Dear Sahra and Ron.

Thank you mostly for submitting your ms on Antarctic sea ice using IS-2 and CS-2 to The Cryosphere.

I am happy to share with you that both reviewers and myself recommend "minor revisions". As you have seen and responded to the reviewers comments, pls consider my comments (see below) to produce a revised manuscript.

I look forward to your resubmission.
Best wishes, Petra
-----------------------

tc-2020-145: Kamici and Kwok

General comments:
* Use of SI units:
Similar to reviewer 2, who asked for the uniform use of units, and recommended the use
of SI units, I would like to request the same. Including to remove "PSU" as salinity is
now given without any units, not even "PSU". (1-16).
* Hyphenation: Pls review your use of hyphens, especially change "snow-radar" to "snow
radar" throughout the manuscript (ms).
* Include information on cloud etc affecting IS-2 data (i.e., missing data) and how this
lack of data coverage affects the comparison. Similar, explore effects of different
instrument footprints and repeat/overlapping swaths.
(I found some info in section 4.12 but would prefer the basic info upfront, when the
datasets are introduced.)
* In the Southern Ocean, changes in snow thickness/cover are largely driven by a combination
of solid precipitation as well as by snow redistribution (incl. loss of snow into open water,
such as leads) -- in addition to snow-ice formation.
--> Pls include the "snow redistribution" (with appropriate reference) in your ms,
i.e., 4-10 to 4-13.
* Suggest to rename "East Weddell" and "West Weddell" to "eastern Weddell Sea" and "western
Weddell Sea", respectively. Abbreviations may remain the same.
* Provide essential information for both primary datasets (IS-2 FB and CS-2 radar FB)
(Sections 2.1 and 2.2). For example, information on the data granularity for CS-2 radar
FB needs to be presented here - despite provision of the KC2016 reference.
See below for specific comments.
* Fluxgates: How are they set and what contributes to the lesser ice area in the larger
fluxgate? (6-1ff)
* Your discussion of the regional freeboard evolutions states that the E-Wedd sector exhibits
the "lowest area-averaged freeboards" around Antarctica. Tab. 2 however shows similarly low
freeboards for the Indian and not much higher for the Pacific. Would you kindly explore this?
* The discussion on snow-depth estimates (p9 & 10) should also consider the episodic
events during which solid precipitation is delivered, versus the more frequent
redistribution of snow (by wind-induced drift). -- This is an area of research
by itself, but worthwhile to mention here.
* Update the final lines (15-34ff) as this CS-2 alignment to IS-2 has taken place by now.
Suggest to give a small outlook of the anticipated benefits of the Cryo2Ice objectives.

Specific comments:
1-7: Provide start date of your analysis: "April xx, 2019".
1-8: Correct "West Weddell sector" to "Western Weddell sector".
1-8: Provide at least a qualitative statement instead of "stands out with a mean sector thickness > 2 m."
1-9: Spell out "Ronne": "Ronne Ice Shelf".
2-2: Correct "sea ice extents" to singular "sea ice extent".
2-3: Suggest to change "decay rates" to singular as well, i.e., interpreting it as the
interannual decay rate.
2-37: "OIB" needs to be defined. So do this here: "IceBridge [OIB]),".
3-15ff: Need to provide some more info on the ATLAS and its build, i.e., 3 pairs of 2 beams and
some essential info. Short will be fine. Consider a reference too... but need to include
essential information here, so reader, for example, can understand meaning of "strong beam".
3-20: Specify "Vertical" to read "Vertical uncertainty".
3-24: Provide information on which "satellite-derived ice concentration(s)" have been used.
3-25: Provide information on why "freeboard is approximately one-ninth of ice thickness",
i.e., include density argument and a reference. This might make the sentence long,
consider splitting into 2 sentences, as required.
3-26: Move "(Kwok & Cunningham, 2015)" forward to read "differences (Kwok & Cunningham, 2015)".
3-30: What changes are meant here? "expected changes in IS-2 and CS-2 freeboards": Temporal. -->
Specify here.
3-34: Suggest to change "east sector and west sector" to "eastern sector and western sector".
3-34: Change "added a coastal Amundsen-Bellingshausen region" to "divided the Amundsen-Bellingshausen
Sea into a coastal region and remainder". Include info on which latitude was chosen for the
separation.
3-35: Could be more specific than "remarkable" in "remarkable ice convergence".
3-35: Change "seen" to "observed" or "recorded".
4-2: Suggest to change "worthwhile reviewing" to "necessary to review".
4-5: Add a space " " before "and" near beginning of line.
4-5: Remove a space " " before "deltah_i".
4-5: Add a space " " before "(Figure 2)".
4-7: Correct "Arctic Ocean export" to "Arctic Ocean exports".
4-7ff: Pls rewrite this longwinded sentence for clarity. Also avoid a "(...)" following another
set of brakets "Kwok et al., 2013)".
4-11: Include a reference for "larger ice divergence" (i.e., for Antarctic sea ice).
4-11: In "larger ice divergence", larger than ??? Pls complete sentence.
4-12: Replace "export" with "transport" in "large-scale export".
4-15: Appears as if there are erronous spaces " " before and after "h_fs" and "h_fi".
4-17: Appears as if there is an erronous space " " before "beta".
4-20: Correct "fvalue" to "value".
4-21: "spatially" is redundant. Could be cut.
4-21: Change "wind forcing" to "wind stress".
4-21: Change "is sometimes" to "may be".
4-27: Correct "Mechanical convergence/divergence" to "Mechanical redistribution due to
convergence/divergence"
4-31: Remove "no doubt".
4-33: Suggest to refocus "is the large export and sea ice melt at the margins." to also consider the
advective changes in the regional freeboard estimates, i.e., different 'parcels of sea ice (with
snow)' are found in a certain region at a certain time due to the ice being advected.
5-5: Clarify if the "Amundsen-Bellingshausen (A-B)" includes the data for the "coastal
Amundsen-Bellingshausen (CoA-B)".
5-8: Correct "Amundsen and Bellingshausen Seas" to "Amundsen and Bellingshausen seas".
5-10: Naming here "CoA-B sector" but in Fig.1 it is named "A-B Int". --> Unify.
5-20: Add "atmospheric" and remove "setup" to "The atmospheric circulation".
5-23: "i.e., ice freeboard tends to be anti-correlated to snow accumulation": Pls clarify if
this is a statement based on previous publications (then pls include reference), or
based on the data analyzed here (then add an exact figure reference). -- In general,
the thick or deformed ice also exhibits thick snow cover (i.e., Uto et al., 2006;
Maksym and Markus, 2008; Sugimoto et al., 2016).
5-31: Correct "40^oW and 62^oW" to "40^o and 62^oW".
5-32: Need to mention as early as here that the Weddell Sea is a (cyclonic) gyre. Otherwise
any reader without prior knowledge would miss out crucial information to interprete the
statement "both with boundaries that are open to the north."
5-32: Replace "areas" with "regions".
5-33: Add note that not all sea ice in the Weddell Sea is formed in the E-Wedd ... but some also
arrives in the Weddell Sea via advection within the westward coastal current.
5-35: Change "as well," to "as well as".
5-36: Change "ice areas added" to "ice areas are included".
5-37: Remove "are entrained in the outflow".
5-36: Rewrite "and formed in the Ronne and Brunt ice shelves" to correct. Sea ice does not form
in ice shelves per se.
6-2: Pls provide some information on the "flux gate" extent (in km).
6-2: Do you mean "~1100km." or "~1100m.", i.e., refernce to another isobar??
6-9: Change "On an area-averaged sense," to "Genearlly,".
6-16: Clarify the location by replacing "in the sector" with "in the E-Wedd". Suggest to remove
"As for the E-Wedd,".
6-23: Correct "Sound Polynyas." to "Sound polynyas."
7-4: Change "160^oW and 90^oE" to "90^oE and 160^oW".
7-4: Correct "90^oE and 15^oE" to "15^o and 90^oE".
7-5: Clarify text by chagning "the broader extent of the ice cover in Indian Ocean
Sector (around 15^oE and 40^oE)" to "wider latitudinal pack ice extent in the
Indian Ocean Sector (from 15^o and 40^oE)".
7-6: Change "the ice cover occupies a very narrow band, and" to "the ice covers a
narrow band, that"
7-7: Regarding the 2019 ice drift (being westward): Why is this remarkable? Mention
the separation of the westward coastal current with eastward drift in the southern
bands of the ACC.
7-10: Rewrite to improve readability "the Indian Ocean sector is seasonal ice from
coastal polynyas and from the Pacific Sector." and include that sea ice forms
locally in the Indian Ocean sector OUTSIDE "coastal polynyas". Text currently
reads as if all sea ice formed in the Ind Oc has done so in a coastral polynya.
7-19: This sentence is incomplete: "We have filtered most of these anomalous freeboards
in the IS-2 and CS-2 processing some are still present."
At least start with "Although we have".
--> Provide some detail and a refernce on the filtering of wave-effected data.
8-8: Remove comma ",' before " (Ulaby".
8-10: Include "snow" to read "bulk snow density".
8-10: Pls use SI units. I.e., avoid "0.32 g/cm 3". - Throughout ms, pls.
8-20: Include brief motivation for chooseing 30cm freeboard differences, for completeness.
9-7: Change "(compared to the Arctic)" to "than the Arctic". Or better simplify the complete
sentence. I.e.: Antarctic sea ice is found at lower latitudes, hence a lesser coverage
by polar-orbiting satellites proves difficult when deriving snow depth from IS-2 or
CS-2 freeboards.
9-8: "Gridded IS-2 freeboards are averages of the three strong IS-2 beams ..." -- Provide
footprint comparison of IS-2 freeboards with CS-2 freeboards.
9-10ff: Are both, IS-2 and CS-2 derived/treated the same way here? I.e., what about
adjusting IS-2 for ice concentration?
I am also concerned about the temporal coverage (per location pixel) for each
derived data set. --> Would you pls include some background on this here? (I know
IS-2 data are only there for ice concentration above 50%.
9-15: Correct "75-km" to "75 km".
9-19: This "advantage", however, reduces the true sample variability and due to IS-2
data gaps this is likely to bias the derived results.
9-30: Would you agree that the spatio-temporal averaging plus the footprint limitations
contribute to make this variance in snow depth appear so low? -- Some discussion
on this would be useful here. There is also the loss of snow when entering into
the open ocean during a deformation event, i.e., it is not accounted for as snow-ice.
9-31: Avoid use of "results" twice in same sentence: "These results suggest that the
effect of sea-ice deformation in biasing the derived snow depth may be small."
^^^^^^^^^^^
9-31: Ensure to replace "dynamics" with "deformation".
10-9: Correct "southern Ross and Weddell Seas" to "southern Ross and Weddell seas".
10:31: The zero freeboard/zero snow thickness argument leaves room for further discussion.
Is this based on Ozsoy-Cicek et al (2013)? Suggest to include a qualifier here.
11-1ff: Provide reference(s) for the retracker and related information such as temperature
dependence.
12-3: Consistency is important: Here densities are in kg/m^3. Pls use this SI unit
throughout the ms.
12-16: Correct "(mean 2.40±1.00 m) in May)" to "(mean 2.40±1.00 m in May)".
12-16: Correct "CoA-B sectors" to "CoA-B sector".
12-19: Correct "Ross Sea polynyas" to "Ross Sea Polynya".
12-26: Change "between April and November" to "from April to November".
12-27: Change "field records" to "field observations".
12-29: There are updates to the ASPeCt database from those included in Worby et al. (2008).
No updated climatology. The cleaned and calibrated data can be accessed at:
https://data.aad.gov.au/aspect/
Select "Download cruises". (Access via AADC, so "free login" required.)
12-35: Correct "Bellingshausen and Amundsen Seas" to "Bellingshausen and Amundsen seas".
12-35: This is correct for "operational underway data". If a vessel however travels
along a science transect, then it follows the waypoint line without deviations
motivated by the "hunt for thinner ice". -- ASPeCt should flag these.
13-3: As a field going scientist, I refute this. Sea-ice transects should be laid
out to be representative of the ice conditions of the entire ice floe and
the general region, so would include ridged areas and thick ice, and a range
of snow covers.
13-8 and 13-10: Be consistent: Reporting ice thicknesses from the same source should
provide them in a uniform presentation: I.e., number of decimals: "2.4 to 2.6 m"
versus "0.48 and 0.99 m".
13-16: Fullstop over "unlikely" missing.
14-33: Change "In this paper," to "In this study".
15-6: Correct "Ross Sea polynyas" to "Ross Sea Polynya". Alternatively rewrite to
"Ross Sea and Ronne polynyas".
15-20: Remove erroneous "the" from "from basal-layer salinity the is sound."
15-26: Add a sentence here to recommend urgent need for sustained and extensive field
measurements.
15-30: Add fullstop at end of sentence.
15-32: Correct "altimeter" to "altimeters".
16-4: Include acknowledgement/source of CS-2 data.
Similar for the PM ice-concentration data used, and any other data (i.e., atmospheric
reanalysis if the Davis Strait Low pressure pattern was updated here).
20-7f: Check doi in Giles et al. (2008) for correctness. - Remove linebreak.
20-15: Remove "Doi " (including space).
20-39: Remove "Doi".
20-43f: Correct doi for Maksym and Markus (2008).
20-46: Remove "Doi " (including space).
20-48: Remove "Doi " (including space).
21-29: Remove "Doi " (including space).
21-36f: Correct doi for Maksym and Markus (2008).
21-43f: Correct doi for Yi et al. (2008).

Fig1: Change caption to "Naming convention for the sea-ice sectors around Antarctica." or similar.
What is "A-B Int"?
Fig3: Include info on pixel size for IS-2 and CS-2 data shown in figure (and hence also for derived
snow depth).
Fig4a: Colourbar missing.
Fig5: Colourbar and scale for ice drift are missing.
Fig6a&b: Colourbar missing.
Fig9a&b: Colourbar missing.

Thank you for the revised manuscript. I am happy to recommend
publication, under the provision you check the following comments,
pls.

Best wishes, Petra

Minor comments:

Caption, Fig 1: "Naming of the sea ice sectors around Antarctica."
--> Are these "sectors" in general, or specifically "sea ice sectors"?

Figs 4, 6 and 9: While you advise that no colourvar is needed,
the use of colour without "code to interprete" distracts from
the figures themselves. -- This might be an individual preference,
however, I enchourage you to provide this aid (colourbar) to your
figures.

Caption, Fig 3: There appears to me some missing text in the sets
of brackets following directly after "IS-2", "CS-2" and "snow
depth (".

Caption, Fig 4: There appears to me some missing text in the sets
of brackets following directly after "IS-2" as well as "CS-2".

Caption, Fig 6: There appears to me some missing text in the sets
of brackets following directly after "IS-2" as well as "CS-2".

Caption, Fig 8: There appears to me some missing text in 4 places
within this caption: After "(a)", "differences (", "(b)" and "i.e.,".

Caption, Fig 9: There appears to me some missing text in 4 places
within this caption: After "(a)", "differences (", "(b)" and "i.e.,".

Caption, Fig 10: There appears to me some missing text in 4 places
within this caption: After ("i.e.,".