Efficiency and adaptability of the benthic methane filter at Quepos Slide cold seeps, offshore of Costa Rica

Abstract

Abstract. Large amounts of methane are delivered by fluids through the erosive forearc of the convergent margin offshore of Costa Rica and lead to the formation of cold seeps at the sediment surface. Besides mud extrusion, numerous cold seeps are created by landslides induced by seamount subduction or fluid migration along major faults. Most of the dissolved methane migrating through the sediments of cold seeps is oxidized within the benthic microbial methane filter by anaerobic oxidation of methane (AOM). Measurements of AOM and sulfate reduction as well as numerical modeling of porewater profiles revealed a highly active and efficient benthic methane filter at the Quepos Slide site, a landslide on the continental slope between the Nicoya and Osa Peninsula. Integrated areal rates of AOM ranged from 12.9 ± 6.0 to 45.2 ± 11.5 mmol m −2 d −1 , with only 1 to 2.5 % of the upward methane flux being released into the water column.Additionally, two parallel sediment cores from Quepos Slide were used for in vitro experiments in a recently developed sediment-flow-through (SLOT) system to simulate an increased fluid and methane flux from the bottom of the sediment core. The benthic methane filter revealed a high adaptability whereby the methane oxidation efficiency responded to the increased fluid flow within ca. 170 d. To our knowledge, this study provides the first estimation of the natural biogeochemical response of seep sediments to changes in fluid flow.

Hydrocarbon Degradation in Caspian Sea Sediment Cores Subjected to Simulated Petroleum Seepage in a Newly Designed Sediment-Oil-Flow-Through System

“…Petroleum droplets visibly seeped out of the sediment close to the core liner wall. High fluid flow through sediment cores can induce channelizing effects between the wall of the core liner and the sediment core, causing some fluid to move faster than the bulk volume (Steeb et al, 2014, 2015). Upon termination and slicing of the SOFT core we observed that although most of the petroleum seemed to be evenly distributed throughout the sediment, some petroleum accumulated in vein-like structures indicating such channelizing effects (Supplement 3).…”

The Impact of Methane Seepage on the Pore-Water Geochemistry across the East Siberian Arctic Shelf

“…The AOM is always the predominant reaction in seep environments. In low-methane flux seep environments, all the methane can be consumed by AOM, while in high methane flux seep environments, a proportion of the methane may pass through the SMTZ and escape to the bottom water [25,26]. Both AOM and OSR processes strengthen the alkalinity of pore-water, which facilitates the precipitation of authigenic carbonate (Ca 2+ + HCO 3 − → CaCO 3 + H + ), and decrease the calcium concentration in pore-water.…”