LATE PLEISTOCENE CARBONATE STRATIGRAPHY ON ONTONG JAVA']JAVA PLATEAU IN THE WESTERN EQUATORIAL PACIFIC

Late Pleistocene carbonate cycles on Ontong-Java Plateau are characterized by maxima during deglaciations (deglacial preservation spikes) and by minima during transitions from interglacial to glacial conditions (ice growth dissolution spikes). Superimposed on these short-period fluctuations there is a long-term oscillation of carbonate contents with a period of nearly 400 ky, the Brunhes Dissolution Cycle. Dissolution-related sand fraction profiles (> 63-mu-m) indicate that the lysocline was at a water depth of about 3.6 km during deglacial transitions, and that it rose up to 2.6 km during the stages of ice growth. A fluctuation of the lysocline by 1 km can account for more than half of the total amplitude of the observed carbonate cycles, assuming a linear increase in carbonate dissolution rates with increasing water depth below the lysocline and a constant CCD. A shoaling of the lysocline during ice buildup may result from downward transfer of metabolic CO2 from intermediate waters to greater depths in the water column. Enhanced carbonate dissolution below 2.6 km increases alkalinity in deep waters, predisposing the system toward reducing atmospheric CO2 partial pressure during a subsequent period.