High rates of organic carbon burial in submarine deltas maintained on geological timescales

• Published in: Nature geoscience 2022-11, Vol.15 (11), p.919-924
• Main Authors: Hage, Sophie, Romans, Brian W., Peploe, Thomas G. E., Poyatos-Moré, Miquel, Haeri Ardakani, Omid, Bell, Daniel, Englert, Rebecca G., Kaempfe-Droguett, Sebastian A., Nesbit, Paul R., Sherstan, Georgia, Synnott, Dane P., Hubbard, Stephen M.
• Format: Article
• Language: English
• Subjects: 704/2151/209; 704/2151/3930; 704/47/4113; Carbon; Carbon budget; Carbon dioxide; Carbon sinks; Complex systems; Cretaceous; Deltas; Earth and Environmental Science; Earth Sciences; Earth System Sciences; Fluvial deposits; Geochemistry; Geology; Geophysics/Geodesy; Marine sediments; Oceans; Organic carbon; Sediment; Sediments; Stratigraphy; Total organic carbon
• ISSN: 1752-0894; 1752-0908
• DOI: 10.1038/s41561-022-01048-4

Burial of terrestrial organic carbon in marine sediments can draw down atmospheric CO 2 levels on Earth over geologic timescales (≥10 5  yr). The largest sinks of organic carbon burial in present-day oceans lie in deltas, which are composed of three-dimensional sigmoidal sedimentary packages called clinothems, dipping from land to sea. Analysis of modern delta clinothems, however, provides only a snapshot of the temporal and spatial characteristics of these complex systems, making long-term organic carbon burial efficiency difficult to constrain. Here we determine the stratigraphy of an exhumed delta clinothem preserved in Upper Cretaceous (~75 million years ago) deposits in the Magallanes Basin, Chile, using field measurements and aerial photos, which was then combined with measurement of total organic carbon to create a comprehensive organic carbon budget. We show that the clinothem buried 93 ± 19 Mt terrestrial-rich organic carbon over a duration of 0.1–0.9 Myr. When normalized to the clinothem surface area, this represents an annual burial of 2.3–15.7 t km −2  yr −1 organic carbon, which is on the same order of magnitude as modern-day burial rates in clinothems such as the Amazon delta. This study demonstrates that deltas have been and will probably be substantial terrestrial organic carbon sinks over geologic timescales, a long-standing idea that had yet to be quantified. Organic carbon burial rates in an Upper Cretaceous river delta are similar to those in modern deltas, suggesting that high burial rates can persist over geological timescales in these common settings, according to stratigraphic and geochemical analysis of exhumed delta sediments.