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

Core collection

MC-800 tubes were labeled (EN651-“Site number”-MC”coring attempt number”“letter of core”,ex: EN651-01-MC01A) and photographed before sectioning. The water on top of the core was syphoned off and a thin piece of stainless-steel sheet was slid under the foot of the tube. The foot was bent up and the stainless-steel sheet was used to transfer the core to the core extruder. Cores were sectioned at 1 cm intervals down to 10 cm, then 2 cm intervals down to 20 cm, using the piece of stainless-steel and a cake spatula to cut them. The remainder of the core was wrapped in combusted aluminum foil and placed in a zip-lock bag for storage. Sections of cores were stored in amber glass jars placed in a freezer. One core was transferred with the extruder to a PVC tube and capped for archival storage. If 5 or more cores were recovered, 0.5 cm sections would be taken down to 10 cm and the remainder of the core wrapped in foil and zip-lock bagged before being frozen. Due to a limited supply of jars, the 0.5 cm core sections were wrapped in combusted aluminum foil and placed in a ziplock bag before being stored with other samples. All cores and core sections were stored at -20 ̊C.

Analytical methods
Surface sediment samples (0 – 1 cm) were dried at 60 ˚C until dry and passed through a 420 µm sieve before analysis. Total organic carbon (TOC) samples were weighed into silver capsules (Elemental microanalysis silver capsules ultra-clean pressed 8 x 5 mm, D2030), acidified to remove inorganic carbon (2 M HCl), and folded into tin capsules (Costech tin capsules 10 x 10 mm, 041073). Black carbon was isolated using the CTO 375 method (Gustafsson et al. 1997, 2001). 100 mg of samples where weighed out into ceramic crucibles and spread into a thin layer to prevent charring. Samples were combusted at 375 ˚C for 24 hrs. under the flow of ultra high purity air (0.4 L min^-1). The remaining sediment was transferred to GC (gas chromatography) vials for storage, then processed the same as the TOC samples to remove any inorganic carbon present (as detailed above).

Sampling equipment

Sediment cores were collected using an MC-800

Analytical instrumentation

 An Elemental Analyzer (Costech 4010 Elemental Analyzer) was used for quantification of the BC and TOC fractions. The same elemental analyzer coupled to an Isotope Ratio Mass Spectrometer (Thermo Delta V Advantage) was used for the sample carbon isotopes.  Radiocarbon isotopes were measured at the National Ocean Sciences Accelerator Mass spectrometry.

Sediment cores availability

Sediment cores are stored at the NSF-funded Rock and Core Repository at GSO-URI and access to the samples is available through established protocols. Solid material, in the form of cores are curated and retained after the expedition and are available to other investigators that wish to use them for other means (Lohmann 2020).