1. Quantification of hydrothermal fluxes between seawater and ocean crust Circulation of seawater through ridge flanks occurs at low temperatures (<100°C), but because the fluid fluxes are so large the chemical effects are comparable to or greater than the more spectacular high-temperature axial systems that result in black smokers and sulfide deposits.  These flank systems may be the main sink for seawater Mg in the crust, and the uptake of alkalis may balance the input from high temperature reactions at the ridge axes.
 In a recently submitted paper (Alt and Teagle, 1998) we show that Carbon uptake in these flank systems exceeds outgassing at ridges, and should be significant in the sedimentary carbon cycle and subduction recycling.  We have also documented evolution of temperature and fluid composition in different portions of a well-documented ridge flank circulation system (Alt et al., 1996a,b; Teagle et al., 1996), and I am continuing this work at other seafloor sites.  This work also has significance for understanding recycling of altered ocean crust in subduction zones.
 Other projects focusing on the 2 km Hole 504B upper crustal section are dedicated to understanding the evolution of water-rock interaction and controls on the isotopic compositions of hydrothermal fluids, and the net composition of altered crust. (Alt et al., 1996a,b,c; Teagle et al., 1995, 1997, 1998).   We have extablised profiles for Li contents and isotopic compositions (Chan et al., 1996 abstract), documenting a balance between ridge crest and flank activity.
 Data for alteration and vein abundances and distributions (Alt et al., 1996a,b) are being combined with ICP-MS data for trace elements in order to understand the mobility and distribution of these elements, and to quantify their alteration budgets (Alt et al., 1997 abstract) In collaboration with J. Erzinger, GeoForschungZentrum, Potsdam, FRG, and W. Bach, Woods Hole Oceanographic Institution.  Elements of particular interest that exhibit significant mobility include Pb, U, Th, Cs, Tl, Rb, and Ba.  We also provide the first data for significant hydrothermal mobility of Sb, Sn, Mo, and Cd.