Glacial‐Interglacial Shifts Dominate Tropical Indo‐Pacific Hydroclimate During the Late Pleistocene

Abstract

The Indo-Pacific Warm Pool (IPWP) has the warmest sea surface temperatures (SSTs) in the tropics and some of the highest annual precipitation on the planet. The IPWP sits under the ascending branch of two Walker Circulation cells, where converging surface winds and warm SSTs supply large amounts of water vapor to the atmosphere. Today, rainfall gradients in the IPWP follow the seasonal position of the Intertropical Convergence Zone (ITCZ), which is in the Northern Hemisphere (NH) during boreal summer and shifts to the Southern Hemisphere during boreal winter (Aldrian & Dwi Susanto, 2003;Schott et al., 2009). Accordingly, some studies suggest that tropical precipitation changes on geological timescales primarily respond to the 23-and 19-ky precession cycles in Earth's orbit (Clement et al., 2004;Jalihal et al., 2019;Merlis et al., 2013), which control the seasonal amount of incoming solar radiation (insolation). The precession theory posits that when NH summer insolation is high, average ITCZ position is farther north, resulting in wetter conditions over northern IPWP and eastern China. Precessional signals in atmospheric methane reconstructions from ice cores have been used to support this theory, that is, high NH insolation leads to increased monsoon intensity and tropical methane production (Guo et al., 2012;Ruddiman & Raymo, 2003), although the tropical control on these records has recently come into question (Thirumalai et al., 2020). Alternatively, other studies suggest that IPWP precipitation is more sensitive to changes in ice sheets and sea level over glacial-interglacial time scales, where exposure of the Sunda and Sahul Shelves altered moisture

Milankovitch theory and monsoon

“…The orbital-scale hydroclimate variations in parts of the Indo-Pacific Warm Pool (IPWP), the South China Sea, and the Bay of Bengal appear to show significant ∼100-ka glacial-interglacial cycles as inferred by precipitation and precipitation isotope records. 140 Similar to the alternative interpretations for the Bay of Bengal and South China Sea records ( Figures 5 and 6 ), 93 the records from the IPWP (Borneo, Malaysia, and Sumatra, Indonesia) may be tentatively explained by their specific locations in the transition regions between the two “precession regimes” with opposite precipitation amounts and δ 18 O variations. 76 , 77 , 119 In these regions, like the central Chinese Loess Plateau, muted precession signals may facilitate the powers of other cyclicities.…”

“…Additionally, the shelf exposure influence because of sea level change on the IPWP hydroclimate is presumably large, affecting regional ocean and atmosphere circulation and amplifying glacial-interglacial cyclicity. 140 The broad anti-phase relationship between NH-SH monsoons on the precession scale implies that the ice volume forcing of monsoons would not be primary because the ice volume forcing is nearly synchronous globally to first order. However, various ice volume forcing effects seem to manifest in the monsoon regime in different ways, particularly in the EAM domain.…”

Expansion and Intensification of the North American Monsoon During the Pliocene

“…While our initial 1σ precision for δD w measurements is 2‰, 1σ uncertainty for our final estimate of δD p is 4-6‰. This Bayesian approach has been previously used to study paleohydrological signals in leaf waxes (Tierney et al, 2017;Windler et al, 2021), including within the NAM domain (Bhattacharya et al, 2018).…”

Biomarker Approaches for Reconstructing Terrestrial Environmental Change

“…lake levels). The variety of information in δ 2 Hprecip is also an asset; in the mid-latitudes δ 2 Hwax can be used to distinguish between different seasonal moisture sources (Bhattacharya et al 2018) while in the tropics δ 2 Hwax reveals general trends in aridity (Tierney & deMenocal 2013) or atmospheric convection (Windler et al 2021). Comparisons between δ 2 Hwax and ice core or speleothem δ 18 O demonstrates that δ 2 Hwax captures similar information and also records rapid climate changes such as the Younger Dryas cooling (Fornace et al 2014) (Figure 4).…”