A high-resolution record of climate instability spanning ∼1.0 million years across the mid-Pleistocene transition.

摘要

I use oxygen isotopes of planktonic foraminiferal species Globigerinoides ruber from Ocean Drilling Program (ODP) Site 1058 in the subtropical northwestern Atlantic to construct a high-resolution climate record spanning the mid-Pleistocene transition from ∼411 Ka to 1.35 Ma. The main purpose of this study is to analyze climatic instability on both orbital and suborbital scales during a long transitional interval from dominant 41-kyr glacial cycles to more developed 100-kyr cycles. I provide age control based on two different models using Northern Hemisphere summer insolation and the ODP Site 677 G. ruber delta18O record of Shackleton et al. (1991) as tuning targets. The results indicate that independent of age control, the appearance and recurrence of significant millennial-scale variability with periods between 3 kyr and 8 kyr begins around 800 Ka. At this time, high-amplitude 4 to 8 kyr cycles become more frequent, with the highest amplitude millennial-scale variability occurring at ∼420 kyr during the most extreme glacial interval (Marine Isotope Stage, MIS 12) within the length of the record. I believe that the appearance of millennial-scale variability in association with the evolution of 100-kyr glacial cycles and the occurrence of high-amplitude millennial-scale variability during the most extreme glacial interval is consistent with the strong influence of a tall, thick northern ice sheet on atmospheric circulation patterns. In addition, consideration of the long-term trends in the delta18O record from ODP Site 1058 indicates a dramatic cooling event just after 900 Ka (MIS 22). This excursion is recorded in other regions in the Atlantic and Pacific Oceans supporting a global-scale, large magnitude cooling event during one of the major Pleistocene climate transitions.