Table 2. Methane oxidation in long-term water incubations at 12 °C.
| Latitude/longitude | Sample water depth (m) | Ambient oxygen (μmol l−1) | Ambient methane (nmol l−1) | 13C-DIC produced (nmol) | Initial isotope spikes | 15N-N2 produced (nmol) |
|---|---|---|---|---|---|---|
| 13°21 N/91°23 W | 195 | 1.9 | 3.1 | 0.2±0.03 | 264 nM 13CH4 | NA |
| 200 | 1.5 | 2.8 | 0.6±0.34 | |||
| 205 | ⩽1.4 | 4.4 | 0.1±0.09 | |||
| 210 | ⩽1.4 | 3.4 | 0.20±0.22 | |||
| 13°15 N/91°08 W | 47 | 132.1 | 4.8 | −0.1±0.06 | ||
| 226 | ⩽1.4 | 2.1 | −0.02±0.08 | |||
| 13°16 N/ 91°08 W | 65 | 11.4 | 2.4 | 0.2±0.02 | ||
| 228 | ⩽1.4 | 3.9 | 0.3±0.11 | |||
| 13°25 N/ 91°23 W | 235 | ⩽1.4 | 4.3 | 2.6±1.25a | ||
| 235* | 2.4±1.11a | 80.5±30.11 | ||||
| 13°16 N/ 91°08 W | 322 | ⩽1.4 | 14.8 | 10.4±0.18a | 3.4 μM 13CH4 and for *samples also 11.4 μM 15NO2− | |
| 322* | 11.8±3.50a | 16.0±2.64 | ||||
| 412 | ⩽1.4 | 33.9 | 12.3±4.03a | |||
| 412* | 15.4±0.78a | 14.5±4.11 | ||||
| 13°16 N/91°08 W | 264 | ⩽1.4 | 9.4 | 1.3±1.20a | ||
| 264* | 12.0±6.00a | 29.3±18.22 | ||||
| 256 | ⩽1.4 | 6.1 | 11.2±0.00a | |||
| 256* | 0.9±1.37a | 8.9±0.61 |
Abbreviations: NA, not applicable; OFN, oxygen-free nitrogen.
Mean values (± s.e., n=3). Samples marked with 'a' had a 2 ml OFN headspace throughout the incubation. Samples marked with * are those where 15N-NO2 (11.4 μmol l−1) was introduced and the production of 15N-N2 measured after 5 months. Where oxygen was at or below the limit of detection it was assumed to be ⩽1.4 μmol l−1.