Dear Dr. Loeptien,

thank you for addressing the reviewers’ comments so thoroughly. The manuscript is now acceptable for publication but requires a few minor technical corrections and one additional point that needs to be addressed. Please make these changes detailed below before submitting the final version of the manuscript.

Also, one point that you should address (unless you already have and I have missed this - please be sure to send some feedback on this to me) relates to your exclusion of icebreakers from the analysis. As you describe in Section 2.1 icebreakers introduce an element of uncertainty that complicates analysis. However, under divergent or zero-divergence ice conditions, icebreaker channels and icebreaker fragmentation of the ice pack persists on time scales much larger than equivalent to your exclusionary criterion and may result in comparatively high ship speeds despite high ice thicknesses. Please include some brief discussion of whether this may introduce a potential bias into your analysis.
Also, could persistence of broken channels or fragmented ice be part of the explanation of your finding that for ice thicknesses greater than 30cm no systematic drop in ship speed is observed? Otherwise this is a somewhat perplexing finding since you have excluded icebreakers themselves from the study. Please clarify in the text (and in a response to me through the editorial system).

With best regards,

Hajo Eicken.


Loeptien & Axell, TC2014-98

Minor corrections

- l. 6: Use of “allocated” is a bit awkward, please consider rewording to “Typically, the forecast comprises several ice properties that are distributed as prognostic variables, but…”
- l. 19: correct spelling of “employs” (below I will leave out “correct to” and just show the correct text in quotes)
- l. 43: “and thus receive increasing attention from”
- l. 51: “worst case”
- l. 54/55: “described above”
- l. 56: “choose”
- l. 67: Include N and E in the geographic range
- l. 70/71: “circumnavigate”
- l. 72: “but in”
- l. 100: “Section 4”
- l. 106/107: “This so-called mixed effect model”
- l. 110: “1990s”
- l. 111: “the system”
- l. 120: “a unique”
- l. 135: Here and throughout ms. please correct spelling of “icebreaker” which is written as one word.
- l. 156: Should this be “Axell”?
- l. 159: “forecasts include”
- l. 172: “Apart from”
- l. 179: “analyses, since”
- l. 180: “from the”
- l. 191: “from the Swedish”
- l. 195: “these relatively”
- l. 215: Not sure what “extra” refers to here. If landfast ice is not considered then “as landfast ice is not considered by the model” is sufficient.
- l. 220: “too patchy”
- l. 255: Figure 6 is referenced in the text before Figure 5, please reverse order accordingly.
- l .293: “exists, in addition to ice”
- l. 321: “particularly problematic”
- l. 379/380: “is the relatively rare situation where”
- l. 381: Ice drift directed towards the side of the ship? Please clarify.
- l. 395: “is listed”
- l 409: “illustrates that”
- l. 415: “obtained from”
- l. 428: “from ship”
- l. 436: “yet to be solved”
- l. 454: Should this be “Axell”?
- l. 503: Loeptien & Dietze reference is missing full bibliographic information (pages numbers or DOI, volume etc.)
- l. 516: Suominen & Kujala reference is missing full bibliographic information (pages numbers or DOI, volume etc.)

- Figure 1: The contour line numbers are difficult to see, please enlarge. Also, since the text and other figures quote ice concentrations in % you may want to be consistent and change from fractions to % here as well.
- Figure 2: Squares are difficult to see, please use black or some other prominent color/shade and increase line width.
- Figure 3: Since the regressor variable considered is level ice thickness, you need to clarify whether this figure shows level ice thickness or total ice thickness. If this is total ice thickness then some discussion of whether or not this is dominated by either the ridge or level ice fraction would be needed.
- Figure 4 caption: “20 January” and “21 January” (and the same for February) or “21st of January” “20th of January” and so on. Also “SAR-based” in 4th row needs to be corrected.
- Figure 6, caption 3rd line: “is drifting very slowly”

Dear Dr. Loeptien,
thank you for your thorough revision of the manuscript.
The paper is now ready for publication, subject to just a few minor technical corrections, listed below.
In submitting the final version please include these corrections.
With best regards,
Hajo Eicken.


l. 139: Change to “Note that nevertheless icebreaker channels”
l. 446ff.: Change to “they do not decrease further with increasing ice thickness”
l. 454ff.: Change to “is that some of the thickest level ice occurs in the fast ice zone. Ships benefit from the fact that convergent ice motion or ice deformation is typically absent in such ice conditions.”