A New Messinian 87Sr/86Sr Curve for the Ain El Beida Section (Morocco): An Atlantic Perspective of the Mediterranean Salinity Crisis

We present a new 87Sr/86Sr curve for the time interval between 6.5 and 5.5 Ma of the Ain El Beida section (AEB, Atlantic side of Morocco). The location and the precessional-scale resolution of our curve allow to investigate the possible relationships between global paleoclimatic and palaeoceanographic trends and the high-amplitude hydrological changes of the Mediterranean during the Messinian salinity crisis (MSC). The values, obtained from planktic foraminifers, plot in the upper portion of the global ocean curve and show long- (at eccentricity scale) and short-term (precessional scale) oscillations; the latter are more evident during the maximum of eccentricity for both the 100 and 400 ka components, between 6.00 and 5.85 Ma. Negative 87Sr/86Sr anomalies are observed at insolation minima in phase with δ18O maxima, marking the glacial stages from TG34 to TG26. It is unclear whether these oscillations originated from local (river runoff) or global (glacial/interglacial) climatic forcing. Conversely, the evaporites of the coeval Primary Lower Gypsum (5.97–5.62 Ma) accumulated in the Mediterranean at insolation minima show positive anomalies at glacial stages TG32, 30, 28, and 26. Such an opposite trend is possibly related to the greater sensitivity of the Mediterranean Sea to river runoff during insolation maxima compared to the global ocean, as recorded at the Moroccan Atlantic margin. These observations and the deviation toward lower values of the Mediterranean Sr isotope curve starting at around 6.5 Ma, support the hypothesis of a progressive restriction of the Atlantic connections since the early Messinian, leading to the MSC.