Increase in acetate concentrations during sediment sample onboard storage: a caution for pore-water geochemical analyses

Abstract

Microbial activity in marine sediment plays an important biogeochemical role in cycling of carbon and other elements. Acetate is a key intermediate of various microbial metabolic pathways. In this study, we measured concentrations and stable carbon isotopic compositions (δ¹³C) of acetate in pore water of two core samples stored at near in-situ temperatures (4°C) within 3 hours and at room temperatures (25°C) for 19 hours after sample recovery. Acetate concentrations at 4°C were less than 3 μM throughout the sediment column, whereas they increased up to 13 μM in the samples stored at 25°C and corresponding δ¹³C values of acetate were enriched up to 8.7‰ relative to those of total organic carbon. Our results indicate that acetate-mediated microbial activity is rapidly changed with temperature increase and possible air contamination, and also suggest that sample processing at near in-situ temperatures in the short-term is required for accurate pore-water geochemical analysis.