emissions from throughout the ridgecrest system and an assessment 

 of the temporal variability of these emissions. We present here 

 the preliminary results of our efforts to quantify the chemical 

 source strengths and variabilities associated with hydrothermal 

 venting from a single component of the northeastern Pacific 

 ridgecrest system: the Axial Volcano segment of the Juan de Fuca 

 Ridge (Fig. 1). In addition, sampling protocols conceived and 

 implemented as a result of the interpretive limitations inherent 

 to conventional vent fluid data are discussed in the context of 

 the VENTS hypothesis. 



Neutrally buoyant hydrothermal plumes characterized by large 

 chemical and thermal anomalies have been observed over seven 

 regions of the Juan de Fuca/Explorer/Gorda Ridge (Figs. 1 and 2; 

 Massoth et al., 1982; Lupton et al., 1985; Baker and Massoth, 

 1987; Baker et al., 1987a-c; McConachy and Scott, 1987). The 

 sharply defined portions of these plumes, which we shall 

 henceforth refer to as proximal plumes, typically extend no more 

 than a few kilometers from the venting site and lie within a 

 single near-bottom layer 100-250 m thick. In contrast to this 

 common distribution pattern, the chemical signals associated with 

 these plumes can be significantly different (Massoth et al . , 

 1985, Baker and Massoth, 1987). Because of this chemical diver- 

 sity, characteristic and often unique, linear relationships 

 result when plume elemental concentrations are compared to the 

 respective thermal anomalies. The collective element-temperature 

 relationships for a given plume are defined here as the "proximal 

 plume signature." It has been shown that this signature for 

 plumes overlying the Cleft Segment of the Juan de Fuca Ridge is 

 not simply related to the high-temperature fluids venting at that 

 site (Baker and Massoth, 1986, Baker et al . , 1987, Massoth et 

 al . , in preparation). For example, the concentrations of ^He, 

 Si, Mn, and Fe determined by extrapolation of plume data to 

 endmember temperatures differ by factors of 2-15 from the 

 concentrations determined directly from the vent fluid data. 

 Factors which contribute to the disparity between the proximal 

 plume and discrete vents are: the regional integration of 

 chemically distinct low- and high- temperature vent fluids by 

 buoyancy induced mixing processes, the formation of "black 

 smoker" particulates and their subsequent local deposition (Feely 

 et al., 1987), and the scavenging of the oxyanions of phosphorous 

 and several trace metals from seawater by Fe-oxyhydroxides 

 (Massoth, manuscript in preparation). It is important to 

 distinguish, especially relative to the goals of the VENTS 

 Program, that it is the more chemically evolved proximal plume 

 chemistry that is dispersed into the regional ocean (Massoth et 

 al., 1984, 1985). Thus, knowledge of the proximal plume 

 signature is required to predict the distributions and effects of 

 hydrothermal effluents in the far-field. 



Accordingly, since 1985 VENTS investigators have conducted 

 systematic regional assessments of the thermal and chemical 



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