Oxygen as a control on sea floor biological communities and their roles in sedimentary carbon cycling

Abstract

Abstract13 C tracer experiments were conducted at sites spanning the steep oxygen, organic matter, and biological community gradients across the Arabian Sea oxygen minimum zone, in order to quantify the role that benthic fauna play in the short-term processing of organic matter (OM) and to determine how this varies among different environments. Metazoan macrofauna and macrofauna-sized foraminiferans took up as much as 56 6 13 mg of added C m 22 (685 mg C m 22 added) over 2-5 d, and at some sites this uptake was similar in magnitude to bacterial uptake and/or total respiration. Bottom-water dissolved oxygen concentrations exerted a strong control over metazoan macrofaunal OM processing. At oxygen concentrations .7 mmol L 21 (0.16 ml L 21 ), metazoan macrofauna were able to take advantage of abundant OM and to dominate OM uptake, while OM processing at O 2 concentrations of 5.0 mmol L 21 (0.11 ml L 21 ) was dominated instead by (macrofaunal) foraminiferans. This led us to propose the hypothesis that oxygen controls the relative dominance of metazoan macrofauna and foraminifera in a threshold manner, with the threshold lying between 5 and 7 mmol L 21 (0.11 to 0.16 ml L 21 ). Large metazoan macrofaunal biomass and high natural concentrations of OM were also associated with rapid processing of fresh OM by the benthic community. Where they were present, the polychaete Linopherus sp. and the calcareous foraminiferan Uvigerina ex gr. semiornata, dominated the uptake of OM above and below, respectively, the proposed threshold concentrations of bottom-water oxygen.1 Present address: Danish Meteorological Institute, Lyngbyvej 100, 2100 Copenhagen, Denmark. AcknowledgmentsThe experimental work in this study was conducted aboard the RRS Charles Darwin. We thank Oli Peppe and Eric Breuer for running the lander and megacorer. We also thank two anonymous reviewers for their constructive feedback.

Oxygen dynamics in shelf seas sediments incorporating seasonal variability

“…Variability in sediment pore water oxygen concentration can be seen in Sites H and I, and is probably attributable to faunal burrows Rabouille et al 2003;Viollier et al 2003). Infaunal activity within burrows (bioturbation and bioirrigation), in addition to respiration, will directly increase the TOU rate (Viollier et al 2003;Woulds et al 2007), and this was apparent in the May bloom measurements, likely due to increased faunal activity in response to the input of fresh organic matter. The difference in the oxygen concentrations of the overlying water between the high and lowresolution profiles, with the exception of Site A for the March cruises (Figs.…”

“…Benthic oxygen uptake provides a good proxy for benthic mineralisation (Glud et al 2016;Jahnke et al 2000;Woulds et al 2007), however spatial and temporal variability of oxygen dynamics may present a bias in interpretation if careful consideration is not given to the methodology used and caveats of each approach, e.g. incubations favour diffusive processes so may lead to over or underestimation in permeable sediments (Lohse et al 1996;Tengberg et al 2004).…”

“…Continental shelf sediments play a vital role in biogeochemical cycling, accumulating and burying organic matter (Jahnke et al 2005;Woulds et al 2007). Shelf sediments receive up to 50% of primary productivity from the overlying surface waters (Stahl et al 2004a), and as this source of carbon reaches the benthos it is recycled, mineralised or buried (Canfield et al 1993;Glud 2008).…”

“…Shelf sediments receive up to 50% of primary productivity from the overlying surface waters (Stahl et al 2004a), and as this source of carbon reaches the benthos it is recycled, mineralised or buried (Canfield et al 1993;Glud 2008). One of the determinants of burial efficiency of organic matter is the presence and the depth of oxygen penetration (Burdige 2007;Glud 2008;Woulds et al 2007). The ability to sequester organic carbon is influenced by the presence and activity of macrofauna and meiofauna (Woulds et al 2007), and the type of sediment (cohesive vs permeable (Fuchsman et al 2015;Glud 2008)).…”

“…One of the determinants of burial efficiency of organic matter is the presence and the depth of oxygen penetration (Burdige 2007;Glud 2008;Woulds et al 2007). The ability to sequester organic carbon is influenced by the presence and activity of macrofauna and meiofauna (Woulds et al 2007), and the type of sediment (cohesive vs permeable (Fuchsman et al 2015;Glud 2008)). The efficiency of organic carbon burial has been directly linked to the pore water oxygen concentration and exposure time (Hartnett et al 1998), and the availability of oxygen regulates different benthic biogeochemical processes (Glud 2008;Klar et al 2017;Scholz et al 2014;Serpetti et al 2016).…”