the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 06 Jan 2021
Brief communication: Grease Ice in the Antarctic Marginal Ice Zone
Abstract. Frazil ice, consisting of loose disc-shaped ice crystals, is the very first ice that forms in the annual cycle in the marginal ice zone (MIZ) of the Antarctic. A sufficient number of frazil ice crystals forms the surface grease ice
layer taking a fundamental role in the freezing processes in the MIZ. As soon as the ocean waves are sufficiently damped, a closed ice cover can form. In this brief communication we investigate the rheological properties of frazil ice, which has a crucial influence on the growth of sea ice in the MIZ. Grease ice shows shear thinning flow behavior.
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Interactive discussion
Status: closed
-
RC1: 'Comment on tc-2020-362', Anonymous Referee #1, 11 Jan 2021
First, this reviewer was not involved in the previous submission of this manuscript. The review record of the previous submission shows that the authors have changed the submission from a full paper to a brief communication, because of the limited scope of the manuscript. Such change is appropriate.
The shear-thinning possibility of frazil mixture reported in this study is novel, which makes this study particularly interesting.
However, there is a big question associated with the interpretation of their data: is the shear inside the viscometer linearly distributed throughout the stationary and the rotating boundaries? Furthermore, are the two boundaries really at Rs and Rv? Their Eq. (2) relies entirely on these assumptions. A relatively less but still important question: Is the frazil concentration constant in the entire shear zone, i.e. can phase separation play a role? It is known for many fluid-solid mixtures that when sheared a boundary layer may developed so that the material only shears in a narrow band. Phase separations are also common. For frazil mixtures, the reviewer remembers that years ago researchers at HSVA (Hamburgische Schiffbau-Versuchsanstalt) tried to develop an ice slurry viscometer nicknamed “Kosmoski” and found the above-mentioned situations. Maybe the present viscometer design could avoid these problems, but the authors must first verify that the kinematics inside the apparatus agrees with their assumptions: linear shear distribution from the vane tip to the wall of the apparatus, and almost uniform ice concentration. The reviewer recognizes that such verification is challenging to do in the field. Hence, the best approach is to test the performance of the viscometer using frazil mixtures grown in a lab first. The authors may start with a surrogate mixture if no access to cold rooms.
The reviewer suggests the following to move forward with the manuscript:
Decline, but strongly encourage this study to move forward, because it is interesting and relevant for the basic understanding of the initial ice cover. The authors should focus on establishing the validity of their assumptions behind Eq. (2) and the nearly uniform ice concentration in the viscometer and resubmit.
For the future submission of this work, it is suggested that:
- A schematic of the interior of the viscometer should also be given. Fig. 1-III now only has the photo of the exterior. In this schematic, all dimension including the Rs value missing in the current manuscript should be added.
- Add explanation of the 2/3 in Eq. (1).
- Add a reference “Daly SF ed. 1994. IAHR Working Group on Thermal Regimes: report on frazil ice. CRREL Spec. Rep. 94-23, 52pp.” This report can save the authors from explaining the formation of frazil crystals. Contrary to what the authors said on line 31, frazil crystals do NOT only form in turbulent waters. However, turbulence enables “secondary” nucleation hence a rapid growth of frazil accumulation under most natural field conditions.
- In future data analysis, it would be very interesting to relate the viscosity to ice crystal size. The reviewer is also interested in knowing if the crystal size is related to their salinity, though the latter has negligible effect on viscosity.
Citation: https://doi.org/10.5194/tc-2020-362-RC1 -
RC2: 'Comment on tc-2020-362', Anonymous Referee #2, 24 Mar 2021
This paper presents measurements of the viscosity of frazil ice that potentially will be of interest to many readers. The description of the design for their frazil ice sampler may also prove to be quite useful. However, the paper does not currently meet the standard for publication in terms of its scientific quality or rigour. The authors present almost no evidence that their method used to make the viscosity measurements is valid and suitable. They write that the viscosity was measured using a commercial rheometer and then present equations used to compute the viscosity. None of the underlying theory is presented and no references justifying the use of this instrument and the equations are provided.
The main conclusions of the paper appear to be that:
- The measured viscosities are in good agreement with previous laboratory measurements.
- Two fundamentally different viscosity regimes occur in grease ice and these need to be accounted for in models.
The previous laboratory measurements reviewed in the paper ranged from 14 to 60 Pas and the reported field measurements range from ~10 to 450 Pas. Therefore, it is debatable if this should be characterized as good agreement. The authors attribute the much higher viscosities to differences between the different measurement methods. However, their arguments supporting this explanation need to be more thorough and convincing. The second conclusion is potentially quite significant, but it is undermined by the fact that the validity and accuracy of the measurements is uncertain.
The authors have made some interesting and novel measurements and I encourage them undertake the necessary revisions to address the paper's current shortcomings and make it suitable for publication.
Specific comments and questions:
The experimental equipment and methodology are not explained in sufficient detail or in some cases at all. For example, how was frazil concentration and salinity measured? How were the error-bars in Figure 2 estimated? Did the variation in air temperature or the time between sampling and testing have an impact on your measurements? I noted that 12 samples were gathered but why were results for only 10 presented?
Lines 74-80: The theoretical and/or empirical support for equations (1) and (2) needs to be fully explained and references supplied.
Lines 96-97: I found this confusing. You observed nearly constant water salinity and then concluded this is due to dilution and that this enhances diffusion to the underlying water. But this does not seem to explain why the water salinity was constant.
Lines 108-113: This should probably be explained in the methodology section.
Lines 139-140: It is stated that: “The viscosity can then be calculated from the torque using proven formulas from other fields.” Since the entire paper is based on these viscosity measurements the authors must present evidence to support this statement.
Lines 144-147: This discussion of sampler size and geometry is poorly worded and unclear.
Citation: https://doi.org/10.5194/tc-2020-362-RC2
Interactive discussion
Status: closed
-
RC1: 'Comment on tc-2020-362', Anonymous Referee #1, 11 Jan 2021
First, this reviewer was not involved in the previous submission of this manuscript. The review record of the previous submission shows that the authors have changed the submission from a full paper to a brief communication, because of the limited scope of the manuscript. Such change is appropriate.
The shear-thinning possibility of frazil mixture reported in this study is novel, which makes this study particularly interesting.
However, there is a big question associated with the interpretation of their data: is the shear inside the viscometer linearly distributed throughout the stationary and the rotating boundaries? Furthermore, are the two boundaries really at Rs and Rv? Their Eq. (2) relies entirely on these assumptions. A relatively less but still important question: Is the frazil concentration constant in the entire shear zone, i.e. can phase separation play a role? It is known for many fluid-solid mixtures that when sheared a boundary layer may developed so that the material only shears in a narrow band. Phase separations are also common. For frazil mixtures, the reviewer remembers that years ago researchers at HSVA (Hamburgische Schiffbau-Versuchsanstalt) tried to develop an ice slurry viscometer nicknamed “Kosmoski” and found the above-mentioned situations. Maybe the present viscometer design could avoid these problems, but the authors must first verify that the kinematics inside the apparatus agrees with their assumptions: linear shear distribution from the vane tip to the wall of the apparatus, and almost uniform ice concentration. The reviewer recognizes that such verification is challenging to do in the field. Hence, the best approach is to test the performance of the viscometer using frazil mixtures grown in a lab first. The authors may start with a surrogate mixture if no access to cold rooms.
The reviewer suggests the following to move forward with the manuscript:
Decline, but strongly encourage this study to move forward, because it is interesting and relevant for the basic understanding of the initial ice cover. The authors should focus on establishing the validity of their assumptions behind Eq. (2) and the nearly uniform ice concentration in the viscometer and resubmit.
For the future submission of this work, it is suggested that:
- A schematic of the interior of the viscometer should also be given. Fig. 1-III now only has the photo of the exterior. In this schematic, all dimension including the Rs value missing in the current manuscript should be added.
- Add explanation of the 2/3 in Eq. (1).
- Add a reference “Daly SF ed. 1994. IAHR Working Group on Thermal Regimes: report on frazil ice. CRREL Spec. Rep. 94-23, 52pp.” This report can save the authors from explaining the formation of frazil crystals. Contrary to what the authors said on line 31, frazil crystals do NOT only form in turbulent waters. However, turbulence enables “secondary” nucleation hence a rapid growth of frazil accumulation under most natural field conditions.
- In future data analysis, it would be very interesting to relate the viscosity to ice crystal size. The reviewer is also interested in knowing if the crystal size is related to their salinity, though the latter has negligible effect on viscosity.
Citation: https://doi.org/10.5194/tc-2020-362-RC1 -
RC2: 'Comment on tc-2020-362', Anonymous Referee #2, 24 Mar 2021
This paper presents measurements of the viscosity of frazil ice that potentially will be of interest to many readers. The description of the design for their frazil ice sampler may also prove to be quite useful. However, the paper does not currently meet the standard for publication in terms of its scientific quality or rigour. The authors present almost no evidence that their method used to make the viscosity measurements is valid and suitable. They write that the viscosity was measured using a commercial rheometer and then present equations used to compute the viscosity. None of the underlying theory is presented and no references justifying the use of this instrument and the equations are provided.
The main conclusions of the paper appear to be that:
- The measured viscosities are in good agreement with previous laboratory measurements.
- Two fundamentally different viscosity regimes occur in grease ice and these need to be accounted for in models.
The previous laboratory measurements reviewed in the paper ranged from 14 to 60 Pas and the reported field measurements range from ~10 to 450 Pas. Therefore, it is debatable if this should be characterized as good agreement. The authors attribute the much higher viscosities to differences between the different measurement methods. However, their arguments supporting this explanation need to be more thorough and convincing. The second conclusion is potentially quite significant, but it is undermined by the fact that the validity and accuracy of the measurements is uncertain.
The authors have made some interesting and novel measurements and I encourage them undertake the necessary revisions to address the paper's current shortcomings and make it suitable for publication.
Specific comments and questions:
The experimental equipment and methodology are not explained in sufficient detail or in some cases at all. For example, how was frazil concentration and salinity measured? How were the error-bars in Figure 2 estimated? Did the variation in air temperature or the time between sampling and testing have an impact on your measurements? I noted that 12 samples were gathered but why were results for only 10 presented?
Lines 74-80: The theoretical and/or empirical support for equations (1) and (2) needs to be fully explained and references supplied.
Lines 96-97: I found this confusing. You observed nearly constant water salinity and then concluded this is due to dilution and that this enhances diffusion to the underlying water. But this does not seem to explain why the water salinity was constant.
Lines 108-113: This should probably be explained in the methodology section.
Lines 139-140: It is stated that: “The viscosity can then be calculated from the torque using proven formulas from other fields.” Since the entire paper is based on these viscosity measurements the authors must present evidence to support this statement.
Lines 144-147: This discussion of sampler size and geometry is poorly worded and unclear.
Citation: https://doi.org/10.5194/tc-2020-362-RC2
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