INVESTIGATION OF INORGANIC AND ORGANIC TRAGE COMPOUNDS OVER THE ATLANTIC

The main ernphasis of our tests on inorganic trace compounds was the collection of aerosol samples to analyse the following environ- mentally relevant heavy metals: thallium, copper, cadmium, lead, zinc, nickel, chrorne and iron. For the first time, a five stage im- pactor was used for the collection of aerosol samples according to size.

Continuous sampling began On 13.3.89 On "Polarstern's" upper deck a day after sailing frorn Cape Town. The complete aerosol residue on the cellulose nitrate filters (pore size 8 prn) was sucked off at 12 hourly intervals, and parallel to that, the five stage impactor was put into operation, and sea Spray was separated before. The aerodynamic diameters of the individual particle fractions include:

1. step: > 7.2 prn 2. step: 3.0

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7.2 pm 3. step: 1.5

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3.0 pm 4. step: 0.95

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1.5 pm 5. step: 0.49

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0.95 pm

Backup: < 0.49 pm

The separating effect of the impactor was clearly Seen in the area where dust from the Sahara entered it (approx: between latitude1Â N and 16' N). The large sand particles

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up to 1.5 pm

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precipitated with a red-brown colour on the first three impactor positions whilst those particles with a smaller aerodynarnic diarneter were found with a dark brown to black colour on the following positions. Pre- paration of the samples to establish the total content of the ele- ments thallium, cadrnium, lead and zinc were carried out on board

"Polarstern" for the mass spectrornetrical isotope dilution analysis (MS-IVA) process. The measurement itself as well as finishing the work On the impactor measurements are taking place at the in- stitute in Regensburg. The concentration of the other elements over and above the average values for the earth's crust

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and thereby possible anthropogenic influences

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are to be established by determining the content value of the element iron. An indication of aerosol sources is expected from their size distribution Pattern in the irnpactor analysis. Questions of element distribution and elernent-elernent correlation in top surface water and in aerosols are also to be investigated in cooperation with the heavy metals work-group of the AWI's chernistry section.

The airn of further investigations was the quantitative analysis of volatile biogenically formed sulphur and seleniurn compounds and halogenated hydrocarbons i n sea water. The parallel determination of DMS, the rnost irnportant biogenic sulphur compound, and the halogenated hydrocarbons Mel, MeBr and MeCI should provide Information about a possible cornmon forrnation mechanism. By gas chrornatography using a flame

photometric detector, it was possible to continually analyse water samples for volatile sulphur and selenium compounds on board.

The compounds were driven out of the water samples (between 10 and 30 ml) with helium, enriched in a cooling trap with liquid nitrogen and separated in a capillary column. The water samples were taken together with the ATP- and DMSP working groups using a bucket from the ship's Stern. Apart from the regular sampling (at 8.30, 12.30 and 16.30), samples were often taken in a two-hourly cycle, and in several depth profiles which were also immediately analysed. Halogenated hydrocarbon analysis will take place in a laboratory at the University of Regensburg according to the Same measuring principle but with an electron capture detector. In addition, 55 water samples were shrink-wrapped in glass containers and deep-frozen. At the Same time, 60 water samples were cryogenically enriched On Tenax GC On the ship's upper deck. The analysis which resulted from thermal desorption was partly carried out on board.

Direct gas chromatographic analysis made possible a comparison of measurement results with other groups. A correspondence was revealed with the ATP results from Ernst's group and the chlorophyll results from Ohm's group. A comparison with DMSP content

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the direct DMS precursor

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will take place with the results of the Karsten, Meyerdierks, (Kirst group).

The ascertained DMS concentrations in the top surface water Span a range from 30 to 550 ng/I. The highest concentrations were found in the Iberian Basin, in an area in which rich neuston catches of mainly young animals (Schulz-Baldes group) point to a recently present Algal bloom. The sulphur compounds COS, CHsSH, CS2 and DMDS were found as well as the main component, DMS.

DETERMINATION OF NUTRIENTS

The nutrients nitrate, nitrite, phosphate and silicate were constantly determined from Cape Town to the English Channel with an autoanalyzer system. The water was sucked up from a depth of about 7 m via the ship's pure sea water pipe and then pumped into the analysis System. The analyses were carried out in 4-hourly cy- des. After each 4-hourly measuring phase, measurements were interrupted in order to calibrate and service the equipment. Results were recorded on a printer, and stored every two minutes.

Furthermore, nutrients were determined from all the various sam- ples frorn the five deep water stations in order to get an Impression of the expanse of the nutrient-deficient surface layer, and in order to be able to carry out a characterization of the bodies of water at the greater depths. As an example, Fig. 58 shows the nutrient distribution in the southern Canary Basin.

The concentration of nitrate and nitrite during the whole cruise was almost below the equipment's recording level, that is, the nitrogen containing nutrients were used up and thereby limiting phytoplankton growth. The first signs of measurable nitrate

concentrations were detected only between latitudes 41 ^O N

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42O N, which then continuously rose, sometimes sporadically, up to 4 pmolll, as far as the English Channel.

The phosphate concentrations were similarly very low, but in most cases still measurable. A rise of 0.3-0.4 pmolll resulted parallel to the nitrate increase.

Silicate showed variations in concentration between 0 and 2 pmolll during the whole cruise. These variations are possibly related to the various bodies of water in the Atlantic. Only the final evaluation can reveal further details. The data is to be compared and evaluated with the hydrographical results from Ohm's working group (such as salinity, temperature, chlorophyll and turbidity).

N U T R I E N T S ( p m o l / l )

Figure 58: Vertical profiles of nitrate, silicate and phosphate at St. 141374 (Canary Basin, 25'23'N 2 8 ' 0 7 ' W )

Im Dokument 3) nd VIIl5 of 'Polarstern" in (Seite 189-192)