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

Abstract

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.

Aridification of Northwest Australia and Nutrient Decline in the Timor Sea During the 40 Kyr World

“…As discussed above, the variability in terrigenous input and productivity at Site U1483 reveals a significant transition period such that more power was concentrated at orbital bands and was more coherent with orbital forcing after ∼1,650 ka (Figures 4 and 5). In the obliquity band, the increase in sensitivity and coherence from ∼1,800 to ∼1,600 ka observed in our productivity and bottom oxygen records has also been observed in globally widespread records (deMenocal, 1995;Lawrence et al, 2006;Li et al, 2011;Martinez-Garcia et al, 2010;Peterson et al, 2020). To explain the increase in sensitivity to obliquity forcing, previous studies proposed that orbital-scale pCO 2 change likely played a major role to coordinate the response of tropical climate to high-latitude forcing, potentially through coupling with the enhanced iron fertilization-CO 2 feedback due to increased subantarctic iron deposition (Herbert et al, 2010;Lawrence et al, 2006;Martínez-Garcia et al, 2011;Peterson et al, 2020).…”

“…In the obliquity band, the increase in sensitivity and coherence from ∼1,800 to ∼1,600 ka observed in our productivity and bottom oxygen records has also been observed in globally widespread records (deMenocal, 1995;Lawrence et al, 2006;Li et al, 2011;Martinez-Garcia et al, 2010;Peterson et al, 2020). To explain the increase in sensitivity to obliquity forcing, previous studies proposed that orbital-scale pCO 2 change likely played a major role to coordinate the response of tropical climate to high-latitude forcing, potentially through coupling with the enhanced iron fertilization-CO 2 feedback due to increased subantarctic iron deposition (Herbert et al, 2010;Lawrence et al, 2006;Martínez-Garcia et al, 2011;Peterson et al, 2020). Atmospheric pCO 2 feedbacks likely amplify the climatic response to obliquity forcing as global ice expanded, resulting in a higher sensitivity of the climate system to obliquity forcing.…”

Southward Shift and Intensification of the Intertropical Convergence Zone in the North Pacific Across the Mid‐Pleistocene Transition

“…As strengthening Walker Circulation across the MPT would typically induce a rainfall decline in the CEP, we suggest that the intensification of the Walker Circulation is not the driver of our SSS change. Instead, we suggest that the decreasing SSS trend reflects the increased precipitation due to the southward shift and intensification of ITCZ in the North Pacific, and/or the increased advection of (Dyez & Ravelo, 2013 this study), mid-NH (ODP1208, ODP1020, ODP1021, ODP1014, ODP1012; Brierley et al, 2009;Dekens et al, 2007;LaRiviere et al, 2012;Liu et al, 2008) and mid-SH (DSDP593, ODP1125, ODP1123, ODP1237; Crundwell et al, 2008;Dekens et al, 2007;McClymont et al, 2016;Peterson et al, 2020); (b) meridional SST gradient anomaly (Fedorov et al, 2015) and SST gradient anomaly between the WEP and northeast Pacific (NEP, ODP1020, ODP1021, ODP1012, ODP1014), and SST gradient anomaly between the eastern equatorial Pacific (EEP, U1337 and ODP846; Herbert et al, 2010;Liu et al, 2019) (Cai et al, 2012). The SST anomaly is calculated from the 200 kyr running average subtracting the maximum value over the whole-time window.…”

“…Comparison of proxy records of sea surface temperature (SST) gradients and sea surface salinity (SSS). (a) SST anomalies of the western equatorial Pacific (WEP) (MD2140, ODP806; de Garidel-Thoron et al, 2005; Medina-Elizalde & Lea, 2005), ODP871(Dyez & Ravelo, 2013 this study), mid-NH (ODP1208, ODP1020, ODP1021, ODP1014, ODP1012;Brierley et al, 2009;Dekens et al, 2007;LaRiviere et al, 2012;Liu et al, 2008) and mid-SH (DSDP593, ODP1125, ODP1123, ODP1237;Crundwell et al, 2008;Dekens et al, 2007;McClymont et al, 2016;Peterson et al, 2020); (b) meridional SST gradient anomaly(Fedorov et al, 2015) and SST gradient anomaly between the WEP and northeast Pacific (NEP, ODP1020, ODP1021, ODP1012, ODP1014), and SST gradient anomaly between the eastern equatorial Pacific (EEP, U1337 and ODP846;Herbert et al, 2010;Liu et al, 2019) and southeast Pacific (southeastern Pacific, ODP1237;Dekens et al, 2007); (c) SST gradient anomalies between northern and southern margin of WPWP; (d) SSS records in the WPWP; (e) East Asian summer monsoon rainfall index in the Chinese Loess Plateau(Meng et al, 2018); (f) pollen A/C in Qaidam Basin(Cai et al, 2012). The SST anomaly is calculated from the 200 kyr running average subtracting the maximum value over the whole-time window.…”

Seascape Genomics and Phylogeography of the Sailfish (Istiophorus platypterus)

“…The Plio–Pleistocene transition (PPT) (∼3.3–2.8 Ma) paved the way for the interglacial cycles of the Pleistocene, resulting in cooler temperatures between the ATL and Indo-Pacific oceans ( Peterson et al 2020 ). In addition, the closure of major oceanic gateways, such as the Isthmus of Panamá and the Indonesian Throughflow constriction, are both accountable for the escalation of glacial conditions during the PPT strengthening phylogeographic barriers worldwide ( Bahr et al 2022 ).…”