S. Rapsomanikis

A global database of sea surface dimethylsulfide (DMS) measurements and a procedure to predict sea surface DMS as a function of latitude, longitude, and month

A database of 15,617 point measurements of dimethylsulfide (DMS) in surface waters along with lesser amounts of data for aqueous and particulate dimethylsulfoniopropionate concentration, chlorophyll concentration, sea surface salinity and temperature, and wind speed has been assembled. The database was processed to create a series of climatological annual and monthly 1°×1° latitude-longitude squares of data. The results were compared to published fields of geophysical and biological parameters. No significant correlation was found between DMS and these parameters, and no simple algorithm could be found to create monthly fields of sea surface DMS concentration based on these parameters. Instead, an annual map of sea surface DMS was produced using an algorithm similar to that employed by Conkright et al. [1994]. In this approach, a first-guess field of DMS sea surface concentration measurements is created and then a correction to this field is generated based on actual measurements. Monthly sea surface grids of DMS were obtained using a similar scheme, but the sparsity of DMS measurements made the method difficult to implement. A scheme was used which projected actual data into months of the year where no data were otherwise present.

Nitrous oxide in coastal waters

We determined atmospheric and dissolved nitrous oxide (N2O) in the surface waters of the central North Sea, the German Bight, and the Gironde estuary. The mean saturations were 104 ± 1% (central North Sea, September 1991), 101 ± 2% (German Bight, September 1991), 99 ± 1% (German Bight September 1992), and 132% (Gironde estuary, November 1991). To evaluate the contribution of coastal areas and estuaries to the oceanic emissions we assembled a compilation of literature data. We conclude that the mean saturations in coastal regions (with the exception of estuaries and regions with upwelling phenomena) are only slightly higher than in the open ocean. However, when estuarine and coastal upwelling regions are included, a computation of the global oceanic N2O flux indicates that a considerable portion (approximately 60%) of this flux is from coastal regions, mainly due to high emissions from estuaries. We estimate, using two different parameterizations of the air-sea exchange process, an annual global sea-to-air flux of 11–17 Tg N2O. Our results suggest a serious underestimation of the flux from coastal regions in widely used previous estimates.

Speciation of mercury and methylmercury compounds in aqueous samples by chromatography-atomic absorption spectrometry after ethylation with sodium tetraethylborate

Abstract A procedure for the rapid, precise and accurate determination of CH3Hg+ in aqueous solutions is described. In situ derivatization by NaB(C2H5)4 to CH3HgC2H5 and Hg(C2H5)2 results in easily chromatographed species, detected by quartz furnace atomic absorption spectrometry. The absolute limit of detection for CH3HgCl is 167 pg.

Bioaccumulation of methylmercury and transformation of inorganic mercury by macrofungi

The terrestrial biogeochemical cycle of mercury between humus and fungi was investigated in a mercury-contaminated former mining area of Germany. We used a variable volume extraction procedure and aqueous sodium boron tetraethyl derivatization to determine accurately and precisely methylmercury bioconcentration factors for fungi. The methylmercury and total mercury content for fungi carpophores ranged from 0.08 to 7.94 μg/g of Hg as methylmercury and from 6.2 to 144.0 μg/g of inorganic Hg, respectively. The levels in humus material were between 0.01 and 0.09 μg/g of Hg as methylmercury and 15.8 and 140.2 μg/g of inorganic Hg, respectively. The bioconcentration factors obtained are generally lower than 1 for total mercury and between 3.0 and 199.0 for methylmercury. By an in vitro methylation experiment with two axenic cultures of Coprinus comatus and Coprinus radians, we could show for the first time that these saprophytic macromycetes are able to methyl ate mercury.

The Aegean Sea as a source of atmospheric nitrous oxide and methane

Abstract During the EGAMES ( E vasion of GA ses from the ME diterranean Sea) expedition in July 1993 we determined the concentrations of nitrous oxide and methane in the atmosphere and in the surface waters of the Aegean Sea, the northwestern Levantine Basin, the eastern Ionian Sea and the Amvrakikos Bay. Both gases were found to be supersaturated in all sampled areas. Nitrous oxide was homogeneously distributed with a mean saturation of 105 ± 2%, showing no differences between shelf and open ocean areas, whereas methane saturation values ranged from about 1.2 times (northwestern Levantine Basin) to more than 5 times solubility equilibrium (Amvrakikos Bay estuary). Therefore the Aegean Sea and the adjacent areas were sources of atmospheric nitrous oxide and methane during the study period.

Methylation of tin and lead in the environment: oxidative methyl transfer as a model for environmental reactions.

Tin(II) and lead(II) compounds have been converted to methyltin and methyllead derivatives under conditions that model the natural environment, and the feasibility of environmental methylation for these elements and their compounds has been demonstrated. Methylating agents that transfer methyl groups by oxidative addition and that occur environmentally have been used (viz., CH/sub 3/I, (CH/sub 3/)/sub 3/S/sup +/I/sup -/, and (CH/sub 3/)/sub 2/N/sup +/CH/sub 2/COO/sup -/). The reactions occurred at ambient temperatures in aqueous media. Observations of methyltin products in natural waters (oceans, estuaries, rivers, and harbors) is explicable in terms of the proposed oxidative mechanism.

Nitrous oxide emissions from the Arabian Sea

Dissolved and atmospheric nitrous oxide (N2O) were measured on the legs 3 and 5 of the R/V Meteor cruise 32 in the Arabian Sea. A cruise track along 65°E was followed during both the intermonsoon (May 1995) and the southwest (SW) monsoon (July/August 1995) periods. During the second leg the coastal and open ocean upwelling regions off the Arabian Peninsula were also investigated. Mean N2O saturations for the oceanic regions of the Arabian Sea were in the range of 99–103% during the intermonsoon and 103–230% during the SW monsoon. Computed annual emissions of 0.8–1.5 Tg N2O for the Arabian Sea are considerably higher than previous estimates, indicating that the role of upwelling regions, such as the Arabian Sea, may be more important than previously assumed in global budgets of oceanic N2O emissions.

Determination of butylin compounds in sediment using gas chromatography-atomic absorption spectrometry: comparison of sodium tetrahydroborate and sodium tetraethylborate derivatization methods

Abstract Aqueous ethylation and hydride generation, two rapid, convenient speciation techniques used for the determination of bityltin species in river sediments, were compared. After extracting the sediment with methanol containing 0.5 M HCl, the extract was derivatized and analysed by gas chromatography-atomic absorption spectrometry. Monobutyltin and dibutyltin can be determined quantitatively using the hydride generation method; for tributyltin the analysis suffers from critical interference from the sediment extract. With the ethylation method, quantitative determination of dibutyltin and tributyltin in the sediment can be achieved, while a lower recovery of monobutyltin is observed. The detection limits for butyltins in sediments are significantly improved by this method because no foaming occurs during the ethylation step and because the analytical procedure is not hampered by interference from sediment extracts. The detection limits are 0.20, 0.10 and 0.44 ng Sn g−1 dry sediment for mono-, di- and tributyltin, respectively.

Environmental implications of methylation of tin(II) and methyltin(IV) ions in the presence of manganese dioxide.

This paper examines formation of mono-, di-, tri-, and tetramethyltin compounds from aqueous Sn(II) and relates the processes to possible environmental ones. Factorially designed experiments allowed us to understand separate and combined effects of a dimethylcobalt complex carbanion donor, the carbocation donor iodomethane, and oxidizing agent manganese dioxide. The following are the range of yields: monomethyltin ions, 0-14.4%; dimethyltin ion, 0.8-8.8%; trimethyltin ion, 0-2.65%; tetramethyltin, 0-3.32%; total methyltin compounds, 0-20.5%. Results of the experimental design clarify the role of each reactant and verify various methylation mechanisms. This research also includes studies on the formation of tetramethyltin in 7.3-36.7% yields from reactions of the dimethylcobalt carbanion donor with mono-, di-, and trimethyltin ions.

Methane in surface waters of the Arabian Sea

More than 2000 measurements of atmospheric and dissolved methane (CH4) were performed in the central and northwestern Arabian Sea as part of the German JGOFS Arabian Sea Process Study during three cruises in March, May/June, and June/July 1997. Mean CH4 saturations in the surface waters of the central Arabian Sea were in the range of 103-107%. Significantly enhanced saturations were observed in the coastal upwelling area at the coast of Oman (up to 156%) and in an upwelling filament (up to 145%). The CH4 surface concentrations in the upwelling area were negatively correlated to sea surface temperatures. Area- weighted, seasonally adjusted estimates of the sea-air fluxes of CH 4 gave annual emissions from the Arabian Sea of 11-20 Gg CH4, suggesting that previously reported very high surface CH4 concentrations might be atypical owing to the interannual variability of the Arabian Sea and that the emissions derived from them are probably overestimates.