than dMn because of the difference in removal kinetics. In contrast, relatively nutrient-poor Atlantic-sourced water exists in the Makarov and Amundsen Basins. A positive correlation between the fraction of meteoric water (river water and precipitation), dFe, and humic-like colored dissolved organic matter (CDOM) in Atlantic-sourced water confirmed a common freshwater source for dFe and CDOM. Terrigenous organic ligands likely stabilized Fe in the dissolved phase, which was not the case for Mn. The fraction of sea ice meltwater was not correlated with dFe and dMn in any part of the sampling domain. Our results indicate that the major factors controlling these metal concentrations in the LESS continental margins are river discharge and the input of shelf sediment.
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RC1: 'Comment on egusphere-2024-1834', Anonymous Referee #1, 20 Aug 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1834/egusphere-2024-1834-RC1-supplement.pdf
- AC1: 'Reply on RC1', Naoya Kanna, 26 Sep 2024
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RC2: 'Comment on egusphere-2024-1834', Anonymous Referee #2, 26 Aug 2024
This research investigates the concentrations and distributions of dissolved iron (dFe) and manganese (dMn) in the surface waters of the Laptev and East Siberian Seas (LESS) during the late summer of 2021. The study concludes that the concentrations of dFe and dMn in the LESS are primarily controlled by river discharge and shelf sediment inputs rather than by sea ice melt. The manuscript contributes important data to the relatively understudied area of trace metal dynamics in the Arctic. The descriptions of sampling and analyzing methods are solid. While this manuscript leans more toward descriptive analysis, it still offers valuable insights into the region's biogeochemical processes. I have several comments on this manuscript:
Major Comments:
- Revise the Abstract: The abstract lacks clarity and does not efficiently summarize the entire article. The wording is awkward in places, such as in the phrase "Nutrient-rich Pacific-sourced water exists...," which does not clearly convey that this water mass is dominant in the region. The conclusion section is clearer and does a better job of summarizing the findings. Please rewrite or revise the abstract for better clarity and conciseness.
- Reorganize the structure. The method for calculating water mass fractions, described in lines 181–210, should be moved to Section 2 (Methods)
- Lines 211–220 do not present the mass fraction of Atlantic water. This information should be included. And its also not shown in Figure 3.
- Section 4.2.1: The sedimentary contribution to dFe and dMn is not adequately discussed.
- Line 334–335: This section is unclear. Although sedimentary inputs to dFe and dMn were discussed in Section 4.2.1, the correlations between TdFe, TdMn, dFe, and dMn should be more clearly explained.
- Figure 6 and Line 297: What are the possible explanations for the outliers with high TdFe and TdMn? Are these stations heavily influenced by sedimentary inputs? Please address these points.
- Section 4.4 and Figure 11: The comparison with other studies is valuable, but Figure 11 caption is not informative enough and needs to be modified. Please properly cite data sources in the figure captions. Use different symbols for different data sources instead of the same symbols, and highlight the data from this study using distinct symbols. Additionally, I suggest adding a summary figure by region to show how the data from this study compares with or complements the range of data reported in previous research.
Minor Comments:
- Considering color figure 2 by the δ¹⁸O values and using different symbols to distinguish the different ice stations.
- The differences between total dissolved iron (TdFe) and total dissolved manganese (TdMn) should be clearly defined in the methods section. A detailed explanation is not provided until line 184. It should be clarified that total dissolved Fe includes both dissolved and particulate Fe in the water column.
- Line 257–260: The phrase "deviated towards" is confusing in this context. The surface water is not close to the meteoric δ¹⁸O values, although the salinity is close. It seems you might mean "deviated from" instead. Please revise this sentence for clarity.
- Definition of fmw: On line 306, clarify that fmw includes river runoff and local precipitation in the calculation of water mass fractions. (Please refer to Major Comment 3)
- Figure 7b and Line 319: I am curious about the r and p values for AMW and PMW separately. Please include these in the figure, as you have done in Figure 7a, even if they are not statistically significant.
- Figure 10b: Please report the r and p values in Figure 10b, as you did in Figure 10a, even though the correlations are not statistically significant.
Citation: https://doi.org/10.5194/egusphere-2024-1834-RC2 - AC2: 'Reply on RC2', Naoya Kanna, 26 Sep 2024
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