Interstitial water studies on small core samples, Deep Sea Drilling Project, Leg 1

The most dramatic variations in pore water composition occurred in Holes 2 and 3 in the Gulf of Mexico. Both holes showed a strong increase in salinity with depth, evidently owing to diffusion from underlying salt bodies. However, on Challenger Knoll (Hole 2) a sharp drop in salinity was observed in the cap rock of the salt dome in which chloride fell to only 4.8 percent. The drop is attributed to production of fresh water during the formation of native sulfur.

Outside of the Gulf of Mexico, changes in total salinity with depth did not exceed a few percent, but differences in diagenetic modification of the ionic ratios of sea water were pronounced. In nondiapiric strata in the Gulf of Mexico (Hole 1) both magnesium and potassium were depleted in the pore waters, whereas in the open ocean holes (4, 5, 6, and 7), potassium appeared in excess. Water content (porosity) of the cores was irregular.