More than 25000 individual aerosol particles in 51 particulate matter samples, all taken from a research vessel over the North Sea and the English Channel, in a time range of 4 years, were analyzed by automated electron probe X-ray microanalysis (EPXMA). Multivariate methods were used to reduce the total data set. Singleparticle analysis combined with hierarchical cluster analysis yields nine major particle types. The North Sea aerosol is predominantly composed of sea salt, sulfur-rich particles, silicates, and calcium sulfate particles. Their abundance is dependent on meteorological conditions and sample location. Differences between all samples were studied on the basis of the abundance variations by using principal component analysis. Three factors explain 91% of the total covariance between the samples. The first component represents the marine-derived aerosol fraction and is more important as wind speed increases or at more remote sampling locations. The second component differentiates anthropogenically derived CaS04-rich samples.Their relative abundance is much more pronounced as the sampled air masses spend longer residence times over the south of England. The samples of the third cluster are related to high silicate and sulfur abundances. Source apportionment of this group was obtained by a second principal component analysis. Two different clusters separate mixed marine/ continental samples from pure continental-derived silicate and sulfur-rich particulate samples.

Particulate Ba profiles were measured in the Indian sector of the southern ocean. The largest fraction (>80%) of this barium is present as barite microcrystals. The profiles of total barium are characterized by a subsurface maximum between 200 and 500 m depth in the vicinity of the oxygen minimum. Highest barium values are found just south of the Polar Front, while lowest values occur close to the Antarctic Divergence. Between the divergence and the Polar Front a tight inverse relationship is observed between oxygen in the oxygen minimum and barium in the barium maximum. This relationship disappears north of the Polar Front. Since suspended barite is known to be of biological origin, the correlation of barite with oxygen suggests that the observed decrease of oxygen in the oxygen minimum, between the divergence and the Polar Front is due to local consumption of oxygen. It is proposed that deep low oxygen water is advected towards the Divergence where upwelling occurs and where this water subsequently partly spreads out to the north, north‐east, as entrained by the Antarctic Circumpolar Current. Oxidation of locally produced organic matter, with which barite crystals are associated, consumes oxygen and sets free individual discrete barites. As a result, oxygen decreases and barite increases away from the divergence, with barite integrating former biological processes.

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