Major role of particle fragmentation in regulating biological sequestration of CO2 by the oceans

• Published in: Science (American Association for the Advancement of Science) 2020-02, Vol.367 (6479), p.791-793
• Main Authors: Briggs, Nathan, Dall'Olmo, Giorgio, Claustre, Hervé
• Format: Article
• Language: English
• Subjects: Automation; Carbon; Carbon cycle; Carbon dioxide; Carbon dioxide concentration; Carbon sequestration; Floats; Fluctuations; Flux; Fragmentation; Measuring instruments; Ocean floor; Oceans; Organic carbon; Pelagic zone; Remineralization; Sediments
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.aay1790

Breaking up is easy to doSinking particles transport carbon to the seafloor, where they are buried in sediments and either provide food for benthic organisms or sequester the carbon they contain. However, only ∼30% of the maximum flux reaches depths of a kilometer. This loss cannot be fully accounted for by current measurements. Briggs et al. used data collected by robotic Biogeochemical-Argo floats to quantify total mesopelagic fragmentation and found that this process accounts for roughly half of the observed flux loss (see the Perspective by Nayak and Twardowski). Fragmentation is thus perhaps the most important process controlling the remineralization of sinking organic carbon.Science, this issue p. 791; see also p. 738A critical driver of the ocean carbon cycle is the downward flux of sinking organic particles, which acts to lower the atmospheric carbon dioxide concentration. This downward flux is reduced by more than 70% in the mesopelagic zone (100 to 1000 meters of depth), but this loss cannot be fully accounted for by current measurements. For decades, it has been hypothesized that the missing loss could be explained by the fragmentation of large aggregates into small particles, although data to test this hypothesis have been lacking. In this work, using robotic observations, we quantified total mesopelagic fragmentation during 34 high-flux events across multiple ocean regions and found that fragmentation accounted for 49 ± 22% of the observed flux loss. Therefore, fragmentation may be the primary process controlling the sequestration of sinking organic carbon.