Small sinking particles control anammox rates in the Peruvian oxygen minimum zone

Abstract

Anaerobic oxidation of ammonium (anammox) in oxygen minimum zones (OMZs) is a major pathway of oceanic nitrogen loss. Ammonium released from sinking particles has been suggested to fuel this process. During cruises to the Peruvian OMZ in April–June 2017 we found that anammox rates are strongly correlated with the volume of small particles (128–512 µm), even though anammox bacteria were not directly associated with particles. This suggests that the relationship between anammox rates and particles is related to the ammonium released from particles by remineralization. To investigate this, ammonium release from particles was modelled and theoretical encounters of free-living anammox bacteria with ammonium in the particle boundary layer were calculated. These results indicated that small sinking particles could be responsible for ~75% of ammonium release in anoxic waters and that free-living anammox bacteria frequently encounter ammonium in the vicinity of smaller particles. This indicates a so far underestimated role of abundant, slow-sinking small particles in controlling oceanic nutrient budgets, and furthermore implies that observations of the volume of small particles could be used to estimate N-loss across large areas.

Microbial Activities and Selection from Surface Ocean to Subseafloor on the Namibian Continental Shelf

“…Oxygen minimum zones (OMZs) have long been recognized as hot spots for oxygen-sensitive nitrogen microbial transformations ( 1 , 2 ) and are traditionally seen as regions dominated by heterotrophic denitrification and anaerobic ammonium oxidation (anammox) fueled by the sinking of organic matter (OM) produced via photosynthesis in the sunlit surface ocean ( 3 – 5 ). In regions such as the eastern tropical Pacific ( 6 , 7 ), the Arabian Sea ( 8 , 9 ), and the Benguela Current coastal upwelling ( 10 ), dropping oxygen concentrations in OMZ waters initiate a dynamic nitrogen cycle ( 11 , 12 ), in which nitrate serves as the main terminal electron acceptor for the oxidation of OM and is successively converted to nitrite ( 13 ), nitrogen (N 2 ), and nitrous oxide (N 2 O) gases through processes of denitrification ( 14 ) and autotrophic anammox ( 11 ).…”

Simultaneous visualization of flow fields and oxygen concentrations to unravel transport and metabolic processes in biological systems

“…In organic aggregates, the high carbon content and associated microbial activity lead to the formation of distinct microenvironments. When respiration exhausts O 2 inside aggregates ( Ploug, 2001 ), anaerobic processes are favored (e.g., denitrification and anammox), resulting in the enhanced removal of nutrients in wastewater treatment plants ( Speth et al., 2016 ) and the ocean ( Bianchi et al., 2018 ; Karthäuser et al., 2021 ). Inside aggregates, the duration and extent of O 2 depletion is governed by the external supply of O 2 and its transport through the aggregate boundary layer.…”

Bridging the gaps between particulate backscattering measurements and modeled particulate organic carbon in the ocean

“…6, S5-S7 and S10), owing to their connection with the upper-ocean through numerous biological and physical processes (Boyd et al, 2019;Briggs et al, 2020). Despite being less reactive on average than upper-ocean POC, meso-and bathypelagic organic particles are microbial hotspots that host key biogeochemical functions, from enzymatic decomposition of macromolecules (Arnosti et al, 2012;Baltar et al, 2010aBaltar et al, , 2010b to aerobic and anaerobic respiration (e.g., Karthäuser et al, 2021) and chemosynthesis (Arístegui et al, 2009;Pachiadaki et al, 2017). Moreover, mesopelagic particles are consumed by upper trophic levels that sustain fisheries (Bode et al, 2021;Woodstock et al, 2021).…”