Preprints
https://doi.org/10.5194/egusphere-2022-516
https://doi.org/10.5194/egusphere-2022-516
 
27 Jun 2022
27 Jun 2022

Contrasts in dissolved, particulate and sedimentary organic carbon from the Kolyma River to the East Siberian Shelf

Dirk J. Jong1, Lisa Bröder1,2, Tommaso Tesi3, Kirsi H. Keskitalo1, Nikita Zimov4, Anna Davydova4, Philip Pika1, Negar Haghipour2, Timothy I. Eglinton2, and Jorien E. Vonk1 Dirk J. Jong et al.
  • 1Department of Earth Sciences, Vrije Universiteit, Amsterdam, the Netherlands
  • 2Geological Institute, Swiss Federal Institute of Technology, Zürich, Switzerland
  • 3Institute of Polar Sciences, National Research Council, Bologna, Italy
  • 4Pacific Geographical Institute, Far East Branch, Russian Academy of Sciences, Northeast Science Station, Cherskiy, Russia

Abstract. Arctic rivers will be increasingly affected by the hydrological and biogeochemical consequences of thawing permafrost. During transport, permafrost-derived organic carbon (OC) can either accumulate in floodplain and shelf sediments or be degraded into greenhouse gases prior to final burial. Thus, the net impact of permafrost OC on climate will ultimately depend on the interplay of complex processes that occur along the source-to-sink system. Here, we focused on the Kolyma River, the largest watershed completely underlain by continuous permafrost, and marine sediments of the East Siberian Sea as a transect to investigate the fate of permafrost OC along the land-ocean continuum. Three pools of riverine OC were investigated for the Kolyma main stem and five of its tributaries: dissolved OC (DOC), suspended particulate OC (POC), and riverbed sediment OC (SOC) and compared to earlier findings in marine sediments. Carbon isotopes (δ13C, Δ14C), lignin phenol, and lipid biomarkers show a contrasting composition and degradation state of these different carbon pools. Dual isotope source apportionment calculations imply that old permafrost-OC is mostly associated with sediments (SOC; contribution of 68 ± 10 %), and less dominant in POC (38 ± 8 %), while autochthonous primary production contributes around 44 ± 10 % to POC in the main stem and up to 79 ± 11 % in tributaries. Biomarker degradation indices suggest that Kolyma DOC is relatively degraded, regardless of its generally young age shown by previous studies. In contrast, SOC shows the lowest Δ14C signal (oldest OC), yet relatively fresh compositional signatures. Furthermore, decreasing mineral surface area-normalised OC- and biomarker loadings suggest that SOC is reactive along the land-ocean continuum supporting the idea that floodplain and shelf sediments are efficient reactors. A better understanding of DOC and POC dynamics in Arctic rivers is still necessary, however, this study highlights that sedimentary dynamics play a crucial role when targeting permafrost-derived OC in aquatic systems. Chemical and physical processes (e.g. degradation, sorption) along fluvial-marine transects will determine to what degree thawed permafrost OC may be destined for long-term burial, therewith attenuating further global warming.

Dirk J. Jong et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-516', Anonymous Referee #1, 22 Jul 2022
    • AC1: 'Reply on RC1', Dirk Jong, 15 Sep 2022
  • RC2: 'Comment on egusphere-2022-516', Anonymous Referee #2, 15 Aug 2022
    • AC2: 'Reply on RC2', Dirk Jong, 15 Sep 2022

Dirk J. Jong et al.

Dirk J. Jong et al.

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Short summary
With this study, we want to highlight the importance of studying both land and ocean together, and water and sediment together, as these systems function as a continuum and determine how organic carbon derived from permafrost is broken down, and its effect on global warming. While on one hand it appears that organic carbon is removed from sediments along the pathway of transport from river to ocean, it also appears to remain relatively ‘fresh’, despite this removal and its very old age.