(Table 1) Interstitial water chemistry at DSDP Leg 73 Holes

Interstitial waters obtained from a transect east from the Mid-Atlantic Ridge on progressively older oceanic crust (Sites 519-522) indicate a general absence of concentration gradients in calcium and magnesium. The lack of gradients indicates little or no exchange of these seawater constituents with the underlying basalts. Only at Site 520, where there are increases in calcium and decreases in magnesium, do reactions in the silica-enriched zone appear to have affected interstitial water composition. At Site 524, on the eastern flank of the Walvis Ridge, large changes in calcium and magnesium occur as a result of reactions involving the volcanic materials that are both dispersed in the sediment column and present in the underlying basalts.