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Determining the timing and amplitude of tropical sea surface temperature (SST) change
is an important part of solving the puzzle of the Plio-Pleistocene ice ages. Alkenone-based
tropical SST records from the major ocean basins show coherent glacial-interglacial
temperature changes of 1 degrees to 3 degrees C that align with (but slightly lead)
global changes in ice volume and deep ocean temperature over the past 3.5 million
years. Tropical temperatures became tightly coupled with benthic delta18O and orbital
forcing after 2.7 million years. We interpret the similarity of tropical SST changes,
in dynamically dissimilar regions, to reflect "top-down" forcing through the atmosphere.
The inception of a strong carbon dioxide-greenhouse gas feedback and amplification
of orbital forcing at approximately 2.7 million years ago connected the fate of Northern
Hemisphere ice sheets with global ocean temperatures since that time.