This is an interesting and valuable manuscript that introduces new geomorphological mapping and geochronology (cosmogenic ¹⁰Be and IRSL dating) that firmly establishes the timing of the local Last Glacial Maximum (LGM) of the Lago Argentino glacier lobe.  This glacier lobe reached its maximum during Marine Isotope Stage (MIS) 3, at about 45 ka and again at about 37 ka, rather than during the global LGM, which occurred more recently during MIS 2.  It also shows that there are older glacial moraines preserved in the valley that could indicate a more extensive advance dating to the penultimate MIS 6 glaciation (~160 ka), but that is less certain as I will discuss later. The authors find no evidence for glacial advances in the valley that correspond in timing to the global LGM and suggest such deposits could be less extensive and therefore remain preserved beneath the present lake.  The overall timing of the local maximum is quite similar to other valleys in southern Patagonia, such as the Torres del Paine and Ultima Esperanza valleys just to the south.  The authors suggest ideas as to why the local LGM occurred earlier than the global LGM, inferring more intense winters and a northward expansion of the southern westerly winds (SWW) causing an increase in precipitation during MIS 3.

The manuscript makes a valuable contribution to knowledge on glacier behaviour during the last glacial cycle in a part of Patagonia where this data is currently limited.  The paper's thrust tackles the local LGM, and the data presented supports the interpretations made.  However, the interpretations made regarding the age of the older moraine system are, in my view, not supported by the data. I would suggest some changes to this part of the manuscript before publication.  When those changes are made, I would recommend publication of the manuscript.

Main Revisions

The cosmogenic ¹⁰Be ages from moraine boulders on the Arroyo Verde II moraines are few and widely scattered.  Four exposure ages range from 132-243 ka.  While two of the exposure ages are similar (~160 ka), the data are insufficient to conclude that this moraine was formed during MIS 6.  It may well prove to be a correct age assignment, but the current data are not sufficient evidence.  I recommend the manuscript is changed to indicate that this age assignment is no more than tentative, given the paucity of data to support the age.  This will require changes in the abstract, conclusions and throughout the body of the text (e.g., section 5.3) and figures (e.g., Figure 6) where the MIS 6 age is currently indicated as the definitive age of the advance. 

There has been a significant amount of published work in similarly dry environments in neighbouring valleys within Argentine Patagonia demonstrating that outwash terrace surfaces are better targets for exposure dating of “old” glacial advances (i.e., pre-last glacial cycle) than corresponding moraine limits, which tend have scattered and too-young exposure ages (e.g., Hein et al., 2009; 2011; 2017; Darvill et al., 2015; Mendelova et al., 2020; Leger et al., 2023).  In the Lago Pueyrredón and Lago Buenos Aires valleys’, the outwash terraces linked directly to (and in between) moraines with MIS 6 boulder ages, instead had MIS 8 outwash cobble ages (i.e., 100 ka older), suggesting moraine degradation had led to erroneously young boulder exposure ages (Hein et al., 2009; 2017).  In a more extreme case, moraine boulders in the Lago Pueyrredón valley with exposure ages mostly between 190 – 230 ka, but with a single 600 ka outlier, had corresponding outwash ages of ~600 ka, consistent with the age of the oldest boulder outlier (suggesting all of the other moraine boulders were too young). Given this regional context from neighbouring valleys, it could be the case that the 243 ka boulder age in this study is closer to the age of the Arroyo Verde II moraine.  In other words, it may very well be that the Arroyo Verde II moraine was deposited during MIS 8 instead of MIS 6, much like the “Hatcher” and “Moreno” moraine systems in the Lago Pueyrredón and Lago Buenos Aires valleys a little further north (47S) in central Patagonia. The revisions to the present manuscript should leave open the possibility that the sampled moraines could indeed be older.  Moving forward, this could be tested by increasing the dataset and targeting the outwash cobbles. If both outwash and moraine boulders give MIS 6 ages, then the uncertainty in age assignment would be greatly reduced (e.g., Leger et al., 2023).

 Suggested minor changes

Abstract:L0-5: “Despite synchronous ice-volume and extent change across hemispheres, evidence from the southern mid-latitudes indicates that local glacial maxima occurred earlier in the glacial cycle” – this sentence appears to contradict itself.  Suggest re-writing.

L35: It’s not necessarily that they are poorly preserved to the west, but the LGM ice sheet probably terminated in the sea, so fewer moraines exist to the west.

L40: Capitalise “Late” Glacial

L115: I have sampled outwash cobbles in the Lago Argentino valley, and looked at several boulders.  Many of these were fluted and ventifacted as a consequence of being downwind of the dust source (outwash plains).  I would imagine this type of aeolian erosion would be most severe in the centre of the valley. Was this observed?  Did the samples collected have evidence for aeolian erosion?

• Please indicate whether such aeolian erosion is present (and its severity) at an appropriate point in the manuscript.
• Please also note any evidence for moraine degradation at the sample sites (I note from Figure 3I that boulder AV-01 appears to have ~50 cm of recent exhumation). Is this common across the sampling sites?

L131: I would encourage aborting use the 1.4 mm ka-1 erosion rate, but instead use the 0.2 mm ka-1 rate from Douglass et al., 2007.  Kaplan always meant for the 1.4 rate to indicate a “maximum” erosion rate, but it seems to have been adopted as “the” erosion rate in a lot of literature – check discussion on this topic in Hein et al. (2017).  If it is used, please explicitly indicate this is a maximum erosion rate.

 L175: state how far west of Arroyo Verde I in km (for consistency with subsequent description)

L175: It is not clear from where the elevations of the moraines are taken from, the terminal moraine elevation? The maximum height in the mapping area east of the lake?  Or is it just the maximum elevation before they are no longer traceable? 

L194: remove “in” before “Strelin and Malagnino”

Figure 2: hard to see palaeo channels

Section 5.1: Earlier the young age of 132 ka was rejected as recently exposed through exhumation, so I’m wondering why it is included in the calculation of the mean age of 153 ka. Is a mean age sensible with so few data, and such large geological scatter? Some take the oldest boulder age as a strategy (e.g., Kaplan et al., 2005).  Please explain interpretation here.

L243: “Isotope” rather than “Isotopic”

L255: “Isotope” rather than “Isotopic”

Section 5.2: a potential added issue for the samples from the centre of the valley is subsequent fluvial erosion causing undercutting/slumping of moraines and therefore degradation/exhumation of boulders if the sampled surfaces were in contact with former drainage routes.

Figure 6: Depending on how the MIS 6/8 discussion evolves, it may be sensible to increase the age scale to include MIS 8 and the chronologies that align with that age.

• Please indicate how the “Patagonian moraine age distribution” sites were chosen for this figure. For example, other major valleys not mentioned include Lago Buenos Aires, Lago Pueyrredón, and others. 

Section 5.3: A relevant reference may be a new marine core off the Chilean coast that indicates glacier activity during MIS 6.  Hagemann et al., 2024: https://doi.org/10.1073/pnas.230298312  

L300: I don’t think there is evidence that these are separate re-advances?  If so, make this clear (i.e., cross-cutting relationships, etc).

L306: “and were more extensive than during the global LGM”

L315: The reference to çiner et al. 2022 should be under “c” in the reference list

L350 – Currently the core of westerlies is at about 50 S (i.e., Lago Argentino), so it seems cooling would be more important than a northward migration of the westerlies?

L361 – suggest adding Mendelova 2020 to that reference list

This manuscript presents an important new reconstruction of the Lago Argentino glacier in Argentine Patagonia based on geomorphological mapping and Be-10 and IRSL dating of glacial landforms. The authors’ principle finding is that the glacier reached its maximum extent during Marine Isotope Stages 6 and 3, with no evidence found for an MIS 2 / global Last Glacial Maximum limit (although they note it may still exist). The new evidence adds to a growing body of work from the Southern Andes showing numerous glaciers were more extensive prior to the global Last Glacial Maximum during the last glacial cycle. They add weight to ideas in the literature that this could have been caused by longer, colder winters earlier during the last glacial cycle, combined with movement of the Southern Westerly Wind system. Overall, the paper provides a valuable new record for pre-LGM glacial activity in Patagonia and will be a useful addition to the literature. The paper is well-written and presented, with excellent figures and clear discussion. This is an impressive piece of work. I have only one major issue relating to the authors’ interpretation of older ages in the Lago Argentino system—which I believe needs amending throughout the manuscript—and offer an additional list of minor changes that I hope might also strengthen their final paper.

Major revision

The MIS 3 glacial limit is convincing; the older glacial limit assigned to MIS 6 much less so and should be handled more speculatively. The manuscript currently presents this limit as unambiguously dating to MIS 6 within the abstract, discussion and conclusion, but there are two major issues with this interpretation based on the data presented:

1. The older Arroyo Verde II limit is assigned to MIS 6 based on only four exposure ages: two in good agreement at ~163 ka, one younger at ~132 (roughly on the MIS 5/6 boundary), and one older at ~243 ka (roughly on the MIS 7/8 boundary). What these clearly show is that the Lago Argentino glacier was more extensive than its MIS 3 El Tranquilo I limit at some point during the Mid-to-Late Quaternary: a valuable conclusion and important addition to the literature. However, the conclusion that this is an unequivocal MIS 6 glacial limit seems too strong, particularly without other supporting evidence (e.g. additional dating approaches and limiting glacial limits, as per Leger et al., 2023, Climate of the Past). I find the rationale for excluding the older exposure age unclear and not reflective of other approaches in the literature, and either way do not see a strong enough body of evidence for such a strong MIS 6 conclusion. In addition:
2. Older (e.g. > MIS 2) glacial limits across the Southern Andes have proven challenging to date, with a large body of work demonstrating potential issues, particularly involving dating boulders on moraines like this study. There are lots of examples from the literature, but a good starting point is Hein et al. (2017; Quaternary Science Reviews). Hein et al. show that boulders on older limits may typically underestimate glacial activity quite substantially (e.g. by a glacial cycle). This makes rejection of the older exposure age and categorical assignment of the Arroyo Verde II limit to MIS 6 problematic. Even without the older age, so few ages should be treated more cautiously, particularly given work around Lago Buenos Aires has shown substantial numbers of moraine boulders may still underestimate the timing of glacial retreat.

In summary, it is quite possible the Arroyo Verde II limit does indeed date to MIS 6, but I do not find sufficiently convincing evidence presented here for that conclusion to be so strong. Better to consider MIS 6 as a possibility, but also to consider that the limit may be older. The older exposure age should not be rejected so readily, and the abstract, discussion and conclusion updated to consider a variety of possibilities. I also urge the authors to update their Figure 6, both to factor in the potential for an older limit (i.e. include the older age), and to consider a greater number of existing records in Panel (B) to reflect the fact that numerous MIS 8 limits also exist in Patagonia.

Minor suggestions

Line 71: "a relative ages"; there's a plural mismatch.

Line 73: Can you specify which you mean by "these moraines", you listed four systems but I think you are just referring to the Puerto Banderas at the end of the preceding sentence.

Line 75: I think you mean Caldenius' framework, not Strelin (the last work you cited). I suggest moving the final sentence in Line 74 to the end of the next paragraph (e.g. Line 81) so the chronology of work is in order.

Line 86: "Last two glaciations" is ambiguous (in terms of them/you naming them? Or in terms of timing?) You can just state that you only focus on the Arroyo Verde and El Tranquilo moraines, or provide their stratigraphic order.

Line 133: I'm not sure this scans quite right: I think you are deciding to report with zero erosion given ages overlap within uncertainties and doing so does not alter your main findings. Perhaps adjust the wording here because I do not think you can assume the erosion rate was zero based on the evidence provided.

Line 144: Blomdin et al. used IRSL in southern Patagonia; perhaps a useful reference here (Blomdin, R., Murray, A., Thomsen, K.J., Buylaert, J.P., Sohbati, R., Jansson, K.N. and Alexanderson, H., 2012. Timing of the deglaciation in southern Patagonia: Testing the applicability of K-Feldspar IRSL. Quaternary Geochronology, 10, pp.264-272.)

Line 166: Should "by moraine ridges" be "of moraine ridges"?

Line 182: Figure 3: Please include photos of all sampled boulders, if possible. It is useful for assessing what was sampled, and for anyone wanting to revisit sample sites in the future.

Line 191: Point to Figure S2 again.

Line 188: Should be "inboard of", I think.

Line 194: "by in"; should be one or the other.

Line 203: "glacial transgressive facies" implies overlapping / overriding glacial sedimentology to me, but do you mean glaciofluvial, like the rest of the section? Perhaps you are referring to moraines overriding glaciofluvial features? In which case, start with the glaciofluvial features about which this section focusses and then explain that sorm landforms are indicative of glacial transgression.

Line 211: Why are meltwater channels not descrived in Section 4.1.3 on Glaciofluvial features?

Line 213: Why are palaeo(lacustrine) features mentioned here again, rather than just in Section 4.1.4 on Glaciolacustrine features?

Line 249: The rationale for excluding the oldest age here and not the youngest is unclear. With only four ages, I question whether any samples should be removed at all. See broader point about these older ages in the major revisions section. There is a good argument that removing outliers should be done with great caution, or that all ages should be kept in and metrics such as the median be used instead (outlined in Dortch, J.M., Tomkins, M.D., Saha, S., Murari, M.K., Schoenbohm, L.M. and Curl, D., 2022. A tool for the ages: the probabilistic cosmogenic age analysis tool (P-CAAT). Quaternary geochronology, 71, p.101323.) Additionally, there is a lot of work on understanding age distributions from these sorts of environments in Patagonia that would counter you rejecting older ages as inherited (Kaplan, M.R., Douglass, D.C., Singer, B.S., Ackert, R.P. and Caffee, M.W., 2005. Cosmogenic nuclide chronology of pre-last glacial maximum moraines at Lago Buenos Aires, 46 S, Argentina. Quaternary Research, 63(3), pp.301-315.; Hein, A.S., Cogez, A., Darvill, C.M., Mendelova, M., Kaplan, M.R., Herman, F., Dunai, T.J., Norton, K., Xu, S., Christl, M. and Rodés, Á., 2017. Regional mid-Pleistocene glaciation in central Patagonia. Quaternary Science Reviews, 164, pp.77-94.)

Line 250: Correspondance with MIS 6 needs to be much more speculative here.

Line 258: The wording does not quite work here; needs slight editing.

Line 250: Here and elsewhere (so perhaps state if it applies to all), explain what constitutes ther uncertainty here, and if it is weighted or not.

Line 260: I think the word "preserved" needs inserting, as it's possible (though unlikely) that moraines recording a more extensive advance were subsequently destroyed by outwash from the El Tranquilo advance in such a topographically-constrained system.

Line 262: Here, please give the raw mean age and associated error before moving on to explain why you are removing some ages and providing an updated mean and error.

Line 265: "the valley center".

Line 265: Small boulders do not inherently indicate exhumation, but they might be more susceptible to it if it occurred. Alter framing to reflect this here.

Line 268: Be clear throughout about number of samples. E.g. here "we exclude three ages".

Line 280: Figure 6: This should include all ages, so extend back to >243 ka. The moraine ages are rather selective here. A classic of the region—Lago Buenos Aires—is missing (e.g. Kaplan's work, and Hein et al., 2017), as is Hein's work in Lago Pueyrredon. Their chronologies are highly relevant for this work.

Line 281: I feel this section needs to better reflect uncertainties in the new chronology; see major revisions.

Line 300: Not clear why this is a separate section; it could be added to the start of Section 5.4.1

Line 323: "a millennial-scale moraine chronology"?

Line 359: Here and elsewhere, worth reflecting that Davies et al. looked at 35 ka to present, so were not necessarily saying maxima occurred then, just that advances were not exceeded after that point.

Line 361: Mendelova et al. (2020) talked about the role of ice masses changing moisture patterns and should be referenced here (Mendelová, M., Hein, A.S., Rodés, Á. and Xu, S., 2020. Extensive mountain glaciation in central Patagonia during Marine Isotope Stage 5. Quaternary Science Reviews, 227, p.105996.).

Line 416: This does not sound right. There is evidence for glacial activity (retreating from moraines) during the Holocene (e.g. Sagredo et al., 2021; Reynhout et al., 2019; Strelin et al., 2014; Kaplan et al., 2016; Garcia et al., 2020). See Briner & Darvill 2024 for reference (https://doi.org/10.1016/B978-0-323-99931-1.00198-7). You cite some of these papers, so I wonder if it is just unclear what you mean here.