A contracting Intertropical Convergence Zone during the Early Heinrich Stadial 1

Abstract

Despite the fact that the response of tropical hydroclimate to North Atlantic cooling events during the Heinrich Stadial 1 (HS1) has been extensively studied in African, South American and Indonesia, the nature of such responses remains debated. Here we investigate the tropical hydroclimate pattern over the Indo-Asian-Australian monsoon region during the HS1 by integrating hydroclimatic records, and examining a δ18Oseawater record from Globigerinoides ruber (white) in the tropical Indian Ocean. Our findings indicate that tropical hydrological conditions were synchronously arid in both hemispheres during the early HS1 (~18.3-16.3 ka) in the Indo-Asian-Australian monsoon region, except for a narrow, wet hydrological belt in northern low latitudes, suggesting the existence of a contracted tropical precipitation belt at that time. This study reveals that the meltwater discharge and resulting changes in global temperatures and El Niño exerted a profound influence on the tropical hydroclimate in the Indo-Asian-Australian monsoon region during the early HS1.

Wind-driven sediment exchange between the Indian marginal seas over the last 18 000 years

“…We also note that the smectite content reached zero during some periods (e.g. HS1) (figures S2 and 3(a)), which was probably related to a very weak southward WICC at these times (Yang et al 2023). However, the proxy is not expected to provide a quantitative measure of the EICC and/or WICC strength, due to possible non-linearities over its range, such as the above feature, as well as the potential for variable monsoondriven sediment inputs to exert a secondary control through time.…”

Rapid Climate Links Between High Northern Latitudes and Tropical Southeast Asia Over the Last 40 ka

“…As a result, it is evident that an El Niño‐Southern Oscillation‐like system was not the primary cause of flooding in NW Borneo during these cold spells. However, owing to anomalous warming caused by El Niño under this state, the tropical troposphere becomes warmer while the subtropical troposphere is cooler, enhancing the meridional temperature gradient and shrinking the Hadley circulation in both hemispheres, a condition that is conducive to a contracted ITCZ in the northern low latitudes as occurred during the early HS1 (Guo & Li, 2016; Yang et al., 2023). In general, these mechanisms associated with the AMOC‐forced changes in the EAWM and ITCZ could explain the occurrence of flooding in NW Borneo during the D‐O stadials, as observed by our data.…”

“…On the other hand, recent findings suggest that the higher MAR values observed in core CG02 off the northern Sunda Shelf during the early Heinrich Stadial 1 (HS1, 17.5–14.7 ka; Denton et al., 2006; Figure S5g in Supporting Information ) are due to a contracted Intertropical Convergence Zone (ITCZ) in the northern low latitudes caused by meltwater discharge from the Eurasian ice sheet into the North Atlantic and the resulting slowdown in AMOC and cooling in the northern high latitudes (J. Huang et al., 2019; Yang et al., 2023). Thus, it implies that a contracted ITCZ rain belt in the northern low latitudes, probably associated with a moderately weaker AMOC comparable to that observed during the early HS1, may have also had a role in contributing to flood events in NW Borneo (Figure 3l).…”