An Easy-to-Construct Automated Winkler Titration System

The instrument described in this report is an updated version of the high precision, automated Winkler titration system described by Friederich et al.(1984). The original instrument was based on the work of Bryan et al. (1976) who developed a colorimetric endpoint detector and on the work of Williams and Jenkinson (1982) who produced an automated system that used this detector. The goals of our updated version of the device described by Friederich et al. (1984) were as follows: 1) Move control of the system to the MS-DOS environment because HP-85 computers are no longer in production and because more user-friendly programs could be written using the IBM XT or AT computers that control the new device. 2) Use more "off the shelf" components and reduce the parts count in the new system so that it could be easily constructed and maintained. This report describes how to construct and use the new automated Winkler titration device. It also includes information on the chemistry of the Winkler titration, and detailed instructions on how to prepare reagents, collect samples, standardize and perform the titrations (Appendix I: Codispoti, L.A. 1991 On the determination of dissolved oxygen in sea water, 15pp.). A disk containing the program needed to operate the new device is also included. (pdf contains 33 pages

New Constraints on Methane Fluxes and Rates of Anaerobic Methane Oxidation in a Gulf of Mexico Brine Pool via In Situ Mass Spectrometry

Deep-sea biogeochemical cycles are, in general, poorly understood owing to the difficulties of making measurements in situ, recovering samples with minimal perturbation, and, in many cases, coping with high spatial and temporal heterogeneity. In particular, biogeochemical fluxes of volatiles such as methane remain largely unconstrained because of the difficulties with accurate quantification in situ and the patchiness of point sources such as seeps and brine pools. To better constrain biogeochemical fluxes and cycling, we have developed a deep-sea in situ mass spectrometer (ISMS) to enable high-resolution quantification of volatiles in situ. Here we report direct measurements of methane concentrations made in a Gulf of Mexico brine pool located at a depth of over 2300 m. Concentrations of up to 33 mM methane were observed within the brine pool, whereas concentrations in the water directly above were three orders of magnitude lower. These direct measurements enabled us to make the first accurate estimates of the diffusive flux from a brine pool, calculated to be $1.1\pm0.2 mol m^{-2} yr^{-1}$. Integrated rate measurements of aerobic methane oxidation in the water column overlying the brine pool were $~320 \mu mol m^{-2} yr^{-1}$, accounting at most for just 0.03% of the diffusive methane flux from the brine pool. Calculated rates of anaerobic methane oxidation were $600-1200 \mu M yr^{-1}$, one to two orders of magnitude higher than previously published values of AOM in anoxic fluids. These findings suggest that brine pools are enormous point sources of methane in the deep sea, and may, in aggregate, have a pronounced impact on the global marine methane cycle.Organismic and Evolutionary Biolog

Enhanced lifetime of methane bubble streams within the deep ocean

We have made direct comparisons of the dissolution and rise rates of methane and argon bubbles experimentally released in the ocean at depths from 440 to 830 m. The bubbles were injected from the ROV Ventana into a box open at the top and the bottom, and imaged by HDTV while in free motion. The vehicle was piloted upwards at the rise rate of the bubbles. Methane and argon show closely similar behavior at depths above the methane hydrate stability field. Below that boundary (∼520 m) markedly enhanced methane bubble lifetimes are observed, and are attributed to the formation of a hydrate skin. This effect greatly increases the ease with which methane gas released at depth, either by natural or industrial events, can penetrate the shallow ocean layers

Changing concentrations of CO, CH₄, C₅H₈, CH₃Br, CH₃I, and dimethyl sulfide during the Southern Ocean Iron Enrichment Experiments

Oceanic iron (Fe) fertilization experiments have advanced the understanding of how Fe regulates biological productivity and air–sea carbon dioxide (CO₂) exchange. However, little is known about the production and consumption of halocarbons and other gases as a result of Fe addition. Besides metabolizing inorganic carbon, marine microorganisms produce and consume many other trace gases. Several of these gases, which individually impact global climate, stratospheric ozone concentration, or local photochemistry, have not been previously quantified during an Fe-enrichment experiment. We describe results for selected dissolved trace gases including methane (CH₄), isoprene (C₅H₈), methyl bromide (CH₃Br), dimethyl sulfide, and oxygen (O₂), which increased subsequent to Fe fertilization, and the associated decreases in concentrations of carbon monoxide (CO), methyl iodide (CH₃I), and CO₂ observed during the Southern Ocean Iron Enrichment Experiments

Spatial and temporal variability in the chemical properties of the oxic and suboxic layers of the Black Sea

The Black Sea, a land-locked deep basin with sulfide bearing waters below 150-200 m, has been subject to anthropogenic pressures since the 1970s. Large inputs of nutrients (nitrate - N, phosphate - P, silicate - Si) with high N/P but low Si/N ratios and subsequent development of intensive eutrophication over the basin have changed vertical distributions and inventories of nutrients and redox-sensitive metals in the oxic, suboxic and anoxic layers. Chemical data sets obtained between 1988 and 2010, and older data from before 1970 were evaluated to assess spatial/temporal variations of the dissolved oxygen (O-2), nutrients and dissolved/particulate manganese (Mn-d, Mn-p) in the water column from the lower salinity, oxygenated surface waters through the SubOxic Layer (SOL; O-2 50). The surface waters over the basin were rich in silicate (25-70 mu M), but poor in nitrate (500) but very low N/P (<1.0) ratios. After the mid 1970s, construction of dams, especially on the Danube River, resulted in lower Si concentrations. At this time the increased loads of anthropogenic nitrate and phosphate by the major rivers resulted in lower Si/N, but still high N/P molar ratios, which enhanced eutrophication (production of particulate organic matter, POM) drastically in the coastal waters. This led to reductions in the surface Si/N ratio by up to 500-fold in the western basin while the N/P ratio increased. The enhanced POM export increased the nitrate inventory and thus N/P ratios of the NW shelf waters spreading over the whole basin. The increased export of POM decreased the Si inventory of the upper layer down to the boundary of sulfidic waters. This export also increased O-2 consumption and removal of nitrate to N-2 form by denitrification in the oxic/suboxic interface, leading to seasonal/decadal changes in the boundaries of the nitracline and main oxycline and changes in the slopes of the nitrate-phosphate and Apparent Oxygen Utilization (AOU)-nitrate regressions in the steep oxycline down to the SOL. These slopes are much smaller than those observed in the lower layer of Marmara Sea fed by the Black Sea outflow. The enlargement of SOL by similar to 15-20 m after the 1970s modified the vertical features of nitrate, phosphate and manganese (Mn-d, Mn-p) species in the redox gradient zone

Surface seawater distributions of inorganic carbon and nutrients around the Galapagos Islands: results from the PlumEx experiment using automated chemical mapping

During the second leg (PlumEx) of the 1993 IRONEX cruise, the partial pressure of CO 2 and the concentrations of nitrate and silicate in the surface waters around the Galapágos Islands were continuously measured using automated underway systems. Based on salinity-versus-constituent mixing diagrams, physical mixing processes dominate the pCO 2 and nutrient distributions upstream of the Galápagos Islands. Downstream of the islands, slight removal of nitrate and CO 2 can be discerned because of the high resolution of the underway measurements. The high spatial resolution of the underway measurements allowed evaluation of fine features such as sharp fluorescence peaks on the “warm” side of frontal boundaries. In the waters immediately adjacent to Fernandina and Isabela islands (Bolivar channel), dramatic drawdown of pCO 2 and nutrients was measured, coincident with the highest measured levels of iron (3 nM) and chlorophyll (>13 μg l -1) (Martin et al., 1994). The nearly constant alkalinity of the waters was combined with the measured pCO 2 to calculate total carbon dioxide in the waters. Based on mixing diagrams, the ratio of ΔTCO 2 to ΔNO - 3 was found to be highly variable, ranging from approximately 6.4 to >10 in the waters near Isabela Island. The ratio of ΔTCO 2 to ΔNO - 3 is approximately 8.5 in the waters west of the Galápagos where slight removal of nitrate and TCO 2 occurs. In these waters, the physical process of mixing and CO 2 degassing due to warming of the water becomes significant relative to the biological uptake and the ratio is driven higher

A carbon budget for the northern and central California coastal upwelling system

Poster.-- ASLO summer meeting, Santiago de Compostela, 19-24 July 2005N

The Northern and Central California Coastal Upwelling System

16 pagesOver the past 150 years, carbon dioxide (CO2) has accumulated in the atmosphere and the partial pressure of CO2 (pCO2) has increased from approximately 280 to 370 ppm primarily due to the burning of fossil fuels, currently at a rate of about 6.5Gt carbon yr−1 (see overview in Miller 2004). Because CO2 absorbs infrared radiation, increased atmospheric CO2 decreases radiative heat loss to space – the ‘Greenhouse effect’ – leading to the prediction that human activity is warming the earth’s climate. While data confirm that climate is warming, many associated rates, patterns, and interactions remain poorly understood. These uncertainties have prompted considerable study of carbon cycles, of which this article and book are partN