Millennial-scale variability in mean ocean temperature

Abstract:

The mean ocean temperature (MOT) noble gas proxy has provided an opportunity for new insight into the links between ocean temperature, greenhouse gas forcing, and high latitude climate processes, because it allows for ocean temperature reconstruction on the ice core timescale. Due to its relatively recent development, the application of this proxy has been limited to the last two terminations and interglacial intervals. Here we present a new MOT reconstruction from 74 to 59 ka BP, covering the Marine Isotope Stage (MIS) 5-4 boundary, MIS 4, and part of the MIS 4-3 transition. Our record suggests that the 0.9±0.3°C of mean ocean cooling was not the main driver of the ~40 ppm decline in CO₂ during the MIS 5-4 transition but can explain most of the CO₂ drawdown that occurred over MIS 5. Intriguingly, the MOT lowering during the 5-4 transition is much shorter-lived than the atmospheric CO₂ concentration decrease, despite the fact that they begin simultaneously, consistent with the view that carbon cycle reorganization played a prominent role in this particular CO₂ decrease. The timing of ocean warming and cooling in our record indicates that millennial scale climate variability plays a crucial role in setting mean ocean temperature during this interval, as seen during other time periods such as the last deglaciation.