Sediment cores were obtained by Piston coring (using commercial PVC core liners) onboard R/V El Puma. The sediment cores were recovered during the RV El Puma cruise in October 2014. Core PO3 is from the northwestern ridge flanks [27°N 37.6759/111°W 52.5740; 1611 m depth], P10 is from ca. 1 mile west of Ringvent [27°N 30.5193/111°W 42.1722 W; 1731 m depth], core P11 is from the center of Ringvent [27°N 30.5090/111°W 40.6860, 1749 m], core P12 is from the upper Sonora Margin [27°N 52.1129/111°W 41.5902, 667 m], and core P13 is from the southeastern ridge flank of Guaymas Basin [27°N 12.4470/111°W 13.7735, 1859m]. Sedimentation rates were not inferred from cores P5 and P6 due to distortions by slumping. Measurements were made on bulk sediment without authigenic carbonate phases, and thus the majority of carbon in the samples is organic carbon produced by primary producers.

Samples selected for radiocarbon analyses were freeze-dried, homogenized, and acidified to remove CaCO₃, allowing for the analysis of remaining organic matter, and preventing the distortion of radiocarbon ages by methane-derived carbonates. Acidification was performed on ~200 mg of sample, which was treated with ~5ml buffered pH 5 acetic acid solution for ~24 hours to dissolve the CaCO₃. Samples were then rinsed with Milli-Q water 6 to 8 times to remove the acetic acid. Acidified samples were then freeze-dried again, re-homogenized and stored for ¹⁴C and ¹³C analysis. Radiocarbon dating was performed at Lawrence Livermore National Laboratory Center for Accelerator Mass Spectrometry, and a reservoir age of 406 years was used before conversion to calendar years using CALIB REV7.1.0. (Stuiver et al. 2019). The d¹³C values of all the acidified samples used for radiocarbon analyses were approximately -20 to -22‰, as expected from marine (primary producers) derived organic matter.