Response of the Central Pacific Intertropical Convergence Zone to Northern Hemisphere Cooling During the Last Glacial Maximum and Heinrich Stadial 1

Abstract

The latitudinal position of the Intertropical Convergence Zone (ITCZ) reflects the energy imbalance between the hemispheres. Southward displacements of the ITCZ during the Last Glacial Maximum (LGM; 19-26.5 ka) and Heinrich Stadial 1 (HS1; 14.6-17.5 ka), are widely accepted, but their magnitude is controversial. Geochemistry of detrital fractions in down-core sediments collected from 6 degrees N to equator along the 131.5 degrees W transect reveal a distinct shift in epsilon Nd, La/Yb, and La-Sc-Th composition from predominantly northern hemisphere-sourced to mixed northern and southern hemisphere-sourced signal at 3 degrees N-4 degrees N during the LGM and 3 degrees N-6 degrees N during HS1. These contrasting provenance signals point to the past ITCZ functioning as a dust barrier. Given that a comparable geochemical demarcation currently occurs at 6 degrees N-7 degrees N, our data suggest that the ITCZ migrated southward by similar to 3 degrees during the LGM and similar to 1 degrees-3 degrees during HS1 relative to its modern position in the central Pacific. The tropical rainbelt, called the Intertropical Convergence Zone (ITCZ), plays a major role in the Earth's climate system. It encircles the equatorial region slightly biased to the northern hemisphere in latitude. Wind-blown dust deposited on the deep-sea floor to the north and south of this belt have distinct composition because heavy rainfall prevents the dust from passing through. We collected sediments at regular intervals in a north-south direction in the equatorial central Pacific (0 degrees-6 degrees N, 131.5 degrees W), and analyzed the chemical composition of dust deposited during two cold intervals, the Last Glacial Maximum (LGM; 19-26.5 ka) and Heinrich Stadial 1 (HS1; 14.6-17.5 ka). The results show that the latitudinal boundary where the dust chemistry diverges was similar to 3 degrees south during the LGM and similar to 1 degrees-3 degrees south during HS1 relative to today, which provides an estimate of the past movement of the ITCZ. The mean ITCZ position can be traced geochemically with hemispheric shift in dust provenance along a meridional transect The hemispheric shift in dust provenance occurred similar to 3 degrees and similar to 1 degrees-3 degrees farther south than today during the LGM and HS1, respectively In the central Pacific, the ITCZ responded with a similar or greater southward displacement during the LGM compared to HS1