1 )uring the last climatic cycle, sea surface temperature and salinity changed in the whole ocean, noticeably in the North Atlantic, which is an area of deep water formation. This change resulted in major variations of the thermo-haline circulation and the CO2 cycle. This chapter describes the main mechanisms responsible for these changes: (a) insolation forcing responsible for changes in the climate system exhibiting periodicities of 19, 23, and 41 kyr and (b) interaction between the cryosphere and the ocean, which resulted in rapid (centennial) climatic changes.

The palcoclimatic record shows that the thermo-haline circulation and the Earth's climate are extremely sensitive to minor perturhations, such as freshwater discharge at high latitude into the North Atlantic Ocean. Under pure natural conditions, the geological data indicate that warm times arc associated with active thermo-haline circulation, whereas reduced thermo-haline circulation prevailed during glacial times. If the global warming induced by human activities would result in enhanced precipitation over the North Atlantic, the resulting salinity changes might act as a massive iceberg discharge occurring during the glaciation. This would reduce the mean flux of deep water formed annually, the rate of thermo-haline circulation, and the oceanic heat flux brought to the Norwegian Sea, and it would deeply affect the European climate.

14.1 Introduction

Over the past 20 years, micropaleontological and stable isotope analysis of deep sea sediments has shown alternations between glacial and interglacial conditions, which are manifested by waning and waxing of large continental ice sheets. They coincide with changes in temperature, salinity, and circulation in the ocean, as well as changes in temperature and humidity over the continents. Geological data also provides strong support for the Milankovitch theory, which relates climatic variations to insolation changes due to changes in the Earth's orbital parameters (Hays et aL, 1976). This mechanism leads primarily to changes in the intensity of the seasonal cycle, whereas the mean annual insolation budget is rather constant. This shows that the climate system is extremely sensitive to minor perturbations of the atmosphere energy budget.

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