The oxygen deficient zones (ODZs) are confined to small volumes of the ocean but exert large influence on biogeochemical cycles, by altering the redox chemistry and microbial transformation of nutrients in these regions. The factors that regulate the size and sensitivity of ODZs to oceanic change are numerous, complex, and remain poorly understood. We synthesize recent autonomous and...
This study investigates the mechanisms of interannual and decadal variability of dissolved oxygen (O$_2$) in the North Pacific using historical bottle O$_2$ data and a physical-biogeochemical hindcast simulation. An ocean-ice configuration of the Community Earth System Model (CESM) is used to for the hindcast. The simulated variability of upper ocean (200m) O$_2$ is broadly consistent with...
Deoxygenation has been a big concern because oxygen is an essential element for all levels of marine life. Data has shown an expansion of Oxygen-Minimum-Zone (OMZ) with a declining trend in dissolved oxygen (DO) over the past decades in the tropical Pacific. However, there is a lack of quantitative analyses of sources and sinks to elucidate the underlying mechanisms. Here, we employ a...
The highly productive eastern boundary upwelling system of the South Pacific is characterized by the presence of an intense and shallow oxygen minimum zone (OMZ). Near the coast of South America these oxygen depleted waters are advected poleward by the Peru-Chile Undercurrent extending the southern limit of the OMZ along the coast as far south as ~40°S. Off central Chile (30°S-40°S) mesoscale...
While observations suggest a long-term expansion of the OMZ in the South Eastern Pacific (SEP) which has been suggested to be due to global warming, the SEP OMZ also apparently exhibits a notable decadal variability in its upper and lower limits. Large uncertainties of the fate of the SEP OMZ in a warmer climate as simulated by Earth system models also questions to which extent natural...
The El Niño Southern Oscillation (ENSO) with its warm (El Niño) and cold (La Niña) phase has strong impacts on marine ecosystems off Peru. This influence extends from changes in nutrient availability to productivity and oxygen levels. While several studies have demonstrated the influence of ENSO events on biological productivity, less is known about their impact on oxygen concentrations. In...
In the framework of the German collaborative research centre SFB754 and associated programs, a large data set consisting of shipboard and moored observations has been collected in the eastern tropical North Atlantic (ETNA) during the past 10 years. This data provides an unprecedented comprehensive insight into the variability of oxygen, hydrography and velocity of the oxygen minimum zone (OMZ)...
The equatorial deep jets and the quasi-steady flanking jets are part of the zonal jet system in the equatorial ocean and play a role in setting the equatorial maximum in oxygen that has been known since the Meteor cruises from the 1920’s. Nevertheless, these zonal jets are missing from the models we use for ocean/climate studies, even ocean models with high horizontal resolution. Here we...
Increased observational efforts have revealed a multi-decadal decrease of oxygen concentrations with superimposed interannual to decadal variability in the oxygen minimum zone (OMZ) of the eastern tropical North Atlantic (ETNA). Recent studies have linked this variability to long-term changes in the ventilation by the latitudinally alternating zonal jets (LAZJs).
In this study a 1.5 layer...
Among the eastern boundary systems, the Eastern tropical North Atlantic (ETNA) has the least extreme deoxygenation condition, both in terms of OMZ geographical extent and also of oxygen depletion level. On the other hand, the vertical structure of the oxygen distribution is such that low hypoxic values are found at ~ 100 m depth offshore of Senegal and Mauritania. This depth is approximately...
In the Oxygen Minimum Zone (OMZ) of the Eastern Tropical North Atlantic (ETNA) oxygen values vary on daily to multidecadal time scales. The OMZ is ventilated by weak eastward flowing zonal currents, among them the North Equatorial Undercurrent (NEUC). It is located between $4^{\circ}$N and $6^{\circ}$N in a depth range of $50\,$m to $400\,$m and its core velocity varies between...
The response of oxygen concentrations in the subpolar North Atlantic (SPNA) to future climate change is poorly understood. Here, we investigate the multi-decadal variability in the interior oxygen at 1500 m depth and its association with the North Atlantic subpolar gyre index (a proxy for the subpolar gyre strength) for both models and data. During its positive phase, persistent anomalously...
The Eastern Pacific (EP) hosts one of the most productive eastern boundary upwelling systems (EBUS) of the world oceans, encompassing an extended Oxygen Minimum Zone (OMZ). EBUS is characterized by complex dynamical processes spanning a wide range of spatio-temporal variability due to the strong coupling between the ocean and atmosphere. In particular, the EP OMZ is strongly modulated by the...
The tropical thermocline that covers the strongly stratified region below the oceanic mixed layer accommodates extended oxygen minimum zones (OMZs). The subtropical-tropical circulation of the Pacific and Atlantic oceans characterized by the wind-driven equatorward and westward flow of newly subducted water masses sets the poleward boundaries of the OMZs in both oceans. Energetic circulation...
We investigate century and multi-millennial scale changes in marine oxygen (O2), marine emissions of nitrous oxide (N2O), warming, and compound hazard in terms of metabolic conditions for a range of temperature targets, including those mentioned in the Paris Agreement. Scenarios, where radiative forcing is stabilized by 2300, are used in ensemble simulations with the Bern3D Earth System Model...
A multi-millennial global-warming simulation with an Earth system model of intermediate complexity with fixed phosphorus inventory and driven by business-as-usual CO2 emissions until year 2100 and a linear decline to zero emissions in year 2300 and thereafter, yields a marine oxygen inventory that exceeds the preindustrial oxygen inventory in the simulated warmer future climate, with surface...
Coupled climate model simulations consistently project for the 21st century reduced ventilation of the deep ocean and a loss of oxygen in response to global warming, yet the warming at the end of the last ice age – similar in amplitude to the warming projected for the end of the century – resulted in a better ventilated deep ocean. Here, we use multi-millennial global warming simulations with...
The near-surface atmosphere layer, and in particular the wind intensity, controls the ocean properties. The Ekman circulation depends of the wind stress, which strength also determines the amount of diffusion in the upper layer. The intensity of the latent and sensible fluxes at surface depend linearly of the wind speed. The wind also directly impacts the biogeochemical cycles as it modulates...
Climate projections with Earth System Models (ESM) suggest that strong deoxygenation is projected to occur by the end of the 21st century in the temperate gyres of the North Pacific and North Atlantic. This deoxygenation trend is the consequence of a balance between 1) reduced oxygen solubility associated with warmer temperatures 2) reduced ventilation, and 3) is partly counter-balanced by...
We use a simple 1D model and 3D global ocean biogeochemical models to evaluate the concept of computing the subsurface oceanic oxygen utilization rate (OUR) from the changes of apparent oxygen utilization (AOU) and water age along trajectories on isopycnal surfaces. We find that OUR underestimates globally averaged total oceanic oxygen consumption (respiration) substantially. Most of this...
Recent modelling studies revealed the importance of mesoscale eddies for a lateral transport of water mass anomalies from the eastern boundary upwelling systems into oxygen minimum zones (OMZ). Observational studies on individual eddies show that mesoscale dynamic change the biogeochemical eddy characteristics “en-route”. Vertical nutrient flux into the euphotic layer controls local...
More than thirty years ago the interaction between near-inertial wave (NIW) propagation and geostrophic flow was already investigated. It was theoretically shown that anticyclonic eddies can trap and enhance downward propagation of NIW energy. A critical-layer can be formed below these eddies where the associated vorticity anomaly vanishes. Today, several recent model studies point out the...
The dynamics of Oxygen Minimum Zones (OMZs) are influenced by supply and consumption of oxygen through a range of processes. These include the supply of oxygen through diffusive processes across (diapycnal diffusivity, Kz), and along (isopycnal diffusivity, Kx and Ky, for zonal and meridional diffusivity) isopycnals, but also the flow of nutrients from the deeper layers to the photic zone that...
The Black Sea, the largest semienclosed anoxic basin on Earth, can be considered as an excellent natural laboratory for oxic and anoxic biogeochemical processes. The suboxic zone, a thin interface between oxic and anoxic waters, still remains poorly understood because it has been undersampled. This has led to alternative concepts regarding the underlying processes that create it. Existing...
Life in the Black Sea is confined in a thin surface oxygenated layer, bounded by a strong and permanent salinity gradient (halocline) that maintains the remaining 90% of the water column in euxinic conditions. We showed that from 1955 to 2016, the oxygen inventory in the Black Sea has decreased by 44 % and that the basin-averaged oxygen penetration depth has decreased from 140 m in 1955 to 80...
Semi-enclosed seas are prone to amplified warming under future climate change due to their landlocked nature and strong sensitivity to continental climate. This is particularly true for the Arabian Gulf (AG) due to its shallow depth and proximity to the fast warming Arabian Peninsula. While the predicted rapid warming of the AG is expected to challenge its local ecosystem already subject to...