the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 28 Jul 2026
Glycan purification reveals persistence of algal fucoidan in millennia-old marine sediments
Abstract. Marine sediments are an important sink for the carbon fixed by photosynthetic algae in the sunlit ocean. Glycans represent a substantial fraction to the organic carbon buried globally in marine sediments. However, assigning the origin and contribution of specific glycans remains challenging with commonly used methods that are designed to measure the total glycan carbon content. Glycan-specific detection using monoclonal antibodies previously revealed diatom- and brown algae-derived fucoidans in marine sediments of various ages. These complex anionic glycans may contribute to long-term carbon sequestration, while their quantitative significance remains unknown. Here, we combined anion exchange chromatography with glycan-specific monoclonal antibodies to isolate and detect fucoidans from marine sediments. Applying this method to a sediment core from the Bransfield Strait in the Southern Ocean revealed that fucoidan was buried and persisted for the extent of the Holocene (11.8 ka). Our results highlight that glycan purification from sediments can help to resolve the importance of different algal glycans to the sequestration of carbon in the ocean.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-4401', Anonymous Referee #1, 29 Jul 2026
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RC2: 'Comment on egusphere-2026-4401', Anonymous Referee #2, 28 Aug 2026
Mundanett et al. present improved methods to detech glycans in marine sediments, and demonstrate that fucoidan, a long-chain sulfated polysaccharide typically associated with brown algae, persists in sediment on at least Holocene time scales in a core collected off the coast of Antarctica. The topic is well within the scope of Biogeosciences, and the manuscript is generally clear and presents interesting results. I think some aspects of the manuscript organization could be improved, the motivation and implications of the study could be clarified, and some aspects of the results could be placed in a bit more context. There were also several minor grammatical errors, some of which I detailed below.
Specific comments:
Line 19: I would briefly define fucoidans here.
Lines 158-166, lines 179-188: A lot of this information seems out of place for the results section. I think it might fit better in the methods, and you can just report the results here. There are other isolated sentences in the results that are describing/justifying methods. I think in general these are not needed in the results section. Reviewer 1’s suggestion to add a schematic of the analytical workflow to the methods section is a good one, and would help readers be able to place your results into the context of the work that was done, without writing out so many methods in the results section.
Lines 206-207: Rhamnose seems like it is not even present in the isolated fucoidans? I would comment on that, rather than saying it is less abundant
Lines 208-210, 232-234: What does this selection/omission imply for the reliability of the anion exchange chromatography for evaluating the role of glycans in long-term C-sequestration?
Lines 241-242: It would be helpful to explain why it is important to determine the source of fucoidans
Lines 264-271: The content of the outlook section seems out of place to me. The motivation to understand carbon sequestration potential of brown algae seems like an underlying reason to do this type of investigation, and should be presented in the introduction. This would also help the reader understand why we should even care about which algae were responsible for producing sedimentary fucoidans (see above comment). I would rather finish with a concluding section that briefly summarizes the key findings of the study and explains why they are important in a broader context. I think there would be some scope within the discussion to outline remaining uncertainties in this approach and/or identify goals for follow-up work.
Figure S4: What is going on with the value at 192 cm? Why would matrix effects have such a big impact on this sample, but not any of the others? Seems like something could have been messed up in the calculations or in the lab handling of this sample
Typos and minor corrections (not an exhaustive list, please proofread the revised manuscript carefully):
Line 25: add “the” before “form”
Line 39: delete “for”
Line 81: “was” should be “were”
Line 118: add “the” before “dark”
Line 130: add “The” before “protocol”
Line 162: delete the comma after both
Figure 3: Have you checked that the color scheme here is appropriate for color blind readers?
Citation: https://doi.org/10.5194/egusphere-2026-4401-RC2
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- 1
General comments
This manuscript presents an interesting method for detecting fucoidan-like glycans in marine sediments. The authors extract glycans and separate the water- and EDTA-extractable material by anion-exchange chromatography. They then examine the extracts and chromatographic fractions using three methods with different roles. First, BAM1-based ELISA detects an epitope related to fucoidan. Second, the L-cysteine assay estimates the amount of deoxyhexoses, including fucose. Third, HPAEC-PAD shows the relative monosaccharide composition after acid hydrolysis.
When the BAM1 signal and the deoxyhexose peak occur in the same chromatographic fractions, and the monosaccharide composition is also consistent with fucoidan, the evidence for fucoidan is stronger than that from only one analysis. However, none of these methods alone can prove that the detected material is fucoidan. The experiments in this study were carefully designed, and I highly appreciate this point.
I am generally positive about publication after revision. My main concern is that the method enriches and detects material consistent with fucoidan, but some parts of the Results and Conclusions appear to describe the measured values as concentrations of total fucoidan. The authors should clearly state that the material extracted and measured by this method is operationally defined as fucoidan in this study.
Most of issues can be addressed by clearly defining the measured material, explaining the calculations and analytical limits in more detail, and using more careful wording in the Conclusions. I do not consider extensive additional experiments using the limited Bransfield Strait samples necessary for the present manuscript.
Major comments
1. Define “fucoidan”
Please explain early in the manuscript which chemical features are used to define fucoidan. The extraction and analytical procedure used in this study enriches an acidic glycan fraction that contains deoxyhexoses and reacts with BAM1. However, these properties alone cannot prove that all the measured material is fucoidan. In addition, the water and EDTA extractions measure only an extractable fraction, not total fucoidan in the sediment. However, it would be difficult for readers if the authors repeated “putative fucoidan fraction” throughout the manuscript. I suggest providing one clear operational definition near the end of the Introduction or at the beginning of the Methods. For example:
“In this study, the amount of material extracted with water and EDTA, reactive with BAM1, containing deoxyhexoses, and recovered in the selected anion-exchange fractions is operationally reported as the fucoidan concentration.”
After this definition, the shorter terms “fucoidan” and “fucoidan concentration” may be used. However, the Abstract, main conclusions, and figure and table captions should remind readers that these values are operationally defined and do not represent total fucoidan in the sediment.
2. Overview of the analytical workflow
A short overview of the analytical workflow would also help readers. Please briefly explain the purpose of each main step. Sequential extraction separates different extractable glycan pools. The water and EDTA extracts are combined for further analysis. Anion-exchange chromatography enriches acidic glycans and separates them from part of the sediment matrix. BAM1-based ELISA and the L-cysteine assay provide complementary measurements of the collected fractions. Silica treatment removes salts before HPAEC-PAD. Acid hydrolysis releases monosaccharides for compositional analysis. Please also make clear that ELISA, the deoxyhexose assay, and HPAEC-PAD are complementary analyses. They are not successive extraction steps.
3. Clarify the apparent recovery and matrix effects
The apparent recovery of 200% at 192 cm indicates an unresolved matrix effect or analytical interference. This value should be described as quantitatively uncertain and should preferably not be used for quantitative interpretation. This issue does not invalidate the qualitative detection of BAM1-reactive material. However, it limits the comparison of absolute concentrations among different depths. For future quantitative validation, a whole-procedure spike-recovery test would be useful. An available and well-characterized BAM1-reactive fucoidan could be added to an alternative natural sediment before extraction. For example, the Wadden Sea sediment already used in this study could be considered. I do not request this additional experiment for the present manuscript. However, I suggest discussing it as an important topic for future work.
4. Revise the interpretation of the 30% value
The 2 cm sample is the uppermost sediment sample. However, it does not represent material immediately after deposition from the water column. A 2 cm sediment interval contains material accumulated over a certain period, for example. It may represent at least several months and possibly several years. Fucoidan may already have been degraded during this period. Therefore, the value at 2 cm does not represent the amount produced at the sea surface, the amount that started to sink, or the amount that first reached the seafloor.
5. Discuss possible inhibition of BAM1 by humic-like substances
Marine sediments contain large amounts of humic-like organic matter. Humic-like substances may bind to glycans or antibodies and reduce the access of BAM1 to its target. They may also interfere with adsorption to the ELISA plate or increase the background colour. The purification procedure used in this study may reduce these effects. However, the manuscript does not clearly show that these effects were sufficiently removed or were similar at all depths. Please explain how possible inhibition by humic-like substances was evaluated and how it may affect the results. If inhibition is stronger in deeper samples, a lower BAM1 signal may indicate not only a lower fucoidan concentration but also stronger inhibition. I understand that it may be difficult to remove the effects of humic-like substances completely. However, this limitation should be clearly stated.
Specific and minor comments
Figure 2: The x-axis is labelled only as “Chromatographic fractions.” Please provide the x-axis unit, fraction numbers, or other information needed to identify the fractions.
Line 81: “Samples of known weight was” should be changed to “Samples of known weight were.”
Lines 250–251: “The binding ... also suggest” should be changed to “The binding ... also suggests.”