the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Jul 2026
Rain, wind or fire: which led the PAH fallout in Northern Madagascar across the Holocene?
Abstract. The interactions between wildfire, human and climate variability are not well understood. To have better predictions, past studies are useful for observing their behaviours on a long-time scale. To infer past fire activity, studies used charcoal and molecular biomarkers derived from biomass burning, such as Polycyclic Aromatic Hydrocarbons (PAHs). In the north of Madagascar, charcoals are of local origin and have shown increased abundance since 1000 cal a BP. In contrast, PAH are present throughout the Holocene. Therefore, PAHs likely provide a more regional information. Due to the seasonal wind regime, they are thought to originate from East Africa. However, the PAH signal pattern differs from the fire activity record of East Africa. Instead, it shows a similar pattern to precipitation variability in northern Madagascar. Higher PAH concentrations are observed during wetter period, whereas lower concentrations occur during drier periods. This suggest that PAH preservation is enhanced, which may facilitate leaching processes prior to their deposition in sediments. These results challenge the direct interpretation of PAH as straightforward indicators of fire events and dry periods.
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RC1: 'Comment on egusphere-2026-3726', Anonymous Referee #1, 05 Aug 2026
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AC1: 'Reply on RC1', Emeline Bellet, 28 Sep 2026
Dear reviewer,
First, we would like to extend our gratitude to the reviewers, for their time and constructive comments, which allowed us to substantially enhance the quality of our manuscript. Please find below our responses to each of the comments made by the reviewer 1. The text in black represents our response and in red are the questions from reviewer 1.
Best regards,
Emeline Bellet, on behalf of the coauthors
Specific comments
Thank you for your comments. Concerning the analytical methodology, the section has been improved following your comments. Thank you to have highlighted the sentences and the figures that required clarification. We took your comments into consideration for the revised manuscript and improved the conclusion.
Technical corrections
We have preferred to use the terms ‘cal a BP’ rather than ‘cal BP’ or ‘cal yr BP’ following the comment of a reviewer from a previous paper. He said that when reporting a duration of time it is better to use ‘yrs’, but when reporting a date to use ‘cal a BP’ and that in “cal BP” and “BP” there is no time unit. He had suggested me to consult the following webpage https://www.sedgeochem.uni-bremen.de/kiloyears.html.
Thank you for your comments on grammar, spelling and missing references, we have modified the manuscript accordingly.
Charcoal is limited as a regional wildfire proxy contrary to PAHs because they are heavier and deposited in closer to the sources.
We have also completed the text concerning the origin of the charcoal as follows:
« Finally, from ca. 1000 yr ago, an increase in Cyperaceae and Poaceae supports the development of a peat bog, which currently covers a large part of the lake and indicates increasingly shallow conditions (Teixeira et al., 2021). At the same time, charcoal particles began to occur in the sediment core, indicating an increase in fire activity. However, today, the rainforest surrounding the lake in the Montagne d’Ambre is too humid to burn regularly, whereas fires occur frequently in the drier piedmont areas. Charcoals recorded in the uppermost sedoments have thus likely been transported by wind from these surrounding drier areas rather than produced directly within the rainforest surrounding the lake. The same process may have contributed to the occurrence of charcoals in the sediment record during the past 1000 years. This interpretation is further supported by evidence from a second lake in the Montagne d’Ambre, also surrounded by rainforest (Lake Mahasarika; Montade et al., 2024). At this site, shallower conditions were also recorded at around the same time, suggesting that the increase in fire activity and human influence documented in the region may have occurred in association with drier environmental conditions (Montade et al., 2024). »
We did not spike the samples with an internal standard prior to the extraction for PAH. The two possible internal standards are marked either with 2H or with 13C. Because the fraction F1 was subsequently analysed for alkanes and their isotopy, we didn’t use molecules marked with 2H or 13C, in order not to damage the analytical machine used to determine the alkane isotopy.
Concerning the solution for the elutions. Yes, we really made the solution with the proportion 98/2 v/v. Then the proportion is 80/20 v/v for the 2mL of Hep/DCM. The F2 is the elution of those two fractions. Initially when our laboratory extracted the PAHs, they realized those two fractions and they kept them separately. But they discovered that some PAHs remain in the elution of the second fraction (Hep/DCM, 80/20, v/v) so they decided to pool the two fractions for the analysis of the PAH. In this project we have extracted not only the PAH but also the alkanes and the GDGT. That is why we realized 3 fractions.
If pigment remained in fraction 1, a second separation by SiO2 column chromatography was performed. When the pigment remained, a second separation was realised to remake the same separation described just above in the text. Then, we obtained from this F1 three fractions (F1, F2, F3) that we grouped with the corresponding fractions F1, F2 or F3. The sentences have been added in the manuscript to clarify it. We were obliged to do it otherwise the analysis of PAH by HPLC-fluo will be distorted because some pigments absorb and emit at the selected wavelength.
Change has been made between lines 186 and 187 : «The second separation of F1 was performed to repeat the same separation described just above. Then the new three fractions were added to their corresponding fractions. »
Thank you for your comment on the final tasks of the extraction of PAHs. More details have been added. The two fractions, F1 and F2, have been evaporated and analysed separately. We did not combine them. The DMSO cannot be removed before the analyses because it is soluble with methanol. It is just used to change the solvent without passing through a dry step (which generates a loss of PAH). The DMSO did not evaporate and kept its volume. Like this, we can control this final volume to compute the concentration of PAH in the solution and then in the sediment.
Change has been made between lines 189 and 194 : «The fractions 1 and 2 were evaporated separately under a nitrogen flux. Dimethylsulfoxide (DMSO) was used as a keeper and to change the solvent to methanol for the analysis. It is used to change the solvent for the analyses without passing through a dry step, which could generate a loss of PAH. During the evaporation, just under a nitrogen flux, the DMSO keeps its volume and the rest of the solvent evaporates. Then a known volume of methanol was added. The DMSO cannot be removed before the analyses because it is soluble in methanol. Then, the fractions 1 and 2 were analysed separately. »
Concerning the analytical procedure of PAHs more information will be added notably in including a schedule a table listing the wavelengths used for excitation and emission for each PAH analysed.
Changes have been made between lines 201 and 203 : « Briefly, nine phases of excitation and emission detection have been scheduled. The selected wavelengths depend on the PAH sensitivity. Different wavelengths have been selected for the excitation and emission (Table SM 0). »
Thank you for your remark on PAH solubility. As you mention, by nature PAHs are not hydrophilic. We added some sentences to insist upon the fact that PAHs are hydrophobic naturally but separated them into two groups based on their relative hydrophobicity strength, based on the study by Garagnon et al. (2024). We have however preferred using the solubility criteria rather than the coefficient of partitioning water/organic-carbon, because solubility represents better the physical mechanisms triggering the incorporation – or not - of PAHs within the rain droplets. We clarified the hydrophobic nature of PAHs in lines 223 to 226 : « For the rest of the article we will use the terms “hydrophobic group” and ”hydrophilic group” to characterise those two groups. However, one must note that all PAHs are hydrophobic. This separation hence separates the most hydrophobic from the least – yet still - hydrophobic PAH congeners.”
For lines 205-206, the sentence was incomplete. Thank you to have note this. There was an equation but the special characters had disappeared : « However, if the value of a PAH concentration in a sample is comprised between the value of the LOD and the the LOQ, then its concentration is estimated equal to LOQ/√2 »
For the reference “(Ana Lúcia C. Lima et al., 2005)” , the part ‘Ana Lucia C.” have been deleted.
For Line 298, the Per is present in the figure SM2 and Pyr, Flu, Fla, Phe in figure SM3. A precision has been added in the text.
Concerning the charcoal data, the plot presents the fraction of particles >160µm. The charcoal fraction presented in the figure 4 has been added, in line 326 « We confronted our PAH data with the charcoal record of particles >160 µm »
For line 312, the sentence has been modified: « These results effectively demonstrate that charcoal particles >160 µm capture a proximal/local fire signal originating from a few km away, i.e., the drier, low-elevation dry forest/savanna zones where wildfires occur nowadays. ». It is unlikely that the evergreen forest of Ambre Mountain is subjected to wildfire, the fire activity surely occurred – as it does nowadays - at the savanna-covered foothill.
Lines 320-321: “Therefore, the northern region of Madagascar cannot be considered as a source of PAHs”
It is the comparison between the PAH and charcoal signals which gives the information that PAH come from a distal source, because the charcoal signal represents local wildfires.
Line 322-323: “but this would reflect more remote sources supplying PAHs.” Supplying all PAHs, or the "hydrophilic" ones?
For all PAHs, because we observe no charcoal but high concentrations of both “hydrophobic” and ‘hydrophilic’ PAH groups.
Lines 341-342: “Therefore, this implies that although distant, the fire source is not excessively far.” What does this mean in terms of distance? Is there any study of the atmospheric transportation distances of PAHs that can be cited here?
Vachula et al. (2022) compared a historical fire calendar with a PAH signal from lake sediments. They concluded that each individual PAH presents its own behaviour. They hence concluded that the heavier congeners (Ace, Flu, Phe) accurately record any fire within a distance of 40 km whereas the lighter ones (BbF, BkF) record fire within a 150 km distance. However, this depends also on the efficiency of the transportation. Halshall et al. (2001), modelled the transportation of PAH over longer distances (~3500 km). They show that lighter PAHs travel on longer distances. This depends on deposition and degradation. In our study, as we observed the presence of both heavier and lighter PAH showing similar signals we supposed that the predominant PAHs source is not too far away, like the Australian region, where maybe the partitioning between heavy and light molecules would be more important due to the long transport with the photodegradation and deposition processes which also depend on gaz/particule partitioning. We decided to not add the numerical distance because it depends on a lot of parameters such as the meteorology, the degradation or the climate of the study site (Halshall et al. 2001 conducted their study in high latitudes).
Line 367: Please correct to “In a different site” and clarify which one is it.
This sentence was misleading and has thus been deleted.
Lines 375-376: “PAHs likely originate from regional biomass burning, but the variation was not due to fire activity variation.” Please clarify this information.
Thank you for your remark. The figure 4 now displays new curves of charcoal fluxes in Eastern Africa. We interpret the discrepancy between these signals and our Madagascar curve, between 8000 and 6000 cal a BP, as a change in the efficiency of the atmospheric fallout of PAHs. The modification in the text is between lines 425 and 435:
“The fire activity reconstructed from the Eastern Africa charcoal records (Fig. 4H) exhibits a pattern markedly distinct from the Lake Maudit PAH record during the mid-Holocene. The charcoal records from Eastern Africa presented high values during the Early Holocene until 8000 cal a BP as did our PAH record. However, between 8000 and 5500 cal a BP our PAH record presented high value of concentration. PAH concentration increased in Lake Maudit sediment from 8000 to 6000 cal a BP, whereas during the same period, the biomass burning in Eastern Africa decreased and presented its lowest values. As a consequence, we note that whereas PAHs likely originate from African biomass burning, their variations in concentration seem decoupled from the gross amount of African biomass burning during the period from 8000 to 5500 cal a BP.”
Thank you for your comment on figure 4. This figure have been improved in taking in consideration your comments.
The conclusion has been reworked taking in consideration your remark on the lack of information as well as comments from reviewer 2:
« Concentration profiles of PAH in sedimentary archives are usually used to infer palaeofires in complementarity with charcoal records. In our record from the North of Madagascar, despite the absence of charcoal prior to 1000 cal a BP, the concentrations in PAH present high values and significant variations over the Holocene. This suggests they represent a remote signal of fire activities from East Africa, thanks to monsoon winds. However, the signal of PAH does not perfectly match the recorded fire activity from Eastern Africa, especially between 8000 and 5500 cal a BP, when PAHs concentrations reach a maximum in Madagascar and an independent precipitation record from Madagascar. To explain this pattern, two hypotheses can be highlighted: 1) PAHs originated from specific region of the Eastern Africa where biomass still burned, or 2) enhanced precipitation led to a more efficient atmospheric PAH fallout. Our preliminary study does not permit to decide between these hypothesis, however, we argue that changes in wet deposition must not be neglected when interpreting pluri-centennial PAH profiles. Under some conditions which remain to be constrained, PAH could hence be a complementary tool in the attempt to reconstruct past hydroclimate fluctuations.»
Thank you for having taken the time to check the bibliography. The references which needed information have been completed. The references’ DOIs have been added or changed when necessary.
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AC3: 'Reply on RC1', Emeline Bellet, 28 Sep 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-3726/egusphere-2026-3726-AC3-supplement.pdf
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AC1: 'Reply on RC1', Emeline Bellet, 28 Sep 2026
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RC2: 'Comment on egusphere-2026-3726', Anonymous Referee #2, 24 Aug 2026
Review of manuscript: egusphere-2026-3726 for Climate of the Past
Bellet et al present a new record of polycyclic aromatic hydrocarbon (PAH) concentrations––a widely used biomarker for past fire activity––from a sediment core from Lake Maudit, Northern Madagascar which spans the Holocene. By comparing their PAH record with previous estimates of fire activity in Eastern Africa and local precipitation, they conclude that PAHs are sourced from fires in Eastern Africa but their presence in Lake Maudit is not sensitive to fire amount in the source region, but instead to local rainfall conditions and their impact on wet scavenging of these compounds out of the atmosphere.
This work is well written, logically organized, contains well-made figures, and is an important new study that will provide meaningful information to understanding the past fire activity in Macassar and Eastern Africa. However, I have major issues with the arguments presented in this paper and do not think the conclusions follow from the data. However, I think with major revisions, namely a re-interpretation of the main conclusion, this record will be an important contribution to the field and worthy of prompt publication in Climate of the Past. Therefore, I recommend major revisions.
My major concern revolves around the authors conclusion that wet deposition rather than fire amount in the source region is the main driver of PAHs in their lake sediment core. Outlined below are my overarching comments followed by in-line comments and suggestions.
Major concerns:First a methodological concern. Concentrations of paleo-proxies in a sediment core are inherently confounded by changes in sediment accumulation that can bias the signal (for example see Marlon et al. 2013, QSR). The gold standard is to instead report the influx of a chemical or physical constituent of the sediment using the mass accumulation rate determined by the age model of the sediment core, which mitigates the impact of accumulation rate change effects on concentration. At a minimum, the authors should determine the accumulation rate of the PAHs instead of the concentration as this will provide a more appropriate comparison to regional fire activity.
Second, the authors appear to flip-flop on when PAH concentration in their core is driven by wet deposition vs increased fire activity. They claim that high PAHs early in the Holocene are the result of higher wet deposition, but when PAHs also increase in the last few thousand years, despite no accompanying rise in rainfall, they attribute that to higher fire activity. They can’t have it both ways. Moreover, they gloss over a growing body of evidence that changes in fire activity in grassy ecosystems is dominantly controlled by rainfall via controls on fuel abundance {refs}. Their claim that wet deposition is driving the signal needs to supersede the existing literature showing that rainfall increases lead to higher fires in grassy regions (e.g., Eastern Africa which the authors (I believe) rightfully identify as the source area of the PAHs). I feel like the authors set up a strong argument for PAHs in this Malagasy lake being sensitive to fire activity in Eastern Africa. A very interesting and useful result but instead pivot toward the end of the paper into a poorly supported alternative hypothesis, the reason for which is unclear to me.
Third, the authors need to improve the description of the modern conditions (e.g., add fire and compare the wind fields and potential transport from source to sink of PAHs to show that the timing of fire and transport align in the potential sources they discuss) and bolster the data they compare their results to, e.g., including all of the fire records they discuss in the text and improve the labeling of figures. A description of the current fire regime of Madagascar and its relation to moisture and fuel as well as connecting the fire regimes of the potential source areas to Lake Maudit via wind direction comparison would greatly improve the background the reader needs to understand the paper.
Fourth, there are multiple mislabelings of hydrophobic vs hydrophilic PAHs that make some of the arguments difficult to parse. In revision, the authors should much more carefully make sure they are using the correct terms in each instance otherwise, their argument requires undue inspection by the reader.
In-line comments:
18: “past studies”, I think you mean “paleo studies”, as written implies studies done in the past
32: This is a large oversimplification; we know that fires are differentially changing particularly across ecosystem type (in opposite directions). See Andela et al., 2017, Science
48-50: PAHs used to study human impacts on fires, not as biomarkers of human impacts generally
69-70: I don’t think this is really the central question of the paper. The wet deposition impact should be considered as a caveat, it could have a role in determining PAH accumulation in lakes, but existing literature also shows that they correspond to historical fires (e.g., Vachula et al. 2022, Paleo3). Your evidence that the PAHs correspond to Eastern African fire activity is stronger than the evidence for rainfall control, so I disagree with this framing
74-76: Do these studies actually do a frequency analysis (e.g., Higuera et al., 2007, QSR)? A rise in grass combustion does not imply more frequent fires, just more burning (which could be higher burned area). You need to be very careful when discussing fire activity vs amount vs frequency as all have related but distinctly different meanings.
84-95: This paragraph and the previous to some extent read as discussion-like. The introduction should lead up to your central question, but you appear to do that mid-way through leading to (as previously discussed) a question that I do not think should be the central point of the paper. This warrants reframing and reorganizing.
101-115: The potential fire sources are a large component of this paper, yet in the region description you only discuss the winds, temperature and rainfall. Why not the modern distribution/seasonality of fire? They claim later that the wind regimes exclude the southern portion of Madagascar as a PAH source for lake Maudit, so it would be good to set this up. Moreover, how does the Eastern African fire seasonality correspond with the timing of northwesterly winds? Setting up these potential sources at the beginning here would make your job in the discussion a lot easier. Same goes for the Equatorial Asia and Australia argument. I think that you may be able to just skip that because it is so unlikely to be the dominant source due to its distance but showing that the winds and fire timing align is the baseline to set up if that source even makes sense to consider.
133: Figure 1D??
136: “East Africa”: It is my understanding that "Eastern" is preferred due to the colonial association with "East Africa". This is not a science comment, just a cultural one, so make of that what you will.
144: “supports” should be “supported”
145-147: What is the evidence of the fire location?
157: RStudio is an R editor, you need to credit the R language not RStudio here. And it appears you used CLAM not BACON, so it’s a little concerning you are citing the wrong software here.
178: correct French spelling of “series”
205-206: comprised is not the correct word here, and the sentence just stops in the middle??
208-209: More information here? What did the blanks look like? What was removed? This is really vague.
211-212: I don’t know what this means, do you mean the extraction efficiency? How does that compensate for evaporative loss, which happens post-extraction?
223-224: Where are the exclusion criteria discussed? Why do you choose the dates that you kept? Are their physical indicators of erosion, and if so is it safe to assume the ages can be linearly interpolated across this disturbed interval?
239: Linearly interpolated age depth model
271: Figure 3 requires panel labels and reference to where the reader can find the PAH abbreviation key
283: What regions?
286: “Perylen” should be “Perylene”
307-308: What size class of charcoal is this? And what do you mean by "and Poaceae?" in the fig caption. Is this a true charcoal count or char:pollen ratio? If this is a macro charcoal count, it is not surprising that it will not correspond with PAHs becasue larger charcoal has a more local source. If this is a char:pollen ratio however, this does not provide direct fire information but instead a mixture of burning relative to grassy fuel availably.
319-320: Presence of charcoal does not imply fire frequency, only occurrence. You cannot separate frequency from burned area with charcoal amount. To get frequency you have to look at a peak vs background analysis (see Higuera et al., 2007, QSR).
337-338: “We suppose… variation”. This similarity runs counter to your deposition control argument. If wet deposition rather than production via fires is driving the signal, you would expect a stronger rainfall/PAH connection between the hydrophilic vs hydrophobic PAHs.
337-339: You are mixing up the hydrophobic/hydrophilic, hydrophobic = heavy, particle bound. This is mislabeled in figure 4.
343-345: “Secondly… Holocene.” What is this sentence saying? You should just state what each record shows and how it relates to yours. Also, what is the “cf” in the first line?
346-347: “In the southeastern… Holocene.” Why isn’t this plotted in figure 4 as well? This is important to your argument.
350-351: See my major comment, this needs to be set up earlier in the manuscript.
3543-355: “distinctive wind pattern” You can really drive this home with a supp figure showing the wind field during peak Eastern African fire season.
365: “Lake Tanganika and Lake Victoria” You are comparing your record to these records of fire in the source region you identify for the PAHs, why not include these in the comparison plot (Fig 4), being able to visually compare these records is critical to your readers to make the comparison and evaluate your claim that they are "markedly distinct" from your record.
367-368: Delete sentence and just start next sentence with "In contrast..."
368: Replace “huge” with “high”
369: “until 11,000 cal a BP” This mischaracterizes the data, they show elevated fire activity in Turkana from ~15-6ka.
370: Karp et al. show that fire declined with local declines in rainfall showing that declining fuel availability drove reductions in fire.
374-375: Is is different, but overall consistent that fires where high during 11-6 ka and had a secondary increase in the last few thousand years. But agreed that this supports your assertion that the lake PAHs are sourced generally from Eastern Africa.
375-376: What is the evidence for this?? They broadly agree with the Eastern Africa fire history.
378: Figure 4: You should more clearly label the time series to show which are from the same lake and which are not. Especially because some of these records are from the mainland vs. Madagascar. “Hydrophilic” should also be replaced with “Hydrophobic”.
379-380: Panel B: What is plotted here? Caption says charcoal and pollen, but y-axis says charcoal?
381: Two panel D’s, which is which?388: “This period…” Yes, and Karp 2023 argues that the precipitation is the main control on the fuel abundance and thus fire activity. If you disagree with this conclusion, you need to provide a strong counter argument.
392-393: This is context dependent. It matters if you are in a forest or grassland because precipitation controls on fire can have opposite effects (fuel vs moisture limited fire regimes).
401-403: Then why do your hydrophilic and hydrophobic PAHs follow the same patter? If PAH accumulation is all deposition driven, there should be deviation between the philic/phobic PAH time series, which there does not appear to be.
414-415: This can just as easily (and has been previously) interpreted as a fuel driven change in fire occurrence. In a few sentences you report that PAHs increased with modern human activity driving more fires without an associated increase in rainfall. So why is it that when rainfall is high, it is deposition that drives PAHs and not fire amount, but when rainfall is low it doesn’t matter and PAHs are driven by fire amount. How do you have this both ways?
428-429: I do not agree with this, if anything this speleothem record shows disagreements in the timing of PAH accumulation and local rainfall change: e.g., between 10-6 ka PAHs have a broad decline between 9-7 ka but while precipitation declines at 10.5-9 ka, it is just as high from 8.5-6 ka. If deposition was the main control one would expect a much tighter relationship with the local precipitation that displayed.
445: Huh? It's elevated. When did you discuss it being reduced during this time?
448-449: “However,… precipitation.” I don’t think this argument is supported by the data.
Citation: https://doi.org/10.5194/egusphere-2026-3726-RC2 -
AC2: 'Reply on RC2', Emeline Bellet, 28 Sep 2026
Dear reviewer,
First, we would like to extend our gratitude to the reviewers, for their time and constructive comments, which allowed us to substantially will enhance the quality of our manuscript. Please find below our responses to each of the individual comments made by the reviewer 2. The text in black represents our response whereas reviewer 2’s queries are in red. This response have citation from the revised manuscript with in green changed or added parts.
Best regards,
Emeline Bellet, on behalf of the coauthors
Major comments
Thank you for your comments.
First a methodological concern. Concentrations of paleo-proxies in a sediment core are inherently confounded by changes in sediment accumulation that can bias the signal (for example see Marlon et al. 2013, QSR). The gold standard is to instead report the influx of a chemical or physical constituent of the sediment using the mass accumulation rate determined by the age model of the sediment core, which mitigates the impact of accumulation rate change effects on concentration. At a minimum, the authors should determine the accumulation rate of the PAHs instead of the concentration as this will provide a more appropriate comparison to regional fire activity.
We agree with reviewer that it would have been better to report influx rather than concentration. Unfortunately, we did not have the possibility to calculate the flux from our data. We used the remaining samples after other analysis were performed (Teixeira et al. 2021) and the volume weight of the sediment had not been computed. However, the sedimentation rate of the Holocene part of this sediment core is relatively constant (cf. figure 2), which prevents changes in concentration due to be potentially related to changes of sedimentation rate.
Second, the authors appear to flip-flop on when PAH concentration in their core is driven by wet deposition vs increased fire activity. They claim that high PAHs early in the Holocene are the result of higher wet deposition, but when PAHs also increase in the last few thousand years, despite no accompanying rise in rainfall, they attribute that to higher fire activity. They can’t have it both ways.
Thank you for your remark, we acknowledge we were not sufficiently clear in the paper’s first version. During the Early and Mid- Holocene, we assume that there is no fire event in the coring site vicinity because the charcoal signal is null (Teixeira et al, 2021). As a consequence, we must interpret high concentrations of PAHs as the predominant influence of Eastern Africa wildfires. On the contrary, over the last thousand years, a local source cannot be neglected as charcoals were identified within our studied core. We did not exclude that precipitation favoured the scavenging of PAHs from the atmosphere to the lake, during this period. We highlight that a new source of PAHs appeared and we cannot deconvolute the two signals. Moreover, on the same period the PAH composition changed, which reinforces the argument of another source which at this time could have been local. Based on your remark, we attempted at making our statement clearer with the following sentence (line 494-497):
“Then, over the last millennium, the PAH signal may also have been significantly influenced by local fire activity, which not mean that precipitation did not improve the efficiency of PAHs scavenging. If precipitation had rise on this period, the PAHs signal could be a convolution of the two signals (local fire and precipitation). With our knowledge it is impossible to deconvolute the two signals, Therefore our data did not bring new knowledge about variation of precipitation on the last 1000 cal a BP in Madagascar.”
Moreover, they gloss over a growing body of evidence that changes in fire activity in grassy ecosystems is dominantly controlled by rainfall via controls on fuel abundance {refs}. Their claim that wet deposition is driving the signal needs to supersede the existing literature showing that rainfall increases lead to higher fires in grassy regions (e.g., Eastern Africa which the authors (I believe) rightfully identify as the source area of the PAHs). I feel like the authors set up a strong argument for PAHs in this Malagasy lake being sensitive to fire activity in Eastern Africa. A very interesting and useful result but instead pivot toward the end of the paper into a poorly supported alternative hypothesis, the reason for which is unclear to me.
Thank you for this comment which pushes us to distinguish two consequences of our results: i) PAH flux in Madagascar mostly originates from Africa – at least until the 1000 years and ii) our argument favouring an enhanced atmospheric aerosol scavenging rather than a higher wildfire activity in Africa during the African Humid Period. We are well aware about the literature showing in some places in Eastern Africa, a rise in fire activity during humid periods due to its control by the fuel abundance (Karp et al., 2021). However, the same authors also mention that in some places where the fuel is abundant, fire activity is on the contrary limited by moisture. We have based our first interpretation on a curve of fire activities based on the different charcoal records from the Eastern Africa. This curve shows that in average there is no peak in fire activity in Eastern Africa during the Early Holocene. However, thanks to your comment we have distinguish some uncertainties from this curve. So, we have realised an extraction from Bremond et al 2024 to compute a plausible curve of biomass burning from Eastern Africa and added it to the figure 4 of our manuscript (see this figure in supplementary). This curve indeed shows an increase in biomass burning from the onset of the Holocene up to 8000 cal a BP. Therefore, it is not impossible that our high concentrations in PAHs before 8000 cal a BP was due to an increase in biomass burning in East Africa. However, after this date the biomass burning clearly dropped in Eastern Africa, whereas our concentration in PAH increased and reached its highest value. Therefore, with the actual knowledge, we conclude that the high value of PAHs between 8000 and 55000 cal BP are not caused by an increase in fire activity in the Eastern Africa. Based on your comment we modified our discussion to make it clearer and clearly separate the questions of i) PAH sources and ii) processes explaining a higher PAH concentration between 8000 to 5500 cal a BP .
We have modified the initial manuscript between lines 431 and 437:
“The charcoal records from the Eastern Africa presented high value during the Early Holocene until 8000 cal a BP as our PAH record. However, between 8000 and 5500 cal a BP our PAH record presented high value of concentration. PAH concentration increase in Lake Maudit sediment from 8000 to 6000 cal a BP. Whereas on the same period the biomass burning in the Eastern Africa decrease and present its lowest values. As a consequence, we note that whereas PAHs likely originate from African biomass burning, their variations in concentration seems decoupled from the gross amount of African biomass burning on the period from 8000 to 5500 cal a BP.”
Third, the authors need to improve the description of the modern conditions (e.g., add fire and compare the wind fields and potential transport from source to sink of PAHs to show that the timing of fire and transport align in the potential sources they discuss) and bolster the data they compare their results to, e.g., including all of the fire records they discuss in the text and improve the labelling of figures. A description of the current fire regime of Madagascar and its relation to moisture and fuel as well as connecting the fire regimes of the potential source areas to Lake Maudit via wind direction comparison would greatly improve the background the reader needs to understand the paper.
We have improved the description on modern conditions in adding 2 paragraphers between lines 114 and 127. However, we want to highlight that nothing proves that the current fire seasonality was similar during the African Humid Periods. We think about this potential difference due to the paper of Tierney et al. (2011) showing that at 6000 cal BP, the wet season (June to November) was drier, whereas the dry season (December to February) was wetter than today.
“Moreover, from the point of view of air mass origin, those wind contions isolate the Northern Madagascar from the rest of the Island. Wind codition prevent air masses to passing from the central of Madagascar to the Northern part. The southward shift of the ITCZ during the southern summer period (DJF), allowing the air masses originated from the Eastern Africa to reach the Northen of Madagascar (Fig. 1B).
The current fire distribution presents a seasonal pattern (Fig. 1E). Both at Madagascar and Eastern Africa, the fire season currently extends from August to November. However, it is important to note that nothing proves that this fire seasonality was the same during the whole Holocene. The fire activity depends on the precipitation cycle (Giglio et al., 2006; Karp et al., 2021; Vachula et al., 2022). Yet, Tierney et al. (2001) showed that the seasonality of precipitation was notably different during the Mid-Holocene. In Eastern Africa, the annual increase in precipitation was due to wetter dry periods whereas wet periods were drier than today (Tierney et al., 2011). Therefore, it is possible that the seasonality of fire activities has changed throughout the Holocene.”
Fourth, there are multiple mislabelings of hydrophobic vs hydrophilic PAHs that make some of the arguments difficult to parse. In revision, the authors should much more carefully make sure they are using the correct terms in each instance otherwise, their argument requires undue inspection by the reader.
Thank you to have note it. The whole manuscript has been edited accordingly.
In-line comments
Thank you for the comments concerning the grammar, spelling and for the words preferable to used.
line 18 : as recommand ‘paleo studies’ have been used instead of ‘past studies’
line 32 : thank you to your remarks. We will rework on this introduction sentence to not realise an oversimplification.
“However, the interactions between wildfire dynamics and human land uses, climate, and environmental perturbations, particularly in the tropics, are complex (Bremond et al., 2024; Daniau and Brücher, 2016; Denis et al., 2012). Observation on the past decanals showed that agricultural expansion tends to a decrease in wild fire in tropical environments (Andela et al. 2017). Moreover, past studies provide a better understanding of wildfire behaviour and improve predictions (Daniau and Brücher, 2016; Karp et al., 2020a). Karp et al. notably showed that the response of rainfall on savana wildfire activities was not linear.”
Line 48-50 : More precision have been added to said that “PAHs are used to study fire event or anthropogenic pollution”.
74-76: Do these studies actually do a frequency analysis (e.g., Higuera et al., 2007, QSR)? A rise in grass combustion does not imply more frequent fires, just more burning (which could be higher burned area). You need to be very careful when discussing fire activity vs amount vs frequency as all have related but distinctly different meanings.
319-320: Presence of charcoal does not imply fire frequency, only occurrence. You cannot separate frequency from burned area with charcoal amount. To get frequency you have to look at a peak vs background analysis (see Higuera et al., 2007, QSR).
The words “frequency” have been delated.
84-95: This paragraph and the previous to some extent read as discussion-like. The introduction should lead up to your central question, but you appear to do that mid-way through leading to (as previously discussed) a question that I do not think should be the central point of the paper. This warrants reframing and reorganizing.
Thank you for your remarks. Our central question is which influence the PAH sediment record in the Northern of Madagascar. Is it the importance of fire event, the transport efficiency or the deposition efficiency? We have noted that this part looks like a discussion we have worked on it to be more an introduction part.
Two paragraphers have been deleted (lines 89-95 from the initial manuscript). The question has been simplified to
“In this paper, we take advantage of known climatic and local wildfire frameworks of northern Madagascar to investigate PAH deposition pathways over the whole Holocene.”
101-115: The potential fire sources are a large component of this paper, yet in the region description you only discuss the winds, temperature and rainfall. Why not the modern distribution/seasonality of fire? They claim later that the wind regimes exclude the southern portion of Madagascar as a PAH source for lake Maudit, so it would be good to set this up. Moreover, how does the Eastern African fire seasonality correspond with the timing of northwesterly winds? Setting up these potential sources at the beginning here would make your job in the discussion a lot easier. Same goes for the Equatorial Asia and Australia argument. I think that you may be able to just skip that because it is so unlikely to be the dominant source due to its distance but showing that the winds and fire timing align is the baseline to set up if that source even makes sense to consider.
Two paragraphers have been added on the origin of air masses and on current fire seasonality.
« Moreover, from the point of view of air mass origin, those wind contions isolate the Northern Madagascar from the rest of the Island. Wind codition prevent air masses to passing from the central of Madagascar to the Northern part. The southward shift of the ITCZ during the southern summer period (DJF), allowing the air masses originated from the Eastern Africa to reach the Northen of Madagascar (Fig. 1B).
The current fire distribution present a seasonal partern (Fig. 1D). At Madagascar and in the Eastern Africa, the fire season currently extend from August to November. However, it important to note that nothing prove that this fire seasonality was the same during the all Holocene. The fire activities depend on the precipitation cycle (Giglio et al., 2006; Karp et al., 2021; Vachula et al., 2022). Yet, Tierney et al. (2001) have proved that the seasonality of precipitation was different notably during the Mid-Holocene. In the Eastern Africa, the annual increase in precipitation was due to wetter dry periods whereas wet periods were drier (Tierney et al., 2011). Therefore, it is possible that the seasonality of fire activities has change during the Holocene. »
« Simultaneously, charcoal counts exhibit that fires started to occur, probably not in Montagne d’Ambre, but more likely occurring in the low elevation areas surrounding the mountains. » What is the evidence of the fire location?
Following your question, we have changed the text to be clearer.
“Finally, from ca. 1000 yr ago, an increase in Cyperaceae and Poaceae supports the development of a peat bog, which currently covers a large part of the lake and indicates increasingly shallow conditions (Teixeira et al., 2021). At the same time, charcoal particles began to occur in the sediment core, indicating an increase in fire activity. However, today, the rainforest surrounding the lake in the Montagne d’Ambre is too humid to burn regularly, whereas fires occur frequently in the drier piedmont areas. Charcoal recorded in the uppermost core sediments is therefore likely to have been transported by wind from these surrounding drier areas rather than produced directly within the rainforest or its immediate catchment. The same process may have contributed to the occurrence of charcoal in the sediment record during the past 1000 years. This interpretation is further supported by evidence from a second lake in the Montagne d’Ambre, also surrounded by rainforest (Lake Mahasarika; Montade et al., 2024). At this site, shallower conditions were also recorded at around the same time, suggesting that the increase in fire activity and human influence documented in the region may have occurred in association with drier environmental conditions (Montade et al., 2024). “
For lines 205-206, we have not note that the special character has disappeared, sorry for this mistake.
“However, if the value of a PAH concentration in a sample is comprised between the value of the LOD and the the LOQ, then its concentration is estimated equal to LOQ/√2”
208-209: More information here? What did the blanks look like? What was removed? This is really vague.
During the extraction we realised also a blank which was the procedure of extraction which is repeated without sediment. Like this if there is some extern PAHs contamination, we can subtract the PAHs quantities of the blank from the PAHs quantities of the sample. The behind concept is that if there is a contamination during the extraction it appear in the blank and we can remove it from the PAHs results of the samples. More information has been added to be clearer in the manuscript.
“During chemical procedures, blank controls were performed, meaning that the same extraction procedure was realised without sediment. The potential contamination quantities in PAHs found in the blanks analysis were removed from the sample PAHs results.”
211-212: I don’t know what this means, do you mean the extraction efficiency? How does that compensate for evaporative loss, which happens post-extraction?
Yes, we used certified soil to determine the efficiency of the extraction. In the certified soil, the concentration in PAHs was known. We realised on 5 certified soil the extraction of PAHs and we quantified their PAHs. Usually, the extraction has not an efficiency at 100%. For PAHs it dependent mostly from PAHs evaporation. Then, we quantified the loss in PAHs thanks to the certified soils, and the loss percentage was applied to the PAHs quantified in the samples. Like this we prevent the losses of PAHs during and post extraction.
223-224: Where are the exclusion criteria discussed? Why do you choose the dates that you kept? Are their physical indicators of erosion, and if so is it safe to assume the ages can be linearly interpolated across this disturbed interval?
Exclusion criteria were discussed by Teixeira et al. (2021), and we followed the same approach. However, as eight new radiocarbon ages have been added and as the reviewer requested, we considered it useful to more explicitly recall the processes that may explain the observed age inversions and to clarify the exclusion criteria applied here.
The text was modified as follows (see also lines 255-270):
“The calibrated ages are provided in Table 1, and the resulting age-depth model is shown in Figure 2. In the lowermost part of the core (>15 ka BP; >970 cm), three of the five radiocarbon dates are notably older and become progressively older with increasing depth. These age inversions may result from contamination by old carbon, potentially related to the dissolution and erosion of older carbon-rich soils during this period (see Teixeira et al., 2021, for further details). As artificially younger ages are generally more difficult to explain, the two younger ages were retained, while the three older ages were considered outliers and excluded from the age-depth model. Between 15 and 10 ka BP (940–630 cm), five additional radiocarbon dates also show age inversions, although the difference is less pronounced. This interval coincides with the onset of the African Humid Period, marked by increasing humidity and lake-level rise, as evidenced by vegetation changes (Teixeira et al., 2021). This wetter period was also associated with increased erosion, which may have promoted the reworking of older sediments or soils from the lake shore, potentially explaining the observed age inversions. As this study mainly focuses on the Holocene period, eight new radiocarbon dates were added to the initial age model. No age inversions were observed among either the new or previously retained dates, further strengthening the revised age-depth model and providing a very robust chronology for the Holocene reconstruction presented in this study.”
157: RStudio is an R editor, you need to credit the R language not RStudio here. And it appears you used CLAM not BACON, so it’s a little concerning you are citing the wrong software here.
A first age-model depth model was initially built on the 11-m sediment core using 19 radiocarbon ages by Teixeira et al. (2021) on CLAM. A total of 8 new radiocarbon dates were added to the first 7 m to strengthen the Holocene section. The new age model was performed as a function of the composite depth with RStudio software using the R-package ‘Bacon’ (v. 4.0.5) (Blaauw and Christen 2011) and using SHCal20 calibration curve and bomb 14C curve (Hogg et al. 2020, Hua et al. 2016). The ages are expressed in calibrated years before present (years BP).
283: What regions?
The words “from region’ have been deleted because the sentence was not understable with it.
307-308: What size class of charcoal is this? And what do you mean by "and Poaceae?" in the fig caption. Is this a true charcoal count or char:pollen ratio? If this is a macro charcoal count, it is not surprising that it will not correspond with PAHs becasue larger charcoal has a more local source. If this is a char:pollen ratio however, this does not provide direct fire information but instead a mixture of burning relative to grassy fuel availably.
Thank you for your comments and sorry for the mistake. Initially, we plot the curve of Poaceae in the figure 4 but finally we have removed it but we forget to change the title. It is well the curve of charcoal counting uniquely. Before counting, the sample were sieved through a 160 μm mesh (Teixeira et al., 2021). Following your comment, we have completed the information in the text and in the legend.
Legend is now : “B. Counting of charcoal (particules >160 µm) in lake Maudit (Teixeira et al., 2021). ”
In the text line 326 : “We confronted our PAH data with the charcoal record of particles >160 µm (Teixeira et al. 2021; Fig. 4A, B and C). ”
337-338: “We suppose… variation”. This similarity runs counter to your deposition control argument. If wet deposition rather than production via fires is driving the signal, you would expect a stronger rainfall/PAH connection between the hydrophilic vs hydrophobic PAHs.
Thank you for your comments. The reviewer 1 suggest that our terminology hydrophobic vs hydrophilic was not well explained and confusing. All PAH are hydrophobics there is just some wich are less hydrophobic that we name the hydrophilics groups. This explain why there is not a much more difference between the two groups between lines 323 and 327:
“For the rest of the article we will use the terms “hydrophobic group” and ”hydrophillic group” to characterise those two groups. However, one must note that all PAHs are hydrophobic. This separation hence separates the most hydrophobic from the least – yet – still - hydrophobic PAH congeners.”
337-339: You are mixing up the hydrophobic/hydrophilic, hydrophobic = heavy, particle bound. This is mislabeled in figure 4.
Thank you for your comments. We have changed it.
343-345: “Secondly… Holocene.” What is this sentence saying? You should just state what each record shows and how it relates to yours. Also, what is the “cf” in the first line?
The sentence has been deleted to have directly the description of the curves.
346-347: “In the southeastern… Holocene.” Why isn’t this plotted in figure 4 as well? This is important to your argument.
The figure 4 will be reworked following your comments. Please see it in supplementary of this response.
350-351: See my major comment, this needs to be set up earlier in the manuscript.
Thank you for your comment. We have added a paragraphe on the origin of air masses in the “material and methods” l.119-123.
3543-355: “distinctive wind pattern” You can really drive this home with a supp figure showing the wind field during peak Eastern African fire season.
In Figure 1 we have add a map of the seasonality of biomass burning following your advices in figure 1.
365: “Lake Tanganika and Lake Victoria” You are comparing your record to these records of fire in the source region you identify for the PAHs, why not include these in the comparison plot (Fig 4), being able to visually compare these records is critical to your readers to make the comparison and evaluate your claim that they are "markedly distinct" from your record.
375-376: What is the evidence for this?? They broadly agree with the Eastern Africa fire history.
For the two previous comments, the figure 4 have been reworked. For the comparison the curve of Lake Tanganika and Lake Victoria will be added. Moreover, an extraction of charcoals records from the Eastern Africa have been added. The comparison with the different lake one by one it is may be an issue, because it is more probable that the air masses arriving from the Eastern Africa to the North of Madagascar is a mixture from air masses from the global region and not just from one lake area.
369: “until 11,000 cal a BP” This mischaracterizes the data, they show elevated fire activity in Turkana from ~15-6ka.
We agree with you. We have added the record of the lake Turkana in figure 4. We think that air masses did not come from a unique lake but from the region which is subjected to different fire regime.
374-375: Is is different, but overall consistent that fires where high during 11-6 ka and had a secondary increase in the last few thousand years. But agreed that this supports your assertion that the lake PAHs are sourced generally from Eastern Africa.
Thank you for your comment. We have adapted our interpretation following your comment and the curve of the Eastern Africa as mentioned before and for your comment line 388.
379-380: Panel B: What is plotted here? Caption says charcoal and pollen, but y-axis says charcoal?
381: Two panel D’s, which is which?Thank you for your two last comments. Initially, we plot the curve of Poaceae in the figure 4 but finally we have removed it but we forget to change the title. It is well the curve of charcoal counting uniquely. We also remake the panel notation.
370: Karp et al. show that fire declined with local declines in rainfall showing that declining fuel availability drove reductions in fire.
388: “This period…” Yes, and Karp 2023 argues that the precipitation is the main control on the fuel abundance and thus fire activity. If you disagree with this conclusion, you need to provide a strong counter argument.
We agree with the conclusion of Karp et al. (2023) that increased precipitation does not necessarily result in increased fire activity. The relationship between precipitation and fire activity is nonlinear and varies among environments. As shown by Karp et al. (2023), the response to similar precipitation changes differs among sites: fire activity increased at Lake Turkana, increased initially and then decreased at Lake Tanganyika, whereas it decreased at Lake Victoria. When the data were available, they have been added in Figure 4. Moreover, based on the available fire reconstructions from Eastern Africa, we added a syntheses of these records into a regional-scale fire activity curve (Bremond et al. 2024).
As explained before your comments allowed to improve the characterisation of the Eastern Africa fire activity, notably in choosing a better curve. The interpretation and the text have been adapted in adequation.
“ The charcoal records from the Eastern Africa presented high value during the Early Holocene until 8000 cal a BP as our PAH record. However, between 8000 and 5500 cal a BP our PAH record presented high value of concentration. PAH concentration increase in Lake Maudit sediment from 8000 to 6000 cal a BP. Whereas on the same period the biomass burning in the Eastern Africa decrease and present its lowest values. As a consequence, we note that whereas PAHs likely originate from African biomass burning, their variations in concentration seems decoupled from the gross amount of African biomass burning on the period from 8000 to 5500 cal a BP.”
392-393: This is context dependent. It matters if you are in a forest or grassland because precipitation controls on fire can have opposite effects (fuel vs moisture limited fire regimes).
We agree with your comment.
401-403: Then why do your hydrophilic and hydrophobic PAHs follow the same patter? If PAH accumulation is all deposition driven, there should be deviation between the philic/phobic PAH time series, which there does not appear to be.
Thank you for your comments. The fact is the PAHs are not hydrophilic but hydrophobic. The group of hydrophilic are just less hydrophobics than the other. This explain why hydrophobics are also scavenging in a lesser quantity than hydrophillics. This explain why there is not a much more difference between the two groups between lines 323 and 327:
“For the rest of the article we will use the terms “hydrophobic group” and ”hydrophillic group” to characterise those two groups. However, one must note that all PAHs are hydrophobic. This separation hence separates the most hydrophobic from the least – yet – still - hydrophobic PAH congeners.”
414-415: This can just as easily (and has been previously) interpreted as a fuel driven change in fire occurrence. In a few sentences you report that PAHs increased with modern human activity driving more fires without an associated increase in rainfall. So why is it that when rainfall is high, it is deposition that drives PAHs and not fire amount, but when rainfall is low it doesn’t matter and PAHs are driven by fire amount. How do you have this both ways?
On the last 1000 cal a BP, the regional context in the Northern of Madagascar change. At this time there is a local source. We see it also because there is change in PAH composition with heavier PAHs. We did not say that precipitation did not help the scavenging of PAH. We would like to said that there is potentially several factors the local sources which emitted PAHs and potentially the precipitation. We will try to review this paragrapher to be more understandable between lines 460 and 465:
“Then, over the last millennium, the PAH signal may also have been significantly influenced by local fire activity, which not mean that precipitation did not improve the efficiency of PAHs scavenging. If precipitation had rise on this period, the PAHs signal could be a convolution of the two signals (local fire and precipitation). With our knowledge it is impossible to deconvolute the two signals, therefore our data did not bring new knowledge about variation of precipitation on the last 1000 cal a BP in Madagascar. “
428-429: I do not agree with this, if anything this speleothem record shows disagreements in the timing of PAH accumulation and local rainfall change: e.g., between 10-6 ka PAHs have a broad decline between 9-7 ka but while precipitation declines at 10.5-9 ka, it is just as high from 8.5-6 ka. If deposition was the main control one would expect a much tighter relationship with the local precipitation that displayed.
We think that firstly the divergence is accrued by the low resolution of our PAH records.
445: Huh? It's elevated. When did you discuss it being reduced during this time?
Sorry, you right its is not ‘reduced’ but ‘elevated”.
448-449: “However,… precipitation.” I don’t think this argument is supported by the data.
Thank you for your two last comments. We have reworked the conclusion in consequence of the change realised in the all manuscript.
“Concentration profiles of PAH stored in sedimentary archive, are usually used to infer palaeofires. In the North of Madagascar, whereas there was no fire activity until 1000 cal a BP, the concentrations in PAH present high values and significant variations over the Holocene, which means they represent a remote signal of fire activities from East Africa, thanks to monsoon winds that are set in motion when the ITCZ is its southern seasonal position. However, the signal of PAH differs from the fire activity signal from Eastern Africa between 8000 and 5500 cal a BP but is similar to the one of precipitation in Madagascar. To explain this pattern, two hypotheses can be highlighted: 1). PAHs originated from specific region of the Eastern Africa where biomass still burned, 2). We argue that variations wet deposition must not be neglected when interpreting pluri-centennial PAHs profiles. Under some conditions which remain to be constrained, PAH could hence be complementary tool in the attempt of reconstructing past hydroclimate fluctuations. “
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AC4: 'Reply on RC2', Emeline Bellet, 28 Sep 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-3726/egusphere-2026-3726-AC4-supplement.pdf
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AC2: 'Reply on RC2', Emeline Bellet, 28 Sep 2026
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General comments
This manuscript presents the results of a scientific research into the use of Polycyclic Aromatic Hydrocarbons (PAHs) as biomarkers of biomass burning, measured in a mountain lake in northern Madagascar throughout the Holocene, and their relationship with regional climatic drivers such as wind and rainfall patterns. This work is relevant to the research field, presenting an interesting approach based on the different chemical characteristics of PAH compounds to improve the estimation of their origin and location, and to determine whether they can be used as a proxy for wildfire signals preserved in environmental archives. Text editing and additional information, where demanded, would be beneficial.
Specific Comments
This manuscript addresses relevant scientific questions within the scope of CP by presenting novel data that supports the use of the concept of physicochemical properties to trace the geographic origin of chemical compounds and the main mechanisms by which they are transported over time.
The scientific hypothesis is clearly outlined, as is the methodology used to test it. However, the analytical methodology for determining PAHs requires further clarification to ensure it is fully understandable and reproducible without consulting the references.
While some sentences and figures require clarification, the results of this study are clearly presented and sufficient to test the stated hypothesis, providing adequate support for the interpretations, particularly given the approach based on the physicochemical properties of PAHs. However, the originality of this work should be better highlighted. Some insights have been presented and a comprehensive understanding based on this data has been achieved. However, the conclusions section needs improvement as it is too condensed.
The references used are adequate for the discussion of this topic. The title is OK. Although it contains all the mandatory elements, the abstract and the rest of the text should be improved in terms of language editing to make them clearer and more fluent. Some terms/words are highlighted in the technical corrections section.
Technical Corrections
I would prefer the terms 'Cal BP' or 'Cal yr BP', as these are more common, but this is just a suggestion.
Lines 57-59: It is missing a reference for this information.
Line 60: Why? Neither the above paragraph nor this text makes it clear why charcoal is limited as a regional wildfire proxy. Please could you improve this explanation?
Line 63: “current observations” - is this related to the 2017 reference? Is there a more recent study on the seasonality of PAH concentrations in the environment?
Line 81: “no CHARCOAL was found”.
Line 120 (Figure 1 Legend): Please complete the legend of Figure A with the winter, summer and annual mean precipitation information shown.
Line 133: Correct to “Fig. 1D”.
Line 134: I suggest the following text correction: “…we USED the 11-metre-LONG sediment cores LM1A and LM1B, taken in 2017 using a Russian PEAT corer (Teixeira et al., 2021).”
Please also include any other information from the sampling methodology described by Teixeira et al. (2021) that is relevant to PAH analysis and interferences, such as sample preservation. Also, please specify which analytical controls were employed to address potential contamination issues arising from the sampling procedures.
Lines 145-147: “Simultaneously, charcoal counts exhibit that fires started to occur, probably not in Montagne d’Ambre, but more likely occurring in the low elevation areas surrounding the mountains.”
Could you please rewrite this sentence to make it clearer?
Line 162: Were the samples spiked with internal standards prior to extraction? If so, which internal standards were added?
Lines 165-170: Please standardise the chemical notation for solutions according to the IUPAC recommendations. For example: 1:1 (v/v); heptane/dichlorometane (98:2, v/v)…
Do you really mean 98/2 v/v? Mostly heptane (4.9 ml), with just a few drops of DCM (100 µl)? Or was a different proportion used for this fraction's eluent? Which fraction is this, F2? Which proportion was used for the 2mL HEP/DCM solution for F2?
It is informed that “If pigment remained in fraction 1, a second separation by SiO2 column chromatography was performed.” How exactly? Is it just for F1, and are the same eluents used?
Please review the methodology information regarding the eluents and their proportions used to recover each fraction of compounds and use standard terms throughout the text.
Lines 171-172: Could you please review this sentence, as it is not clear enough? Could you also provide more information on whether fractions 1 and 2 were evaporated together or separately after being combined? Or were the two extracts analysed for PAHs separately? Was the DMSO removed from the extract prior to injection?
More detailed information on these steps is needed to make them reproducible.
Line 180: Instead of merely citing the reference, I strongly recommend that you provide a brief description of the applied method, highlighting any possible adaptations.
Line 196: Please correct “at at 25ºC”
Line 197: I would be careful using this concept, given that PAHs are not naturally hydrophilic. Instead, I would use the concept of increasing hydrophobicity as described by Garagnon et al. (2024).
Line 197: “solubility coeficient > 10-2 mg.L-1 (N, Ace, Flu, Phe, Ant, Fla and Pyr)”. Please provide the reference for this information, which was used to support this grouping.
Lines 205-206: This is an incomplete sentence. Please review it and provide the full information, including the equation, not just the reference.
Line 235 (Legend of Table 1): I suggest rewriting this sentence, e.g.: "Bold and italic lines represent inverse age, which were not taken into account in the model.”
Line 239 (Legend of Figure 2): I suggest rewriting these sentences, e.g.: "Linear age-depth model of Lake Maudit created using the CLAM package. Red points represent inverse age, which were not considered in the model.”
Line 258: “since 2800 cal a BP” is repeated. Please review this sentence.
Line 271 (Legend of Figure 3): I suggest using the lettering scale (A–D) for these four graphs and including this information in the legend.
Line 282: Please format this reference “(Ana Lúcia C. Lima et al., 2005)” along the text in accordance with the journal's rules.
Line 298: “(Pyr, Flu, Fla, Fig. SM 3)” - Figure 3 shows the distribution of N, Phe, Flu and Fla. It does not show Per or Pyr. Please adapt the figure to show the comparisons mentioned in the text.
Line 307: Please correct to correct to “… few CHARCOAL particles”
Lines 309-310: Where can it be seen/checked? In which figure? It cannot be seen clearly in Fig. 4.
“Particles >160um”? Which results show this? Do you mean the results of Teixeira et al. (2021)? If so, please clarify the size fractionation used.
Line 312: What do you mean by “presently occur”? When?
Lines 312-314: These two sentences are not easy to understand. Could you please rewrite this text to explain it further?
Lines 320-321: “Therefore, the northern region of Madagascar cannot be considered as a source of PAHs”
Which PAHs does this refer to? The pyrogenic ones? Could you please explain this relationship further, given that you pointed out a contrast between charcoal and PAHs above?
Line 322-323: “but this would reflect more remote sources supplying PAHs.”
Supplying all PAHs, or the "hydrophilic" ones?
Line 327: Please correct to “originated”
Line 329: “Where came from PAH during the Early and Mid-Holocene?”
Please review the grammar of this sentence.
Lines 341-342: “Therefore, this implies that although distant, the fire source is not excessively far.”
What does this mean in terms of distance? Is there any study of the atmospheric transportation distances of PAHs that can be cited here?
Line 367: Please correct to “In a different site” and clarify which one is it.
Line 371: Please correct to “Lake Masoko recorded high value of charcoal accumulation…”
Lines 375-376: “PAHs likely originate from regional biomass burning, but the variation was not due to fire activity variation.”
Please clarify this information.
Lines 378-383 (Legend of Figure 4):
Is there any data within the blue scale in Figure 4A? Could the scale be adapted to display the values more clearly, as was done in Fig. 4-C?
In the axis titles of Figures 4-D and 4-E, please indicate the locations and references of the charcoal data.
The legend is incoherent with Figure 4D. Please check it.
Line 443-452: I recommend rewriting the conclusion to make it clearer and address/clarify the following points:
“which are molecules produced by incomplete combustion” - that CAN be produced.” As mentioned in this manuscript, some PAHs can also have a biogenic origin.
“However, the signal of PAH differs from the fire activity signal” – fire activity of where?
“These results challenge the direct interpretation of PAHs in terms of fire events and dry periods”. Could you please clarify here the challenges you mention in terms of dry periods?
Lines 501-502: Please complete this reference
Lines 503-504: Please inform this reference’s DOI
Lines 596-599: Please inform this reference’s DOI
Lines 611-612: Please complete this reference
Line 643: DOI not found. Please check it.