Oxygen Replenishment Research Articles

A Closed-Circuit Neonatal Xenon Delivery System: A Technical and Practical Neuroprotection Feasibility Study in Newborn Pigs

Asphyxia accounts for 23% of the 4 million annual global neonatal deaths. In developed countries, the incidence of death or severe disability after hypoxic-ischemic (HI) encephalopathy is 1-2/1000 infants born at term. Hypothermia (HT) benefits newborns post-HI and is rapidly entering clinical use. Xenon (Xe), a scarce and expensive anesthetic, combined with HT markedly increases neuroprotection in small animal HI models. The low-Xe uptake of the patient favors the use of closed-circuit breathing system for efficiency and economy. We developed a system for delivering Xe to mechanically ventilated neonates, then investigated its technical and practical feasibility in a previously described neonatal pig model approximating the clinical scenario of global HI injury, prolonged Xe delivery with and without HT as a potential therapy, subsequent neonatal intensive care unit management, and tracheal extubation. Sixteen newborn pigs underwent a global 45 min HI insult (4%-6% inspired oxygen reducing the electroencephalogram amplitude to <7 microV), then received 16 h 50% inspired Xe during normothermia (39.0 degrees C) or HT (33.5 degrees C). A conventional neonatal ventilator provided breaths of oxygen to a lower chamber compressing a hanging bag within. This bag communicated with the upper closed part of the breathing system containing soda lime, unidirectional valves, Xe/oxygen analyzers, and a tracheal tube connection. At each end-inspiration, this bag emptied fully and a bolus of oxygen, the driving gas, crossed from the lower to upper chamber via an additional valve. This mechanically substituted the gas uptake from the circle during the previous breath cycle (oxygen + small volume of Xe) with an equivalent volume of oxygen creating a slow-rising inspired oxygen concentration. This was offset by manual injection of Xe boluses, infrequently at steady state, due to the low-Xe uptake of the patient. Total mean Xe usage was 0.18 (0.16-0.21) L/h with no differences between Xe-HT and Xe-NT groups, which had weights of 1767 (1657-1877) g and 1818 (1662-1974) g, respectively (95% CI). HT reduced heart rate in the cooled animals; 180 (165-195) vs 148 (142-155) bpm (P < 0.0001) with no differences in arterial blood pressure, oxygen saturation, arterial carbon dioxide tension, or weaning times between these groups. We describe a closed-circuit Xe delivery system with automatic mechanical oxygen replenishment, which could be developed as a single use device. Gas exchange was maintained while Xe consumption was minimal (<$2/h at $10/L*). We have shown it is both feasible and cost-efficient to use this Xe delivery method in newborn pigs for up to 16 h with or without concurrent cooling after a severe HI insult.

Effect of salt exclusion from lake ice on seasonal circulation

We describe the circulation of Tailings Lake, located 220 km north of Yellowknife, Northwest Territories, Canada. From Jul 2004 to Sep 2007, temperature and conductivity profiles were collected together with data from three moored temperature chains and a meteorological station. The salt content of the lake was elevated (salinity 1 g L−1) relative to surrounding natural waters (~0.1 g L−1). Winter ice cover included 60–80 cm of transparent "black" ice, which excluded up to 99% of the salt from the water as the ice formed. During winter, the salt excluded from the ice was mixed throughout the water column under the ice. In spring, ice melt and snow runoff resulted in a freshwater cap; the density contrast between this fresh epilimnion and the more saline hypolimnion was sufficient to inhibit spring turnover. In summer, the epilimnion was deepened by storms, mixing anoxic water from the hypolimnion into the surface layer. Because spring turnover was suppressed, oxygen replenishment of the hypolimnion occurred only in fall. Although Tailings Lake has been subject to numerous anthropogenic changes, similar effects can be expected in other natural and manmade water bodies with elevated salinity and significant ice cover.

Intrinsic kinetics of reoxidation reaction for a multicomponent molybdate catalyst by thermal analysis method

Abstract The reoxidation of a multicomponent molybdate catalyst is studied by thermal analysis method along with X-ray photoelectron spectroscopy (XPS). It is found that the reoxidation of the catalyst is mainly attributed to the replenishment of lattice oxygen combined with Mo. Further, the intrinsic kinetic model of this reaction is obtained by Kissinger–Akahira–Sunose isoconversional and master-plot method. The activation energy and pre-exponential factor (ln A ) are 140.01 ± 11.10 kJ mol −1 and 21.527 ± 0.076 min −1 , respectively. The kinetic model is best expressed by Avrami–Erofeyev equation, i.e., g ( α ) = [−ln(1 − α )] 1/(0.922 ± 0.026) , suggesting a nucleation and growth mechanism.

Distribution of Molidae in the Northern Gulf of Mexico

We compiled all available sighting, stranding and bycatch data for the Family Molidae (molas) in the northern Gulf of Mexico (NGOM) to assess spatial and temporal distribution. Overall, 483 records were collected from shipboard and aerial surveys, fisheries bycatch, and strandings. Molas were recorded year-round, with a ubiquitous distribution in both nearshore and offshore waters. Ocean sunfish (Mola mola) were sighted with greatest frequency during the winter (December thru April) in sea surface temperature < 24° C. Potential reasons for increased sightings during winter may be related to the lack of a well-defined thermocline in the NGOM; the species' "basking" behavior associated with thermoregulation; and oxygen replenishment after long, deep dives to oxygen-deficient depths.

Twenty years of spatially coherent deepwater warming in lakes across Europe related to the North Atlantic Oscillation

Twenty to fifty years of annual mean deepwater (hypolimnetic) temperature data from twelve deep lakes spaced across Europe (2°95'W to 14°0'E, 46°27' to 59°00'N) show a high degree of coherence among lakes, particularly within geographic regions. Hypolimnetic temperatures vary between years but increased consistently in all lakes by about 0.1–0.2°C per decade. The observed increase was related to the weather generated by largescale climatic processes over the Atlantic. To be effective, the climatic signal from the North Atlantic Oscillation (NAO) must affect deep lakes in spring before the onset of thermal stratification. The most consistent predictor of hypolimnetic temperature is the mean NAO index for January–May (NAOJ–M), which explains 22–63% of the interannual variation in deepwater temperature in 10 of the 12 lakes. The two exceptions are remote, less wind‐exposed alpine valley lakes. In four of the deepest lakes, the climate signal fades with depth. The projected hypolimnetic temperature increase of approximately 1°C in 100 yr, obtained using a conservative approach, seems small. Effects on mixing conditions, thermal stability, or the replenishment of oxygen to deep waters result in accumulation of nutrients, which in turn will affect the trophic status and the food web.

Air-Breathing Laminar Flow-Based Microfluidic Fuel Cell

This communication reports the design and characterization of an air-breathing laminar flow-based microfluidic fuel cell (LFFC). The performance of previous LFFC designs was cathode-limited due to the poor solubility and slow transport of oxygen in aqueous media. Introduction of an air-breathing gas diffusion electrode as the cathode addresses these mass transfer issues. With this design change, the cathode is exposed to a higher oxygen concentration, and more importantly, the rate of oxygen replenishment in the depletion boundary layer on the cathode is greatly enhanced as a result of the 4 orders of magnitude higher diffusion coefficient of oxygen in air as opposed to that in aqueous media. The power densities of the present air-breathing LFFCs are 5 times higher (26 mW/cm2) than those for LFFCs operated using formic acid solutions as the fuel stream and an oxygen-saturated aqueous stream at the cathode ( approximately 5 mW/cm2). With the performance-limiting issues at the cathode mitigated, these air-breathing LFFCs can now be further developed to fully exploit their advantages of direct control over fuel crossover and the ability to individually tailor the chemical composition of the cathode and anode media to enhance electrode performance and fuel utilization, thus increasing the potential of laminar flow-based fuel cells.

Design of peripheral airways for efficient gas exchange

Peripheral airways combine branched tubes for ventilation with the gas exchanging alveoli in the pulmonary acini, defined as the complex of airways supplied by one first order respiratory or transitional bronchiole. In this part, the replenishment of oxygen at the alveolar surface occurs by a combination of convective air flow with diffusion of oxygen in the air. The transition between convection and diffusion depends on the morphometric properties of the airways. The design of the peripheral airways in the acinus of the human lung is described quantitatively on the basis of measurements obtained on casts of the acinar airways. Comparable data for rat and rabbit are also discussed. On the basis of this morphometric information, a typical path model for human acinar airways is derived. These studies also form the basis for advanced modeling studies of gas exchange and ventilation. In particular the problems occurring because of diffusional screening and the design conditions for minimizing this effect are discussed.

Topography of anatase TiO2 film synthesized on LaAlO3(001)

The surface of an anatase titanium dioxide(TiO2) filmgrown on LaAlO3(001) was observed using noncontact atomic force microscopy (NC-AFM). Aftercleaning with cycles of argon ion sputtering and annealing in vacuum,(1 × 4)- and(1 × 5)-reconstructed terraces appeared. In addition to the terraces, thesputter-annealed surface included many agglomerations. The presence ofTin+ () shown by x-ray photoelectron spectroscopy indicates that the agglomerations are due toTiOx () species. Limited replenishment of oxygen by the substrate and the low diffusivity of theTin+ to the substrate are possible causes for the generation of theTiOx.

Complex effects of winter warming on the physicochemical characteristics of a deep lake

Recent winter warming over Central Europe associated with a positive phase of the North Atlantic Oscillation (NAO) strongly influenced the thermal and water column stability properties of deep Lake Constance (zmean = 101 m). Volumetrically weighted average water temperatures have increased since the 1960s by an average of 0.017°C yr−1, and its interannual variability was strongly related to the variability in winter air temperature and the NAO winter index (NAOW). The influence of NAOW on water temperature was more persistent than its influence on air temperature. The seasonal persistence of the NAOW signal increased with water depth. Deep‐water temperatures were related to the NAOW from one spring mixing period to the next. This caused a time lag of 1 yr in the response of deep‐water winter temperatures to the NAOW. Reduced winter cooling during high‐NAOW years resulted in the persistence of small temperature gradients that possibly resisted complete mixing. This, in turn, resulted in less upward mixing of nutrients (total phosphorus and total silica), which accumulated in the hypolimnion during the previous stratification period. A second effect of incomplete mixing was the lack of the replenishment of deepwater oxygen during high‐NAOW years. Hence, besides its strong impact on the thermal regime, climate variability influenced both the causes (nutrient supply for phytoplankton growth) and symptoms (the degree of hypolimnetic oxygen deficiency) of trophic changes in Lake Constance.

Dissolved Oxygen Characteristics of the Gamtoos Estuary, South Africa

The fall and recovery of dissolved oxygen (DO) is documented throughout the Gamtoos Estuary, South Africa during dry conditions and following light and heavy rainfall over a 13-month period from November 1992 to November 1993. Hypoxic conditions generally occurred in the near-bottom waters of the upper estuary. Localized fluctuations in DO levels are related to the natural diurnal fluctuation associated with photosynthesis of aquatic flora. The drop in DO levels following light rainfall is associated with the volume of oxygen-consuming compounds entering the estuary via runoff from adjacent agricultural fields. This hypoxia was short-lived. Following an extreme rainfall event, however, almost immediate hypoxia was recorded throughout the estuary, and DO levels deteriorated for some time thereafter as a result of the substantial input of organic matter into the estuary. The area of hypoxia and recovery was governed by the freshwater input at the tidal head, estuarine hydrometry and hydrodynamics. Tidal processes were identified as a source of replenishment of oxygen when, during high tide, seawater with a higher DO content penetrated the estuary.

P31-02 航行型海中ロボット用閉鎖式ディーゼル機関

This paper presents details of an air-independent power (AIP) system of a Closed Cycle Diesel Engine System (CCDE) for a cruising type autonomous underwater vehicle (AUV) called "R-One Robot" The CCDE is controlled fully automatically, and produces 5kW output and its capacity is about 60kWh, which corresponds to 24 hour and 100 km range continuous dive of the robot. The CCDE consists of a diesel engine and peripheral equipment for closed cycle operation such as a chemical absorber for carbon dioxide removal from exhaust gas using potassium hydro-oxide, an oxygen replenishment system including oxygen sensor in the control system and a liquid oxygen tank. Vibration and noise of the engine are sufficiently isolated for the vehicle hull. The R-One Robot is 8 m length and 4.8 tons in weight, and its depth rate is 400 m. The first autonomous dive of the robot was carried out in 1996,and has been used for scientific research of the ocean so far.

The role of nanosized gold particles in adsorption and oxidation of carbon monoxide over Au/Fe2O3 Catalyst

The presence of gold is found to promote the development of weakly bonded (CO)ad species over the surface of Au/Fe2O3 catalyst during interaction with carbon monoxide (CO) or a mixture of carbon monoxide and oxygen. The concentration of these species and the nature of the bonding depend on the gold particle size. No such species are formed for gold particles larger than ∼11 nm or over gold-free iron oxide. The bulk carbonate-like species, formed in the process with the involvement of the hydroxy groups of the support, are merely side products not responsible for the low temperature activity of this catalyst. Thermochemical measurements reveal that the oxidation of carbon monoxide on both Fe2O3 and Au/Fe2O3 occurs via similar redox mechanisms, involving the abstraction and replenishment of lattice oxygen, where the presence of nanosize gold particles promotes these processes. This is attributed to their capacity to adsorb carbon monoxide because of their inherent defective structural sites. It is suggested that the energy that evolves during chemisorption of CO is responsible for the surge in temperature at the Au-Fe2O3 interfaces, which in turn serve as sites for the accelerated reaction between CO and the support. The role of gold particle size is discussed in terms of the effect of geometry of surface metal atoms in the nanosize clusters.

Mechanism of Low-Temperature Oxydehydrogenation of 1-Butene to 1,3-Butadiene over a Novel Pd–Fe–O Catalyst

The minimum operating temperature for sustainable oxydehydrogenation of butene to butadiene over Fe2O3 can be reduced from ca. 300° to ≤150°C by including Pd in the catalyst formulation. This effect would not be predicted on the basis of the widely accepted redox mechanism for selective oxidation, in which transport of the essential oxide ions can become limiting at low temperatures. Temperature-programmed desorption and temporal analysis reveal that the selective oxygen within the Pd–Fe–O catalyst is localised near the surface, and can be replenished easily from the gas phase. The ability of Pd to activate oxygen at low temperatures is critical to the process of oxygen replenishment, but just as important, it promotes the removal of site-blocking species from the surface of the catalyst. We show that whereas unmodified α-Fe2O3 is in fact capable of converting 1-butene to 1,3-butadiene at temperatures as low as 150°C, the activity is extremely short-lived because of the buildup of site-blocking carbonaceous species at this temperature. The addition of Pd enables the removal of these undesirable species at low temperatures.

Kinetics of the partial oxidation of methane to formaldehyde on silica catalyst

AbstractThe kinetics of the partial oxidation of methane to formaldehyde (MPO) on a “precipitated” silica catalyst in the 500–800°C range was investigated. The influence of temperature and reaction mixture composition on the density of reduced sites of the catalyst under steady state was evaluated by in situ reaction temperature oxygen chemisorption measurements. The kinetics of the MPO on silica is pseudo first and zero‐order on P and P, respectively, while the density of reduced sites depends upon the square root of the P/P ratio. The rate‐determining step is the activation of C–H bond of CH4 molecules (Ered = 142 kJ·mol−1), while oxygen replenishment is a nonactivated reaction step (Eox≈20 kJ·mol−1). A Langmuir‐Hinshelwood kinetic model, accounting for a two‐site‐dissociative activation mechanism of both CH4 and O2, thoroughly describes the steady state of the silica surface and the reaction kinetics of the MPO in the 500–800°C range.

Microcalorimetry, Adsorption, and Reaction Studies of CO, O2, and CO+O2 over Au/Fe2O3, Fe2O3, and Polycrystalline Gold Catalysts

To understand the effect of catalytic activity of Au/Fe2O3 at low temperatures on a CO oxidation reaction, adsorption and changes in enthalpy were determined for the interaction of CO, O2, or CO+O2 (2:1) pulses over Au (5 at.%)/Fe2O3, Fe2O3, and polycrystalline gold catalysts between 300 and 470 K. The results demonstrate that the oxidation of CO on both Fe2O3 and Au/Fe2O3 occur by means of similar redox mechanisms involving the removal and replenishment of lattice oxygen, where the presence of gold promotes these processes. The FTIR data reveal that gold facilitates the chemisorption of CO on Au/Fe2O3, leading predominantly to the formation of Au0–CO species. The carbonate-like species, formed on both Fe2O3 and Au/Fe2O3 during the adsorption of CO or CO+O2, are stable below 375 K and are regarded to be mere by-products that do not play a major role in the CO oxidation process, particularly at low reaction temperatures (<400 K). The larger gold particles inhibited the formation of COad species during exposure of Au/Fe2O3 to CO+O2; this was accompanied by a decrease in the adsorption of both CO and O2 and a decrease in the formation of CO2. The promotional effect of gold is attributed to the presence of small (nanosize) Au crystallites that facilitate the chemisorption of CO molecules because of their inherent defective structural sites. It is suggested that the energy that evolves during the chemisorption of CO molecules is responsible for the surge in temperature at the Au–Fe2O3 interfaces; these eventually serve as sites for the accelerated reaction between CO and the support.

Microcalorimetry, Adsorption, and Reaction Studies of CO, O2, and CO+O2 over Fe2O3, Au/Fe2O3, and Polycrystalline Gold Catalysts as a Function of Reduction Treatment

Thermochemical and volumetric measurements were made for the adsorption and reaction of CO, O2, and CO+O2 on catalysts from 300 to 470 K, as a function of H2 pretreatment. The transformation of Au/Fe2O3 to Au/Fe3O4 led to inhibited adsorption and oxidation of CO. The exposure of a reduced Au/Fe2O3 to CO+O2 resulted in an O2(ad)/CO(ad) ratio >1 as well as the reoxidation of the support and the progressive restoration of its catalytic activity. The reaction routes involved in the oxidation of CO over polycrystalline gold were different from those over the Au/Fe2O3 catalyst. Thus, while the simultaneous adsorption of the reactant molecules was responsible for this reaction on Au metal, the redox mechanism involving the removal and subsequent replenishment of lattice oxygen played a role in both the Au/Fe2O3 and Fe2O3 catalysts, where the presence of gold promoted these steps.

Oxygen supply and the adaptations of animals in groundwater

1. The first part of this review focuses on the oxygen status of natural groundwater systems (mainly porous aquifers) and hyporheic zones of streams. The second part examines the sensitivity of groundwater organisms, especially crustaceans, to low oxygen concentrations (&lt; 3.0 mg L−1 O2).2. Dissolved oxygen (DO) in groundwater is spatially heterogeneous at macro‐ (km), meso‐ (m) and micro‐ (cm) scales. This heterogeneity, an essential feature of the groundwater environment, reflects changes in sediment composition and structure, groundwater flow velocity, organic matter content, and the abundance and activity of micro‐organisms. Dissolved oxygen also exhibits strong temporal changes in the hyporheic zone of streams as well as in the recharge area of aquifers, but these fluctuations should be strongly attenuated with increasing distance from the stream and the recharge zone.3. Dissolved oxygen gradients along flow paths in groundwater systems and hyporheic zones vary over several orders of magnitude (e.g. declines of 9 × 10−5 to 1.5 ×10−2 mg L−1 O2 m−1 in confined aquifers and 2 × 10−2 to 1 mg L−1 O2 m−1 in parafluvial water). Several factors explain this strong variation. Where the water table is close to the surface, oxygen is likely to be consumed rapidly in the first few metres below the water table because of incomplete degradation of soil‐generated labile dissolved organic carbon (DOC) in the vadose zone. Where the water table is far from the surface, strong oxygen depletion in the vicinity of the water table does not occur, DO being then gradually consumed as groundwater flows down the hydraulic gradient. In unconfined groundwater systems, oxygen consumption along flow paths may be compensated by down‐gradient replenishment of DO, resulting either from the ingress of atmospheric oxygen or water recharge through the vadose zone. In confined groundwater systems, where replenishment of oxygen is impossible, the removal time of DO varies from a few years to more than 10 000 years, depending mainly on the organic carbon content of the sediment. Comparison of the hyporheic zones between systems also revealed strong differences in the removal time and length of underground pathways for DO. This strong variability among systems seems related to differences in contact time of water with sediment.4. Although groundwater macro‐crustaceans are much more resistant to hypoxia than epigean species, they cannot survive severe hypoxia (DO &lt; 0.01 mg L−1 O2) for very long (lethal time for 50% of the population ranged from 46.7 to 61.7 h). In severe hypoxia, none of the hypogean crustaceans examined utilized a high‐ATP yielding metabolic pathway. High survival times are mainly a result of the combination of three mechanisms: a high storage of fermentable fuels (glycogen and phosphagen), a low metabolic rate in normoxia, and a further reduction in metabolic rate by reducing locomotion and ventilation. It is suggested here that the low metabolic rate of many hypogean species may be an adaptation to low oxygen and not necessarily result from an impoverished food supply.5. An interesting physiological feature of hypogean crustaceans is their ability to recover from anaerobic stress and, more specifically, rapidly to resynthesize glycogen stores during post‐hypoxic recovery. A high storage and rapid restoration of fermentable fuels (without feeding) allows groundwater crustaceans to exploit a moving mosaic of suboxic (&lt; 0.3 mg L−1 O2), dysoxic (0.3–3.0 mg L−1 O2) and oxic (&gt; 3 mg L−1 O2) patches.6. It is concluded that although hypogean animals are probably unsuited for life in extensively or permanently suboxic groundwater, they can be found in small or temporarily suboxic patches. Indeed, their adaptations to hypoxia are clearly suited for life in groundwater characterized by spatially heterogeneous or highly dynamic DO concentrations. Their capacity to survive severe hypoxia for a few days and to recover rapidly would explain partly why ecological field studies often reveal the occurrence of interstitial taxa in groundwater with a wide range of DO.

Effects of Injector-Combustor Geometry on the Performance of Supersonic Combustor

Experimental studies were made on supersonic combustion in a two dimensional combustor using Hydrogen as fuel. A Hydrogen vitiation air heater with oxygen replenishment was used for simulating high temperature air entering the supersonic combustor. Transverse fuel injection was employed from the walls (Single wall and Double wall)of the combustor at upstream (Pilot injection) and downstream (Primary injection) of backward-facing step. Experiments were also conducted with single wall injection and in the absence of step and pilot injection. Ignition and pressure drop characteristics of the combustor were determined. Wall static pressures were considered as a measure to find the advantages of pilot and double wall injections. The effects of pilot injection, double wall injection and the step on the performance of the supersonic combustor were studied in terms of combustion efficiency and stagnation pressure drop. It is found that the combustor with pilot fuel and step configuration, employing double wall injection yielded better results.

Analysis of the mean annual cycle of the dissolved oxygen anomaly in the World Ocean

A global climatology of the dissolved oxygen anomaly (the excess over saturation) is created with monthly resolution in the upper 500 m of the ocean. The climatology is based on dissolved oxygen, temperature and salinity data archived at the National Oceanographic Data Center. Examination of this climatology reveals statistically significant annual cycles throughout the upper 500 m of the World Ocean, though seasonal variations are most coherent in the North Atlantic, where data density is greatest. Vertical trends in the phase and amplitude of the annual cycle are noted. The cycle in surface waters is characterized by a summer maximum and a winter minimum, consistent with warming and high rates of photosynthesis during the summer, and cooling and entrainment of oxygen-depleted water during the winter. In low and middle latitudes, the amplitude increases with depth and the maximum occurs later in the year, a trend consistent with the seasonal accumulation of oxygen associated with the shallow oxygen maximum. At a depth that varies between about 30 and 130 m, the phase of the annual cycle undergoes an abrupt shift. We call this depth the oxygen nodal depth. Below the nodal depth, the annual cycle is characterized by an early-spring maximum and a late-fall minimum, consistent with a cycle dominated by respiration during the spring and summer and replenishment of oxygen from the atmosphere by ventilation during the fall and winter. Below the nodal depth, the amplitude of the annual cycle generally decreases with depth, indicative of decreasing respiration and ventilation rates, or less seasonality in both processes. We postulate that the nodal depth in middle and high latitudes corresponds closely to the summertime compensation depth, where photosynthesis and net community respiration are equal. With this interpretation of the nodal depth and a simple model of the penetration of light in the water column, a compensation light intensity of 1 W m -2 (4 μE m -2 s -1 ) is deduced, at the low end of independent estimates. Horizontal trends in the phase and amplitude of the annual cycle are also noted. We find that the nodal depth decreases toward the poles in both hemispheres and is generally greater in the Southern Hemisphere, patterns found to be consistent with light-based estimates of the compensation depth. The amplitude of the annual cycle in the oxygen anomaly increases monotonically with latitude, and higher latitudes lag lower latitudes. In the North Atlantic and North Pacific, the amplitude of the annual cycle tends to increase from east to west at all depths and latitudes, as expected considering that physical forcing has greater seasonal variability in the west. The tropics and the North Indian Ocean have features that distinguish them from other regions. Below about 75 m, these waters have pronounced annual cycles of the oxygen anomaly that are shown to be caused mainly by wind-driven adiabatic displacements of the thermocline. A semiannual cycle of the oxygen anomaly is found in the surface waters of the North Indian Ocean, consistent with the known semiannual cycle of surface heat flux in this region.

Spatial and seasonal variation of methane emission from an Amazon floodplain lake

Methane (CH4) emission from a floodplain lake in central Amazonia was measured during a complete annual cycle using a static chamber method. The results show significant differences in the CH4 flux rates from different habitats in the lake: open water, floating vegetation (mainly the aquatic grass Paspalum repens) and floodplain forest. The highest CH4 emission rates (10–198 mg CH4 m−2 d−1) were recorded during inundation in the seasonally flooded forest. Lower emission rates occurred in the floating vegetation (3–79 mg CH4 m−2 d−1), which is found in areas with a short subaerial phase and in the permanently aquatic part of the lake (4–65 mg CH4 m−2 d−1) free of macrophytes and with the lowest productivity. Seasonal fluctuations in water level resulted in distinct seasonal patterns in CH4 release at different sites in the lake. The permanently aquatic part of the lake had lowest emission rates during periods of water inflow and subsurface oxygen replenishment into the lake. At the periodic aquatic...