Upwelling of hydrothermal solutions through ridge flank sediments shown by pore water profiles.

High calcium ion and low magnesium ion concentrations in sediment pore waters in cores from the Galápagos Mounds Hydrothermal Field on the flank of the Galápagos Spreading Center are believed to be due to a calcium-magnesium exchange reaction between circulating seawater and basement basalt. The nonlinearity of the calcium ion and magnesium ion gradients indicates that these discharging hydrothermal solutions on the ridge flank are upwelling at the rate of about 1 centimeter per year through the pelagic sediments of the Mounds Field and at about 20 centimeters per year through the hydrothermal mounds themselves.