20 Oct 2021

20 Oct 2021

Review status: this preprint is currently under review for the journal BG.

Age and Chemistry of Dissolved Organic Carbon Reveal Enhanced Leaching of Ancient Labile Carbon at the Permafrost Thaw Zone

Karis J. McFarlane1, Heather M. Throckmorton2,a, Jeffrey H. Heikoop2, Brent D. Newman2, Alexandra L. Hedgpeth1,3, Marisa N. Repasch1, Thomas P. Guilderson1,b, and Cathy J. Wilson2 Karis J. McFarlane et al.
  • 1Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, 94550, USA
  • 2Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, 87545, USA
  • 3Department of Geography, University of California, Los Angeles, 90095, USA
  • acurrently at: Agilent Technologies, Lexington, 02421, USA
  • bcurrently at: University of California, Santa Cruz, 95064, USA

Abstract. Climate change will alter the balance between frozen and thawed conditions in Arctic systems. Increased temperatures will make the extensive northern permafrost carbon stock vulnerable to decomposition and translocation. Production, cycling, and transport of dissolved organic carbon (DOC) are crucial processes for high-latitude ecosystem carbon loss that result in considerable export off the Arctic landscape. To identify where and under what conditions permafrost DOC is mobilized in an Arctic headwater catchment, we measured radiocarbon (14C) of DOC and assessed DOC composition with ultraviolet-visible spectroscopy (UV-vis), of surface waters and shallow and deep subsurface pore waters from 17 drainages in the Barrow Environmental Observatory in Alaska. Samples were collected in July and September 2013 to assess changes in age and chemistry of DOC over time. DOC age was highly variable ranging from modern (19 ‰ Δ14C) to approximately 7000 y BP (−583 ‰ Δ14C). DOC age increased with depth, over the summer as the active layer deepened, and with increasing drainage size. DOC quality indicators reflected a DOC source rich in high-molecular weight and aromatic compounds throughout the summer and a weak relationship with DOC age. In deep porewaters, DOC age was also correlated with several biogeochemical indicators, suggesting a coupling between carbon and redox biogeochemistry influencing methane production. In the drained thawed lake basins included in this study, DOC concentrations and contributions of vegetation-derived organic matter declined with increasing basin age. The weak relationship between DOC age and chemistry and consistency in DOC chemical indicators over the summer suggest high lability of old DOC released by thawing permafrost.

Karis J. McFarlane 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 bg-2021-272', Anonymous Referee #1, 05 Nov 2021
    • AC1: 'Reply on RC1', Karis McFarlane, 03 Dec 2021
  • RC2: 'Comment on bg-2021-272', Anonymous Referee #2, 15 Nov 2021

Karis J. McFarlane et al.

Data sets

Inorganic Carbon Isotopes and Chemical Characterization of Watershed Drainages, Barrow, Alaska, 2013 Throckmorton, H. M.; Heikoop, J. M.; McFarlane, K.; Newman, B. D.; Wilson, C. J.

Karis J. McFarlane et al.


Total article views: 332 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
259 65 8 332 10 4 10
  • HTML: 259
  • PDF: 65
  • XML: 8
  • Total: 332
  • Supplement: 10
  • BibTeX: 4
  • EndNote: 10
Views and downloads (calculated since 20 Oct 2021)
Cumulative views and downloads (calculated since 20 Oct 2021)

Viewed (geographical distribution)

Total article views: 298 (including HTML, PDF, and XML) Thereof 298 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
Latest update: 03 Dec 2021
Short summary
Planetary warming is increasing seasonal thaw of permafrost, making this extensive old carbon stock vulnerable. In Northern Alaska, we found more and older dissolved organic carbon in small drainages later in summer as more permafrost was exposed by deepening thaw. Younger and older carbon did not differ in chemical indicators related to biological lability suggesting this carbon can cycle through aquatic systems and contribute to greenhouse gas emissions warming increases permafrost thaw.