A 3 million year index for North African humidity/aridity and the implication of potential pan-African Humid periods

QUATERNARY SCIENCE REVIEWS

卷:171

Article

Grant, Katharine M.¹  Rohling, Eelco J.^1,2  Westerhold, Thomas³  Zabel, Matthias³  Heslop, David¹  Konijnendijk, Tiuri⁴  Lourens, Lucas⁴ 

[1] Australian Natl Univ, Res Sch Earth Sci, Canberra, ACT, Australia

[2] Univ Southampton, Natl Oceanog Ctr, Ocean & Earth Sci, Southampton, Hants, England

[3] Univ Bremen, MARUM, D-28359 Bremen, Germany

[4] Univ Utrecht, Dept Earth Sci, NL-3584 CD Utrecht, Netherlands

关键词: ODP Site 967;    Scanning XRF;    Sapropels;    African monsoon;    Aeolian dust;    Pilo-Pleistocene;   

DOI  :  10.1016/j.quascirev.2017.07.005

来源: Elsevier

【 摘 要 】

Mediterranean sediments are valuable archives of both African monsoon variability and higher-latitude climate processes, and can also be used to provide an environmental context for early human migrations and settlements. However, the long history of Mediterranean palaeoclimate studies largely pre-dates the advent of widespread x-ray fluorescence (XRF) core-scanning, so there are few continuous and high resolution geochemical records from this key region that extend beyond the last glacial cycle. Here we present XRF core-scanning results for ODP Site 967 (Eastern Mediterranean) that have been fully calibrated into element concentrations spanning the last 3 million years (My). Comparison with independent geochemical data from conventional XRF highlights disparities for certain element/element ratios, thus suggesting the need for caution when taking ratios of scanning XRF data. Principal component analysis of the calibrated XRF dataset reveals two dominant components: detrital inputs (PC1) and a 'sapropel' (approximate to monsoon run-off) signal (PC2), which we use to establish a new orbitally-tuned chronology. We observe inverse covariation between PC2 and a previously published aeolian dust record from ODP Site 967 (Larrasoana et al., 2003), and combine these records to produce a composite index of humidity and aridity for the wider North African region over the past 3 My. We propose that by combining run-off and dust signals in a single metric, our index captures the effects of both strengthening/northward migration (increased run-off) and weakening/southward retreat (increased dust) of the North African monsoon. Comparison of the index with published records of Northwest and East African palaeohumidity suggests that it tracks the timing of Green Sahara Periods throughout the Plio-Pleistocene, and that at least 30 of these intervals coincided with increased humidity across East Africa. We tentatively suggest that these specific episodes may be termed pan-African Humid Periods, as a means to highlight large-scale climate trends and to provide an environmental framework for palaeoanthropological research. (C) 2017 Elsevier Ltd. All rights reserved.

【 授权许可】

Free