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

Abstract

The Indonesian Throughflow (ITF), as the sole low‐latitude conduit connecting the Pacific and Indian Oceans, regulates the thermohaline balance between these oceans. Thus, investigating the variability in the ITF and its relationship with the precessional forcing is crucial for understanding the drivers of tropical climate change. Here, we reconstruct the history of the ITF over the past ∼120 kyr based on high‐resolution (∼400 years) δ18O and Mg/Ca records of Globigerinoides ruber and Pulleniatina obliquiloculata from core SO217‐18540 retrieved from the Flores Sea upwelling region within the main pathway of the ITF. A comparison of these new records with published paleo‐oceanographic and climatological data from the western tropical Pacific Ocean suggests that annual mean conditions in the Flores Sea were controlled by ITF variability rather than by monsoonal upwelling. Our results further indicate that precessional insolation was a major forcing for the hydrological evolution of the ITF during the past 120 kyr. We suggest that the precessional insolation forcing paced ITF variability by modulating the mean state of El Niño‐Southern Oscillation‐like conditions and latitudinal shifts and/or expansion/contraction of the Intertropical Convergence Zone.

Obliquity Induced Latitudinal Migration of the Intertropical Convergence Zone During the Past ∼410 kyr

“…Recent studies indicated that Core U1483 ln(K/Ca) could be regarded as a reliable Australian summer monsoonal precipitation proxy with high values denoting increased terrigenous runoff due to intensified precipitation on land (Kuhnt et al, 2015;Zhang et al, 2020). Cross-spectral analysis between δ 18 O sw-c and ln(K/Ca) of Core U1483 displays no significant coherence on the precession band (Figure 2e), suggesting that the precession signal in Core U1483 δ 18 O sw-c is not primarily influenced by precipitation at the southern margin of the ITCZ's latitudinal displacement, further supporting the viewpoint of Zhang et al (2021).…”

“…Spectral analysis shows that δ 18 O sw-c variability is dominated by precession and obliquity (Figure S2a in Supporting Information S1). On the precession band, Zhang et al (2021) suggested that the δ 18 O sw-c of Core MD01-2378, which was drilled at the same location as Core U1483 (Figure 1), was influenced by the transport of the isotopic signal within the advected near-surface water masses of the ITF rather than by local precipitation. Recent studies indicated that Core U1483 ln(K/Ca) could be regarded as a reliable Australian summer monsoonal precipitation proxy with high values denoting increased terrigenous runoff due to intensified precipitation on land (Kuhnt et al, 2015;Zhang et al, 2020).…”

Thermal coupling of the Indo-Pacific warm pool and Southern Ocean over the past 30,000 years

“…3 , 4 ). A prevailing weaker and eastward tropical Pacific Walker circulation 25 in the glacial consequently contributed to a reduced northward heat transfer through the weakened Kuroshio Current 26 and the cooling of Indonesian seas by the weakened Indonesian Throughflow 19 .

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“…The last glacial maximum (LGM) SST cooling in the IPWP has a range of 2–5 °C based on geochemical proxies 10 , 12 , 13 , while cooling in the eastern equatorial Pacific (EEP) cold tongue varies between 0.3 and 3.5 °C 14 , 15 . Some previous ENSO investigations included cores that were distant from the central western Pacific warm pool (WPWP) 16 , 17 , or in areas close to shore that were impacted by coastal upwelling, fresh water runoff and coastal currents 13 , 18 , 19 . Other ENSO investigations were based on the meridional SST gradient between the EEP cold tongue and the northeastern Pacific warm pool, which is under debate as an indication of ENSO or seasonality assessment 20 , 21 .…”

“…Other ENSO investigations were based on the meridional SST gradient between the EEP cold tongue and the northeastern Pacific warm pool, which is under debate as an indication of ENSO or seasonality assessment 20 , 21 . These discrepancies ultimately result in opposing assertions about the prevalence of La Niña-like 10 , 13 , 17 , 19 , 20 or El Niño-like conditions 5 , 11 , 12 , 14 , 16 in the last glacial period.…”