Oxygen Cycle Research Articles

Dark biological superoxide production as a significant flux and sink of marine dissolved oxygen.

The balance between sources and sinks of molecular oxygen in the oceans has greatly impacted the composition of Earth's atmosphere since the evolution of oxygenic photosynthesis, thereby exerting key influence on Earth's climate and the redox state of (sub)surface Earth. The canonical source and sink terms of the marine oxygen budget include photosynthesis, respiration, photorespiration, the Mehler reaction, and other smaller terms. However, recent advances in understanding cryptic oxygen cycling, namely the ubiquitous one-electron reduction of O2 to superoxide by microorganisms outside the cell, remains unexplored as a potential player in global oxygen dynamics. Here we show that dark extracellular superoxide production by marine microbes represents a previously unconsidered global oxygen flux and sink comparable in magnitude to other key terms. We estimate that extracellular superoxide production represents a gross oxygen sink comprising about a third of marine gross oxygen production, and a net oxygen sink amounting to 15 to 50% of that. We further demonstrate that this total marine dark extracellular superoxide flux is consistent with concentrations of superoxide in marine environments. These findings underscore prolific marine sources of reactive oxygen species and a complex and dynamic oxygen cycle in which oxygen consumption and corresponding carbon oxidation are not necessarily confined to cell membranes or exclusively related to respiration. This revised model of the marine oxygen cycle will ultimately allow for greater reconciliation among estimates of primary production and respiration and a greater mechanistic understanding of redox cycling in the ocean.

Ferromanganese crusts as recorders of marine dissolved oxygen

The distinct triple oxygen isotope composition of tropospheric O2 relative to seawater is the result of biogeochemical reactions (e.g. primary productivity, respiration), exchange with the stratosphere, and the relative size of different oxygen-containing reservoirs, namely O2, O3, and CO2. This difference in isotopic composition gives tropospheric O2 utility as a record of biogeochemical and atmospheric processes and may also be used for determining where in the rock record isotopic fingerprints of tropospheric oxygen may be preserved. The isotopic record of tropospheric oxygen in previous studies is largely limited to analyses of gas trapped in continental glaciers and a patchwork of other proxies, most notably the triple oxygen signature of sulfate. Here we show the uppermost layers of hydrogenetic, deep-ocean ferromanganese crusts from each of the major ocean basins have a triple oxygen isotope composition consistent with the direct incorporation of dissolved oxygen. The range of δ18O and Δ′17O in ferromanganese crusts suggests the Mn oxide endmember contains a near 50:50 mixture of oxygen from water and dissolved O2. Our data indicate this signal also persists into older layers of the crusts, potentially preserving near 75 million years of the oxygen isotopic composition of the lower troposphere and subsequent deep-ocean respiration. Our analysis of oxygen isotope values, bulk chemistry, and estimated local dissolved oxygen for crust top samples reveals that variations in bulk chemistry ultimately exhibit more influence on the oxygen mass balance than changes in dissolved oxygen, presenting a challenge for unambiguous determination of local dissolved oxygen. Although analytical challenges remain, these widespread, layered deposits of ferromanganese crust may offer a viable path for future interrogation of the history or relative history of the oxygen cycle of the troposphere and deep ocean millions of years into the past.

Constraints on Meso- to Neoproterozoic seawater from ancient evaporite deposits

Marine sulfate (SO42−) is intimately connected to the global carbon and oxygen cycles through its important role as an electron acceptor for the microbial respiration of organic carbon. The biogeochemical feedbacks within the sulfur, carbon, and oxygen cycles may have changed through time, reflecting changes in the concentration of sulfate in the oceans. Unfortunately, there is much uncertainty about the size of the marine sulfate reservoir throughout Earth history. In particular, conflicting estimates for marine sulfate exist during the latest Neoproterozoic, an interval of time associated with striking changes in Earth system evolution and oxidation: published interpretations of fluid inclusion chemistry place sulfate greater than 16 mmol/kg, whereas other interpretations of carbonate-associated sulfate data suggest concentrations less than 2 mmol/kg. Calcium isotope ratios in evaporite successions provide an independent method for deriving semi-quantitative constraints on sulfate concentrations, as well as other properties of seawater chemistry. Here, the calcium isotope behavior of bedded sulfate evaporites from ∼1050 Ma (Baffin and Bylot Islands, Nunavut, Canada), ∼830 Ma (Officer Basin, Western Australia), and ∼545 Ma (South Oman Salt Basin, Sultanate of Oman) are examined. In combination with other geological observations, the results suggest relatively low, millimolal-level sulfate in the latest Mesoproterozoic and a more specific range of 6–10 mmol/kg sulfate during the latest Neoproterozoic. These new constraints suggest that previous interpretations of sulfate concentrations and seawater chemistry need to be revised, opening up new possible solution spaces for the major ion composition of seawater.

Stepping to an internal beat

Ancient Atmosphere What caused the stepwise nature of the rise of molecular oxygen in Earth's atmosphere since it appeared in large quantities more than 2 billion years ago? Alcott et al. argue that a set of internal feedbacks involving the global phosphorus, carbon, and oxygen cycles, not individual external forces, could be responsible. Their model, which depends only on a gradual shift from reducing to oxidizing surface conditions over time, produces the same three-step pattern observed in the geological record. Science , this issue p. [1333][1] [1]: /lookup/doi/10.1126/science.aax6459

Stepwise Earth oxygenation is an inherent property of global biogeochemical cycling.

Oxygenation of Earth's atmosphere and oceans occurred across three major steps during the Paleoproterozoic, Neoproterozoic, and Paleozoic eras, with each increase having profound consequences for the biosphere. Biological or tectonic revolutions have been proposed to explain each of these stepwise increases in oxygen, but the principal driver of each event remains unclear. Here we show, using a theoretical model, that the observed oxygenation steps are a simple consequence of internal feedbacks in the long-term biogeochemical cycles of carbon, oxygen, and phosphorus, and that there is no requirement for a specific stepwise external forcing to explain the course of Earth surface oxygenation. We conclude that Earth's oxygenation events are entirely consistent with gradual oxygenation of the planetary surface after the evolution of oxygenic photosynthesis.

Investigation of Zr, Gd/Zr, and Pr/Zr – doped ceria for the redox splitting of water

There is a renewed interest in CeO2 for use in solar-driven, two-step thermochemical cycles for water splitting. However, despite fast reduction/oxidation kinetics and high thermal stability of ceria, the cycle capacity of CeO2 is low due to thermodynamic limitations. In an effort to increase cycle capacity and reduce thermal reduction temperature, we have studied binary zirconium-substituted ceria (ZrxCe1-xO2, x = 0.1, 0.15, 0.25) and ternary praseodymium/gadolinium-doped Zr-ceria (M0.1Zr0.25Ce0.65O2, M = Pr, Gd). We evaluate the oxygen cycle capacity and water splitting performance of crystallographically and morphologically stable powders that are thermally reduced by laser irradiation in a stagnation flow reactor. The addition of zirconium dopant into the ceria lattice improves O2 cycle capacity and H2 production by approximately 30% and 11%, respectively. This improvement is independent of the Zr dopant level, up to 25%, suggesting that above 10% Zr dopant level, Zr might be displaced during the high temperature annealing process. The addition of Pr and Gd to the binary Zr-ceria mixed oxide, on the other hand, is detrimental to H2 production. A kinetic analysis is performed using a model-based analytical approach to account for effects of mixing and dispersion, and to identify the rate controlling mechanism of the water splitting process. We find that the water splitting reaction at 1000 °C and with 30 vol% H2O, for all doped ceria samples, is surface limited and best described by a deceleratory power law model (F-model), similar to undoped CeO2. Additionally, we used density functional theory (DFT) calculations to examine the role of Zr, Pr, and Gd. We find that the addition of Pr and Gd induce non-redox active sites and, therefore, are detrimental to H2 production, in agreement with experimental work. The calculated surface H2 formation step was found to be rate limiting, having activation barriers greater than bulk O diffusion, for all materials. This agrees with and further explains experimental findings.

Time‐series observations of photosynthetic oxygen production in the subtropical western North Pacific by an underwater profiling buoy system

AbstractWe conducted time‐series observations in the northwestern part of the North Pacific subtropical gyre (30°N, 145°E) from July 2012 to March 2013 using a profiling buoy system equipped with a fast repetition rate fluorometer and dissolved oxygen (DO) sensor in order to understand vertical and temporal variations in gross oxygen production (GOP) by phytoplankton and its contribution to the oxygen cycle in the upper ocean. Under stratified conditions (July–November), daily GOP slightly exceeded 2 mmol O2 m−3 d−1 and only in near‐surface waters. However, during periods of vertical mixing (December–March) when phytoplankton blooms occurred, daily GOP increased in the upper 30 m and often exceeded 5 mmol O2 m−3 d−1. The depth‐integrated daily GOP within the euphotic layer (∫GOPEL) was relatively low (84.0 ± 23.6 mmol O2 m−2 d−1) during stratification, but increased gradually with vertical mixing and reached 460 mmol O2 m−2 d−1 on 17 March 2013. Additionally, during stratified conditions, a subsurface oxygen maximum (SOM) formed below the mixed‐layer depth (MLD) because the steep density gradient constrained upward diffusion of oxygen produced below the MLD. During the period of vertical mixing, the SOM disappeared, and DO concentrations within the upper 100 m increased through both increasing ∫GOPEL and atmospheric oxygen uptake. Using our buoy observations and air–sea gas flux model, we estimated that 24% ± 7% of ∫GOPEL was emitted to the atmosphere during the stratification period, and ∫GOPEL during the mixing period was about 2.4 times the rate of oxygen uptake by the ocean from the atmosphere.

Evolution and enhancement of the oxygen cycle in the catalytic performance of total toluene oxidation over manganese-based catalysts

An investigation of the effect of oxygen and silver species on the oxidation of toluene has been launched to identify the reaction process and mechanism over MnOx/SBA-15 and Ag–MnOx/SBA-15 catalysts. Detailed knowledge of the effect and cycle of oxygen species under reaction is typically missing, and this study points at the behavior of oxygen species over MnOx/SBA-15 for toluene oxidation for the first time, using in situ mass spectrum techniques with the isotope 18O2. It is found that the Langmuir–Hinshelwood and Mars–van Krevelen mechanism coexist in toluene oxidation over MnOx/SBA-15 catalyst. In this study, surface and bulk lattice oxygen are shown to be vital active oxygen species in the whole reaction. The consumed oxygen species are replenished with gaseous oxygen, and the process follows the Mars–van Krevelen mechanism, as confirmed by detection of isotopic products. The adsorbed oxygen species with good mobility is also found to start up and participate in the reaction at lower temperatures, which follows the Langmuir–Hinshelwood reaction mechanism. The addition of Ag increases the amount of surface lattice oxygen species and improves the transformation rate and the migration of lattice oxygen, which effectively facilitates the low-temperature activity of toluene oxidation.

The redox budget of the Mariana subduction zone

Assessing the efficiency of material recycling at convergent margins is critical to constraining the impact of plate tectonic processes on the composition of surface and deep mantle reservoirs on geologic timescales. In particular, oceanic lithosphere bearing oxidized phases such as Fe-oxy-hydroxides, Fe-oxides, serpentine, carbonate, and sulfate minerals, subduct at convergent margins and the infiltration of aqueous fluids and sediment melts from the subducting slab into the mantle beneath arc volcanoes may thus carry oxidized forms of multi-valent elements (e.g., S, Fe, C) and lead to the generation of primitive arc melts that record elevated oxygen fugacities relative to mid-ocean ridge primitive melts. It is unclear, however, how efficiently aqueous fluids and silicate melts transport the oxidized signatures of any given subducting slab into the mantle wedge in a single subduction zone, and how much, if any, of these oxidized phases may be recycled into the deeper mantle. We present a mass balance of Fe3+, S2−, S6+, and C4+, as well as the O2 associated with these species, through the Mariana subduction zone to assess the efficiency of recycling oxidized materials in an end-member type subduction zone, where old oceanic lithosphere and a thick sediment package is subducted. To do this, we report Fe3+/ΣFe ratios of bulk sediments and altered oceanic crust recovered from ODP Site 801 in the western Pacific in order to constrain the bulk Fe3+/ΣFe ratio of the Pacific plate prior to subduction in the Mariana convergent margin. Site 801 sediments have Fe3+/ΣFe ratios >0.69 and the altered oceanic crust (801 Super Composite) has Fe3+/ΣFe of 0.51. Bulk Fe3+/ΣFe ratios of altered oceanic crust at Site 801 increase from 0.14 (pristine Jurassic-aged MORB glass) to 0.78 with increasing extent of alteration. We find that 68–95% of the O2 added to the subducting crust by sedimentation, in situ alteration of basaltic crust on the seafloor, and serpentinization of the mantle lithosphere is not output by Mariana arc or back-arc magmas. This result demonstrates that significant amounts of oxidized materials from Earth's surface are transported into the deeper mantle beyond subduction zones, despite the production of oxidized arc and back-arc basalts, and may contribute to elevated oxygen fugacities recorded by ocean island lavas such as Iceland and Hawaii. This oxygen cycle is likely to have been operating at least for the past 400–800 million years, and potentially for the duration of plate tectonics.

The Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP): A Platform for Integrated Multidisciplinary Ocean Science

The Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP) provides a globally coordinated network and oversight of 55 sustained decadal repeat hydrographic reference (core) lines as part of the global ocean/climate observing systems (GOOS/GCOS) for study of physical oceanography, the ocean carbon, oxygen and nutrient cycles, and marine biogeochemistry. GO-SHIP enables assessment of the ocean sequestration of heat and carbon, changing ocean circulation and ventilation patterns, and their effects on ocean health and Earth's climate. Rapid quality control and open data release along with incorporation of the GO-SHIP effort in the Joint Technical Commission for Oceanography and Marine Meteorology (JCOMM) in situ Observing Programs Support Center (JCOMMOPS) have increased the profile of, and participation in, the program and led to increased data use for a range of efforts. In addition to scientific discovery, GO-SHIP provides climate-quality observations, often at the point of deployment, but also for ongoing calibration of measurements from existing and new autonomous platforms. This includes biogeochemical observations for the nascent array of biogeochemical (BGC)-Argo floats; temperature and salinity for Deep Argo; and salinity for the core Argo array. GO-SHIP provides the relevant suite of global, full depth, high quality observations and co-located deployment opportunities that, for the foreseeable future, remain crucial to maintenance and evolution of Argo’s unique contribution to climate science. The evolution of GO-SHIP from a program primarily focused on physical climate to increased emphasis on ocean health and sustainability, in support of UN Sustainable Development Goal 14, has put an emphasis on the addition of essential ocean variables (EOVs) for biology and ecosystems in the program measurement suite. In conjunction with novel automated measurement systems, ocean color, particulate matter, and phytoplankton enumeration are being explored as GO-SHIP variables. The addition of biological and ecosystem measurements will enable GO-SHIP to determine trends and variability in these key indicators of ocean health. The active and adaptive GO-SHIP community has sustained the network, quality and relevance of the global repeat hydrography effort through societally important scientific results, increased exposure, and interoperability with new efforts and opportunities within the community.

Study on Sequent Test Effects of Atomic Oxygen/thermal Cycling

Two kinds of unidirectional laminates made from carbon/epoxy composite named M40/DFA-1 & M40/DFA-N3(nano TiO2 contained) are selected to study the different effects between different test sequences of atomic oxygen/thermal cycling. Based on the ground simulating test of atomic oxygen and thermal cycling, several kinds of tests and analysis are conducted, such as surface morphology observation, mass loss test, inter-laminar shear strength test, and X-ray photoelectron analysis of surface components. After the exposure of atomic oxygen and thermal cycling, surface erosions is observed on both of the materials, in addition, mechanical properties are both changed. It must be highlight that, under the condition of 1.5×1020 atoms/cm2 AO and 200 thermal cycles within the range of -150°C∼+150°C, different sequences lead to different results, either the extend or the tendency. In which, samples under AO+TC sequence exhibited relatively higher mass loss and erosion rate as well as more severe mechanical performance degradation.

The regulation of oxygen to low concentrations in marine oxygen-minimum zones

The Bay of Bengal hosts persistent, measurable, but sub-micromolar, concentrations of oxygen in its oxygen-minimum zone (OMZ). Such low-oxygen conditions are not necessarily rare in the global ocean and seem also to characterize the OMZ of the Pescadero Basin in the Gulf of California, as well as the outer edges of otherwise anoxic OMZs, such as can be found, for example, in the Eastern Tropical North Pacific. We show here that biological controls on oxygen consumption are required to allow the semistable persistence of low-oxygen conditions in OMZ settings; otherwise, only small changes in physical mixing or rates of primary production would drive the OMZ between anoxic and oxic states with potentially large swings in oxygen concentration. We propose that two controls are active: an oxygen-dependent control on oxygen respiration and an oxygen inhibition of denitrification. These controls, working alone and together, can generate low-oxygen concentrations over a wide variability in ocean mixing parameters. More broadly, we discuss the oxygen regulation of organic matter cycling and N2 production in OMZ settings. Modern biogeochemical models of nitrogen and oxygen cycling in OMZ settings do contain some of the parameterizations that we explore here. However, these models have not been applied to understanding the persistence of low, but measurable, concentrations of oxygen in settings like the Bay of Bengal, nor have they been applied to understanding what biological/physical processes control the transition from a weakly oxygenated state to a “functionally” anoxic state with implications for nitrogen cycling. Therefore, we believe that the approach here illuminates the relationship between oxygen and the biogeochemical cycling of carbon and nitrogen in settings like the Bay of Bengal. Furthermore, we believe that our results could further inform large-scale ocean models seeking to explore how global warming might influence the spread of low-oxygen waters, influencing the cycles of oxygen, carbon, and nitrogen in OMZ settings.

Mitigation of Extreme Ocean Anoxic Event Conditions by Organic Matter Sulfurization

AbstractPast occurrences of widespread and severe anoxia in the ocean have frequently been associated with abundant geological evidence for free hydrogen sulfide (H2S) in the water column, so‐called euxinic conditions. Free H2S may react with, and modify, the chemical structure of organic matter settling through the water column and in marine sediments, with hypothesized implications for carbon sequestration. Here, taking the example of Ocean Anoxic Event 2, we explore the potential impact of organic matter sulfurization on marine carbon and oxygen cycling by means of Earth system modeling. Our model experiments demonstrate that rapid sulfurization (ksulf≥ = 105 M−1 year−1) of organic matter in the water column can drive a more than 30% enhancement of organic carbon preservation and burial in marine sediments and hence help accelerate climate cooling and Ocean Anoxic Event 2 recovery. As a consequence of organic matter sulfurization, we also find that H2S can be rapidly scavenged and the euxinic ocean volume reduced by up to 80%—helping reoxygenate the ocean as well as reducing toxic H2S emissions to the atmosphere, with potential implications for the kill mechanism at the end‐Permian. Finally, we find that the addition of organic matter sulfurization induces a series of additional feedbacks, including further atmospheric CO2 drawdown and ocean reoxygenation by the creation of a previously unrecognized net source of alkalinity to the ocean as H2S is scavenged and buried.

Modelling nitrogen-oxygen dynamics in the central Arabian Sea: Large-scale meridional structure and seasonal variations

The oxygen minimum zone (OMZ) of the central Arabian Sea is investigated with a biogeochemical model that couples the marine nitrogen and oxygen cycles and includes euphotic, aphotic, aerobic and anaerobic processes. The model is used to quantify the strength, location and relative timing of governing processes, in particular, nitrite generation, nitrogen losses and oxygen consumption. In an idealized two-dimensional physical environment the model is able to reproduce the observed meridional-vertical structure of oxygen and nitrate, as well as the secondary nitrite maximum layer. Characteristic features of vertical profiles are well represented and the modelled nitrogen transformation rates are in good agreement with observed values. The model results show that (i) the OMZ is neither vertically nor horizontally homogeneous, (ii) minute differences in oxygen concentration determine the thickness of the nitrite layer, (iii) there is hardly any seasonal cycle in the extent of the OMZ but a pronounced seasonal cycle in nitrite, and (iv) the nitrogen loss in the OMZ is accomplished by a succession of denitrification and anammox, based on the seasonal supply of labile detritus. We conclude that the nitrogen loss in the Arabian Sea can only be understood by taking into account the diversity, vertical arrangement and temporal succession of microbial processes.

Winter’s role in annual nitrate regulation in Buzzards Bay estuaries

Long term, year round nitrate records from two adjacent estuaries on Buzzards Bay provide the opportunity to investigate the role of winter nitrate in the annual nitrate budget. This is the fourth paper in this program that extends from 1988 to 2019. One of the estuaries had two markedly different nitrate groundwater inputs over time, one with high and the other with low Nitrogen-loading, with an abrupt transition between the two states The absence of a trend in nitrate over the 30 years, along with a normal oxygen cycle, indicates effective internal regulation of nitrate, even under dramatic increases. A graph of monthly average water column nitrate over the 30 years for both estuaries revealed a winter surge of nitrate only for the high N-load case. The comparison of the nitrate difference between the two estuaries against water temperature and month suggested that there is a critical N-load and temperature that triggered the transition between the two states. After that critical point was exceeded, as in the high N-load case, a winter nitrate surge appeared. This increased N-load could be considered a transition to nitrogen pollution however, with a residence time of 2 days, tidal export in the winter then provided the steady state annual nitrate balance. Because of the high variability, one objective of this paper is to encourage other researchers to take winter measurements to improve the statistics and general applicability of these conclusions.

Atmosphere oxygen cycling through the Proterozoic and Phanerozoic

Variations in atmosphere oxygen and ocean sulfate concentrations through time are regarded as important controls on the cycles of sediment-hosted and volcanic-hosted ore deposits. However, estimates of atmosphere oxygen in the Proterozoic have been frustrated by the lack of a direct measurement method and conflicting evidence from various proposed geochemical proxies. Studies in the 1970s to 1990s suggested a relatively oxygenated atmosphere (> 3 wt% O2) in the Proterozoic. However, since the late 1990s, new proxies and modelling have suggested very much lower levels of oxygen (< 0.02 wt% O2). Focusing on redox-sensitive trace elements, here we combine a dataset of over 3000 LA-ICP-MS trace-element analyses on sedimentary pyrite, standardised against Berner’s Phanerozoic O2 modelling and direct measurement of oxygen concentrations in fluid inclusions in sedimentary halite, to develop the first detailed estimate for atmosphere O2 concentration and secular variation from 2200 Ma to the present. The estimates suggest dynamic cycles of atmosphere oxygen that increased in frequency through time. There were possibly three first-order cycles in the Proterozoic varying from 400 to 600 million years in length and a further five first-order cycles in the Phanerozoic from 60 to 120 million years in length. Our estimates of oxygen concentration are at odds with most previous estimates. We suggest, rather than very low atmosphere oxygen in the Proterozoic, the mean concentration was about 7 wt%, rising to a mean of about 10 wt% in the Phanerozoic, but with significant cyclic variation of up to a maximum concentration of possibly over 30 wt%. We observe that the proposed oxygen cycles correlate with biodiversity cycles and to the timing of major stratiform base-metal deposits in sedimentary basins. For example, minima in atmosphere oxygenation correlate with mass extinction events and stratiform Zn–Pb–Ag deposits, whereas maxima in oxygenation correlate with major evolutionary events, global periods of evaporite formation and the timing of stratiform copper deposits.

Extremophile deep-sea viral communities from hydrothermal vents: Structural and functional analysis

Ten publicly available metagenomic data sets from hydrothermal vents were analyzed to determine the taxonomic structure of the viral communities present, as well as their potential metabolic functions. The type of natural selection on two auxiliary metabolic genes was also analyzed. The structure of the virome in the hydrothermal vents was quite different in comparison with the viruses present in sediments, with specific populations being present in greater abundance in the plume samples when compared with the sediment samples. ssDNA genomes such as Circoviridae and Microviridae were predominantly present in the sediment samples, with Caudovirales which are dsDNA being present in the vent samples. Genes potentially encoding enzymes that participate in carbon, nitrogen and sulfur metabolic pathways were found in greater abundance, than those involved in the oxygen cycle, in the hydrothermal vents. Functional profiling of the viromes, resulted in the discovery of genes encoding proteins involved in bacteriophage capsids, DNA synthesis, nucleotide synthesis, DNA repair, as well as viral auxiliary metabolic genes such as cytitidyltransferase and ribonucleotide reductase. These auxiliary metabolic genes participate in the synthesis of phospholipids and nucleotides respectively and are likely to contribute to enhancing the fitness of their bacterial hosts within the hydrothermal vent communities. Finally, evolutionary analysis suggested that these auxiliary metabolic genes are highly conserved and evolve under purifying selection, and are thus maintained in their genome.

Putting It All Together: Adding Value to the Global Ocean and Climate Observing Systems With Complete Self-Consistent Ocean State and Parameter Estimates

In 1999, the consortium for Estimating the Circulation and Climate of the Ocean (ECCO) set out to synthesize the hydrographic data collected by the World Ocean Circulation Experiment (WOCE) and satellite sea surface height measurements into a complete and coherent description of the ocean afforded by an ocean general circulation model. Twenty years later, the versatility of ECCO's estimation framework enables production of global and regional ocean and sea-ice state estimates that incorporate not only the initial suite of data and its successors, but nearly all data streams available today. New observations include measurements from Argo floats, marine mammal-based hydrography, satellite retrievals of ocean bottom pressure and sea surface salinity, and ice-tethered profiler data in polar regions. The framework also produces improved estimates of uncertain inputs, including initial conditions, surface atmospheric state variables, and mixing parameters. The freely available state estimates and related efforts are property-conserving, allowing closed budget calculations that are a requisite to detect, quantify, and understand the evolution of climate-relevant signals as mandated by the Coupled Model Intercomparison Project Phase 6 (CMIP6) protocol. The solutions can be reproduced by users through provision of the underlying modeling and assimilation machinery. Regional efforts have spun off that offer increased spatial resolution to better resolve relevant processes. Emerging foci of ECCO are on global sea level change, in particular contributions from polar ice sheets, and the increased use of biogeochemical and ecosystem data to constrain global cycles of carbon, nitrogen and oxygen. Challenges in the coming decade include provision of uncertainties, informing observing system design, globally increased resolution, and moving toward coupled Earth system estimation with consistent momentum, heat and freshwater fluxes between the ocean, atmosphere, cryosphere and land.

Energy and Exergy Analysis of a New Power, Heating, Oxygen and Hydrogen Cogeneration Cycle Based on the Sabalan Geothermal Wells

In this paper, a new power, heating and hydrogen cogeneration cycle from Sabalan geothermal two wells is proposed and analyzed. In the proposed system, a new double flash cycle and organic Rankine cycle are used for power production. A proton exchange membrane (PEM) is also used for hydrogen production and the domestic water heater is used for heating. The impacts of some design parameters, such as separators pressures, evaporator temperature, pinch point temperature difference and PEM temperature on the integrated system performance are investigated and then optimization is done from exergy point of view for three considered scenarios. According to the optimization results, the value of heating, net output power, hydrogen production and thermal and exergy efficiencies of the cogeneration system are obtained as 15751 kW, 18436 kW, 11.13 kg/h, 29.48% and 65.23%, respectively.

Kinetic and equilibrium fractionation of O2 isotopologues during air-water gas transfer and implications for tracing oxygen cycling in the ocean

Oxygen isotopologues are useful tools for understanding biogeochemical processes and chemical budgets in the ocean. For example, the triple‑oxygen isotope composition of dissolved oxygen in the ocean mixed layer (i.e., its δ17O and δ18O values) is widely used to estimate gross oxygen productivity (GOP), a quantity closely related to gross primary productivity. While recent work has demonstrated the importance of upwelling and horizontal transport to these estimates, the isotopic effects of gas exchange when the mixed layer is out of solubility equilibrium have only been measured for 18O/16O. Oxygen is rarely at 100% saturation in the surface ocean, so most regions experience net ingassing or outgassing; kinetic fractionation across the air-water boundary is therefore expected to be important. Here, we present the results of air-water gas transfer experiments designed to obtain the kinetic and equilibrium fractionation factors for the four rare O2 isotopologues 16O17O, 16O18O, 17O18O, and 18O18O relative to 16O16O. Furthermore, we examine their potential effects on isotopologue-based GOP estimates and connect the observed air-water kinetic fractionation factors to dissolved-phase diffusive isotopic fractionation. These kinetic fractionation effects may provide additional constraints on O2 cycling at the surface and in the deep ocean.