100‐kyr Paced Climate Change in the Pliocene Warm Period, Southwest Pacific

Abstract

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.

Plio‐Pleistocene Hemispheric (A)Symmetries in the Northern and Southern Hemisphere Midlatitudes

“…For 0.13–1.0 Ma, our age model is in alignment with the age model used by Schaefer et al (). In the oldest part of our record, our chronology also agrees well with the age model developed for the Pliocene interval of Site 1125 by Caballero‐Gill et al (), though both chronologies imply an offset toward younger ages during the latest Pliocene and early Pleistocene than those assigned to Site 1125 by Sabaa et al (). Our age model is much more highly temporally resolved than the biostratigraphy for Site 1125 (Shipboard Scientific Party, ) and is based on tuning cycles recorded by the same proxy (e.g., ∂ 18 O) rather than aligning related proxies (reflectance and ∂ 18 O), which may account for the different results.…”

“…Site 1125 SST (green—this study, Caballero‐Gill et al, ) is shown in the context of North Pacific SST (yellow—Site 1012; LaRivière et al, ; brown—Site 1012; Venti et al, ), tropical upwelling SST (red—Site 846; Lawrence et al, ), South Atlantic SST (purple—Site 1090; Martínez‐Garcia et al, ), North Atlantic SST (blue—Site 607; Lawrence et al, ), and the benthic ∂ 18 O stack (black—Lisiecki & Raymo, ). Heavy lines represent a running 200 kyr average.…”

“…The sampling resolution implied by our age model is 2.1 ± 0.9 kyr over the last 2.8 Ma. We join our novel SST data to the Site 1125 SST record from 2.8–4.2 Ma published by Caballero‐Gill et al (), which has a sampling resolution of 2 kyr. The two records overlap over an interval of approximately 100 kyr, where they show strong agreement in both U k′ 37 and ∂ 18 O values (Figure S2) and in inferred age.…”

“…The two records overlap over an interval of approximately 100 kyr, where they show strong agreement in both U k′ 37 and ∂ 18 O values (Figure S2) and in inferred age. From 2.8–4.2 Ma, we adopt the age model of Caballero‐Gill et al (), adding 0.4 m to the depth scale to accommodate our revised composite depth scale for 0.13–2.8 Ma. Combined, the two data sets comprise the most highly resolved (2 kyr) Southern Hemisphere SST record to span the last 4.2 Myr.…”

“…Martínez‐Garcia et al () observed weak 41‐kyr spectral power in South Atlantic SST at Site 1090 (43°S) during the late Pliocene and early Pleistocene, followed by the emergence of a strong 41‐kyr signal around 1.6 Ma. In addition, Caballero‐Gill et al () note a dominant 100‐kyr signal in southwest Pacific SST during the Pliocene. Taken together, existing data sets establish tight coupling across Northern Hemisphere and tropical upwelling climate records over the course of the Plio‐Pleistocene, including a dominant and well‐coordinated 41‐kyr beat.…”