Stable aerobic and anaerobic coexistence in anoxic marine zones
"Mechanistic description of the transition from aerobic to anaerobic metabolism is necessary for diagnostic and predictive modeling of fixed nitrogen loss in anoxic marine zones (AMZs). In a metabolic model where diverse oxygen- and nitrogen-cycling microbial metabolisms are described by underlying redox chemical reactions, we predict a transition from strictly aerobic to predominantly anaerobic regimes as the outcome of ecological interactions along an oxygen gradient, obviating the need for prescribed critical oxygen concentrations. [...]"
Source: The ISME Journal
Authors: Emily J. Zakem et al.
Annual plankton community metabolism in estuarine and coastal waters in Perth (Western Australia)
"The planktonic metabolic balance that is the balance between gross primary production (GPP) and community respiration (CR) was determined in Matilda Bay (estuarine) and Woodman Point (coastal) in Perth, Western Australia. The rates of net community production (NCP = GPP – CR) and the ratio between GPP and CR (P/R) were assessed to evaluate whether the metabolic balance in the two coastal locations tends to be net autotrophic (production exceeding community respiration) or net heterotrophic (respiration exceeding production). [...]"
Authors: Susana Agusti, Lorena Vigoya, Carlos Manuel Duarte
Accurate estimation of net community production from O2/Ar measurements
"Under physically isolated conditions, net community production (NCP) can be accurately estimated from the rate of oxygen evasion to the atmosphere derived from local mixed layer oxygen/argon measurements. We use a simple box model to demonstrate that, when physical inputs are negligible, the sea‐to‐air flux of biological oxygen (bioflux) represents the average NCP exponentially weighted over the past several residence times of oxygen in the mixed layer. This new weighting scheme shows that there is no apparent lag between bioflux and exponentially‐weighted time‐averaged NCP. [...]"
Source: Global Biogeochemical Cycles
Authors: Lianna Teeter et al.
The devil's in the disequilibrium: multi-component analysis of dissolved carbon and oxygen changes under a broad range of forcings...
...in a general circulation model
"The complexity of dissolved gas cycling in the ocean presents a challenge for mechanistic understanding and can hinder model intercomparison. One helpful approach is the conceptualization of dissolved gases as the sum of multiple, strictly defined components. Here we decompose dissolved inorganic carbon (DIC) into four components: saturation (DICsat), disequilibrium (DICdis), carbonate (DICcarb), and soft tissue (DICsoft). The cycling of dissolved oxygen is simpler, but can still be aided by considering O2, O2sat, and O2dis. [...]"
Authors: Sarah Eggleston and Eric D. Galbraith
Diapycnal dissolved organic matter supply into the upper Peruvian oxycline
"The Eastern Tropical South Pacific (ETSP) hosts the Peruvian upwelling system, which represents one of the most productive areas in the world ocean. High primary production followed by rapid heterotrophic utilization of organic matter supports the formation of one of the most intense oxygen minimum zones (OMZ) in the world ocean where dissolved oxygen (O2) concentrations reach well below 1 µmol kg−1. The high productivity leads to an accumulation of dissolved organic matter (DOM) in the surface layers that may serve as a substrate for heterotrophic respiration. [...]"
Authors: Alexandra N. Loginova et al.
Drivers and mechanisms of ocean deoxygenation
"Direct observations indicate that the global ocean oxygen inventory is decreasing. Climate models consistently confirm this decline and predict continuing and accelerating ocean deoxygenation. However, current models (1) do not reproduce observed patterns for oxygen changes in the ocean’s thermocline; (2) underestimate the temporal variability of oxygen concentrations and air–sea fluxes inferred from time-series observations; and (3) generally simulate only about half the oceanic oxygen loss inferred from observations. [...]"
Source: Nature Geoscience
Authors: Andreas Oschlies et al.
A Giant Blob of Floodwater From Harvey Is Still Moving Through the Gulf
"The rain began on August 25, and it would fall, remarkably, for four more days. We know now that Hurricane Harvey dumped as much as 60 inches of rain over parts of Texas. Twenty trillion gallons in all. The equivalent of the entire Chesapeake Bay. Enough to push the Earth’s crust down two centimeters. [...]
What oceanographers do know about the interface of freshwater and ocean comes from studying rivers that naturally empty into the sea. The key is density. Because freshwater lacks dissolved salt, it is less dense and floats atop seawater. It becomes a barrier between the air and the ocean water, which can have nasty consequences. “The freshwater sitting on the salty water cuts off the oxygen from the atmosphere getting into the ocean, and then you get the dead zone,” says Steve DiMarco [...]"
Source: The Atlantic
The ocean’s vital skin: Towards an integrated understanding of the sea surface microlayer
"Despite the huge extent of the ocean’s surface, until now relatively little attention has been paid to the sea surface microlayer (SML) as the ultimate interface where heat, momentum and mass exchange between the ocean and the atmosphere takes place. Via the SML, large-scale environmental changes in the ocean such as warming, acidification, deoxygenation and eutrophication potentially influence cloud formation, precipitation and the global radiation balance. Due to the deep connectivity between biological, chemical and physical processes, studies of the SML may reveal multiple sensitivities to global and regional changes. [...]"
Source: Frontiers in Marine Science
Authors: Anja Engel et al.
Impacts of ENSO on air-sea oxygen exchange: observations and mechanisms
"Models and observations of Atmospheric Potential Oxygen (APO ≃ O2 + 1.1*CO2) are used to investigate the influence of El Niño Southern Oscillation (ENSO) on air-sea O2 exchange. An atmospheric transport inversion of APO data from the Scripps flask network shows significant interannual variability in tropical APO fluxes that is positively correlated with the Niño3.4 index, indicating anomalous ocean outgassing of APO during El Niño. Hindcast simulations of the Community Earth System Model (CESM) and the Institut Pierre-Simon Laplace (IPSL) model show similar APO sensitivity to ENSO, differing from the Geophysical Fluid Dynamic Laboratory (GFDL) model, which shows an opposite APO response. [...]"
Source: Global Biochemical Cycles
Authors: Yassir A. Eddebbar et al.