FIG. 3.

(A and B) Overlays of a photograph, a beta imager micrograph, and spots measured by SIMS of mat sections 1 (A) and 2 (B) incubated with H¹⁴CO₂⁻ and ¹⁴CH₄, respectively. The mat sections are oriented vertically with the former mat-water interface at the top. The photograph includes the outer border of the mat section. A high level of ¹⁴C radioactivity (expressed in counts per hour) in the beta imager micrograph is indicated by red, and a low level of radioactivity is indicated blue, as shown by the radioactivity bar. Colored spots indicate the δ¹³C values of the bulk biomass determined by SIMS, as indicated in the chart. The precise δ¹³C value for each spot is shown in Tables 2 and 3. The scale bar in panel A (indicating depth) allows a comparison of activity and δ¹³C values with the distribution of dominant methanotrophic groups identified by CARD-FISH shown in Fig. 4. (C and D) Photographs of mat pieces in panels A and B, respectively, before sectioning. The scale is in centimeters. In panel D, the piece is embedded in Tissue Tek OCT compound for easier sectioning. (E and F) Beta imager micrographs of the mat sections in panels A and B, respectively. Each micrograph shows the distribution of ¹⁴C in two consecutive mat sections.