Estimating Plio‐Pleistocene North African Monsoon Runoff Into the Mediterranean Sea and Temperature Impacts

Abstract

Sapropels are dark, organic‐rich layers found in Mediterranean sediments that formed during periods of bottom water anoxia. While various mechanisms have been proposed to have caused anoxic conditions, a primary factor is considered to be water column stratification induced by freshwater runoff related to intensified North African monsoon precipitation during precession minima. Monsoon intensification also induced Green Sahara Periods that may have impacted North African hominin dispersal. In this study, we present a novel regression‐based deconvolution of a high‐resolution planktonic foraminiferal oxygen isotope record to estimate the combination of freshwater runoff reaching the eastern Mediterranean and associated surface warming of the water column over the past 5 million years. Sapropels are known to occur in clusters associated with periods of high orbital eccentricity. Our analysis reveals a consistent influence of orbital eccentricity in modulating the North African monsoon, and a possible shift in runoff source area induced by the initiation of Northern Hemisphere ice sheets. Our findings provide important insights into the role of the North African monsoon in shaping Mediterranean environmental changes over the past 5 million years.

Constraining Plio‐Pleistocene Shifts in Northwest African Hydroclimate, Ecosystem Distributions, and Marine Productivity: New Paleo‐Records Across the Mid‐Pleistocene Transition

“…However, δD Precip data from this same core which include both wet and dry monsoon conditions show no change in mean value between 1.9–1.6 Ma and 3.1–2.9 Ma (Rose et al., 2016) suggesting the mean state of the monsoon did not vary much over this interval, perhaps due to compensatory drying during weak monsoon intervals (Figure 5d). This lack of mean monsoon strength change is also consistent with recent estimates of steady monsoon runoff to the Eastern Mediterranean from planktic foraminifera δ 18 O isotope records also from ODP 967 since 5 Ma (Heslop et al., 2023). A shift toward more negative δ 18 O values occurred after 2.6 Ma, but this has been explained by a shift toward more southerly monsoon rainfall source area following iNHG, which is also supported by model simulations (De Boer et al., 2021).…”

“…intervals (Figure 5d). This lack of mean monsoon strength change is also consistent with recent estimates of steady monsoon runoff to the Eastern Mediterranean from planktic foraminifera δ 18 O isotope records also from ODP 967 since 5 Ma (Heslop et al, 2023). A shift toward more negative δ 18 O values occurred after 2.6 Ma, but this has been explained by a shift toward more southerly monsoon rainfall source area following iNHG, which is also supported by model simulations (De Boer et al, 2021).…”

“…First, δD Precip records changes in monsoon rainfall amount not necessarily the spatial or seasonal distribution of monsoon rainfall. It is possible that despite the similar δD Precip values between the Pliocene intervals (5.0-4.6 Ma and 3.6-3.0 Ma) and our new MPT interval (1.1-1.0 Ma), monsoon rainfall may have penetrated deeper into the North African interior or fallen over longer wet seasons during the Pliocene (De Boer et al, 2021;Heslop et al, 2023). Increased ventilation by subtropical airmasses as Northern Hemisphere ice sheets developed may have served as an increasingly strong barrier to the penetration of monsoon moisture along its northern edge, as suggested by some climate model simulations (Chou & Neelin, 2003).…”