Quaternary climate change as revealed by calcium carbonate fluctuations in western Equatorial Atlantic sediments

Abstract

Fluctuations of total calcium carbonate content in eight western Equatorial Atlantic cores are used to evaluate Quaternary climate change. Both pelagic Mid-Atlantic Ridge and terrigenous-rich continental-rise cores that span the last 130,000 years show identical carbonate fluctuations which accurately reflect climatic oscillations during the Holocene, Wisconsin Glacial, and Last Interglacial. The carbonate fluctuations reveal a 20,000-year periodicity for warm-cold (interstadial-stadial) cycles with carbonate maxima reflecting interstadials and minima reflecting stadials. The carbonate fluctuations correlate in detail with other time scales for climatic oscillations deduced previously from radiometrically-dated sea-level maxima, solar insolation fluctuations, and North American ice-margin fluctuations. Pelagic cores spanning the last 500,000 years do not clearly reflect the 20,000-year cold-warm cycles but do show the 100,000-year glacial-interglacial cycles previously revealed by oxygen-isotope variations. The carbonate fluctuations in another core, which contains a continuous record of the last 1,800,000 years, indicates that 15 to 20 of these 100,000-year cycles have occurred during this period. The carbonate fluctuations of two cores suggest that the Atlantic circulated faster during glacials than during interglacials. A core from the Demerara Plateau (2000-m depth) has anomalous carbonate fluctuations plus expanded interglacial and shortened glacial sections that suggest faster circulation of surface water masses during glacials. The sediments of a pelagic core, which were deposited beneath the Antarctic Bottom Water, have undergone severe carbonate dissolution during glacials. These cycles apparently indicate an increase in production and faster circulation of the Antarctic Bottom Water during glacials.