Climate-modulated paleoceanographic changes in the Alboran Basin triggered by tectonic restriction at the Atlantic–Mediterranean Seaway during the Tortonian–Messinian transition

The evolution of restricted marine basins offers unique insights into the interplay between climatic variability and tectonic processes. This study focuses on the western Mediterranean Sea, which underwent progressive isolation beginning in the late Tortonian (∼8 Ma) and culminating with the Messinian Salinity Crisis (5.97–5.33 Ma), when the basin experienced quasi-disconnection from the Atlantic Ocean. Here, we present reconstructions of sea surface temperature and salinity derived from coupled analysis of organic biomarkers and oxygen isotopes on planktic foraminifera from the West Alboran Sea (ODP site 976B) for the 7.505 to 7.063 Ma time interval. The combined results show four phases with distinct paleoenvironmental conditions prevailing in this westernmost Mediterranean. During Phase 1 (7.505–7.369 Ma), the sea surface temperatures showed low-frequency, large-amplitude fluctuations (25.7 to 29.7 °C) accompanied by large sea surface salinity variations (37.1 to 43.3). In Phase 2 (7.369–7.241 Ma), the marine conditions shifted to low variability, high sea surface temperatures (27.9 to 29.6 °C) accompanied by stable and high salinities (42.7 to 43.7). In Phase 3 (7.241–7.177 Ma), stable hypersaline conditions (43.0 to 44.3) persisted alongside an even lower variability in sea surface temperatures (28.3 to 29.1 °C). Phase 4 (7.177–7.063 Ma) is marked by a pronounced cooling and unexpected freshening. During Phase 4, the large-amplitude, high-frequency sea surface temperature (25.3 to 29.8 °C) and sea surface salinity changes (35.9 to 44.0) were likely driven by the progressive closure of the Betic and Rifian gateways around 7.1 Ma, with a superimposed precession modulation. This study highlights the sensitivity of the Western Mediterranean Basin to gateway restrictions and provides a framework for understanding the broader climatic and oceanographic impacts of tectonically triggered restriction events. The system was highly sensitive to global climate variations, especially during the latest Tortonian, when the Alboran basin had a fully functional connection to the Atlantic. Starting with the earliest Messinian, changes in connectivity through the Atlantic–Mediterranean gateway likely played a pivotal role in regulating temperature and salinity of the western Mediterranean with consequences propagating further to the east, in the entire basin.