100-kyr paced climate change in the Pliocene warm period, Southwest Pacific

The mid to late Pliocene (~4.2-2.8 Ma.) represents an experiment in climate
sensitivity to orbital pacing in which nearly all continental ice was confined to the
Southern Hemisphere. Most studies have emphasized the dominant role of obliquity in
determining changes in ice volume and temperature at this time, although most records
come from the Northern Hemisphere, instead of the hemisphere where the bulk of ice
volume resided. We present the first orbitally-resolved, mid to late Pliocene Southern
Hemisphere paired records of surface and subsurface variability from two deep ocean
archives from the Southwest Pacific Ocean. These records indicate dominance of low
frequencies centered at ~100 kyr for this time period. Because these signatures extend
coherently and synchronously from mid-depth water properties (δ13C, δ18O of benthic
foraminifera), which have their chemistry set in the subantarctic belt, to the surface
(alkenone-derived SST estimates), we infer the fingerprint of the ~ 100 kyr cycles must
have extended over a large region of the Southern Hemisphere. We propose that
nonlinearities in climate response to precessional forcing- most likely through ice sheet
and/or carbon cycle behavior- generated the observed low frequency behavior. A review
of previously published mid to late Pliocene time series suggests that the ~100 kyr
pacing may be a global phenomenon and that major circa-100 kyr excursions in
Pliocene climate were an important overlay to the underlying 41 kyr glacial-interglacial
rhythm. These results caution against using existing Pliocene isotopic templates as a
ways to assessing stratigraphy or developing a time scale.