Meridional shifts of the Atlantic intertropical convergence zone since the Last Glacial Maximum

The intertropical convergence zone is a near-equatorial band of intense rainfall and convection. Over the modern Atlantic Ocean, its annual average position(1) is approximately 5 degrees N, and it is associated with low sea surface salinity and high surface temperatures. This average position has varied since the Last Glacial Maximum, in response to changing climate boundary conditions(2-15). The nature of this variation is less clear, with suggestions that the intertropical convergence zone migrated north-south away from the colder hemisphere(10-15) or that it contracted and expanded symmetrically around its present position(2). Here we use paired Mg/Ca and delta O-18 measurements of planktonic foraminifera for a transect of ocean sediment cores to reconstruct past changes in tropical surface ocean temperature and salinity in the Atlantic Ocean over the past 25,000 years. We show that the low-salinity, high-temperature surface waters associated with the intertropical convergence zone migrated southward of their present position during the Last Glacial Maximum, when the Northern Hemisphere cooled, and northward during the warmer early Holocene, by about +/- 7 degrees of latitude. Our evidence suggests that the intertropical convergence zone moved latitudinally over the ocean, rather than expanding or contracting. We conclude that the marine intertropical convergence zone has migrated significantly away from its present position owing to external climate forcing during the past 25,000 years.