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

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

Climatological mean and decadal change in surface ocean pCO2, and net sea-air CO2 flux over the global oceans

A climatological mean distribution for the surface water pCO2 over the global oceans in non-El Niño conditions has been constructed with spatial resolution of 4° (latitude) ×5° (longitude) for a reference year 2000 based upon about 3 million measurements of surface water pCO2 obtained from 1970 to 2007. The database used for this study is about 3 times larger than the 0.94 million used for our earlier paper [Takahashi et al., 2002. Global sea-air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects. Deep-Sea Res. II, 49, 1601-1622]. A time-trend analysis using deseasonalized surface water pCO2 data in portions of the North Atlantic, North and South Pacific and Southern Oceans (which cover about 27% of the global ocean areas) indicates that the surface water pCO2 over these oceanic areas has increased on average at a mean rate of 1.5 µatm y-1 with basin-specific rates varying between 1.2±0.5 and 2.1±0.4 µatm y-1. A global ocean database for a single reference year 2000 is assembled using this mean rate for correcting observations made in different years to the reference year. The observations made during El Niño periods in the equatorial Pacific and those made in coastal zones are excluded from the database. Seasonal changes in the surface water pCO2 and the sea-air pCO2 difference over four climatic zones in the Atlantic, Pacific, Indian and Southern Oceans are presented. Over the Southern Ocean seasonal ice zone, the seasonality is complex. Although it cannot be thoroughly documented due to the limited extent of observations, seasonal changes in pCO2 are approximated by using the data for under-ice waters during austral winter and those for the marginal ice and ice-free zones. The net air-sea CO2 flux is estimated using the sea-air pCO2 difference and the air-sea gas transfer rate that is parameterized as a function of (wind speed)2 with a scaling factor of 0.26. This is estimated by inverting the bomb 14C data using Ocean General Circulation models and the 1979-2005 NCEP-DOE AMIP-II Reanalysis (R-2) wind speed data. The equatorial Pacific (14°N-14°S) is the major source for atmospheric CO2, emitting about +0.48 Pg-C y-1, and the temperate oceans between 14° and 50° in the both hemispheres are the major sink zones with an uptake flux of -0.70 Pg-C y-1 for the northern and -1.05 Pg-C y-1 for the southern zone. The high-latitude North Atlantic, including the Nordic Seas and portion of the Arctic Sea, is the most intense CO2 sink area on the basis of per unit area, with a mean of -2.5 tons-C month-1 km-2. This is due to the combination of the low pCO2 in seawater and high gas exchange rates. In the ice-free zone of the Southern Ocean (50°-62°S), the mean annual flux is small (-0.06 Pg-C y-1) because of a cancellation of the summer uptake CO2 flux with the winter release of CO2 caused by deepwater upwelling. The annual mean for the contemporary net CO2 uptake flux over the global oceans is estimated to be -1.6±0.9 Pg-C y-1, which includes an undersampling correction to the direct estimate of -1.4±0.7 Pg-C y-1. Taking the pre-industrial steady-state ocean source of 0.4±0.2 Pg-C y-1 into account, the total ocean uptake flux including the anthropogenic CO2 is estimated to be -2.0±1.0 Pg-C y-1 in 2000

Southern Ocean iron enrichment experiment: carbon cycling in high- and low-Si waters

The availability of iron is known to exert a controlling influence on biological productivity in surface waters over large areas of the ocean and may have been an important factor in the variation of the concentration of atmospheric carbon dioxide over glacial cycles. The effect of iron in the Southern Ocean is particularly important because of its large area and abundant nitrate, yet iron-enhanced growth of phytoplankton may be differentially expressed between waters with high silicic acid in the south and low silicic acid in the north, where diatom growth may be limited by both silicic acid and iron. Two mesoscale experiments, designed to investigate the effects of iron enrichment in regions with high and low concentrations of silicic acid, were performed in the Southern Ocean. These experiments demonstrate iron's pivotal role in controlling carbon uptake and regulating atmospheric partial pressure of carbon dioxide