Biological Production Rates Research Articles

Dimethylsulfide production in Sargasso Sea eddies

Abstract Lagrangian time series of dimethylsulfide (DMS) concentrations from a cyclonic and an anticyclonic eddy in the Sargasso Sea were used in conjunction with measured DMS loss rates and a model of vertical mixing to estimate gross DMS production in the upper 60 m during summer 2004. Loss terms included biological consumption, photolysis, and ventilation to the atmosphere. The time- and depth (0–60 m)-averaged gross DMS production was estimated to be 0.73±0.09 nM d −1 in the cyclonic eddy and 0.90±0.15 nM d −1 in the anticyclonic eddy, with respective DMS replacement times of 5±1 and 6±1 d. The higher estimated rate of gross production and lower measured loss rate constants in the anticyclonic eddy were equally responsible for this eddy's 50% higher DMS inventory (0–60 m). When normalized to chlorophyll and total dimethylsulfoniopropionate (DMSP), estimated gross production in the anticyclonic eddy was about twice that in the cyclonic eddy, consistent with the greater fraction of phytoplankton that were DMSP producers in the anticyclonic eddy. Higher rates of gross production were estimated below the mixed layer, contributing to the subsurface DMS maximum found in both eddies. In both eddies, gas exchange, microbial consumption, and photolysis were roughly equal DMS loss terms in the surface mixed layer (0.2–0.4 nM d −1 ). Vertical mixing was a substantial source of DMS to the surface mixed layer in both eddies (0.2–0.3 nM d −1 ) owing to the relatively high DMS concentrations below the mixed layer. Estimated net biological DMS production rates (gross production minus microbial consumption) in the mixed layer were substantially lower (by almost a factor of 3) than those estimated in a previous study of the Sargasso Sea, which may explain the relatively low mixed-layer DMS concentrations found here during July 2004 (∼3 nM) compared to previous summers (∼4–6 nM).

New estimates of Southern Ocean biological production rates from O 2/Ar ratios and the triple isotope composition of O 2

We report O 2/Ar ratios (a constraint on net community production) and the triple isotopic composition of dissolved O 2 (a constraint on gross primary production) in samples collected from the surface mixed layer on 23 Southern Ocean transits. Samples were collected at 1–2° meridional resolution during the austral summer. Methodological limitations notwithstanding, the results constrain the net/gross production ratio, net O 2 production, and gross O 2 production at unprecedented resolution throughout the Southern Ocean mixed layer. Gross O 2 production rates inferred from the oxygen triple isotopes are greater than production rates calculated from a model based on remotely sensed chlorophyll. This result agrees with previous 18O and 14C incubations along 170°W. O 2/Ar ratios exceeding saturation are consistently observed within the Subantarctic and Polar Frontal Zones south of New Zealand and Australia, showing that a net autotrophic community predominates during austral summer. Lower O 2/Ar values are observed within the Drake Passage and Antarctic Zone, suggesting unresolved influences of low net community production, net heterotrophy, and upwelling of O 2-undersaturated waters. In autotrophic waters of the austral summer mixed layer, ratios of net community production/gross O 2 production scatter about 0.13, corresponding to f ratios of ∼0.25. Net community/gross O 2 production ratios show no meridional gradient across the Antarctic Circumpolar Current, suggesting that an approximately constant fraction of gross primary productivity is regenerated or exported. Our calculated net O 2 production rates are in satisfactory agreement with comparable published estimates. Net and gross O 2 production rates are highest in the Subantarctic and decline to the south, paralleling the well-known trend of chlorophyll a concentrations. In an analysis of variance of net O 2 production and gross O 2 production with other environmental variables, the strongest correlations are between net O 2 production and sea surface temperature (SST) (direct correlation), climatological [NO 3 −] (inverse correlation), and estimates of primary productivity derived from a remote sensing (direct correlation). These trends are as expected if aerosol iron input is the most important influence on production. They are unexpected if upwelling-derived SiO 2 and iron are the leading influence or if lower SSTs promote greater export in this region.

Depth-dependent fate of biologically-consumed dimethylsulfide in the Sargasso Sea

Biological consumption is a major sink for dimethylsulfide (DMS) in the surface ocean, but the fate of DMS is poorly known. We determined the fate of sulfur from biologically consumed DMS in samples from the upper 60 m of the Sargasso Sea during July 2004. Using tracer levels of 35S-DMS in dark incubations we found that DMS was transformed into three identifiable non-volatile, sulfur-containing product pools: dimethylsulfoxide (DMSO), sulfate, and particle-associated macromolecules. Together, DMSO and sulfate accounted for most (81–93%) of the non-volatile sulfur products. Only a small fraction (∼ 2%) of the consumed DMS-sulfur was recovered in cellular macromolecules, leaving 5–17% of the metabolic products of DMS consumption unidentified. The relative importance of the two major products varied with depth. DMSO was the main sulfur product (∼ 72%) from DMS metabolism in the surface mixed layer, whereas sulfate was the most important product (∼ 74%) below the mixed layer. Changes in temperature and photosynthetically-active radiation (PAR) did not cause shifts in DMS fate in short term incubations (7–12 h), however these or other factors (e.g., exposure to ultraviolet radiation), operating over longer time scales, could potentially influence the observed pattern of DMS fate with depth. Biological DMSO production rates ranged from 0.07 to 0.33 nM day − 1 , with the highest rate found at 30 m, just below the surface mixed layer. With DMSO concentrations ranging from 4.0 to 8.6 nM, turnover times for DMSO were long (15–61 days) when only the biological production from DMS was considered. Identification of the main sulfur containing products from DMS metabolism improves understanding of this important process in the marine sulfur cycling. Detection and quantification of DMSO production from biological DMS consumption also provides a more complete picture of DMSO biogeochemistry in the ocean.

Ocean warming and freshening in the northern Gulf of Alaska

Water column temperatures on the shelf in the northern Gulf of Alaska have increased more than 0.8°C and vertical density stratification has increased since 1970 near Seward, Alaska throughout the 250 m depth. This high latitude marine system has low water temperatures, high rates of precipitation, glacial melting, high wind speeds and high rates of biological productivity. A more than 300 km alongshore shift (locally westward) of isotherms is suggested. The observations are consistent with a conceptual ocean‐atmosphere circulation model that employs coastal freshwater discharge, glacial ablation and wind forcing. Positive regional feedback mechanisms accelerate the discharge and poleward heat flux, leading to even higher temperatures, increased ocean stratification and increased storminess. This warming and ocean freshening will have significant impacts on the atmosphere and marine ecosystems of the Northeast Pacific, Bering Sea, Arctic Ocean and quite possibly global ocean circulation.

Triple oxygen isotope composition of dissolved O2 in the equatorial Pacific: A tracer of mixing, production, and respiration

As a contribution to the study of equatorial Pacific biogeochemistry, we measured the O2/Ar ratio and the triple isotope composition (18O, 17O, and 16O) of O2 along six meridional lines in the equatorial Pacific (8°N–8°S at 95°W, 110°W, 125°W, 140°W, 155°W, and 170°W). O2/Ar ratios and δ18O were close to equilibrium values within the mixed layer and followed the general trend of increasing δ18O with decreasing O2/Ar at greater depths. The 17Δ (≈δ17O–0.5δ18O) constrains the fraction of photosynthetic O2; 17Δ was slightly elevated with respect to equilibrium within the mixed layer due to local photosynthetic production. In aphotic zone waters above 250 m depth the average 17Δ values were higher than in the mixed layer. There are four sources of this photosynthetic signal in the dark ocean: production in the euphotic zone prior to subduction in the distant source regions, production below the mixed layer during travel to the equatorial zone, diapycnal mixing with shallower waters bearing photosynthetic O2, and accumulation of photosynthetic O2 produced at very low rates below the 1% light level. Our results also constrain biological production rates within the mixed layer at several locations along 95°W and 110°W. Our average rate of 14C production (53 ± 34 mmol C m−2 d−1) agreed well with other estimates in the equatorial Pacific, while our average rate of net C production (6.9 ± 6.2 mmol C m−2 d−1) and f ratio (0.12 ± 0.11) were somewhat lower than other estimates. Adding δ18O and 17Δ as tracers to three‐dimensional biogeochemical ocean GCMs and comparing results with observations will extend our understanding of metabolic rates in the study region.

Roles of Biogeochemical Processes in the Oceanic Carbon Cycle Described with a Simple Coupled Physical-Biogeochemical Model

To evaluate the contribution of biogeochemical processes to the oceanic carbon cycle and to calculate the ratio of calcium carbonate to organic carbon downward export, we have incorporated biological and alkalinity pumps in the yoked high-latitude exchange/interior diffusion-advection (YOLDA) model. The biogeochemical processes are represented by four parameters. The values of the parameters are tuned so that the model can reproduce the observed phosphate and alkalinity distributions in each oceanic region. The sensitivity of the model to the biogeochemical parameters shows that biological production rates in the euphotic zone and decomposition depths of particulate matters significantly influence horizontal and vertical distributions of biogeochemical substances. The modeled vertical fluxes of particulate organic phosphorus and calcium carbonate are converted to vertical carbon fluxes by the biological pump and the alkalinity pump, respectively. The downward carbon flux from the surface layer to the deep layer in the entire region is estimated to be 3.36 PgC/yr, which consists of 2.93 PgC/yr from the biological pump and 0.43 PgC/yr from the alkalinity pump, which is consistent with previous studies. The modeled rain ratio is higher with depth and higher in the Pacific and Indian Oceans than in the Atlantic Ocean. The global rain ratio at the surface layer is calculated to be 0.14 to 0.15. This value lies between the lower and higher ends of the previous estimates, which range widely from 0.05 to 0.25. This study indicates that the rain ratio is unlikely to be higher than 0.15, at least in the surface waters.

Carbon cycle feedbacks and the initiation of Antarctic glaciation in the earliest Oligocene

The initiation of Antarctic glaciation in the early Oligocene (∼34 Ma) is represented by a distinct positive anomaly in the marine δ 18O record designated Oi-1 and accompanied by positive excursions in the mean δ 13C of oceanic dissolved inorganic carbon and biogenic sediment accumulation rates. Within 400 ky of the onset of Oi-1, the climate system settled into a more moderate but stable “glacial” state. Here, through modeling, we investigate two of the principal biogeochemical processes involved in this response: silicate weathering and marine organic carbon cycling. We initiate the event with a rapid drawdown in atmospheric CO 2 resulting from increased weatherability of the continents associated with Himalayan orogeny. This perturbation triggers the overshoot and adjustment of the δ 18O record because of feedback among ice-sheet coverage, silicate weathering rates, and atmospheric CO 2. The system is a damped oscillator, the strength of which depends on the sensitivity of chemical weathering rates to climate change and climate to changes in atmospheric CO 2. Increased oceanic mixing associated with initial transition into a glacial world accelerates the rates of biological productivity and carbon burial, lowering atmospheric CO 2 and accelerating global cooling and ice-sheet growth, and generating a carbon isotope response that crudely approximates that observed. The Oi-1 overshoot appears to require a rapid (<1 million year) application of the forcing (e.g., tectonic drawdown of atmospheric CO 2). Although further investigation and more sophisticated models ultimately may show that other triggers and feedbacks prevailed during Oi-1, the modeling presented here demonstrates that simple feedbacks in the climate system can explain the overshoot and adjustment response to early Oligocene climate forcing.

Physical modelling of the composting environment: A review. Part 1: Reactor systems

In this paper, laboratory- and pilot-scale reactors used for investigation of the composting process are described and their characteristics and application reviewed. Reactor types were categorised by the present authors as fixed-temperature, self-heating, controlled temperature difference and controlled heat flux, depending upon the means of management of heat flux through vessel walls. The review indicated that fixed-temperature reactors have significant applications in studying reaction rates and other phenomena, but may self-heat to higher temperatures during the process. Self-heating laboratory-scale reactors, although inexpensive and uncomplicated, were shown to typically suffer from disproportionately large losses through the walls, even with substantial insulation present. At pilot scale, however, even moderately insulated self-heating reactors are able to reproduce wall losses similar to those reported for full-scale systems, and a simple technique for estimation of insulation requirements for self-heating reactors is presented. In contrast, controlled temperature difference and controlled heat flux laboratory reactors can provide spatial temperature differentials similar to those in full-scale systems, and can simulate full-scale wall losses. Surface area to volume ratios, a significant factor in terms of heat loss through vessel walls, were estimated by the present authors at 5.0–88.0 m 2/m 3 for experimental composting reactors and 0.4–3.8 m 2/m 3 for full-scale systems. Non-thermodynamic factors such as compression, sidewall airflow effects, channelling and mixing may affect simulation performance and are discussed. Further work to investigate wall effects in composting reactors, to obtain more data on horizontal temperature profiles and rates of biological heat production, to incorporate compressive effects into experimental reactors and to investigate experimental systems employing natural ventilation is suggested.

Marine microorganisms and global nutrient cycles

The way that nutrients cycle through atmospheric, terrestrial, oceanic and associated biotic reservoirs can constrain rates of biological production and help structure ecosystems on land and in the sea. On a global scale, cycling of nutrients also affects the concentration of atmospheric carbon dioxide. Because of their capacity for rapid growth, marine microorganisms are a major component of global nutrient cycles. Understanding what controls their distributions and their diverse suite of nutrient transformations is a major challenge facing contemporary biological oceanographers. What is emerging is an appreciation of the previously unknown degree of complexity within the marine microbial community.

The biogeochemistry of inorganic carbon and nutrients in the Pearl River estuary and the adjacent Northern South China Sea

The Zhu-jiang (Pearl River) estuary and its adjacent continental shelf in the Northern South China Sea (SCS) is unique in that its drainage basin is located entirely in a subtropical zone with heavy population development, and therefore represents an important regime for biogeochemical studies on how large rivers influence continental shelves. The near-zero salinity end member has high nutrient concentrations (silicate 130–140 μM, nitrate 75–100 μM and phosphate 0.2–1.2 μM) and relatively high total dissolved inorganic carbon (DIC) (1500 μM) and alkalinity (∼1650 μM) values. Water column DIC, alkalinity, and nutrient in the estuary are largely controlled by mixing of waters from different tributaries with different drainage basin chemistry, anthropogenic influence, and degree of estuarine recycling. Biological uptake of nutrients and inorganic carbon occur in the outer estuary and inner shelf areas supported by riverine nutrients. The N/P and Si/P ratios are generally very high within the estuary. The summertime area-integrated biological production rate of 0.8 gC m −2 d −1 is estimated based on the depletion of DIC and alkalinity relative to the conservative mixing line and a plume travel time. This estimate agrees reasonably well with 14C based primary production rates (PP) and with that from effective river phosphate flux. Biological production decreases about 10-fold in the open continental shelf and slope and is largely supported by mixing with subsurface water. A comparison of DIC, phosphate, and nitrate concentrations in the surface mixing layer and at the bottom of the euphotic zone with the 14C-based PP (0.13 gC m −2 d −1) suggests that the surface water residence time in the Northern SCS is ∼1.3 years. The N/P, Si/P, and Si/C ratios are 15, 25, and 0.15, respectively. The subtropical Pearl River study is also compared to other large rivers with regard to differences in both natural processes (i.e., weathering rates) and anthropogenic influences (i.e., nutrient input) between these different river–estuary systems.

Biotic contribution to air‐sea fluxes of CO2 and O2 and its relation to new production, export production, and net community production

The contribution of the marine biota to air‐sea fluxes of CO2 and O2 is often described in terms of biological production concepts, such as new production, export production, and net community production. We evaluate these three quantities using a basin‐scale ecosystem‐circulation model of the North Atlantic Ocean based on Redfield stoichiometry into which we introduce an artificial tracer which records the biotic contribution to air‐sea exchange of gases like O2 and CO2. It is found that on average the biological production rates overestimate the biotically effected air‐sea flux by some 20% and, in some regions, even predict the wrong direction. With primary production restricted to the euphotic zone, but respiration extending to farther below, the discrepancy can largely be attributed to the different integration depths used in the different concepts (euphotic zone, surface mixed layer), and on annual and longer timescales, all rates converge when using the base of the winter mixed layer rather than that of the euphotic zone as the reference depth. For the surface carbon budget, which ultimately controls air‐sea exchange of CO2, it is irrelevant whether carbon atoms cross this boundary in organic or inorganic speciation. Hence the transports of biotically generated surpluses or deficits of dissolved inorganic matter must also be accounted for. While their contribution amounts to only a few percent on the basin scale, the subduction of newly remineralized inorganic matter can locally account for about half of the biotically effected air‐sea flux, for example, in regions of mode‐water formation.

The methane production of poultry slaughtering residues and effects of pre‐treatments on the methane production of poultry feather

The biological methane production rate and yield of different poultry slaughtering residues were studied. Poultry offal, blood, and bonemeal were rich in proteins and lipids and showed high methane yields, 0.7–0.9, 0.5, and 0.6–0.7 m3 kg‐1 volatile solidsadded, respectively (270–340, 100, and 150–170 m3 ton‐1 wet weight). Blood and bonemeal produced methane rapidly, whereas the methane production of offal was more delayed probably due to long‐chain fatty acid inhibition. The length of delay depended on the source and concentration of inoculum and incubation temperature, sewage sludge at 35 °C having the shortest delay of a few days, while granular sludge did not produce methane within 94 days of incubation. Feather showed a somewhat lower methane yield, 0.21 m3 kg‐1 volatile solidsadded (50 m3 ton‐1 wet weight). Combined thermal (120 °C, 5 min) and enzymatic (commercial alkaline endopeptidase, 2–10 g 1‐1) pre‐treatments increased its methane yield by 37 to 51%. Thermal (70–120 °C, 5–60 min), chemical (NaOH 2–10 g 1‐1, 2–24 h), and enzymatic pre‐treatments were less effective, with methane yield increasing by 5 to 32%. Based on the present results, anaerobic digestion of the studied poultry slaughtering residues appears a promising possibility because of the high methane yield and nitrogen content of these residues (8 to 14% N of total solids), whereas pre‐treatments were shown to improve the methane production of feather.

Adapting stream corridor restoration technology to training land rehabilitation and maintenance

The United States has more than 3.5 million miles of rivers and streams that, along with closely associated floodplain and upland areas, comprise corridors of great economic, social, cultural, and environmental value. These corridors support higher rates of biological productivity than almost any other landscape feature. They also contribute significantly to each military installation's unique character. Interest in restoring stream corridor ecosystems is expanding rapidly in the United States. With this in mind, 15 federal agencies formed the Federal Interagency Stream Restoration Working Group in 1995 to seek consensus on the fundamentals of modern approaches to stream restoration and to promote awareness and use of these methods throughout the nation. This unprecedented collaboration produced a comprehensive publication, entitled Stream Corridor Restoration: Principles, Processes, and Practices, which has begun to serve as a foundation of stream corridor restoration knowledge and practice nationwide. Attention to these aquatic and terrestrial ecosystems is a common theme of both Integrated Training Area Management (ITAM) program and stream corridor restoration. ITAM is the Army's strategy for focusing on sustained use of training and testing lands. Cross-program innovation and field-tested stream restoration methods can combine to provide greater sustainability for Department of Defense maneuver areas and ranges over both the short and long term.

Short‐term variability in the open ocean cycle of dimethylsulfide

The marine biogeochemical cycle of dimethylsulfide (DMS), the main natural source of sulfur to the global atmosphere, was studied during a 2‐week Lagrangian experiment in the subpolar North Atlantic, at 60°N 21°W. A bloom of coccolithopores, mostly of the species Emiliania huxleyi, dominated the phytoplankton assemblage over the first week. High surface concentrations of dimethylsulfoniopropionate (DMSP, 37–70 nM) were found along with moderate DMS concentrations (3–9 nM) during the entire experiment. Rates of biological DMSP consumption (8–51 nM d−1) and DMS production (1–14 nM d−1) and consumption (0–6 nM d−1) were measured in short‐term dark incubations of surface seawater. Rates of DMSP biosynthesis (11–31 nM d−1) and DMS photochemical loss (1–10 nM d−1) were estimated by budgeting concentrations and transformation rates between Lagrangian samplings. Air‐sea exchange rates for DMS (0.03–3 nM d−1) were calculated from surface concentrations, seawater temperature, and wind speed. All major processes involved in the DMS cycle showed significant short‐term variability in coupling to the variability of solar radiation, wind speed, and mixing. Biotic and abiotic DMS turnover rates were of similar magnitude and very dynamic, with a prompt response to a rapidly changing physical environment. The rapid impact of meteorological forcing factors on DMS cycling provides the basis for a sulfur‐mediated, short‐term plankton/climate interaction.

A global three‐dimensional atmosphere‐ocean model of methyl bromide distributions

A three‐dimensional ocean‐atmosphere model of the global methyl bromide budget is presented including an analysis of the temporally and spatially varying source and sink distributions. No correlation is found between oceanic net biological CH3Br production, implied by surface water saturation anomaly observations, and oceanic variables such as surface chlorophyll and primary production; therefore model ocean fluxes are constrained directly by the saturation anomaly observations. The resulting diagnosed biological production rates imply net production in the tropics and subtropics and net consumption at high latitudes. Results from this semicoupled ocean‐atmosphere model show substantial longitudinal variability in the atmospheric boundary layer CH3Br concentrations with land‐ocean contrasts of 1–6 ppt due to regional industrial and agricultural emissions on land and net fluxes into the ocean. Owing to an imbalance in current understanding of the global budget, our simulated mixing ratios of 3.5 to 6.5 ppt for the southern and northern hemispheres, respectively, are significantly lower than available measurements. Sensitivity studies reducing the ocean and soil surface sinks slightly improve the global mean CH3Br concentration but increase the interhemispheric ratio further beyond that supported by observations. Accordingly, an apparent terrestrial missing source of 89–104 kT yr−l is derived and applied to the model. This is of the same order as the sum of all other sources in the model (85 kT yr−1). The hemispheric distribution of the missing source is explored, indicating that 50–70% of this source occurs in the southern hemisphere and is likely to be biased toward tropical regions. Modeled seasonal variability in the interhemispheric ratio at specific monitoring sites agrees well with observations. The model‐predicted vertical gradient of CH3Br through the troposphere and lower stratosphere is also presented.

Influence of Water Content on Degradation Rates for Ethanol in Biofiltration

ABSTRACT Treatment of ethanol vapor in a peat biofilter with various initial water contents (70%, 59%, 49%, and 35%) was studied. For water contents ranging from 49% to 70%, elimination capacity was about 30 g/m3/h. For a water content of 35%, elimination capacity decreased to 4 g/m3/h. A low mean CO2 yield coefficient (0.35 g CO2 produced per g ethanol consumed) was found for all of the initial water contents. The value was only 20% of the yield coefficient (1.91 g/g) predicted by stoichiometry. When the packing material was dried from 70% to 59% water content during the biofiltration process, elimination capacity dropped from 27 g/m3/h to 4 g/m3/h. After 24 hours of drying, the biofiltration experiment was restarted and run for two more weeks. During this period, the biofilter did not recover. At 59% water content, the rate of water evaporation was estimated at 59.6 g/m3/h. A simplified mass balance permitted calculation of the biological water production rate, approximately 22.1 g/m3/h.

Chemical tracers of productivity and respiration in the subtropical Pacific Ocean

We determine annual rates of net biological oxygen production in the euphotic zone and respiration in the upper thermocline of the subtropical North Pacific ocean using mass balances of oxygen, argon, and nitrogen measured at the U.S. Joint Global Ocean Flux Study time series station ALOHA. Net evasion of nitrogen and argon to the atmosphere caused by warming of surface waters is balanced by supply primarily from cross‐isopycnal transport. Mixing rates between the euphotic zone and the top of the permanent thermocline required to balance the inert gas flux are 1–2 cm2 s−1 when transformed to units of an eddy diffusion coefficient. Application of mixing rates derived from the inert gas mass balance to the oxygen field yields a net annual euphotic zone production rate of 1.4±1.0 moles O2 m−2 yr−1, one half of which is lost to the atmosphere, with most of the rest mixed into the top of the thermocline. Since cross‐isopycnal gradients of dissolved organic carbon (DOC) are about half to those of oxygen, we estimate that at least one quarter of the carbon flux out of the euphotic zone is via DOC. Because surface ocean dissolved organic matter has a relatively high C/N ratio, the stoichiometry among O2, C, and inorganic N in the upper ocean should be different than that observed in deeper waters.

Impact of carbon dioxide evolution on the calorimetric monitoring of fermentations

Abstract During fermentation, carbon dioxide formation usually takes place. The absorption of carbon dioxide in water is an exothermic reaction; its release from the medium is endothermic. These effects were first analysed in a fermenter-calorimeter using model media and then monitored during anaerobic batch and continuous cultivation of Zymomonas mobilis cells. The heat effects proved to be functions of the carbon dioxide partial pressure, the pH value of the medium, the gas flow rate through the liquid, and the pump rate of the medium through the fermenter (continuous culture). The heat of biological growth is usually diminished by carbon dioxide desorption. The maximum error introduced in the on-line measurement was calculated to be 48% for anaerobic conditions; the average measured was 35%. The worst case calculated for aerobic conditions was 4%. In the case of a pH-controlled fermentation, the neutralization heat from alkaline feeding contributes to the total heat production measured. When the carbon dioxide partial pressure was maintained constant and the volume of the exhaust gas produced and the alkaline consumption were known, monitoring of the small biological heat production rates under anaerobic conditions was possible with reasonable accuracy.

Occurrence and transformation of dissolved dimethyl sulfur species in stratified seawater (western Mediterranean Sea)

Dimethyl sulfide (DMS), dissolved dimethylsulfoniopropionate (DMSPd) and dimethylsulfoxide (DMSO) were measured in Mediterranean seawater. In the open surface waters of late spring to early summer, DMSO (18 nM) was the main methylated sulfur compound and dominated over DMS (1.7 nM) by 1 order of magnitude. Conversely, DMSPd occurred at lower concentrations (0.55 nM) than DMS. The higher abundance of DMS over DMSPd, the poor correlation between surface DMS and chlorophyll a, and microscopic examination of the algal populations suggest that DMS essentially originated from decompos~tion of the DMSP, generated in a late decay phase of the spring phytoplankton development. On the other hand, the vertical profile of the dissolved dimethyl sulfur species and the depth distribution of both biological DMS production and consumption rates point to the concurrence of the biogenic cycles of DMS and carbon. Thus, highest DMS production occurs near the subsurface chlorophyll maximum in coincidence with the water column layers of highest microbial heterotrophic activity. Finally, the high DMSO concentrations suggest that this species may act as a major nonvolatile dimethyl sulfur pool in these waters.

Determination of inorganic and organic traces in the clean room compartment of Antarctica

The concentration of most elements and of their species as well as of organic compounds in Antarctica is in an extremely low range, normally at the pg g −1 and pptv level or even below. Sensitive and reliable analytical methods must therefore be applied to determine these substances in this remote area. Differential pulse anodic stripping voltammetry, ion chromatography, and gas chromatography with electron capture detection can be used directly in Antarctica under strict contamination control for the determination of some heavy metals, anions, and volatile halogenated hydrocarbons, respectively. Isotope dilution mass spectrometry can be applied in the home laboratory for the calibration and completion of this data. The concentration of most of the heavy metals in Antarctica snow and ice lies in the low pg g −1 range and below. Evidently higher concentrations were only found in hoar-frost samples. It could be shown that even at such a low concentration level lead is partially of anthropogenic, chromium only of terrestial origin. First indications have been obtained that cadmium is possibly influenced by biologica processes in the polar sea. The nitrate content of precipitation in Antarctica agrees with the natural background level of 200–230 ng g −1 found in remote areas of the North and South Atlantic. HNO 3 is the most dominant nitrate form in the Antarctic atmosphere and can be re-emitted from snow on the surface after its deposition. A natural cycle of nitrate in Antarctica is presented. High enrichment factors for iodine in relation to the chloride concentration have been observed in Antarctic snow compared with the seawater composition. In the Antarctic atmosphere, iodine is preferably associated with the smallest aerosol particles in contrast to chloride which shows the highest concentration in the larger sea salt particles. From this it follows that different types of substances must be responsible for this enrichment effect. HI 2, I 2, HOI, and organoiodine have been identified as volatile iodine species in the atmosphere. Biogenically produced methyl iodide is the most abundant organoiodine compound and, after photodissociation, can act as a natural iodine conaminant in the interior of Antarctica. From these results a natural cycle could also be established for iodine. However, the most dominant biogenic halogenated methane in Antarctica is bromoform with average concentrations of about 6 ng 1 −1 in the polar surface seawater and 6 pptv in the atmosphere measured during the Antarctic spring. CHBr 3 correlates well in its seawater concentration with those of other brominated methanes, e.g. CH 2Br 2 and CHBrCl 2. Under high biological production rates these halogenated methanes can possibly contribute to the greenhouse effect and they will also influence, at least, the tropospheric ozone.