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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 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 (Sites 594 and 1125). These records indicate dominance of low frequencies centered at ~100 kyr for this time period. Because these signatures extend coherently and synchronously from middepth water properties (δ¹³C, δ¹⁸O of benthic foraminifera), which have their chemistry set in the subantarctic belt, to the surface (alkenone‐derived surface temperature estimates, color reflectance, and magnetic susceptibility), we infer that 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. A review of published mid to late Pliocene time series suggests that the ~100‐kyr pacing may be a widespread phenomenon and that major approximately 100‐kyr excursions in Pliocene climate were an important overlay to the underlying 41‐kyr glacial‐interglacial rhythm. These results caution against uncritical use of existing Pliocene isotopic templates to construct high‐resolution age models.

The transition from the warm, stable climate of the Pliocene to the progressively colder glaciations of the Pleistocene, as well as the climate system's evolving response to stationary orbital forcing over the Pleistocene, beg important questions about fundamental climate processes relevant to understanding the impacts of modern anthropogenic forcing of the Earth's energy budget. Here, we gain insight into the evolution of Plio‐Pleistocene climate by generating an alkenone‐derived, orbitally resolved sea surface temperature (SST) record from Ocean Drilling Program Site 1125 in the southwest Pacific. We compare our data set to midlatitude and equatorial SST records and to the benthic ∂¹⁸O signal in order to evaluate similarities and differences in climate response between the hemispheres and across latitudes over the Plio‐Pleistocene. Secular trends indicate first‐order symmetry between the Northern and Southern Hemispheres in the magnitude of mean, glacial, and interglacial cooling. However, the tight coupling that is observed on both secular and orbital timescales between Northern Hemisphere, high latitude, and tropical upwelling climate throughout the last 4 Ma does not extend to Southern Hemisphere climate records as Northern Hemisphere glaciation intensifies in the late Pliocene. The 41‐kyr signal remains weak at Site 1125 across the late Pliocene transition but strengthens in conjunction with a major increase in global climate system sensitivity to obliquity forcing beginning around 1.8 Ma. Our analysis points to regionally varied responses across the late Pliocene transition and the emergence of a global feedback mechanism and strengthened obliquity‐band climate sensitivity just prior to the mid‐Pleistocene transition.