Publication Date:
2023-06-27
Description:
Hydrogen- and carbon-isotope compositions of methane (dD-CH4 and d13C-CH4) and pore water hydrogen-isotope compositions (dD-H2O) in several samples from the uppermost 100 m of Orca Basin sediments show little variation with depth and have mean values of - 184, -73.5, and 7 per mil, respectively. The dD-CH4 is typical of that generally found in deep-sea sediments and suggests that the methane was produced biologically almost entirely via the CO2 reduction pathway. Production of small amounts of methane (-15% of the total) from acetate dissimilation cannot be completely ruled out, however. The pore water is more enriched in deuterium than present day Gulf of Mexico deep water, suggesting that the brine found at the bottom of Orca Basin was formed at a time when appreciably more isotopically light water was tied up in continental ice sheets than is at present. The d13C-CH4 values reported here are similar to previously determined brine d13C-CH4, but substantially more enriched in 13C than previously determined pore water d13C-CH4. Isotopic evidence and the decrease in interstitial salinity with depth suggest that most of the methane production within the Orca Basin system occurs in sediments deeper than about 5 m sub-bottom. Small deposits of isotopically anomalous methane occurring in near-surface sediments may be the result of spatially variable inputs of slumped material to the sediments underlying the anoxic, hypersaline brine.
Keywords:
96-618; Deep Sea Drilling Project; DEPTH, sediment/rock; DRILL; Drilling/drill rig; DSDP; DSDP/ODP/IODP sample designation; Glomar Challenger; Gulf of Mexico/BASIN; Leg96; Mass spectrometer Finnigan MAT 250; Sample code/label; see reference(s); δ13C, methane; δ Deuterium, methane; δ Deuterium, water
Type:
Dataset
Format:
text/tab-separated-values, 41 data points
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