Boundary conditions have not remained constant throughout the Holocene. Evidence from varved sediments obtained from the anoxic Cariaco Basin off the coast of Venezuela indicates significant migration of the mean latitude of the ITCZ over the last 14,000 years (Haug et al. 2001). This interpretation is based on the fluctuations in the seasonal hydrological cycle displayed in the high-resolution (subdecadal) bulk sedimentary metals record, resulting from the changing length/ intensity of the annual dry and wet seasons. Intensified/lengthened wet seasons result in increased river discharge, rich in metals, while intensified/lengthened dry seasons result in increased biogenic silica, a result of increased trade wind-driven upwelling on the basin.
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