Water

Oceans of ice

When, during the course of a glaciation, large quantities of ice are trapped in the ice-sheets and in the continental ice, the oceans and seas are depleted of large quantities of water. During the course of the glaciations this provoked a general drop in the sea level in the entire planet. During the last glaciation, for example, the sea level  dropped approximately 100 m below the present level. Therefore much land that is now submerged, was above sea level. For example, a bridge of land united Alaska and Siberia, and what is the port of New York today was 160 km from the coast. Also the coasts in Italy must have been very different in appearance, specially the Adriatic coasts, where the shallow sea-bottom  increased the extension of the land above sea level. As the continental ice melted, at the end of the last glaciation, the level of the oceans and seas once again rose to the levels it reached before the glacier expanded. These oscillations in the coast lines and in the sea levels  have been reconstructed studying the morphology of the coasts : for example, ancient beaches above the present sea level are a proof of levels higher than the today sea level. Very precious information may be obtained studying sea caves, which can be found in large numbers in the Mediterranean Sea; in these caves, at depths of even 100 m, forms that are typical “landmarks”  such as concretions and speleothemes, can be found, and their isotopic analysis and dating enables the reconstruction of the temperature variations in the past, variations that show a surprising coincidence with the reconstructions obtained from studies of ice cores.