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. Copyright © 2013 by The Geochemical Society of Japan.