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This report summarizes the results of investigation the oceanographic expedition aboard the F/S METEOR in South Atlantic Ocean including the Drake Passage, the northern Weddell Sea and the eastern South Atlantic during the austral summer of January through March 1990. The total CO{sub 2} concentration in about 1300 seawater samples and CO{sub 2} partial pressure (pCO{sub 2}) in about 870 seawater samples collected at 77 stations were determined aboard the ship using a coulometer and equilibrator/gas chromatograph system. The temperature, salinity, dissolved oxygen and nutrient salt data presented in this report were determined by other participants of the expedition including the members of the Oceanographic Data Facility of the Scripps Institution of Oceanography, Argentine Hydrographic Office and German institutions.

This report summarizes the results of investigation the oceanographic expedition aboard the F/S METEOR in South Atlantic Ocean including the Drake Passage, the northern Weddell Sea and the eastern South Atlantic during the austral summer of January through March 1990. The total CO{sub 2} concentration in about 1300 seawater samples and CO{sub 2} partial pressure (pCO{sub 2}) in about 870 seawater samples collected at 77 stations were determined aboard the ship using a coulometer and equilibrator/gas chromatograph system. The temperature, salinity, dissolved oxygen and nutrient salt data presented in this report were determined by other participants of the expedition including the members of the Oceanographic Data Facility of the Scripps Institution of Oceanography, Argentine Hydrographic Office and German institutions.

Aragonite mineralization was observed in serpentinized peridotites from the Romanche and Vema Fracture Zones in the Atlantic and the Owen Fracture Zone in the Indian Ocean, either in veins or as radial aggregates in cavities within the serpentinites. Evidence of incipient dissolution of the aragonite crystals was observed in one case. The aragonites tend to have lower Mg content ( 0.95%) relative to other marine aragonites. Their 18 O 16 O , 13 C 12 C and 87 Sr 86 Sr isotopic ratios suggest the aragonite was deposited at ocean floor temperatures from solutions derived from sea water circulating in fissures and fractures within the ultramafic rocks. The 18 O 16 O ratios of the serpentines indicate serpentinization occurred at higher temperatures, probably deeper in the crust. Low-T reactions between circulating seawater and Mg-silicates (primarily serpentine and pyroxenes) caused high pH and enrichment of Mg and Ca in the solution, conditions favoring carbonate precipitation. Aragonite was formed rather than calcite presumably because the high Mg2+ concentration in the solution inhibited calcite precipitation. The high Sr content of the aragonites is probably related, at least in part, to their low temperature of formation. Opaque mineral grains containing over 8% NiO and over 40% MnO were observed concentrated along the margins of some of the aragonite veins, suggesting that Ni is one of the elements mobilized during reactions between ultramafic rocks and circulating seawater.

A deposit consisting almost exclusively of the Mg-silicate sepiolite has been sampled from the Owen transform zone in the western Indian Ocean. This deposit is associated with basaltic, gabbroic and ultramafic rocks. On the basis of major, trace and rare earth elemental composition, strontium and oxygen isotopic ratios, as well as of theoretical considerations, the sepiolite deposit appears to have formed neither from seawater nor from solutions resulting from the interaction of seawater with the basaltic crust. Interaction of ultramafic rocks with seawater circulating in the crust, particularly in transform zones, may produce solutions which at low temperature (