Half-precessional cycle of thermocline temperature in the western equatorial Pacific and its bihemispheric dynamics

Abstract

The El Niño−Southern Oscillation (ENSO), which is tightly coupled to the equatorial thermocline in the Pacific, is the dominant source of interannual climate variability, but its long-term evolution in response to climate change remains highly uncertain. This study uses Mg/Ca in planktonic foraminiferal shells to reconstruct sea surface and thermocline water temperatures (SST and TWT) for the past 142 ky in a western equatorial Pacific (WEP) core MD01-2386. Unlike the dominant 100-ky glacial−interglacial cycle recorded by SST and δ18O, which echoes the pattern seen in other WEP sites, the upper ocean thermal gradient shows a clear half-precessional (9.4 ky or 12.7 ky) cycle as indicated by the reconstructed and simulated temperature (ΔT) and δ18O differences between the surface and thermocline waters. This phenomenon is attributed to the interplay of subtropical-to-tropical thermocline anomalies forced by the antiphased meridional insolation gradients in the two hemispheres at the precessional band. In particular, the TWT shows greater variability than SST, and dominates the ΔT changes which couple with the west−east SST difference in the equatorial Pacific at the half-precessional band, implying a decisive role of the tropical thermocline in orbital-scale climate change.

Pacific warm pool subsurface heat sequestration modulated Walker circulation and ENSO activity during the Holocene

“…3A ). The relationship between precession/obliquity and IPWP’s thermocline change has been found before ( 10 – 12 , 27 , 28 ) and was explained by some regional oceanographic processes. Such a common Early Holocene peak, however, implies a common driving mechanism over the entire IPWP thermocline.…”

Variability in Indonesian Throughflow Upper Hydrology in Response to Precession‐Induced Tropical Climate Processes Over the Past 120 kyr

“… Hydrologic records in the western tropical Pacific. (a) Sea surface and (b) thermocline δ 18 O sw‐c from cores SO217‐18540 (this study), MD06‐3067 (Bolliet et al., 2011) and MD01‐2378 (Xu et al., 2006, 2008; Zuraida et al., 2009); (c) Borneo speleothem δ 18 O (Carolin et al., 2013, 2016; Partin et al., 2007); (d) Ti content in core MD10‐3340 (Dang et al., 2015); (e) SST difference between the western (core MD01‐2386) and eastern (core TR163‐22) equatorial Pacific (ΔSST W‐E ) (Jian et al., 2020; Lea et al., 2006) and (f) ENSO index (Clement & Cane, 1999; Clement et al., 1999) and September–October insolation at the Equator (Laskar et al., 2004). The superimposed olive‐colored curve in panel (a) represents the precessional parameter (Berger & Loutre, 1991).…”

“…The ENSO index (Clement & Cane, 1999; Clement et al., 1999) and the SST difference between the western and eastern equatorial Pacific (ΔSST W‐E ) were previously used as reliable proxies to characterize ENSO‐like conditions (Dang et al., 2015; Jian et al., 2020; Wu et al., 2013), with a large ENSO index and small ΔSST W‐E values for El Niño‐like conditions and a small ENSO index and large ΔSST W‐E values for La Niña‐like conditions. A comparison of thermal records from the ITF region with the ENSO index and ΔSST W‐E shows that low SST and TT and large ΔT corresponded to larger ENSO index and smaller ΔSST W‐E values during the past ∼120 kyr (Figures 6a–6c, 6e, and 6f), and vice versa.…”

“…This result is different from core MD01‐2386 from the eastern inflow region of the ITF (Figure 1), which shows distinct half‐precessional periods in its TT and ΔT records. The strong half‐precessional signals in the TT and ΔT records of core MD01‐2386 are caused by the interaction of precessional subsurface temperature anomalies from both hemispheres, because core MD01‐2386 is located at the crossroads of the western boundary pathways from both hemispheres (Jian et al., 2020). In contrast, core SO217‐18540, located within the ITF flow path, is influenced by the western boundary pathways of the Northern Hemisphere (Figure 1) (Fine et al., 1994).…”

“… Map of coring sites referred to in this study. The yellow star marks the location of core SO217‐18540, the yellow dots indicate the stalagmite site of Gunung Buda on Borneo (Carolin et al., 2013, 2016; Partin et al., 2007) and the locations of deep‐sea cores MD06‐3067 (Bolliet et al., 2011), MD10‐3340 (Dang et al., 2015), MD01‐2378 (Xu et al., 2006, 2008; Zuraida et al., 2009), SO139‐74KL (Wang et al., 2018), SO217‐18515 (Zhang et al., 2018) and MD01‐2386 (Jian et al., 2020). Cross‐shaded areas represent the Flores Sea and Java‐Sumatra upwelling areas (Gordon, 2005; Mohtadi et al., 2009).…”