the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Recent significant decline of strong carbon peat accumulation rates in tropical Andes related to climate change and glacier retreat
- 1Universidad Nacional Agraria La Molina (UNALM), Lima, 15012, Peru
- 2Institut de Recherche pour le Développement (IRD), Géosciences Environnement Toulouse (GET), UMR 5563, Toulouse, France
- 3Institut de Recherche pour le Développement (IRD), LOCEAN/IPSL-Sorbonne Université, Bondy, 93141, France
- 4Centro de Competencia del Agua (CCA), Programa Agua–Andes, Lima, 15086, Peru
- 5Université Grenoble Alpes, IRD, CNRS, IGE–UMR 5001, Grenoble, France
- 1Universidad Nacional Agraria La Molina (UNALM), Lima, 15012, Peru
- 2Institut de Recherche pour le Développement (IRD), Géosciences Environnement Toulouse (GET), UMR 5563, Toulouse, France
- 3Institut de Recherche pour le Développement (IRD), LOCEAN/IPSL-Sorbonne Université, Bondy, 93141, France
- 4Centro de Competencia del Agua (CCA), Programa Agua–Andes, Lima, 15086, Peru
- 5Université Grenoble Alpes, IRD, CNRS, IGE–UMR 5001, Grenoble, France
Abstract. Climate change has altered precipitation and temperature patterns in the tropical Andes. As a result, tropical glaciers have retreated significantly over the past 50 years and have even disappeared in some areas. Andean peatlands, one of the most important Andean carbon reservoirs, also seem to be affected by these climate changes, since glaciers have been recognized as one of their vital water sources. Here, we point out the important role of Andean peatlands on carbon accumulation rates (CAR), one of the highest in the world, and the impact of climate on carbon storage over the last 65 years, using four peat cores. The peat cores were radiocarbon-dated and ages were post-bomb calibrated and chronological models indicated basal ages (30 cm depth) ranging from 1957 to 1972 CE, where accumulation rates reached up 1.7 cm yr−1. For both peatlands, carbon accumulation rates are high (mean of 470 and 220 g C m−2 yr−1 at APA 1 and APA 2 sites, respectively) and can reach up to 1010 g C m−2 yr−1. Distichia muscoides is the dominant species in the Peruvian Central Andes peatlands and the high CAR, among other factors, is a characteristic of this species. Our results point out that a marked decrease of CAR after the early 1980s at both peatlands is likely related to an increase in annual temperature, which is responsible for the retreat of glaciers. We use a new high-resolution proxy (Skrzypek et al., 2011) based on the δ13C of Distichia along the cores to evaluate the temperature variability at the site. We observed a general trend of increase in the reconstructed temperature from both studied peatlands from 1.9 to 2 ºC for the period 1970–2015 CE. Comparison with air temperature data from the NCEP-NCAR reanalysis for the higher resolution cores shows a good relationship and an increase of 2.15 °C for the same period. Temperature increase may directly affect CAR by an increase in organic matter degradation rates. The decrease in CAR during the period of study may also be due to a decrease in melt water inflow generated by the retreat of glaciers that have almost disappeared today in the catchments as a consequence of regional warming. Our findings emphasize that marked changes in carbon accumulation rates demonstrate the high ecological sensitivity of tropical high-Andean peatlands, endangering their outstanding role in the regional (and even global) C cycle as large C sinks that contribute to the mitigation of global climate change.
- Preprint
(1104 KB) -
Supplement
(107 KB) - BibTeX
- EndNote
Romina Llanos et al.
Status: final response (author comments only)
-
RC1: 'Comment on bg-2022-47', Anonymous Referee #1, 10 Mar 2022
General comments
Llanos et al. present a record from a sedimentary core from the Apacheta region in the central Peruvian Andes. Four peat cores from high-Andean Distichia cushion-plant peatlands were radiocarbon-dated and C accumulation rates, TOC and C stable isotope composition are presented for the four 29-35 cm long peat cores. Based on the presumption by Skrzypek et al. (2011), who interpreted growing season temperature as a determining factor for δ13C in a high-Andean Distichia peatland in Peru, the authors reconstruct temperature from both studied peatlands for the period 1970-2015 CE.
The presented research would potentially represent an important contribution of paleodata in a region, where paleoenvironmental data is still very scarce. However, the presentation and interpretation of the data need significant improvement, and currently, the presented research does not represent a sound and elaborate work. Overall presentation, methodological concept, and data interpretation are not ready yet for publication. As the presented research work needs significant improvement on several topics, I do not recommend it for publication in Biogeosciences.
Specific comments
1. The exact coordinates of the investigated sites are missing. However, the sites can somewhat be located with help of Figure 1. By checking the "sub-catchments", I absolutely do not agree with the presented "sub-catchment" area of 130 km² for APA 1, which is situated in a kar valley of Nevado Portuguesa (aka Chicllarazo or Apacheta) and has no connection to the yellow-shaded area. However, without exact coordinates, this remains unclear.
2. The "study area" chapter lacks important information. Distichia muscoides is the only plant species mentioned. In the central Peruvian Andes, cushion-plant peatlands are often dominated by Distichia, but accompanied by other species, which - depending on site factors - might dominate specific areas of the peatlands (other cushion-formers like Plantago rigida, Zameioscirpus muticus, Phylloscirpus deserticola or reed grasses like Deyeuxia/Calamagrostis) or grow into the Distichia cushions. Further, these peatlands are usually characterized by shallow pools, which form between the cushions (Coronel et al. 2004). No information is given on that, nor on the topography of the peatland, nor on the influence of grazing or other impact by the local population. Further, no information is provided on the possible influence of geothermal springs, which might contribute to the springwater. The presented study did not conduct analysis of the peatlands` spring and surface water (at least pH and conductivity), which is a prerequisite for any peatland study. Noble & McKee (1982) mention geothermal springs for the Nevado Portuguesa area. Can the influence of geothermal water be excluded?
3. The authors point out the relation of carbon peat accumulation rates and glacier retreat, since glaciers have been recognized as "the main water source" for high-Andean peatlands. Line 266 says: "The subsequent reduction in peat growth rates could have been due in part to the decrease in the rate of water inflow from nearby glaciers to peatlands after their complete disappearance." In point of fact, I cannot detect glaciers within the upper catchments of both investigated peatland sites. Many peatlands in the tropical Andes are fed by glacial meltwater. However, the majority of high-Andean peatlands is fed by permafrost (Ruthsatz et al. 2020), and water originates from high-elevation cryogenic soils and glaciolithic deposits (Trombotto 2000). This is the case for the two investigated peatlands (as far as I presume from Figure 1 and Google Earth). Therefore, the whole climate change-related argumentation should not solely focus on glaciers, but also on the very important role of permafrost.
4. For radiocarbon dates, the authors use the SH calibration dataset. Due to a significant influx of Northern Hemisphere air masses and moisture over a substantial part of the continent, especially the tropical central Andes, during the South American Summer Monsoon (SASM), Marsh et al. (2018) recommend using a mixed calibration curve. During the austral spring and summer seasons, the south shift in the ITCZ brings atmospheric CO2 from the Northern Hemisphere to the Andes, which is taken up by the vegetation during the growing season (Schittek et al. 2016). How do the authors explain the use of the SH calibration set?
5. The authors do not pay attention to the effect that bulk peat stable carbon isotopes may reflect the dilution of atmospheric δ13CO2 and the effects of early stage kinetic fractionation during diagenesis (Esmeijer-Liu et al. 2012) or other factors like dust influx or vegetational changes. For a scientifically sound reconstruction of paleotemperatures, this has to be taken into account.
6. A scientifically sound "high-resolution" record concerning the past 50 years would require age control by applying the Pb/Cs dating method rather than applying CaliBomb upon radiocarbon dating for only 3 samples per core.
7. The stable isotope measurement method is described in only one sentence. How about the use of calibrated laboratory standards and what is the analytical uncertainty?
line 43: change "High-altitude" into "High-elevation"
line 46: "Their most important ecological role..." This sentence should be reworked. First, it should not be evaluated what is the most important ecological role of peatlands. Second, tropical peatlands do not control decomposition processes in the soil!!!
lines 52-75: The focus should be rather on permafrost than on glaciers as the investigated peatlands seemingly are not fed by glacial meltwater.
line 81: Vegetation is not dominated by Distichia muscoides! (What is meant by "vegetation"??? Peatland? Steppe?). This is only the case for peatland areas with permanent saturation. The cited literature in this paragraph has no relation to the Apacheta region.
line 90: "The climate of the Apacheta peatlands..." I do not agree with this statement. First, it should be "Apacheta region", second, there definitely is a rainy and a dry season, as this area is affected by the South American summer monsoon.
line 199: Chimner
line 200: Oxychloe
line 200: Azorella is typical for high-Andean steppe vegetation and never grows inside a peatland.
line 250: "...which are typically associated with glacial dynamics..." I do not agree. Distichia muscoides is associated to permanent saturation above 4000 m asl. Its distribution is not restricted to the presence of glaciers.
line 292: "good relationship" What does that mean? Did you conduct any correlation analysis?
Figure 8: The reconstructed air temperatures of the two presented cores, in some parts, differ significantly, although the two coring sites are very close to each other. How do the authors explain this? How about the other two retrieved cores? Is there any results for them?
The following publications are mentioned in the manuscript, but not listed in the references:
Salvador et al. 2014, Huaman et al. 2020, Thompson et al. 2006, Kalnay et al. 1996, Hribljan et al. 2015, Hribljan et al. 2016, Drexler et al. 2015, Cooper et al. 2010, Lourencato et al. 2017, Roa-Garcia et al. 2016, Lähteenoja et al. 2013, Hapsari et al. 2017, Craft & Richardson 1993, Tolonen & Turunen 1996, Turunen et al. 2001, Chimner & Cooper 2003, Turunen et al. 2004, Beilman et al. 2009, Van Bellen et al. 2011, Nakatsubo et al. 2014, Chimner et al. 2016, Bao et al. 2010, Mitsch & Gosselink 2007References:
Coronel J.S., Declerck S., Maldonado M., Ollevier, F. & Brendonck L. (2004): Temporary shallow poolsin high-Andes bofedal peatlands: a limnological characterization at different spatial scales. Archives des Sciences 57: 85-96.Noble D.C. & McKee E.H. (1982): Nevado Portugueza volcanic center, central Peru; a Pliocene central volcano-collapse caldera complex with associated silver mineralization. Economic Geology 77(8): 1893-1900.
Ruthsatz B., Schittek K. & Backes B. (2020): The vegetation of cushion peatlands in the Argentine Andes and changes in their floristic composition across a latitudinal gradient from 39°S to 22°S. Phytocoenologia 50(3): 249-278.
Trombotto, D. (2000): Survey of cryogenic processes, periglacial forms and permafrost conditions in South America. Revista do Instituto Geológico 21: 33–55.
Marsh E.J., Bruno M.C., Fritz S.C., Baker P, Capriles J.M. & Hastorf C.A. (2018): IntCal, SHCal, or a Mixed Curve? Choosing a 14C Calibration Curve for Archaeological and Paleoenvironmental Records from Tropical South America. Radiocarbon 60(3): 925-940.
Schittek, K., Kock, S.T., Lücke, A., Hense, J., Ohlendorf, C., Kulemeyer, J.J., Lupo, L.C. & Schäbitz, F. 2016. A high-altitude peatland record of environmental changes in the NW Argentine Andes (24°S) over the last 2100 years. Climate of the Past 12: 1165–1180.
Esmeijer-Liu A.J., Kürschner W.M., Lotter A.F., Verhoeven J.T.A. & Goslar T. (2012): Stable carbon and nitrogen isotopes in a peat profile are influenced by early stage diagenesis and changes in atmospheric CO2 and N deposition. Water Air Soil Pollut 223: 2007-2022.
-
RC2: 'Comment on bg-2022-47', Anonymous Referee #2, 14 Mar 2022
Dear Editor,
Now I can inform you about the paper titled “Recent significant decline of strong carbon peat accumulation rates in the tropical Andes related to climate change and glacier retreat” by Romina Llanos et al.
In this work, four-peat cores from high-Andean Distichia cushion-plant peatlands close to tropical glacial were radiocarbon-dated to estimate the C accumulation rates. The paper would potentially contribute to paleoenvironmental data since they are scarce. However, the data interpretation is highly speculative. For this reason and those explained below, I suggest rejecting the manuscript.
This work does not present hypotheses: The authors state that the retreat of the glaciers could have affected the rate of C accumulation due to temperature change from the 1970s, but this effect could have impacted both sites where the carbon accumulate were lower in the southern sites than the northern ones (only 6 km away and similar elevation, nothing is said about how far or glacial description). As the authors state, the increase in temperature could have impacted the primary production rates and decomposition rates. However, neither of these were measured; therefore, it is difficult to sustain that the temperature change was the primary driver because both sites received a similar impact (Figure 8 shows a similar average), and other factors such as topography and drainage conditions, other potential factors mentioned were not measured either or described properly. In general, this paper is highly speculative, and it lacks rugosity with many imprecise sentences and often confusing ones (see below).
Other important and minor details
Abstract
L.15-17 “…Here, we point out the important role of Andean peatlands on carbon accumulation rates (CAR), one of the highest in the world, and the impact of climate on carbon storage over the last 65 years, using four peat cores”. From the sentence above it is not clear what is the highest in the world, the Andean peatlands in general, or your study using four-peat cores?
- 19 “For both peatlands”: Never mention before the two peatlands sites.
- 25 Where did depth accumulation rates reach up to? What is CE?
- L.20 Annual mean temperature cannot be responsible; only humans are responsible for something.
- L.25 The authors indicate a decrease in CAR during the study period may be due to a decrease in meltwater by the retreat of the glaciers and the increase in temperature (the last tested); however, an increase in temperature is not the only factor even when you do not mention if there was a type of control to confirm your findings. For comparison you have to be sure that the primary productivity was similar 50-60 years ago.
Introduction
- 38 say: …researches, …must say: researches, however,..
- L.76-103 move this section to M&M. The authors need to clearly describe the differences between APA-1 and APA-2 in the results section, as the calibrated age from APA-1 and APA-2 are compared.
M&M
I generally miss the statistical analysis for setting the differences of CAR and depths.
- L.105 says: between 29 and 35 cm-long, it must say: intervals layers between 2 and 31 cm depth.
- L.105-107 The authors need to clarify how they named the samples in Table 1. In M&M, there is no clear description.
- L. 114 says: accelerator mass spectroscopy, it must say: accelerator mass spectrometry. This mistake comes from another article, Xing et al. (2015) that used the same terminology.
- L. 127 says C stable isotope. It must say. The natural abundance of stable isotope…
- L. 131-132 Even though you are citing a source, please give the equation and units of each variable. How were C accumulation rates calculated? It is not straightforward and familiar for all readers. By the way, Lähteenoja et al., 2009 and Cooper et al., 2015 are not listed in the reference.
- L.133 says: strong. It must say: significant and positive (or negative) …
- L.136-137 says: …can be used to estimate relative paleotemperature changes recorded in Andean Distichia peat, as they mentioned. It must say: can be used to estimate relative paleotemperature changes recorded in Andean Distichia peat during the growth season (See Skrzypek et al. 2011).
- L. 138-139 Please expand the explanation about the resolution used because I understand that NCP-NCAR uses 5ºxº5 pixel. I know you cite Kalnay et al., 1996; however, the last reference is not in the list of references.
Results
- 146-147 The authors say “…an abrupt change occurred at the end of the 1970s when the rates visibly decreased”… Compared with? APA-2 ? I see such abrupt change from Fig 2 if I only compare APA-2 with APA-1.
- L161. “Mean TOC content…” Figure 3: Neither the text tells us if these results average the three depths or only the upper part? The authors refer to supplementary information to prompt the reader to seek information, but this must be carried over to the main text.
- L.174 The authors say, “…CAR varied depending on age and elevation” however, the elevation of these sites is similar (see sites description).
- L. 184. It is hard to see differences without statistical analysis. The variability is so high.
- L193. I do not see the difference for APA-2, even when it was the site that present lower CAR.
Discussion
- L.197 The authors introduce Fig 6 for tropical versus boreal and temperate climate; however tropical high latitude presents an enormous error bar, invalidating the comparison. Please remove this Figure from the Discussion.
- L. 234-235 “…The author says: ...differences found in CAR (Fig. 4) ...were related to the different drainage area surfaces, much more prominent for APA-1 than for APA-2. These differences must be described in the site descriptions first and later discussed.
- L 237. Again other differences that were not described “…specific topographic factors,...”
- L.239-240 “…Although there is a similar downward trend in the CAR at both sites after the early 1980s,..” I do not see the difference in APA-1 in Fig. 2.
- L. 256. Move Fig. 7 to the results section.
- L.255-260 What about photosynthesis. The increase in CO2 must have a consequence?
- L.280-285. Ok, here photosynthesis is discussed.
- L.283 “…The strong gradients in δ13C…” Insist I do not see this gradient in APA-2 having a similar temperature.
- 286 Figure 8 should be the first figure that the authors must show in the result section.
- L. 292 Say: “showed a good relationship especially in trends”. It must say: showed a good relationship”
- L. 291-294 “…this comparison is difficult because the NCEP data … because we do not know precisely what time period each peat sample corresponds to”, this sentence is not clear.
- L. 296 “between 1.9 and 2ºC” is different than “from 1.9 and 2ºC” what do you mean?
Conclusions
- L 307-311 Sentences are more summary than conclusions.
- L. 314-316. “…This decline in C accumulation was mainly related to the temperature rise which increases the organic matter degradation rate…”
The lower CAR probably comes from a lower primary biomass production in APA-2, which was not measured neither discussed. This may have shed light on the input, prevented speculation such as high decomposition rate, and reduced water supply from glacier retreats. The hypothesis that the temperature causes the differences been CARs in my view has not been demonstrated.
-
RC3: 'Comment on bg-2022-47', Anonymous Referee #3, 14 Mar 2022
The authors present an interesting study on the impact of climate change on Andean peatlands carbon storage. Given the importance of peatlands for the global carbon cycle and climate, I believe this paper is of interest to the readership of this journal. Although the methodology is not particularly novel, the Andean peatlands appear poorly studied (after a quick search on web of science) and any good evidence of climate change impact on this ecosystem woudl be worth being published.
I have some major comments on the methodology and interpretation of the data that led to certain conclusions and some minor comments to help improve the manuscript overall.
- I have some concerns about the derivation of accumulation rates and carbon accumulation rates and the logic behind these estimations. First, how is the accumulation rate obtained? This is not presented. Second, why is the CAR computed directly from the accumulation rate? Is the assumption behind this step that carbon moves only top to bottom? I am not able to determine because this methodology is only briefly mentioned here. But if this is the case, what about carbon released from the roots? Could not plant release carbon directly at depth as root exudates? We just need more details and discussion of the assumptions to better evaluate conclusions originating from this approach.
- The authors somewhat try to infer the evolution of soil carbon over time as a result of the balance between inputs (from plants) and outputs (decomposition). Is there any estimate of how plant productivity changed over time? Although only from year 2000, MODIS from NASA could help.
- Most importantly, I believe the authors should considerably improve their discussion of the methodology, give more context about these peatlands, and elaborate more on their research question.
Minor comments:
- There are some issues with the abstract. First, in line 16 the authors introduce carbon accumulation rates (CAR), but then the following line they quantify accumulation rates. From reading the rest of the paper these two quantities are different and have different units. From the abstract it seems they are the same quantity, and it is measured in cm per year. Second, there is no reason to mention APA1 and APA2 here, because a reader does not know what they are at this point. Third, the sentence in lines 20-23 on Distichia muscoides does not seem to fit here. This seems a preliminary information that could be mentioned earlier, if necessary. In summary, I would simplify the abstract and keep only information and conclusions that are needed to invite a reader to look at the entire paper.
- Give at least a brief description of the age-depth model.
- Rather than just a simple map, Figure 1 could be used to introduce also trends in temperature and other relevant preliminary information about the sites (e.g., what is presented in fig. 7).
- Line 174. replace “that” with “than”.
- Line 242. Maybe topographic “location” is better than “conditions”.
- Lines 276-285. Could you rephrase this whole paragraph?
-
RC4: 'Comment on bg-2022-47', Anonymous Referee #4, 01 Apr 2022
The authors use 4 short peat cores from 2 high-elevation Peruvian peatlands to discuss recent changes in carbon accumulation rates (CARs). They found very high apparent rates of carbon accumulation at these sites. They document a decrease in CAR after 1980 that could be caused by an increase in annual temperature; they corroborate this hypothesis with d13C values from the peat cores. The authors assume that d13C values are proxies for temperature (this assumption comes from a different article). Overall, this is an interesting study that could be appropriate for CofP readership, but I am afraid it is not ready for publication. I have numerous methodological issues (some may be flaws), which are described below. In particular, the CAR calculations may not represent true recent changes in carbon dynamics. Likewise, I have serious doubt about the application of the temperature transfer function to the d13C of bulk (?) peat. I hope the comments below are of use to the authors, who should definitely review their study and submit at a later time.
Idea: It would be interesting to read about why you think these young peat deposits started developing less than 100 years ago -- could make for a good discussion of the article.
GENERAL COMMENTS:
Study area: I would have liked to read more about the hydrology of the area, its vegetation, whether it is pristine or impacted by local communities (and animals), etc. Why did you choose those 2 sites should also be covered, as well as brief descriptions of those 2 sites (including the coring sites themselves). As of now, this section lacks important information.
Methods: lots of important information is missing (see the list below).
Results: (1) the trends in CAR that "slow down" in the early 1980s might be due to an autogenic process: the young peat has not decomposed and compacted yet, making TOC values smaller than the older peat. This would potentially yield lower CARs... (2) the changes in d13C are not considering the Suess effect. Other factors impacting d13C should also be tested/discussed, including hydrological changes.
SPECIFIC COMMENTS:
Abstract:
lines 14-15: "...since glaciers have been recognized as one of their vital water sources" -- this is true for some Andean peatlands, but certainly not for MANY of them. This statement is therefore too general and misleading.
line 23: a "new" proxy... the reference you are using is over 10 years old! not so "new" (and they were not the first ones to use it either...)
Introduction:
line 35: This statement about "all carbon in the atmosphere" is incorrect!! "The amount of C stored in peatlands is similar to the total C stocks in all living biomass or in the atmosphere"
line 68: what are you referring to here? "between 500 and 700m in length"
line 72: this is not a "new" method!!
Study Area
line 77 / Figure 1: I'm a bit surprised by your delienation of the watersheds; I'm not familiar with this region, but why is watershed 1 so large and watershed 2 so small? Is watershed 2 in fact part of watershed 1? I don't understand why you are reporting the size of the watersheds...
Methods
line 105: why are the cores shorter than the PVC tubes? Are the peat deposits only 29 to 35 deep? If so, you need to mention this important "detail".
line 110-113: please add references to the methods you describe.
line 120: why not use a Bayesian approach? It seems like the standard in paleoecological studies these days. Bacon can accomodate for your postbomb dates.
line 129: by convention, you must report against which international standard your d13C values were calibrated against! (VPDB?). Also, and perhaps more importantly, how did you sample and prepare for d13C measurements? Did you measure the bulk peat, the Distichia leaves, or something else? Did you extract the cellulose or not? What weight did you use in the lab? A lot of information missing here... that would hinder replication of your study.
line 131: you should use organic matter density (rather than dry bulk density) to truly estimate CAR... You can do it since you have OM% from the LOI measurements...
lines 134-135: you need to explain the mechanism that links d13C with temperature... If I remember the Skrzypek study, they used an elevational gradient to build their relationship, which means that temperature may NOT be the main factor, but rather changes in pressure...
lines 135-136: this sentence does not make sense to me; what do you mean? "This value was similar to the previously reported range for other species (included Sphagnum peat: -0.5 to -0.6‰/°C)"
line 139: why did you use 600 mb in this case? Are there known limitations/issues with using the NCEP/NCAR reanalysis in the high Andes that should be documented?
Results:
Table 1: you say that you report "2 sigmas", but clearly you do not. Instead, you only report the calibrated age - it's unclear if this is the mean, median, or most probable age provided by Clam. Since those are post-bomb dates, it would be useful to know the most plausible age ranges (on either sides of the postbomb calibration curve).
Figure 2: I cannot tell which dates (and error bars) belong to which cores! would it be possible to have 4 panels (one for each core)? It could go in the supplementary file...
lines 163-165: you say that "there was a general upward trend in TOC content from the peat basal depth of the cores from both studied peatlands to approximately 13 cm (the early 1980s) and then the TOC values decreased to the top of the cores (2015 CE)". This is likely because the uppermost samples are "fresher", being that they have not undergone decomposition and compaction. This is likely why your recent CARs are lower than your older CARS... In other words, this could all be an autogenic signal that has nothing to do with a temperature change.
line 174: mean CAR were higher at APA1 than at APA2 - probably because APA1 has high bulk density?! It would be worth to calculate organic matter density for a fairer comparison of those sites.
line 189: did you consider the Suess effect at your sites? It is expected that d13C become more negative over time because of fossil fuels mixing in the global atmosphere... "At both peatlands, there was a general trend to more negative δ13C values from the basal depth to the top of the cores". Getting rid of the Suess effect would be very useful. Then, I see that your 2 cores tell different stories: one of them (the red line on Fig 5) would show increasing d13C values vs. the blue curve would show a decreasing d13C trend. As mentioned in my intro, I am not convinced that these are temperature records. These could relate to hydrological changes: could it be that one site is becoming wetter )blue line) vs the other one is becoming drier (red line)? Please look into the literature that discusses stomatal closure.
Discussion:
lines ~ 200: you should read the paper by Benfield and Yu, Distichia deposits from Columbia were analyzed... You'll see that they also document very high recent CARs.
lines 195-205: you cannot compare your core tops with Holocene-aged cores and say that your cores have greater CARs! This is obvious: short peat hasn't decomposed much, especially compared to old sites... Figure 6 is a misrepresentation and flawed way to compare these data. For a fairer discussion, only look at recent CARs from around the world... There are plenty of data to play with!
I did not comment on the rest of the discussion, as I question the validity of the results.
Romina Llanos et al.
Romina Llanos et al.
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 369 | 121 | 16 | 506 | 29 | 9 | 6 |
- HTML: 369
- PDF: 121
- XML: 16
- Total: 506
- Supplement: 29
- BibTeX: 9
- EndNote: 6
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
