Multiproxy Reduced‐Dimension Reconstruction of Pliocene Equatorial Pacific Sea Surface Temperatures

Abstract

A controversial aspect of the Pliocene climate system is a posited permanent sea surface temperature (SST) distribution resembling that during El Niño events, which is largely inferred from sea surface temperatures reconstructed from several sites in the equatorial Pacific. We utilize a reduceddimension methodology on a compilation of previously published multiproxy (Mg/Ca, U k′ 37 , TEX 86 , and foraminifer assemblages) Pliocene SST records from the equatorial Pacific to reconstruct spatial and temporal snapshots of SST anomalies and a time series of Niño indices from 5 to 1 Ma. The use of multiple proxies increases the number of study sites and thereby improves the robustness of the reconstruction. We find that the early Pliocene equatorial Pacific was characterized by a reduced zonal SST difference due to minimal change in the west and extreme warmth in the east which peaked at 4.3 Ma. The intensity of this mean El Niño-like SST state then gradually diminished toward modern conditions. We also use the Pliocene Niño 4 time series to estimate the past strength of Indian Summer Monsoon given the modern correlation of it to the Niño 4 index. Results indicate the monsoon was weaker throughout the study interval with weakest conditions (~37% less rainfall than modern) occurring at 4.3 Ma, congruent with regional proxy records. In summation, this reduced-dimension approach spatially and temporally resolves the warm mean state of the Pliocene equatorial Pacific and has numerous applications to inferences of paleoclimate conditions in distal regions teleconnected to El Niño today.

Constraints on the paleoelevation history of the Eastern Cordillera of Colombia from its palynological record

“…In the other approach, one virtually ignores taxonomy and uses only the physiognomic characteristics of different taxa (without assigning them names), including sizes and shapes of the plant organs. Most commonly, leaves are used (e.g., Spicer et al, 2009Spicer et al, , 2011Wolfe, 1993Wolfe, , 1995. Investigators first estimate the fractions (percentages) of the many characteristics in fossil assemblages, like leaves with (or without) teeth or sizes, within a given range.…”

“…Such differences tend to be greater at high than low latitudes, and therefore even if the mean temperature of Earth at 15-3 Ma was, for example, 3 °C warmer than today, that greater warmth seems likely to have been smaller, and perhaps negligible in the Eastern Cordillera. Before 4-3 Ma, however, the eastern tropical Pacific Ocean was warmer than today by ~4 °C, as it is during major El Niño events (e.g., Dekens et al, 2007;Lawrence et al, 2006;Ravelo et al, 2006;Wara et al, 2005;Wycech et al, 2020). Assuming that modern El Niño teleconnections apply to past climates, the Sabana de Bogotá before 4-3 Ma would have been warmer by ~2 °C than today (Pérez-Angel and Molnar, 2017).…”

Coupled Mg/Ca and Clumped Isotope Measurements Indicate Lack of Substantial Mixed Layer Cooling in the Western Pacific Warm Pool During the Last ∼5 Million Years

“…Recent data compilations show that the exact magnitude of the reconstructed Pliocene temperature gradient depends on the time window within the Pliocene selected for comparison, which proxy data is used and how they are analyzed (McClymont et al, 2020). Nonetheless, there is agreement that the equatorial temperature gradient was reduced during the Pliocene (Tierney, Haywood, et al, 2019;Wycech et al, 2020), mainly because there is unequivocal evidence that the East Pacific cold tongue was considerably warmer than today in the Pliocene. Thus, the debate centers on data from the west, specifically, the Mg/Ca-based evidence that indicates that the IPWP was not warmer than today in the Pliocene (Wara et al, 2005).…”

Reconstructing Pliocene West Pacific Warm Pool Hydroclimate Using In Situ Microanalyses on Fossil Planktic Foraminifer Shells

“…However, modern-like SSTs for the early Pliocene WPWP are suspect given that these previous foraminifer Mg/Ca-derived records did not account for Pliocene Mg/Ca sw ratios and the fact that U k' 37 is an imprecise paleothermometer at temperatures greater than 30°C (Tierney and Tingley, 2018). These discrepancies notwithstanding, we note that the Pliocene SST record presented in this study for Site 806 (revised from Wara et al, 2005) was included in a recent statistical multi-proxy reconstruction of equatorial Pacific SSTs (Wycech et al, 2019). The study concluded that the Pliocene west-east SST difference was reduced by 4.4°C relative to the recent (0-0.5 Ma) average, which is consistent with El Padre conditions during the early Pliocene.…”

“…The redistribution of moisture in the modern equatorial Pacific is governed by Walker atmospheric circulation, which imparts an asymmetric zonal (E-W) precipitation gradient with wetter conditions in the west relative to the east (Bjerknes, 1969). However, several previous studies have posited that El Niño-like conditions, termed "El Padre" (Ravelo et al, 2014), prevailed across the equatorial Pacific during the early Pliocene as evidenced by a weakened zonal SST gradient and a deeper thermocline in the east Pacific (Cannariato and Ravelo, 1997;Chaisson and Ravelo, 2000;Dekens et al, 2008;Ford et al, 2015;Lawrence et al, 2006;Molnar and Cane, 2002;Philander and Fedorov, 2003;Ravelo et al, 2006;Seki et al, 2012;Wara et al, 2005;Wycech et al, 2019).…”