Pore water acetate and hydrogen, helium and methane gas concentrations in ODP Leg 204 sediments

Acetate and hydrogen concentrations in pore fluids were measured in samples taken at seven sites from southern Hydrate Ridge (SHR) offshore Oregon, USA. Acetate concentrations ranged from 3.17 to 2515 µM. The maximum acetate concentrations occurred at Site 1251, which was drilled on a slope basin to the east of SHR at depths just above the bottom-simulating reflector (BSR) that marks the boundary of gas hydrate stability. Acetate maxima and localized high acetate concentrations occurred at the BSR at all sites and frequently corresponded with areas of gas hydrate accumulation, suggesting an empirical relationship. Acetate concentrations were typically at a minimum near the seafloor and above the sulfate/methane interface, where sulfate-reducing bacteria may consume acetate. Hydrogen concentrations in pressure core samples ranged from 16.45 to 1036 parts per million by volume (ppmv). In some cases, hydrogen and acetate concentrations were elevated concurrently, suggesting a positive correlation. However, sampling of hydrogen was limited in comparison to acetate, so any relationships between the two analytes, if present, were difficult to discern.本数据集测定了采自美国俄勒冈州近海南部水合物脊（southern Hydrate Ridge, SHR）7个站位的孔隙流体（pore fluids）样本中的乙酸盐与氢气浓度。乙酸盐浓度范围为3.17至2515微摩尔（µM），最高值出现在1251站位——该站位钻取于SHR东侧的斜坡盆地，取样深度恰好位于标识天然气水合物稳定带边界的似海底反射层（bottom-simulating reflector, BSR）上方。所有站位的似海底反射层处均出现乙酸盐浓度峰值与局域性高浓度乙酸盐，且该分布特征常与天然气水合物富集区域对应，提示二者存在经验性关联。乙酸盐浓度通常在海底及硫酸盐-甲烷界面（sulfate/methane interface）上方处达到最低值，此处硫酸盐还原菌（sulfate-reducing bacteria）可能会消耗乙酸盐。加压岩心样本（pressure core samples）中的氢气浓度范围为16.45至1036体积百万分率（parts per million by volume, ppmv）。部分案例中氢气与乙酸盐浓度同步升高，提示二者存在正相关关系。不过相较于乙酸盐样本，氢气的采样量有限，因此即便二者间存在关联，也难以明确辨识。