Can the ocean amplify climate change or regulate it? In collaboration with Ros Rickaby of Oxford University, we have just provided some new insights into this question (Bard & Rickaby, 2009, Nature). Our work focuses on a problem that is still debated, but fundamental to climatology: the CO2-temperature relationship on glacial-interglacial timescales and ocean feedbacks. We propose an amplification mechanism linked to the "warm route" of the large-scale oceanic circulation return, overly named global thermohaline circulation and often represented, to oversimplify, by an enormous "conveyor belt" connecting the various deep basins of the Atlantic, Indian and Pacific oceans.
To this end, we have studied the role of the spatio-temporal variability of theAgulhas Current and its dependencies (retroflection and eddies), in particular the marine current of warm, salty water that flows at the surface from the Indian Ocean to the Atlantic Ocean, south of Africa. This is a complex oceanographic phenomenon, which originates in the Strait of Mozambique, between Madagascar and the African continent. In this region, a warm surface current, the Agulhas Current - similar to the Gulf Stream or Kuroshio in the Pacific - flows southwards along the coast of Africa. For the most part, it flows back eastwards just south of Madagascar (retroflection current). But part of it escapes westwards in the form of eddies, or rings, of warm, salty water that pass the Cape of Good Hope and mix with the surface waters of the South Atlantic. This "hot route" is studied today by satellites observing the ocean's topography, as well as by those looking at the "color" of surface waters to deduce their temperature (IR) or chlorophyll content.
