the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
MOdern River archivEs of Particulate Organic Carbon: MOREPOC
- Final revised paper (published on 28 Oct 2022)
- Preprint (discussion started on 27 Jul 2022)
RC1: 'Review of essd-2022-161', Anonymous Referee #1, 10 Aug 2022
AC1: 'Reply on RC1', Yutian KE, 19 Sep 2022
Dear Reviewer 1,
Thanks for the detailed comments, which really helped to improve the MOREPOC dataset and the manuscript. Please check our reply to the comments below:
We have made several modifications to MOREPOC v1.0, and now version 1.1 is available on Zenodo. Each data entry is an individually collected sample unless several size fractions were reported in the original study.
- Renamed field header. The names of some fields were changed to make them more intuitive, e.g., "riv_na" was changed to "bas-id" to refer to the sampled drainage basin and "bas_na" was changed to "riv_id" to refer the name of the sampled river. “RCA” was changed to “age_14C”, and “cn_mar” and “as_mar” were changed to “cn_ratio” and “alsi_ratio”, respectively.
- Added extra fields. The “country” column was created to separate it from “riv_id”; “perc_poc_1sd”, ”d13C_1sd”, and ” D14C_1sd” columns were added to provide analytical uncertainties for POC content, δ13C and Δ14C data, respectively.
- Corrections made. There were some wrong entries about the country where samples were collected in the “country” column, which has been corrected. The content of the “time_m” column was changed from strings to numeric. In addition, we removed brackets, points, commas or empty spaces in the data fields. Coordinates were carefully checked through, and wrong entries were corrected. The reversed latitude and longitude of the one sample (Amazon River at Obidos, 2005) were corrected. Only the average is now presented in Figure 1 if several samples exist from a given location.
- Added data. We incorporated data from some recently published or missed articles, e.g., Menges et al., 2020 and Holmes et al., 2022. Besides, we looked through all references from MOREPOC v1.1 to add analytical uncertainties if available. However, most papers do not report uncertainties. We also added more sampling date information, such as those from Bouchez et al., (2014). Now there are only 3 samples without associated dates. However, some data entries only have the sampling date information as a period (year) because there is no specific date reported for each data entry, such as for a large amount of data from Taiwan rivers (Hilton et al., 2010).
- Reorganized references. References not cited in MOREPOC v1.1 were removed, and newly incorporated references were added.
- Added extra fields. The “para_m” and “para_c” columns were added to clarify the sources of parameters in MOREPOC v1.1. Data entries of some parameters were directly taken from the cited references, while some were obtained through later calculations and conversions.
- Completed information. Some missing information in “filter” and “Note” were added.
Besides, a Readme.txt was provided with the MOREPOC v1.1 dataset, also available on Zenodo.
- Manuscript text
Line 7-8: Rephrased.
Line 31: Corrected.
Line 45: We agree that SOC in permafrost has a dynamical turnover time subjected to varying climate conditions, especially the current elevation of ambient temperature will accelerate the thawing of permafrost. In the manuscript, we now explain the term "turnover time" following Eglinton et al. (2021), which is the ratio of soil carbon stock to input flux, to make it more proper to discuss the relative long SOC turnover time in permafrost regions.
Line 47: Carvalhais et al. (2014) was removed from the Introduction.
Line 53: Replaced.
Line 66: Rephrased.
Line 81: We agree that “carbonate removal” is more appropriate and is now used to replace “decarbonization” in the manuscript. “acid adopted” means the type of acid used for removing carbonate - this is clarified now.
Lines 134-136: Time is in units of hours and temperature is in units of Celsius degrees. We added this information in the manuscript to explain the parameter in MOREPOC v1.1_RM.
Line 142: Rephrased.
Line 146: Corrected.
Lines 142-154: We agree that the definition of F14C should be in included in the manuscript - the equation was added.
Line 170: Corrected.
Line 259: Good suggestion, we rephrased the expression to “MOREPOC will benefit the scientific community carrying out research on riverine POC sources, transport, and fate, furthermore, helping inform and validate Earth system models to improve the ability to model and understand the global carbon cycle.”
- AC1: 'Reply on RC1', Yutian KE, 19 Sep 2022
RC2: 'Comment on essd-2022-161', Anonymous Referee #2, 16 Aug 2022
Ke and colleagues provide a large (~ 4x the size of previously compiled sets) compilation of published data on riverine particulate organic carbon (POC, incl. isotopic composition and related N content), suspended particulate matter concentrations (SPM),and Al/Si weight ratios of the corresponding sediment. This comprehensible dataset is f good quality and accompanied by a wealth of metadata, such as geographical or methodological information, improving its interpretability and usability of the database. However, uncertainties are commonly reported alongside carbon isotopic values and could be integrated into the database. Clarity and variable naming could also be improved. Otherwise, I have only a few minor comments regarding the database (see PDF).
The descriptive article adequately summarizes database content, structure and patterns within the data. It gives most background information necessary to understand relevance, quality and acquisition of the data. At times the article is written too much in a POC-expert language and misses a few explanations necessary to fully understand the data. More specific comments are attached.
This publication seems timely, relevant and useful to the Earth science community and, generally, researchers interested in riverine and coastal organic matter processes and carbon cycling. The size and high spatial coverage of the set provide a proper statistical basis and will certainly help improving our understanding of terrestrial and marine carbon cycling. Detailed comments on data and article can be found in the attached PDF. After these issues have been addressed, I strongly support publication in Earth System Science Data.
AC2: 'Reply on RC2', Yutian KE, 19 Sep 2022
Dear Reviewer 2,
Thanks for the detailed comments and recommendations. We hope MOREPOC can benefit the Earth Science community, in particular, researchers interested in understanding OC-related Earth surface processes and carbon cycling at different time- and spatial scales. Now the compilation includes more data entries with 265 more radiocarbon activity (Δ14C) values, providing exciting observations.
We provide our reply to your comments below.
- A readme file with information on variables and units was added to the database and is now available on Zenodo too. Equations for parameter definition and conversion were included.
- These variable names were changed to a more intuitive term ("riv_na" to "bas_id", "bas_na" to "riv_id").
- Uncertainties were added for elemental and isotopic carbon values if available. “perc_poc_1sd”, ”d13C_1sd”, and ” D14C_1sd” columns were added to provide analytical uncertainties for POC content, δ13C and Δ14C data, respectively.
- We added extra fields to clarify which variable was given in which paper. The columns “para_m” and “para_c” were added to clarify the sources of parameters in MOREPOC v1.1: data entries of some parameters were directly taken from the cited references, while some were obtained through later calculations and conversions.
- As explained above, we added two columns to clarify the sources of the compiled data.
For references only reporting POC wt.% and concentration, we did use the two parameters to derive SPM concentration. Parameters obtained from this conversion were clarified.
- Format problems: We did not change “modern” to “0”, since some high 14C activity data are because of the influence of the bomb carbon effect. As a consequence, we would like to have users decide how to use these values themselves. However, we changed the field name as suggested. For ‘values’ in data fields, we converted strings to a numeric format, and eliminated the use of brackets, points, commas, or empty spaces.
- Country information is now included in a new column “country”.
L21: We added a sentence on the role of alteration and degradation on fluvial POC goes during transport in terrestrial environment before entering the coastal environment and being buried in the ocean.
L24: We clarified this statement about the composition of biospheric OC. Riverine authigenic POC is now mentioned to partly explain the depleted 13C signals in riverine POC (section 3.1).
L32: We now refer to the global POCbio burial in the ocean, as well as to the oxidation of POCpetro. The terrestrial POCbio burial can be up to around 70 MtC/yr considering an average burial efficiency of 30% to an input of ~110-230 MtC/yr (Blair and Aller, 2012; Burdige, 2005; Galy et al, 2015), while the oxidation of POCpetro in sedimentary rocks can contribute ~40-100 MtC/yr to atmospheric CO2 (Petsch, 2014; Hilton and West, 2020).
L47-48: We highlighted that the input of aged biospheric OC from thawing permafrost is the major reason (Wild et al., 2019; Hilton et al., 2015). Besides, we extended the discussion on permafrost-derived fluvial POC in section 3 (in particular section 3.2) and figures 6 and 7.
L50-51: We agree that sediment dynamics and oxygen availability in marine environments are important factors (Blair and Aller, 2012). However, in this paragraph, we want to discuss how POC can be altered in terrestrial settings before entering the marine environment. We do emphasize the importance of sediment dynamics in the terrestrial environment due to the different tectonic settings.
L54: Reference added. Besides, we also added some clarification on how human activities influence erosion and on the resulting changes in the fluxes of sediments and associated POC.
L61-62: We added a sentence on the improvement of water quality datasets and increasingly sophisticated models of riverine carbon cycling as you suggested.
L65: We added more explanation for D14C and Fm14C in section 2.7.
L79: This is based on non-numeric string detection in value fields, categorical summarization, and extreme numbers detection. We were wrong here to use the term – statistical examinations, so we deleted this expression.
L155: We added explanations on why Al/Si ratio is an important parameter that is included in MOREPOC as follows:
"Lastly, if available, the aluminum-to-silicon mass ratio (Al/Si) is also provided in MOREPOC v1.1. This elemental ratio is an efficient proxy for the particle size of riverine sediment, allowing to characterize the particle size effect of sediments on POC loading in fluvial delivery (Galy et al., 2008b; Bouchez et al., 2011; Hilton et al., 2015). The mineralogy and particle size of sediments are generally not totally independent of each other, coarse particles tend to be quartz-rich (low Al/Si ratios) and fine particles tend to be clay-rich (high Al/Si ratios) (Galy et al., 2008b). POC contents are usually positively correlated with proportions of fine-grained fractions (Mayer, 1994; Galy et al., 2008b; Bouchez et al., 2014)."
L158: We added this information “The MOREPOC database also indicates the lack of study on POC in fluvial systems in high-latitude regions such as the Antarctic and Greenland, as well as in arid regions including Australia or vast areas spanning from northern Africa to middle east Asia (Figure 1).”
L178-179: We added this information: “Around the Qinghai-Tibet Plateau, where most large river systems in eastern and southern Asia share similar high-elevation headwaters, POC is usually characterized by relatively depleted 14C signals due to strong erosion of sedimentary rocks, such as the Ganges-Brahmaputra (Galy et al., 2007) or the Changjiang (Wang et al., 2012; Wang et al., 2019), and to the erosion of soil, pre-aged OC, e.g. the Huanghe (Tao et al., 2015).”
L197: Net primary production does not show any clear relation with 14C in fluvial POC nor with the relative abundance of biospheric OC. It is rather the erosion rate of the catchment which controls the flux of biospheric OC (Galy et al., 2015). We added additional explanations for this trend: “This might reflect the existence of major POC components: 1) for rivers dominated by POCbio, the combined effects of increasing coverage of C4 plants towards tropical regions and the input of pre-aged OCbio from C3-derived OC from degrading permafrost at high latitudes (Cerling et al., 1997; Still et al., 2003); 2) for rivers dominated by POCpetro, for example in mountainous regions, strong erosion of 13C-enriched petrogenic OC (Hilton et al., 2010; Galy et al., 2007). In addition, in-river ("authigenic") POC production can be an important mechanism contributing 13C-depleted and 14C-enriched POC (Longworth et al., 2007; Marwick et al., 2015; Wu et al., 2018).”
Figure 2: We did not add different potential endmembers because we want users to interpret possible sources for fluvial POC.
L211: Potential explanations for this observation were added.
L216: This occurrence was not about carbon loading, we are sorry about the confusion caused. We were talking about the POC flux that is loaded in a specific SPM concentration. It is now clarified in the text.
L219: We added a figure as suggested, providing POC concentration vertical variation in the water column as obtained from depth profiles in large rivers. Selected depth profiles are from the Yukon (Holmes et al., 2022), Mackenzie including Peel and Arctic Red (Hilton et al., 2015), Amazon (Bouchez et al., 2014), and Ganges-Brahmaputra-Meghna systems (Galy et al., 2007, 2008b).
L221: We found this sentence was not correct under certain circumstances, so we reworded it to “Small SPM concentrations (less than 10 mg/L) are generally found in rivers in frozen seasons or rivers draining either high-latitude or tropical areas characterized by low-relief settings, in which POC content is relatively high (Gao et al., 2007; Holmes et al., 2022).”
L244: Good point, we now refer to petrogenic OC mobilization. However, this paragraph is focused on the erosion of sediments and aims to explain the depleted 14C nature of fluvial POC observed in some conditions. As a consequence, the role of oxidation of petrogenic OC is not mentioned in the text.
- AC2: 'Reply on RC2', Yutian KE, 19 Sep 2022
RC3: 'Comment on essd-2022-161', Anonymous Referee #3, 23 Aug 2022
The manuscript Ke et al. presents a new openly-accessible global database of organic carbon (OC), OC isotopes (13C and 14C) and key element ratios (Al/Si) in riverine suspended matter entitled “MOdern River archivEs of Particulate Organic Carbon – MOREPOC”. The database aims to provide data to study OC release, transport and cycling across river-basin systems, which serves the increasingly-important purpose of understating global carbon cycling. The MOREPOC builds on a large number of earlier studies that laid out the ground work and published most of the data that is now curated in this database. Hence, this compilation increases the accessibility and usefulness of already-published work, and harmonizes POC measurements across studies and regions in one easy-understandable data set. Standalone, or along with other data collections from land or ocean, I expect this database to be very useful to facilitate a range of biogeochemical studies and I commend the authors for this effort.
The paper is comprehensible, well-structured and fulfills the purpose of describing the database very well. In their writing, the authors also provide a rough outline of the large-scale differences in fluvial OC concentrations and composition, and provide a short perspective of their interpretations. I only have a few minor comments that are described below, and I recommend publication after the authors have addressed these and the other comments provided by the other reviewers.
Line 26 “radiocarbon-enriched POC”: May not apply to soils, deeper soils are more depleted in radiocarbon
line 27: Similar comment like above, if 14C ages are “multi-millennial” they cannot be enriched
Line 29 “full erosion/sedimentation/exhumation cycle”: If the authors mean rocks would this also include diagenesis and organic carbon maturation processes?
Line 35 “role played by POC”: first, I would rephrase this to “the role of POC in the global carbon cycle”. Second, POC probably plays only a very small role in the global carbon cycle when compared to other fluxes. However, POC provides very valuable information about the global carbon cycle as it provides an integrated signal of biogeochemical processes over large drainage-basin areas.
Introduction: A clear definition of POC, and how it distinguishes from DOC and other OC phases, should be included in my opinion.
Line 84: It is unclear what the authors mean by “projected in a Geographic Coordinate System”. Do the authors mean that the data entries have coordinates according to this coordinate system? Or were the coordinates converted (and re-projected) from one to another coordinate system?
Section 2.4: This is all good information but I am missing a description about the sampling location along the course of the river (e.g. river mouth, headwater, center of the river, …). Is this information somehow included in the database (e.g. via the coordinates) or can the authors describe where POC usually is sampled in a river?
Line 121: “mesh size” instead of “porosity”?
Line 172: This value is for C3 vegetation only – what about C4 plants?
General 3.1: Could 13C values also be affected by degradation of POC during fluvial transport, and thus affect the isotopic source signal? Some of the values (e.g. <-30‰) are outside the typical window of plant OC.
Line 257: Have the Al/Si ratios been introduced and described somewhere? I suggest to include a brief description in the introduction. Al/Si ratios and its purpose for river-based investigations may not be obvious to all readers.
AC3: 'Reply on RC3', Yutian KE, 19 Sep 2022
Dear Reviewer 3,
Thanks for your comments, which helped to improve the dataset. MOREPOC v1.1 is now available on Zenodo. This refined version of the database now includes 3,546 SPM data entries, among which 3,053 with POC content, 3,402 with stable carbon isotope (δ13C) values, 2,283 with radiocarbon activity (Δ14C) values, 1,936 with total nitrogen content. This represents a significant update compared to MOREPOC v1.0.
Our replies to your comments are as follows:
Line 26, Line 27: We rephrased this sentence in more appropriate terms: "Land plants, soils, aquatic organisms, and microbes can all contribute radiocarbon-active POCbio to riverine POC, with ages ranging from modern to multi-millennial (Galy et al 2007; Blair et al., 2010; Hilton et al., 2011)".
Line 35: The sentence was rephrased: "The terrestrial POCbio burial can be up to around 70 MtC/yr considering an average burial efficiency of 30% to an input of ~110-230 MtC/yr (Blair and Aller, 2012; Burdige, 2005; Galy et al, 2015), while the oxidation of POCpetro in sedimentary rocks can contribute ~40-100 MtC/yr to atmospheric CO2 (Petsch, 2014; Hilton and West, 2020). These fluxes are comparable to those induced by silicate weathering, carbonate weathering by oxidation of sulfides and volcanism, demonstrating that POC could play an important role in the Earth’s long term carbon cycle (Berner, 2003; Hilton et al., 2014; Petsch, 2014; Galy et al., 2007; Galy and Eglinton, 2011; Hilton and West, 2020)."
Introduction: we added the definition of POC to the text: "POC is the fraction of total organic carbon that remains on a filter of a given mesh size".
Line 84: We were referring to the coordinate system used when digitalizing MOREPOC data entries in a shapefile layer in ArcGIS 10.3, We rephrased this sentence: “The location of samples was digitalized if available, and an associate ArcGIS data layer in shapefile format (see MOREPOC_v1.1.rar) is provided with all points projected in a Geographic Coordinate System using the World Geodetic System 1984 (WGS1984).”
Section 2.4: This is definitely a good point that will need more work in the future. In such a wide compilation, sampling locations correspond to catchments of different scales, i.e., main channels vs. tributaries as well as sub-tributaries. However, it is challenging to summarize the information on whether samples were collected at a river mouth, along the flowing routing or the headwater. Nevertheless, we believe that by looking into the map of MOREPOC sampling points (such as the ArcGIS product provided with MOREPOC) the reader will be able to find that most sampling locations represent integrated signals of biogeochemical processes over a whole catchment.
Line 121: We changed to use mesh size.
Line 172: C3 plants make up over 95% of the global biomass, such that it would be hard to find significant C4 signals in global POC patterns. However we now explain in section 3.1: “However, it can also be observed that POC-rich riverine SPM can be relatively enriched in 13C, with δ13C values larger than -20‰ (Figure 2 and Figure 3). This pattern might indicate the presence of an additional pool of 14C- and 13C-rich POC in the terrestrial environment (Cerling et al., 1997), consisting of modern C4-plants in catchments dominated by grasslands or savannah (e.g., Marwick et al., 2015).”
General 3.1: δ13C values can be affected by the degradation of POC during fluvial transport, as shown by Mayorga et al. (2005), with the preferential degradation of young, labile biospheric OC resulting in an increase of δ13C values. However, such effect typically does not result in δ13C values outside the range of C3 plant OC. We added an explanation for the very 13C-depleted signals in fluvial POC in Section 3.1. Actually, these samples are mostly from permafrost-draining rivers; and secondly, aquatic authigenic OC production can be an important mechanism contributing 13C-depleted and 14C-enriched POC (Longworth et al., 2007; Marwick et al., 2015; Wu et al., 2018).
Line 257: Al/Si was not introduced properly in the previous version of the manuscript. We now explain in section 2.7 why MOREPOC features Al/Si data: “Lastly, if available, the aluminum-to-silicon mass ratio (Al/Si) is also provided in MOREPOC v1.1. This elemental ratio is an efficient proxy for the particle size of riverine sediment, allowing to characterize the grain size effect of sediments on POC loading in fluvial load (Galy et al., 2008b; Bouchez et al., 2011; Hilton et al., 2015). The mineralogy and particle size of sediments are generally related, with coarse particles being quartz-rich (low Al/Si ratios) and fine particles being clay-rich (high Al/Si ratios) (Galy et al., 2008b). POC contents are usually positively related to the fraction of fine grains in the sediment (Mayer, 1994; Galy et al., 2008b; Bouchez et al., 2014).
- AC3: 'Reply on RC3', Yutian KE, 19 Sep 2022
RC4: 'Comment on essd-2022-161', Jin Wang, 27 Aug 2022
In this paper, Ke and co-workers compiled a global database of river POC, including the carbon isotopes, nitrogen content and aluminum-to-silicon ratios. Using this dataset, the authors showed the pattern of stable carbon and radiocarbon isotopic ratios of the global river POC and investigated the controls on the source of the POC. The dataset of this paper is very useful for the studies of river organic carbon and therefore, is useful for global carbon cycle and modelling.
The dataset is generally well formatted, and this paper is well-written. It would be interested a broad biogeochemistry community. I only have some minor questions, which I hope are useful for the authors to strength the paper.
General comment: 1. Grain size is a very important factor controlling the characteristics and fate of the POC. Since the Al/Si ratio has been compiled in the dataset, the paper could have some text to address the controlling of grain size on the concentration, source, and characteristics of the POC.
- the expression of POC concentration is confusing. I see the authors try to separate POC in the unit % and mg/L, using POC content for the unit wt.% and using POC concentration for the unit mg/L. but there is still someplace confusing, e.g., Line 210. Please clarify them in the text.
- please consider adding POC in wt.% versus SPM into Fig. 4 as panel B. I guess there would be a dilution trend.
Specific comments in the text:
Line 47: need to specify that the “riverine POC” is “riverine POCbio”. The conclusion is not right if taken the petrogenic OC in account. For instance, Taiwan rivers have high fraction of petrogenic carbon, thus very old total POC.
Line 78: Why error could be generated during the compilation? I guess some papers only show data on the figure, how did you convert them to values?
Line 129: There is another decarbonization method that has been used in some papers. Carbonate is in-situ removed by adding liquid HCl in silver capsule, and then oven-dried (Menges et al., 2020, GCA). Also, I found this paper is missed in the data compilation.
Line 201-205: The argument should be careful here. First, I don’t see a very clear trend. Second, the δ13C and Δ14C of the POC is generally controlled by the fraction of petrogenic versus biospheric POC in the global rivers (Fig. 2). Therefore, the high or low δ13C and Δ14C are more related to the fraction of different endmembers (including the C3, rock and in situ production beside C4 plants). I found that the Taiwan rivers and Congo rivers both have high δ13C, but the reason is different, the former is because of high contribution from rock.
Line 220: reference Hilton et al. (2008) studied the impact of typhoon on the POC source and flux. Please consider adding the reference Wang et al. (2015, Geology) or Firth et al. (2018, Nature Geoscience) for referring to the impact of earthquake.
Line 222: This sentence may be not correct. Taiwan, Amazon and Ganges are tropical rivers, but are very high in SPM and the POC content is not high in Taiwan either.
Reference: some references are missing, e.g., Wang et al., 2012, Wang et al., 2019.
AC4: 'Reply on RC4', Yutian KE, 19 Sep 2022
Dear Dr. Jin Wang,
Thanks for the comments. We have revised the manuscript accordingly.
MOREPOC v1.1 is an updated version of MOREPOC v1.0, both available on Zenodo. The number of data entries increases to an amount of 3,546 during revision, among which 3,053 with POC content, 3,402 with stable carbon isotope (δ13C) values, 2,283 with radiocarbon activity (Δ14C) values, 1,936 with total nitrogen content.
Our replies to your comments are as follows:
- We realized that there was only a poor introduction to the interest of the Al/Si ratio in the context of POC studies, a parameter included in MOREPOC v1.1. We added to section 2.7: “Lastly, if available, the aluminum-to-silicon mass ratio (Al/Si) is also provided in MOREPOC v1.0 1. This elemental ratio is an efficient proxy for the particle size of riverine sediment, allowing to characterize the particle size effect of sediments on POC loading in fluvial delivery (Galy et al., 2008b; Bouchez et al., 2011; Hilton et al., 2015). The mineralogy and particle size of sediments are generally related, with coarse particles being quartz-rich (low Al/Si ratios) and fine particles being clay-rich (high Al/Si ratios) (Galy et al., 2008b). POC contents are usually positively related to the fraction of fine grains in the sediment (Mayer, 1994; Galy et al., 2008b; Bouchez et al., 2014).”
- This confusion has been resolved in the revised manuscript: in Line 210, we changed the term "POC concentration" to "POC content".
- We added a color bar (for POC wt.%) in Figure. 4 to indicate the dilution of organic carbon by inorganic materials. The constant-POC contour lines drawn in the figure also provide the same information.
Specific comments in the text:
- Line 47: We changed to “riverine POCbio” in the text.
- Line 78: In some references, data tables were indeed images, such that we had to use automatic conversion tools to transfer image data into tables. However, this may result in some numbers being converted into letters, which we had to carefully check. We should have not taken any data from figures that need to use Digitalizer to take the approximate number, we sent emails to corresponding authors to inquire data.
- Line 129: Reference to this carbonate removal method was added to the manuscript, although it seems more common in soil OC studies than riverine POC studies. We also added the data from Menges et al. (2020) to MOREPOC v1.1 (section 2.6).
- Line 201-205: We provided extra explanations to strengthen the statement: “This might reflect the major POC components: 1) dominated by POCbio, the combined effects of increasing coverage of C4 plants in tropical regions and the input of pre-aged OCbio of C3 plants from degrading permafrost at high latitude (Cerling et al., 1997; Still et al., 2003); 2) dominated by POCpetro, rivers in mountainous regions tend to erode 13C-enrich petrogenic OC (Hilton et al., 2010; Galy et al., 2007).”
- Line 220: We added the suggested references.
- Line 222: We realized that there was a problem with this sentence, which we reworded to “Small SPM concentrations (less than 10 mg/L) are generally found in rivers during cold seasons, or in rivers draining either high-latitude or tropical areas characterized by low-relief settings, in which POC content is relatively high (Gao et al., 2007; Holmes et al., 2022).”
- Missing references were added to the Reference section.
Peer review completion
- Full-text XML
This dataset is a comprehensive inventory of TOC, d13C, F14C, C:N ratios, Al:Si ratios, and important methods related metadata for particulate organic carbon collected and analyzed from rivers around the world. This builds significantly upon previously compiled datasets, which have an order of magnitude fewer datapoints that this new dataset submitted by Ke and colleagues. The publication of this dataset is timely, as the number of studies measuring the geochemistry of fluvial POC has increased over the past decade, and more studies are adopting the dual isotope measurement approach. I am excited about the future studies this dataset will enable.
This dataset seems to be thorough with respect to including all available published data and the dataset includes the relevant parameters and metadata needed to understand how the data were collected. However, there are some issues with the dataset, particularly with respect to reporting measurement uncertainties, naming the variables used to represent the data, and formatting and populating sampling dates. There are also minor issues throughout the text that need to be addressed before this manuscript can be published.
After the dataset and manuscript have been revised to address all issues detailed below, I support publication of this manuscript in Earth System Science Data.
Please see the attached PDF file for detailed comments and suggestions for revision.