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The production of organic matter at the ocean's surface, its transport, and subsequent remineralization in the ocean interior maintains a vertical carbon and nutrient gradient that sequesters atmospheric CO2, controls the distribution of dissolved oxygen, and modulates the flux of nutrients to the euphotic zone that fuels marine ecosystems. Collectively we refer to the set of processes maintaining these gradients as the biological pump and they are the central focus of this thesis. To advance our understanding of the biological pump, this thesis uses models to analyze and quantify individual processes within the larger biological pump system. Chapter 1 introduces the key processes at question and outlines the specific goals of each research chapter. Chapter 2 uses empirical models and a global database of in-situ observations to examine the environmental drivers of carbon export efficiency, defined as the fraction of organic matter production that is transported from the surface to the interior. We find significant regional variability in the relationship between export efficiency and environmental parameters that are shown to have important consequences for the prediction of global export. Chapter 3 further develops empirical models of carbon export efficiency with a focus on regional export variability in the Southern Ocean. We find new evidence that silica controls Southern Ocean export efficiency via interactions with ocean temperature. Chapter 4 uses a global ocean circulation and biogeochemistry model to examine the sensitivity of the global oxygen distribution to changes in the depth at which sinking organic matter is remineralized. Model experiments demonstrate that raising the remineralization depth of organic matter leads to net oxygen uptake and simultaneous expansion of oxygen minimum zones. Chapter 5 examines the consequences of long term climate-driven changes in the biological pump for the productivity of marine ecosystems and fisheries. The thesis concludes in Chapter 6 with a discussion of the challenges and opportunities in understanding the biological pump in a changing climate, along with my recommendations for follow up research.

As an important contributor to the habitability of our planet, the oxygen cycle is interconnected with the emergence and evolution of complex life and is also the basis to establish Earth system science. Investigating the global oxygen cycle provides valuable information on the evolution of the Earth system, the habitability of our planet in the geologic past, and the future of human life. Numerous investigations have expanded our knowledge of the oxygen cycle in the fields of geology, geochemistry, geobiology, and atmospheric science. However, these studies were conducted separately, which has led to one-sided understandings of this critical scientific issue and an incomplete synthesis of the interactions between the different spheres of the Earth system. This review presents a five-sphere coupled model of the Earth system and clarifies the core position of the oxygen cycle in Earth system science. Based on previous research, this review comprehensively summarizes the evolution of the oxygen cycle in geological time, with a special focus on the Great Oxidation Event (GOE) and the mass extinctions, as well as the possible connections between the oxygen content and biological evolution. The possible links between the oxygen cycle and biodiversity in geologic history have profound implications for exploring the habitability of Earth in history and guiding the future of humanity. Since the Anthropocene, anthropogenic activities have gradually steered the Earth system away from its established trajectory and had a powerful impact on the oxygen cycle. The human-induced disturbance of the global oxygen cycle, if not controlled, could greatly reduce the habitability of our planet.

Significance Extracellular production of the reactive oxygen species (ROS) superoxide results from the one-electron reduction of O2. Nearly all major groups of marine microbes produce extracellular superoxide. In this global estimate of marine microbial superoxide production we determine that dark extracellular superoxide production is ultimately a net sink of dissolved oxygen comparable in magnitude to other major terms in the marine oxygen cycle. This abundant source of superoxide to the marine water column provides evidence that extracellular ROS play a significant role in carbon oxidation and the redox cycling of metals in marine environments. Consideration of this significant reductive flux of dissolved oxygen is essential for field, laboratory, and modeling techniques for determining productivity and oxygen utilization in marine systems., 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.

The cycle’s catalytic reactions account for just 1% of the Sun’s energy, but they are the dominant energy producers in heavier stars.

Cycling of elements with multiple valences (e.g., Fe, C, and S) through subduction and magmatism may dictate the redox evolution of the deep mantle and atmosphere. To investigate the potential of Fe isotopes as a tracer of such cycles, here we report Fe isotopic compositions of thirty-seven Cenozoic basalts from eastern China. A nephelinitic melt component with δ 56 Fe up to 0.29 has been identified, which cannot be explained by weathering, alteration, magma differentiation, or chemical diffusion. Its low Fe/Mn ∼58, relatively low TiO2 and high Na2O + K2O argue against a significant contribution of pyroxenite melting. Instead, the heavy Fe component requires enhanced isotope fractionation during partial melting of a peridotitic source with Fe3+/ΣFe ≥ 0.15. Low Ba/Th ∼ 50 and depleted 87Sr/86Sr(i) and eNd(t) suggest that the source was insignificantly affected by hydrous fluids and recycled terrigenous sediments. The heavy Fe component is known to be unique in its low δ 26 Mg and high δ 66 Zn and indicates hybridization by recycled carbonates. The source Fe3+/ΣFe was most likely enhanced at cost of reduction of recycled carbonates to diamonds in a mantle depth ≥300 km. The origin of the heavy Fe component illustrates a pathway with net transportation of oxidizer back to Earth's surface: CO2 (in carbonates) → C (as diamond frozen in the deep mantle) + O2 (ferric Fe being scavenged by melt extraction). Secular cooling of global subduction zones may have stepwisely increased the efficiency of this carbon driven deep oxygen cycle in the past, providing an alternative explanation for the rise of atmospheric O2.

Atmospheric abundance of oxygen (O2) has been co-evolved with different aspects of the Earth system since appearance of oxygenic photosynthesis by cyanobacteria around 2.4 109 years before present (Ga). Therefore, much attention has been paid to understand the changes in O2 and the underlying mechanisms over the Earth’s history. The pioneering work by Stolper et al. (2016) revealed the long-term decreasing trend of O2 mixing ratios over the last 800,000 years using the ice-core composite record of molar ratios of O2 and nitrogen (δ(O2/N2)), implying a slight imbalance between sources and sinks. Over geological time scale, O2 is mainly controlled by burial and oxidation of organic carbon and pyrite, but also by oxidation of volcanic gases and sedimentary rocks. Nevertheless, the O2 cycle of the late Pleistocene has not been well understood, partly due to the lack of knowledge about the individual sources and sinks. Since then, Kölling et al. (2019) proposed a simple model to estimate the O2 release/uptake fluxes due to the pyrite burial/oxidation that predicts up to ~70% of the O2 decrease of the last 800,000 years could be explained by pyrite burial/oxidation.Building on this, we present here our preliminary, tentative attempt for reconstruction of the net organic carbon burial flux over the last 800,000 years by combining available information (including new δ(O2/N2) data) and assuming constant O2 fluxes associated with volcanic outgassing and rock weathering. The long-term organic carbon burial flux trend obtained with our new calculations is similar to the global ocean δ13C records but also to simulations using a conceptual carbon cycle model (Paillard, 2017). These results partly support the geomorphological hypothesis that the major sea-level drops during the earlier period of the last 800,000 years lead to enhanced organic carbon burial, and that significant changes in the net organic carbon happen around Marine Isotopic Stage (MIS) 13. In addition, we present the long-term decreasing trend of the global biosphere productivity, or gross photosynthetic O2 flux, reconstructed from new measurements of triple-isotope composition of atmospheric O2 trapped in ice cores. As the largest O2 flux, the observed decrease in gross photosynthesis requires to be compensated by parallel reduction of global ecosystem respiration.

The marine phosphorus cycle plays a critical role in controlling the extent of global primary productivity and thus atmospheric pO2 on geologic time scales. However, previous attempts to model carbon–phosphorus-oxygen feedbacks have neglected key parameters that could shape the global P cycle. Here we present new diagenetic models to fully parameterize marine P burial. We have also coupled this diagenetic framework to a global carbon cycle model. We find that seawater calcium concentration, by strongly influencing carbonate fluorapatite (CFA) formation, is a key factor controlling global phosphorus cycling, and therefore plays a critical role in shaping the global oxygen cycle. A compilation of Cenozoic deep-sea sedimentary phosphorus speciation data provides empirical support for the idea that CFA formation is strongly influenced by marine Ca concentrations. Therefore, we propose a previously overlooked coupling between Phanerozoic tectonic cycles, the major-element composition of seawater, the marine phosphorus cycle, and atmospheric pO2.

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Oceanography and Applied Ocean Science and Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2020.

The Kuroshio Extension (KE) is a current associated with the largest CO 2 flux into the Pacific Ocean, a broad region of uptake that extends across the Pacific basin between the subarctic and subtropical regions. The relative importance of the biological and physical processes controlling this sink is uncertain. Because oxygen is stoichiometrically linked to changes in dissolved inorganic carbon due to photosynthesis and respiration and subject to many of the same physical drivers as the CO 2 flux, in situ oxygen measurements help to determine the processes driving this large CO 2 flux. We analyzed data from eight Argo profiling floats equipped with oxygen sensors to estimate oxygen fluxes in the upper ocean of the KE region (approximate bounds: 25°N to 45°N, 135°E to 155°E). In situ air calibrations of these sensors allowed us to accurately measure air-sea oxygen differences, which largely control the flux of oxygen to and from the atmosphere. To characterize distinct biogeographical regions in the Kuroshio Extension and to accommodate seasonal north-south shifts in the location of the regional boundaries, we averaged oxygen measurements from different floats along isopycnal surfaces into 3 regions based on temperature-salinity relationships: North KE, Central KE, and South KE. Using these regional concentration time series, we determined the physical fluxes using an upper ocean layered model and calculated the residual oxygen flux, a combination of column-integrated net community production and physical processes unexplained by the model. The annual oxygen budget is largely a balance of air-sea exchange and the residual oxygen term. Residual oxygen fluxes are -5.4 ± 1.1, -5.9 ± 0.1, and 2.1 ± 2.2 mol O 2 m -2 yr -1 (where negative is a loss from the upper ocean) for the North, Central, and South KE regions, respectively. The North and Central KE are regions of mode water formation, which balances the large air-sea fluxes into the ocean. The South KE oxygen residual indicates a biologically produced flux to the atmosphere in two out of three years that agrees with previous estimates of subtropical annual net community production (ANCP) but exhibits high interannual variability. This study suggests that physical processes are the primary drivers for the annual uptake of the gases oxygen and carbon dioxide in the Central KE region where the annual CO 2 uptake is strongest.

Iron migration forms and variations of its concentrations in water and bottom sediments of the Vygozero Reservoir were studied in period from 1993 to 2014. The decrease in wastewater volume discharged from the pulp and paper mill in the early 1990s caused stabilization of water oxidation regime and accumulation of iron in bottom sediments, from which it returns into the water mass when the environmental conditions change in the seasonal oxygen cycle.

In this brief communication we provide an estimate of the part of the incident solar energy used for oxygen evolution as well as the time, in years, needed for the generation of the present amount of molecular oxygen in the biosphere by photosynthesis on land and in the ocean. We find this to be ≈3,000 yr. We also find that the ocean produces 22% more oxygen than the land surface.

Recycling of solid waste for oxygen recovery in manned spacecraft is extremely important during long-term space missions. In the current study, pyrolysis process was evaluated to investigate the recovery potential of oxygen from spaceflight solid waste (SSW). A low fidelity waste surrogate (LFWS) was employed to simulate the solid waste produced during long-term space missions, and the oxygen distribution and oxygen-containing species in various pyrolysis products were investigated. In comparison with terrestrial municipal solid waste, SSW has higher content of oxygen, nitrogen and sulfur, but the content of carbon is much lower. The amount of oxygen recovered from SSW was higher than from terrestrial solid waste by pyrolysis treatment. Moreover, much more oxygen in SSW could be easily converted into the gaseous phase for oxygen recovery by adjusting treatment temperature. Nearly 50% of oxygen in SSW was recovered in the form of the gaseous product, and the optimal oxygen recovery efficiency was 29.54% at 700 °C. Recycling oxygen from SSW is a desirable approach to improve the closure level of oxygen cycle in the life support system. This work provides fundamental information for oxygen recycling from SSW during long-term space missions.

The emergence and expansion of complex eukaryotic life on Earth is linked at a basic level to the secular evolution of surface oxygen levels. However, the role that planetary redox evolution has played in controlling the timing of metazoan (animal) emergence and diversification, if any, has been intensely debated. Discussion has gravitated toward threshold levels of environmental free oxygen (O2) necessary for early evolving animals to survive under controlled conditions. However, defining such thresholds in practice is not straightforward, and environmental O2 levels can potentially constrain animal life in ways distinct from threshold O2 tolerance. Herein, we quantitatively explore one aspect of the evolutionary coupling between animal life and Earth's oxygen cycle-the influence of spatial and temporal variability in surface ocean O2 levels on the ecology of early metazoan organisms. Through the application of a series of quantitative biogeochemical models, we find that large spatiotemporal variations in surface ocean O2 levels and pervasive benthic anoxia are expected in a world with much lower atmospheric pO2 than at present, resulting in severe ecological constraints and a challenging evolutionary landscape for early metazoan life. We argue that these effects, when considered in the light of synergistic interactions with other environmental parameters and variable O2 demand throughout an organism's life history, would have resulted in long-term evolutionary and ecological inhibition of animal life on Earth for much of Middle Proterozoic time (∼1.8-0.8 billion years ago).

Marine pollution occurs due to the entry of organized or unorganized, point or non – point land based releases of industrial, agricultural and residential waste. Biodegradable organic waste rich in microorganisms lead to potentially harmful effects and alter oxygen cycle, where as excessive inputs of nutrients like nitrogen and phosphorus stimulate algal growth leading to eutrophication. Thermodynamics play an important role in chemicals reactions occurring in ocean during degradation of organic waste. The rate of reactions is altered due to temperature and high salinities. This aspect is very crucial while predicting the self purification capacity of the water body. Adequate experimental work pertaining to the order of reaction and thermodynamic constants is essential to prove the basis of the predicted assimilative capacity of the system. In Mumbai, huge quantity of domestic waste is generated. Due to land restrictions, complete treatment of tertiary level is not feasible. The Municipal administrators take the advantage of coastal location and discharge this waste into the ocean with just meagre preliminary treatment. The disposal practices are advanced and well planned but still expected purification or dilution is not achieved in the near shore region. This has resulted in spoiling the impact zone of coastal areas creating stress on the living biota and non compliance of the marine water quality standards. Three major issues in coastal system, viz. Operation and control of waste discharges, degradation patterns of pollutants and self purification capacity needs systematic evaluation to maintain favorable conditions for aquatic life. Hence it is essential to study the reaction kinetics and thermodynamic behaviour of the biodegradation of carbonaceous waste occurring under highly saline conditions. Experiments are conducted to confirm the kinetics and thermodynamics of biodegradation of domestic waste water into marine water at variable salinities. The paper presents the findings of kinetic behaviour particularly the values for rate of reaction, Activation energy and related constants.

The paper deals with changes in temperature of lead acid battery cell during discharge and pulse charging in oxygen cycle regime. It is studied the effect of different pulse charging modes on increase of cell temperature and influence of oxygen cycle on temperature changes of the lead acid battery cell.

Water splitting to generate O2 and H2 fuel is an ongoing focus of (photo)electrochemical energy storage and conversion efforts. While water oxidation to generate O2 through the oxygen evolution reaction (OER) accounts for the majority of energy loss in this process, water reduction to generate H2 through the hydrogen evolution reaction (HER) in alkaline is also sluggish, with over two orders of magnitude less activity than in acid. For OER, NiFe layered double hydroxides have attracted significant interest due to their comparable performance with precious metal-based RuO2 and IrO2 catalysts. In spite of extensive study, however, the 3D crystal structure of the active phase under catalytic oxygen evolution reaction conditions remains unclear, and the lack of atomic-scale details concerning the crystal structure makes it challenging to choose appropriate structural models for first principles-based mechanistic studies. Similarly, for alkaline HER, ultrathin (oxy)hydroxide films on precious metal substrates have shown impressive activity improvements compared to pure Pt, but the films’ structure and stability are still largely unknown, and the catalytic mechanism remains unclear. In this presentation, we will begin by showing our recent efforts to elucidate the catalytically active phase and OER mechanism on NiFe layered double hydroxides by combining electrochemical measurements, operando experiments, DFT calculations, and ab initio molecular dynamics simulations. Next, for HER, we will turn to monolayer Ni (oxy)hydroxide films, wherein we will demonstrate that these ultrathin films can be dramatically stabilized with respect to the corresponding bulk analogs and that the bifunctional interface provides ideal sites for water activation. Finally, if time permits, we outline our recent work on oxygen reduction reaction electrochemistry, discussing both tunable intrinsic strain in two-dimensional transition metal electrocatalysts for the ORR, as well as recent developments in the study of stability of PGM-free electrocatalysts.

Herein, we attempted to identify the active sites behavior of perovskite catalysts in the oxidative coupling of methane (OCM) reaction, using ten types of ABO3 perovskite catalysts with different structural properties according to their A and B site elements. The results showed that the catalyst surface lattice oxygen species are responsible for the selective conversion of methane. In particular, surface lattice oxygen species with moderate binding energies selectively catalyzed the OCM to produce C2 hydrocarbons. The surface oxygen vacancies, resulting from the reaction of lattice oxygen and CH4, were refilled with adsorbed surface oxygen and bulk lattice oxygen species. This oxygen cycle was closely related to the oxygen ion conductivity of perovskites, which could be determined based on their structural factors, such as the tolerance factor and the specific free volume. Accordingly, a facile oxygen cycle resulted in a high CH4 conversion during this reaction. Finally, we concluded that the lattice oxygen properties and the oxygen ion conductivity of perovskite catalysts are key factors in determining the catalytic activity and should, therefore, be precisely controlled for the systematic design of efficient OCM catalysts.

Water splitting to generate O2 and H2 fuel has been a major focus of (photo)electrochemical energy storage and conversion efforts, but many challenges remain. While water oxidation to generate O2 through the oxygen evolution reaction (OER) accounts for the majority of energy loss in this process, water reduction to generate H2 through the hydrogen evolution reaction in alkaline is over two orders of magnitude slower than that in acid. For OER, NiFe layered double hydroxides have attracted significant interest due to their comparable performance with precious metal-based RuO2 and IrO2 catalysts. In spite of extensive study, however, the 3D crystal structure of the active phase under catalytic oxygen evolution reaction conditions remains unclear. The lack of the atomic-scale details of crystal structure makes it challenging to choose appropriate structural models for first principles-based mechanistic studies. Therefore, it is of significant interest to identify these materials’ in-situ crystal structure and, subsequently, determine the intrinsic catalytic mechanism. Similarly, for alkaline HER, ultrathin (oxy)hydroxide films on precious metal substrates possess impressive activity improvement, but the films’ structure and stability are still largely unknown, and the catalytic mechanism remains unclear. In this presentation, we will begin by showing our recent efforts to elucidate the catalytically active phase and OER mechanism on NiFe layered double hydroxides by combining electrochemical measurements, operando experiments, DFT calculations, and ab initio molecular dynamics simulations. Next, for HER, we will introduce the methodologies we have recently developed towards the highly accurate prediction of Pourbaix diagram of transition metal (oxy)hydroxides. Subsequently, using monolayer Ni (oxy)hydroxide films as an example, we will describe a simple scheme to study the structures and the stability of these films on precious metal surfaces. We will show how the ultrathin films can be dramatically stabilized with respect to the corresponding bulk analogs. Then, using the hydrogen evolution reaction as an example, we will demonstrate how these techniques can be applied to understand the steady state, the active phases, and the catalytic mechanism of bi-functional interfaces. We will then demonstrate the extension of the present understanding to real-world catalysts, i.e. precious metal nanoparticles supported on ultrathin transition metal (oxy)hydroxide films. Finally, we will show this understanding can be used to design new bi-functional catalysts with improved performances. If time permits, we will also show our recent work on tunable intrinsic strain in two-dimensional transition metal electrocatalysts for the oxygen reduction reaction. References: 1. Z. Zeng, K.-C. Chang, J. Kubal, N. M. Markovic, J. Greeley, Nature Energy 2, 17070 (2017). 2. L. Wang, Y. Zhu, Z. Zeng, C. Lin, M. Giroux, L. Jiang, Y. Han, J. Greeley, C. Wang, J. Jin, Nano Energy 31, 456-461 (2017). 3. L. Wang, Z. Zeng, W. Gao, T. Maxson, D. Raciti, M. Giroux, X. Pan, C. Wang, J. Greeley, Science 363, 870-874 (2019). 4. F. Dionigi, Z. Zeng, I. Sinev, T. Merzdorf, S. Deshpande, M. Bernal Lopez, S. Kunze, I. Zegkinoglou, H. Sarodnik, D. Fan, A. Bergmann, J. Drnec, J. Ferreira de Araujo, M. Gliech, D. Teschner, J. Greeley, B. Roldan Cuenya, P. Strasser, submitted, 2019.

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.

The possibility of low but nontrivial atmospheric oxygen (O2) levels during the mid-Proterozoic (between 1.8 and 0.8 billion years ago, Ga) has important ramifications for understanding Earth's O2 cycle, the evolution of complex life and evolving climate stability. However, the regulatory mechanisms and redox fluxes required to stabilize these O2 levels in the face of continued biological oxygen production remain uncertain. Here, we develop a biogeochemical model of the C-N-P-O2-S cycles and use it to constrain global redox balance in the mid-Proterozoic ocean-atmosphere system. By employing a Monte Carlo approach bounded by observations from the geologic record, we infer that the rate of net biospheric O2 production was 3.5 (+1.4 - 1.1) Tmol year-1 (1-sigma), or ~25% of today's value, owing largely to phosphorus scarcity in the ocean interior. Pyrite burial in marine sediments would have represented a comparable or more significant O2 source than organic carbon burial, implying a potentially important role for Earth's sulphur cycle in balancing the oxygen cycle and regulating atmospheric O2 levels. Our statistical approach provides a uniquely comprehensive view of Earth system biogeochemistry and global O2 cycling during mid-Proterozoic time and implicates severe P biolimitation as the backdrop for Precambrian geochemical and biological evolution., Accepted to Geobiology; Final article and Supplementary Information available at https://onlinelibrary.wiley.com/doi/full/10.1111/gbi.12317

Ventilation and dissolved oxygen in Lake Superior are key factors that determine the fate of various natural and anthropogenic inputs to the lake. We employ an idealized age tracer and biogeochemical tracers in a realistically configured numerical model of Lake Superior to characterize its ventilation and dissolved O2 cycle. Our results indicate that Lake Superior is preferentially ventilated over rough bathymetry and that spring overturning following a very cold winter does not completely ventilate the lake interior. While this is unexpected for a dimictic lake, no part of the lake remains isolated from the atmosphere for more than 300 days. Our results also show that Lake Superior's oxygen cycle is dominated by solubility changes; as a result, the expected relationship between biological consumption of dissolved O2 and ventilation age does not manifest.

Evidence is presented that the oxygen demand associated with photochemical processes in the surface layer of oceans and seas worldwide is of the same order of magnitude as the amount of oxygen released by photosynthesis of the world's marine phytoplankton. Both estimates are of necessity quite rough and therefore the agreement between oxygen loss and production, earlier found only locally in the Atlantic Ocean and the North Sea, came as a surprise. The heavy photochemical oxygen demand of the world's oceans must be explored further in oxygen budget studies by biogeochemical modelling in which special attention is paid to regional and temporal-differences in the vertical stratification regime at the surface. Indeed, stratification is the candid() sine qua non for photochemical processes that are driven by ultraviolet radiation. Oxygen cannot be expected to be released from the sea to the atmosphere in the permanently stratified open ocean when year-round the oxygen loss associated with photochemistry is so high. In the upper layer of sea and ocean regions of the temperate zone vertical stratification is only pronounced during spring, summer and early autumn, so photochemical oxygen demand there is restricted to those months. We argue that the constancy of the oxygen concentration observed at the surface of the oceans in the tropics and subtropics (80% of Earth's marine regions) is the consequence of the balance between three processes that influence oxygen dissolved in seawater: loss due to photochemical processes and to the activity of microheterotrophs on the one hand, photosynthetic oxygen production by phytoplankton on the other. (C) 2015 Elsevier B.V. All rights reserved

Abrasion which is occurred in the Sayung coast is triggered by a big role of climate change as well as the sea level rise and land subsidence. Resulting degradation ultimately affects changes in existing environmental conditions. This study has aim to determine the existing water based on biological and chemical content which is affected by increasing suspended solid content in the Sayung waters. Purposive sampling technique was applied, and data is analyzed both statistically and spatially. Suspended solid value has ranged 23,1-199,6 mg/L. Distribution of suspended solid was only simulated during low tide towards high tide phase with current speed has ranged 0-0.41 m/s. We found that dissolved oxygen value is quite high in several observation stations which indicates the fertile area with low pollution and blooming tendency. In the station which is dominated by a high suspended solid and turbidity found that the chlorophyll-a decreases. The increased rate of suspended solid is directly enhancing the turbidity and indirectly declines the photosynthesis activity and inhibits the oxygen cycle. Resulting in the primary productivity reduction in the Sayung waters

Models and observations of Atmospheric Potential Oxygen (APO ≃ O2 + 1.1*CO2) are used to investigate the influence of El Nino 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 Nino3.4 index, indicating anomalous ocean outgassing of APO during El Nino. 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. In all models, O2 accounts for most APO flux variations. Detailed analysis in CESM shows the O2 response is driven primarily by ENSO-modulation of the source and rate of equatorial upwelling, which moderate the intensity of O2 uptake due to vertical transport of low-O2 waters. These upwelling changes dominate over counteracting effects of biological productivity and thermally-driven O2 exchange. During El Nino, shallower and weaker upwelling leads to anomalous O2 outgassing, whereas deeper and intensified upwelling during La Nina drives enhanced O2 uptake. This response is strongly localized along the central and eastern equatorial Pacific, leading to an equatorial zonal dipole in atmospheric anomalies of APO. This dipole is further intensified by ENSO-related changes in winds, reconciling apparently conflicting APO observations in the tropical Pacific. These findings suggest a substantial and complex response of the oceanic O2 cycle to climate variability that is significantly (>50%) underestimated in magnitude by ocean models.