MILANKOVITCH CYCLES, ATLANTIC HEAT TRANSPORT, AND THE MID-PLEISTOCENE CLIMATE TRANSITION

Oxygen isotope values (d¹⁸O) from two planktonic foraminifera (Globigerinoides sacculifer and Neogloboquadrina dutertrei) serve as a proxy for northwestern subtropical surface ocean hydrography. High resolution (1 kyr) d¹⁸O records from an early Pleistocene (~1.1 to 1.5 Ma, Marine Isotope Stages (MIS) 40 to 48) and a mid-Pleistocene interval (~0.4 to 0.7 Ma, MIS 12 to 16) are examined to investigate subtropical ocean climate stability as northern hemisphere ice sheets grew larger and developed their 100 kyr cyclicity. This interval is an interesting period to study as little is known or understood about the mechanisms responsible for this transition. Preliminary results indicate that millennial-scale variability persists throughout the mid-Pleistocene interval. However, variability during glacial MIS 12 and 14 appears to be larger relative to that found during the interglacial period. This finding is consistent with previous studies of the late Pleistocene North Atlantic where the amplitude of millennial-scale variability is consistently higher during glacial than interglacial intervals (McManus et al., 1999). The d¹⁸O record from the 100 kyr dominated mid-Pleistocene interval will be compared to the 41 kyr dominated early Pleistocene interval to determine whether differences exist in the character of the millennial-scale fluctuations during an interval of time when ice sheet variations are known to have been of smaller magnitude.