Seawater ventilation of mid-Pacific guyots drilled during Leg 143

Active exchange between guyot interior pore-waters and surrounding seawater is indicated by ⁸⁷Sr/⁸⁶Sr and δ¹⁸O values of pore waters and by ⁸⁷Sr/⁸⁶Sr values of their host carbonates, sampled from the interior of Allison (Site 865) and Resolution (Site 866) guyots. The ⁸⁷Sr/⁸⁶Sr values and strontium concentrations of the pore fluids are similar to modern seawater, rather than to their host carbonates. This requires that seawater flushing rates adequate to keep the strontium in pore waters in guyots at or near equilibrium with modern seawater. However, some restriction in the seawater circulation is suggested, because δ¹⁸O values of pore waters from the pelagic cap section of Site 865 are not like those of the surrounding seawater and because temperatures increase downhole at both guyots. Large flushing volumes may be an important part of the cementation and corrosion of these platforms. -from Authors