Surface Sedimentary Black Carbon Concentrations, Flux, and Carbon Isotopes Values from the R.V. Endeavor EN651 in the Equatorial Atlantic Ocean from March 2020

Surface sediments (0-1 cm) were obtained from the equatorial Atlantic Ocean and isolated for black carbon using the chemothermal oxidation at 375°C method (CTO 375). Multicores were taken aboard the R.V. Endeavor (EN651) from March 1st through March 15th, 2020, using a multi corer MC-800. Sediment samples were collected from 12 multicore stations along a west-to-east transect of the equatorial Atlantic centered on about 5˚N. Sediment deposition environments included the Amazon Submarine Fan, a series of sites across the Mid-Atlantic Ridge, and sites on the Sierra Leone Rise and adjacent Sierra Leone Basin. See Figure 1 in the EN651 cruise report (Lohmann 2020) for an illustration of coring site locations.

Background information taken from the EN651 cruise report (Lohmann 2020)

Black carbon (BC) is a highly graphitized incomplete combustion byproduct that could be a sink for fixed carbon, especially when deposited to pelagic sediments (Kuhlbusch 1998). There is a general assumption that rivers deliver most or all BC to the ocean (Coppola et al. 2018; Elmquist et al. 2008; Kuhlbusch 1998; Masiello and Druffel 2001; Mitra et al. 2014, 2002; Suman et al. 1997). Yet the effects and fluxes of BC are not well constrained in general circulation models. For example, few BC flux measurements are available in remote ocean sediments due to the expense and difficulty of obtaining samples. The formation of BC during incomplete combustion results in a fraction of carbon not being available for the biological pump and deep ocean respiration. Once deposited to the ocean, BC is buried in sediments and can account for significant fractions of the organic matter preserved in sediments. Hence, our results would contribute towards accounting for some of the ‘missing’ terrestrial OC in sediments, as all BC is landmass derived (Hedges et al. 1997).