deep water. It should be mentioned, however, that there appears 

 to be a net loss of fixed N in the hydrothermal system because 

 the input of each mole of NH4 + is offset by a loss of 6-7 moles 

 of [N03~+NC>2~] • Presumably the N balance is accounted for by 

 gaseous constituents not measured in our initial study. From a 

 microbiological perspective the reduced form of nitrogen (NH^"*") 

 has the potential to serve as an energy source for certain 

 bacteria, so its presence in the hydrothermal vent system is 

 significant . 



It is not easy to compare our results on the dissolved 

 nutrient content of Pele's Vent water samples to other 

 hydrothermal systems (Table 3). Of the numerous publications on 

 the chemistry of hydrothermal solutions, relatively few data are 

 presented on the concentrations of [NC>3~+NC>2 _ ] , NH4 + and SRP. 

 Of the data which are available for comparison, a depletion of 

 oxidized nitrogen has also been observed at the Galapagos Rift 

 (Corliss, Dymond, Gordon, Edmond, von Herzen, Ballard, Green, 

 Williams, Bainbridge, Crane, and van Andel 1979), at 21°N on the 

 East Pacific Rise (Edmond and von Damm 1985) and at the Guaymas 

 Basin (Edmond and von Damm 1985; Karl, Taylor, Novitsky, 

 Jannasch, Wirsen, Pace, Lane, Olsen, and Giovannoni 1987) 

 hydrothermal vents. For Pele's Vents we predict a total 

 depletion of [N03~+N02~] at a Si concentration of 1.2 mM 

 (Fig. 4), a value which corresponds to a temperature of 

 approximately 30-35°C. The [N03~+N02~] measured in the 

 discharged fluids, then, must be derived from mixing of vent 

 waters with ambient bottom seawater. 



The enrichment of NH4 + in Pele's Vent (Fig. 5) is 

 consistent with the data previously reported for high-temperature 

 (>300°C) vent fluids collected at both the Explorer Ridge 

 ( Tunniclif f e, Botros, de Burgh, Dinet, Johnson, Juniper, and 

 McDuff 1986) and the Guaymas Basin (von Damm, Edmond, Measures, 

 and Grant 1985; Karl, Taylor, Novitsky, Jannasch, Wirsen, Pace, 

 Lane, Olsen, and Giovannoni 1987), but conflicts with the 

 extensive data base obtained from the 21°N East Pacific Rise 

 vents. It is conceivable that the different trends which have 

 been observed in the concentrations of dissolved NH4" 4 " are due to 

 mechanisms other than strict seawater-basalt interactions. It 

 has been suggested previously that the presence of elevated NH4 + 

 concentrations in vent water samples collected from Guaymas Basin 

 is the result of thermolytic degradation of sedimented organic 

 matter (von Damm, Edmond, Measures and Grant 1985). The absence 

 of NH4 + in the 21°N hydrothermal solutions is due to the absence 

 of pelagic sediments at the mid-ocean ridge. It is conceivable 

 that the hydrothermal solutions sampled at Pele's Vent are also 

 reacting with a sediment phase at Loihi Seamount. 



The systematic increase in SRP for the water samples 

 collected at Pele's Vent appears to be unique to Loihi Seamount. 

 While there is some scatter in our present data set, we feel 



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