Accurately calibrated X-ray fluorescence core scanning (XRF-CS) record of Ti/Al reveals Early Pleistocene aridity and humidity variability over North Africa and its close relationship to low-latitude insolation

Abstract

In eastern Mediterranean sediments, the titanium-to-aluminum ratio () captures relative variability in eolian to river-derived material and predominantly integrates climate signals over the Saharan and Sahel regions. Long time series can, therefore, provide valuable records of North African humidity and aridity changes. X-ray fluorescence core scanning (XRF-CS) can generate near-continuous records with relatively modest effort and in an acceptable amount of time, provided that accurate values are acquired. Calibration of raw XRF-CS data to those of established analytical methods is an important pathway for obtaining the required accuracy. We assess how to obtain reliable XRF-CS calibration by using different calibration reference sample sets for a long sediment record from ODP Site 967 (eastern Mediterranean Sea). The accuracy of reference concentrations and the number of reference samples are important for reliable calibration. Our continuous record allows detailed time series analysis over the past 3 Myr. Near-direct control of low-latitude insolation on the timing and amplitude of North African aridity and humidity is observed from 3 to ∼ 1.2 Ma. In our record, most arid North African intervals (i.e., with the longest period and highest amplitude) occur after the mid-Pleistocene transition (MPT; ∼ 1.2–0.7 Ma), when ice ages intensified. We also observe a subdued relationship between low-latitude insolation and North African climate after the MPT. These findings support the growing consensus that African climate became more sensitive to remote high-latitude climate when a threshold ice volume was reached during the MPT.