the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 09 Jan 2024
Local Beryllium-10 production rate for the mid-elevation mountainous regions in Central Europe, deduced from a multi-method study of moraines and lake sediments in the Black Forest
Abstract. Beryllium-10 cosmic-ray (CRE) exposure dating has revolutionised our understanding of glacier fluctuations around the globe. A key prerequisite for the successful application of this dating method is a thorough understanding of local production rates of in-situ accumulated 10Be, usually inferred from independently dated regional reference sites. For the mid-elevation (Variscan) mountain ranges of central Europe, no production rate reference site has been available so far. We fill this gap by determining in-situ 10Be concentrations in large boulders on moraines and by applying radiocarbon and luminescence dating to stratigraphically younger lake sediments in the southern Black Forest, SW Germany. The dating methods yielded concordant results and, based on age-depth modelling with 14C ages, we deduced a local 10Be production rate. The resulting Black Forest (BF) production rate is ~11 % lower than both those at the nearest reference site in the Alps and the canonical global 10Be production rate. A stronger weathering and snow cover bias and a higher impact of soil, moss and shrub cover at the stud site likely explain this discrepancy. Due to its internal robustness, we suggest applying the BF production rate in future CRE dating studies in Central Europe and for revising existing age estimates which will have crucial implications for understanding past atmospheric circulation patterns.
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RC1: 'Review of gchron-2023-27', Anonymous Referee #1, 24 Jan 2024
Summary and recommendation
The authors present a new calibration site in Black Forest of SW Germany for the production of cosmogenic 10Be in rock surfaces. Production rate calibration sites are critical to the cosmogenic exposure dating method because they supply empirical constraints on the rate of cosmogenic nuclide production through time. Thus, by applying the independently constrained rate of cosmogenic nuclide production in rock surfaces to sampled surfaces of an unknown age, an age of exposure can be determined.
Production rate calibration sites rely on independent age constraints – most commonly from radiocarbon dating of organic material – so it is incredibly important to ensure that the landform/process being independently dated is the exact same landform/process being sampled for cosmogenic nuclides. In the case of the presented manuscript, the authors measured cosmogenic nuclide inventories on large moraine boulders and recovered organic material for radiocarbon dating from a bog impounded by the moraine. Because they are dating two separate processes/landforms, 1) the culmination of ice advance, abandonment of the moraine and exposure of moraine boulders, and 2) the accumulation of organic material in an impounded bog following ice retreat, the authors were required to produce a ‘modeled’ independent age constraint for the timing of moraine emplacement using assumptions about sediment accumulation in the bog and identifying the contact between organic sediment and till associated with the moraine. In my opinion, this is a less-than-ideal situation for determining a cosmogenic nuclide production rate because they are required to rely only on a minimum independent age constraint instead of a true age constraint.
The resulting reference production rate from their site in the Black Forest of SW Germany is significantly lower than several other nearby regional and local reference production rates, which is perplexing. The authors conclude that local factors – namely boulder surface cover from snow, soil and organic matter and postdepositional surface weathering – effectively hindered 10Be accumulation and/or removed accumulated 10Be from rock surfaces, making the reference production rate lower than expected. This is not the most satisfying conclusion, especially since these factors are difficult to quantify and presumably impact every production rate calibration site, but I appreciate the effort from the authors to attempt to quantify these factors and their recommendation that use of the production rate calibration site should be restricted to only samples collected in the vicinity of the calibration site.
I would be supportive of publication after revision and consideration of some potential further discussion points.
General comments
Below, please find a few general comments that I feel the authors should address in their revision.
- Potential errors in data reporting: After a thorough review of the data presented in this manuscript, I believe I might have found some mathematical errors that I strongly encourage the authors to double check, mainly in the calculation of cosmogenic 10Be concentrations that I found to be 2-3% too low compared to my own calculations. See below for more information on that. Moreover, the authors remove from consideration three samples in the calibration dataset - one sample is an extreme value that could rightfully warrant removal in my opinion, one sample they argue had sample measurement issues and should be disregarded, but the last one (FS-01a) seemingly does not have any explanation from the authors. My only thought is that perhaps it was removed because the sampled boulder was situated on a moraine stratigraphically above the bog and the authors only wanted to consider the modeled radiocarbon date as a minimum age constraint. However, the normalized concentration that I calculated for this boulder is nearly identical to the other samples within the resolution of the dating method so I am not sure it should be removed. In fact, the radiocarbon constraint from the bog could conceivably be considered a maximum age constraint for the younger moraine. I would like to see either a much clearer explanation as to why they removed this sample from consideration, or I feel the authors should reconsider including it in the calibration dataset.
- Sediment coring approach: Although I am not requesting the authors specifically address this if it is outside their scope, I am very curious about their (and previous studies') sediment coring approach. As far as I can tell, the authors only measured radiocarbon on macrofossils collected in one sediment core even though there have been 13 cores recovered from this bog according to the text and figure 4. Is there a specific reason the authors noted all the other cores in this manuscript even though I assume they are not reporting radiocarbon dates from any of the other cores? Have the authors (or original core collectors) recovered macrofossils in any other cores to help corroborate the results from the one core presented here? I recommend the authors either shift focus away from, and perhaps even omit mention of the other cores, or present radiocarbon data from the cores if they exist to help support the reported dates. Afterall, the independent age constraint essentially hinges on just 3 three radiocarbon constraints from one section in one core in the bog.
- Figures and tables: In terms of general comments, I feel that readers would benefit from revisions to some of the figures and tables in the paper. See specific comments below. I also recommend the authors include one additional figure of normalized concentrations from every sampled boulder so readers can more clearly assess the measurement results from each boulder relative to each other (see my comments on table 6 and suggested additional figure), and one additional figure plotting normalized concentrations versus boulder heights for all samples.
- Alternative explanation for the relatively low reference production rate: The authors identify (Line 250) an important point about post-depositional disruption and exhumation impacting 10Be accumulation. Because this PR calibration site is so much lower than other sites, it forces me to wonder if there really is an exhumation/stabilization issue going on here. I recommend the authors dedicate more discussion around the morphology of the moraines. In my experience, boulders embedded in moraines (as opposed to fully atop or even better, clast-supported) are likelier candidates for exhumation issues, especially if there is local, late Pleistocene seismicity. Additionally, the authors observe a lack of protruding quartz veins on their boulders (Line 610-611), which in my experience could mean the boulders were shielded from weathering and potentially exhumed long after deposition. Can exhumation issues be truly ruled out here? As written, I am not fully convinced, and I recommend the authors discuss this issue in more detail.
Specific Comments
Figures and Tables
Figure 3: I recommend the authors give readers some better geographic context for the samples collected, especially given the high-resolution basemap here. Please consider adding dots or some sort of markers to the figure (with labels) for each sample collected. I recognize that the authors more or less did this on Figure 7 but it would be helpful in this zoomed in image. Moreover, the moraine delineations are a little complicated and confusing simply as outlines using the same color for the lines. I recommend coloring each moraine with differing shades of light, transparent fill or something like this so readers can more easily distinguish moraine boundaries.
Figure 4: As previously stated, I am unsure what the purpose is of including every core collected from the bog if they are ultimately not used in the study. I recommend either removing the cores from the figure, or if there is relevant data from multiple cores, include that data in the paper to help corroborate the radiocarbon results from the single (I am assuming?) core. At the very least, the authors need to identify which of the 13 cores on this figure was sampled for radiocarbon dating because I cannot easily tell from the figure. It might even be helpful (if possible at this scale) to put stars or some sort of marker for the relative depths of sample collections for radiocarbon and IRSL.
Figure 6: A general comment on the approach to generating the age-depth model shown in this figure. Why did the authors not include the IRSL ages in the age-depth model? If they are not used in the age-depth model, I am unsure why they are even included in the study. In fact, if the lowermost IRSL age is considered in the age-depth model, it might impact the modeled independent age, at least in respect to the uncertainty in the modeled independent age assignment. I feel this is important for the authors to reconcile, especially if they are concerned with leaning too heavily on just one independent dating method (Lines 33-37). If OxCal cannot accommodate IRSL ages in the age-depth model, I recommend the authors use different software like BACON to generate an updated age-depth model that incorporates the IRSL ages.
Second, could the authors somehow make it a little more obvious in the figure that the tephra layer is hypothesized specifically as the Laacher See Tephra? I got a little confused here.
Tables 1 and 3: stylistically, I would recommend the authors combine these tables, I am not sure what the purpose is of separating this information. In fact, table 3 comes after figure 6 in the text so readers see the age-depth model before they even see the raw radiocarbon dates and calibrated ages.
Table 6: I am not sure why this information needs to be separate from the information in table 5. Moreover, I am unsure why the authors did not report information for the samples they elected to remove from the dataset. I recommend combining the two tables. I also recommend the authors move this combined table up in the text closer to the paragraph in line 280. As is, I had to scroll back and forth several times between the table and the relevant text while reading.
Here and in table 5, based on the information provided, I recalculated 10Be concentrations (and I commend the authors for providing sufficient data to do so), but they are not identical to the concentrations provided. For example, the first sample in table 5 (FS-01a), the authors report a concentration of 134500 at/g but my calculations for that sample were 137938 at/g, approximately 2.5% higher. All other reported concentrations are lower than my recalculations at roughly the same percentage. Except FS-03a, which was somehow 10% lower than my calculation. Because this is a production rate calibration and has important implications for calculating exposure ages elsewhere, I strongly encourage the authors to reaffirm their reported concentrations and/or if my calculations are correct, update the tables and the entire manuscript accordingly.
As a final point, I am not sure how useful the ‘normalized concentrations’ column is. These reported concentrations may be normalized for shielding and thickness, but they are not scaled down to SLHL so one still cannot compare ‘apples to apples’. I recommend the authors make the full effort to normalize concentrations by including the scaling factor as well as the shielding and thickness corrections and report the completely normalized values.
Additional Figure 1: building off the fully normalized concentrations that I feel should be reported for every sample measured (even the one with a low AMS current), I recommend that the authors make an additional figure to graphically display the normalized concentrations. My preference would be for the authors to make normal probability density functions for each sample and a summed pdf (e.g., ‘camelplot’) so readers can see the normalized concentrations in the context of each other to quickly assess the distribution, but I leave that up to the authors how they want to graphically display normalized concentrations.
Additional Figure 2: Because the authors are identifying issues with shielding of cosmogenic production, a commonly adopted approach to mitigate some of these issues is by selecting only the largest boulders (higher likelihood of being wind-swept of snow, less likely to have been exhumed post-depositionally or significantly covered by soil/vegetation, etc.), so I recommend the authors consider adding a plot of normalized concentrations versus boulder height. If there is a trend, that might support some of the conclusions drawn by the authors and/or highlighted in this review.
Line-by-line comments:
Line 74: You surveyed and sampled 3 moraines, correct? Fix please. Could say something like “the bog is situated stratigraphically between some of the moraines” if that is correct.
Line 242-244: I am confused by this paragraph. You collected samples from FS-03 and FS-02, and then one sample from FS-01, which is the moraine that dams the lake, correct? As written, it makes it seem like you collected more than one sample on FS-01, which I think is not true. I recommend rewriting this paragraph and including the total number of samples collected per moraine (perhaps in parentheses).
Line 250-252: Here is where I think you could inject a little more discussion on the morphology/stability of the moraines themselves. Are they mostly matrix supported and susceptible to degradation, is local seismicity an issue, etc.
Line 305: There are more potential factors that get integrated into a ‘baseline’ production rate, e.g., glacial isostatic adjustment, atmospheric redistribution, etc. that are elegantly accounted for with reference production rate calibrations. It might be worth mentioning these other factors as well.
Line 307: Just curious, how do the resulting reference production rates compare between using CREp and the online exposure age calculator? Are they virtually identical?
Line 320: I am not sure how appropriate it would be to use the erosion rate estimated from Reuther, 2007. The erosion rate is certainly environmentally controlled, but it is also controlled by the lithology – density, age, grain size, etc. Unless the authors specify that the bedrock at their Black Forest site is of a similar lithology, age, density, grain size, etc. to the site in the referenced paper, I feel it would be difficult to assess the validity of using this erosion rate.
Line 328-329: might be a sentence/spelling error in this sentence.
Line 465: Just to confirm, the 10Be concentrations reported in table 5 and 6 are the blank corrected concentrations, right? The text is slightly vague here. I would recommend explicitly stating that “values reported in the table are blank corrected” so there is no ambiguity.
Line 610-611: I think it is a useful finding that there were no protruding quartz veins in the sampled boulders, unlike what was observed in Reuther (2007). To me, this could signify that boulder surfaces were better-preserved and much less weathered than the authors hypothesize. If true, this observation might lend support to the minimally discussed idea of moraine stabilization/exhumation processes impacting cosmogenic nuclide inventories in sampled boulders. I recommend the authors consider and discuss this possibility in more detail.
Line 652-656: In terms of data availability, I suggest the authors consider contributing their cosmogenic nuclide measurements to ICE-D (www.ice-d.org) for community discoverability and use.
Citation: https://doi.org/10.5194/gchron-2023-27-RC1 -
AC1: 'Reply on RC1', Felix Martin Hofmann, 23 Feb 2024
Dear reviewer,
We thank you for your thoughtful and critical comments that resulted in considerable improvements to the
manuscript. We thoroughly considered all comments and revised the manuscript accordingly. For
responses to the comments, see the attached file. We hope that the manuscript will be accepted for
publication in its revised form.Thank you very much for your kind consideration.
On the behalf of all co-authors,
Felix Martin Hofmann
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RC2: 'Comment on gchron-2023-27', Anonymous Referee #2, 04 Feb 2024
Review of Black Forest Production Rate
After reading through Reviewer #1’s comments and suggestions, I will state that I agree with their thoughtful and thorough review. The introduction to their review covers major points and objectives of the manuscript, so I will avoid duplicating the same text. I will note that while modeled, independent radiocarbon ages are, perhaps, not ideal, many Be-10 production rates have been calibrated successfully calibrated against radiocarbon ages of related deposits or landforms. In the case of the Black Forest Be-10 production rate, I think it is worth considering this site and the radiocarbon age control used to calculate it.
That said, overall, I found much of the text in this manuscript to be vague or unclear. It was difficult to discern a linear path of reasoning and to easily follow how the final production rates were calculated. To the best of my knowledge, it was not until the Discussion that I first read, definitively, that the production rates were calibrated against the radiocarbon age of 15630 cal yr BP. After reading the manuscript in full, I am unsure, but assume, that the production rates listed in Table 7 are average SLHL Be-10 production rates that include all the surface samples from different moraines collected for analysis. Individual rates are not listed by sample. It isn’t specified. (Are the uncertainties 1-sigma or 2-sigma?) The final, average production rate is not stated in either the abstract, the results text, or the conclusions.
The last part of the paper, in my opinion, seems to veer off in a somewhat unrelated(?) direction, discussing comparison of exposure ages of Black Forest samples calculated by using the production rate calibrated at the sites to ages calculated using the production rate of Claude et al. (2014). First, I feel that calculating exposure ages from the production rate this study calibrated in those samples seems to be circular in reasoning. Secondly, the comparison of ages seems to be outside the scope of this production-rate calibration paper. In my opinion, it seems better suited for another paper/discussion.
Reading through the paper, I can see that there is certainly meaningful data here. The text needs to be more specific and precise in language and in presentation of the data. The organization needs to be improved such that it takes the reader on linear path from selection of the sample sites to independent age control to the production rates (presented as individual rates and then combined into an arithmetical average or error-weighted mean, SLHL value). I encourage the authors to consider resubmission of the paper after major, and thorough, revisions.
General Comment about tables:
Several of the tables could be combined.
Often, information is included in the table caption that is better suited in properly annotated footnotes.
Often, the table captions are vague or imprecise.
Tables often include incomplete citations. For example, please properly cite the scaling methods, etc. in column headings of Table 7.
Comments/Suggestions by line, table, and/or figure:
Line 12: Instead of “understanding” maybe “determination would be better?
Line 13: Until now might be added before “For the midelevation (Variscan)…”.
Line 16: specify that the study uses IRSL, and define its acronym, instead of luminescence dating.
Line 18: …rate in quartz. (Add “in quartz”.)
Line 20: study site, instead of stud site.
Line 21: Seems broadly outside the scope of this manuscript and to the best of my knowledge isn’t really addressed in the text. Please reword or remove this line from the abstract.
Line 27: Worth citing the CReP calculator Martin et al., 2017 here, too, particularly because it is used later in calculations.
Line 29 and throughout text: Please consider using production-rate calibration site, or calibration site, instead of reference site.
Line 30: “At independently dated reference sites…” and yet only one (Claude et al., 2014) is cited. Please consider adding more references and associated citations.
Line 31: Determination of the rate
Line 31: Cosmogenic nuclide production-rate calibration instead of Geological calibration.
Line 33: several authors, yet only one is cited. Please add appropriate references/citations.
Line 35: involving multiple, independent dating methods.
Line 36: the resulting cosmogenic nuclide production rate might be…
Line 39: such as the CRONUS-Earth and CRONUS-EU projects (Cosmic-Ray prOduced NUclide Systematics)
Lines 39-54: global canonical Be-10 production rate is mentioned in the abstract, but the value and associated scaling method are neither provide in the abstract nor in this paragraph, which seems to be introducing the background to Be-10 production rates. Ranges of rates produced at European calibration sites could be added and all associated references with citations could be included, rather than directing the reader to read the references in Martin et al. (2017).
Line 46: more strongly, rather than stronger
Line 48: may also differ from those (rates) at production-rate calibration sites
Lines 59 – 62: run-on sentence. Please break into shorter sentences.
Lines 69 and 70: Obtaining… this sentence reads out of scope, out of place in this paper.
Line 73: Because instead of since.
Line 74: two well-preserved moraines
Line 76: accumulated, in situ cosmogenic…
Line 76: in quartz from moraine-boulder surfaces
Line 77: Radiocarbon and IRSL dating techniques were used to date layers in sediment cores.
Line 77: Reading through the paper, I thought dating was only used on the FSM borehole.
Line 78: a minimum radiocarbon(?) age
Line 78-79: IRSL dating was used as a separate dating technique which independently verifies the sequence of radiocarbon ages in the FSM core. (Or something similar).
Line 81: We propose that calibrating the regional production rate finally offers…
Line 82: I’m not sure this is accurate, the evaluation of other authors’ correction factors. The case to do this with a minimum radiocarbon age (for calibration) and the BF sites own set of vegetation, forestation, snow cover, and weathering/erosion issues seems weak at best.
Line 85: Paragraph needs a topic sentence to introduce the details that are coming. Figure 1 should also be mentioned in the first few lines.
Line 86: specify what “it” is in the sentence that begins “It is situated east…”
Line 87: Feldsee, a moraine-dammed lake up to 33 m deep
Line 93: The dominant(?) lithology in the study area is a quartz-bearing basement rock of the …
Lines 94-97: Starting with “With the denudation…” and ending with “Mezozoic sedimentary rock.” Is this information relevant to this study? The reader only needs to know what rocks are present that could have been incorporated into glacial and/or lake/bog deposits.
Figure 1: Include a citation/reference in the figure for the assumed late Pleistocene maximum ice extent.
Figure 1 caption: Location of the study area in the southern Black Forest, DE…
Line 104: “…was repeatedly glaciated.” Citations/References?
Line 106: refer to Figure 1.
Lines 109 to 111: there are three ranges of ages presented and only two valleys mentioned. What does “respectively” refer to in this sentence?
Figure 2 caption:
Oblique aerial photograph of the study area (study sites?)…
Shown are the headwall of the Feld see Cirque…
Label the prominent moraine in the figure.
The semi-circular moraine is also represented by a dotted line (as is the prominent moraine). Use a different symbol?
Line 119: This needs a topic sentence that moves the reader from Pleistocene glacial times into the present day and leading them to the connection you’re trying to make.
Lines 119 – 121: Run-on sentence. Please break into shorter sentences.
Line 120: Why is this specific 30-yr period used? Why not a longer period of time? Why not a period of time that goes farther back in time?
Line 121 and 122: I read the sentence that starts with “Snowfall…” and found myself asking “And…?” after reading it. Why is this important? What does it indicate relative to your study?
Figure 126: refer to Figure 3?
Figure 3:
Don’t abbreviate position to pos.
What does FSM stand for? It should also be in the legend.
Line 155: Why is only coring site 5 mentioned? Isn’t there the same sequence in each core?
Line 159: Make it clear to the reader that this ash in this core was not dated. It has been hypothesized to correlate with the Laacher See Tephra which has a reported age of…
Line 168: Specify the FSM core in this section?
Line 174: …content of organic matter in layers?
Figure 4 caption: Sedimentary successions at 13 coring sites of Lang (2005). Instead of redrawn from, write Modified after Lang (2005).
Line 182: describe method used to determine water content.
Line 184: individual conversion factors should be listed (in a table?) for each of the 1 m core lengths. Percent adjustment should be specified (values?). Brief explanation of decompacted depths is needed.
Line 187: This paragraph/section needs a topic sentence.
Line 187: Samples of macrofossils were hand picked… “See Supplement for photos of macrofossil samples (Figures ___ - ____).” should be its own sentence.
Line 195: It is unclear what “were assumed to be in correct stratigraphical order” means.
Table 1. Consider combining tables 1 and 3. There is redundancy between them.
3.3 should be IRSL dating.
Line 202: This section needs a topic sentence.
Line 202: Seven samples were obtained from the core… Specify which core and the depth at which each sample was collected. List sample names or refer reader to a table with them listed.
Line 212: For all samples, a standard IRSL protocol was used. Please add a reference/citation.
Lines 214-215: the word latter is used twice, making the second latter unclear. What does it refer to?
Line 217: first mention of OSL. Should that also be in the section title?
Line 234: uranium is not capitalized. This small error occurs several times in this section.
Line 242: Edit to: We collected surface-rock samples…
Line 244: We also sampled the surface of one boulder
Table 2:
Add a column indicating which moraine or site from which each of the samples was collected.
Column for measured sample density?
Column for dip angle and azimuth for each sloping surface?
Significant figures in the topographic shielding factor?
Line 254: Indicate that the angle and azimuth of sloping surfaces was collected and used to add to the total shielding correction.
Line 261: mention that you account for deep-forest shielding in your total shielding.
Lines 271 and 273: These concentrations of acid are very strong. Are these not typically diluted for treatment of mineral separates?
Line 290: local, unscaled production rates? SLHL production rates? Please be specific.
Line 293: mean latitude, longitude, and elevation? Why not use sample specific latitude, longitude, and elevation?
Line 294: Peirce. Incomplete citation?
Line 297: uncertainties are 1-sigma? 2-sigma?
Line 300: Give the actual age and uncertainty of the modeled radiocarbon age against which production rates are calibrated.
Line 302: It appears only two scaling methods were applied, rather than “all scaling schemes and…” Please be specific in language. Lm and LSD were applied, if I understand correctly.
Line 354: Hofmann et al. (2022) recently recalculated CRE ages…Why is this important here? It feels out of place in this manuscript. Is there additional text you could add to explain to the reader why this is relevant?
Line 356: To assess the effect of the choice of production rate… Do you refer to the choice of production rate in this study? The study of Hofmann et al. (2022)? It’s not clear why this is relevant to this calibration study.
Line 359: Were the production rates not also scaled using LSD?
Lines 365 – 378: It seems like circular reasoning to me to calibration a production rate from moraine boulder Be-10 concentrations and then use that same production rate to calculate exposure ages.
Line 381: This section needs a topic sentence. Does this section give descriptions for each core collected? Is it just for the FSM core? If the latter, why only the FSM and not the others?
Lines 381 – 384: This paragraph is very unclear and confusing. Context?
Line 396: Maybe move this paragraph to the beginning of this section?
Figure 6:
Caption mention cores. Is this figure only for the FSM core?
The * and ** should be a complete sentence or two in the caption. Do you mean dark read lines instead of curves?
List sample numbers for IRSL ages.
Hard to tell triangles(?) from circles(?).
I was unable to see any symbol/line that is light blue.
Line 416: Needs a topic sentence. Also, specify if the radiocarbon ages are from the FSM core.
Table 4: is this related to the FSM borehole? Please specify.
Line 468: Paragraph needs topic sentence.
Line 470: Consider using “samples were scaled” rather than “normalized. Also, table 6 doesn’t exemplify this. The scaling factors are listed in the table as are the scaled Be-10 concentrations.
Table 6: Please consider adding a column with LSD scaling factors. Specify the other column is the “Lm” scaling factors.
Table 7: Are these global, arithmetical means? Error-weighted means? SLHL values? How many samples contribute to these? Please specify. Consider combining tables 6 and 7.
Sections 6.2 and 6.3 don’t seem relevant, in my opinion, to the scope of this calibration paper.
The title of section 6.4 would be better posed more like a statement rather than as a question.
Citation: https://doi.org/10.5194/gchron-2023-27-RC2 -
AC2: 'Reply on RC2', Felix Martin Hofmann, 23 Feb 2024
Dear reviewer,
We thank you for your thoughtful and critical comments that resulted in considerable improvements to the
manuscript. We thoroughly considered all comments and revised the manuscript accordingly. For
responses to the comments, see the attached file. We hope that the manuscript will be accepted for
publication in its revised form.Thank you very much for your kind consideration.
On the behalf of all co-authors,
Felix Martin Hofmann
-
AC2: 'Reply on RC2', Felix Martin Hofmann, 23 Feb 2024
Status: closed
-
RC1: 'Review of gchron-2023-27', Anonymous Referee #1, 24 Jan 2024
Summary and recommendation
The authors present a new calibration site in Black Forest of SW Germany for the production of cosmogenic 10Be in rock surfaces. Production rate calibration sites are critical to the cosmogenic exposure dating method because they supply empirical constraints on the rate of cosmogenic nuclide production through time. Thus, by applying the independently constrained rate of cosmogenic nuclide production in rock surfaces to sampled surfaces of an unknown age, an age of exposure can be determined.
Production rate calibration sites rely on independent age constraints – most commonly from radiocarbon dating of organic material – so it is incredibly important to ensure that the landform/process being independently dated is the exact same landform/process being sampled for cosmogenic nuclides. In the case of the presented manuscript, the authors measured cosmogenic nuclide inventories on large moraine boulders and recovered organic material for radiocarbon dating from a bog impounded by the moraine. Because they are dating two separate processes/landforms, 1) the culmination of ice advance, abandonment of the moraine and exposure of moraine boulders, and 2) the accumulation of organic material in an impounded bog following ice retreat, the authors were required to produce a ‘modeled’ independent age constraint for the timing of moraine emplacement using assumptions about sediment accumulation in the bog and identifying the contact between organic sediment and till associated with the moraine. In my opinion, this is a less-than-ideal situation for determining a cosmogenic nuclide production rate because they are required to rely only on a minimum independent age constraint instead of a true age constraint.
The resulting reference production rate from their site in the Black Forest of SW Germany is significantly lower than several other nearby regional and local reference production rates, which is perplexing. The authors conclude that local factors – namely boulder surface cover from snow, soil and organic matter and postdepositional surface weathering – effectively hindered 10Be accumulation and/or removed accumulated 10Be from rock surfaces, making the reference production rate lower than expected. This is not the most satisfying conclusion, especially since these factors are difficult to quantify and presumably impact every production rate calibration site, but I appreciate the effort from the authors to attempt to quantify these factors and their recommendation that use of the production rate calibration site should be restricted to only samples collected in the vicinity of the calibration site.
I would be supportive of publication after revision and consideration of some potential further discussion points.
General comments
Below, please find a few general comments that I feel the authors should address in their revision.
- Potential errors in data reporting: After a thorough review of the data presented in this manuscript, I believe I might have found some mathematical errors that I strongly encourage the authors to double check, mainly in the calculation of cosmogenic 10Be concentrations that I found to be 2-3% too low compared to my own calculations. See below for more information on that. Moreover, the authors remove from consideration three samples in the calibration dataset - one sample is an extreme value that could rightfully warrant removal in my opinion, one sample they argue had sample measurement issues and should be disregarded, but the last one (FS-01a) seemingly does not have any explanation from the authors. My only thought is that perhaps it was removed because the sampled boulder was situated on a moraine stratigraphically above the bog and the authors only wanted to consider the modeled radiocarbon date as a minimum age constraint. However, the normalized concentration that I calculated for this boulder is nearly identical to the other samples within the resolution of the dating method so I am not sure it should be removed. In fact, the radiocarbon constraint from the bog could conceivably be considered a maximum age constraint for the younger moraine. I would like to see either a much clearer explanation as to why they removed this sample from consideration, or I feel the authors should reconsider including it in the calibration dataset.
- Sediment coring approach: Although I am not requesting the authors specifically address this if it is outside their scope, I am very curious about their (and previous studies') sediment coring approach. As far as I can tell, the authors only measured radiocarbon on macrofossils collected in one sediment core even though there have been 13 cores recovered from this bog according to the text and figure 4. Is there a specific reason the authors noted all the other cores in this manuscript even though I assume they are not reporting radiocarbon dates from any of the other cores? Have the authors (or original core collectors) recovered macrofossils in any other cores to help corroborate the results from the one core presented here? I recommend the authors either shift focus away from, and perhaps even omit mention of the other cores, or present radiocarbon data from the cores if they exist to help support the reported dates. Afterall, the independent age constraint essentially hinges on just 3 three radiocarbon constraints from one section in one core in the bog.
- Figures and tables: In terms of general comments, I feel that readers would benefit from revisions to some of the figures and tables in the paper. See specific comments below. I also recommend the authors include one additional figure of normalized concentrations from every sampled boulder so readers can more clearly assess the measurement results from each boulder relative to each other (see my comments on table 6 and suggested additional figure), and one additional figure plotting normalized concentrations versus boulder heights for all samples.
- Alternative explanation for the relatively low reference production rate: The authors identify (Line 250) an important point about post-depositional disruption and exhumation impacting 10Be accumulation. Because this PR calibration site is so much lower than other sites, it forces me to wonder if there really is an exhumation/stabilization issue going on here. I recommend the authors dedicate more discussion around the morphology of the moraines. In my experience, boulders embedded in moraines (as opposed to fully atop or even better, clast-supported) are likelier candidates for exhumation issues, especially if there is local, late Pleistocene seismicity. Additionally, the authors observe a lack of protruding quartz veins on their boulders (Line 610-611), which in my experience could mean the boulders were shielded from weathering and potentially exhumed long after deposition. Can exhumation issues be truly ruled out here? As written, I am not fully convinced, and I recommend the authors discuss this issue in more detail.
Specific Comments
Figures and Tables
Figure 3: I recommend the authors give readers some better geographic context for the samples collected, especially given the high-resolution basemap here. Please consider adding dots or some sort of markers to the figure (with labels) for each sample collected. I recognize that the authors more or less did this on Figure 7 but it would be helpful in this zoomed in image. Moreover, the moraine delineations are a little complicated and confusing simply as outlines using the same color for the lines. I recommend coloring each moraine with differing shades of light, transparent fill or something like this so readers can more easily distinguish moraine boundaries.
Figure 4: As previously stated, I am unsure what the purpose is of including every core collected from the bog if they are ultimately not used in the study. I recommend either removing the cores from the figure, or if there is relevant data from multiple cores, include that data in the paper to help corroborate the radiocarbon results from the single (I am assuming?) core. At the very least, the authors need to identify which of the 13 cores on this figure was sampled for radiocarbon dating because I cannot easily tell from the figure. It might even be helpful (if possible at this scale) to put stars or some sort of marker for the relative depths of sample collections for radiocarbon and IRSL.
Figure 6: A general comment on the approach to generating the age-depth model shown in this figure. Why did the authors not include the IRSL ages in the age-depth model? If they are not used in the age-depth model, I am unsure why they are even included in the study. In fact, if the lowermost IRSL age is considered in the age-depth model, it might impact the modeled independent age, at least in respect to the uncertainty in the modeled independent age assignment. I feel this is important for the authors to reconcile, especially if they are concerned with leaning too heavily on just one independent dating method (Lines 33-37). If OxCal cannot accommodate IRSL ages in the age-depth model, I recommend the authors use different software like BACON to generate an updated age-depth model that incorporates the IRSL ages.
Second, could the authors somehow make it a little more obvious in the figure that the tephra layer is hypothesized specifically as the Laacher See Tephra? I got a little confused here.
Tables 1 and 3: stylistically, I would recommend the authors combine these tables, I am not sure what the purpose is of separating this information. In fact, table 3 comes after figure 6 in the text so readers see the age-depth model before they even see the raw radiocarbon dates and calibrated ages.
Table 6: I am not sure why this information needs to be separate from the information in table 5. Moreover, I am unsure why the authors did not report information for the samples they elected to remove from the dataset. I recommend combining the two tables. I also recommend the authors move this combined table up in the text closer to the paragraph in line 280. As is, I had to scroll back and forth several times between the table and the relevant text while reading.
Here and in table 5, based on the information provided, I recalculated 10Be concentrations (and I commend the authors for providing sufficient data to do so), but they are not identical to the concentrations provided. For example, the first sample in table 5 (FS-01a), the authors report a concentration of 134500 at/g but my calculations for that sample were 137938 at/g, approximately 2.5% higher. All other reported concentrations are lower than my recalculations at roughly the same percentage. Except FS-03a, which was somehow 10% lower than my calculation. Because this is a production rate calibration and has important implications for calculating exposure ages elsewhere, I strongly encourage the authors to reaffirm their reported concentrations and/or if my calculations are correct, update the tables and the entire manuscript accordingly.
As a final point, I am not sure how useful the ‘normalized concentrations’ column is. These reported concentrations may be normalized for shielding and thickness, but they are not scaled down to SLHL so one still cannot compare ‘apples to apples’. I recommend the authors make the full effort to normalize concentrations by including the scaling factor as well as the shielding and thickness corrections and report the completely normalized values.
Additional Figure 1: building off the fully normalized concentrations that I feel should be reported for every sample measured (even the one with a low AMS current), I recommend that the authors make an additional figure to graphically display the normalized concentrations. My preference would be for the authors to make normal probability density functions for each sample and a summed pdf (e.g., ‘camelplot’) so readers can see the normalized concentrations in the context of each other to quickly assess the distribution, but I leave that up to the authors how they want to graphically display normalized concentrations.
Additional Figure 2: Because the authors are identifying issues with shielding of cosmogenic production, a commonly adopted approach to mitigate some of these issues is by selecting only the largest boulders (higher likelihood of being wind-swept of snow, less likely to have been exhumed post-depositionally or significantly covered by soil/vegetation, etc.), so I recommend the authors consider adding a plot of normalized concentrations versus boulder height. If there is a trend, that might support some of the conclusions drawn by the authors and/or highlighted in this review.
Line-by-line comments:
Line 74: You surveyed and sampled 3 moraines, correct? Fix please. Could say something like “the bog is situated stratigraphically between some of the moraines” if that is correct.
Line 242-244: I am confused by this paragraph. You collected samples from FS-03 and FS-02, and then one sample from FS-01, which is the moraine that dams the lake, correct? As written, it makes it seem like you collected more than one sample on FS-01, which I think is not true. I recommend rewriting this paragraph and including the total number of samples collected per moraine (perhaps in parentheses).
Line 250-252: Here is where I think you could inject a little more discussion on the morphology/stability of the moraines themselves. Are they mostly matrix supported and susceptible to degradation, is local seismicity an issue, etc.
Line 305: There are more potential factors that get integrated into a ‘baseline’ production rate, e.g., glacial isostatic adjustment, atmospheric redistribution, etc. that are elegantly accounted for with reference production rate calibrations. It might be worth mentioning these other factors as well.
Line 307: Just curious, how do the resulting reference production rates compare between using CREp and the online exposure age calculator? Are they virtually identical?
Line 320: I am not sure how appropriate it would be to use the erosion rate estimated from Reuther, 2007. The erosion rate is certainly environmentally controlled, but it is also controlled by the lithology – density, age, grain size, etc. Unless the authors specify that the bedrock at their Black Forest site is of a similar lithology, age, density, grain size, etc. to the site in the referenced paper, I feel it would be difficult to assess the validity of using this erosion rate.
Line 328-329: might be a sentence/spelling error in this sentence.
Line 465: Just to confirm, the 10Be concentrations reported in table 5 and 6 are the blank corrected concentrations, right? The text is slightly vague here. I would recommend explicitly stating that “values reported in the table are blank corrected” so there is no ambiguity.
Line 610-611: I think it is a useful finding that there were no protruding quartz veins in the sampled boulders, unlike what was observed in Reuther (2007). To me, this could signify that boulder surfaces were better-preserved and much less weathered than the authors hypothesize. If true, this observation might lend support to the minimally discussed idea of moraine stabilization/exhumation processes impacting cosmogenic nuclide inventories in sampled boulders. I recommend the authors consider and discuss this possibility in more detail.
Line 652-656: In terms of data availability, I suggest the authors consider contributing their cosmogenic nuclide measurements to ICE-D (www.ice-d.org) for community discoverability and use.
Citation: https://doi.org/10.5194/gchron-2023-27-RC1 -
AC1: 'Reply on RC1', Felix Martin Hofmann, 23 Feb 2024
Dear reviewer,
We thank you for your thoughtful and critical comments that resulted in considerable improvements to the
manuscript. We thoroughly considered all comments and revised the manuscript accordingly. For
responses to the comments, see the attached file. We hope that the manuscript will be accepted for
publication in its revised form.Thank you very much for your kind consideration.
On the behalf of all co-authors,
Felix Martin Hofmann
-
RC2: 'Comment on gchron-2023-27', Anonymous Referee #2, 04 Feb 2024
Review of Black Forest Production Rate
After reading through Reviewer #1’s comments and suggestions, I will state that I agree with their thoughtful and thorough review. The introduction to their review covers major points and objectives of the manuscript, so I will avoid duplicating the same text. I will note that while modeled, independent radiocarbon ages are, perhaps, not ideal, many Be-10 production rates have been calibrated successfully calibrated against radiocarbon ages of related deposits or landforms. In the case of the Black Forest Be-10 production rate, I think it is worth considering this site and the radiocarbon age control used to calculate it.
That said, overall, I found much of the text in this manuscript to be vague or unclear. It was difficult to discern a linear path of reasoning and to easily follow how the final production rates were calculated. To the best of my knowledge, it was not until the Discussion that I first read, definitively, that the production rates were calibrated against the radiocarbon age of 15630 cal yr BP. After reading the manuscript in full, I am unsure, but assume, that the production rates listed in Table 7 are average SLHL Be-10 production rates that include all the surface samples from different moraines collected for analysis. Individual rates are not listed by sample. It isn’t specified. (Are the uncertainties 1-sigma or 2-sigma?) The final, average production rate is not stated in either the abstract, the results text, or the conclusions.
The last part of the paper, in my opinion, seems to veer off in a somewhat unrelated(?) direction, discussing comparison of exposure ages of Black Forest samples calculated by using the production rate calibrated at the sites to ages calculated using the production rate of Claude et al. (2014). First, I feel that calculating exposure ages from the production rate this study calibrated in those samples seems to be circular in reasoning. Secondly, the comparison of ages seems to be outside the scope of this production-rate calibration paper. In my opinion, it seems better suited for another paper/discussion.
Reading through the paper, I can see that there is certainly meaningful data here. The text needs to be more specific and precise in language and in presentation of the data. The organization needs to be improved such that it takes the reader on linear path from selection of the sample sites to independent age control to the production rates (presented as individual rates and then combined into an arithmetical average or error-weighted mean, SLHL value). I encourage the authors to consider resubmission of the paper after major, and thorough, revisions.
General Comment about tables:
Several of the tables could be combined.
Often, information is included in the table caption that is better suited in properly annotated footnotes.
Often, the table captions are vague or imprecise.
Tables often include incomplete citations. For example, please properly cite the scaling methods, etc. in column headings of Table 7.
Comments/Suggestions by line, table, and/or figure:
Line 12: Instead of “understanding” maybe “determination would be better?
Line 13: Until now might be added before “For the midelevation (Variscan)…”.
Line 16: specify that the study uses IRSL, and define its acronym, instead of luminescence dating.
Line 18: …rate in quartz. (Add “in quartz”.)
Line 20: study site, instead of stud site.
Line 21: Seems broadly outside the scope of this manuscript and to the best of my knowledge isn’t really addressed in the text. Please reword or remove this line from the abstract.
Line 27: Worth citing the CReP calculator Martin et al., 2017 here, too, particularly because it is used later in calculations.
Line 29 and throughout text: Please consider using production-rate calibration site, or calibration site, instead of reference site.
Line 30: “At independently dated reference sites…” and yet only one (Claude et al., 2014) is cited. Please consider adding more references and associated citations.
Line 31: Determination of the rate
Line 31: Cosmogenic nuclide production-rate calibration instead of Geological calibration.
Line 33: several authors, yet only one is cited. Please add appropriate references/citations.
Line 35: involving multiple, independent dating methods.
Line 36: the resulting cosmogenic nuclide production rate might be…
Line 39: such as the CRONUS-Earth and CRONUS-EU projects (Cosmic-Ray prOduced NUclide Systematics)
Lines 39-54: global canonical Be-10 production rate is mentioned in the abstract, but the value and associated scaling method are neither provide in the abstract nor in this paragraph, which seems to be introducing the background to Be-10 production rates. Ranges of rates produced at European calibration sites could be added and all associated references with citations could be included, rather than directing the reader to read the references in Martin et al. (2017).
Line 46: more strongly, rather than stronger
Line 48: may also differ from those (rates) at production-rate calibration sites
Lines 59 – 62: run-on sentence. Please break into shorter sentences.
Lines 69 and 70: Obtaining… this sentence reads out of scope, out of place in this paper.
Line 73: Because instead of since.
Line 74: two well-preserved moraines
Line 76: accumulated, in situ cosmogenic…
Line 76: in quartz from moraine-boulder surfaces
Line 77: Radiocarbon and IRSL dating techniques were used to date layers in sediment cores.
Line 77: Reading through the paper, I thought dating was only used on the FSM borehole.
Line 78: a minimum radiocarbon(?) age
Line 78-79: IRSL dating was used as a separate dating technique which independently verifies the sequence of radiocarbon ages in the FSM core. (Or something similar).
Line 81: We propose that calibrating the regional production rate finally offers…
Line 82: I’m not sure this is accurate, the evaluation of other authors’ correction factors. The case to do this with a minimum radiocarbon age (for calibration) and the BF sites own set of vegetation, forestation, snow cover, and weathering/erosion issues seems weak at best.
Line 85: Paragraph needs a topic sentence to introduce the details that are coming. Figure 1 should also be mentioned in the first few lines.
Line 86: specify what “it” is in the sentence that begins “It is situated east…”
Line 87: Feldsee, a moraine-dammed lake up to 33 m deep
Line 93: The dominant(?) lithology in the study area is a quartz-bearing basement rock of the …
Lines 94-97: Starting with “With the denudation…” and ending with “Mezozoic sedimentary rock.” Is this information relevant to this study? The reader only needs to know what rocks are present that could have been incorporated into glacial and/or lake/bog deposits.
Figure 1: Include a citation/reference in the figure for the assumed late Pleistocene maximum ice extent.
Figure 1 caption: Location of the study area in the southern Black Forest, DE…
Line 104: “…was repeatedly glaciated.” Citations/References?
Line 106: refer to Figure 1.
Lines 109 to 111: there are three ranges of ages presented and only two valleys mentioned. What does “respectively” refer to in this sentence?
Figure 2 caption:
Oblique aerial photograph of the study area (study sites?)…
Shown are the headwall of the Feld see Cirque…
Label the prominent moraine in the figure.
The semi-circular moraine is also represented by a dotted line (as is the prominent moraine). Use a different symbol?
Line 119: This needs a topic sentence that moves the reader from Pleistocene glacial times into the present day and leading them to the connection you’re trying to make.
Lines 119 – 121: Run-on sentence. Please break into shorter sentences.
Line 120: Why is this specific 30-yr period used? Why not a longer period of time? Why not a period of time that goes farther back in time?
Line 121 and 122: I read the sentence that starts with “Snowfall…” and found myself asking “And…?” after reading it. Why is this important? What does it indicate relative to your study?
Figure 126: refer to Figure 3?
Figure 3:
Don’t abbreviate position to pos.
What does FSM stand for? It should also be in the legend.
Line 155: Why is only coring site 5 mentioned? Isn’t there the same sequence in each core?
Line 159: Make it clear to the reader that this ash in this core was not dated. It has been hypothesized to correlate with the Laacher See Tephra which has a reported age of…
Line 168: Specify the FSM core in this section?
Line 174: …content of organic matter in layers?
Figure 4 caption: Sedimentary successions at 13 coring sites of Lang (2005). Instead of redrawn from, write Modified after Lang (2005).
Line 182: describe method used to determine water content.
Line 184: individual conversion factors should be listed (in a table?) for each of the 1 m core lengths. Percent adjustment should be specified (values?). Brief explanation of decompacted depths is needed.
Line 187: This paragraph/section needs a topic sentence.
Line 187: Samples of macrofossils were hand picked… “See Supplement for photos of macrofossil samples (Figures ___ - ____).” should be its own sentence.
Line 195: It is unclear what “were assumed to be in correct stratigraphical order” means.
Table 1. Consider combining tables 1 and 3. There is redundancy between them.
3.3 should be IRSL dating.
Line 202: This section needs a topic sentence.
Line 202: Seven samples were obtained from the core… Specify which core and the depth at which each sample was collected. List sample names or refer reader to a table with them listed.
Line 212: For all samples, a standard IRSL protocol was used. Please add a reference/citation.
Lines 214-215: the word latter is used twice, making the second latter unclear. What does it refer to?
Line 217: first mention of OSL. Should that also be in the section title?
Line 234: uranium is not capitalized. This small error occurs several times in this section.
Line 242: Edit to: We collected surface-rock samples…
Line 244: We also sampled the surface of one boulder
Table 2:
Add a column indicating which moraine or site from which each of the samples was collected.
Column for measured sample density?
Column for dip angle and azimuth for each sloping surface?
Significant figures in the topographic shielding factor?
Line 254: Indicate that the angle and azimuth of sloping surfaces was collected and used to add to the total shielding correction.
Line 261: mention that you account for deep-forest shielding in your total shielding.
Lines 271 and 273: These concentrations of acid are very strong. Are these not typically diluted for treatment of mineral separates?
Line 290: local, unscaled production rates? SLHL production rates? Please be specific.
Line 293: mean latitude, longitude, and elevation? Why not use sample specific latitude, longitude, and elevation?
Line 294: Peirce. Incomplete citation?
Line 297: uncertainties are 1-sigma? 2-sigma?
Line 300: Give the actual age and uncertainty of the modeled radiocarbon age against which production rates are calibrated.
Line 302: It appears only two scaling methods were applied, rather than “all scaling schemes and…” Please be specific in language. Lm and LSD were applied, if I understand correctly.
Line 354: Hofmann et al. (2022) recently recalculated CRE ages…Why is this important here? It feels out of place in this manuscript. Is there additional text you could add to explain to the reader why this is relevant?
Line 356: To assess the effect of the choice of production rate… Do you refer to the choice of production rate in this study? The study of Hofmann et al. (2022)? It’s not clear why this is relevant to this calibration study.
Line 359: Were the production rates not also scaled using LSD?
Lines 365 – 378: It seems like circular reasoning to me to calibration a production rate from moraine boulder Be-10 concentrations and then use that same production rate to calculate exposure ages.
Line 381: This section needs a topic sentence. Does this section give descriptions for each core collected? Is it just for the FSM core? If the latter, why only the FSM and not the others?
Lines 381 – 384: This paragraph is very unclear and confusing. Context?
Line 396: Maybe move this paragraph to the beginning of this section?
Figure 6:
Caption mention cores. Is this figure only for the FSM core?
The * and ** should be a complete sentence or two in the caption. Do you mean dark read lines instead of curves?
List sample numbers for IRSL ages.
Hard to tell triangles(?) from circles(?).
I was unable to see any symbol/line that is light blue.
Line 416: Needs a topic sentence. Also, specify if the radiocarbon ages are from the FSM core.
Table 4: is this related to the FSM borehole? Please specify.
Line 468: Paragraph needs topic sentence.
Line 470: Consider using “samples were scaled” rather than “normalized. Also, table 6 doesn’t exemplify this. The scaling factors are listed in the table as are the scaled Be-10 concentrations.
Table 6: Please consider adding a column with LSD scaling factors. Specify the other column is the “Lm” scaling factors.
Table 7: Are these global, arithmetical means? Error-weighted means? SLHL values? How many samples contribute to these? Please specify. Consider combining tables 6 and 7.
Sections 6.2 and 6.3 don’t seem relevant, in my opinion, to the scope of this calibration paper.
The title of section 6.4 would be better posed more like a statement rather than as a question.
Citation: https://doi.org/10.5194/gchron-2023-27-RC2 -
AC2: 'Reply on RC2', Felix Martin Hofmann, 23 Feb 2024
Dear reviewer,
We thank you for your thoughtful and critical comments that resulted in considerable improvements to the
manuscript. We thoroughly considered all comments and revised the manuscript accordingly. For
responses to the comments, see the attached file. We hope that the manuscript will be accepted for
publication in its revised form.Thank you very much for your kind consideration.
On the behalf of all co-authors,
Felix Martin Hofmann
-
AC2: 'Reply on RC2', Felix Martin Hofmann, 23 Feb 2024
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