Stable isotope ratios of benthic foraminifera in mid-Pleitsocene sediments of ODP Site 108-664 in the equatorial Atlantic

Five delta13C records from the deep ocean, extending back to 1.3 Ma, were examined in order to constrain changes in mean ocean carbon isotope composition and thermohaline circulation over the 41- to 100-ka climate transition. These data show that significant perturbations in mean ocean carbon chemistry were associated with the mid-Pleistocene climate transition. Notable features of the last 1.3 Myr are (1) a pronounced ~0.3? decrease in mean ocean delta13C between 0.9 and 1.0 Myr, followed by a return to pre-1.0 Ma values by 400 ka B.P., which we propose was due to the onetime addition of isotopically depleted terrestrial carbon to the ocean, possibly associated with an increase in global aridity (and decrease in the size of the biosphere) across the 41- to 100-ka transition; (2) no change in the Atlantic-Pacific (A-P) delta13C gradient over the last 1.3 Myr, suggesting no change in mean ocean nutrient content accompanied the addition of light carbon; and (3) stronger vertical nutrient fractionation in the North Atlantic in the middle Pleistocene between sites 607 and 552, suggesting weaker North Atlantic Deep Water formation at this time relative to the early and late Pleistocene. We also find evidence for a more pronounced deep recirculation gyre in the western North Atlantic basin in the early Brunhes, as evidenced by "aging" of deep northern basin water (site 607) relative to deep water in the equatorial Atlantic (site 664).

B-isotope and Mg/Ca ratios of planktonic foraminifera from ODP Hole 108-668B and esimates of salinity, alkalinity and pCO2 (Table 1)

Knowledge of past atmospheric pCO2 is important for evaluating the role of greenhouse gases in climate forcing. Ice core records show the tight correlation between climate change and pCO2, but records are limited to the past ~900 kyr. We present surface ocean pH and pCO2 data, reconstructed from boron isotopes in planktonic foraminifera over two full glacial cycles (0-140 and 300-420 kyr). The data co-vary strongly with the Vostok pCO2-record and demonstrate that the coupling between surface ocean chemistry and the atmosphere is recorded in marine archives, allowing for quantitative estimation of atmospheric pCO2 beyond the reach of ice cores.