the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 01 Feb 2024
The Laurentide Ice Sheet in southern New England and New York during and at the end of the Last Glacial Maximum – A cosmogenic-nuclide chronology
Abstract. We present 40 new 10Be exposure ages of moraines and other glacial deposits left behind by the southeastern sector of the Laurentide Ice Sheet (LIS) in southern New England and New York, summarize the regional moraine record, and interpret the dataset in the context of previously published deglaciation chronologies. The regional moraine record spans the Last Glacial Maximum (LGM), with the outermost ridge of the terminal complex dating to ~26–25 ka, the innermost ridge of the terminal complex dating to ~22 ka, and a series of smaller recessional limits within ~50 km of the terminal complex dating to ~21–20.5 ka. The chronology generally agrees with independent age constraints from radiocarbon and glacial varves. A few inconsistencies among ages from cosmogenic-nuclide measurements and those from other dating methods are explained by geologic scatter where several bedrock samples and boulders from the outer terminal moraine exhibit nuclide inheritance, while exposure ages on large moraines are likely affected by postdepositional disturbance. The exposure-age chronology places the southeastern sector of the LIS at or near its maximum extent from ~26 to 21 ka, which is broadly consistent with the LGM sea-level lowstand, local and regional temperature indicators, and local summer insolation. The net change in LIS extent represented by this chronology occurred more slowly (<5 to 25 m yr-1) than retreat through the rest of New England, consistent with a slow general rise in insolation and modeled summer temperature. We conclude that the major pulse of LIS deglaciation and accelerated recession, recorded by dated glacial deposits north of the moraines discussed here, did not begin until after atmospheric CO2 increased at ~18 ka, marking the onset of Termination 1.
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RC1: 'Review of The Laurentide Ice Sheet in southern New England and New York during and at the end of the Last Glacial Maximum – A cosmogenic nuclide chronology', Christopher Halsted, 01 Mar 2024
Summary
In this manuscript, Balter-Kennedy et al. date the timing of southeastern Laurentide Ice Sheet (LIS) maximum advance and initial retreat using 40 new cosmogenic nuclide exposure ages from southern New England and New York. They provide a comprehensive background of the geomorphology of ice-contact features marking the maximum extent and initial retreat of the southeastern (LIS), including the extensive terminal moraines and prominent recessional moraines, and existing chronologic constraints for these features. Their new exposure ages generally agree with previous dating constraints, albeit with some isolated instances of old or young ages that are attributed geologic scatter. Importantly, Balter-Kennedy et al. infer a lack of more widespread inheritance in their sample populations based on the normal distribution of exposure ages at each sample site. Skewed distributions characterize sample populations at other sites near the Laurentide Ice Sheet terminal moraine, and samples from these sites are thus believed to contain some unknown amount of nuclide inheritance. The ages presented here confirm previous estimations that the southeastern Laurentide Ice Sheet remained near its maximum extent from 26 – 21 ka, with marginal areas exhibiting minor fluctuations during this time. The exact timing of initial retreat likely varied across this region, but generally occurred around 22 ka. This initial ice recession was slow (5 – 25 m/yr) and likely triggered by regional climatological changes such as the steady increase in local summer insolation that began around 24 ka and the slow increase in local summer temperatures that began around 26 ka. This ice margin recession represented a small areal loss of the overall Laurentide Ice Sheet (<2%) and most likely did not represent a shift in behavior of the entire ice sheet. Widespread Laurentide Ice Sheet deglaciation did not occur until the rise in atmospheric CO2 around 18 ka that signaled the onset of Termination 1.
General Impressions
This manuscript and the data within are much-needed and valuable additions to deglacial chronologies in this region. The timing of initial ice recession from the local terminal moraines has been a thorny issue for some time, complicated by large disagreements between available cosmogenic exposure ages and radiocarbon ages, and the relative lack of other constraints. I have personally hypothesized that some of the existing exposure ages did not correspond exactly to the timing of ice recession due to inherited nuclides and/or post-glacial disturbance of ice-contact features. Here, the authors did a fantastic job of assessing the geomorphic context of each sampled ice-contact feature and estimating ice recession ages, providing reasonable justification for discarded ages that likely contain inherited nuclides, and are thus too old, or were subject to post-glacial disturbance, and are thus too young. The decision to remove certain ages was done carefully and in line with established practices. By adding confident date constraints to many ice-contact features near the local terminal moraines, Balter-Kennedy et al. have provided a much clearer picture of initial ice recession in southern New England and New York.
The manuscript itself reads very well. I particularly appreciated the background section providing a summary of the regional glacial geomorphology. These are old, complex moraines with discontinuities, cross-cutting relationships, and a long history of interpretation. I found this detailed background helpful for orienting myself with the study area. The sampling and processing procedures, choices of scaling scheme and calibration data set, and normalization of older measurements all look good. The interpretation of the data makes sense to me, and I appreciated the in-depth discussion about how you used the age distributions to gauge the presence of inheritance or post-glacial disturbance.
Overall I recommend this manuscript for publication with minor revisions. Most of my suggested revisions are small line edits, as this manuscript already reads very well. I agree with the authors’ interpretations and the data supports their conclusions.
Line Edits (indicated by line number)
Figure 3 – Peekamoose Mt. samples are identified as bedrock, but were actually boulder samples
222 – There is a big jump here between detailed deglacial chronology in southern New England up to ~18 ka and the timing of ice recession from northern New England around 13.5 ka. It might be worth adding a line or two in here to briefly summarize what happened in the intervening 5 kyr. Something as simple as “systematic retreat between 50 – 300 m/yr with relatively minor standstills in northern New Hampshire and Maine around 14 ka” would give the reader just a bit more insight into what happened in the rest of the region.
232 – “Jones Point, New York” is repeated twice in this sentence. Remove the second occurrence.
294 – Elaborate what the “Glaciotectonic structures” were that indicate the moraine depositional history
Figure 5 – I really like this figure, especially the inset showing retreat rates as slopes, but I wonder if there is a way to identify which specific moraines are represented by the solid symbols. For example, the outer terminal moraine appears to have two solid circles, but in Figure 6 (and in the text), four moraines segments are grouped into the “outer terminal moraine” classification (Martha’s Vineyard, Ronkonkoma, Budd Lake, Staten Island). This might not be easily do-able in the figure itself, so maybe providing some more information in the caption would help.
567 – Again, the samples from Peekamoose Mt. were boulders, not bedrock
Supplementary Tables
Table S3:
- The header row in this table says “Table S2”, check for consistency
- Add units to the “Distance from terminal moraine” column
- Units for age columns should be kyr, correct?
Citation: https://doi.org/10.5194/egusphere-2024-241-RC1 -
AC1: 'Reply on RC1', Allie Balter-Kennedy, 24 Apr 2024
We thank Chris Halsted for his review of the manuscript and insightful comments. Below, we address referee comments, supplied in bold, with our responses in regular text.
Line Edits (indicated by line number)
Figure 3 – Peekamoose Mt. samples are identified as bedrock, but were actually boulder samples
Great catch, thank you! Reference to the “Mt. Peekamoose bedrock ages” will be updated to “Peekamoose Mountain boulder ages” in Figure 3 and all instances in the text.
222 – There is a big jump here between detailed deglacial chronology in southern New England up to ~18 ka and the timing of ice recession from northern New England around 13.5 ka. It might be worth adding a line or two in here to briefly summarize what happened in the intervening 5 kyr. Something as simple as “systematic retreat between 50 – 300 m/yr with relatively minor standstills in northern New Hampshire and Maine around 14 ka” would give the reader just a bit more insight into what happened in the rest of the region.
We will update these sentences to read:
“The NAVC reveals systematic ice retreat through New England at 50–300 m yr-1 (Ridge et al., 2012), with relatively minor advances or stillstands at least in the White Mountains and Maine (e.g., Borns et al., 2004; Bromley et al., 2015; Davis et al., 2015; Dorion et al., 2001, Hall et al., 2017; Kaplan, 2007; Koester et al., 2017; Thompson et al., 2017). The position of the retreating ice margin is also marked by annual DeGeer moraines spaced 100 to 300 m apart in northern New England (Sinclair, 2018; Todd, 2007; Wrobleski, 2020). The LIS margin retreated north of New England by 13.6 ka (Ridge et al., 2012).”
232 – “Jones Point, New York” is repeated twice in this sentence. Remove the second occurrence.
We will remove the second occurrence.
294 – Elaborate what the “Glaciotectonic structures” were that indicate the moraine depositional history
We will update this sentence to read “Glaciotectonic structures, such as imbricated thrust sheets and dislocated strata, within the moraine stratigraphy indicate that the moraine was likely deposited during a readvance of the ice margin, rather than a representing a standstill (Oldale and O’Hara, 1984; Boothroyd and Sirkin, 2002).”
Figure 5 – I really like this figure, especially the inset showing retreat rates as slopes, but I wonder if there is a way to identify which specific moraines are represented by the solid symbols. For example, the outer terminal moraine appears to have two solid circles, but in Figure 6 (and in the text), four moraines segments are grouped into the “outer terminal moraine” classification (Martha’s Vineyard, Ronkonkoma, Budd Lake, Staten Island). This might not be easily do-able in the figure itself, so maybe providing some more information in the caption would help.
Figure 5 depicts ages only for the Connecticut-Narragansett-Buzzards Bay Lobes of the LIS, where there are enough dated landforms to estimate retreat rates between limits, while Figure 6 shows the chronology across the entire region separated by ice lobe.
We agree that adding moraine names to Figure 5 will make it easier to follow along with the text. Below each grouping of symbols, we will add shortened versions of the moraine names, in order from oldest to youngest, and update the caption to explain this (see figure in attachment).
567 – Again, the samples from Peekamoose Mt. were boulders, not bedrock
Updated!
Supplementary Tables
Table S3:
- The header row in this table says “Table S2”, check for consistency
- Add units to the “Distance from terminal moraine” column
- Units for age columns should be kyr, correct?
Thank you for catching this. We will update Table S3 to include the correct units and table number.
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RC2: 'Comment on egusphere-2024-241', Alberto Reyes, 14 May 2024
I reviewed this manuscript by Balter-Kennedy et al. as the handling editor, adding one more set of eyes to complement the review by Christopher Halstead. The authors are to be commended on a well-written, clearly-structured manuscript that strikes a good balance between comprehensive coverage and concise presentation. The geomorphic and nuclide-production explanations for various aspects of the exposure age dataset are clear and justified. I particularly liked the concise synthesis of the climate context for the LGM/deglacial moraine chronology in the region, in section 5.2. Tables are a model of clarity. Figures are appropriate and nicely drafted. The manuscript could be published with very minor revision, though I do have a few suggestions for the authors to consider.
Suggestions and line-corrections follow:
line 112: “…are interpreted as….”
Figs 1,2,3: For those less familiar with the geography in this field area, a blue shading for ocean would be helpful
Fig 2: It is sometimes difficult to quickly link varve/14C locations mentioned explicitly in the main text to this otherwise clear figure. For this map, consider adding more short placename tags to any mapped localities discussed in the main text?
Fig. 3: I think it actually be easier to assess the data if the coloured ice-margin-positions were retained from Fig 1. I found myself trying to draw them in by hand in colour, to help me compare text to the figure when assessing geomorphic superposition.
lines 228-234: Is it possible to briefly indicate what kind of material is being dated when reporting 14C dates? It’s possible this is just opening a can of worms, a detailed treatment of which the authors correctly suggest is beyond the scope of the manuscript.
throughout: At several points I found myself wanting to see a more detailed hillshade map of specific sites where morphology of glacial landforms was referred to when justifying rejection of certain dated boulders or when explaining geomorphic/crosscutting relations between landforms (e.g. lines 273-275, 291-294, 312-314, 329-331, 490-493). There’s room for this in main text but could also be as supplemental figures. On a related note, I also found myself hoping to see more field photos of boulders/sampling sites, since authors acknowledge that some of these are problematic (more boulder photos can for sure go in supplement).
lines 583-585: Does moraine stratigraphy/sedimentology support this preferred interpretation too?
lines 644: <2% of margin position change, and probably way less than that when expressed volumetrically…
Citation: https://doi.org/10.5194/egusphere-2024-241-RC2 -
AC2: 'Reply on RC2', Allie Balter-Kennedy, 11 Jul 2024
We appreciate Alberto Reyes’ review of our manuscript and helpful suggestions. Below, we address referee comments, supplied in bold, with our responses in regular text. We’ve also included a description of several unsolicited changes that we plan to make to the manuscript.
Suggestions and line-corrections follow:
line 112: “…are interpreted as….”
Good catch, we will update this.
Figs 1,2,3: For those less familiar with the geography in this field area, a blue shading for ocean would be helpful
We will add blue shading for the ocean in all three figures.
Fig 2: It is sometimes difficult to quickly link varve/14C locations mentioned explicitly in the main text to this otherwise clear figure. For this map, consider adding more short placename tags to any mapped localities discussed in the main text?
We agree that several place names mentioned in the main text were not included on this map. We will add the following places to the map and figure caption: Manhattan, New York City (MH), Port Washington, NY (PW), Totoket (TT), Cedar Swamp (CS), Rocky Hill (RH), Jones Point (JO), Great Swamp (GS), and Nantucket. We will also change the abbreviation for Newburgh, NY from NB to NW to avoid confusion with Narraganset Bay, shown as NB in Figure 1.
In addressing this comment, we also noticed a few places missing from Figure 1. We will add Port Washington, NY (PW) and Staten Island (SI). We will also change the abbreviation for Manorville, NY to MN from MV (a common abbreviation for Martha’s Vineyard, although not used in the figures), and will update the abbreviation for Newburgh, NY (NW) in the figure caption, which had been misstated as NB (used for Narraganset Bay).
Fig. 3: I think it actually be easier to assess the data if the coloured ice-margin-positions were retained from Fig 1. I found myself trying to draw them in by hand in colour, to help me compare text to the figure when assessing geomorphic superposition.
We agree and will add the colored ice margins to Figure 3. We will also retain the color on the ice margins in Figure 2 for consistency. Please see attachment with the new figures and captions.
lines 228-234: Is it possible to briefly indicate what kind of material is being dated when reporting 14C dates? It’s possible this is just opening a can of worms, a detailed treatment of which the authors correctly suggest is beyond the scope of the manuscript.
We will update the text to specify that the ages discussed in lines 228-234 (as well as the next paragraph) are bulk radiocarbon ages on the described sediment.
throughout: At several points I found myself wanting to see a more detailed hillshade map of specific sites where morphology of glacial landforms was referred to when justifying rejection of certain dated boulders or when explaining geomorphic/crosscutting relations between landforms (e.g. lines 273-275, 291-294, 312-314, 329-331, 490-493). There’s room for this in main text but could also be as supplemental figures. On a related note, I also found myself hoping to see more field photos of boulders/sampling sites, since authors acknowledge that some of these are problematic (more boulder photos can for sure go in supplement).
We agree that adding more detailed hillshades and photos would aid the discussion of moraine morphology and sample positioning. We will add supplemental figures with hillshade maps in the vicinity of our new sample locations (Long Island, Staten Island, and Southern Rhode Island; see attachment). We are also in the process of also adding additional sample photos to the online database, ICE-D:Laurentide, that hosts our dataset (https://version2.ice-d.org/laurentide/publication/1187/). The url is included in the methods section, the Data Availability statement and in the references, and we will update it to point the reader directly to the new samples associated with this manuscript. The photo upload will be complete before publication.
lines 583-585: Does moraine stratigraphy/sedimentology support this preferred interpretation too?
Yes, this interpretation is also supported by the sedimentology, as described in Sections 1.1.1 and 2.2.1. We will add this important detail to this sentence to read:
“We prefer the latter interpretation given that the geomorphology and sedimentology of these moraines indicate construction by an advancing LIS and note that it is unknown how far ice retreated between readvances (Boothroyd et al., 1998; Oldale and O’Hara, 1984; Sections 1.1.1 and 2.2.1).”
lines 644: <2% of margin position change, and probably way less than that when expressed volumetrically…
Certainly true. We will update the sentence on Lines 642–646 to read:
“We emphasize, however, that the ~50 km of net change in ice-margin position from the outer terminal moraine to the Ledyard-Congdon Hill limit is modest in the context of the entire ice sheet. This distance represents <2% of total LIS margin change considering that the former LIS is now restricted to the Barnes and Penny Ice Caps on the central Baffin plateau ~3000 km to the north (Dalton et al., 2020; Dyke, 2004; Hooke, 1976; Hooke and Clausen, 1982; Refsnider et al., 2014), and likely significantly less when expressed volumetrically since the LIS would have been thinner at its margin than towards the centre of the ice sheet (e.g., Stokes et al., 2012).”
Unsolicited changes
- We will update the label for a boulder photo in Figure 4, which was erroneously labeled LI-6 rather than the correct sample ID, LI-3.
- We will add a bit of additional information about LIS retreat chronologies in northern New England, in addition to what was requested by Reviewer #1. We will further update the sentences beginning Line 222 to read:
“The NAVC reveals systematic net ice retreat through New England at 50–300 m yr-1 (Ridge et al., 2012), interrupted by relatively minor advances or stillstands at least in the White Mountains and Maine, documented by comprehensive 14C-based chronologies and 10Be dating (e.g., Borns et al., 2004; Bromley et al., 2015; Davis et al., 2015; Dorion et al., 2001, Hall et al., 2017; Kaplan, 2007; Koester et al., 2017; Thompson et al., 2017). The position of the retreating ice margin is also marked by annual DeGeer moraines spaced 100 to 300 m apart in northern New England (Sinclair, 2018; Todd, 2007; Wrobleski, 2020). The LIS margin had retreated north of New England by 13.6 ka (Ridge et al., 2012) , with slightly later retreat or pockets of smaller residual glaciers perhaps lasting only briefly longer in areas of northern Maine (Borns et al., 2004).”
- We will correct the age for UDP-2 in Table 1 and throughout the text, which was written as 200 years older than calculated. The age for this sample was already correct in Table S2.
- An accepted preprint in Climate of the Past suggests that stratigraphic disturbance in lakes affected by postglacial permafrost may be one reason that basal radiocarbon ages older than 16 ka are absent in southern New England. Will include this reference in our brief discussion of the difference between radiocarbon-based and cosmogenic-nuclide-based chronologies in the region near line 671. Point v) will read:
“difficulty in coring to the till contact and/or stratigraphic disturbance in lake sediment affected by postglacial permafrost (Prince et al., 2024)”
We currently cite the preprint, but hope the reference can be updated if Prince et al. (2024) is published prior to our manuscript.
- Finally, we will make small line edits throughout to improve the clarity of the paper.
Additional References
Borns, H. W., Doner, L. A., Dorion, C. C., Jacobson, G. L., Kaplan, M. R., Kreutz, K. J., Lowell, T. V., Thompson, W. B., and Weddle, T. K.: The deglaciation of Maine, U.S.A., Dev. Quat. Sci., 2, 89–109, https://doi.org/10.1016/s1571-0866(04)80190-8, 2004.
Hall, B. L., Borns, H. W., Bromley, G. R. M., and Lowell, T. V.: Age of the Pineo Ridge System: Implications for behavior of the Laurentide Ice Sheet in eastern Maine, U.S.A., during the last deglaciation, Quaternary Sci Rev, 169, 344–356, https://doi.org/10.1016/j.quascirev.2017.06.011, 2017.
Kaplan, M. R.: Retreat of a tidewater margin of the Laurentide ice sheet in eastern coastal Maine between ca. 14 000 and 13 000 14C yr B.P., GSA Bull., 111, 620–632, https://doi.org/10.1130/0016-7606(1999)111<0620:roatmo>2.3.co;2, 1999.
Prince, K. K., Briner, J. P., Walcott, C. K., Chase, B. M., Kozlowski, A. L., Rittenour, T. M., and Yang, E. P.: New age constraints reveal moraine stabilization thousands of years after deposition during the last deglaciation of western New York, USA, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2023-2655, 2024.
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AC2: 'Reply on RC2', Allie Balter-Kennedy, 11 Jul 2024
Interactive discussion
Status: closed
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RC1: 'Review of The Laurentide Ice Sheet in southern New England and New York during and at the end of the Last Glacial Maximum – A cosmogenic nuclide chronology', Christopher Halsted, 01 Mar 2024
Summary
In this manuscript, Balter-Kennedy et al. date the timing of southeastern Laurentide Ice Sheet (LIS) maximum advance and initial retreat using 40 new cosmogenic nuclide exposure ages from southern New England and New York. They provide a comprehensive background of the geomorphology of ice-contact features marking the maximum extent and initial retreat of the southeastern (LIS), including the extensive terminal moraines and prominent recessional moraines, and existing chronologic constraints for these features. Their new exposure ages generally agree with previous dating constraints, albeit with some isolated instances of old or young ages that are attributed geologic scatter. Importantly, Balter-Kennedy et al. infer a lack of more widespread inheritance in their sample populations based on the normal distribution of exposure ages at each sample site. Skewed distributions characterize sample populations at other sites near the Laurentide Ice Sheet terminal moraine, and samples from these sites are thus believed to contain some unknown amount of nuclide inheritance. The ages presented here confirm previous estimations that the southeastern Laurentide Ice Sheet remained near its maximum extent from 26 – 21 ka, with marginal areas exhibiting minor fluctuations during this time. The exact timing of initial retreat likely varied across this region, but generally occurred around 22 ka. This initial ice recession was slow (5 – 25 m/yr) and likely triggered by regional climatological changes such as the steady increase in local summer insolation that began around 24 ka and the slow increase in local summer temperatures that began around 26 ka. This ice margin recession represented a small areal loss of the overall Laurentide Ice Sheet (<2%) and most likely did not represent a shift in behavior of the entire ice sheet. Widespread Laurentide Ice Sheet deglaciation did not occur until the rise in atmospheric CO2 around 18 ka that signaled the onset of Termination 1.
General Impressions
This manuscript and the data within are much-needed and valuable additions to deglacial chronologies in this region. The timing of initial ice recession from the local terminal moraines has been a thorny issue for some time, complicated by large disagreements between available cosmogenic exposure ages and radiocarbon ages, and the relative lack of other constraints. I have personally hypothesized that some of the existing exposure ages did not correspond exactly to the timing of ice recession due to inherited nuclides and/or post-glacial disturbance of ice-contact features. Here, the authors did a fantastic job of assessing the geomorphic context of each sampled ice-contact feature and estimating ice recession ages, providing reasonable justification for discarded ages that likely contain inherited nuclides, and are thus too old, or were subject to post-glacial disturbance, and are thus too young. The decision to remove certain ages was done carefully and in line with established practices. By adding confident date constraints to many ice-contact features near the local terminal moraines, Balter-Kennedy et al. have provided a much clearer picture of initial ice recession in southern New England and New York.
The manuscript itself reads very well. I particularly appreciated the background section providing a summary of the regional glacial geomorphology. These are old, complex moraines with discontinuities, cross-cutting relationships, and a long history of interpretation. I found this detailed background helpful for orienting myself with the study area. The sampling and processing procedures, choices of scaling scheme and calibration data set, and normalization of older measurements all look good. The interpretation of the data makes sense to me, and I appreciated the in-depth discussion about how you used the age distributions to gauge the presence of inheritance or post-glacial disturbance.
Overall I recommend this manuscript for publication with minor revisions. Most of my suggested revisions are small line edits, as this manuscript already reads very well. I agree with the authors’ interpretations and the data supports their conclusions.
Line Edits (indicated by line number)
Figure 3 – Peekamoose Mt. samples are identified as bedrock, but were actually boulder samples
222 – There is a big jump here between detailed deglacial chronology in southern New England up to ~18 ka and the timing of ice recession from northern New England around 13.5 ka. It might be worth adding a line or two in here to briefly summarize what happened in the intervening 5 kyr. Something as simple as “systematic retreat between 50 – 300 m/yr with relatively minor standstills in northern New Hampshire and Maine around 14 ka” would give the reader just a bit more insight into what happened in the rest of the region.
232 – “Jones Point, New York” is repeated twice in this sentence. Remove the second occurrence.
294 – Elaborate what the “Glaciotectonic structures” were that indicate the moraine depositional history
Figure 5 – I really like this figure, especially the inset showing retreat rates as slopes, but I wonder if there is a way to identify which specific moraines are represented by the solid symbols. For example, the outer terminal moraine appears to have two solid circles, but in Figure 6 (and in the text), four moraines segments are grouped into the “outer terminal moraine” classification (Martha’s Vineyard, Ronkonkoma, Budd Lake, Staten Island). This might not be easily do-able in the figure itself, so maybe providing some more information in the caption would help.
567 – Again, the samples from Peekamoose Mt. were boulders, not bedrock
Supplementary Tables
Table S3:
- The header row in this table says “Table S2”, check for consistency
- Add units to the “Distance from terminal moraine” column
- Units for age columns should be kyr, correct?
Citation: https://doi.org/10.5194/egusphere-2024-241-RC1 -
AC1: 'Reply on RC1', Allie Balter-Kennedy, 24 Apr 2024
We thank Chris Halsted for his review of the manuscript and insightful comments. Below, we address referee comments, supplied in bold, with our responses in regular text.
Line Edits (indicated by line number)
Figure 3 – Peekamoose Mt. samples are identified as bedrock, but were actually boulder samples
Great catch, thank you! Reference to the “Mt. Peekamoose bedrock ages” will be updated to “Peekamoose Mountain boulder ages” in Figure 3 and all instances in the text.
222 – There is a big jump here between detailed deglacial chronology in southern New England up to ~18 ka and the timing of ice recession from northern New England around 13.5 ka. It might be worth adding a line or two in here to briefly summarize what happened in the intervening 5 kyr. Something as simple as “systematic retreat between 50 – 300 m/yr with relatively minor standstills in northern New Hampshire and Maine around 14 ka” would give the reader just a bit more insight into what happened in the rest of the region.
We will update these sentences to read:
“The NAVC reveals systematic ice retreat through New England at 50–300 m yr-1 (Ridge et al., 2012), with relatively minor advances or stillstands at least in the White Mountains and Maine (e.g., Borns et al., 2004; Bromley et al., 2015; Davis et al., 2015; Dorion et al., 2001, Hall et al., 2017; Kaplan, 2007; Koester et al., 2017; Thompson et al., 2017). The position of the retreating ice margin is also marked by annual DeGeer moraines spaced 100 to 300 m apart in northern New England (Sinclair, 2018; Todd, 2007; Wrobleski, 2020). The LIS margin retreated north of New England by 13.6 ka (Ridge et al., 2012).”
232 – “Jones Point, New York” is repeated twice in this sentence. Remove the second occurrence.
We will remove the second occurrence.
294 – Elaborate what the “Glaciotectonic structures” were that indicate the moraine depositional history
We will update this sentence to read “Glaciotectonic structures, such as imbricated thrust sheets and dislocated strata, within the moraine stratigraphy indicate that the moraine was likely deposited during a readvance of the ice margin, rather than a representing a standstill (Oldale and O’Hara, 1984; Boothroyd and Sirkin, 2002).”
Figure 5 – I really like this figure, especially the inset showing retreat rates as slopes, but I wonder if there is a way to identify which specific moraines are represented by the solid symbols. For example, the outer terminal moraine appears to have two solid circles, but in Figure 6 (and in the text), four moraines segments are grouped into the “outer terminal moraine” classification (Martha’s Vineyard, Ronkonkoma, Budd Lake, Staten Island). This might not be easily do-able in the figure itself, so maybe providing some more information in the caption would help.
Figure 5 depicts ages only for the Connecticut-Narragansett-Buzzards Bay Lobes of the LIS, where there are enough dated landforms to estimate retreat rates between limits, while Figure 6 shows the chronology across the entire region separated by ice lobe.
We agree that adding moraine names to Figure 5 will make it easier to follow along with the text. Below each grouping of symbols, we will add shortened versions of the moraine names, in order from oldest to youngest, and update the caption to explain this (see figure in attachment).
567 – Again, the samples from Peekamoose Mt. were boulders, not bedrock
Updated!
Supplementary Tables
Table S3:
- The header row in this table says “Table S2”, check for consistency
- Add units to the “Distance from terminal moraine” column
- Units for age columns should be kyr, correct?
Thank you for catching this. We will update Table S3 to include the correct units and table number.
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RC2: 'Comment on egusphere-2024-241', Alberto Reyes, 14 May 2024
I reviewed this manuscript by Balter-Kennedy et al. as the handling editor, adding one more set of eyes to complement the review by Christopher Halstead. The authors are to be commended on a well-written, clearly-structured manuscript that strikes a good balance between comprehensive coverage and concise presentation. The geomorphic and nuclide-production explanations for various aspects of the exposure age dataset are clear and justified. I particularly liked the concise synthesis of the climate context for the LGM/deglacial moraine chronology in the region, in section 5.2. Tables are a model of clarity. Figures are appropriate and nicely drafted. The manuscript could be published with very minor revision, though I do have a few suggestions for the authors to consider.
Suggestions and line-corrections follow:
line 112: “…are interpreted as….”
Figs 1,2,3: For those less familiar with the geography in this field area, a blue shading for ocean would be helpful
Fig 2: It is sometimes difficult to quickly link varve/14C locations mentioned explicitly in the main text to this otherwise clear figure. For this map, consider adding more short placename tags to any mapped localities discussed in the main text?
Fig. 3: I think it actually be easier to assess the data if the coloured ice-margin-positions were retained from Fig 1. I found myself trying to draw them in by hand in colour, to help me compare text to the figure when assessing geomorphic superposition.
lines 228-234: Is it possible to briefly indicate what kind of material is being dated when reporting 14C dates? It’s possible this is just opening a can of worms, a detailed treatment of which the authors correctly suggest is beyond the scope of the manuscript.
throughout: At several points I found myself wanting to see a more detailed hillshade map of specific sites where morphology of glacial landforms was referred to when justifying rejection of certain dated boulders or when explaining geomorphic/crosscutting relations between landforms (e.g. lines 273-275, 291-294, 312-314, 329-331, 490-493). There’s room for this in main text but could also be as supplemental figures. On a related note, I also found myself hoping to see more field photos of boulders/sampling sites, since authors acknowledge that some of these are problematic (more boulder photos can for sure go in supplement).
lines 583-585: Does moraine stratigraphy/sedimentology support this preferred interpretation too?
lines 644: <2% of margin position change, and probably way less than that when expressed volumetrically…
Citation: https://doi.org/10.5194/egusphere-2024-241-RC2 -
AC2: 'Reply on RC2', Allie Balter-Kennedy, 11 Jul 2024
We appreciate Alberto Reyes’ review of our manuscript and helpful suggestions. Below, we address referee comments, supplied in bold, with our responses in regular text. We’ve also included a description of several unsolicited changes that we plan to make to the manuscript.
Suggestions and line-corrections follow:
line 112: “…are interpreted as….”
Good catch, we will update this.
Figs 1,2,3: For those less familiar with the geography in this field area, a blue shading for ocean would be helpful
We will add blue shading for the ocean in all three figures.
Fig 2: It is sometimes difficult to quickly link varve/14C locations mentioned explicitly in the main text to this otherwise clear figure. For this map, consider adding more short placename tags to any mapped localities discussed in the main text?
We agree that several place names mentioned in the main text were not included on this map. We will add the following places to the map and figure caption: Manhattan, New York City (MH), Port Washington, NY (PW), Totoket (TT), Cedar Swamp (CS), Rocky Hill (RH), Jones Point (JO), Great Swamp (GS), and Nantucket. We will also change the abbreviation for Newburgh, NY from NB to NW to avoid confusion with Narraganset Bay, shown as NB in Figure 1.
In addressing this comment, we also noticed a few places missing from Figure 1. We will add Port Washington, NY (PW) and Staten Island (SI). We will also change the abbreviation for Manorville, NY to MN from MV (a common abbreviation for Martha’s Vineyard, although not used in the figures), and will update the abbreviation for Newburgh, NY (NW) in the figure caption, which had been misstated as NB (used for Narraganset Bay).
Fig. 3: I think it actually be easier to assess the data if the coloured ice-margin-positions were retained from Fig 1. I found myself trying to draw them in by hand in colour, to help me compare text to the figure when assessing geomorphic superposition.
We agree and will add the colored ice margins to Figure 3. We will also retain the color on the ice margins in Figure 2 for consistency. Please see attachment with the new figures and captions.
lines 228-234: Is it possible to briefly indicate what kind of material is being dated when reporting 14C dates? It’s possible this is just opening a can of worms, a detailed treatment of which the authors correctly suggest is beyond the scope of the manuscript.
We will update the text to specify that the ages discussed in lines 228-234 (as well as the next paragraph) are bulk radiocarbon ages on the described sediment.
throughout: At several points I found myself wanting to see a more detailed hillshade map of specific sites where morphology of glacial landforms was referred to when justifying rejection of certain dated boulders or when explaining geomorphic/crosscutting relations between landforms (e.g. lines 273-275, 291-294, 312-314, 329-331, 490-493). There’s room for this in main text but could also be as supplemental figures. On a related note, I also found myself hoping to see more field photos of boulders/sampling sites, since authors acknowledge that some of these are problematic (more boulder photos can for sure go in supplement).
We agree that adding more detailed hillshades and photos would aid the discussion of moraine morphology and sample positioning. We will add supplemental figures with hillshade maps in the vicinity of our new sample locations (Long Island, Staten Island, and Southern Rhode Island; see attachment). We are also in the process of also adding additional sample photos to the online database, ICE-D:Laurentide, that hosts our dataset (https://version2.ice-d.org/laurentide/publication/1187/). The url is included in the methods section, the Data Availability statement and in the references, and we will update it to point the reader directly to the new samples associated with this manuscript. The photo upload will be complete before publication.
lines 583-585: Does moraine stratigraphy/sedimentology support this preferred interpretation too?
Yes, this interpretation is also supported by the sedimentology, as described in Sections 1.1.1 and 2.2.1. We will add this important detail to this sentence to read:
“We prefer the latter interpretation given that the geomorphology and sedimentology of these moraines indicate construction by an advancing LIS and note that it is unknown how far ice retreated between readvances (Boothroyd et al., 1998; Oldale and O’Hara, 1984; Sections 1.1.1 and 2.2.1).”
lines 644: <2% of margin position change, and probably way less than that when expressed volumetrically…
Certainly true. We will update the sentence on Lines 642–646 to read:
“We emphasize, however, that the ~50 km of net change in ice-margin position from the outer terminal moraine to the Ledyard-Congdon Hill limit is modest in the context of the entire ice sheet. This distance represents <2% of total LIS margin change considering that the former LIS is now restricted to the Barnes and Penny Ice Caps on the central Baffin plateau ~3000 km to the north (Dalton et al., 2020; Dyke, 2004; Hooke, 1976; Hooke and Clausen, 1982; Refsnider et al., 2014), and likely significantly less when expressed volumetrically since the LIS would have been thinner at its margin than towards the centre of the ice sheet (e.g., Stokes et al., 2012).”
Unsolicited changes
- We will update the label for a boulder photo in Figure 4, which was erroneously labeled LI-6 rather than the correct sample ID, LI-3.
- We will add a bit of additional information about LIS retreat chronologies in northern New England, in addition to what was requested by Reviewer #1. We will further update the sentences beginning Line 222 to read:
“The NAVC reveals systematic net ice retreat through New England at 50–300 m yr-1 (Ridge et al., 2012), interrupted by relatively minor advances or stillstands at least in the White Mountains and Maine, documented by comprehensive 14C-based chronologies and 10Be dating (e.g., Borns et al., 2004; Bromley et al., 2015; Davis et al., 2015; Dorion et al., 2001, Hall et al., 2017; Kaplan, 2007; Koester et al., 2017; Thompson et al., 2017). The position of the retreating ice margin is also marked by annual DeGeer moraines spaced 100 to 300 m apart in northern New England (Sinclair, 2018; Todd, 2007; Wrobleski, 2020). The LIS margin had retreated north of New England by 13.6 ka (Ridge et al., 2012) , with slightly later retreat or pockets of smaller residual glaciers perhaps lasting only briefly longer in areas of northern Maine (Borns et al., 2004).”
- We will correct the age for UDP-2 in Table 1 and throughout the text, which was written as 200 years older than calculated. The age for this sample was already correct in Table S2.
- An accepted preprint in Climate of the Past suggests that stratigraphic disturbance in lakes affected by postglacial permafrost may be one reason that basal radiocarbon ages older than 16 ka are absent in southern New England. Will include this reference in our brief discussion of the difference between radiocarbon-based and cosmogenic-nuclide-based chronologies in the region near line 671. Point v) will read:
“difficulty in coring to the till contact and/or stratigraphic disturbance in lake sediment affected by postglacial permafrost (Prince et al., 2024)”
We currently cite the preprint, but hope the reference can be updated if Prince et al. (2024) is published prior to our manuscript.
- Finally, we will make small line edits throughout to improve the clarity of the paper.
Additional References
Borns, H. W., Doner, L. A., Dorion, C. C., Jacobson, G. L., Kaplan, M. R., Kreutz, K. J., Lowell, T. V., Thompson, W. B., and Weddle, T. K.: The deglaciation of Maine, U.S.A., Dev. Quat. Sci., 2, 89–109, https://doi.org/10.1016/s1571-0866(04)80190-8, 2004.
Hall, B. L., Borns, H. W., Bromley, G. R. M., and Lowell, T. V.: Age of the Pineo Ridge System: Implications for behavior of the Laurentide Ice Sheet in eastern Maine, U.S.A., during the last deglaciation, Quaternary Sci Rev, 169, 344–356, https://doi.org/10.1016/j.quascirev.2017.06.011, 2017.
Kaplan, M. R.: Retreat of a tidewater margin of the Laurentide ice sheet in eastern coastal Maine between ca. 14 000 and 13 000 14C yr B.P., GSA Bull., 111, 620–632, https://doi.org/10.1130/0016-7606(1999)111<0620:roatmo>2.3.co;2, 1999.
Prince, K. K., Briner, J. P., Walcott, C. K., Chase, B. M., Kozlowski, A. L., Rittenour, T. M., and Yang, E. P.: New age constraints reveal moraine stabilization thousands of years after deposition during the last deglaciation of western New York, USA, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2023-2655, 2024.
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AC2: 'Reply on RC2', Allie Balter-Kennedy, 11 Jul 2024
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Allie Balter-Kennedy
Joerg M. Schaefer
Greg Balco
Meredith A. Kelly
Michael R. Kaplan
Roseanne Schwartz
Bryan Oakley
Nicolás E. Young
Jean Hanley
Arianna M. Varuolo-Clarke
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