Oxygen isotope and cation composition of DSDP pore waters and the alteration of Layer II basalts

Systematic decreases with depth of 1-3‰ in the pore water ¹⁸O/ ¹⁶O and increases with depth of up to four times the seawater concentration in pore water Ca ²⁺ observed in DSDP cores are attributed principally to the alteration of basalt in Layer II of the ocean floor and secondarily to alteration of volcanic ash in the sediments. At sites 70 and 71 of the Equatorial Pacific alteration of basalt near the Clipperton Fracture Zone seems to be the dominant factor. At site 149 in the Caribbean the alteration of volcanics in the sediments is probably an important factor. Ca ²⁺ is being added to the ocean while ¹⁸O and probably also K ⁺ and Mg ²⁺ are being removed as a result of these processes.