Summary
Oxygen isotope ratios (d18O) of foraminifera in marine sediment records have fundamentally shaped our understanding of the ice ages and global climate change. Interpretation of these records has, however, been challenging because they reflect contributions from both ocean temperature and ice volume. Here, instead of disentangling, we reconstruct global benthic foraminiferal d18O across the last deglaciation (18-11.5 ka) with ice volume constraints from fossil corals and ocean temperature constraints from ice core noble gases. We demonstrate that, while ocean temperature and ice volume histories are distinct, their summed contributions to d18O agree remarkably well with benthic d18O records. Given the agreement between predicted and observed d18O, we further build upon recent insight into global energy fluxes and introduce a framework to quantitively reconstruct top-of-atmosphere net radiative imbalance, or Earth's energy imbalance, from d18O. Finally, we reconstruct 150,000 years of energy imbalance, which broadly follows Northern Hemisphere summer insolation but shows millennial-scale energy gain during the cold intervals surrounding Heinrich events. This suggests that, in addition to external forcing, internal variability plays an important role in modifying the global energy budget on long (millennial-plus) timescales. While generally tracking Northern Hemisphere summer insolation, the Earth gained energy during cold millennial scale events throughout the past 150,000 years, according to an analysis of benthic oxygen isotopes.
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