Biogenic and terrigenous sedimentation at Ceara Rise, western tropical Atlantic, supports Pliocene–Pleistocene deep-water linkage between hemispheres

Abstract

Calcium carbonate percentages at Þve Ceara Rise sites were estimated at 1-to 2-k.y. intervals over the past 5 m.y., using reßectance spectroscopy and magnetic susceptibility proxies. From these estimates and detailed correlations between sites, gradients of calcite and terrigenous sediment accumulation rates in a depth transect of sites reveal variations in local climate and calcite dissolution related to deep-water masses. Relative to shallow sites on the southern Ceara Rise, accumulation rates of ter-rigenous sediments at deeper sites near the Amazon Fan were higher during glacial periods. Analogous variations in terrige-nous sedimentation before the expansion of Northern Hemisphere ice sheets ~3 m.y. ago suggests that tropical climate cycles occurred independently of polar glaciation. Decreasing accumulation rates of calcite with increasing water depth reveal patterns of carbonate dissolution, which varied on orbital timescales (10-100 k.y. periods) throughout the PlioceneÐPleistocene. Maximum dissolution at deep relative to shallow sites occurred in the transition from interglacial to glacial conditions, and maximum preservation occurred during global warming, at all orbital periods. If the local dissolution gradient is linked to relative contributions of North Atlantic Deep Water and Antarctic Bottom Water, this phasing of events conÞrms a key prediction of SPECMAP that deep-water adjustments may translate climate changes between hemispheres. Dissolution and preservation events, however, may also reßect a transient response to a net ßux of organic matter between the continents and the oceans during ice-age climate transitions.