CONCLUSIONS

Examination of results of minor and trace element determinations conducted aboard the JOIDES Resolution and in our laboratory reveal that extreme care should be taken when analyzing Li⁺ onboard ship in the presence of extreme concentrations (mM range) of dissolved Sr²⁺. Shipboard determinations of dissolved Sr²⁺ are extremely reliable. Results of shipboard determinations of dissolved Fe, however, are subject to artifacts including contamination and matrix effects. The passage of Fe colloids through 0.45-µm acrodiscs also leads to overestimation of the dissolved Fe content of interstitial water. Thus, filtration through 0.2-µm membranes is recommended if a more restricted measure of the dissolved Fe concentration is desired.

The minor and trace metal composition of pore fluids in sediments of the GBB transect sites is mediated principally by the effects on pore water properties of early diagenesis of carbonates resulting from the microbial degradation of organic matter, and by the abundance of detrital materials that serve as a source of these elements. Concentrations of dissolved Li⁺ derive from two principal sources: (1) release from biogenic carbonate during their recrystallization, and (2) release from Li-bearing detrital phases by ion-exchange reactions with NH₄⁺. The source of dissolved Sr²⁺ is almost exclusively biogenic carbonate, particularly aragonite. Concentrations of dissolved Sr²⁺, however, are mediated by the presence of SO₄^2-, as are those of dissolved Ba²⁺. The sources of the latter are primarily barite associated with remineralization of organic matter and, to a lesser extent, detrital minerals. Concentrations of Fe and Mn²⁺ in anoxic pore fluids are mediated by the insolubility of sulfides and incorporation into mixed carbonate minerals. The principal sources of these elements are easily reduced Fe-Mn-rich phases including Fe-rich clays found in lateritic soils and aeolian dust.