We also know through the counting of annual layers in cores from Greenland's ice cap that transitions from one of these states to another were accomplished in three to four decades and that during these transitions climate flickered much as fluorescent lights do when first turned on. The impacts of these changes in state were very large and global in extent. I believe that these reorganizations were triggered from below, i.e., by changes in the pattern of the major ocean current systems. It turns out that there exists a large-scale interaction between the ocean and atmosphere. The geography of surface temperature, of wind regimes and of mountain ranges leads to net transports of water vapor from one place to another on our planet.
Polar regions receive more water as precipitation and river runoff than they lose via evaporation.
The consequent dilution of the salt content of polar surface waters counters the enhancement of density created by the cold temperature. Water evaporated from the Atlantic Ocean finds its way to the Pacific. This tends to enrich the salt content of surface waters in the Atlantic and deplete it in those in the Pacific, allowing deep water to form in the northern Atlantic but not in the northern Pacific. The salt content differences created by atmospheric transport of water vapor must be compensated by transports of salt through the sea. In other words, salt must move from the warm regions of the planet to polar regions and from the Atlantic to the Pacific.