NOAA/WDS Paleoclimatology - Raymo 1992 DSDP Site 607 Isotope Data and Age Models

Deep sea δ18O records from benthic foraminifera provide a high-resolution overview of global ice volume changes over the last three million years, the interval typically referred to as the Northern Hemisphere Ice Ages. Prior to 2.7 Ma global climate appears to have been typically warmer than at present and the possibility of Antarctic deglaciation is suggested by depleted δ18O values observed prior to 2.9 Ma. Between 3.1 and 2.6 m.y., cold/warm oscillations are superimposed upon a gradual cooling trend which culminated with the growth of significant continental ice sheets in the northern hemisphere (equivalent to ~60m sea level change). Climate conditions during these cold extremes would be most analogous to late Pleistocene isotopic substages 5b and 5d. Since 2.7 Ma interglacial climate extremes have rarely been warmer than the Holocene. Significant 100 Kyr variance is observed during the late Pliocene interval and suggests that large ice sheets are not needed for climate to vary at the 100 Kyr eccentricity frequency. However, the rapid rates of climate change observed for late Pleistocene “terminations” are not typically observed earlier in the Plio-Pleistocene, although rates of ice decay are still usually faster than rates of ice growth. Fluctuations in North Atlantic Deep Water production (indicated by a δ13C gradient proxy) are not uniquely linked with climate transitions as indicated by δ18O and ice core CO2 records, implying that NADW production may be responding to factors other than global continental ice volume.