The submarine hydrothermal activity on and near the Galápagos Rift has been explored with the aid of the deep submersible Alvin. Analyses of water samples from hydrothermal vents reveal that hydrothermal activity provides significant or dominant sources and sinks for several components of seawater; studies of conductive and convective heat transfer suggest that two-thirds of the heat lost from new oceanic lithosphere at the Galápagos Rift in the first million years may be vented from thermal springs, predominantly along the axial ridge within the rift valley. The vent areas are populated by animal communities. They appear to utilize chemosynthesis by sulfur-oxidizing bacteria to derive their entire energy supply from reactions between the seawater and the rocks at high temperatures, rather than photosynthesis.

In the Amazon Basin, substrate lithology and erosional regime (seen in terms of transport-limited and weathering-limited denudation) exert the most fundamental control on the chemistry of surface waters within a catchment. Secondary effects, such as the precipitation of salts within soils and in stream beds, biological uptake and release, and cyclic salt inputs, are more difficult to discern. Samples can be separated into four principal groupings based on relationships between total cation charge (TZ+) and geology. (1) Rivers with O3OOO •eq/1 drain massive evaporites. These rivers are rich in Na and C1. In the third and fourth categories, rivers tend to have 1:1 (equivalent) ratios of Na:C1 and (Ca+Mg):(alkalinity+S04) , caused primarily by the weathering of carbonates and evaporites. [1972] use factor analysis to deduce that for the major dissolved species, clear relationships exist between the geology of the sample catchment and the chemistry of the samples. Relatively high concentrations of certain species have been related to catchment geologies in the following associations: Mg, Ca, Sr, HC03, and SO 4 with carbonate rocks and gypsum; X, B, and Na with illitic bedrock; Si with bentonites and hot spring areas; Na and C1 with evaporites; and Fe and B with glauconitic substrates. Both U and PO 4 show river-specific chemical behavior which, however, could not be related unambiguously to geology, while F, NO3, Ni, Cu, and Zn show no clear geological relationships or exceptional behavior. The present work focuses on the relationship between the chemistry of major dissolved species in rivers of the Amazon system, and the geology, topography, and soils of their catchments. Data were collected in conjunction the 1976-1977 R/V Alpha Helix Amazon expedition. Like the Mackenzie project, the bulk of the Amazon samples was collected during one part of.the year. Precipitation chemistry, lacking in the Mackenzie work, was also studied [Stallard and Edmond, 1981], so that at...

No abstract

Earth and Planetary Science Letters 119 (1993) 85-101. doi:10.1016/0012-821X(93)90008-WReceived by publisher: 1992-08-18Harvest Date: 2016-01-04 12:19:37DOI: 10.1016/0012-821X(93)90008-WPage Range: 85-10