Biomarker analysis of cold seeps along the United States Atlantic Margin

Carbonate and sediment samples from pushcores were collected from ROV operations. Samples were stored frozen. The biomarker composition of the authigenic carbonate and sediment samples was determined by gas chromatography-mass spectrometry (GC-MS) at the USGS Organic Geochemistry laboratory in Santa Cruz, California. The samples were subsequently extracted using the Dionex ASE with a mixture of dichloromethane and methanol (9:1; v:v). Prior to extraction, internal standards were added (5-α androstane, 5α- 3β androstanol, ortho-terphenyl, and nonadecanoic acid). The total lipid extracts were passed though funnels containing sodium sulfate to remove excess water followed by saponification with 6% KOH (w/v) in methanol at 70°C for 3 hours. After cooling, the neutral fractions were extracted 3–5 times with hexane until the extracts turned colorless. To obtain fatty acids, the residuals were treated with 10% HCl to pH ~ 2 and extracted 3 times with hexane. The neutral fractions were separated by column chromatography into compound classes: (1) hydrocarbons (n-hexane), (2) aromatics (toluene:hexane) and (3) alcohols (ethyl acetate:hexane, methanol). The alcohols were converted to trimethylsiloxyl derivatives by bis (trimethylsilyl) trifluoroacetamide (BSTFA with 1% TMCS) heated at 60 °C for 1 h prior to GC–MS analysis. Fatty acids were converted to methyl esters by drying and subjecting the fraction to 14% BF3-methanol in a screw cap vial at 60 °C for 2 h. Compound specific isotope analysis (CSIA) on select biomarkers in the carbonate and sediment samples was determined by GC-combustion isotope ratio mass spectrometry (GC-C-IRMS). Carbon isotopic compositions of sterols and n-alkanes were measured at the Stable Isotope Facility at University of California, Davis using a Thermo GC-C-IRMS system composed of a Trace GC Ultra gas chromatograph coupled to a Delta V Advantage IRMS through a GC-C-III interface with compound identification support for the CSIA laboratory provided by a Varian CP3800 gas chromatograph coupled to a Saturn 2200 ion trap MS/MS. CSIA composition of the fatty acids was performed at the Marine Organic and Isotope Geochemistry lab at the University of Miami by GC-C-IRMS. Samples were dissolved in hexane and injected manually in splitless mode into a Thermo GC-C-IRMS system (Trace GC 1310 coupled to an Isolink II combustion interface, Conflo IV interface, and MAT 253 isotope ratio mass spectrometer). Results from the all lab analyses were combined into a comma-delimited text document (USAM_MDAC_Biomarker.csv) for this data release.

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