The paper “Spatio-temporal variability and controlling factors for postglacial erosion dynamics in the Dora Baltea catchment (western Italian Alps)” presents new 10Be-dervied catchment averaged denudation rates and investigates the parameters driving differences in 10Be nuclide concentrations. The authors find that lithologically controlled topographic differences control denudation rates, and that the sediment input from the Mont Blanc massive is the main source of sediment along the Dora Baltea.

I think the paper has potential and the data are good. However, the paper needs revision in terms of structure and language to improve readability. I also found that a more vigorous analysis is required to support the main findings. I therefore suggest major revisions.

Several sentences were long and hard to follow, had wrong punctuation, missing words, or wording that should be revised. I highlight only a few of the mistakes in the line-by-line comments. I think that the authors can improve the readability and language of the manuscript with a thoroughly revised version of the article.

The observation of almost constant 10Be concentration along the main stem is very interesting and I think it deserves much more attention within the paper. The authors show that the same signal can be seen in sediment gauging data, which indicates that this is not due to differences in quartz fertility. I would suggest to put more emphasis on this observation, expand the mixing model analysis, and provide more detailed discussion on this observation. Currently, the mixing model is in the discussion, but I think it should be in the results.

The authors often make links between erodibility of a rock (e.g. its mechanical strength), topography, and the denudation rate, where lower erodibilities are inferred to support steeper topography AND higher denudation rates. It is important to note that this would not be the case in a steady-state landscape. In a steady-state fluvial landscape, differences in erodibility would only be expressed as differences in topography, and denudation would be constant throughout the entire landscape. I understand that the studied landscape was recently glaciated and is likely far from a steady-state topography, however it is important to note that steeper slopes do not necessary equal higher denudation rates.

The authors argue that the lower erodibility bedrock units allow higher geophysical relief to form, which in turn increases denudation rates. However, the slope distributions between the rock units only show minor differences. The authors point to the higher geophysical relief in external and internal units, but it remains unclear why that parameter should be a better predictor of gravitationally driven physical erosion processes than slope. In the current version of the manuscript, it comes across as if the authors choose to ignore the fact that all rock units exhibit similar slopes. I think a better way of presenting the data would be to either, to try and argue that the differences in slope, while minor, are still close enough to erosional thresholds that they actually matter, OR that the denudation rates mostly depend on elevation.

All regressions in this study seem to be done with an ordinary least squares regression (OLS). The results from an OLS depend on which variable is defined as dependent and which as independent. I suggest to revise all regressions and use a total least squares (TLS) approach. A TLS is independent of variable definition. This will probably change the r² and p-values of the regressions.

Figure 7 should be presented in section 4.3, otherwise there is a missing piece in the logical flow. The authors show that denudation rates vary between different rock types, but this variation could just be circumstantial because the distribution of topographic and climatic variables may be heterogeneous among the different rock units. As a reader, I need to know if the faster eroding external units are also steeper, to assess if the external units erode faster because they’re steeper or because they have a higher erodibility.

Below are some line-by-line comments:

Line 29: I suggest to cite the first study applying this technique (Brown et al., 1995)

Line 44: I think there are much earlier papers than Godard 2014 to make the point that an increase in tectonic uplift increases denudation.

Line 44-45. Please, be more precise in your formulations. In a steady-state fluvial landscape, erodibility would only govern the steepness of the topography but not denudation. I kind of get what you mean, but here and in other places the formulations should be more precise.

Line 45-47: This statement needs to be revised (see above). Commonly, we assume that denudation rates tend to balance rock uplift rates. If this is true, erodibility only controls topographic steepness and not denudation rates. I understand that this region was heavily glaciated and does not represent a steady-state fluvial topography. However, the way the statements in this paragraph are set up, this is unclear. The paragraph discusses controls on denudation rates, but does not indicate what spatial and temporal scales are being discussed in the second part of the paragraph. I can guess that the authors refer to millennial scale denudation rates on a catchment/landscape scale, but it’s better to be precise to avoid misunderstandings.

Line 76: “precipitation is”

Line 98: I assume glaciers covered the entire catchment except for some peaks that were sticking out. If so, this point should be made more clearly, or the LGM ice extent could be on figure 1 (unless it would cover the entire fig. 1 area).

Line 107-109: an “a” is missing close to the beginning of your sentence.

Line 132: It has been argued that topographic shielding corrections should not be performed in most settings (Di Biase, 2018). Personally, I do not use it anymore and would suggest the same for this study, unless there is a particular reason to stick to the correction. Also, the abbreviation LIA is only defined later in the same paragraph.

Line 141-144: This sentence needs some English revision.

Line 144-146: I would appreciate a short sentence explaining how this shielding correction looks like, what percentage area it affects, its magnitude, and how it is calibrated.

Line 165: “Average”

Line 169: “subjected to more erosion” or simply “erode faster”. The paragraph contains several long sentences that would benefit from some language revision.

Line 171: The influence “on” instead of “to”. The word “rates” is missing after “10Be derived denudation”.

Line 176: for THE studied catchments.

Line 238: For a bivariate regression the r-value is written in lower case.

Line 241-2: You could instead simply calculate Cook’s distance to evaluate if DB01 significantly affects your regression results.

Line 330-335: Similar to my comment above, I would not call this trend “counterintuitive”. Differences in erodibility can be expressed through surface slope, and therefore do not require any impact on denudation rates.

Line 339: As a reader, it’s unclear to me what exactly your hypothesis is (based on the sentence before). There are several places were the text is written imprecisely, in the sense that I can guess what the authors mean but it’s not formulated explicitly. I suggest to revise the text carefully to avoid such ambiguities.

Line 354-364: This paragraph should be revised. The authors suggest that there should be a glacial imprint on denudation rates but have trouble arguing for it based on the regression and eventually leave the reader hanging. Please, be more explicit in your interpretation and feel free to speculate as to why the correlation may not be as good as expected.

Line 365: The authors sometimes start paragraphs with a sentence that ends without being finished. Here the paragraph starts by stating “we propose a hypothesis” but the sentence ends without the proposal. If you want to state the hypothesis in the subsequent sentences you need to add something like “in the following”.

Line 393-396: It is a valid hypothesis. Please, add a calculation to test this hypothesis. It seems like you know all the necessary parameters to set up a mixing model.

Line 400-412: To me this is the most interesting part of the paper. The mixing model has to go into the results. The high contribution from the Mont Blanc massive is obvious in figure 3, and the reader needs to go through many pages of text to finally see this point addressed. Moreover, if there is a way to get quartz bedrock content estimates for the catchment, the quartz fertility should be included in the mixing model (especially since the higher quartz content of the Mont Blanc massive was already mentioned before).

Line 456: A strong time-scale bias on erosion rates has been shown for glacial environments (Ganti et al., 2016), where decadal scale erosion rates have been shown to be an order of magnitude higher than millennial scale rates due to the stochasticity of erosional processes.

Tab 1: I do not understand why the caption of table 1 lists all of the details that are already described in the main text. Please, reduce the text within this caption significantly.

Tab 2: Same as for Tab. 1. Do not repeat all the methods in the caption.

Tab S2: I appreciate the detailed reporting of production and denudation rates.

Figure 1: Increase line width of rivers, and size of sampling dots for better visibility. Do not use the colors green and red for the sampling dots, since this is the most common color blindness.

Figure 2: Please, increase line width of rivers and symbol size. I suggest to change the color palette, because the current colors are not color-blind friendly.

Figure 3: Maybe enlarge symbol size a little bit.

Review Serra et al. ESurf

General comments:

This paper provides new ¹⁰Be measurements in the Dora Baltea catchment located in the Italian Alps. The authors offer a well-thought analysis of the potential controlling factors of the variability of denudation rates in the studied catchment. Overall, the study is well constructed and well written, providing a new dataset and an interesting discussion. The study is presented logically and the authors make convincing arguments for their interpretation.

I have one general comment and a few minor comments that should be easily addressed by the authors. I think this paper would make a good contribution to the scientific community and recommend its publication with minor corrections.

The only general comment is concerning the way the topographic, environmental, and geological metrics have been calculated. Page 5, line 136, the authors write that they excluded non-quartz-bearing bedrocks for the ¹⁰Be production rates because they do not contribute quartz to the sedimentary system which is the correct way to approach this calculation. However, on page 5 line 155, when discussing the aforementioned metrics, the authors do not specify if they excluded non-quartz-bearing bedrocks and leave the impression that they indeed included all lithologies in their calculations. If this is the case, I recommend that the authors also exclude non-quartz-bearing lithologies in all their metric calculations (topographic, environmental, and geological); otherwise Mafic and Sedimentary areas can potentially skew the values.

Specific comments:

Erosion and denudation are both used in this paper. I would advise to either define both terms as they are stricto sensu not the same thing or pick one term and stick with it.

page 1, line 28: a few major citations are missing. It is considerate to cite Brown et al. (1995), Granger et al. (1996), and Bierman and Steig (1996) when the method regarding ¹⁰Be derived denudation rates is brought up.

page 1, line 33: you provide citations later on for climate and tectonic forcings but not for anthropogenic forcing. Please add some or modify the sentence.

page 1, line 38: clarify what you mean by "recent timescales".

page 2, line 60: "relatively similar climatic conditions" is at odd with page 3 line 75 "mean annual temperatures range from -10°C (high elevation zones) to 15°C" and page 3 line 76 "precipitations are spatially variable". Please rephrase.

page 3, line 65: there is an issue with the legend of figure 1: the elevation color ramp is wrong because of the hillshade. You could also add more information to this figure like the location of quartz-bearing rocks or replace this figure with the figure S1.

page 6, line 184: specify the type of uncertainties.

page 5, line 149: add in the methods the equation used to derive denudation rates from ¹⁰Be concentrations. A reader should be able to reproduce the data from the raw values (¹⁰Be concentration and production rates).

page 7, line 212: "integration time" would be a more meaningful heading than "apparent ages". Also please be mindful of the significant figures, the "apparent ages" values are too precise.

page 8, line 215: would it be better to add the contributing quartz surface area of each tributary by varying the size of each circle? It could help drive the point that the DB01 sample is the main contributor to the overall ¹⁰Be signal in the sedimentary system. Please change the symbol of the sample T12 from a circle to something else.

page 8, line 230: please add in this table the km² or % of quartz-bearing rock in each drainage area.

page 8, line 231: I'm curious as to why the authors didn't check for temperatures as a controlling variable. It is mentioned on page 3 line 75 that "mean annual temperatures range from -10°C (high elevation zones) to 15°C" which would be partially compatible with the frost cracking window proposed by Delunel et al., 2010.

page 10, line 264: did you check for a correlation between mean elevation and the litho-tectonics units? Looking at Figure 2, it seems like some units are only found at high elevation (External Massifs and Internals Massifs) and you also have a correlation between elevation and denudation rates in Fig. 4A. Could the high denudation rates associated with the External / Internal Massifs be related to an elevation-dependent process (like frost-cracking) rather than rock properties?

page 12, line 305: I appreciate the effort the authors made in section 5.1. Could you investigate if the corrections have a significant impact on the correlations calculated with the controlling variables?

page 15, line 385: what do you mean by "unequal sediment mixing"? The fact that there are low ¹⁰Be concentrations along the DB river compared to the tributaries does not mean that the mixing is inefficient, especially because the tributaries are relatively small (from 54 km² to 450 km² - these values are from table 2, please make sure to add the % of contributing quartz-bearing rocks in each catchment) and thus might not have the capacity to drive the ¹⁰Be concentrations up. One way to strengthen your argument is to check the measured ¹⁰Be concentrations vs the expected ¹⁰Be concentrations along the DB river (see Mariotti et al., 2019 for another example of sediment mixing in the Alps).

page 17, line 461: you should also discuss here the fact that the ¹⁰Be denudation rates are calculated on quartz-bearing rocks only while the modern rates are not lithology-dependent.

page 17, line 487: I don't agree with the assessment that one sub-catchment contributing to 77 % of the ¹⁰Be signal implies poor mixing. The ¹⁰Be signal can be driven by one part of the catchment and still be well mixed if the other sub-catchments export low sediment fluxes. Please rephrase or strengthen your argument.

The Manuscript by Serra et al present a suite of Be-10 derived basin-averaged erosion rates from the European Alps and relates them to various topographic and lithological metrics. Additionally, they consider the implications of sediment supply and mixing between sub-catchments and contrast their rates with those derived for the area over longer and shorter timescales. They propose lithological and relief-based parameters as being most important with regards to driving denudation. They suggest high erosion of the Mont Blanc area dominates the sediment production of the larger catchment area, and also that frequency magnitude effects, and/or bias in the Be-10 concentrations due to working in a glacial setting can best explain slower modern rates versus the TCN derived rates.

A problem with applying the basin-wide cosmogenic Be-10 approach to determine erosion rates of glacial/post glacial areas is that you risk violating several of the key assumptions inherent in the method. We might not expect glacial topography to have experienced steady-state erosion for a few multiples of the averaging time and that the concentrations in the surface bedrock/soil cover being eroded are in some approximate equilibrium with the rate of erosion. In addition, these landscapes often contain glacial deposits (moraines, tills, fluvioglacial sediments, etc), which which confound the basin-wide approach if they are being introduced significantly into the fluvial system. The Be-10 work I’m familiar with that attempts to constrain erosion in glacial/post-glacial regions has generally tried to understand the amount to which the rates might be biased in such settings by sampling contributing glacial features and different landscape elements within the basins (e.g. Wittmann et. al., 2007; Norton et al., 2010; as cited in the MS), or at least performing some sensitivity analysis of the effects (e.g. Dixon et al., 2016; as cited in the MS). The authors recognize these potential problems, e.g. the end of section 5.1, or 5.4, where they suggest it can explain why the Be-10 derived rates differ from modern sediment export rates. Based on the discord between the low rates of the contributing catchments rates versus the high rates inferred for the trunk stream, I would say potential bias is a fair assessment and so one that needs some consideration in relation to the robustness of the denudation rate results. However, this is not quantitatively addressed and assertions are made about (assumed linear) correlations, or lack of, between the derived denudation rate and topography, lithology, precipitation, etc. This is the main problem I have with the manuscript. I want to be convinced that the Be-10 derived rates are reflecting actual rates of erosion to subsequently accept later interpretations but the manuscript doesn’t achieve this. The discussions about sediment mixing and the interesting result about the high concentrations in the tributaries versus the trunk stream are useful and likely valid. However, they are based on results that suggest the application of the technique to derive denudation rates, despite the efforts the authors have gone to in order to constrain appropriate production rates, might be flawed, and this needs tested before making statements about what the denudation rates mean.

In my view, major restructuring is required to reduce the manuscripts focus on correlations of the denudation rates with various metrics (that are at best showing weak correlations), and to place more emphasis on the robustness, or not, of the results in this setting, and the implications of their results for sediment mixing. Alternatively, the authors should include convincing support for their interpretation of Be-10 concentrations as valid denudation rates.

Some other comments/concerns listed by line number/figure are:

It’s not entirely clear how lithology/quartz content is being dealt with in regards to the Be-10 approach.

Specifically:

1. L458, how would carbonate dissolution contribute to the Be-10 results?
2. Are the areas excluded from contributing to the Be-10 inventory because of lithology also excluded from the topographic (etc) metrics? I don't see this mentioned in the methods.
3. Are these exclusions not somehow biasing the conclusion that resistant lithologies are a main driver of the rates (assuming the rates are valid, see above)?
4. Do the exclusions also get taken into account for the sediment mixing/contributing area interpretations, e.g. the suggestion that Mont Blanc regions contributes the most to the downstream sediment yield?

L160 “geophysical relief” needs more explanation. It needs to be more clearly stated how it’s derived and how it represents “locally increased erosion”.

Related to the correlations given in the plots of Figs 4 and 5: why assume linear relationships? We already have a lot of evidence showing, for example, slope and denudation rate are non-linear at such steep slope values?

Suggested language edits and minor points:

On a few occasions I found the text difficult to follow/understand (for example, but not limited to, point (1) on L458) and proof reading of any future versions before submission would be recommended. Some other minor points about the text are:

L31 around the globe covers the Alps

L38 What is meant by “recent” in this context?

L74 “greater than” 4000m peaks?

Section 2 (and later section 5.4) over-use parentheses

L109 Is this rate a result, or background info? Better to say - was obtained by Wittmann et al (2016, sample T12). The similar location to the sample measured here can be mentioned in the methods.

L124 Is the blank values used from a long-term lab average, or a blank measured at the same time as the samples?

L159 It’s worth acknowledging that slope may be underestimated at the resolution of the DEM. For example, see Zhang and Montgomery (1994) Digital elevation model grid size, landscape representation, and hydrologic simulations. Water Resources Research, 30(4), 1019-1028.

L184 1.49±0.13 mm/yr is not in the table.

Table 1 Give units for the coords (decimal degrees?).

L403 The Be-10 concentrations were normalized to the basin averaged production rates. Is this not commensurate with simply using the denudation rate (also a normalization of concentration to the production rate)?

L460 How is the landscape dissected by sediment export?