Isotopic imaging was performed using the NanoSIMS 50L ion microprobe at the Department of Terrestrial Magnetism, Carnegie Institution of Washington. The selected area (in Fig. 1) of the sample was first presputtered using a 5- to 10-nA Cs beam to remove surface contamination and to sputter down through the sample until the area of interest was reached and exposed; an electron flood gun was used for charge compensation. We then used a 200-pA primary beam of Cs ions focused to a diameter of 400 nm for obtaining isotopic images. Simultaneous detection and imaging of 1H, 2D, and 13C were obtained by rastering the primary beam over areas of 15 μm by 15 μm starting at the surface of the section over the feature shown in Fig. 1 and sputtering down into the section for a distance of ~8 μm. For image acquisition, the sputter crater was divided into 256 pixels by 256 pixels, and beam blanking was not used. Data were recorded as scanning ion images obtained simultaneously on each isotopic mass at a depth of profile of ~2 μm per data acquisition for a total of four data acquisitions. Data were extracted and processed from the ion images using the L’Image software package for PV-Wave written by L. Nittler [Department of Terrestrial Magnetism, Carnegie Institution of Washington (DTM-CIW)]. Data were first collected on an organic standard supplied by L. Nittler and were used to correct the instrument mass fractionation effects. Count rates were corrected for detector dead time (44 ns), and the data were standardized using the series of analysis on several areas of the standard with known isotopic compositions. Additional details of the method can be found in Hauri et al. (59). Thin section polymer signal was analyzed and corrected = −150‰.

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