Early Miocene Intensification of the North African Hydrological Cycle: Multi-Proxy Evidence From the Shelf Carbonates of Malta

During the Miocene (23.0-5.3 Ma) North Africa experienced both humid and arid intervals, but the underlying cause of these transitions is unknown. Earth's climate was characterized by a unipolar icehouse with a dynamic Antarctic ice sheet, which may have influenced regional hydrology through atmospheric teleconnections. However, the Miocene also witnessed the restriction of the Mesopotamian Seaway, which may have had significant climatic impacts. The Maltese il-Blata section (Central Mediterranean) comprises Late Oligocene to Early Miocene marine deposits previously used to constrain the timing of the Mesopotamian Seaway restriction using the epsilon Nd tracer. The location of this section also makes it sensitive to climatic changes in the North African region, and biogeochemical changes in the central Mediterranean. Here, we present lithological and geochemical records of the il-Blata section. We find a marked shift in lithology and an increase in sedimentation rate coeval with the Early Miocene (similar to 19-20 Ma) restriction of the Mesopotamian Seaway. Concomitant changes in bulk sediment CaCO3, Sr/Ca, K/Al, Ti/Al, Zr/Al, and Si/Ti support a major humid climate transition and associated intensification of river systems over western North Africa. We propose that these changes in North African hydroclimate reflect either a tipping point effect in a gradually warming global climate, or are the result of the initial restriction of the Mesopotamian Seaway, perhaps through consequent changes in Atlantic Meridional Overturning Circulation and the West African Monsoon. We also suggest the restriction of the Mesopotamian Seaway inhibited phosphorite deposition at low latitudes. Plain Language Summary The climate over the densely populated areas of North Africa and the Central Mediterranean is influenced by the West African Monsoon system. Climate data from the region is limited and models fail to make consistent predictions in the context of Anthropogenic global warming. Therefore, it is important to examine the geological past when atmospheric carbon dioxide levels were similar to values predicted for the end of the century. The il-Blata section in Malta (central Mediterranean) holds a geological record from 25 to 18 million years ago. This time interval is not well represented elsewhere in the region. Geological records from this section indicate a large increase in regional humidity around 19 million years ago. This humid transition followed a tectonic event that resulted in the closure of the Mesopotamian Seaway which connected the Indian Ocean with the Mediterranean Sea. This may reflect an important role for tectonic forcing in the evolution of the West African Monsoon system through changes in ocean circulation patterns. The change to a wetter climate also occurred against a backdrop of gradually warming global climate, so an alternative interpretation is that it reflects a regional tipping point in the climate system.

Automated summary

This article examines the alternating humid and arid intervals in North Africa during the Miocene, focusing on the impact of the restriction of the Mesopotamian Seaway and the global climate. It provides valuable insights into the regional hydroclimate and highlights the importance of tectonic forcing and ocean circulation patterns in the evolution of the West African Monsoon system.