Total O2 Uptake Research Articles

The effect of temperature on Antarctic lichen cytochrome and alternative respiratory pathway rates

Respiration is a crucial process that provides all living organisms with energy and metabolites for growth and cellular maintenance. The processes that control respiration in lichens remain poorly understood. We investigated the effects of short-term temperature changes on the respiration rate, as well as the relative contributions of the cytochrome and alternative pathways of thalli from four green-algal lichen species collected from their natural habitats in Antarctica. Lichen respiration was sensitive to short-term temperature increases over a range of 5–35 °C. The total O2 uptake rate was increased by fourfold, and the mean respiratory coefficient (Q10) decreased from 2.5 to 1.3 as the temperature increased. An increase in temperature from 5 to 15 °C had a positive effect on cytochrome respiration coupled with energy production. Temperatures above 15 °C stimulated the activation of the alternative (energy-dissipating) respiratory pathway. Hyperthermia led to increased O2 consumption that was not associated with mitochondrial oxidases. The effects of increased temperature on the respiration rates were more pronounced in the bipolar lichens Umbilicaria decussata and Usnea sphacelata than in the Usnea aurantiaco-atra species with a narrower geographical distribution.

Benthic Carbon Mineralization in Hadal Trenches: Insights From In Situ Determination of Benthic Oxygen Consumption

AbstractHadal trenches have been proposed as depocenters of organic material and hot spots for organic matter mineralization. In this study, we for the first time quantified the total benthic O2 uptake in hadal trenches using in situ chamber incubations. Three trenches in the tropical Pacific were targeted and exhibited relatively high diagenetic activity given the great water depths, that is, the Mariana Trench (2.0 × 102 μmol O2 m−2 d−1, 10,853 m), the Mussau Trench (2.7 ± 0.1 × 102 μmol O2 m−2 d−1, 7,011 m), and the New Britain Trench (6.0 ± 0.1 × 102 μmol O2 m−2 d−1, 8,225 m). Combined with the analyses of total organic carbon and δ13C of total organic carbon in the sediments and previously published in situ O2 microprofiles from hadal settings, we suggest that hadal benthic carbon mineralization partly is governed by the surface production and also is linked to the distance from land. Therefore, we highlight that terrestrial organic matter can be of importance in sustaining benthic communities in some hadal settings.

Oceanic Uptake of Oxygen During Deep Convection Events Through Diffusive and Bubble‐Mediated Gas Exchange

The concentration of dissolved oxygen (O2) plays fundamental roles in diverse chemical and biological processes throughout the oceans. The balance between the physical supply and the biological consumption controls the O2 level of the interior ocean, and the O2 supply to the deep waters can only occur through deep convection in the polar oceans. We develop a theoretical framework describing the oceanic O2 uptake during open‐ocean deep convection events and test it against a suite of numerical sensitivity experiments. Our framework allows for two predictions, confirmed by the numerical simulations. First, both the duration and the intensity of the wintertime cooling contribute to the total O2 uptake for a given buoyancy loss. Stronger cooling leads to deeper convection and the oxygenation can reach down to deeper depths. Longer duration of the cooling period increases the total amount of O2 uptake over the convective season. Second, the bubble‐mediated influx of O2 tends to weaken the diffusive influx by shifting the air‐sea disequilibrium of O2 toward supersaturation. The degree of compensation between the diffusive and bubble‐mediated gas exchange depends on the dimensionless number measuring the relative strength of oceanic vertical mixing and the gas transfer velocity. Strong convective mixing, which may occur under strong cooling, reduces the degree of compensation so that the two components of gas exchange together drive exceptionally strong oceanic O2 uptake.

Effects of 8 Weeks' Training on Systemic and Muscle Oxygen Dynamics in University Rugby Players.

The aim of this study was to investigate the effects of 8 weeks of training on O2 dynamics in university rugby players. University rugby players (n = 15) participated in 5 strength training sessions and 4 field-based training sessions per week for 8 weeks. Before and after 8-weeks' training, the subjects performed ramp cycling exercise until exhaustion. Muscle O2 saturation (SmO2), relative changes from rest in deoxygenated hemoglobin concentration (∆Deoxy-Hb) and total hemoglobin concentration, cardiac output (CO), and pulmonary O2 uptake (VO2) were monitored continuously during exercise. Peak VO2 and CO were normalized by fat-free mass. Though peak VO2 tended to be increased after training, there were no significant changes in CO, nor any muscle O2 dynamic variables at peak exercise between before and after training. However, an increase in peak VO2 was significantly correlated with diminishment of deoxy-Hb and an increase in SmO2. Changes in CO caused by training were not related to improved peak VO2. The improvement of peak VO2 during 8 weeks of rugby training may have been caused by muscle O2 supply, rather than increased CO or muscle O2 extraction.

Effect of Creatine Loading on Oxygen Uptake during a 1-km Cycling Time Trial.

For the first time, we investigated the effects of altering cellular metabolic capacitance, via a 5-d creatine (Cr) loading protocol (20 g·d⁻¹), on oxygen uptake (VO2), accumulated oxygen deficit, muscle recruitment, and performance during a 1-km cycling time trial. In a double-blind, randomized, placebo-controlled design, 19 amateur cyclists were allocated to a Cr (n = 10, VO2peak = 56.0 ± 7.8 mL·kg⁻¹·min⁻¹) or placebo (n = 9, VO2peak = 56.0 ± 8.4 mL·kg⁻¹·min⁻¹) group, and performed a 1-km cycling time trial before and after the supplementation period. Body mass was significantly increased in the Cr group (P < 0.05), but not in the placebo group. Participants adopted an "all-out" pacing strategy in both groups. However, Cr loading reduced VO2 immediately after the beginning (12th to 23th seconds), and this was accompanied by a reduced aerobic and increased anaerobic contribution. The VO2 mean response time was slower (pre: 17.2 ± 5.6 s vs post: 19.9 ± 4.6 s), the total O2 uptake was reduced (pre: 4.64 ± 0.59 L vs post: 4.47 ± 0.53 L), and the oxygen deficit was increased (pre: 0.82 ± 0.27 L vs post: 0.98 ± 0.25 L) after Cr loading. No differences were observed in the placebo group for these variables. Plasma lactate and integrated electromyography were not altered in either group, nor was the time to complete the trial (Cr group: pre: 89.1 ± 6.7 s vs post 89.1 ± 6.2 s and placebo group: pre 85.9 ± 4.9 s vs post 87.0 ± 5.4 s). Cr loading slows the V˙O2 response and increases the anaerobic contribution during a 1-km cycling time trial.

Benthic mineralization and solute exchange on a Celtic Sea sand-bank (Jones Bank)

Benthic carbon mineralization and solute exchange was investigated on a Celtic Sea sandbank during July 2008. The sediment on the top of the bank consisted of consolidated sand, characterized by advective porewater transport and was difficult to sample, this to some extent compromised the investigations at this site. However, intact sediment cores were sampled at 4 stations at the slopes, base of the bank and off the bank (reference site). This sediment was used to assess rates and pathways for benthic diagenesis. Total sediment O2 uptake (TOU) ranged from 5.8 to 9.0mmolm−2d−1 and total sediment release rates of dissolved inorganic carbon (DIC) ranged between 8.60 and 13.8mmolm−2d−1. Microbial denitrification and sulfate reduction accounted for <2% and 12–28% of the total benthic carbon mineralization, respectively. The remaining mineralization is ascribed to O2 and Fe/Mn respiration, respectively. Activity profiles of unsupported 210Pb from all stations indicated deep mixing, presumably caused by intense trawling activity in the area. Calculation based on satellite tracking of fishing vessels suggest that on average 33% of the sediment is affected by trawling activity every year. This is presumed to facilitate high metal respiration rates by continuously oxidizing reduced Fe that would otherwise accumulate in the sediment. Extracted porewater profiles reflected elevated NO3- levels as compared to microsensor determined NO3- profiles that were measured in parallel. We suggest that this reflects NO3- leakage from meiofauna – and that the intracellular NO3- pool in the top 5cm of the sediment exceeds the porewater pool up to a factor of 45. However, this intracellular pool is presumably turned over at very slow rates, compared to the porewater pool subject to microbial denitrification.

Molecular mechanism for the selective impairment of cancer mitochondrial function by a mitochondrially targeted vitamin E analogue

The effects of α-tocopheryl succinate (α-TOS), α-tocopheryl acetyl ether (α-TEA) and triphenylphosphonium-tagged vitamin E succinate (mitochondrially targeted vitamin E succinate; MitoVES) on energy-related mitochondrial functions were determined in mitochondria isolated from AS-30D hepatoma and rat liver, bovine heart sub-mitochondrial particles (SMPs), and in rodent and human carcinoma cell lines and rat hepatocytes. In isolated mitochondria, MitoVES stimulated basal respiration and ATP hydrolysis, but inhibited net state 3 (ADP-stimulated) respiration and Ca2+ uptake, by collapsing the membrane potential at low doses (1–10μM). Uncoupled mitochondrial respiration and basal respiration of SMPs were inhibited by the three drugs at concentrations at least one order of magnitude higher and with different efficacy: MitoVES>α-TEA>α-TOS. At high doses (>10μM), the respiratory complex II (CII) was the most sensitive MitoVES target. Acting as an uncoupler at low doses, this agent stimulated total O2 uptake, collapsed ∆ψm, inhibited oxidative phosphorylation and induced ATP depletion in rodent and human cancer cells more potently than in normal rat hepatocytes. These findings revealed that in situ tumor mitochondria are preferred targets of the drug, indicating its clinical relevance.

Effects of hypoxia on oxygen uptake and surfacing behavior in the giant aquatic salamander Siren lacertina

The greater siren (Siren lacertina) can acquire oxygen from both air and water (bimodal breathing). Currently, only physiological measurements have been made on bimodal breathing, with little work being done on the unique surfacing behaviors associated with this process. Flow-through respirometry was used to measure O2 uptake in increasingly hypoxic water. In addition, video recordings were made to capture and quantify the surfacing behavior of greater sirens in response to progressive hypoxia. Greater sirens showed an increase in aerial O2 uptake, a decrease in aquatic O2 uptake, and no change in total O2 uptake as the aquatic O2 tension decreased. Also, greater sirens shifted only the number of surfacing trips they made as the aquatic O2 tension decreased; all other surfacing behaviors remained unchanged. Greater sirens appear to maintain their metabolic rate despite the aquatic O2 tension solely by modifying the number of trips they take to the surface.

The importance of the cloacal bursae as the primary site of aquatic respiration in the freshwater turtle,Elseya albagula

The ability of freshwater turtles to exchange respiratory gases with their aquatic environment is well known and facilitates prolonged dive durations among several species. Three main sites have been implicated in aquatic respiration (skin, cloaca and buccopharynx) yet the relative contribution of each to total aquatic O2 uptake has been poorly examined among Australian chelids. In this study we investigated the diving physiology of Elseya albagula, a bimodally respiring turtle from Queensland, Australia. Through partitioning experiments we tested the hypothesis that the cloacal bursae are the main site of aquatic O2 uptake in this species. Aquatic oxygen uptake accounted for 70 ± 8% of total oxygen requirements demonstrating the impressive ability of the species to respire underwater, although this was negatively correlated with body mass. Further, the cloacal bursae were found to account for 48% of total aquatic oxygen uptake, providing strong evidence that they are the primary site of aquatic respiration in E albagula.

Temperature‐dependent changes in respiration rates and redox poise of the ubiquinone pool in protoplasts and isolated mitochondria of potato leaves

In many environments, leaves experience large diurnal variations in temperature. Such short‐term changes in temperature are likely to have important implications for respiratory metabolism in leaves. Here, we used intact leaf, protoplasts and isolated mitochondria to determine the impact of short‐term changes in temperature on respiration rates (R), adenylate concentrations and the redox poise of the ubiquinone (UQ) pool in mitochondria of potato leaves. The Q10 (i.e. proportional change in R for each 10°C rise in temperature) of respiration was 1.8, both for intact leaves and protoplasts. In protoplasts, the redox poise of the extracted UQ pool (UQR/UQT) increased from 0.33 at 22°C, to 0.76 at 15°C. Further decreases in temperature (from 15 to 5°C) resulted in UQR/UQT decreasing to 0.40. Adenylate ratios in protoplasts were also temperature dependent. At high adenosine 5′‐triphosphate (ATP) adenosine 5′‐diphosphate (ADP) ratios (i.e. low ADP concentrations), UQR/UQT values were low, suggesting that adenylates restricted flux via the UQ‐reducing pathways more than they restricted flux via pathways that oxidized UQH2. To assess whether high rates of alternative oxidase (AOX) activity could have uncoupled respiratory flux (and thus UQR/UQT) from adenylate restriction of the cytochrome (Cyt) pathway, we constructed kinetic curves of O2 uptake (via the two pathways) vs UQR/UQT in isolated mitochondria, measured at two temperatures (15 and 25°C); measurements were made for mitochondria operating under state 3 (i.e. +ADP) and state 4 (i.e. −ADP) conditions. In contrast to the Cyt pathway, flux via the AOX was temperature insensitive, with maximal rates of AOX activity representing 21–57% of total O2 uptake in isolated mitochondria. We conclude that temperature‐dependent variations in UQR/UQT are largely dependent on temperature‐dependent changes in adenylate ratios, and that flux via the AOX could in some circumstances help reduce maximal UQ values.

Oxygen dynamics in the rhizosphere of Zostera marina: A two-dimensional planar optode study

The oxygen dynamics in the rhizosphere of Zostera marina was studied by use of planar optodes. Oxygen leakage to the rhizosphere was restricted to the root tip and extended only up to ~8 mm up along the root. The oxic sediment volume around the roots increased linearly with irradiance in the interval of 0–250 µmol photons m−2 s−1, but the leakage rate saturated at the maximum irradiance of 500 µmol photons m−2 s−1. Oxygen leakage decreased by ;60% from light to darkness and Z. marina was able to maintain an oxic zone around the root tip even in darkness as long as oxygen in the overlying water was at 100% air saturation (280 µmol L−1). O2 leakage from the root tips stopped at 25% air saturation (70 µmol L−1) and the oxic microniche rapidly disappeared. Increasing the oxygen concentration above 100% air saturation induced oxygen leakage from zones that otherwise appeared impermeable to oxygen. The roots on average grew by 8.7 mm d−1, and a series of O2 images documented the high spatial and temporal dynamics of the oxic microniches around the root tips. The estimated total oxygen release to the rhizosphere of Z. marina beds was 2.3 mmol m−2 d−1, which only corresponded to 12% of the diffusive oxygen uptake at the primary sediment-water interface. Rhizospheres of seagrass are thus probably of minor importance for total benthic O2 uptake rates.

Small‐scale spatial and temporal variability in coastal benthic O2 dynamics: Effects of fauna activity

In situ measurements in a shallow water sediment were performed using three different modules—a microprofiling unit, a transparent benthic chamber, and a planar optode periscope. The combined data set revealed an extremely patchy and variable benthic O2 distribution primarily due to temporal variations in fauna activity and photosynthesis. A distinct diel pattern in the fauna activity, dominated by Hediste diversicolor, resulted in strongly elevated O2 uptake rates of ~5.3 mmol m𠈒2 h𠈒1 at the onset of darkness. The activity gradually diminished during the night, and the O2 uptake decreased to less than half the maximum rate just before sunrise. The volume of oxic sediment around burrow structures was influenced by changing environmental conditions (benthic photosynthesis and fauna activity) but grossly exceeded that below the primary sediment surface. The volume specific respiration rate around burrows was more than seven times higher than the equivalent value at the sediment surface. A budget of the O2 consumption revealed that the O2 uptake through the burrow walls just after sunset accounted for the major part of the total O2 uptake on a diel scale. The study demonstrates that light‐driven variations in fauna activity can have great effects on the total benthic O2 consumption rate with large implications for estimated benthic mineralization rates.

Respiration and sequestering of organic carbon in shelf sediments of the oligotrophic northern Aegean Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 269:33-48 (2004) - doi:10.3354/meps269033 Respiration and sequestering of organic carbon in shelf sediments of the oligotrophic northern Aegean Sea H. Ståhl1, P. O. J. Hall1,*, A. Tengberg1, A. B. Josefson2, N. Streftaris3, A. Zenetos3, A. P. Karageorgis3 1Department of Chemistry, Marine Chemistry, Göteborg University, Kemivägen 10, 412 96 Göteborg, Sweden 2National Environmental Research Institute, PO Box 359, 4000 Roskilde, Denmark 3National Centre for Marine Research, PO Box 712, Mavro Lithari, Anavyssos, 19013 Attiki, Greece *Corresponding author. Email: perhall@chem.gu.se ABSTRACT: Respiration and sequestering of organic carbon was investigated in northern Aegean Sea sediments (NE Mediterranean). Benthic total carbonate (CT, also called …CO2 or dissolved inorganic carbon, DIC) fluxes and O2 uptake rates were measured in situ using a benthic lander. Dissolved organic carbon (DOC) fluxes were calculated from pore water gradients, taking into account the influence of biodiffusion/bioirrigation. Macrofaunal biomass was determined in the sediment collected by the chambers of the benthic lander. Chl a distributions were used as a tracer of high-quality sedimentary organic carbon. The measured benthic CT fluxes were positively correlated with the O2 uptake rates. The obtained average apparent respiration ratio (CT flux:O2 flux) of 0.90 ± 0.36 suggests a clear dominance of aerobic respiration in these organic carbon-poor shelf sediments. The CT efflux, the O2 uptake rate, and the DOC flux were significantly higher in spring than in fall at 2 of the stations. The Black Sea water, which enters the Aegean Sea in the study area, did not influence benthic respiration rates or organic carbon sequestering rates. A strong positive correlation between both the CT and O2 fluxes and the mean chl a concentration in surficial sediment suggests that benthic respiration, to a large extent, was controlled by the availability of labile phytodetrital organic matter. There was no influence of macrofaunal biomass (dry weight) on CT fluxes or oxygen uptake rates. The calculated benthic DOC fluxes made up 7.2 to 27% (average 14 ± 8.1%) of the CT fluxes, indicating that their contribution to the overall recycling of organic carbon in these sediments was important. The organic carbon burial efficiency ranged from 0.1 to 5.3%, but at Stn KA1 it was considerably higher (average 4%) than at the other stations (average 0.3%). Except for this station, the obtained burial efficiencies were very low compared to other sediments with similar accumulation rates. The average burial flux of organic carbon corresponded to less than 1% of the annual mean primary production (PP) for the Aegean Sea at Stn KA1, and to less than 0.1% of PP at the other stations. KEY WORDS: Northern Aegean Sea · Sediment · Organic carbon · Dissolved inorganic carbon · Dissolved organic carbon · Oxygen · Chlorophyll · Benthic lander Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 269. Online publication date: March 25, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

Effect of the brittle star Amphiura filiformis (Amphiuridae, Echinodermata) on oxygen flux into the sediment

O2 plays a key role in early sedimentary diagenetic processes, but the effect of most macrofaunal species on the pathways and rates of supply of O2 into the seabed are not well known. We investigated the effect of the ophiuroid Amphiura filiformis, one of the dominant macrobenthic species on soft bottoms in the northeast Atlantic, at depths of ~15–100 m, in a laboratory environment. We determined how the presence of the ophiuroid changed the total O2 uptake of macrofauna‐free sediment by combining measurements from a microcosm approach and an approach that uses microelectrodes and a flushed aquarium. We suggest that natural populations of A. filiformis can account for 80% of the total flux of O2 into the soft bottom. At least 67% of this portion is due to the diffusion of O2 across additional sediment‐water interfaces excavated by the brittle star.

Seasonal dynamics of benthic O2 uptake in a semienclosed bay: Importance of diffusion and faunal activity

The benthic O2 uptake and the O2 microdistribution in a coastal sediment of Aarhus Bay, Denmark, were investigated during a seasonal study. Measurements were performed in situ by a profiling lander and a flux chamber lander, as well as on recovered sediment cores. The O2 penetration depth, the diffusive O2 uptake, and the volumespecific O2 consumption rate strongly depended on the seasonal changes in bottom water O2 concentration and the sedimentation of organic carbon. The in situ O2 penetration depth varied between 0.5 mm in summer and 4.5 mm in winter. The diffusive O2 uptake varied between 8 and 30 mmol m−2 d−1, whereas the volume‐specific O2 consumption rate varied by a factor of 13. The O2 distribution was very sensitive to environmental controls, and microprofiles obtained in the laboratory tended to overestimate the in situ O2 penetration depths and underestimate the in situ diffusive O2 uptake. Three‐dimensional O2 flux calculations based on in situ microtopographic mapping showed that the actual diffusive exchange rate was ~10% higher than the simple one‐dimensional, microprofilederived diffusive O2 exchange. The total O2 uptake measured in the laboratory showed less distinct seasonal variation, but on the average, it was ~20% higher than the diffusive O2 uptake. The difference reflected the microtopography of the sediment surface and the contribution from benthic macrofauna. In situ total O2uptake was generally twice as high as laboratory rates, reflecting a higher fauna‐related O2 consumption in the larger enclosures incubated in situ. Annually, the in situ three‐dimensional diffusive O2 consumption was 6.2 mol O2 m−2, whereas the additional benthos‐mediated O2 uptake was 3.9 mol O2 m−2. Thus, 40% of the total O2 uptake was due to faunal activity and respiration. The present study demonstrates the importance of realistic faunal representation during sediment incubations in order to obtain correct benthic mineralization rates.

THE SLOW COMPONENT OF O2 UPTAKE KINETICS DURING HEAVY EXERCISE IN YOUNG AND OLDER MEN

Previous studies examining the effect of aging on O2 uptake kinetics have focused on the transition to light- or moderate-intensity exercise. Age-related differences in O2 uptake kinetics during heavy exercise (above anaerobic threshold) have yet to be examined. PURPOSE To examine the effect of aging on on-transient kinetics, and the relationship between muscle electromyography (EMG) activity and the slow component of O2 uptake kinetics during heavy exercise. METHODS Nine young (21.7±0.9 yr) and 9 older (71.6±0.8 yr) men performed a 7 min square-wave bout of exercise on a cycle ergometer at an intensity corresponding to 50% of the difference between the power output achieved at the anaerobic threshold and that attained at peak O2 uptake. Oxygen uptake and surface EMG activity of the right vastus lateralis muscle were measured during constant-load exercise. The O2 uptake data were fit with a 2-term exponential model to determine O2 uptake kinetics and the slow component. RESULTS The time constant (τ) of the primary component was significantly longer in the older (42±4 s) compared to the young (27±4 s) group. In contrast, the τ for the slow component was not different between the two groups, although the onset of the slow component occurred ∼ 60 s earlier in the young than in the older group. The absolute amplitude of the primary and slow components were greater in the young compared to older subjects. The slow component expressed relative to the total O2 uptake response was not different between the two groups (young: 24±2%; older: 20±3%). The mean power frequency (MPF) of the EMG increased significantly during the slow component phase of exercise by 6.4±1.0% in the young and by 5.4±0.7% in the older group. The increase in MPF was not significantly different between the two groups. CONCLUSION On-transient O2 uptake kinetics during heavy exercise are slowed, whereas the relative slow component is unaltered with increasing age. The EMG results are consistent with the hypothesis that the slow component of O2 uptake kinetics is caused in part by increased recruitment of fast-twitch muscle fibers.

Diffusion and advection within and around sinking, porous diatom aggregates

Fluid motion within and around sinking aggregates is an important factor in particle scavenging and solute exchange between sinking aggregates and the surrounding water and, hence, vertical fluxes and remineralization processes in the ocean. In the present study, we analyzed O2 uptake rates in &gt;2‐mm porous diatom aggregates and in model aggregates impermeable to flow by measuring, on the same aggregates, the interface diffusive uptake rates with microsensors and the total (diffusive + advective) O2 uptake rate by the Winkler method. The uptake rates were measured in a flow field similar to that experienced by sinking aggregates. The ratio of total O2 uptake rate to diffusive uptake rate was 0.97 ± 0.10 (n = 14) in model aggregates impermeable to flow. In contrast, total O2 uptake was similar to or higher than diffusive uptake rate calculated from the O2 gradients at the aggregate‐water interface in 85% of all field‐sampled and roller tank diatom aggregates examined. The highest ratio of total O2 uptake rate relative to diffusive uptake rate measured in &lt;1‐cm field‐sampled diatom aggregates was 3.91 ± 1.39 (n = 22). Hence, diffusive O2 uptake calculated from the O2 gradients in aggregates is a conservative (minimum) estimate of total O2 uptake. The estimated average fluid velocity through the cross‐sectional area of field‐sampled diatom aggregates, which could explain the measured differences in O2 uptake, ranged between 5 and 40 µm s-1. The average value was 16 µm s-1, which was equal to 1.3% of aggregate sinking velocity.

The effects of chamber size on benthic oxygen uptake measurements: A simulation study

Abstract A freely available simulation routine for estimating the inaccuracy of Total O2 Uptake rates (FTOU) measured by incubation chambers is presented. The software allows replicate incubations of any given chamber size at an user defined macrofauna inhabited sediment to be performed. The software is used to assess the number of replicate measurements required to obtain FTOU with a given accuracy for typical coastal environments. Results quantitatively demonstrate that large benthic chambers are to be preferred and that extrapolation form single or few incubations, especially with small chambers should be done with caution.

Organic matter degradation through oxygen respiration, denitrification, and manganese, iron, and sulfate reduction in marine sediments (the Kattegat and the Skagerrak)

Abstract A comprehensive study is reported on organic matter degradation through O2 respiration, denitrification and manganese- iron- and sulfate reduction in continental shelf sediments at 10 localities in the Kattegat and the Skagerrak (Denmark, Sweden and Norway). Total sediment community mineralization ranged from 4 to 31 mmol C m-2 d-1 with an average DIC:O2 ratio of 1.1. Most sediments exhibited an oxygen penetration depth of 0.33-0.6 cm except for a deeper-water (695 m) locality in the Skagerrak where O2 penetrated 1.9 cm into the sediment. The ratio of total O2 uptake measured by intact flux core incubation to diffusive O2 uptake rates measured with microelectrodes varied from -1 to 3.5 due to differences in benthic animal activity at the stations. Denitrification activity ranged from 0.01 to 1.03 mmol N m-2 d-1 and was primarily regulated by sediment nitrification activity. Manganese reduction was only significant at the deep-water locality in the Skagerrak. Iron reduction rates of 0 to 9.6 mmol C m-2 d-1 were found, and the activity was largely determined by the amount of poorly crystalline Fe(III) in the sediment. Sulfate reduction activity ranged from 0.1 to 9.6 mmol SO4 2- m-2 d-1at the stations investigated. A large heterogeneity was found between stations regarding the relative importance of the different carbon oxidation pathways. Within the Kattegat/Skagerrak region one may find sites where any one of the four carbon oxidation pathways, heterotrophic oxygen respiration, manganese reduction, iron reduction and sulfate reduction, is dominant. Thus, the present study demonstrates that even within short geographical distances a large variation in the relative importance of the different carbon oxidation pathways is to be expected in marine sediments.

Oxygen interaction with disordered and nanostructured Ag(001) surfaces

We investigated O2 adsorption on Ag(001) in the presence of defects induced by Ne+ sputtering at different crystal temperatures, corresponding to different surface morphologies recently identified by scanning tunneling microscopy. The gas-phase molecules were dosed with a supersonic molecular beam. The total sticking coefficient and the total uptake were measured with the retarded reflector method, while the adsorption products were characterized by high resolution electron energy loss spectroscopy. We find that, for the sputtered surfaces, both sticking probability and total O2 uptake decrease. Molecular adsorption takes place also for heavily damaged surfaces but, contrary to the flat surface case, dissociation occurs already at a crystal temperature, T, of 105 K. The internal vibrational frequency of the O2 admolecules indicates that two out of the three O2− moieties present on the flat Ag(001) surface are destabilized by the presence of defects. The dissociation probability depends on surface morphology and drops for sputtering temperatures larger than 350 K, i.e., when surface mobility prevails healing the defects. The latter, previously identified with kink sites, are saturated at large O2 doses. The vibrational frequency of the oxygen adatoms, produced by low temperature dissociation, indicates the formation of at least two different adatom moieties, which we tentatively assign to oxygen atoms at kinks and vacancies.