Mid‐ to Late Holocene Contraction of the Intertropical Convergence Zone Over Northeastern South America

Abstract

Modern rainfall over northeastern (NE) South America is highly sensitive to and strongly controlled by the position of the Intertropical Convergence Zone (ITCZ), that is, the rising limb of the Hadley circulation (meridionally oriented overturning circulation cell) (Hastenrath, 2012;Poveda et al., 2006;Schneider et al., 2014). Today, semi-arid northern NE Brazil receives ca. 50% of its total annual precipitation during March-April, when the ITCZ and the associated equatorial precipitation reach its seasonal southernmost position over NE South America (Figure 1). A suggested mid-to late Holocene southward migration of the Abstract Modern precipitation over northeastern (NE) South America is strongly controlled by the seasonal meridional migration of the Intertropical Convergence Zone (ITCZ). Ample evidence from the Northern Hemisphere suggests a mid-to late Holocene southward migration of the ITCZ. Such a shift would be expected to increase precipitation over semi-arid northern NE Brazil (Southern Hemisphere). However, the most robust precipitation record from northern NE Brazil shows a drying trend throughout the Holocene. Here, we address this issue presenting a high-temporal resolution reconstruction of precipitation over northern NE Brazil based on data from a marine sediment core, together with analyses of mid-and late Holocene simulations performed with the fully coupled climate model FGOALS-s2. Both, our data and the climate model simulations show a decrease in precipitation over northern NE Brazil from the mid-to the late Holocene. The model outputs further indicate a latitudinal contraction of the seasonal migration range of the ITCZ that, together with an intensification of the regional Walker circulation, were responsible for the mid-to late Holocene changes in precipitation over NE South America. Our results reconcile apparently conflicting precipitation records and climate mechanisms used to explain changes in precipitation over NE South America.

Late Holocene Precipitation Fluctuations in South America Triggered by Variability of the North Atlantic Overturning Circulation

“…This long-term trend to drier conditions in the northern portion of eastern Brazil agrees with increasing austral summer insolation (Fig. 5a), which leads to an intensification of the Nordeste Low and thus higher aridity in the Jequitinhonha catchment (Cruz et al, 2009;Chiessi et al, 2021).…”

“…The general trend toward drier conditions over the past 5 kyr as indicated by the ln(K/Al) record is also reflected by the δ 2 H record (despite diverging excursions between both records at 4.4 and 0.6 ka), corroborating the robustness of the retrieved climatic signal. This long-term trend to drier conditions in the northern portion of eastern Brazil agrees with increasing austral summer insolation (Figure 5a), which leads to an intensification of the Nordeste Low and thus higher aridity in the Jequitinhonha catchment (Chiessi et al, 2021;Cruz et al, 2009). A general trend to drier conditions at least over the past 2 ka is also registered in speleothem δ 18 O records from the neighborhood of the Jequitinhonha catchment (Diva de Maura and Lapa Grande Caves, Figures 6a and 6b; Novello et al, 2012;Stríkis et al, 2011).…”

South American precipitation dipole forced by interhemispheric temperature gradient

“…Ti/Ca) from marine sediment cores collected off NEB 15 – 17 neither show precession-paced precipitation changes, except for the last ca. 5.2 ka 18 . Since NEB hydroclimate records showing precession-paced precipitation changes only cover the last precession cycle (ca.…”

“…Since NEB hydroclimate records showing precession-paced precipitation changes only cover the last precession cycle (ca. 26 ka) 6 , 18 , the very existence of a precession-driven east–west tropical SA precipitation dipole remains unsettled. Additionally, changes in the seasonal range of the latitudinal migration of the Intertropical Convergence Zone (ITCZ) was recently suggested to also play a crucial role in controlling precession-scale precipitation over NEB 18 .…”

Coupled changes in western South Atlantic carbon sequestration and particle reactive element cycling during millennial-scale Holocene climate variability

“…The rapid changes observed in Southern Hemisphere climatic records suggests that the South American Monsoon System (SAMS) and the western South Atlantic surface ocean circulation varied at same timing 8 – 11 . Both SAMS and the South Atlantic surface circulation are sensitively linked to North Atlantic variability by the Intertropical Convergence Zone (ITCZ), which shows a seasonal meridional migration and a latitudinal contraction following the orbital-scale insolation-driven changes 12 .…”