Anaerobic methane oxidation in a coastal oxygen minimum zone: spatial and temporal dynamics
"Coastal waters are a major source of marine methane to the atmosphere. Particularly high concentrations of this potent greenhouse gas are found in anoxic waters, but it remains unclear if and to what extent anaerobic methanotrophs mitigate the methane flux. Here we investigate the long-term dynamics in methanotrophic activity and the methanotroph community in the coastal oxygen minimum zone (OMZ) of Golfo Dulce, Costa Rica, combining biogeochemical analyses, experimental incubations and 16S rRNA gene sequencing over 3 consecutive years. [...]".
Source: Environmental Microbiology
Authors: Herdís G. R. Steinsdóttir et al.
Temperature and oxygen supply shape the demersal community in a tropical Oxygen Minimum Zone
"The organisms that inhabit Oxygen Minimum Zones (OMZ) have specialized adaptations that allow them to survive within a very narrow range of environmental conditions. Consequently, even small environmental perturbations can result in local species distribution shifts that alter ecosystem trophodynamics. Here, we examined the effect of changing sea water temperatures and oxygen levels on the physiological performance and metabolic traits of the species forming marine demersal communities along the OMZ margins in the Costa Rican Pacific. The strong temperature and oxygen gradients along this OMZ margin provide a “natural experiment” to explore the effects of warming and hypoxia on marine demersal communities. [...]".
Source: Environmental Biology of Fishes
Authors: Tayler M. Clarke et al.
Mid-Holocene intensification of the oxygen minimum zone in the northeastern Arabian Sea
"The Arabian Sea is characterized by a strong Oxygen Minimum Zone (OMZ) bearing sub-oxic conditions at the intermediate water depth. We analyzed a sediment core near the upper margin of OMZ (174 m water depth) from offshore Saurashtra, northeastern (NE) Arabian Sea to reconstruct multi-proxy biogeochemical response in the area during the Early-Middle Holocene (∼10–4 ka before present). The results indicate lower foraminiferal productivity (both benthic and planktic) and weak sub-surface denitrification causing mild OMZ conditions at the study site during the early Holocene (∼10–8 ka). Subsequently, an increased foraminiferal productivity and sub-surface (both the water column and sediment) denitrification in the area led to intensified OMZ conditions during the mid-Holocene (after ∼8 ka). [...]".
Source: Science Direct
Authors: Syed Azharuddin et al.
Observed denitrification in the northeast Arabian Sea during the winter-spring transition of 2009
"The central and northeast Arabian Sea (AS) has an intense and thick oxygen minimum zone (OMZ) and denitrification zone. It is comparable with the strongest OMZ of the north-equatorial Pacific Ocean. Denitrification in the AS is revisited using a set of cruise observations collected during February–March of 2009 by the Centre for Marine Living Resources, India. The region possesses one of the most robust N* depleted water reaching as low as -20 μmol l−1 at depths (~600 m). In AS, the oxygen depletion is mainly due to sluggish circulation, weak lateral and vertical ventilation. The biological respiration in oxygen deficit condition depletes nitrate and further modifies the Redfield ratio at intermediate depths (200-600 m) from 16N:1P to 8N:1P. [...]".
Source: Science Direct
Authors: Anju Mallissery et al.
Oxygen gradients shape the unique structure of picoeukaryotic communities in the Bay of Bengal
"Picoeukaryotic communities respond rapidly to global climate change and play an important role in marine biological food webs and ecosystems. The formation of oxygen minimum zones (OMZ) is facilitated by the stratification of seawater and higher primary production in the surface layer, and the marine picoeukaryotic community this low-oxygen environment is topic of interest. To better understand the picoeukaryotic community assembly mechanisms in an OMZ, we collected samples from the Bay of Bengal (BOB) in October and November 2020 and used 18S rDNA to study the picoeukaryotic communities and their community assembly mechanisms that they are controlled by in deep-sea and hypoxic zones. The results show that deterministic and stochastic processes combine to shape picoeukaryotic communities in the BOB. [...]".
Source: Science Direct
Authors: Zhuo Chen et al.
Sensitivity of asymmetric oxygen minimum zones to mixing intensity and stoichiometry in the tropical Pacific using a basin-scale model
"The tropical Pacific Ocean holds the two largest oxygen minimum zones (OMZs) in the world's oceans, showing a prominent hemispheric asymmetry, with a much stronger and broader OMZ north of the Equator. However, many models have difficulties in reproducing the observed asymmetric OMZs in the tropical Pacific. Here, we apply a fully coupled basin-scale model to evaluate the impacts of stoichiometry and the intensity of vertical mixing on the dynamics of OMZs in the tropical Pacific. We first utilize observational data of dissolved oxygen (DO) to calibrate and validate the basin-scale model. Our model experiments demonstrate that enhanced vertical mixing combined with a reduced O:C utilization ratio can significantly improve our model capability of reproducing the asymmetric OMZs. Our study shows that DO concentration is more sensitive to biological processes over 200–400 m but to physical processes below 400 m. [...]".
Source: Geoscientific Model Development
Authors: Kai Wang et al.
Responses of Horizontally Expanding Oceanic Oxygen Minimum Zones to Climate Change Based on Observations
"Due to climate change, global oceanic dissolved oxygen (DO) has been decreasing, and oxygen minimum zones (OMZs) have been expanding. Here, we estimate the annual global and regional OMZ areas using geostatistical regression combined with Monte Carlo. From 1960 to 2019, annual global OMZ20 (DO < 20 μmol/kg) and OMZ60 (DO < 60 μmol/kg) areas cover 5%–14% and 15%–32% of the global ocean, respectively. The global and most regional OMZ areas after the late 2000s were all significantly larger than those in previous years. [...]".
Source: Wiley Online Library
Authors: Yuntao Zhou et al.
Distribution and biomass of gelatinous zooplankton in relation to an oxygen minimum zone and a shallow seamount in the Eastern Tropical North Atlantic
"Physical and topographic characteristics can structure pelagic habitats and affect the plankton community composition. For example, oxygen minimum zones (OMZs) are expected to lead to a habitat compression for species with a high oxygen demand, while upwelling of nutrient-rich deep water at seamounts can locally increase productivity, especially in oligotrophic oceanic waters. Here we investigate the response of the gelatinous zooplankton (GZ) assemblage and biomass to differing oxygen conditions and to a seamount in the Eastern Tropical North Atlantic (ETNA) around the Cape Verde archipelago. [...]."
Source: Science Direct
Authors: Florian Lüskow et al.
Biogeochemical feedbacks may amplify ongoing and future ocean deoxygenation: a case study from the Peruvian oxygen minimum zone
"A new box model is employed to simulate the oxygen-dependent cycling of nutrients in the Peruvian oxygen minimum zone (OMZ). Model results and data for the present state of the OMZ indicate that dissolved iron is the limiting nutrient for primary production and is provided by the release of dissolved ferrous iron from shelf and slope sediments. Most of the removal of reactive nitrogen occurs by anaerobic oxidation of ammonium where ammonium is delivered by aerobic organic nitrogen degradation. Model experiments simulating the effects of ocean deoxygenation and warming show that the productivity of the Peruvian OMZ will increase due to the enhanced release of dissolved iron from shelf and slope sediments. A positive feedback loop rooted in the oxygen-dependent benthic iron release amplifies, both, the productivity rise and oxygen decline in ambient bottom waters. [...]".
Authors: Klaus Wallmann et al.
Oxygen minimum zone along the eastern Arabian Sea: Intra-annual variation and dynamics based on ship-borne studies
"The oxygen minimum zone (OMZ) in the eastern Arabian Sea (EAS, ∼6° to 21°N), within Indian Exclusive Economic Zone (EEZ), is mapped, for the first time, for one year through ten repeated ship-based observations between December 2017 and January 2019 at seven to ten stations along the 2000 m depth contour. On an annual basis, the OMZ (<20 µM oxygen) in the EAS varied between 60 and 1350 m; its thickness decreased from north to south. During the winter monsoon, the upper boundary of the OMZ in the north and south was deeper (150–160 m) than the central EAS (∼110 m). [...]".
Source: Science Direct
Authors: Sudheesh Valliyodan et al.