the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
A high-resolution marine mercury model MITgcm-ECCO2-Hg with online biogeochemistry
Siyu Zhu
Peipei Wu
Siyi Zhang
Oliver Jahn
Yanxu Zhang
Abstract. Mercury (Hg) is a global persistent contaminant. Modeling studies are useful means of synthesizing a current understanding of the Hg cycle. Previous studies mainly use coarse-resolution models, which makes it impossible to analyze the role of turbulence in the Hg cycle and inaccurately describes the transport of kinetic energy. Furthermore, all of them are coupled with offline biogeochemistry, so they cannot respond to short-term variability in oceanic Hg concentration. Here we use a high-resolution (horizontal resolution is 1/5°) ocean model (MITgcm-ECCO2, high-resolution-MITgcm) coupled with the online biogeochemistry of Darwin project to simulate the global Hg cycle. The finer portrayal of surface Hg concentrations in estuarine and coastal areas, strong western boundary flow and upwelling areas, and concentration diffusion as vortex shapes demonstrate the effects of turbulence that are neglected in previous models. Ecological events such as algal blooms can cause a sudden enhancement of phytoplankton biomass and chlorophyll concentrations, which can also result in a dramatic change in particle-bound mercury sinking flux at the same time in our simulation. In the global estuary region, the inclusion of riverine Hg input in the high-resolution model allows us to reveal the outward spread of Hg in an eddy shape driven by fine-scale ocean currents. With faster current velocities and diffusion rates, our model captures the transport and mixing of Hg from river discharge in a more accurate and detailed way and improves our understanding of Hg cycle in the ocean.
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Siyu Zhu et al.
Status: closed
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RC1: 'Comment on gmd-2023-89', Maodian Liu, 20 Jul 2023
This manuscript presents the development and evaluation of a high-resolution online biogeochemical ocean mercury model. The model improves the resolution of mercury modeling to resolve better the influences including rivers and coastal areas, ocean turbulence, and the horizontal and vertical transport of substances in the ocean. The study is significant, as it fills the gap of only coupling offline biogeochemical models for ocean mercury research. The workload and computational cost are both considerable and impressive. I appreciate what this research group has done. It’s an overall well-written paper that deserves publication. I have some comments but they are all minor.
- Comment: introduction, “Finally, we study the fate of the riverine discharge of Hg and the impact of nutrients over coastal waters near big river mouths on the transport of coastal Hg.” The generalization doesn't seem to be entirely accurate. It is better to explain the specific influence of nutrients transported by rivers on marine mercury.
- Comment: Model description, can you explain why refractory particulate oxidized Hg is chosen as the tracer to characterize the fate of riverine discharge of Hg?
- Comment: line 236-238, “We find that riverine inputs of HgPR to the coastal ocean have a limited impact on Hg concentrations in surface seawater beyond the shelf region. HgPR is transported to the left or right along the coast by the Coriolis force, and the influence of currents and eddies leads to dispersion slightly further away from the coast.” To provide a more accurate depiction, it would be better to check the logical order of the sentences, and give more description about “slightly further away from the coast.”
- Comment: line 251-253, “Hg exports from rivers are important to specific coastal areas, Liu et al. (2021) have raised further concerns about riverine Hg and a deeper understanding of the role of rivers in the global Hg cycle. The discharge of HgPR from rivers greatly impacts environmental pollution in coastal and shelf regions.” This topic sentence does not correspond to the following.
- Comment: line 259-263, “The results show that HgPR spreads outward in an eddy shape, driven by HgPR concentrations and influenced by the kinetic energy transmission by ocean eddies and the mixing of turbulence. This further emphasizes the important role of eddy-driven processes and turbulence mixing, in the transport and distribution of riverine Hg in coastal and shelf regions.” It can be added that in comparison with previous models, your model results are more innovative and evolving.
- Comment: The expression can be more concise:
in lines 20-21, it would be better to replace “the inclusion of” with “including”;
in line 169, replace “takes into account” with “considers”;
in line 194, replace “at the same time” with “simultaneously”;
in line 205, replace “is the area with” with “has”;
in lines 210-211, replace “as compare to” with “more”;
in lines 233-234, replace “To gain a clearer understanding” with “To understand better”;
in line 285, replace “which can lead” with “leading”;
- Comment: in line 243, it is advisable to label which legend corresponds to the description;
- Comment: in line 250, punctuation is lost at the end.
- Comment: Empty filler words and phrases will make your writing not precise enough: in line 155, it is advisable to delete the “which is” in “…, which is a global, spatially explicit…” and in line 169, delete the “of which” in “all of which contribute to differences in oceanic Hg distribution”; in line 203, delete the “the effect of” in “the effect of turbulence across the ocean causes the spread of Hg in a vortical shape.”
- Comment: in line 62, replacing “couldn’t” with " could not " may be suitable.
- Comment: in line 269, it is advisable to modify “And” at the beginning of the sentence with “Moreover” will be more formal.
- Comment: in lines 314-315, “This suggests that the sinking of particle-bound Hg is influenced by ecological changes in seawater.” It will be better to use active voice.
- Comment: lines 318-319, “which promptly reflected the abrupt fluctuations in phytoplankton and enabled us to quickly observe changes in the sinking of Hg particles.” It will be better to replace it with “which promptly reflected the abrupt fluctuations in phytoplankton and enabled us to observe changes in the sinking of Hg particles quickly.”
- Comment: in line 329, you’d better delete “the” in front of “turbulence.”
- Comment: in line 150, you’d better add “that” in later of “infer.”
- Comment: in line 282, “undergo” should be written with “undergoes.”
Citation: https://doi.org/10.5194/gmd-2023-89-RC1 -
RC2: 'Comment on gmd-2023-89', Anonymous Referee #2, 20 Aug 2023
This manuscript introduces a high-resolution marine mercury model with concurrently model simulation of biogeological cycling. The higher resolution of the model makes it able to capture turbulence that can influence the mercury cycling of some local region. The application of concurrently simulated biogeochemistry or the cycling of phytoplankton enables the model to capture the particle-bound mercury sinking due to some ecological related and climate driven event such as increased effects of bio pump. The model also aims to capture the eddy or fine scale ocean current in the estuary region with riverine mercury input. Overall, the paper is well prepared and adds new knowledge and insights into the literature. For the authors to polish the paper, I have a few questions and comments, which I think also represent those from the general readers of GMD. After the authors address those points and include in the revision, I will enthusiastically support the publication of the paper in GMD.
The meaning of the term “online biogeochemistry” as used in the title is not intuitive for general readers who may think online means on the internet. To be friendly for general readers, I suggest authors using another term (e.g. concurrently simulated biogeochemistry processes) or explain the meaning in the abstract as early as possible.
Line 48, reference format
L 50, although this limitation is related to the contribution of this presented study, it would be better to point out all limitations of earlier models and then explain why overcoming this limitation is more important.
L58-59, “anthropogenic disturbances and climate-induced changes” is too general to make reader understand how the processes need to be characterized with high-resolution model.
L150, “Most” is unclear. Is it 50% or 90%? Better to give a the ranges quantitatively.
L192-193, Better to give quantitative information on how much closer to the observations can be brought in by the high-resolution model compared with the lower resolution model.
L206, “significant” is normally associated with statistical meaning. If no statistical test was conducted here, better to use the term “more apparent”.
L213, the figure caption is not intuitive.
L217, since the model is in higher resolution, river discharge being transferred along the seashores can be resolved, it is essential to mention the spatial resolution of the riverine discharge as the model input.
L280, “shorter time scales” How short? Give the specific time scale.
L293, “a certain range of time” what is the time range?
L297 and Fig 7: The description of “peak day” as shown in the figure by the vertical line should be added to the figure caption.
L300-301, it is indeed that nutrient levels during the peak days are above the average but it is unclear how can this suggests the occurrence of algal blooms here.
L325, elemental and divalent Hg
L329, besides turbulent mixing and shear effects, is there any other factors whose spatial variability is not capture by the model simulation? For example, continental input to the coastal sea. Is the emission at a resolution that match the resolution of 18 km. It is recommended that the authors put some discussions on factors that can influence the fine-scale processes and levels of Hg that are still not solved by this study.
Citation: https://doi.org/10.5194/gmd-2023-89-RC2 -
AC1: 'Comment on gmd-2023-89', Yanxu Zhang, 31 Aug 2023
Dear editor and dear reviewers,
Thank you for your letter and the reviews’ comments concerning our manuscript entitled “A high-resolution marine mercury model MITgcm-ECCO2-Hg with online biogeochemistry” (GMD-2023-89). These thoughtful comments are valuable and helpful for improving our paper. We have studied the comments carefully and responded to the referee’s comments. Please refer to the supplement for details.
Status: closed
-
RC1: 'Comment on gmd-2023-89', Maodian Liu, 20 Jul 2023
This manuscript presents the development and evaluation of a high-resolution online biogeochemical ocean mercury model. The model improves the resolution of mercury modeling to resolve better the influences including rivers and coastal areas, ocean turbulence, and the horizontal and vertical transport of substances in the ocean. The study is significant, as it fills the gap of only coupling offline biogeochemical models for ocean mercury research. The workload and computational cost are both considerable and impressive. I appreciate what this research group has done. It’s an overall well-written paper that deserves publication. I have some comments but they are all minor.
- Comment: introduction, “Finally, we study the fate of the riverine discharge of Hg and the impact of nutrients over coastal waters near big river mouths on the transport of coastal Hg.” The generalization doesn't seem to be entirely accurate. It is better to explain the specific influence of nutrients transported by rivers on marine mercury.
- Comment: Model description, can you explain why refractory particulate oxidized Hg is chosen as the tracer to characterize the fate of riverine discharge of Hg?
- Comment: line 236-238, “We find that riverine inputs of HgPR to the coastal ocean have a limited impact on Hg concentrations in surface seawater beyond the shelf region. HgPR is transported to the left or right along the coast by the Coriolis force, and the influence of currents and eddies leads to dispersion slightly further away from the coast.” To provide a more accurate depiction, it would be better to check the logical order of the sentences, and give more description about “slightly further away from the coast.”
- Comment: line 251-253, “Hg exports from rivers are important to specific coastal areas, Liu et al. (2021) have raised further concerns about riverine Hg and a deeper understanding of the role of rivers in the global Hg cycle. The discharge of HgPR from rivers greatly impacts environmental pollution in coastal and shelf regions.” This topic sentence does not correspond to the following.
- Comment: line 259-263, “The results show that HgPR spreads outward in an eddy shape, driven by HgPR concentrations and influenced by the kinetic energy transmission by ocean eddies and the mixing of turbulence. This further emphasizes the important role of eddy-driven processes and turbulence mixing, in the transport and distribution of riverine Hg in coastal and shelf regions.” It can be added that in comparison with previous models, your model results are more innovative and evolving.
- Comment: The expression can be more concise:
in lines 20-21, it would be better to replace “the inclusion of” with “including”;
in line 169, replace “takes into account” with “considers”;
in line 194, replace “at the same time” with “simultaneously”;
in line 205, replace “is the area with” with “has”;
in lines 210-211, replace “as compare to” with “more”;
in lines 233-234, replace “To gain a clearer understanding” with “To understand better”;
in line 285, replace “which can lead” with “leading”;
- Comment: in line 243, it is advisable to label which legend corresponds to the description;
- Comment: in line 250, punctuation is lost at the end.
- Comment: Empty filler words and phrases will make your writing not precise enough: in line 155, it is advisable to delete the “which is” in “…, which is a global, spatially explicit…” and in line 169, delete the “of which” in “all of which contribute to differences in oceanic Hg distribution”; in line 203, delete the “the effect of” in “the effect of turbulence across the ocean causes the spread of Hg in a vortical shape.”
- Comment: in line 62, replacing “couldn’t” with " could not " may be suitable.
- Comment: in line 269, it is advisable to modify “And” at the beginning of the sentence with “Moreover” will be more formal.
- Comment: in lines 314-315, “This suggests that the sinking of particle-bound Hg is influenced by ecological changes in seawater.” It will be better to use active voice.
- Comment: lines 318-319, “which promptly reflected the abrupt fluctuations in phytoplankton and enabled us to quickly observe changes in the sinking of Hg particles.” It will be better to replace it with “which promptly reflected the abrupt fluctuations in phytoplankton and enabled us to observe changes in the sinking of Hg particles quickly.”
- Comment: in line 329, you’d better delete “the” in front of “turbulence.”
- Comment: in line 150, you’d better add “that” in later of “infer.”
- Comment: in line 282, “undergo” should be written with “undergoes.”
Citation: https://doi.org/10.5194/gmd-2023-89-RC1 -
RC2: 'Comment on gmd-2023-89', Anonymous Referee #2, 20 Aug 2023
This manuscript introduces a high-resolution marine mercury model with concurrently model simulation of biogeological cycling. The higher resolution of the model makes it able to capture turbulence that can influence the mercury cycling of some local region. The application of concurrently simulated biogeochemistry or the cycling of phytoplankton enables the model to capture the particle-bound mercury sinking due to some ecological related and climate driven event such as increased effects of bio pump. The model also aims to capture the eddy or fine scale ocean current in the estuary region with riverine mercury input. Overall, the paper is well prepared and adds new knowledge and insights into the literature. For the authors to polish the paper, I have a few questions and comments, which I think also represent those from the general readers of GMD. After the authors address those points and include in the revision, I will enthusiastically support the publication of the paper in GMD.
The meaning of the term “online biogeochemistry” as used in the title is not intuitive for general readers who may think online means on the internet. To be friendly for general readers, I suggest authors using another term (e.g. concurrently simulated biogeochemistry processes) or explain the meaning in the abstract as early as possible.
Line 48, reference format
L 50, although this limitation is related to the contribution of this presented study, it would be better to point out all limitations of earlier models and then explain why overcoming this limitation is more important.
L58-59, “anthropogenic disturbances and climate-induced changes” is too general to make reader understand how the processes need to be characterized with high-resolution model.
L150, “Most” is unclear. Is it 50% or 90%? Better to give a the ranges quantitatively.
L192-193, Better to give quantitative information on how much closer to the observations can be brought in by the high-resolution model compared with the lower resolution model.
L206, “significant” is normally associated with statistical meaning. If no statistical test was conducted here, better to use the term “more apparent”.
L213, the figure caption is not intuitive.
L217, since the model is in higher resolution, river discharge being transferred along the seashores can be resolved, it is essential to mention the spatial resolution of the riverine discharge as the model input.
L280, “shorter time scales” How short? Give the specific time scale.
L293, “a certain range of time” what is the time range?
L297 and Fig 7: The description of “peak day” as shown in the figure by the vertical line should be added to the figure caption.
L300-301, it is indeed that nutrient levels during the peak days are above the average but it is unclear how can this suggests the occurrence of algal blooms here.
L325, elemental and divalent Hg
L329, besides turbulent mixing and shear effects, is there any other factors whose spatial variability is not capture by the model simulation? For example, continental input to the coastal sea. Is the emission at a resolution that match the resolution of 18 km. It is recommended that the authors put some discussions on factors that can influence the fine-scale processes and levels of Hg that are still not solved by this study.
Citation: https://doi.org/10.5194/gmd-2023-89-RC2 -
AC1: 'Comment on gmd-2023-89', Yanxu Zhang, 31 Aug 2023
Dear editor and dear reviewers,
Thank you for your letter and the reviews’ comments concerning our manuscript entitled “A high-resolution marine mercury model MITgcm-ECCO2-Hg with online biogeochemistry” (GMD-2023-89). These thoughtful comments are valuable and helpful for improving our paper. We have studied the comments carefully and responded to the referee’s comments. Please refer to the supplement for details.
Siyu Zhu et al.
Siyu Zhu et al.
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