the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 06 Dec 2023
Seasonal and diurnal variability of sub-ice platelet layer thickness in McMurdo Sound from electromagnetic induction sounding
Abstract. Here, we present observations of temporal variability of sub-ice platelet layer over seasonal and diurnal timescales under Ice Shelf Water-influenced fast ice in McMurdo Sound. Electromagnetic induction (EM) sounding time-series measurements of the thicknesses of fast ice and sub-ice platelet layer were made in winter and late spring of 2018. Winter objectives were to measure the seasonal growth of fast ice and sub-ice platelet layer near the McMurdo Ice Shelf in the east, while in late spring we assessed the diurnal variability of sub-ice platelet layer with coincident EM time-series and oceanographic measurements collected in the main outflow path of supercooled Ice Shelf Water in the west. During winter, we observed when the sub-ice platelet layer formed beneath consolidated ice. Episodes of rapid sub-ice platelet layer growth (~0.5–1 m) coincided with strong southerly-wind-events and polynya activity, suggesting wind-enhanced Ice Shelf Water circulation from the McMurdo-Ross Ice Shelf cavity. In late spring, we investigated how the tides and ocean properties influenced the sub-ice platelet layer. Over a two-week neap-spring tidal cycle, changes in sub-ice platelet layer thickness were observed to correlate with the tides, increasing more during neap than spring tide cycles, and on diurnal timescales, more on ebb than flood tides. Neap and ebb tides correspond with stronger northward circulation out of the cavity, indicating that sub-ice platelet layer growth was driven by tidally-enhanced Ice Shelf Water outflow. The observed variability indicated that wind-driven circulation and the tides influence Ice Shelf Water outflow in McMurdo Sound, and consequently, sub-ice platelet layer evolution over a range of timescales.
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RC1: 'Comment on egusphere-2023-2724', Anonymous Referee #1, 14 Jan 2024
PaperSummary:
EM time-series and oceanographic measurements collected in the main outflow path of supercooled Ice Shelf Water Observations of temporal variability of sub-ice platelet layer over seasonal and diurnal timescales under Ice Shelf Water-influenced fast ice in McMurdo Sound were made. Electromagnetic induction (EM) sounding time-series measurements of the thicknesses of fast ice and sub-ice platelet layer were made in winter and late spring of 2018. Winter objectives were to measure the seasonal growth of fast ice and sub-ice platelet layer near the McMurdo Ice Shelf in the east, while in late spring they assessed the diurnal variability of sub-ice platelet layer with coincident in the west.
Comments: The authors have made a technically challenging set of observations of the time series of Sub-ice platelet layer using EMI induction measurements. The EM measurements were verified by drilling and samlpling profiles at occasional intervals. The paper has a careful accounting of the possible errors due to temperature drift and other factors that could affect the EMI sounding. The conclusions of the paper indicating the episodic dynamic nature of subice platelet layer growth, rather than a steady growth are important findings in the understanding of the platelet layer development. As well the dirurnal dependence on tides of the is also an important aspect. (This reviewer speculates that the high concentrations of algae previously noted for the Sub-ice platelet layer may be supported by a "tidal pumping" of nutrient rich water in the high porosity layer that allows algal growth to reach the high concentrations observed in McMurdo Sound. The current authors have now verified that there are diurnal fluctuations in the platelet layer due to tides.)
I recommend the paper be published in The Cryosphere.
Citation: https://doi.org/10.5194/egusphere-2023-2724-RC1 -
AC2: 'Reply on RC1', Gemma Marie Brett, 26 Feb 2024
Dear Reviewer 1,
Many thanks for reviewing our manuscript and for recommending it to be published. We very much appreciate your time and consideration. We also appreciate your comment on algal responses to tidal-pumping of the SIPL. We have consequently added a statement on L120-121 describing the observations of Arrigo et al., 1995:
‘Arrigo et al., (1995) observed that nutrient exchange within the SIPL in McMurdo Sound co-varied with the tides which they postulated was caused by tidally-induced seawater exchange at the SIPL-ocean interface.’
Reference: Arrigo, K. R., Dieckmann, G., Gosselin, M., Robinson, D. H., Fritsen, C. H., & Sullivan, C. W.: High resolution study of the platelet ice ecosystem in McMurdo Sound, Antarctica: biomass, nutrient, and production profiles within a dense microalgal bloom. Marine Ecology Progress Series, 127, 255-268, 1995.
Many thanks again and best wishes,
Gemma Brett (on behalf of all co-authors).
Citation: https://doi.org/10.5194/egusphere-2023-2724-AC2
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AC2: 'Reply on RC1', Gemma Marie Brett, 26 Feb 2024
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RC2: 'Comment on egusphere-2023-2724', Anonymous Referee #2, 29 Jan 2024
This paper describes and interprets a novel set of data on the thickness of consolidated sea ice and the underlying unconsolidated sub-ice platelet layer (SIPL) in McMurdo Sound. The novel aspect of these observations is the high temporal sampling though winter and spring, that allows unprecedented temporal resolution in the growth rates of the two layers. The main focus is on the SIPL layer and it is found that periods of stronger outflow from the neighbouring ice shelf cavity, caused by ebb tides and southerly winds, give rise to periods of accelerated growth. Those are interesting findings.
The paper is logically presented, with a good summary of the observational methodology and data processing, followed by the presentation of the results. I have just a few minor questions about some of the figures and text. I would recommend publication of the manuscript subject to minor edits to address those points.
Minor questions and corrections:
Figure 1: The caption has missing information, and it took me a while to figure out everything on this figure as a result. I think it would help if the caption described parenthetically how each feature is marked (as it is for some features already). In particular, the line showing the fast ice edge looks white on the image, but presumably is the light grey line in the legend.
Figure 2: Some of the information in the caption is repeated in the text. I think the caption is the most appropriate place for the information, so I’d recommend deleting duplicated information on lines 200-202 of the main text.
Line 217: “… 2) sea ice growth, and 3) gradual SIPL …”.
Figure 4a: The description of wind direction and the numerical values are a little confusing (also in the main text on line 269). Your bearings are the direction the wind vector is pointing in, right, so 180 degrees different from the stated directions of where the wind is coming from? Also, I don’t really know how to interpret wind speed from such a broad range of directions, and why choose those directions anyway? Isn’t the aim to show a correlation with southerly winds? So why not just plot the meridional wind component?
Figure 4b: You discuss the likely errors in the measurements of ice and SIPL thickness in the text, but I think it would be useful to indicate them on the diagram.
Lines 285-294: You refer to specific dates in the text, but the diagram has only the beginning of each month marked, so it takes a while to work out which events you are referring to. I think it would help to show daily tick marks on the axes and/or indicate specific dates by vertical lines.
Figure 5b: Again, could you indicate the uncertainties on all the data?
Figure 5c: I think it would be informative to plot the freezing point on this graph along with the temperature and salinity.
Line 334: How can a temperature measurement alone show super-cooling? You need salinity as well.
Figure 7b: Although the measurements on the western side of the transect show the described pattern of more rapid accumulation during neap tides, those on the eastern side (around 168.5 longitude) show the opposite. Do you have an explanation for that?
Line 480: The statements here (and repeated on line 518) appear a little at odds with earlier ones. Or maybe I misunderstood? Earlier you said that there is deposition on the ebb tide that is stronger during periods of spring tides, but that the net accumulation is lower during spring tides because the stronger currents on the flood tide cause resuspension of the crystals. Here you seem to be saying that the currents are stronger during neap tides, something I don’t really understand.
Figure A1: Two vertical lines are plotted in two of the panels but are not mentioned. I assume that they are to show the alignment of temperature and Q peaks, but why those dates and not the ones mentioned in the main text?
Citation: https://doi.org/10.5194/egusphere-2023-2724-RC2 -
AC3: 'Reply on RC2', Gemma Marie Brett, 26 Feb 2024
Dear Reviewer 2,
Many thanks for reviewing our manuscript and for your comments and suggestions which have improved the clarity of the manuscript. We very much appreciate your thorough assessment of the paper and figures. Please find our responses to your comments below. We hope that your queries have been addressed with the changes and responses. If required, we will endeavour to provide more information
Many thanks for your time and consideration.
Best wishes,
Gemma Brett (on behalf of all co-authors).
Minor questions and corrections:
Figure 1: The caption has missing information, and it took me a while to figure out everything on this figure as a result. I think it would help if the caption described parenthetically how each feature is marked (as it is for some features already). In particular, the line showing the fast ice edge looks white on the image, but presumably is the light grey line in the legend.
Author Response: Thank you for this comment. We have added additional text to the figure caption on L73-78 better describing the features on the map and provided information on their annotation.
Figure 2: Some of the information in the caption is repeated in the text. I think the caption is the most appropriate place for the information, so I’d recommend deleting duplicated information on lines 200-202 of the main text.
Author Response: We have removed some of the detailed text included in the figure caption on L203-205.
Line 217: “… 2) sea ice growth, and 3) gradual SIPL …”.
Author Response: Thank you, changed to ‘3)’ on L223.
Figure 4a: The description of wind direction and the numerical values are a little confusing (also in the main text on line 269). Your bearings are the direction the wind vector is pointing in, right, so 180 degrees different from the stated directions of where the wind is coming from? Also, I don’t really know how to interpret wind speed from such a broad range of directions, and why choose those directions anyway? Isn’t the aim to show a correlation with southerly winds? So why not just plot the meridional wind component?
Author Response: The bearings are the direction the wind is coming from, as per convention (180° being southerly winds). Wind direction recorded at Scott Base, located at the southwestern tip of Hut Point Peninsula (Figure 1), can be affected by the barrier effect of Ross Island and Hut Point Peninsula topography.
Winds that predominately originate from the south (as shown over 4 years at Laurie II on the Ross Ice Shelf in Figure 7a of Brett et al., 2020) are deflected to the east and northeast once they reach Scott Base (Coggins et al., 2013; Jolly et al., 2016; Seefeldt et al., 2003) and can contribute to polynya formation. The range of wind directions was chosen to account for this.
However, we agree that this is confusing to the reader and reduced the range to 110-250° (WSW to ESE). This had minimal impact on the pattern shown in Figure 4a of strong-wind-events corresponding to rapid SIPL thickness increases. The highest speed winds generally originate from these directions.
- Coggins, J.H., McDonald, A.J., Plank, G., Pannell, M., Jolly, B., Parsons, S. and Delany, T., 2013. SNOW-WEB: a new technology for Antarctic meteorological monitoring. Antarctic Science, 25(4), pp.583-599.
- Jolly, B., Mcdonald, A.J., Coggins, J.H., Zawar-Reza, P., Cassano, J., Lazzara, M., Graham, G., Plank, G., Petterson, O. and Dale, E., 2016. A validation of the Antarctic mesoscale prediction system using self-organizing maps and high-density observations from SNOWWEB. Monthly Weather Review, 144(9), pp.3181-3200.
- Seefeldt, M.W., Tripoli, G.J. and Stearns, C.R., 2003. A high-resolution numerical simulation of the wind flow in the Ross Island region, Antarctica. Monthly Weather Review, 131(2), pp.435-458.
Figure 4b: You discuss the likely errors in the measurements of ice and SIPL thickness in the text, but I think it would be useful to indicate them on the diagram.
We appreciate this comment and see the value of adding such an error estimation to the EM time-series plot in both Figures 4b and 5b. However, this is difficult to do in a consistent way as the EM response and associated error are non-linear and will vary as both ice and SIPL thickness change as shown in Figure 2 and stated on L208-209. Instead, we have provided a more detailed statement of associated error with respect to consolidated ice and SIPL thicknesses on L209-212:
Additionally, in the Winter EM time series, the effect of the thin SIPL on inverted ice thickness is significant as described in L286-292. The drill holes provide the best indication of error in the EM inverted thicknesses, although drill holes can have associated error and provide only a point measurement. We have accounted for this in the text on L280-284. We were unable to plot drill hole thickness ranges/error at the Winter site (like we did in Figure 5 at the Spring site) because only single drill hole measurements were made during winter.
Lines 285-294: You refer to specific dates in the text, but the diagram has only the beginning of each month marked, so it takes a while to work out which events you are referring to. I think it would help to show daily tick marks on the axes and/or indicate specific dates by vertical lines.
Author Response: Thank you. Given the long ~3-month time-series and for ease of identifying dates, we added vertical stippled lines to Figure 4 and additional text on L295 and to the figure caption:
Figure 5b: Again, could you indicate the uncertainties on all the data?
Author Response: As above for previous comment for Figure 4b.
Figure 5c: I think it would be informative to plot the freezing point on this graph along with the temperature and salinity.
Author Response: We agree this would be informative to add the plot. However, the T-S time-series presented here was collected at 101 m depth for reasons described in Section 2.4, and thus not within the in situ supercooled water column (to ~40 m depth). The freezing point at 101 m depth would be ~-1.97°C for these salinities and we thought adding this would be confusing.
We could add the freezing point calculated from salinity at the 101 m-depth MicroCat, for a depth of 40 m to support in situ supercooling of the water column or 10 m depth to indicate what the SIPL experienced throughout the time-series? Although again, this might be confusing.
Line 334: How can a temperature measurement alone show super-cooling? You need salinity as well.
Author Response: The reviewer is correct, and we have additional text about salinity measurements to the manuscript accordingly on L343. Applying even the full range of observed salinities from this location (both profile and mooring data across several field campaigns), impacts supercooling estimates only in the 3rd decimal place, since the absolute range of temperatures measured is so narrow.
Figure 7b: Although the measurements on the western side of the transect show the described pattern of more rapid accumulation during neap tides, those on the eastern side (around 168.5 longitude) show the opposite. Do you have an explanation for that?
Author Response: The pattern described in the text is mainly focused on SIPL thickness changes at the Spring site. We have added a statement on L382 and switched the text around on L420-421 to better emphasise this.
The difference may be caused by the eastward expansion and deepening of the supercooled ISW plume (and thus SIPL thickness) over time as observed by Hughes et al., 2014 and Robinson et al., (2014) (and evident in Figure 7b) or differences in the current regimes in this central-east region. The oceanographic regimes in east and west McMurdo Sound are different as described in the text on L94-108.
Line 480: The statements here (and repeated on line 518) appear a little at odds with earlier ones. Or maybe I misunderstood? Earlier you said that there is deposition on the ebb tide that is stronger during periods of spring tides, but that the net accumulation is lower during spring tides because the stronger currents on the flood tide cause resuspension of the crystals. Here you seem to be saying that the currents are stronger during neap tides, something I don’t really understand.
Author Response: That is fair comment. Without coincident visual observations, we can only speculate what is causing the decrease in SIPL thickness on flood tides. We have removed this statement from L475-476. And emphasised that the northward circulation out of the cavity would be comprised of ISW with frazil and platelet ice suspension with additional text on L427 and L493.
Figure A1: Two vertical lines are plotted in two of the panels but are not mentioned. I assume that they are to show the alignment of temperature and Q peaks, but why those dates and not the ones mentioned in the main text?
Author Response: Thank you, we have directed the reader to the stippled lined examples in the text on L541-542 and the figure caption on L562-563.
Citation: https://doi.org/10.5194/egusphere-2023-2724-AC3
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AC3: 'Reply on RC2', Gemma Marie Brett, 26 Feb 2024
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EC1: 'Comment on egusphere-2023-2724', Jean-Louis Tison, 30 Jan 2024
Dear authors,
I am pleased to confirm that I have closed the discussion phase on your paper. Clearly both reviewers are very happy with this new version. I am therefore asking you to post a final response taking into account the minor comments of Reviewer 2, together with a final revised version of the manuscript and a version showing the final changes you have made to the manuscript.
Congratulations,
Jean-Louis Tison
Citation: https://doi.org/10.5194/egusphere-2023-2724-EC1 -
AC1: 'Reply on EC1', Gemma Marie Brett, 26 Feb 2024
Dear Editor Jean-Louis and Reviewers,
Many thanks for handling and reviewing our submission to the Cryosphere. We appreciate your consideration and time taken to review the manuscript and all comments provided.
We are delighted that you have accepted the manuscript for publishing. We thank you for your comments and have endeavoured to integrate them or provide rationale for why we have not.
Please find author responses to your comments below where L# corresponds to line number in the tracked changes version.
Additionally, the 2018 EM time-series and west-east EM transect data are currently being submitted to Pangaea.
Many thanks for your effort and time spent in improving this manuscript.
Best wishes,
Gemma Brett (on behalf of all co-authors).
Citation: https://doi.org/10.5194/egusphere-2023-2724-AC1
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AC1: 'Reply on EC1', Gemma Marie Brett, 26 Feb 2024
Status: closed
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RC1: 'Comment on egusphere-2023-2724', Anonymous Referee #1, 14 Jan 2024
PaperSummary:
EM time-series and oceanographic measurements collected in the main outflow path of supercooled Ice Shelf Water Observations of temporal variability of sub-ice platelet layer over seasonal and diurnal timescales under Ice Shelf Water-influenced fast ice in McMurdo Sound were made. Electromagnetic induction (EM) sounding time-series measurements of the thicknesses of fast ice and sub-ice platelet layer were made in winter and late spring of 2018. Winter objectives were to measure the seasonal growth of fast ice and sub-ice platelet layer near the McMurdo Ice Shelf in the east, while in late spring they assessed the diurnal variability of sub-ice platelet layer with coincident in the west.
Comments: The authors have made a technically challenging set of observations of the time series of Sub-ice platelet layer using EMI induction measurements. The EM measurements were verified by drilling and samlpling profiles at occasional intervals. The paper has a careful accounting of the possible errors due to temperature drift and other factors that could affect the EMI sounding. The conclusions of the paper indicating the episodic dynamic nature of subice platelet layer growth, rather than a steady growth are important findings in the understanding of the platelet layer development. As well the dirurnal dependence on tides of the is also an important aspect. (This reviewer speculates that the high concentrations of algae previously noted for the Sub-ice platelet layer may be supported by a "tidal pumping" of nutrient rich water in the high porosity layer that allows algal growth to reach the high concentrations observed in McMurdo Sound. The current authors have now verified that there are diurnal fluctuations in the platelet layer due to tides.)
I recommend the paper be published in The Cryosphere.
Citation: https://doi.org/10.5194/egusphere-2023-2724-RC1 -
AC2: 'Reply on RC1', Gemma Marie Brett, 26 Feb 2024
Dear Reviewer 1,
Many thanks for reviewing our manuscript and for recommending it to be published. We very much appreciate your time and consideration. We also appreciate your comment on algal responses to tidal-pumping of the SIPL. We have consequently added a statement on L120-121 describing the observations of Arrigo et al., 1995:
‘Arrigo et al., (1995) observed that nutrient exchange within the SIPL in McMurdo Sound co-varied with the tides which they postulated was caused by tidally-induced seawater exchange at the SIPL-ocean interface.’
Reference: Arrigo, K. R., Dieckmann, G., Gosselin, M., Robinson, D. H., Fritsen, C. H., & Sullivan, C. W.: High resolution study of the platelet ice ecosystem in McMurdo Sound, Antarctica: biomass, nutrient, and production profiles within a dense microalgal bloom. Marine Ecology Progress Series, 127, 255-268, 1995.
Many thanks again and best wishes,
Gemma Brett (on behalf of all co-authors).
Citation: https://doi.org/10.5194/egusphere-2023-2724-AC2
-
AC2: 'Reply on RC1', Gemma Marie Brett, 26 Feb 2024
-
RC2: 'Comment on egusphere-2023-2724', Anonymous Referee #2, 29 Jan 2024
This paper describes and interprets a novel set of data on the thickness of consolidated sea ice and the underlying unconsolidated sub-ice platelet layer (SIPL) in McMurdo Sound. The novel aspect of these observations is the high temporal sampling though winter and spring, that allows unprecedented temporal resolution in the growth rates of the two layers. The main focus is on the SIPL layer and it is found that periods of stronger outflow from the neighbouring ice shelf cavity, caused by ebb tides and southerly winds, give rise to periods of accelerated growth. Those are interesting findings.
The paper is logically presented, with a good summary of the observational methodology and data processing, followed by the presentation of the results. I have just a few minor questions about some of the figures and text. I would recommend publication of the manuscript subject to minor edits to address those points.
Minor questions and corrections:
Figure 1: The caption has missing information, and it took me a while to figure out everything on this figure as a result. I think it would help if the caption described parenthetically how each feature is marked (as it is for some features already). In particular, the line showing the fast ice edge looks white on the image, but presumably is the light grey line in the legend.
Figure 2: Some of the information in the caption is repeated in the text. I think the caption is the most appropriate place for the information, so I’d recommend deleting duplicated information on lines 200-202 of the main text.
Line 217: “… 2) sea ice growth, and 3) gradual SIPL …”.
Figure 4a: The description of wind direction and the numerical values are a little confusing (also in the main text on line 269). Your bearings are the direction the wind vector is pointing in, right, so 180 degrees different from the stated directions of where the wind is coming from? Also, I don’t really know how to interpret wind speed from such a broad range of directions, and why choose those directions anyway? Isn’t the aim to show a correlation with southerly winds? So why not just plot the meridional wind component?
Figure 4b: You discuss the likely errors in the measurements of ice and SIPL thickness in the text, but I think it would be useful to indicate them on the diagram.
Lines 285-294: You refer to specific dates in the text, but the diagram has only the beginning of each month marked, so it takes a while to work out which events you are referring to. I think it would help to show daily tick marks on the axes and/or indicate specific dates by vertical lines.
Figure 5b: Again, could you indicate the uncertainties on all the data?
Figure 5c: I think it would be informative to plot the freezing point on this graph along with the temperature and salinity.
Line 334: How can a temperature measurement alone show super-cooling? You need salinity as well.
Figure 7b: Although the measurements on the western side of the transect show the described pattern of more rapid accumulation during neap tides, those on the eastern side (around 168.5 longitude) show the opposite. Do you have an explanation for that?
Line 480: The statements here (and repeated on line 518) appear a little at odds with earlier ones. Or maybe I misunderstood? Earlier you said that there is deposition on the ebb tide that is stronger during periods of spring tides, but that the net accumulation is lower during spring tides because the stronger currents on the flood tide cause resuspension of the crystals. Here you seem to be saying that the currents are stronger during neap tides, something I don’t really understand.
Figure A1: Two vertical lines are plotted in two of the panels but are not mentioned. I assume that they are to show the alignment of temperature and Q peaks, but why those dates and not the ones mentioned in the main text?
Citation: https://doi.org/10.5194/egusphere-2023-2724-RC2 -
AC3: 'Reply on RC2', Gemma Marie Brett, 26 Feb 2024
Dear Reviewer 2,
Many thanks for reviewing our manuscript and for your comments and suggestions which have improved the clarity of the manuscript. We very much appreciate your thorough assessment of the paper and figures. Please find our responses to your comments below. We hope that your queries have been addressed with the changes and responses. If required, we will endeavour to provide more information
Many thanks for your time and consideration.
Best wishes,
Gemma Brett (on behalf of all co-authors).
Minor questions and corrections:
Figure 1: The caption has missing information, and it took me a while to figure out everything on this figure as a result. I think it would help if the caption described parenthetically how each feature is marked (as it is for some features already). In particular, the line showing the fast ice edge looks white on the image, but presumably is the light grey line in the legend.
Author Response: Thank you for this comment. We have added additional text to the figure caption on L73-78 better describing the features on the map and provided information on their annotation.
Figure 2: Some of the information in the caption is repeated in the text. I think the caption is the most appropriate place for the information, so I’d recommend deleting duplicated information on lines 200-202 of the main text.
Author Response: We have removed some of the detailed text included in the figure caption on L203-205.
Line 217: “… 2) sea ice growth, and 3) gradual SIPL …”.
Author Response: Thank you, changed to ‘3)’ on L223.
Figure 4a: The description of wind direction and the numerical values are a little confusing (also in the main text on line 269). Your bearings are the direction the wind vector is pointing in, right, so 180 degrees different from the stated directions of where the wind is coming from? Also, I don’t really know how to interpret wind speed from such a broad range of directions, and why choose those directions anyway? Isn’t the aim to show a correlation with southerly winds? So why not just plot the meridional wind component?
Author Response: The bearings are the direction the wind is coming from, as per convention (180° being southerly winds). Wind direction recorded at Scott Base, located at the southwestern tip of Hut Point Peninsula (Figure 1), can be affected by the barrier effect of Ross Island and Hut Point Peninsula topography.
Winds that predominately originate from the south (as shown over 4 years at Laurie II on the Ross Ice Shelf in Figure 7a of Brett et al., 2020) are deflected to the east and northeast once they reach Scott Base (Coggins et al., 2013; Jolly et al., 2016; Seefeldt et al., 2003) and can contribute to polynya formation. The range of wind directions was chosen to account for this.
However, we agree that this is confusing to the reader and reduced the range to 110-250° (WSW to ESE). This had minimal impact on the pattern shown in Figure 4a of strong-wind-events corresponding to rapid SIPL thickness increases. The highest speed winds generally originate from these directions.
- Coggins, J.H., McDonald, A.J., Plank, G., Pannell, M., Jolly, B., Parsons, S. and Delany, T., 2013. SNOW-WEB: a new technology for Antarctic meteorological monitoring. Antarctic Science, 25(4), pp.583-599.
- Jolly, B., Mcdonald, A.J., Coggins, J.H., Zawar-Reza, P., Cassano, J., Lazzara, M., Graham, G., Plank, G., Petterson, O. and Dale, E., 2016. A validation of the Antarctic mesoscale prediction system using self-organizing maps and high-density observations from SNOWWEB. Monthly Weather Review, 144(9), pp.3181-3200.
- Seefeldt, M.W., Tripoli, G.J. and Stearns, C.R., 2003. A high-resolution numerical simulation of the wind flow in the Ross Island region, Antarctica. Monthly Weather Review, 131(2), pp.435-458.
Figure 4b: You discuss the likely errors in the measurements of ice and SIPL thickness in the text, but I think it would be useful to indicate them on the diagram.
We appreciate this comment and see the value of adding such an error estimation to the EM time-series plot in both Figures 4b and 5b. However, this is difficult to do in a consistent way as the EM response and associated error are non-linear and will vary as both ice and SIPL thickness change as shown in Figure 2 and stated on L208-209. Instead, we have provided a more detailed statement of associated error with respect to consolidated ice and SIPL thicknesses on L209-212:
Additionally, in the Winter EM time series, the effect of the thin SIPL on inverted ice thickness is significant as described in L286-292. The drill holes provide the best indication of error in the EM inverted thicknesses, although drill holes can have associated error and provide only a point measurement. We have accounted for this in the text on L280-284. We were unable to plot drill hole thickness ranges/error at the Winter site (like we did in Figure 5 at the Spring site) because only single drill hole measurements were made during winter.
Lines 285-294: You refer to specific dates in the text, but the diagram has only the beginning of each month marked, so it takes a while to work out which events you are referring to. I think it would help to show daily tick marks on the axes and/or indicate specific dates by vertical lines.
Author Response: Thank you. Given the long ~3-month time-series and for ease of identifying dates, we added vertical stippled lines to Figure 4 and additional text on L295 and to the figure caption:
Figure 5b: Again, could you indicate the uncertainties on all the data?
Author Response: As above for previous comment for Figure 4b.
Figure 5c: I think it would be informative to plot the freezing point on this graph along with the temperature and salinity.
Author Response: We agree this would be informative to add the plot. However, the T-S time-series presented here was collected at 101 m depth for reasons described in Section 2.4, and thus not within the in situ supercooled water column (to ~40 m depth). The freezing point at 101 m depth would be ~-1.97°C for these salinities and we thought adding this would be confusing.
We could add the freezing point calculated from salinity at the 101 m-depth MicroCat, for a depth of 40 m to support in situ supercooling of the water column or 10 m depth to indicate what the SIPL experienced throughout the time-series? Although again, this might be confusing.
Line 334: How can a temperature measurement alone show super-cooling? You need salinity as well.
Author Response: The reviewer is correct, and we have additional text about salinity measurements to the manuscript accordingly on L343. Applying even the full range of observed salinities from this location (both profile and mooring data across several field campaigns), impacts supercooling estimates only in the 3rd decimal place, since the absolute range of temperatures measured is so narrow.
Figure 7b: Although the measurements on the western side of the transect show the described pattern of more rapid accumulation during neap tides, those on the eastern side (around 168.5 longitude) show the opposite. Do you have an explanation for that?
Author Response: The pattern described in the text is mainly focused on SIPL thickness changes at the Spring site. We have added a statement on L382 and switched the text around on L420-421 to better emphasise this.
The difference may be caused by the eastward expansion and deepening of the supercooled ISW plume (and thus SIPL thickness) over time as observed by Hughes et al., 2014 and Robinson et al., (2014) (and evident in Figure 7b) or differences in the current regimes in this central-east region. The oceanographic regimes in east and west McMurdo Sound are different as described in the text on L94-108.
Line 480: The statements here (and repeated on line 518) appear a little at odds with earlier ones. Or maybe I misunderstood? Earlier you said that there is deposition on the ebb tide that is stronger during periods of spring tides, but that the net accumulation is lower during spring tides because the stronger currents on the flood tide cause resuspension of the crystals. Here you seem to be saying that the currents are stronger during neap tides, something I don’t really understand.
Author Response: That is fair comment. Without coincident visual observations, we can only speculate what is causing the decrease in SIPL thickness on flood tides. We have removed this statement from L475-476. And emphasised that the northward circulation out of the cavity would be comprised of ISW with frazil and platelet ice suspension with additional text on L427 and L493.
Figure A1: Two vertical lines are plotted in two of the panels but are not mentioned. I assume that they are to show the alignment of temperature and Q peaks, but why those dates and not the ones mentioned in the main text?
Author Response: Thank you, we have directed the reader to the stippled lined examples in the text on L541-542 and the figure caption on L562-563.
Citation: https://doi.org/10.5194/egusphere-2023-2724-AC3
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AC3: 'Reply on RC2', Gemma Marie Brett, 26 Feb 2024
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EC1: 'Comment on egusphere-2023-2724', Jean-Louis Tison, 30 Jan 2024
Dear authors,
I am pleased to confirm that I have closed the discussion phase on your paper. Clearly both reviewers are very happy with this new version. I am therefore asking you to post a final response taking into account the minor comments of Reviewer 2, together with a final revised version of the manuscript and a version showing the final changes you have made to the manuscript.
Congratulations,
Jean-Louis Tison
Citation: https://doi.org/10.5194/egusphere-2023-2724-EC1 -
AC1: 'Reply on EC1', Gemma Marie Brett, 26 Feb 2024
Dear Editor Jean-Louis and Reviewers,
Many thanks for handling and reviewing our submission to the Cryosphere. We appreciate your consideration and time taken to review the manuscript and all comments provided.
We are delighted that you have accepted the manuscript for publishing. We thank you for your comments and have endeavoured to integrate them or provide rationale for why we have not.
Please find author responses to your comments below where L# corresponds to line number in the tracked changes version.
Additionally, the 2018 EM time-series and west-east EM transect data are currently being submitted to Pangaea.
Many thanks for your effort and time spent in improving this manuscript.
Best wishes,
Gemma Brett (on behalf of all co-authors).
Citation: https://doi.org/10.5194/egusphere-2023-2724-AC1
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AC1: 'Reply on EC1', Gemma Marie Brett, 26 Feb 2024
Data sets
Drill hole measurements of fast ice and sub-ice platelet layer thickness, and snow depth in McMurdo Sound - November 2018 G. M. Brett, G. H. Leonard, F. Isaacs, and N. J. Robinson https://doi.org/10.1594/PANGAEA.933050
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