A Cross‐System Comparison of Dark Carbon Fixation in Coastal Sediments

Abstract

Dark carbon fixation (DCF) by chemoautotrophic microorganisms can sustain food webs in the seafloor by local production of organic matter independent of photosynthesis. The process has received considerable attention in deep sea systems, such as hydrothermal vents, but the regulation, depth distribution, and global importance of coastal sedimentary DCF have not been systematically investigated. Here we surveyed eight coastal sediments by means of stable isotope probing (13C‐DIC) combined with bacterial biomarkers (phospholipid‐derived fatty acids) and compiled additional rates from literature into a global database. DCF rates in coastal sediments range from 0.07 to 36.30 mmol C m−2 day−1, and there is a linear relation between DCF and water depth. The CO2 fixation ratio (DCF/CO2 respired) also shows a trend with water depth, decreasing from 0.09 in nearshore environments to 0.04 in continental shelf sediments. Five types of depth distributions of chemoautotrophic activity are identified based on the mode of pore water transport (advective, bioturbated, and diffusive) and the dominant pathway of microbial sulfur oxidation. Extrapolated to the global coastal ocean, we estimate a DCF rate of 0.04 to 0.06 Pg C year−1, which is less than previous estimates based on indirect measurements (0.15 Pg C year−1), but remains substantially higher than the global DCF rate at deep sea hydrothermal vents (0.001–0.002 Pg C year−1).

New insights into large-scale trends of apparent organic matter reactivity in marine sediments and patterns of benthic carbon transformation

“…Sources and composition Burdige (2006), Canfield (1994), , Meyers (1997), Middelburg (2019) Oxygen exposure time (settling and burial) Hartnett et al (1998), Hoefs et al (2002), Sinninghe , Huguet et al (2008), Sun andWakeham (1994), Wakeham et al (1997) Terminal electron acceptor availability Aller (1994), Aller and Aller (1998), Canfield et al (1993), Canfield (1994) Microbial activity LaRowe et al (2020a, b), Stevenson et al (2020), Bradley et al (2020) Sediment biological mixing (bioturbation and bioirrigation) Aller (1980Aller ( , 1994, Aller and Aller (1998), Boudreau (1994), Grossi et al (2003), Middelburg (2018), Aller and Cochran (2019) Ageing and transport history Bianchi et al (2018), Cathalot et al (2010), Griffith et al (2010), Mollenhauer et al (2003Mollenhauer et al ( , 2007, Ohkouchi et al (2002), Ausín et al (2021) OM-sediment association Bianchi et al (2018), Hemingway et al (2019), Keil and Cowie (1999), Mayer (1994b, a) OM-iron mineral adsorption Salvadó et al (2015), Shields et al (2016), Wang et al (2019), Faust et al (2021) Priming van Nugteren et al (2009), Guenet et al (2010),…”

Chemoautotrophic sulphur oxidizers dominate microbial necromass carbon formation in coastal blue carbon ecosystems

“…As microbial pathways associated with S oxidation were speculated to be a key process that detoxifies sulphide and provides energy for plant growth, the high functional potential of S oxidation in the nativevegetated coastal sediment microbiome might increase their plant primary productivity and remove toxic sulphide from plants (Rolando et al, 2022). Also, we observed higher abundances of S oxidation and C fixation and a closer interaction of gene families involved in C fixa- (Rolando et al, 2022;Vasquez-Cardenas et al, 2020). Second, ATP and NADPH generated from the oxidation of reduced sulphur compounds coupled with nitrate/nitrite reduction could be utilized for CO 2 fixation (Dyksma et al, 2016).…”

“…lignin) transformed macromolecules into low molecular weight intermediates, which could support the persistence of uncultivated bacteria (Yu et al, 2023). In this study, the high functional potential of methane C degradation (Rolando et al, 2022;Vasquez-Cardenas et al, 2020).…”

Reviews and syntheses: Heterotrophic fixation of inorganic carbon – significant but invisible flux in environmental carbon cycling

“…Dark DIC fixation has been reported for all types of ecosystems, including marine habitats (Wuchter et al, 2003;Middelburg, 2011;DeLorenzo et al, 2012;Molari et al, 2013;Lengger et al, 2019;Smith et al, 2019;Vasquez-Cardenas et al, 2020), brackish and freshwater systems (Bräuer et al, 2013;Santoro et al, 2013;Noguerola et al, 2015;Signori et al, 2017;Vick-Majors and Priscu, 2019;Zhao et al, 2020), cave waters and groundwater ecosystems (Pedersen and Ekendahl, 1992a, b;Kotelnikova and Pedersen, 1998;Kellermann et al, 2012;Lazar et al, 2017), and soil habitats (Ehleringer et al, 2000;Miltner et al, 2004Miltner et al, , 2005Šantrůčková et al, 2005Akinyede et al, 2020, and references therein). In the absence of solar radiation, particularly in the dark ocean, CO 2 fixation rates of up to ∼ 125 mg C m −3 d −1 have been measured, amounting to 30 % (on a per volume basis) of the phototrophic CO 2 fixation in ocean surface waters (Zopfi et al, 2001;Detmer et al, 1993;Casamayor et al, 2001;Baltar et al, 2010).…”