|Comments on revised Neuhaus et al|
The revised paper is substantially improved from the original version I reviewed and I believe that the authors have addressed almost all of my comments. The figures in particular are clearer, the captions explain them better and uncertainty is better represented throughout the figures. As I noted previously I think the paper is a novel contribution to the debate and provides important constraints for understanding Holocene grounding line retreat in the Ross Sea. I also would point out again the importance seeing novel work using innovative approaches to archived samples: this sort of study is very welcome.
In the abstract I think that it would be helpful to include the word ‘primarily’ or ‘dominantly’ when referring to climatic controls. The authors have not ruled out GIA processes, only that they suggest climate was dominant. Indeed in the introduction the authors only say that their results are ‘consistent with a climatic forcing..’. So last sentence of abstract could read: Based on these results, we propose that the Siple Coast grounding line motions in the mid- to late-Holocene were primarily driven by relatively modest changes in regional climate, rather than by ice sheet dynamics and glacioisostatic rebound, as hypothesized previously (Kingslake et al., 2018).
A similar edit is likely to be needed in discussion. This is important and scientifically prudent because the authors do not find a complete match and they cannot rule out some GIA control on readvance.
In my first review I noted that the fields on Fig 9 (now Fig 3) were plotted in Lamb et al (2006) using wt%:wt% not atom:atom (molar) ratios. My point was that there is a conversion between these two units (x1.17) and this needed to be applied if the authors were to plot their data from the atim:atiom measurements. The response claims that Lamb et al uses atom:atom and that therefore the plot in Fig 3 is unmodified. This is not my specialism but I have to note again I have checked and Lamb et al (2006) note very clearly in the text on their p.30 that they use wt% ratios unless stated otherwise (and their field diagram does not state otherwise):
“The weight ratio of organic carbon to total nitrogen (C/N) is normally measured alongside d13C, and can also help to distinguish carbon sources. Occasionally, the weight ratio is converted into an atomic/molar ratio by multiplying by 1.17; however, the ratio used is not always stated. Here, C/N refers to the weight ratio unless stated otherwise.” Lamb et al (2006)
I am not a specialist in this field but unless I have missed something, the response implies that the Lamb et al (2006) fields and the data from this study continue to be plotted on different x-scales in Fig 3 and therefore are offset and the plot is in error. This may need someone more expert to take a look or to ask Angela Lamb directly.
Line 645: Additional
Symbology on Fig 9 - the captions in the revised paper are much richer and more helpful than in the original submission but fig 9 still needs some further explanation of the shaded colour bars at the base of the figure - what does the shading mean, what are the red (?) boxes towards their younger ends and so on. Would be helpful to more clearly and explicitly match the symbology to the plots in Fig 8 e.g. by placing a dot at the optimal GL retreat timing (along with the lines for uncertainty) and a box and whisker for the readvance timing. This might need a small zoom in inset for this part of the figure
The discussion of saloon door and swinging gate is now much better: it is nuanced, and points out clearly that the model results presented here cannot distinguish between these two canonical models. The discussion of bathymetric controls is good but I would note, however, that the dependence of retreat on bathymetry has been discussed in many of John Anderson’s papers on Antarctic deglaciation for several decades and he should be cited here. The most recent paper, and perhaps most generally applicable is perhaps this one: Anderson,John B. et al.. 2019. Seismic and geomorphic records of Antarctic Ice Sheet evolution in the Ross Sea and controlling factors in its behaviour, Geological Society, London, Special Publications(2019),475(1):223 https://doi.org/10.1144/SP475.5 but there are several earlier examples.
Mike Bentley, July 2021