Macroalgal influence on particulate organic matter sources and early transformation in an Arctic fjord

Jagtap, Ashok Shivaji; Singh, Archana; Jain, Anand; Raj, Nandini; Tiwari, Manish

doi:10.5194/egusphere-2026-843

Preprints

https://doi.org/10.5194/egusphere-2026-843

Preprints

23 Feb 2026

| 23 Feb 2026

Status: this preprint is open for discussion and under review for Biogeosciences (BG).

Macroalgal influence on particulate organic matter sources and early transformation in an Arctic fjord

Ashok Shivaji Jagtap, Archana Singh, Anand Jain, Nandini Raj, and Manish Tiwari

Abstract. Accelerated Arctic warming is promoting the expansion of coastal macroalgal habitats, yet their influence on pelagic organic carbon cycling remains unresolved. This study investigate the influence of macroalgal beds on the biochemical composition of surface particulate organic matter (POM) in Kongsfjorden, Svalbard, during late summer 2023. Surface waters were sampled at four macroalgal-dominated sites (MDS) and from adjacent waters (Adj-W) located 500 m and 1500 m away. A multi-proxy approach integrating elemental composition, stable isotopes, biopolymeric fractions, monosaccharides, and amino acids was used to trace macroalgal contributions and their lateral redistribution. Concentrations of particulate organic carbon, particulate nitrogen, particulate carbohydrates, and proteins were consistently higher at MDS than in Adj-W, indicating localized enrichment of biochemically labile organic matter within macroalgal habitats. Molecular analyses revealed elevated concentrations of monosaccharides and amino acids at MDS, including macroalgal-associated sugars (glucose, galactose, fucose, mannuronic acid) and labile amino acids (Asp, Glu, Gly, Ser, Ala), demonstrating incorporation of macroalgal-bed derived matter into surface POM. Declining concentrations and composition shift in Adj-W, together with internal reorganization of biopolymeric and molecular composition, indicate efficient lateral export with selective early-stage transformation of POM. Bulk δ¹³C showed minimal spatial variation (−26.8 to −29.1 ‰), suggesting that macroalgal influence is expressed through biochemical restructuring rather than isotopic dominance. Principal component analysis identified a continuous macroalgal–pelagic gradient, with MDS occupying the macroalgal-influenced end. Overall, these findings indicate that Arctic macroalgal beds act as dynamic coastal biogeochemical hotspot, redistributing and transforming organic carbon beyond their immediate habitat.

Received: 12 Feb 2026 – Discussion started: 23 Feb 2026

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.

Download & links

Preprint (PDF, 1516 KB)

Supplement (536 KB)

Download & links

Ashok Shivaji Jagtap, Archana Singh, Anand Jain, Nandini Raj, and Manish Tiwari

Status: open (until 25 May 2026)

Post a comment Subscribe to comment alert

RC1: 'Comment on egusphere-2026-843', Anonymous Referee #1, 21 Apr 2026 reply

This manuscript investigates the influence of macroalgal beds in the Arctic Kongsfjorden on the sources and early transformation processes of surface particulate organic matter. By comparing surface water samples from four macroalgae-dominated sites and their adjacent waters (500 m and 1500 m), and employing a combination of elemental analysis, stable isotopes, macromolecular composition, and molecular biomarkers, the authors found that macroalgal beds are a significant source of labile carbon and nitrogen compounds in surface POM, with their molecular fingerprints (e.g., monosaccharide and amino acid composition) showing distinct signatures. POM derived from macroalgae can be exported to the fjord scale and undergoes selective transformation during lateral transport. Principal component analysis revealed a continuous biogeochemical gradient from the macroalgal beds to the adjacent waters. Among the sites, Brandal stands out as a distinct biogeochemical hotspot influenced by macroalgae. This study provides important multi-proxy evidence for understanding how expanding macroalgal communities, under rapid Arctic warming, influence the sources, transport, and transformation of coastal organic carbon through benthic-pelagic coupling processes. It holds clear academic value for deepening the understanding of the Arctic coastal carbon cycle and is worthy of publication after revision.
Major Deficiencies and Revision Suggestions
1) The abstract and highlights sections are repetitive and could be further refined. (Lines 14-22, 24-45). It is suggested that the author revisits and integrates the content of these two sections. Consider refining the "Highlights" into the most concise and eye-catching core innovative findings, while the "Abstract" should maintain its independence, providing a complete yet succinct overview of the research background, methods, main results, and conclusions, avoiding simple repetition of the highlight statements.
2) Lines 511-536: The explanation for the mechanism behind the finding that "Brandal is a biogeochemical hotspot influenced by macroalgae" is primarily attributed to "high biomass," "favorable growth conditions," and "possible promotion of detritus retention by hydrological conditions," which is somewhat general. It is suggested to add a subsection or paragraph to explore more specifically the potential local driving factors that make the Brandal site a hotspot. For example, can known information about the site's geographical location, water depth, hydrodynamic characteristics (e.g., whether it is in a circulation or upwelling area), degree of freshwater input, etc., or citations of relevant literature, be incorporated to support the speculation that "hydrological conditions promote retention," making the conclusion more robust.
3) .Specific citation suggestions:
1) Lines 89-91: In the introduction, when discussing the complexity of organic matter sources in the Arctic coastal zone, after ".....(Singh et al., 2024b) and sediments (Roy et al., 2025) in Kongsfjorden", add: "Similarly, studies on the Qinghai-Tibetan Plateau saline lakes have shown that the molecular composition of dissolved organic matter is also strongly influenced by watershed inputs and internal biological processes (Jiang et al., 2022), and that terrestrially derived organic matter can be transformed driven by aquatic microbial communities (Yang et al., 2020)."
2)Line 457: After "observed decline in POC from MDS to Adj-W", insert: "This aligns with the classical understanding of preferential degradation of labile components in marine environments. In lake sediment systems, inputs of algal and terrestrial organic matter have been shown to stimulate significantly different microbial degradation processes (priming effects) (Yang et al., 2023), with methanogenesis potentially dominating the carbon flow under anoxic conditions (Yang et al., 2025), implying the key control of organic matter molecular composition on its transformation pathways."
3)Line 517: After "matter within this macroalgal-dominated habitat", insert: "Habitat heterogeneity is considered a primary factor driving microbial community assembly and functional differentiation in extreme environments (Huang et al., 2026). In Qinghai Lake, the assembly mechanisms of prokaryotic and microeukaryotic communities have been shown to be significantly different and regulated by different environmental factors (Han et al., 2023). Similarly, research in the Aral Sea region indicates that minor differences in salinity and mineralogy can lead to distinctly different responses in microbial and endophytic communities (Jiang et al., 2021). Therefore, the Brandal hotspot may result from the combined action of its unique substrate (macroalgal bed), local hydrodynamics (forming a 'retention zone'), and the resulting unique microbial community, reflecting the high specificity of biogeochemical processes at the microhabitat scale."
Yang et al. (2020) Potential utilization of terrestrially derived dissolved organic matter by aquatic microbial communities in saline lakes. The ISME Journal 14(9): 2313-2324.https://doi.org/10.1038/s41396-020-0689-0
Jiang et al, (2021) Onshore soil microbes and endophytes respond differently to salinity and mineralogy in the Aral Sea. Science of the Total Environment 765: 142675,https://doi.org/10.1016/j.scitotenv.2020.142675
Yang et al. (2022) Positive priming effects induced by allochthonous and autochthonous organic matter input in the lake sediments with different salinity. Geophysical Research Letters 49(5): e2021GL096133. https://doi.org/10.1029/2021GL096133
Jiang*, et al. (2022) Molecular composition of dissolved organic matter in saline lakes of the Qing-Tibetan Plateau. Organic Geochemistry 167: 104400. https://doi.org/10.1016/j.orggeochem.2022.104400
Han, et al. (2023) Distinct assembly mechanisms for prokaryotic and microeukaryotic communities in the water of Qinghai Lake. Journal of Earth Science 34(4): 1189-1200, https://doi.org/10.1007/s12583-023-1812-8
Yang, et al., (2023) Predominance of positive priming effects induced by algal and terrestrial organic matter input in saline lake sediments. Geochimica et Cosmochimica Acta 349: 126–134, https://doi.org/10.1016/j.gca.2023.04.005
Yang, et al., (2025) Methanogenesis rather than carbon dioxide production frives positive priming effects in anoxic sediments of saline lakes. Chemical Geology 678: 122680, https://doi.org/10.1016/j.chemgeo.2025.122680
Huang et al. (2026) Habitat heterogeneity drives microbial community assembly and functional specialization in extreme arid ecosystems. Applied and Environmental Microbiology, https://doi.org/10.1128/aem.02588-25

Reply

Citation: https://doi.org/10.5194/egusphere-2026-843-RC1
RC2: 'Comment on egusphere-2026-843', Anonymous Referee #2, 29 Apr 2026 reply

Overall, this is a strong and timely study that applies a comprehensive multi-proxy approach to explore macroalgal influences on particulate organic matter dynamics in an Arctic fjord. The dataset is robust and the analyses are generally well interpreted, providing valuable insight into benthic–pelagic coupling in a rapidly changing Arctic coastal system. A number of revisions would further strengthen the manuscript, particularly improvements to figure clarity and accessibility, minor typographical and formatting corrections, and additional detail in the statistical methods to improve transparency and reproducibility. The manuscript would also benefit from some streamlining of lengthy results sections and clearer structuring of the discussion, including a brief synthesis of key findings and a slightly stronger emphasis on broader implications. Addressing these points would enhance readability and ensure the study’s contributions are fully accessible to a wide readership.
General typos and suggestions for clarification
Line 26 This study investigates
Lines 67 – 70 not needed, can remove
Lines 71 – 73, how are the macroalgal beds lost? Provide an example of the process/reasons for these losses.
Figure 1 – consider adding place names and enlarge latitude/longitude text.
Section 2.7 Statistical analysis – what packages did you use in R for your statistical analysis? Did you test for equal variance and normality assumptions before proceeding to ANOVA?
Tabel 1 – if you’re abbreviating, include the abbreviation in brackets in your table cation (e.g. sal for salinity).
Figure 2 – this is very hard to read, consider enlarging and making all text bigger
Table 2 – fix table caption
Figure 3 – avoid using red (colour blind implications)
Sections 3.3.2, 3.3.3 and 3.3.4 – consider summarising all the data ranges in tables to avoid big text sections. You could potentially include these in the Appendices since you already include graphs.
Line 351 – PCA analysis should be PCA
Section 4 Discussion – consider adding a short paragraph at the beginning that summarises all your key findings and then expand on the detail in the subsequent sections.
The emphasis on Brandal as a biogeochemical hotspot is well supported by the data; however, a brief discussion on how representative this site may be of Arctic macroalgal beds more broadly, or which site characteristics may limit generalisation, would help place the findings in a wider Arctic context.
Figure 6 – add labels for 55 and 1500, add arrows with the label decreasing for the compounds/concentrations
Line 551 – missing full stop
Section 4.5 Implications – lines 538 – 548 is a summary of your results, consider moving this, along with Figure 6, to the start of your discussion. Expand on the implications sections so it focusses on the ‘so what does this mean for future research and climate/ecosystem implications’. The novelty of the study would benefit from being made more explicit, particularly in relation to previous POM studies in Kongsfjorden. A short clarification of what is fundamentally new here (e.g. molecular resolution, spatial design, or integration of proxies) would help situate the contribution more clearly within the existing literature.

Reply

Citation: https://doi.org/10.5194/egusphere-2026-843-RC2

Ashok Shivaji Jagtap, Archana Singh, Anand Jain, Nandini Raj, and Manish Tiwari

Supplement

https://doi.org/10.5194/egusphere-2026-843-supplement

Ashok Shivaji Jagtap, Archana Singh, Anand Jain, Nandini Raj, and Manish Tiwari

Viewed

Total article views: 218 (including HTML, PDF, and XML)

HTML	PDF	XML	Total	Supplement	BibTeX	EndNote
145	59	14	218	21	14	21

HTML: 145
PDF: 59
XML: 14
Total: 218
Supplement: 21
BibTeX: 14
EndNote: 21

Views and downloads (calculated since 23 Feb 2026)

Month	HTML	PDF	XML	Total
Feb 2026	55	17	4	76
Mar 2026	67	29	8	104
Apr 2026	23	13	2	38

Cumulative views and downloads (calculated since 23 Feb 2026)

Month	HTML	PDF	XML	Total
Feb 2026	55	17	4	76
Mar 2026	67	29	8	104
Apr 2026	23	13	2	38

Viewed (geographical distribution)

Total article views: 203 (including HTML, PDF, and XML) Thereof 203 with geography defined and 0 with unknown origin.

Country	#	Views	%

Latest update: 30 Apr 2026

Short summary

Rapid Arctic warming is driving the expansion of coastal macroalgal forests, yet the role of their organic carbon in Arctic biogeochemistry remain largely unexplored. Here, isotopic, bulk, biochemical, and biomolecular analyses of surface particulate organic matter reveal that labile macroalgal carbon is a major contributor and is laterally transported with selective degradation. Continued expansion of macroalgal forests will enhance their role in Arctic carbon cycling and ecosystem functioning.


Total:	0
HTML:	0
PDF:	0
XML:	0