The enigma of Oligocene climate and global surface temperature evolution

By Charlotte L. O’Brien et al.

Falling atmospheric CO2 levels led to cooling through the Eocene and
the expansion of Antarctic ice sheets close to their modern size near
the beginning of the Oligocene, a period of poorly documented climate.
Here, we present a record of climate evolution across the entire
Oligocene (33.9 to 23.0 Ma) based on TEX86 sea surface temperature
(SST) estimates from southwestern Atlantic Deep Sea Drilling Project
Site 516 (paleolatitude ∼36°S) and western equatorial Atlantic Ocean
Drilling Project Site 929 (paleolatitude ∼0°), combined with a compilation
of existing SST records and climate modeling. In this relatively
low CO2 Oligocene world (∼300 to 700 ppm),warm climates similar to
those of the late Eocene continued with only brief interruptions,
while the Antarctic ice sheet waxed and waned. SSTs are spatially
heterogenous, but generally support late Oligocene warming coincident
with declining atmospheric CO2. This Oligocene warmth, especially
at high latitudes, belies a simple relationship between climate
and atmospheric CO2 and/or ocean gateways, and is only partially
explained by current climate models. Although the dominant climate
drivers of this enigmatic Oligocene world remain unclear, our results
help fill a gap in understanding past Cenozoic climates and the way
long-term climate sensitivity responded to varying background
climate states.

The full article is available on the Proceedings of the National Academy of Science website at https://www.pnas.org/content/117/41/25302


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