<P> Rapid spreading rates will expand the mid-ocean ridge causing basalt reactions with seawater to happen faster . The Magnesium / Calcium ratio will be lower because more magnesium ions are being removed from seawater and consumed by the rock, and more calcium ions are being removed from the rock and released to seawater . A lower Mg / Ca ratio favors the precipitation of Low - Mg calcite polymorphs of calcium carbonate (calcite seas). </P> <P> Slow spreading at mid-ocean ridges has the opposite effect and will result in a higher Mg / Ca ratio favoring the precipitation of aragonite and High - Mg calcite polymorphs of calcium carbonate (aragonite seas). </P> <P> Experiments show that most modern High - Mg calcite organisms would have been Low - Mg calcite in past calcite seas, meaning that the Mg / Ca ratio in an organism's skeleton varies with the Mg / Ca ratio of the seawater in which it was grown . </P> <P> The mineralogy of reef - building and sediment - producing organisms is thus regulated by chemical reactions occurring along the mid-ocean ridge, the rate of which is controlled by sea - floor spreading . </P>

Where are volcanoes located in the mid ocean ridge