The global ocean circulation system is called the thermohaline circulation. Often called the ‘conveyor b

This theory helped explain the Younger Dryas Ice age. Driven by the Milankovitch variations the ice began its retreat about 16,000 years ago. Warm, salty water reached the north giving its heat to Europe along the way before sinking near Greenland and starting up the conveyor. As the conveyor gained power and pulled more warm water north the ice retreated but then for some reason around 12,500 years ago the temperature abruptly plummeted again by nearly 5OC and remained that way for 1,300 years before warming again. During this period deep sea cores show that ice-bergs extended as far south as Portugal. Broecker believes that what happened was the conveyor turned off. Evidence for this is found in sediment in the Gulf of Mexico (depleted in Oxygen 18) and sediment on the slopes of the Bermuda Rise. During the Younger Dryas the mud-dwelling foraminfera showed the chemical imprint of the Antartic bottom water not the Atlantic Deep water that normally flows onto the Bermuda Rise. This is evidence for showing that at that time the conveyor belt was weak if flowing at all.

At the start of the Younger Dryas a huge lake of glacial meltwater called Lake Agassiz started to flow southwareds. At first it flowed into the Gulf of Mexico from the mississipi (oxygen 18 depleted sediment has been discovered there) then thropugh the great lakes to the St Lawrence. All this freshwater flowing into the North Atlkantic diluted the saltwater. The conveyor belt is essentially driven by the dense salty cold water in the North Atlantic sinking. When the waters from Lake Agassiz flowed into the North Atlantic it meant that the water was not salty enough to sink. It is likely that only a 1% change in salinity is enough to tip the balance. When the conveyor belt weakens or stops it has coincided with disruptions in the convection system in the North Sea. Broecker certainly believes that fresh water is the cause of conveyor shutdown as it stops the convection system. If the conveyor belt weakens so does the heat it transports back to the North Atlantic, cooling the Northern Hemisphere even more. This is what scientists believe caused the Younger Dryas Ice-age and probably the cause of smaller ice-ages since. Whether the freshwater comes from icebergs moving down like the Heinrich events or the melting of ice sheets the result is the same. As the temperature cools in the Northern Hemisphere the global hydrological cycle is effected. The air becomes drier and eventually less evaporation and precipitation slows the icy freshwater deluge into the North Atlantic. Cool air holds less moisture. A global cooling will effect the ocean temperatures and currents in the tropical pacific which dramatically affects worldwide weather. This is the system that today p

Some topics in this essay:
North Atlantic, , Laboratory Princeton, Ordovician Silurian, Oxygen Isotopes, Driven Milankovitch, La Nina, Rusty Lotti, Labrador Sea, Past History, conveyor belt, north atlantic, climate changes, oxygen 18, ocean circulation, hydrological cycle, climate change, thermohaline circulation, northern hemisphere, ice sheet, ocean circulation system, thermohaline circulation called, conveyor belt weakens, depleted oxygen 18, medal geological society,