Dataset: Carbon isotope values of porewater DOM in California margin sediments from 2019 (OC1906A) and 2020 (Sikuliaq)

Porewater DIC samples were collected as described in Komada et al. (2016) Geochim. Cosmochim. Acta, 176:259-278. Briefly, sediment cores were sectioned within hours of retrieval, then centrifuged, filtered (0.2 micron pore size), and preserved (poisoned then flame sealed under nitrogen gas). Porewater DOC samples were extracted in the same way from SBB sediments, as well as from gravity cores from all remaining stations (CAT, StaD, StaK). However, porewater DOC samples from multicores retrieved from CAT, StaD and StaK were extracted using Rhizon samplers (Seeberg-Elverfeldt et al., Limnol. Oceanogr. Meth., 8:361-371, 2005) to prevent DOC contamination from squashed benthic macrofauna during centrifugation. DOC samples for radiocarbon analysis were immediately frozen, or acidified to pH 2 with hydrochloric acid and loaded onto a PPL cartridge (Dittmar et al., Limnol Oceanogr. Meth., 6:230-235, 2008) and refrigerated.  Sediment samples were frozen immediately in polycarbonate centrifuge tubes. Bottom water samples were collected using acid-washed Go-Flo bottles. DOC samples were filtered (0.2 micron) and frozen. DIC samples were poisoned with HgCl2 and sealed in glass bottles.

Frozen porewater and bottom-water DOC were submitted to the Druffel Laboratory at UC Irvine for oxidation via UV irradiation (Beaupre et al., Limnol. Oceaongr. Meth., 5:174-184, 2007) followed by determination of 14C content via accelerator mass spectrometry (AMS) at the Keck Carbon Cycle AMS Laboratory. DOC samples loaded onto PPL cartridges were eluted in methanol into quartz tubes and processed via sealed-tube-combustion (STC) as described in Druffel et al. (1992) J. Geophys. Res., 97:15,639-15,659. CO2 thus recovered were graphitized (Xu et al., Nucl. Instr. Meth. Phys. Res. B, 259:320-329, 2007) and submitted to UC Irvine for AMS analysis. Porewater DIC samples were extracted via acidification under vacuum, purified cryogenically, and CO2 yield quantified manometrically as described in Komada et al. (2016) Geochim. Cosmochim. Acta, 176:259-278. CO2 samples were graphitized as described above and submitted to UC Irvine for AMS and IRMS (for 13C). Bottom-water DIC samples were submitted as is to NOSAMS for 14C analysis.

To determine POC, known mass of dried and homogenized sediment samples were acidified (Komada et al., Limnol. Oceanogr. Meth., 6:254-262, 2008) then processed via STC as described above. Total carbon and total nitrogen were determined on non-acidified samples using a Costech elemental analyzer.

All borosilicate glassware were soaped, acid rinsed, then ashed at 550 deg.C for 4 hours. All quartz glass and cupric oxide wires were ashed at 850 deg.C for 4 hours. All plastic-ware were soaped, acid rinsed, then dried under stream of HEPA-filtered air.