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Variations of the Global Overturning Circulation of the Ocean

The aim of the colloquium is to provide an inventory of knowledge on the Global Overturning Circulation (GOC) of the ocean for the past, present and future. Its Atlantic component (AMOC: Atlantic Meridional Overturning Circulation) may be already affected by the present climate change, a notable feature of which is the “warming hole” observed in recent surface temperature of the North Atlantic.

Nevertheless, the presence and amplitude of a long-term trend in AMOC and its relationship with temperature in modern observations remain a subject of debate due to a large high-frequency AMOC variability obscuring the relatively small deviation of instrumental data over the past few decades. However, on longer time-scales, the consequences of AMOC & GOC changes on climate are clearly seen as a global bipolar seesaw effect between both hemispheres.

For the future, numerical models show that AMOC weakening will probably accompany global warming due to the forthcoming emissions of anthropogenic CO2. The impact of the future amplitude of anthropogenic forcing on model simulations is also an additional source of uncertainty.

The invited speakers of the colloquium will provide diverse and up-to-date information on these different aspects and time scales, ranging from in situ observation of the oceanic circulation, its reconstruction on long time scales using paleoclimatic observations, its relationships with the oceanic carbon cycle and the different theories concerning its dynamics based on numerical models.