deep-sea waters. It is within this characteristic hydrothermal 

 vent habitat of well-defined anoxic-to-oxic chemical gradients 

 that much of the chemolithoautotrophic bacterial production is 

 thought to occur. A third major habitat is the region of 

 bacterial mat formation which appears to be in the periphery of 

 the main hydrothermal vent field. At these locations, extensive 

 bacterial mats completely cover the bottom substratum with a 

 thick carpet of organic matter (Fig. 2b). Finally, we also 

 observed an area further down the flank of the volcanic cone 

 which contained a high concentration of what appeared to be 

 organic detritus arranged in "windrow-like" formations (Fig. 2c). 

 This leads us to suspect that material deposited in this area of 

 the seafloor was transported by currents and gravity from an 

 active vent field. We have made numerous observations of this 

 material but have, to date, been unsuccessful at obtaining any 

 samples for chemical and microbiological analyses. 



Dissolved Nutrient Concentrations 



Hydrothermal fluids collected at Pele's Vents are enriched 

 in reactive Si, NH 4 + and SRP and depleted in [NC>3~+NC>2~], 

 relative to ambient bottom seawater collected from that site 

 (Table 2). The enrichment of reactive Si is characteristic of 

 hydrothermal vents, in general, and it is used as a geochemical 

 thermometer due to the highly significant positive correlation 

 between Si concentration and vent water temperature (Corliss, 

 Dymond, Gordon, Edmond, von Herzen, Ballard, Green, Williams, 

 Bainbridge, Crane, and van Andel 1979). When SRP, [N03~+N0 2 ~] 

 and NH4 + concentrations are plotted versus Si for the Loihi 

 Seamount data, the relationships are described adequately by a 

 single mixing curve (Figs. 3-5). These results suggest that the 

 numerous fluid discharges which comprise the Pele's Vent 

 hydrothermal habitat have a common end-member solution. In fact, 

 the single water sample that was collected from the deeper 

 hydrothermal vent field to the south of Pele's Vent also fit the 

 same linear relationship indicating that the hydrothermal 

 emissions from at least two separate Loihi Seamount hydrothermal 

 vents have similar chemical compositions. 



A second consistent trend in the nutrient data set was that 

 the SRP versus Si, and the [NC>3~ + N02~] versus Si relationships 

 for Pele's Vents were not significantly different for water 

 samples collected in February and August (Figs. 3 and 4). 

 These results indicate that the concentrations of [N03~ + NC>2 - ] and 

 SRP may be stable, at least over time periods of months. The 

 NH4 + versus Si curves (Fig. 5), however, indicate that the NH4 + 

 content per unit Si (or per unit of total heat) was approximately 

 two times higher during the February expedition. At the present 

 time these data are not comprehensive enough to be used as 

 reliable evidence for a temporal alteration in dissolved NH4 + at 

 Pele's Vent. Nevertheless, our results clearly indicate that the 

 vent waters are a source of reduced N and SRP to the surrounding 



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