Abstract
Abstract. Over the Plio-Pleistocene interval a strong linkage exists between northern African climate changes and the supply of dust over the surrounding oceans and continental runoff towards the Mediterranean Sea. Both these signatures in the sedimentary record are determined by orbital cycles influencing glacial variability on the one hand and northern African monsoon intensity on the other hand. In this paper, we use the intermediate-complexity model CLIMBER-2 to simulate African climate during the Plio-Pleistocene between 3.2 and 2.3 million years ago (Ma) and compare our simulations with existing and new climate reconstructions. The CLIMBER-2 model is externally forced with atmospheric CO2 concentrations, ice sheet topography, and orbital variations, all of which strongly influence climate during the Pliocene and Pleistocene. Our simulations indicate that the records of northern Africa climate oscillate in phase with climatic precession. For the Earth's obliquity cycle, the time lag between the 41 000-year component in insolation forcing and the climatic response increased after inception of Northern Hemisphere (NH) glaciation around 2.8 Ma. To test the outcome of our simulations, we have put emphasis on the comparison between the simulated runoff of grid boxes encompassing the Sahara desert and the Sahel region and the sedimentary records of marine sediment cores from ODP Site 659 (Atlantic Ocean) and ODP Site 967 (Mediterranean). In this study we will show for the first time an extended Ti∕Al record of Site 967 down to 3.2 Ma. This record strongly correlates with runoff in the Sahara and Sahel regions, whereas correlation with the dust record of Site 659 is moderate and slightly improves after NH ice sheet inception. We investigated the transient variability of the individual and combined contributions of the Sahel and Sahara regions and found significant transient behaviour overlapping the inception of NH ice sheets (2.8 Ma) and the Plio-Pleistocene transition (2.6 Ma). Prior to 2.8 Ma, a larger contribution from the Sahara region is required to explain the variability of Mediterranean dust input. After this transition, we found that a more equal contribution of the two regions is required, representing an increased influence of Sahel runoff and wet periods.
Highlights
It has been generally accepted that climate is influenced by the orbital parameters precession, obliquity, and eccentricity since Milankovitch laid a vital foundation still used today
In this paper we focus on the connection between the African monsoon, using continental runoff, and sediment and dust deposition from the African continent between 3.2 and 2.3 million years ago (Ma), which includes the Plio-Pleistocene transition at 2.6 Ma
The world experienced a large increase in Northern Hemisphere (NH) glaciation, concurrent with a drawdown in atmospheric CO2 concentrations (Fig. 2)
Summary
It has been generally accepted that climate is influenced by the orbital parameters precession, obliquity, and eccentricity since Milankovitch laid a vital foundation still used today. Changes are seen during the late Pliocene and midPleistocene in vegetation in northeast Africa (Rose et al, 2016), during the Pleistocene in Kenya (Lupien et al, 2018), in the West African monsoon (Kuechler et al, 2018), and in hydroclimate variability in southeastern Africa over the past 2 million years (Caley et al, 2018) Another common association with African PlioPleistocene climate variability is early hominin evolution in eastern Africa. In this paper we focus on the connection between the African monsoon, using continental runoff (linked to precipitation, evaporation, and water storage in the soil, lakes, and groundwater), and sediment and dust deposition from the African continent between 3.2 and 2.3 Ma, which includes the Plio-Pleistocene transition at 2.6 Ma. Here, we use a model of intermediate complexity, CLIMBER-2 (Petoukhov et al, 2000), to simulate climate variability. For this purpose we will show for the first time the extended dust record of ODP Site 967 (Wehausen and Brumsack, 2000; Lourens et al, 2001) down to 3.2 Ma
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