In this manuscript, McKenzie et al. present stratigraphic and chronological constraints on the retreat of the Puget Lobe of the Cordilleran Ice Sheet (CIS) in Washington State. This area has been studied by glacial geologists for many years, but there is still some uncertainty about its history. McKenzie et al.’s work largely relies on facies analysis of sediment outcrops on Whidbey Island, supplemented by ¹⁴C dating of marine shells and OSL dating of quartz. From these data, the authors construct a general timeline of events across Whidbey Island, from prior to the LGM up to the present. A key conclusion of the manuscript is that the Puget Lobe lingered near Whidbey Island for several thousand years longer than previous work indicates; this interpretation is based on ¹⁴C-dated shells in a unit that the authors identify as glaciomarine. McKenzie et al. then suggest that the Puget Lobe was stabilized on Whidbey Island by solid-Earth uplift, topographic pinning points, and grounding zone wedges.

I think the sedimentological descriptions and facies interpretations mostly make sense (although that is not my primary research area, so I will yield to other reviewers on this point), but the major weaknesses of the manuscript in its present form are (1) chronology and (2) how these results fit in with existing age constraints in the Puget Lowland. In my view, the authors need to better situate their work in the context of previous research, and offer more thorough (and convincing) explanations for why their results differ so much from what has already been published.

My comments on this submission are below. As I have focused most of my attention on what I believe are major issues with the manuscript in its present form, I have only provided a few line-by-line comments. It is my hope that all of these comments are helpful for the authors as they revise the manuscript.

Specific major comments:

1. I’d like to see a thorough treatment of the existing constraints on CIS and landscape evolution in the Puget Lobe region. Some review of the literature is present in the supplemental material, but I believe these points should appear in the main paper, and that they should appear early (rather than being brought up at the end of the discussion section). Points that need more discussion earlier in the manuscript include:
   • Previous outcrop work in the Puget lowlands
   • ¹⁴C constraints on the Puget Lobe – marine shells, lake sediments
   • Grounding zone wedges on Whidbey Island
   • Cosmogenic ³⁶Cl ages on Whidbey Island – ideally these would be recalculated from Swanson and Caffee (2001) as the production rates have changed slightly, but they indicate deglaciation ~15 ka (much earlier than your results suggest)
2. Related to point 1, I strongly recommend adding a figure that shows the regional context, as the inset map on figure 1 is not sufficient to set the stage. I recommend that at minimum, you include published stratigraphic column locations, age constraints from ¹⁴C and cosmogenic ³⁶Cl, surficial geology (e.g., presence of GZWs), and previously mapped CIS margins (and perhaps the glacial lakes too).
3. I would also like to see a more thorough discussion of your chronology and stratigraphy. There are a few things that would help the readers better evaluate your data, and areas that need clarification:
   • Pictures of outcrops in the main text, or at least in the supplemental material. Without these, it is difficult to evaluate your interpretations of the outcrops, and therefore the geologic history.
   • Double Bluff site: You find ¹⁴C-dead woody debris in the “deglacial” unit. How can you explain this? Remobilization of old material?
   • Fort Casey site 1: How do you explain a 9.3 ka OSL age in your “LGM” unit? You say it’s a minimum age, but what processes could make that age so much younger than regional deglaciation?
   • Fort Casey site 2 and Penn Cove: Unless I’m reading the figure incorrectly (which is possible, see my comments on figures below), you interpret a transition from glacial outwash to landscape emergence between units 4 and 3 at Fort Casey Site 2 and between units 5 and 4 at Penn Cove. Are you interpreting the lower units as submarine glacial outwash? If so, how are you distinguishing that from subaerial outwash? I don't see any discussion of that in the text.
   • More discussion of disagreement between your shell ages and previously published constraints on deglaciation. You are making some pretty strong claims about the timing of Puget Lobe deglaciation (several kyr later than previous work suggests), which need to be backed up by strong evidence. How can you explain the large difference in inferred deglaciation ages, and why should readers trust your chronology over others? I don’t see much of this in the current version of the paper.
4. The marine reservoir correction in the Puget lowlands is controversial, and I’m not sure that calculating the latest Pleistocene reservoir correction using ~1.8 ka shells resolves the issues brought up by other authors. The marine reservoir correction along the northeast Pacific coast has been shown to be variable during the late Pleistocene (e.g., Schmuck et al., 2021), and as you acknowledge, there has been a good bit of work on the MRC around the southwestern CIS already. I recommend including a more thorough discussion of the literature on this topic if you intend to bring it up in the introduction as a main goal of your paper (e.g., line 90).
5. Is it possible that the quartz grains used for OSL dating in the glacial outwash deposits were only partially bleached, leading to too-old burial ages (common in glacial environments)? Could this be another explanation for the disagreement with ¹⁴C and OSL in the “pre-LGM” units?
6. The main title of the paper relates the inferred CIS stability to solid-Earth processes, but the discussion section barely touches on this point – it’s just a few lines. If you want to keep the title as-is, then I strongly recommend expanding this section of the discussion.

Comments on existing figures:

• The colors on figure 1 are somewhat difficult to interpret because the unit numbers/colors aren’t correlated between sites (e.g., the dark purple unit at Double Bluff is not correlative with the dark purple unit at Penn Cove). Please make the key larger and label the stratigraphic units more clearly on the stratigraphic columns.
• Figure 1 also appears to show samples that have no ages (e.g., uppermost shell icon on double bluff site, when the text says that no samples were collected in the upper shell-bearing units).
• In the caption for Figure 1 (line 142), I am not sure what “white dots indicate changes to site collection of samples” means, or what the white dots actually show on figure 1.
• I also found figure 2 difficult to interpret. The blue/gray colors (at least on my screen) were hard to distinguish from one another. And I’m also curious as to why there isn’t a timeline on the side that more clearly shows the ages? It was inconvenient to go back and forth between the table, key for the units, and the main panel of the figure. And it’s not clear which ages these are in the results tables – consider adding sample IDs somewhere on this figure to make comparison easier.

A few technical comments:

• Line 433: not sure what “respectively” means here
• Line 501: Should this be MIS 3, not MIS 5?

In this manuscript, McKenzie et al. present stratigraphic sedimentary analyses, new radiocarbon and OSL ages from coastal outcrops on Whidbey Island, Puget Sound, to reconstruct the behavior of the marine-terminating Puget Lobe during deglaciation. Their scenario differs from that of earlier studies, mainly in that final deglaciation occurred 3000 years later, i.e. ~12 ka.

The manuscript is globally well written, and the methods are well presented. However, figures need to be improved, as detailed below. Also, the new results and interpretation should be put better into the context of earlier findings. I read reviewer 1’s comments, which I agree with and which are very similar to the concerns I had while reading the manuscript. As reviewer 1, I am not a sedimentologists, and cannot assess the quality of the newly proposed marine reservoir correction, either.

Here are my major comments and suggestions:

Given that the subject of this study has been investigated earlier in numerous studies over several decades, I find it hard to understand what has been done and found before. In section 1.1 only a few lines present the state-of-the-art of the subject. The more detailed information given in the supplement should be moved to the main text. It would really be helpful if these earlier findings and controversies could somehow be illustrated in a more comprehensive manner. Would it be possible to show them on a map of the region?

Also, please better specify what is new in your study. E.g. lines 89-90 say that there is “lack of detailed stratigraphic context for age constraints”. Does this mean your study is the first to present detailed sedimentological analyses? Which other studies have used the same approach (at the same sites or different?), and how do your new analyses compare to theirs? Regarding dating, have your sites ever been dated before?

In the discussion your findings and interpretations should be compared to the earlier ones and you should give arguments why your interpretation is more reliable. E.g. specify if the observations and interpretations of all of your seven profiles are consistent with each other and with the proposed scenario? How do you explain the high discrepancy between the earlier and the new 14C ages? Are there any earlier data or observations that support your model?

Figures:

Figure 1: the text is way too small. A legend is missing for the signature of the sediment profiles and the dating symbol (shell etc).

Line 141: what does “correlations” mean here? E.g. yellow stands for the same grain size range in each profile?

Line142: I do not understand what the white dots indicate.

I suggest to make A, B and C individual figures with width that allow the text to be read. Put A in landscape format? Make the grain size plots bigger.

I think it would give great value to the manuscript if a sketch of the different stages of the glacier behavior could be included, either similar to the drawings in Fig. S2 or as schematic maps.

Other minor comments:

Line 182: The citation of Goehring et al. (2019) is surprising here. These authors use a similar method for a specific procedure for cosmogenic in situ 14C analyses, which is however not described in detail. It would be better to add a citation that relates to NOSAMS, if exists.

Table 1: what does “actual age” mean?

Lines 262: add the reference to the corresponding figure.

Title of section 4: better would be “Interpretation and discussion”

Supporting Information:

• Header: the Journal name is wrong

S1.2: Note that Swanson and Caffee (2001) did not produce cosmogenic nuclide measurements to date the ice retreat, but they used the radiocarbon age of the deglaciation to calibrate cosmogenic nuclide production rates. So, the statement “numerous cosmogenic exposure ages consistently indicate …” is not correct.

It needs to be checked with the editor if the supporting information should include a separate reference list. Right now, the citations in the supporting information are included in the reference list of the main text, i.e. there are references that are not cited in the main text.

The manuscript, Evidence of solid Earth influence on stability of the marine-terminating Puget Lobe of the Cordilleran Ice Sheet (CIS) describes new glacial, deglacial, and coastal sedimentological and geochronological data from Whidbey Island in the Puget Lowland of Washington state, USA. The dates span the past approx. 50000 years or longer and the sediments record pre-LGM, LGM, and post-LGM environmental and relative sea level change, including glaciation and deglaciation. A lot of new, detailed sedimentological data are presented here, covering an interesting area near the southernmost margin of the former CIS and I agree with the authors that this area provides a unique opportunity to assess shallow marine and coastal ice-sheet retreat. The sedimentological data, although not presented as clearly as it could be, looks solid, and the dating, although there are some issues as described by the authors, is still useful.

I share many of the same concerns about the manuscript as the other two anonymous reviewers, including that the title is somewhat problematic. I feel that the significance of this work is also not well-anchored in the cited literature and needs more explanation of its relevance (specifically how this story is relevant to Greenland and Antarctica). Furthermore, one of the key findings of the article, that there was a pause in overall glacial retreat between approx. 12.1-12.9 ka BP (due to GIA-caused emergence providing stability to the ice), may be problematic. The five radiocarbon-dated shells from the Penn Cove section may not actually represent an approximately 1000-year timespan, given that they all more or less overlap within their 2 (or 1) sigma calibrated ranges (whether it is 1 or 2 sigma is not stated). I expand on all of these concerns in the line-by-line comments below.

Comments are organized according to the following themes and described below: figures; referencing and literature review; writing and organization; sedimentology, geomorphology, dating

Figures

As stated by Reviewers 1 and 2, Figure 1 is difficult to read and understand. A few points:

1A. Why are the strat logs, grain size, and MS data presented in the Introduction? These are results and as such, should be included in the Results section. I think a bigger, better map should be included as Figure 1 in the Introduction section, however, with the strat logs, etc. presented in the Results as its own figure. 

The lower 14C date from Double Bluff says 48.0 +(?) kya (also on Figure 2), but in the text you have written 46.7+ kya.

A few things are missing from Figure 1, including a legend for the strat column fill patterns, symbols, and colours. Also, what are the white dots?

Generally speaking, larger font size and larger strat column drawings with a legend are needed. Especially if there are no photos of the sections.

For the Double Bluff grain size distribution curves, I cannot see the red curve - can it be placed over the purple curves?

What are the extra, discontinuous columns with different fill patterns on the Penn Cove, West Beach Site 2, and Cliffside strat columns?

The grain size distribution curves would be more reader-friendly if you added the names of the grain size categories below the micron scale on the x axis. I don't have the size range of pebbles in microns memorized, for example. Not 100% necessary, just a suggestion to make this figure easier to understand quickly.

1B. Map text is much too small and inset is also too small. If this were its own figure in the Introduction, you could make it bigger and more clear. Would be helpful to see previous reconstructions of LGM and deglacial ice sheet margins on the same map. Photos of the strat sections would also be helpful, but I appreciate that you put a couple in the Supplementary Info and also that there may be strict limits with the journal. 

1C. Why do some outcrops have low-resolution sampling and others are higher?

Figure 2

A legend is needed for the symbols representing the dates. The shells and suns are fairly intuitive, but the wood/plant material is not.

With respect to the right-hand column labels, is deglaciation not also post-LGM? Also, you have dates of 6.2 and 4.1 ka BP from West Beach Site 1 units classified as ‘Deglaciation’. Was deglaciation still going on this late here? I don’t interpret that from reading the text.

Referencing and literature review:

A more thorough presentation of previous literature describing the last glaciation and deglaciation of the Puget lowland is needed. As Reviewer 1 mentioned, a pretty good review of the literature is included in the Supporting Information, and it was very helpful; however, it should be in the main paper.

Some important interpretations are made that are supported by only one or a few, sometimes quite old, references even though there is a great deal of highly relevant, peer-reviewed literature that could be used to better support your interpretations. For example:

Page 3, lines 71-74 and Page 18 line 572-573: I cannot see clearly where the Whitehouse et al. 2019 and Nield et al. 2014 references indicate that the rheology of the study area is similar to that of the Antarctic Peninsula, although I did not closely read these papers. I am also not sure what you mean by topographic similarities to Greenland – both mountainous? But there are many other factors that control the timing and style of deglaciation, so I am not convinced of the relevance being attributed to this.

Page 5, lines 147-152: references and more explanation of what you mean by multiple approaches, differing classifications, etc., are needed in this paragraph.

Page 12, lines 397-398. I am not a glacial sedimentologist, but I do not think the Boulton and Deynoux, 1981 reference is appropriate on its own, to classify a deposit or unit as glacial outwash. There are more recent textbooks and articles that should be referred to and utilized.

Page 13, line 410: winnowing is a process, not a sedimentary characteristic. Do you mean an absence of fines?

Page 13, line 413: seaward typo. Also, should it be sampled rather than samples? I had some trouble understanding this section.

Page 13, line 428-430: There is no mention of cross-bedded sand with parallel-to-bed oriented clasts in Unit 3 West Beach Site 1 (page 11, lines 332-333).

Page 13, lines 434-435: RSL fall at this time would be a function of GIA or tectonics, so I don’t think you need to state both ‘RSL fall outpacing eustatic SLR’ and ‘GIA response’ as separate factors in this sentence. Coarsening grain sizes may also be related to ice sheet/glacier proximity and have nothing to do with RSL fall/landscape emergence.

Page 13, lines 442-445:  A study documenting coarsening-upward grain size trends in coastal outcrops interpreted as a transition from a marine to coastal environment on northern Svalbard is used to support your assertion that facies transitions where grain sizes coarsen up are associated with landscape emergence. Only two references are listed here, although the McCabe, 1986 reference is a study of glaciomarine facies on Northern Ireland, not Svalbard. Earlier in this paragraph two other references are listed, but both are sedimentology textbooks.

On page 14, lines 453-456, you write that facies transitions where grain sizes fine upwards and are accompanied by the appearance of marine shells are associated with submergence. Fining-upward grain-size trends and the appearance of marine sub-fossil shells represent solid evidence for deepening water/RSL rise - this is no problem. Your presentation of your interpretation here, however, is weakened by the references you use to support your assertion - two sedimentology textbooks and one article from 1986 that links similar facies transitioning from a subaerial to submarine environment in the offshore SW Pacific/onshore New Zealand. It feels a bit random and not quite strong enough to justify the use of the phrasing in the final sentence of this paragraph ('Therefore, the fining of material between Unit 4... are all interpreted as a transition to a submarine setting.'). This interpretation and the study as a whole needs to be better situated in existing, relevant literature.

Writing and organization

General comment: Just refer to diamict deposited subglacially as till, not glacial till. The glacial part is redundant. David Evans’ 2007 entry on Tills in the Encyclopedia of Quaternary Science provides a good overview of the correct terminologies for different glacial diamictons.

On page 14, the sentence beginning on line 439 (which goes to line 442) is somewhat confusing as written. I think you're saying that tectonic activity as a cause for coarsening-upward trends in the stratigraphy can be rejected because the till and sedimentary structures like cross-bedding have been preserved. If so, I think a more clear explanation of why the till and sedimentary structures wouldn't be preserved if tectonics caused land-level changes forcing a fall in relative sea level and coarsening-upwards trends in the stratigraphy is needed. Not sure if that's what you're driving at here, but the fact that I'm not sure means it could probably use a better explanation.

Suggest that you go through the manuscript and check your use of dashes. Lowermost, southernmost, northernmost do not need dashes, for example.

Text size and font seem to change in some places.

Figure 1B is referred to before Figure 1A or Figure 1 in the text.

Page 3, lines 66-67: you have already spelled out the acronym GIA on page 2, line 57 and do not need to do this again.

Page 3, line 100: It should be rate, not magnitude of landscape emergence (cm/a).

Page 5, figure caption, line 141: grain spelled incorrectly.

Page 6, line 156: Suggest: Sediment samples were collected from …

Page 6, line160: ‘…referred to as lenses…’.

Page 7, lines 196-197: ‘…range in beach-front collection date from 1911 to 1931 … and include species …’. This is awkwardly written/grammatically incorrect, and I am not sure why the font/size change for the bivalve spp. The genus and species should be italicized only (with capitalized first letter for genus name).  It is also important to state that the modern bivalves were live-collected, i.e. not just shells that were collected, between 1911 and 1931.

Page 7, Table 1 plus lines 194-203. I am not sure why this is included in Methods, since this is new data and should therefore be in the Results section. It might also be important to clarify that the reservoir correction you have determined isn’t necessarily relevant for earlier periods, for example, during early deglaciation of this area. I realize that it is difficult to develop reservoir corrections through the Holocene and beyond, and great that you have determined one from live-collected bivalves in this area.

Page 7, line 211. You have an extra ‘and’ in this sentence between (Th), and potassium (K).

Page 7, line 221: Why write Materials instead of sediments?

Page 8, line 256: considerably spelled incorrectly.

Page 9, lines 262-264: Not sure what you mean here. What are ‘all possible interpretations that have been conducted across Whidbey Island’?

Page 10, line 297. A bit more clear explanation of what your sites 1 and 2 mean for Fort Casey and West Beach sections mean is needed earlier in the manuscript. I finally realized here that you mean that you logged one part of the section (Site 1) separately from a lower part of the section (Site 2), likely because a continuous section from top to bottom of the cliff face wasn’t accessible or visible or …

Page 12, line 388: The use of the term structure here is a bit confusing when you correctly pointed out at the beginning of this section that structureless diamicton is classified as till.

Page 16, line 508: choose glacimarine or glaciomarine and be consistent throughout the manuscript.

Second paragraph, second sentence in Supporting Information: Figure S2 does not depict a schematic of glacial retreat within a marine environment versus glacial retreat within a subaerial environment (at least according to the arrows drawn on Puget Lobe) – rather it shows Puget lobe advancing across a subaerial environment and retreating in a submarine environment.

Sedimentology, geomorphology, dating

As I read through the descriptions of the strat sections, I was curious about the glacial geomorphology on Whidbey Island. Has it been mapped? How does it relate to your strat sections? It seems to me that it could be quite helpful in interpreting some of this data.

Page 17, lines 515-518: This needs a bit more explanation. When I look at the shell dates on Figure 1 and in Table 1, it appears that all of the ages overlap to some extent. But what are the dates as presented? The midpoints of the 2 sigma ranges? This needs to be indicated in Table 1 and stated in the text. The overlap in ages opens the possibility that there was a potentially much shorter period of time with very high sedimentation rates at this particular location, rather than a 1000-year pause in glacier retreat around this time. Or could it be possible that this is a slide or slump deposit that didn’t manage to dis-articulate the shells? Either way, unless you have very clear peak probabilities within the calibrated age ranges indicating that one specimen is very close to 12000 years old and another very close to 13000 years old, it is difficult to say with confidence that they (together with sedimentological evidence) represent a 1000 year pause in deglaciation.

Page 17, lines 528-532: This is the first mention of grounding zone wedges. Where have they been mapped? Are they dated? I also can’t tell with the way the references are inserted into the text here if these are the references for the GZWs.

Final comment: I really appreciated the acknowledgements and wish I saw this on every paper. Well done.