The polar seas are the lungs of the ocean. When sea iceSea ice forms it makes cold and salty water that is enriched in oxygen. Polar seas are where the oceans “breath in”. Oxygen dead zones are created where rivers polluted by fertilizer reach the ocean and are a growing concern globally. Carbon dioxide is also absorbed by the ocean along with oxygen in the polar seas. In sea water carbon dioxide makes weak carbonic acid causing oceanOcean acidification acidificationAcidification, the “evil twin” of global warming. But the oceans have not always had lungs that work the way they do today. In the geologic past the deep ocean waters were hot, salty and sometimes deprived of oxygen. We will also learn about a time 6 million years ago when the Strait of Gibraltar was closed off and the Mediterranean Sea nearly dried up.