Regulation of benthic oxygen fluxes in permeable sediments of the coastal ocean

Abstract

Large areas of the oceanic shelf are composed of sandy sediments through which reactive solutes are transported via porewater advection fueling active microbial communities. The advective oxygen transport in permeable sands of the North Sea was investigated under in situ conditions using a new benthic observatory to assess the dynamic interaction of hydrodynamics, sediment morphodynamics, and oxygen penetration depth. During 16 deployments, concurrent measurement of current velocity, sediment topography, and porewater oxygen concentration were carried out. In all cases the oxyclines were found at depths of 1-6 cm, correlating with the topography of stationary and migrating bedforms (ripples). Different conditions in terms of bottom water currents and bedform migration led to fluctuating oxygen penetration depths and, hence, highly variable redox conditions in up to 2.5 cm thick layers beneath the surface. Volumetric oxygen consumption rates of surface sediments were measured on board in flow-through reactors. Bedform migration was found to reduce consumption rates by up to 50%, presumably caused by the washout of organic carbon that is otherwise trapped in the pore space of the sediment. Based on the observations we found oxygen penetration depths to be largely controlled by oxygen consumption rates, grain size, and current velocity. These controlling variables are summarized by an adapted Damk€ ohler number which allows for prediction of oxygen penetretion depths based on a simple scaling law. By integrating the oxygen consumption rates over the oxygen penetration depth, oxygen fluxes of 8-34 mmol m 22 d 21 were estimated.

Permeability shapes bacterial communities in sublittoral surface sediments

“…In addition, site NOAH‐B was sampled in March 2014 and February 2015 to study seasonal effects. Data for sediment permeability and oxygen penetration depth taken from Ahmerkamp ().…”

“…(4) Are there seasonal changes in benthic bacterial community composition, and, if yes, do these have a greater influence than sediment permeability? To address these questions, we examined North Sea sediments of different permeability at high vertical resolution considering oxygen penetration depths and redox conditions (Ahmerkamp, ). Dominant bacterial taxa were identified by tag sequencing of 16S rRNA genes and quantified by catalyzed reporter deposition fluorescence in situ hybridization (CARD‐FISH) using newly designed and established oligonucleotide probes.…”

The Coastal Observing System for Northern and Arctic Seas (COSYNA)

“…These landers bridge the observational gap between longterm monitoring stations, remote sensing applications, and ship-based field campaigns. They are mobile, and can be used to spatially interpolate between monitoring stations and provide data with very high temporal resolution (Kwoll et al, 2013(Kwoll et al, , 2014Oehler et al, 2015a;Ahmerkamp et al, 2017). Lander operations aim at measuring various processes close to the seafloor or in the sediment and are designed to have minimal impact on the environment and quantities that are measured.…”

“…The lander was successfully applied on sandy sediments of the North Sea ( Fig. 14; Friedrich et al, 2016;Neumann et al, 2016;Ahmerkamp et al, 2017).…”

Seasonality of Organic Matter Degradation Regulates Nutrient and Metal Net Fluxes in a High Energy Sandy Beach

“…So far, the impact of pore water advection on biogeochemistry and pore water constituent effluxes from permeable sediments has mostly been studied in microtidal sheltered beaches (Beck et al, ; Gonneea & Charette, ; Liu et al, ; O'Connor et al, ; Santos et al, ), tidal flat areas (Beck et al, ; Billerbeck et al, ; Gao et al, ; Huettel & Rusch, ; Marchant et al, ; Riedel et al, ), or subtidal sediments (Ahmerkamp et al, ; Marchant et al, ; Shum & Sundby, ), which are exposed to a lower wave energy level than high energy beaches. In contrast, only few studies have been conducted at wave exposed mesotidal to macrotidal sites like the French Aquitanian coast (Anschutz et al, ; Charbonnier et al, ; Charbonnier et al, ) or the beaches of Spiekeroog Island, Germany (Beck et al, ; Reckhardt et al, ; Seidel et al, ; Waska et al, ).…”