|Review on “Antarctic dynamics contribution to future sea level constrained by ice discharge observations”|
Dear Eveline van den Linden et al.,
Many thanks for your work on the manuscript and taking into account all the suggestions, I think the manuscript has improved a lot! Given that most of the text is new, there are a few new comments from my side. After that, I think the manuscript is fine to be published and I want to congratulate the authors on this work!
From the replies I understand now that you use the historic observations of ice discharge to constrain the melt parameter (e.g., p3 lines 80). There is however one discrepancy in units which you might want to consider - I think you should at least discuss it. In the LARMIP2 paper, the ice sheet modelers were asked to provide the results in units of sea-level equivalent ice loss, which is calculated based on changes in the volume above flotation of the ice sheet. This does not directly compare to changes in ice discharge. In the extreme case, when an ice stream is just about at the flotation limit and very slightly grounded, it could be that its discharge increases and the grounding line retreats, but the sea-level contribution of this is quasi negligible.
- p 1, line 15-16, and p28, lines 587-589: I do not understand your argumentation so far that your results support this statement. If I understand it correctly, it is based on how your calibrated melt parameters compare to the ISMIP6 median parameter. However, the ISMIP6 experiments also included the PIGL calibrations which is much more sensitive, and this is not included in your argumentation, or? So maybe re-calibrating parameters would also reduce the upper range of the ISMIP6 projections based on this parameter calibration, or am I missing something? Please explain your reasoning for this statement better.
- p 2, line 35: that the range of uncertainties appears to be increasing is arguably not because the we know less as implied by this formulation, but because more models and processes are included, i.e., the uncertainties become “visible”
- p 3, line 62: I was a bit surprised by calling this a “melt parameterisation” since in my head this is usually a 2-dimensional field of melt rates, but I think this is fine, maybe add a short explanation to make this clear.
- p 7, line 125: this sentence still sounds weird to me as it is not the water that is changing its temperatures in the cavity.
- equation (4) do you also use the ice shelf cavity mean depth when testing the deeper ocean layers?
- p 9, line 166: show also the equations over which you are optimizing, this would make it easier to understand what you are describing here
- p 10, 180-181: give the median values, so that they are somewhere in the manuscript.
- p 10, section 3.1, please show the discharge curves you use for calibration in the Amundsen Sea and for the whole Antarctic ice sheet
- p 10, line 196: if correct, add “..to sea level while CMIP models indicate an increase in ocean forcing,…”
- p 10, line 200: add citations that support this attribution
- Fig 5: add % to the numbers in the top of the panels
- p 13, line 244-246: not sure I understand this sentence, please clarify
- p 14, line 255-256: earlier you stated that you include the linear parameterisation for comparison with LARMIP2?
- p 21, line 384-398: reformulate this argument, you base your reasoning here on a comparison between projections, but we do not know which projection is correct and hence a conclusion about which methodology is better cannot be drawn. Instead you could use papers that support the quadratic relationship (e.g., Holland et al., 2008).
- p 24, line 466-467: Please explain more. Which numbers do you compare to conclude this?
- p 26, line 598: this could also indicate an insensitivity of discharge to basal melt (in the case of no buttressing)
- p 26, line 508-514: I am not sure I understand what you mean. Are you basically saying that FRIS cannot be calibrated at the moment?
- p 26, line 514: it could be misread at the moment that you calibrate with basal melt (not discharge), maybe be clearer here
- p 26: one point that is missing in your discussion is that you consider a constant basal melt rate increase over the entire ice shelf, no spatial patterns and effects are taken into account
- p 26, line 532: “physically correct” – I do not think that you can derive this from your previous reasoning.
- p 27, line 559-560: LARMIP2 did not mainly focus on the future, it did compare to historic ice loss and found their projections to be consistent