Project OC2

Rainfall in tropical Africa depends on the intensity, width and latitudinal position of the tropical rainbelt that oscillates seasonally between about 20°N and 20°S (Nicholson 2008). Variability of rainfall over Africa is characterized by a strong multi-decadal component. For example, precipitation in West Africa was at least 50% greater in the 1950s and early 1960s than in the subsequent dry decades. Over the same period, other regions (e.g. Amazonia) experienced a pronounced and abrupt increase in precipitation (Soubies et al. 2005). Instrumental records suggest that dry/wet periods are triggered by changes in the large-scale distribution of seasurface temperature (e.g., Balas et al. 2007) which is, among other factors, influenced by the heat transport due to the Atlantic meridional overturning circulation (Newell and Hsiung 1987). However, due to the shortness of the observational record, the influence of the largescale ocean circulation on tropical rainfall is still elusive. In this Project, we intend to study the link between precipitation and ocean circulation by reconstructing the decadal- to millennial-scale variability of surface-water hydrography and tropical rainfall. Our investigations will be based on several high-temporal-resolution sites in the Indian and Atlantic Ocean, covering the latitudinal extent of the modern tropical rainbelt. These sites will allow for a detailed land-sea correlation through the complementary use of terrestrial and marine proxies. In addition to existing core material, a proposal for carrying out a METEOR cruise to the northeast Brazilian shelf has been submitted to the DFG. In close collaboration with Projects OC1, OC4 and OC5 we will use state of the art circulation models to test dynamical hypotheses on the coupling between ocean circulation and tropical precipitation. Our paleoenvironmental reconstructions will be connected to studies of particle transport (GB1) and sediment dynamics at continental margins (SD2 and SD3). The planned Project meets with the goals of PAGES Focus 3 “Global Earth-System Dynamics”.