Dear Jan de Rydt and co-authors,
Your manuscript received 3 thorough and in general positive reviews that highlighted the quality and originality and the relevance and added value of the manuscript with regard to analysis and understanding of the observed dynamic changes at Pine Island Glacier over the last two decades. A all referees agreed that this research and manuscript would valuable contribution to TC and should be published after some revisions.

However, besides quite a few rather minor editing corrections the referees also raised some more substantial points which mainly concerned in brief:

-critical points and further discussion on the joined optimization of A (ice rheology) and C (slipperiness)
-related the robustness of the inversions
-clarification of data quality
-clarification of interaction of grounding line and thinning in optimization
-aspects of eqn 2
-some updating and improvement in the reference to existing literature

Given the authors response to the reviews, it seems the minor and more substantial points are addressable by the authors or have already been addressed very well (see track change document) and the manuscript will likely get into a state to be accepted for publication.

Based on the response there are, however, a few points where the authors have not undertaken revisions or the authors disagree to the referees, and in the response they have given a convincing and detailed explanations or justifications to their decision, which is fine. However, in my view these answers (or parts thereof) may also be relevant for the general reader of the manuscript and not just the referees, and some explicit but very brief additional explanations/justifications (or links to the supplements) in the main text may be helpful.
For example, a lengthy explanation has been given to the referees on the point of the joined optimization od A and C, but it is not clear/explicit if any of these explanations are planned to be incorporated into the manuscript. These explanations/justifications/clarifications should not just go to the referees, but some aspects of it may well be interesting for the general reader and should perhaps be considered in the main text.
Specifically, for the case of the joined A and C optimization (Ref 1 and 3), some additional figures and clarifying text have been added in the supplement B2 which is helpful, but I think in the main text an additional reference to these add-ons in the supplements and maybe a brief discussion in the main text clarifying this point would be useful.

Similar:
-To Ref1 comment 1: quality RS-data: a new figure has been added in the supplement, but in the main text, a reference to this figure and a short comment to it would be useful (relative dh change accurate).

-To Ref1 comment to line 139: data coverage: refer to this fig. A1 also in the main text.

-To Ref1 comment to line 451 and similar Ref3 (robustness of inversion results): the essence of this response would probably also be relevant for the general reader (not just referee) and could be briefly included in the main manuscript.

-For the ease of reference to the author response by the editor it maybe useful to perhaps number the responses the major referee comments (e.g. R1.3….).

Do not get me wrong on the points above, I think the authors addressed the raised referee points or justified their decisions very well, but at times some points could be addressed/included more explicitly.

So I ask to submit a revised manuscript along the lines of the response and addressing the additional comments above with a clear and detailed response. I thank the authors for their cooperation in handling the review process and look forward to the revised manuscript.

Andreas Vieli, editor
30 Okt 2020

Dear Jan de Rydt and co-authors,
Your manuscript received 3 thorough and positive reviews that highlighted the quality and originality and the relevance and added value of the manuscript with regard to analysis and understanding of the observed dynamic changes at Pine Island Glacier over the last two decades. All referees agreed that this research and manuscript would be a very valuable contribution to TC and should be published after some revisions.
However, they also had some minor and more substantial points which in brief asked for:
-clarifications and discussion on the joined optimization of A and C
-related the robustness of the inversions
-clarification of data quality
-clarification of interaction of thinning with grounding line retreat in optimization
-aspects of eqn 2
-some updating and improvement in referencing to existing literature

The authors very carefully and satisfactorily addressed all these points and further documented and explained their revisions in their response in detail.
I am therefore very happy to accept this manuscript for publication in TC as it is and congratulate the authors for this very interesting, systematic and conclusive modelling investigation on the processes behind the observed acceleration of Pine Island Glacier. At this stage I would also like to thank the authors for their cooperation in and their handling of the reviewing phase.
Andreas Vieli, handling editor, 22 Nov 2020