Assessing benthic oxygen fluxes in oligotrophic deep sea sediments (HAUSGARTEN observatory)

Abstract

a b s t r a c tBenthic oxygen fluxes, an established proxy for total organic carbon mineralization, were investigated in oligotrophic deep sea sediments. We used three different in situ technologies to estimate the benthic oxygen fluxes at an Arctic deep sea site (2500 m depth, HAUSGARTEN observatory) with limiting conditions of low oxygen gradients and fluxes, low turbulence and low particle content in the benthic boundary layer. The resolved eddy covariance turbulent oxygen flux ( À 0. ). The agreement between these different techniques revealed that microbial-mediated oxygen consumption was dominant at this site. The average benthic flux equals a carbon mineralization rate of 4.3 g C m À 2 yr À 1 , which exceeds the annual sedimentation of particulate organic matter measured by sediment traps. The present study represents a detailed comparison of different in situ technologies for benthic flux measurements at different spatial scales in oligotrophic deep sea sediments. The use of eddy covariance, so far rarely used for deep sea investigations, is presented in detail.

Carbon and nitrogen turnover in the Arctic deep sea: in situ benthic community response to diatom and coccolithophorid phytodetritus

“…earlier in situ measurements (Donis et al, 2016) and food web modelling results that assigned 93 % of the respiration to bacteria (van Oevelen et al, 2011). An increase in bacterial activity was clearly observed after the deposition of fresh phytodetritus, both in terms of respiration and enzymatic activity, which is in accordance with earlier studies (Boetius and Lochte, 1994;Hoffmann et al, 2017).…”

“…Most of the OM is aerobically mineralized in the upper centimetre of the sediment in our study area (Donis et al, 2016). Hence we assume that denitrification of nitrate does not occur in the oxidized sediment layer of our experiments and that the observed accumulation of nitrate in the overlying water is caused solely by nitrification.…”

Investigating benthic impacts at salmon farms using eddy covariance measurements of benthic oxygen fluxes

“…Attard et al 2015, Koopmans & Berg 2015, Long et al 2015, Rovelli et al 2017. Benthic oxygen fluxes obtained from EC can show good agreement to other techniques such as sediment micro-profiling or benthic chambers, particularly over muddy sediments where little pore water flushing is expected (Berg et al 2003, Attard et al 2015, Donis et al 2016. It is appropriate, therefore, to compare the flux measurements here to those in other studies of aquaculture sites.…”

Technical note: Estimating light-use efficiency of benthic habitats using underwater O<sub>2</sub> eddy covariance

“…chamber incubations) and enables primary production rates to be measured within a wide range of benthic habitats (Chipman et al, 2016;Hume et al, 2011;Long et al, 2013;Volaric et al, 2018;Attard et al, 2019b). Additionally, the EC method can resolve very small benthic fluxes down to ~1 mmol O2 m -2 d -1 or less (Berg et al, 2009;Donis et al, 2016), which allows reliable measurements of primary 5 production to be made in low-activity benthic settings, such as in high-latitude environments in winter and in deep phototrophic communities Attard et al, 2016).…”