confident that the waters discharged from Pele's Vent are a 

 source of phosphorus to the deep ocean habitat surrounding the 

 Hawaiian archipelago. In addition to the SRP contained in the 

 discharged hydrothermal solutions, we have also measured (to be 

 discussed later) a significant enrichment of phosphorus in 

 association with the bacterial carpets. At the present time we 

 believe that the "excess" P contained in the Pele's Vent habitat 

 must be derived ultimately from the reaction between heated 

 seawater and Hawaiian basalts, which are characteristically 

 enriched in P relative to mid-oceanic ridge basalts (Byers, 

 Garcia, and Muenow 1986; M. Garcia, unpublished data from Loihi ) . 



CH 4 and CO ? Content of Pele's Vent 



Water samples collected from Pele's Vent were enriched in 

 both CH4 and E CO2 relative to ambient bottom seawater (Table 4 

 and Fig. 6). The presence of a high CH4 concentration in 

 Pele's Vent was fully expected based on previous reports of 

 elevated CH4 concentrations in hydrothermal plumes sampled at 

 Loihi Seamount (Horibe, Kim, and Craig 1983; Sakai, Tsubota, 

 Nakai, Ishibashi, Akagi, Gamo, Tilbrook, Igarashi, Kodera, 

 Shitashima, Nakamura, Fujioka, McMurtry, Malahoff, and Ozima 

 1987; Gamo, Ishibashi, Sakai, and Tilbrook 1987), and from the 

 presence of CH4 in hydrothermal vents on the East Pacific Rise 

 (Welhan and Craig 1979, 1983; Lilley, Baross, and Gordon 1983) 

 and the Galapagos Rift (Lilley, de Angelis, and Gordon 1982). 

 The concentrations of both gases were positively correlated with 

 dissolved Si, suggesting a hydrothermal origin (Fig. 6). From 

 these linear relationships, the 30°C Pele's Vent water (the 

 warmest vent temperature measured) should contain approximately 

 7 nM CH4 and 300 mM ECO2. The latter estimate is in excellent 

 agreement with direct measurements of E CO2 in the 30°C waters 

 collected using gas tight samples and total gas extraction 

 procedures (Craig, Welhan, and Hilton 1987). This extrapolated 

 E CO2 content is in excess of two orders of magnitude greater 

 than the ECO2 concentration of ambient bottom seawater. 



The concentrations of CH4 measured for the water samples 

 collected at Pele's Vent are similar to the range of values 

 previously measured for the low-temperature vents at the 

 Galapagos Rift spreading center (Lilley, de Angelis, and Gordon 

 1982). When CH4 (y M ) was plotted versus dissolved Si (yM) for 

 three separate Galapagos vent fields, the slopes of the linear 

 regression analyses were 1.4 x 10" , 4.9 x 10"^ and 3.9 x 10"^ 

 for the East of Eden, Mussel Bed and Rose Garden sites (Lilley, 

 de Angelis, and Gordon 1982). These data indicate that, for a 

 given Si (i.e., heat) content, the Galapagos Rift vents vary by 

 a factor of 3-4 with respect to their CH4 enrichment. These 

 substantial variations in the dissolved CH4~Si relationships 

 among vent fields from the same locale may indicate variations in 

 the rates of methane oxidation for regions having 

 characteristically different biota. For Pele's Vent the slope of 



207 



