EGU22-13281, updated on 28 Mar 2022
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

The importance of 'invisible' dissolved organic carbon along the land-ocean aquatic continuum

Stacey L. Felgate1,2 and the Authors*
Stacey L. Felgate and the Authors
  • 1Ocean and Earth Science, University of Southampton, Southampton, UK
  • 2Ocean BioGeosciences, National Oceanography Centre, Southampton, UK
  • *A full list of authors appears at the end of the abstract

Land-ocean dissolved organic carbon (DOC) fluxes are a significant and changing component of the global carbon cycle. The current paradigm assumes that these fluxes are dominated by chromophoric or ‘coloured’ material (cDOC). DOC is often characterised and quantified using optical tools which specifically target this fraction. However, multiple studies point towards a potentially sizeable non-coloured or optically ‘invisible’ DOC (iDOC) pool which is not covered by such characterisations. Only a handful of studies have directly investigated iDOC, and so its source, composition, behaviour, and geographic prevalence remain poorly understood.

Here we show that iDOC accounts for 21 % (0.23 Tg C yr-1) of annual riverine export in Great Britain (GB), with spatial variation in catchment-scale mean annual export depending upon forest cover and mean dairy cattle density. Using > 2,900 samples from across a range of geo-climatic settings across five continents we find a similar result: iDOC accounts for 26 % of the measured DOC flux in freshwaters. Our results indicate that iDOC is more prevalent in systems with a high degree of anthropogenic influence and/or a high residence time. 

We also show that estuarine DOC behaviour is driven by the contributions of cDOC and iDOC, at least within GB estuaries: cDOC almost universally exhibits conservative transport, whilst apparent non-conservative bulk DOC transport is typically caused by fluctuations in the iDOC fraction.

We conclude that iDOC is a globally significant fraction of the land-ocean carbon flux, the broad scale importance of which has been largely overlooked. This has fundamental implications for (1) our understanding of aquatic biogeochemistry and (2) the use and interpretation of optical parameters as they relate to DOC characterisation and quantification.

This work was primarily funded by the National Environment Research Council (NERC) through the SPITFIRE Doctoral Training Programme (grant number NE/L002531/1) and the Land Ocean Carbon Transfer Programme (LOCATE; grant number NE/N018087/1). 


Stacey L. Felgate1,2, Daniel J. Mayor2, Jennifer Williamson3, B. B. Cael2, Mike Peacock4, Daniel J. Lapworth5, Suman Acharya6, Roxane Andersen7, Rupak Aryal8, Chris D. G. Barry3, Joshua Dean9,10, Martyn Futter4, Gloria Pereira11, Al Grinham12, Alicia Holland6, Alex Hunt11, Elizabeth Jakobsson13, Paddy Keenan11, Vasilis Kitidis14, Dolly Kothawala13, Thibault Lambert15,16, Ruth Matthews17, Filip Moldan18, Don Monteith3, Alan Radbourne3, Andrew. P. Rees14, Richard Sanders2,19, Ewen Silvester6, Bryan Spears20, John Stephens14, and Chris D. Evans3

How to cite: Felgate, S. L. and the Authors: The importance of 'invisible' dissolved organic carbon along the land-ocean aquatic continuum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13281,, 2022.