HOLOCENE VARIABILITY IN THE ATLANTIC INTERTROPICAL CONVERGENCE ZONE AND THE SOUTHWEST MONSOON

The abundance of the planktic foraminifer Globigerinoides sacculifer in Gulf of Mexico (GOM) Holocene sediments is a proxy for the average position of the Intertropical Convergence Zone (ITCZ). Comparison of abundance variations in G. sacculifer in marine cores from the western and northern Gulf of Mexico with terrestrial proxy records of precipitation (tree-ring width and packrat-midden occurrences) from New Mexico indicates that G. sacculifer abundance is also a proxy for intensity of the southwest monsoon. Northward migration of the ITCZ results in increased presence of warm tropical waters in the northern and western GOM and a stronger southwest monsoon; southward migration of the ITCZ results in decreased presence of warm tropical waters in the northern and southern GOM and a weaker southwest monsoon. Spectral analyses of G. sacculifer abundance variations in Gulf of Mexico cores and tree-ring precipitation records from New Mexico reveal periodicities that are similar to the periodicities observed in proxy records of solar activity. The GOM and New Mexico proxy records suggest that the average position of the ITCZ and changes in intensity of the southwest monsoon are linked to solar variability.