the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 17 Jun 2025
Distribution and sources of organic matter in submarine canyons incising the Gulf of Palermo, Sicily: A multi-parameter investigation
Abstract. Submarine canyons act as conduits of terrigenous and marine organic carbon (OC) to deep-sea environments, although the contribution of each of these sources can largely vary depending on the canyon morphology and the prevailing sedimentary dynamics. The Gulf of Palermo is incised by several submarine canyons of similar dimension and depth range, but with slightly different morpho-sedimentary characteristics. Using a combination of geochemical parameters (OC, TN, δ13C, δ15N, Δ14C), as well as biomarker signatures (proteins, carbohydrates, phytopigments, glycerol dialkyl glycerol tetraethers, and n-alkyl lipids) and compound-specific δ13C analyses of surficial sediments, we assess the sources of OC deposited on the shelf and in three major canyons (Arenella, Oreto and Eleuterio). The aim is to provide further insights on the role of submarine canyons in transporting terrigenous OC across continental margins. The contribution of terrigenous OC was highest on the shelf (80 %) and decreased offshore, with contributions that ranged between 50 to 70 % across the studied submarine canyons. The dispersal mechanism of terrigenous OC and its specific sources differ among canyons primarily because of local differences of hydro- and sediment dynamics. Arenella Canyon, which is up-current and farthest from any river mouth, exhibited the lowest terrigenous OC contributions (50 %), Oreto Canyon in the central part of the gulf had slightly higher contributions (50–70 %), and Eleuterio Canyon down-current and closest to shore has the highest proportion of terrigenous OC (60–70 %). Besides natural sediment dispersal mechanisms acting on this continental margin, continuous sediment resuspension by bottom trawling activities inside Oreto Canyon contributes to the down-canyon displacement of terrigenous OC, while promoting the ageing and degradation of OC in the canyon axis. Compound-specific δ13C analyses of fatty acids revealed that the sources of terrigenous OC differ across submarine canyons, with Arenella and Oreto canyons receiving OC from a similar terrigenous source up-current from the gulf, whereas terrigenous OC deposited on the shelf and in Eleuterio Canyon originates from the Oreto and Eleuterio rivers that discharge into the Gulf of Palermo. This study provides further evidence that even non-river connected submarine canyons are important sites of terrigenous OC sequestration and transfer to deep-sea environments, and that bottom trawling activities within submarine canyon environments can contribute to its resuspension and dispersal towards deeper regions.
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RC1: 'Comment on egusphere-2025-2587', Anonymous Referee #1, 08 Jul 2025
This is an interesting study which includes an unusually large number of tracers and biomarkers in order to trace the origins of organic matter in shelf and canyon sediments.
The main weaknesses are the limited number of core samples obtained across the Gulf, and the lack of data on the riverine sources of organic matter. As a result, the conclusions are overstated in places.
Line 100: delete “scarce,”
Page 4, line 2: “biomarkers and other sediment organic matter parameters” (or similar – but not just biomarkers)
Line 119: so these two rivers discharge the same amount of water, on average? What about sediment loads? Thae latter would be more relevant tha water discharges. And what about other “distal sources” which could contribute to the canyons – what might they be (other rivers further upstream etc..)
Line 145-155: First you write that 7 cores were collected, but later you write that triplicate cores were collected from one site in each canyon (500m) – please clarify.
Results section:
The descriptions of the data are a bit too long in my opinion.It should be possible to shorten by sticking to the main findings. All the detailed data needs to be shown in a table. The yellow to purple colour ramp used in the figures is not the easiest to interpret.
Also, there are no Results on the mixing models – this should be included here, not in Discussion.
Discussion:
Sediment accumulation rates should be shown in the Results section first. And included in the Methods too.
Line 433: what is BIT index again? Need to remind reader.
The authors should be careful when stating their conclusion – after all, they are based on only 1, 2 or 3 core samples, which may not be representative of the entire canyons. This shortcoming need to be acknowledged and the langage used more careful.
Line 480: This patytern is consistent…
Line 485: need more info on distal sources etc.. see earlier comment
Line 495: remind us what CPI is?
Line 476-500: I think there is a bit of a jump between what the data show and the conclusions about riverine sources. This should be provided as a hypothesis rather than a firm conclusion. Temper the langage and acknowledge that there are weaknesses in your study design and that other processes may be at play (such as x or y).
Figure 8: use same orientation as Figure 1.
Page 21 first sentence: “dire consequences” to strong langage.
Citation: https://doi.org/10.5194/egusphere-2025-2587-RC1 - AC1: 'Reply on RC1', Sarah Paradis, 20 Aug 2025
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RC2: 'Comment on egusphere-2025-2587', Anonymous Referee #2, 12 Jul 2025
Review of Paradis et al. “Distribution and sources of organic matter in submarine canyons incising the Gulf of Palermo, Sicily: A multi-parameter investigation” (egusphere-2025-2587)
Synopsis
Paradis et al. presented a comprehensive study containing geochemical parameters (OC, TN, δ13C, δ15N, and Δ14C), biomarker signatures (proteins, carbohydrates, phytopigments, GDGTs, and n-alkyl lipids), and compound-specific δ13C analyses of surface sediments to assess the sources of OC deposited on the shelf and in the three major canyons in the Mediterranean Sea. A particularly interesting aspect of this study is the use of a wide of source-assignment methods to investigate the role of submarine canyons in transporting terrigenous OC across continental margins. However, due to the limited number of samples (total n=7), any observed differences should be interpreted with caution. While I have no major concerns, I offer several suggestions that could help improve the manuscript.
My specific comments are outlined below.
Line 16: add “, and” before “Δ14C”.
Lines 19-21: please specify which method was used to assess the contribution.
Line 23: It would be better to add “relatively” before “lowest”.
Line 30: Are you referring to the Arenella and Oreto Canyons, which are not connected to rivers? If so, could you explain the potential sources of terrigenous OC into these two canyons?
Lines 48-49: What about differences in marine primary production, which also influence the relative proportion of terrigenous OC.
Lines 72-73: distinguish between specific sub-pools of terrigenous OC (e.g., vegetation, soils, and fossil OC).
Lines 157-159: What is the carbonate content? Could it affect the mean grain size of the terrigenous sediments?
Line 216: the CPI index formulae is wrong, please correct it.
Line 224: rewrite the δ13CCH3 to δ13CMeOH and consider adding a sentence explaining how the δ13C value of HMW compounds (n>24) was calculated.
Table 1: please also include the reference for the marine end-member values.
Lines 275-293: What about the relative proportions of these OC classes based on OC content rather than sediment mass? They could provide insight into the reactivity of OC. Or is it already normalized to OC content?
Line 299: When discussing the concentration of each GDGT, please remember the data are semi-quantitative. It would be more appropriate to present relative abundances rather the absolute.
Figure 4: Specify if HMW FA include all compounds with C≥24 or only even-numbered ones?
Line 320: The CPI value is quite low, could please double-check the calculation? Even in highly degraded, sandy sediments, CPI values typically ranged between 4 and 5.5 (See Wei et al. (2025), https://doi.org/10.1016/j.chemgeo.2025.122712)
Line 484: Are there any specific rivers?
Citation: https://doi.org/10.5194/egusphere-2025-2587-RC2 - AC2: 'Reply on RC2', Sarah Paradis, 20 Aug 2025
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RC3: 'Comment on egusphere-2025-2587', Anonymous Referee #3, 18 Jul 2025
Paradis and co-workers have investigated the distribution and sources of organic matter in sediments from submarine canyons in the Gulf of Palermo, using a combination of bulk sediment properties, a suite of biomarkers, and (compound-specific) stable and radiocarbon isotopes. They find that surficial sediments in the canyons contain between 50-70% terrestrial OC, but that the source of this OC differs between canyons, where some canyons receive OC discharged by nearby rivers, and others receive OC from up-current sources. They also find that bottom trawling has a negative influence on the amount of OC preserved and promotes down-canyon transport.
The manuscript is well written, and the data that is presented is sound. The main remark I have on this work is the limited number of samples (n=7) and the lack of samples from local soils, river(bank) sediments, and marine algae or SPM to serve as endmembers in their calculations to determine contributions of terrestrial OC to submarine canyon sediments. Endmember values are now derived from the literature, and even though the authors used Monte Carlo simulation to compensate for this in their mixing models, the endmember assumptions still introduce uncertainty in the terrestrial OC estimations, and thus the importance on global scale carbon cycling.
In addition, the relatively low number of samples limits comparison of terrestrial OC contributions to sediments inside and outside the canyons to assess e.g., sediment focusing, carbon sequestrations, or verifying dispersal patterns and tracing back OC courses.
Specific comments:
L80: Replace Damsté by Sinninghe Damsté
L81: note that crenarchaeol is not often the most abundant isoGDGT in marine archaea, as its abundance is temperature dependent. At ‘cold’ sites, GDGT-0 will be more abundant than crenarchaeol.
L83: the first study to show brGDGT production in marine sediments is Peterse et al., 2009 Organic Geochemistry.
Method section: there is quite some information on contaminants in the study area, but this information is not further used in the discussion. Reconsider its necessity.
L134: This line mentions ‘naturally high sedimentation rates’. Can you add numbers to provide context? There are a few instances later in the manuscript where sedimentation rates are mentioned and can use some specification. Please check.
L140: this is one of those locations: what kind of rates resemble ‘background sedimentation’?
L172: …stable isotope RATIO mass spectrometer…
L204: I appreciate that the authors assess the sources of brGDGTs even though the BIT index values they present are already very low (<0.05), indicating a primarily marine OC source. Note that the IIIa/IIa ratio used here to assess soil vs marine sources of brGDGTs is not supported by any biophysiological mechanism and also contains a temperature component by capturing part of the degree of methylation of brGDGTs.
L206: Please add what the cutoff of 0.21 for #rings based on. The soil endmember for this ratio is generally based on #rings in local soils and likely differs per location/catchment.
L392: fraction of marine and terrestrial OC depends on marine primary productivity and export to the seafloor -> I fully agree with that. What can you say about marine production in the study area? After all, the Mediterranean Sea is known of its (ultra)oligotrophic conditions. Do you expect large contributions of marine OC at these sites? Especially in comparison to the other canyons mentioned in the text and possible influence of (high discharge) rivers?
L397: add numbers to the ‘high sedimentation rate’ at this site.
L401: I miss some discussion on the possible implications of different OC sources per canyon. Why does this matter?
L413: Thaumarchaeota are now named Nitrososphaerota.
L428: ..age OF OC…
L435: I think the comparison of BIT index values can be a bit more nuanced. Also, Kim et al and Yedema et al only found high(er) BIT index values directly at the river mouth. After that, BIT index values decrease very rapidly with increasing water depth (e.g., Sparkes et al: www.biogeosciences.net/12/3753/2015). A high(er) BIT index can only be found in coastal regions receiving substantial terrestrial input from rivers, which seems to be relatively limited at the shelf site included in this study.
L520: Make sure to not overstate the role of canyons in sequestering terrestrial OC when the study does not present data from sediments
Citation: https://doi.org/10.5194/egusphere-2025-2587-RC3 - AC3: 'Reply on RC3', Sarah Paradis, 20 Aug 2025
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RC4: 'Comment on egusphere-2025-2587', Anonymous Referee #4, 29 Jul 2025
Review of Paradis et al. Biogeosciences
Distribution and sources of organic matter in submarine canyons incising the Gulf of Palermo, Sicily: A multi-parameter investigation
Paradis and co-workers present organic geochemical data for 7 cores collected by multicorer from 1 shelf site and 3 submarine canyons in the area of the Gulf of Palermo, Sicily. The three investigated canyons differ with respect to morpho-sedimentary characteristics and their catchments. The major aim of the study is to assess the sources of OC deposited on the shelf and in three canyons.
The authors have produced an impressive dataset including geochemical parameters (OC, TN, δ13C, δ15N, Δ14C), biomarker signatures (proteins, carbohydrates, phytopigments, glycerol dialkyl glycerol tetraethers, and n-alkyl lipids), compound-specific δ13C analyses of surficial sediments as well as application of mixing models. However, the spatial coverage based on the relatively few sampling sites is rather low – in particular in the Arenello Canyon area, where there is only one sampling site.
Although the spatial coverage of the study area with sampling sites is rather poor, I think the authors could better exploit their comprehensive data sets available for the studied sites. Furthermore, in some parts of the manuscript the discussion and some related statements are still very vague and general.
The manuscript/study has a strong focus on the downslope transport of terrigenous organic carbon (OC) within the canyons. In this context I would then suggest to elaborate a bit more – maybe in the Introduction - on why it is important to assess how much terrigenous carbon is transported downslope within canyons. What about the OC from marine sources? From my point of view it would be similarly important to assess how canyons also act as transport routes of marine OC downslope – in particular in light of the observation that the fraction of marine OC increased downslope. It has been shown that sediment transport in canyons is a rapid process and sedimentation rates at the sites of sediment deposition are high. As has been shown (e.g. Müller et al., 2025; Biogeosciences) sedimentation rate exerts one of the key controls on OC preservation. So, I would assume that in such depositional environments also marine OC would be relatively well preserved.
I also found the parts of the discussion and conclusions that deal with the potential impact of bottom-trawling fisheries (e.g. Zhang et al., 2024) much too vague and general. Do your data allow you to assess how bottom trawling has altered the total OC composition and reactivity? How susceptible/vulnerable is the OM of the different origins/sources to resuspension and oxidation? In other words: How is both the ratio of marine to terrigenous OC as well as the reactivity of OC altered during downslope transport and during (potential) repetitive resuspension induced both by natural processes and anthropogenic activities – namely bottom-trawling – considering that marine organic carbon is more available to remineralization / vulnerable to oxidation when resuspended/re-exposed to oxygen-rich waters.
Also the use of the term „ecosystem functioning“ is much too vague and general. Please, specify what you mean or refer to in detail because I have no idea what precisely you refer to.
Minor/Specific comments
Line 377: Maybe rephrase to „In contrast to …“
L. 380: … had decreasing terrigenous OC contribution „with depth“
L. 394: Do you mean „sediment“ or „OC“ mass accumulation rates here?
L. 448: What precisely do you mean with „very distinct composition“ here? Can you specify a bit more.
Ls. 510 ff.: Can you expand a bit more here how/by which process and condituions resuspension enhances/promotes the degradation of OM … please also cite the relevant references – e.g. Hartnett et al. (1998) … maybe see Zonneveld et al. (2010, Biogeosciences) for a review.
Ls. 512 ff.: needs to be „direct“; Which type of "ecosystem function" precisely do you refer to here? This sounds very vague and needs to be specified – otherwise delete this part of the sentence. Can you also elaborate a bit here how the total amount of OC varies.
Ls. 516/517: Maybe rephrase to: "… and shown to be primarly of phytoplankton origin"
Ls. 529 ff.: What about the total amount of organic carbon? Based on your data does trawling reduce the amount of organic matter transported and deposited in the canyons? How susceptible is the terrigenous OC to trawling-induced resuspension and transport – compared to the OC of marine origin?
L. 531: Again, what precisely do you mean or refer to when you speak of „ecosystem functioning“? Please, explain and specify. Otherwise delete.
Citation: https://doi.org/10.5194/egusphere-2025-2587-RC4 - AC4: 'Reply on RC4', Sarah Paradis, 20 Aug 2025
Status: closed
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RC1: 'Comment on egusphere-2025-2587', Anonymous Referee #1, 08 Jul 2025
This is an interesting study which includes an unusually large number of tracers and biomarkers in order to trace the origins of organic matter in shelf and canyon sediments.
The main weaknesses are the limited number of core samples obtained across the Gulf, and the lack of data on the riverine sources of organic matter. As a result, the conclusions are overstated in places.
Line 100: delete “scarce,”
Page 4, line 2: “biomarkers and other sediment organic matter parameters” (or similar – but not just biomarkers)
Line 119: so these two rivers discharge the same amount of water, on average? What about sediment loads? Thae latter would be more relevant tha water discharges. And what about other “distal sources” which could contribute to the canyons – what might they be (other rivers further upstream etc..)
Line 145-155: First you write that 7 cores were collected, but later you write that triplicate cores were collected from one site in each canyon (500m) – please clarify.
Results section:
The descriptions of the data are a bit too long in my opinion.It should be possible to shorten by sticking to the main findings. All the detailed data needs to be shown in a table. The yellow to purple colour ramp used in the figures is not the easiest to interpret.
Also, there are no Results on the mixing models – this should be included here, not in Discussion.
Discussion:
Sediment accumulation rates should be shown in the Results section first. And included in the Methods too.
Line 433: what is BIT index again? Need to remind reader.
The authors should be careful when stating their conclusion – after all, they are based on only 1, 2 or 3 core samples, which may not be representative of the entire canyons. This shortcoming need to be acknowledged and the langage used more careful.
Line 480: This patytern is consistent…
Line 485: need more info on distal sources etc.. see earlier comment
Line 495: remind us what CPI is?
Line 476-500: I think there is a bit of a jump between what the data show and the conclusions about riverine sources. This should be provided as a hypothesis rather than a firm conclusion. Temper the langage and acknowledge that there are weaknesses in your study design and that other processes may be at play (such as x or y).
Figure 8: use same orientation as Figure 1.
Page 21 first sentence: “dire consequences” to strong langage.
Citation: https://doi.org/10.5194/egusphere-2025-2587-RC1 - AC1: 'Reply on RC1', Sarah Paradis, 20 Aug 2025
-
RC2: 'Comment on egusphere-2025-2587', Anonymous Referee #2, 12 Jul 2025
Review of Paradis et al. “Distribution and sources of organic matter in submarine canyons incising the Gulf of Palermo, Sicily: A multi-parameter investigation” (egusphere-2025-2587)
Synopsis
Paradis et al. presented a comprehensive study containing geochemical parameters (OC, TN, δ13C, δ15N, and Δ14C), biomarker signatures (proteins, carbohydrates, phytopigments, GDGTs, and n-alkyl lipids), and compound-specific δ13C analyses of surface sediments to assess the sources of OC deposited on the shelf and in the three major canyons in the Mediterranean Sea. A particularly interesting aspect of this study is the use of a wide of source-assignment methods to investigate the role of submarine canyons in transporting terrigenous OC across continental margins. However, due to the limited number of samples (total n=7), any observed differences should be interpreted with caution. While I have no major concerns, I offer several suggestions that could help improve the manuscript.
My specific comments are outlined below.
Line 16: add “, and” before “Δ14C”.
Lines 19-21: please specify which method was used to assess the contribution.
Line 23: It would be better to add “relatively” before “lowest”.
Line 30: Are you referring to the Arenella and Oreto Canyons, which are not connected to rivers? If so, could you explain the potential sources of terrigenous OC into these two canyons?
Lines 48-49: What about differences in marine primary production, which also influence the relative proportion of terrigenous OC.
Lines 72-73: distinguish between specific sub-pools of terrigenous OC (e.g., vegetation, soils, and fossil OC).
Lines 157-159: What is the carbonate content? Could it affect the mean grain size of the terrigenous sediments?
Line 216: the CPI index formulae is wrong, please correct it.
Line 224: rewrite the δ13CCH3 to δ13CMeOH and consider adding a sentence explaining how the δ13C value of HMW compounds (n>24) was calculated.
Table 1: please also include the reference for the marine end-member values.
Lines 275-293: What about the relative proportions of these OC classes based on OC content rather than sediment mass? They could provide insight into the reactivity of OC. Or is it already normalized to OC content?
Line 299: When discussing the concentration of each GDGT, please remember the data are semi-quantitative. It would be more appropriate to present relative abundances rather the absolute.
Figure 4: Specify if HMW FA include all compounds with C≥24 or only even-numbered ones?
Line 320: The CPI value is quite low, could please double-check the calculation? Even in highly degraded, sandy sediments, CPI values typically ranged between 4 and 5.5 (See Wei et al. (2025), https://doi.org/10.1016/j.chemgeo.2025.122712)
Line 484: Are there any specific rivers?
Citation: https://doi.org/10.5194/egusphere-2025-2587-RC2 - AC2: 'Reply on RC2', Sarah Paradis, 20 Aug 2025
-
RC3: 'Comment on egusphere-2025-2587', Anonymous Referee #3, 18 Jul 2025
Paradis and co-workers have investigated the distribution and sources of organic matter in sediments from submarine canyons in the Gulf of Palermo, using a combination of bulk sediment properties, a suite of biomarkers, and (compound-specific) stable and radiocarbon isotopes. They find that surficial sediments in the canyons contain between 50-70% terrestrial OC, but that the source of this OC differs between canyons, where some canyons receive OC discharged by nearby rivers, and others receive OC from up-current sources. They also find that bottom trawling has a negative influence on the amount of OC preserved and promotes down-canyon transport.
The manuscript is well written, and the data that is presented is sound. The main remark I have on this work is the limited number of samples (n=7) and the lack of samples from local soils, river(bank) sediments, and marine algae or SPM to serve as endmembers in their calculations to determine contributions of terrestrial OC to submarine canyon sediments. Endmember values are now derived from the literature, and even though the authors used Monte Carlo simulation to compensate for this in their mixing models, the endmember assumptions still introduce uncertainty in the terrestrial OC estimations, and thus the importance on global scale carbon cycling.
In addition, the relatively low number of samples limits comparison of terrestrial OC contributions to sediments inside and outside the canyons to assess e.g., sediment focusing, carbon sequestrations, or verifying dispersal patterns and tracing back OC courses.
Specific comments:
L80: Replace Damsté by Sinninghe Damsté
L81: note that crenarchaeol is not often the most abundant isoGDGT in marine archaea, as its abundance is temperature dependent. At ‘cold’ sites, GDGT-0 will be more abundant than crenarchaeol.
L83: the first study to show brGDGT production in marine sediments is Peterse et al., 2009 Organic Geochemistry.
Method section: there is quite some information on contaminants in the study area, but this information is not further used in the discussion. Reconsider its necessity.
L134: This line mentions ‘naturally high sedimentation rates’. Can you add numbers to provide context? There are a few instances later in the manuscript where sedimentation rates are mentioned and can use some specification. Please check.
L140: this is one of those locations: what kind of rates resemble ‘background sedimentation’?
L172: …stable isotope RATIO mass spectrometer…
L204: I appreciate that the authors assess the sources of brGDGTs even though the BIT index values they present are already very low (<0.05), indicating a primarily marine OC source. Note that the IIIa/IIa ratio used here to assess soil vs marine sources of brGDGTs is not supported by any biophysiological mechanism and also contains a temperature component by capturing part of the degree of methylation of brGDGTs.
L206: Please add what the cutoff of 0.21 for #rings based on. The soil endmember for this ratio is generally based on #rings in local soils and likely differs per location/catchment.
L392: fraction of marine and terrestrial OC depends on marine primary productivity and export to the seafloor -> I fully agree with that. What can you say about marine production in the study area? After all, the Mediterranean Sea is known of its (ultra)oligotrophic conditions. Do you expect large contributions of marine OC at these sites? Especially in comparison to the other canyons mentioned in the text and possible influence of (high discharge) rivers?
L397: add numbers to the ‘high sedimentation rate’ at this site.
L401: I miss some discussion on the possible implications of different OC sources per canyon. Why does this matter?
L413: Thaumarchaeota are now named Nitrososphaerota.
L428: ..age OF OC…
L435: I think the comparison of BIT index values can be a bit more nuanced. Also, Kim et al and Yedema et al only found high(er) BIT index values directly at the river mouth. After that, BIT index values decrease very rapidly with increasing water depth (e.g., Sparkes et al: www.biogeosciences.net/12/3753/2015). A high(er) BIT index can only be found in coastal regions receiving substantial terrestrial input from rivers, which seems to be relatively limited at the shelf site included in this study.
L520: Make sure to not overstate the role of canyons in sequestering terrestrial OC when the study does not present data from sediments
Citation: https://doi.org/10.5194/egusphere-2025-2587-RC3 - AC3: 'Reply on RC3', Sarah Paradis, 20 Aug 2025
-
RC4: 'Comment on egusphere-2025-2587', Anonymous Referee #4, 29 Jul 2025
Review of Paradis et al. Biogeosciences
Distribution and sources of organic matter in submarine canyons incising the Gulf of Palermo, Sicily: A multi-parameter investigation
Paradis and co-workers present organic geochemical data for 7 cores collected by multicorer from 1 shelf site and 3 submarine canyons in the area of the Gulf of Palermo, Sicily. The three investigated canyons differ with respect to morpho-sedimentary characteristics and their catchments. The major aim of the study is to assess the sources of OC deposited on the shelf and in three canyons.
The authors have produced an impressive dataset including geochemical parameters (OC, TN, δ13C, δ15N, Δ14C), biomarker signatures (proteins, carbohydrates, phytopigments, glycerol dialkyl glycerol tetraethers, and n-alkyl lipids), compound-specific δ13C analyses of surficial sediments as well as application of mixing models. However, the spatial coverage based on the relatively few sampling sites is rather low – in particular in the Arenello Canyon area, where there is only one sampling site.
Although the spatial coverage of the study area with sampling sites is rather poor, I think the authors could better exploit their comprehensive data sets available for the studied sites. Furthermore, in some parts of the manuscript the discussion and some related statements are still very vague and general.
The manuscript/study has a strong focus on the downslope transport of terrigenous organic carbon (OC) within the canyons. In this context I would then suggest to elaborate a bit more – maybe in the Introduction - on why it is important to assess how much terrigenous carbon is transported downslope within canyons. What about the OC from marine sources? From my point of view it would be similarly important to assess how canyons also act as transport routes of marine OC downslope – in particular in light of the observation that the fraction of marine OC increased downslope. It has been shown that sediment transport in canyons is a rapid process and sedimentation rates at the sites of sediment deposition are high. As has been shown (e.g. Müller et al., 2025; Biogeosciences) sedimentation rate exerts one of the key controls on OC preservation. So, I would assume that in such depositional environments also marine OC would be relatively well preserved.
I also found the parts of the discussion and conclusions that deal with the potential impact of bottom-trawling fisheries (e.g. Zhang et al., 2024) much too vague and general. Do your data allow you to assess how bottom trawling has altered the total OC composition and reactivity? How susceptible/vulnerable is the OM of the different origins/sources to resuspension and oxidation? In other words: How is both the ratio of marine to terrigenous OC as well as the reactivity of OC altered during downslope transport and during (potential) repetitive resuspension induced both by natural processes and anthropogenic activities – namely bottom-trawling – considering that marine organic carbon is more available to remineralization / vulnerable to oxidation when resuspended/re-exposed to oxygen-rich waters.
Also the use of the term „ecosystem functioning“ is much too vague and general. Please, specify what you mean or refer to in detail because I have no idea what precisely you refer to.
Minor/Specific comments
Line 377: Maybe rephrase to „In contrast to …“
L. 380: … had decreasing terrigenous OC contribution „with depth“
L. 394: Do you mean „sediment“ or „OC“ mass accumulation rates here?
L. 448: What precisely do you mean with „very distinct composition“ here? Can you specify a bit more.
Ls. 510 ff.: Can you expand a bit more here how/by which process and condituions resuspension enhances/promotes the degradation of OM … please also cite the relevant references – e.g. Hartnett et al. (1998) … maybe see Zonneveld et al. (2010, Biogeosciences) for a review.
Ls. 512 ff.: needs to be „direct“; Which type of "ecosystem function" precisely do you refer to here? This sounds very vague and needs to be specified – otherwise delete this part of the sentence. Can you also elaborate a bit here how the total amount of OC varies.
Ls. 516/517: Maybe rephrase to: "… and shown to be primarly of phytoplankton origin"
Ls. 529 ff.: What about the total amount of organic carbon? Based on your data does trawling reduce the amount of organic matter transported and deposited in the canyons? How susceptible is the terrigenous OC to trawling-induced resuspension and transport – compared to the OC of marine origin?
L. 531: Again, what precisely do you mean or refer to when you speak of „ecosystem functioning“? Please, explain and specify. Otherwise delete.
Citation: https://doi.org/10.5194/egusphere-2025-2587-RC4 - AC4: 'Reply on RC4', Sarah Paradis, 20 Aug 2025
Data sets
Geochemical composition of surficial sediments in the Gulf of Palermo Sarah Paradis https://doi.org/10.3929/ethz-b-000738723
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