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

What could cause the conveyor to turn off?

The earth’s past is full of dramatic climate changes. Many glacial advances and retreats have occurred during the last billion years of Earth history. Large, important glaciations occurred during the late Proterozoic (between about800 and 600 million years ago), during the Pennsylvanian and Permian (between about 350 and 250 million years ago), and the late Neogene to Quaternary (the last 4 million years). Somewhat less extensive glaciations occurred during parts of the Ordovician and Silurian (between about 460 and 430 million years ago). It has been discovered that one of the reasons for large climate changes are the Milankovitch cycles; cyclical changes in earths orbit which change the amount of sunlight falling on the northern hemisphere. We have also experienced smaller more abrupt climate changes. Research has been carried out to find out what caused them. The clues are preserved in ice sheets and deep-sea sediments. Cores of sea-sediments record temperatures and circulation patterns. Cores of the two mile thick Greenland ice sheet record Oxygen isotopes, CO2 levels and temperature for tens of thousands of years. Broecker first became very interested in the effect of the conveyor belt on climate change in 1984 after a lecture by Hans Oeschger – University of Bern. Oeschger was studying ice-cores from the Greenland ice sheet. These ice cores are a unique record of what has happened to the weather, for the last hundred thousand years.

Further work has been carried out on sediment cores to determine oceanic influences by various people. In 1995 Delia Oppp and ScottLehman of Woods Hole analysed a core from the east flank of the Mid Atlantic Ridge. They analysed carbon isotopes in forams. Their results showed major shifts in the operation of the conveyor belt. Gerard Bond and his wife Rusty Lotti analysed a core containing iceberg-deposited sediment from latitude 50 degrees north (latitude of the south coast of England) called DSDP 609. The results from this core showed deposits of light and dark sediment some of which contained limestone. This limestone it turned out came from the Hudson Strait. John Andrews – University of Colorado and Hartmut Heinrich had both identified the same layers in core samples from the Labrador Sea and south of DSDP 609. Bond determined that at various points a huge ice sheet had dominated the Hudson strait eventually creating an ‘armada’ of icebergs that floated and melted in the Labrador Sea before moving into the North Atlantic. Bond called these ‘Heinrich events’. Once the freshwater from the ice-bergs hit the North Atlantic the conveyor starts to weaken.

Some topics in this essay:
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