Mid to late 20th century freshening of the western tropical South Atlantic triggered by southward migration of the Intertropical Convergence Zone

In the tropical Atlantic Ocean, Intertropical Convergence Zone (ITCZ) is an important climate feature controlled by interhemispheric sea surface temperature (SST) gradient, and greatly influences rainfall patterns over adjacent continents. To better understand ITCZ dynamics in context of past future change, long-term oceanic records are needed, but observational data limited temporal extent. Shallow-water corals provide seasonally-resolved archives variability ocean. Here we present stable oxygen (δ18O) carbon (δ13C) isotope values a Siderastrea stellata coral from northeastern Brazil (Maracajaú, ~5°S). We show that trends record δ18O not primarily driven SST hydrological changes at surface. Combining with instrumental SST, first reconstruction seawater (δ18Oseawater) western South back to early 20th century, parameter related salinity. The reconstructed δ18Oseawater indicate prominent freshening between mid-1940's mid-1970's, which coincides weakening gradient during this time interval. Our results suggest weakened resulted southward shift thermal equator was accompanied migration ITCZ, resulting mid late century.