Palaeoclimate reconstructions reveal a strong link between El Niño-Southern Oscillation and Tropical Pacific mean state

Abstract

The El Niño-Southern Oscillation (ENSO) is one of the most important components of the global climate system, but its potential response to an anthropogenic increase in atmospheric CO 2 remains largely unknown. One of the major limitations in ENSO prediction is our poor understanding of the relationship between ENSO variability and long-term changes in Tropical Pacific oceanography. Here we investigate this relationship using palaeorecords derived from the geochemistry of planktonic foraminifera. Our results indicate a strong negative correlation between ENSO variability and zonal gradient of sea-surface temperatures across the Tropical Pacific during the last 22 ky. This strong correlation implies a mechanistic link that tightly couples zonal sea-surface temperature gradient and ENSO variability during large climate changes and provides a unique insight into potential ENSO evolution in the future by suggesting enhanced ENSO variability under a global warming scenario.

Constraining foraminiferal calcification depths in the western Pacific warm pool

“…3). This agrees with the general view that N. dutertrei inhabits a shallow water depth close to the DCM (Fairbanks et al, 1982;Bé et al, 1985;Hemleben et al, 1989;Ravelo and Fairbanks, 1992;Dekens et al, 2002;Schmuker and Schiebel, 2002;Sadekov et al, 2013). Our study site at the Manihiki Plateau is at the border of the Pacific Equatorial Divergence (see also Section 3.2).…”

A Review of Paleo El Niño-Southern Oscillation

“…It should be noted that the variance of the foraminifera temperature, if treated as the strength of ENSO, can be used to infer the broad trend of ENSO variability through different time periods [28][29][30]44]. However, since these snapshots are distributed most likely randomly in time, their variance most likely represents the total variability across all the time scales including the seasonal cycle, interannual variability, decadal and longer variabilities.…”

“…For example, surface [29] and subsurface [30] proxies have been interpreted as strengthened ENSO variability at the LGM, while other proxies [28,31] show weakened ENSO. These contradictions suggest that ENSO strength during the glacial period thus remains unclear.…”

“…Sadekov et al [30] also investigated total variance in specimens of subsurface-dwelling N. dutertrei in the eastern equatorial Pacific at intervals of the modern (1.6 ka), the early Holocene (9.1 ka), deglaciation (12.5, 15.1 and 17.9 ka) and the Last Glacial Maximum (20.7 ka) (Figure 3m). ENSO variability was found to be~20% higher than the modern-day during the LGM and increased significantly during early deglaciation (for example, at 17.9 and 15.1 ka interval).…”

“…However, changes in the concentration and hydrogen isotope ratio of alga lipids in a sediment record retrieved from the same location [25] show only 5.6-3.5 ka was characterized by minimum El Nino activities and moderate ENSO events persisted during the early Holocene (Figure 3g). [22]; (c) El Nino (thin red) and La Nina (thin blue) events [26] in Bainbridge Crater Lake [23]; (d) Lithic flux in a marine sediment from off Peru (% of maximum) [27]; (e-g) El Junco sand record and C/N ratio [24] and botryococcene concentration [25]; (h-j) Coral and mollusk synthesis of δ 18 O variability from Western Pacific (WP), Central Pacific (CP) and Eastern Pacific (EP) clusters [33]; (k) δ 18 O variability from speleothem [34]; (l-n) δ 18 O variability in marine sediment records from the tropical eastern Pacific [28][29][30]44].…”