28 Feb 2022
28 Feb 2022
Status: this preprint is currently under review for the journal CP.

Accurately calibrated XRF-CS record of Ti/Al reveals Early Pleistocene aridity/humidity variability over North Africa and its close relationship to low-latitude insolation

Rick Hennekam1, Katharine M. Grant2, Eelco J. Rohling2,3, Rik Tjallingii4, David Heslop2, Andrew P. Roberts2, Lucas J. Lourens5, and Gert-Jan Reichart1,5 Rick Hennekam et al.
  • 1Department of Ocean Systems, NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg, Texel, The Netherlands
  • 2Research School of Earth Sciences, Australian National University, Canberra, ACT 2602 Australia
  • 3Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton, SO14 3ZH, United Kingdom
  • 4GFZ German Research Centre for Geosciences, Section 5.2 – Climate Dynamics and Landscape Evolution, D-14473 Potsdam, Germany
  • 5Department of Earth Sciences, Faculty of Geosciences, Utrecht University, P.O. Box 80.121, 3508 TA Utrecht, The Netherlands

Abstract. In eastern Mediterranean Sea sediments, the titanium to aluminum ratio (Ti/Al) captures relative variability in eolian to riverine derived material, and predominantly integrates climate signals over the Saharan and Sahel regions. Long Ti/Al time series can, therefore, provide valuable records of North African humidity/aridity changes. X-ray fluorescence core scanning (XRF-CS) can generate near-continuous Ti/Al records with relatively modest effort and in an acceptable amount of time, provided that accurate Ti/Al values are acquired. Calibration of the raw XRF-CS data to those of established analytical methods is an important pathway to obtain this required accuracy. We assess how to obtain reliable XRF-CS Ti/Al calibration by using different sets of calibration reference samples for a long sediment record from ODP Site 967 (eastern Mediterranean). The accuracy of reference concentrations and the number of reference samples are important components for reliable calibration. The acquired continuous Ti/Al record allows detailed time-series analysis over the past 3 Ma. A near-direct control of low-latitude insolation on the timing and amplitude of North African aridity/humidity is observed from 3 to ~1.2 Ma. It is evident from our Ti/Al record that the most arid North African intervals (i.e., with longest period and highest amplitude) occur after the mid-Pleistocene transition (MPT; ~1.2–0.7 Ma). Concurrently, correlation between North African aridity/humidity (Ti/Al) and higher latitude climate signals (ice-volume variability) increases around 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.

Rick Hennekam et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2022-14', Anonymous Referee #1, 22 Mar 2022
    • AC1: 'Reply on RC1', Rick Hennekam, 03 Jul 2022
  • RC2: 'Comment on cp-2022-14', Anonymous Referee #2, 27 Apr 2022
    • AC2: 'Reply on RC2', Rick Hennekam, 03 Jul 2022

Rick Hennekam et al.

Rick Hennekam et al.


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Short summary
The ratio of titanium to aluminum (Ti/Al) is an established way to reconstruct North African climate in eastern Mediterranean Sea sediments. We here demonstrate how to obtain reliable Ti/Al data using an efficient scanning method that allows rapid acquisition of long climate records at low expense. Using this method, we reconstruct a 3 million-year North African climate record. African environmental variability was paced predominantly by low-latitude insolation from 3–1.2 million years ago.