7) The ANGUS camera system made a highly detailed pho- 

 tographic survey of the study area using over 57,000 

 individual frames to pinpoint the geological and tectonic 

 setting of the vent areas. This film was processed ship- 

 board and helped to guide the diving program. 



8) One hundred and sixty navigated heat-flow stations from 

 the RV Knorr and 35 stations from the Alvin were 

 conducted to quantify the thermal budget in the study 

 area. 



9) Unique communities of organisms (clams, crabs, limpets, 

 mussels, pogonophora worms, etc.) were discovered 

 around the hot water vents. Sulfide-oxidizing bacteria are 

 believed to be the basis of the food chain in these com- 

 munities. 



10) A collection of organisms, water for bacterial analysis, 

 and ANGUS and Alvin photographs was made that will 

 be the basis for detailed biological studies of these unique 

 communities. 



11) Alvin collected 92 samples of fresh basalt, hydrother- 

 mally altered basalt, iron-manganese crusts and coatings, 

 and cores in known geological relation to the hydrother- 

 mal vents and the general geologic setting. 



12) Thirty-four samples of newly forming precipitates were 

 collected near the hydrothermal vents using a water-filter 

 system developed for use on Alvin. 



13) Ten cores up to 9 m long were obtained directly from 

 the hydrothermally formed sediment mounds south of 

 the spreading center using transponder-navigated piston 

 coring. 



14) Heat-flow measurements from these piston cores indicate 

 that nearly isothermal pore waters up to 12°C are found 

 in the upper portions of these mounds. 



15) In situ pore-water sampling from piston cores and ship- 

 board squeezing of sediments obtained samples of the 

 fluids that are apparently connecting through the sedi- 

 ments at the Fe-Mn mounds area. 



16) Alvin successfully recovered three sediment traps, which 

 had been deployed at two sites in the study area and 

 provide a 7-month record of particle flux to the sea floor. 



17) Eight hydrocasts and seven acoustically navigated Kami- 

 kaze near-bottom casts were made to characterize the re- 

 gional variability and water-column chemistry of the sea. 



18) During the 24 dives made by Alvin, over 18,000 color 

 photographs by the automatic cameras of the submersible 

 and 2,000 hand-held photographs were collected and 

 developed on ship to document and guide the diving 

 program. 



19) Near-bottom water temperatures were monitored during 

 ANGUS camera runs and Kamikaze casts as a recon- 

 naissance tool for discovering new vent areas and as a 

 means for obtaining data on regional bottom water tem- 

 perature. 



20) Near-bottom CTD surveys (5-50 m off the bottom) were 

 made over different vent areas to obtain the three dimen- 

 sional thermal structure of the thermal plumes. 



The accomplishments of the diving expedition provide an ex- 

 tensive set of unique samples and data. Analysis is underway; 

 however, several initial results can be reported: 



1 ) The hydrothermal fluids contain hydrogen sulfide. This 

 leads to extremely low concentrations of cadmium, copper, iron, 

 nickel, and zinc, presumably because they precipitate as stable 

 sulfides. Thus, the thermal springs of the Galapagos Rift are 

 not presently supplying these elements to the ocean. The data 

 indicate that ridge crest hydrothermal systems are clearly a 

 major source of manganese and a major sink for magnesium in 

 the oceans. The linear silicon-temperature relationship in the 

 samples suggests that the fluids sampled are mixtures of normal 

 bottom water and an end-member hydrothermal fluid that inter- 

 acts with the rocks at depth at temperatures around 300°C. The 

 helium-3 flux from the springs can be used to quantify the 

 global thermal flux of these midocean ridge hydrothermal sys- 

 tems, and the estimate is similar to previous estimates based on 

 heat-flow data. 



2) The heat-flow observations clearly support the notion 

 that convective heat loss by hydrothermal circulation, most in- 

 tense at the ridge axis, is a fundamental process cooling the 

 Earth. The mean heat flow in the region, from over 400 sta- 

 tions, is 7 heat flow units, which is about one-third of the value 

 predicted by the purely conductive model. This suggests that 

 two-thirds of the heat entering the ocean at the midocean ridges 

 is transferred by hydrothermal processes. To improve these esti- 

 mates, the detailed maps of the plumes will be used to estimate 

 the actual flux of heat from the thermal springs. 



3) The extensive photographic survey of the area with the 

 ANGUS system has produced a geologic map of the area in 

 which five distinctive basalt types can be defined, based on their 

 morphology and relative ages deduced from sediment cores. In 

 addition, features such as fissures, eruption centers, collapse 

 structures, and faults have been accurately mapped. Petro- 

 chemical studies of the rocks sampled from Alvin will supple- 

 ment these studies. 



4) The biological communities associated with the vents 

 have received careful study. Maps of the distribution of animals 

 of each vent have been produced from ANGUS photographic 

 surveys. Taxonomists have studied the animal specimens; new 

 species, genera, and families will be defined. The microbiology 

 of the vent areas is unique; high concentrations of sulfur- 

 oxidizing bacteria are present in the water and animals, and 

 laboratory measurements of productivity suggest that these or- 

 ganisms could support the large animal populations found at 

 the vents. This leads to a major biological discovery — these 

 animal communities are the first known to derive their energy 

 entirely from geothermal heat, and are thus independent of 

 photosynthesis. 



This preliminary work is continuing, and numerous publica- 

 tions are planned or are in preparation. These results will have 

 far-reaching implications in the understanding of the history of 

 seawater, the formation of deep-sea sediments, the nature and 

 evolution of life in the deep sea, the formation of ore deposits, 

 and the possible importance of submarine geothermal systems 

 as an energy resource. 



58 



