Biological turnovers in response to marine incursion into the Caspian Sea at the Plio-Pleistocene transition

• Published in: Global and planetary change 2021-11, Vol.206, p.103623, Article 103623
• Main Authors: Hoyle, Thomas M., Leroy, Suzanne A.G., López-Merino, Lourdes, van Baak, Christiaan G.C., Martínez Cortizas, Antonio, Richards, Keith, Aghayeva, Vusala
• Format: Article
• Language: English
• Subjects: Akchagylian marine incursion; Biodiversity turnover; Dinoflagellate cysts; Marine connection; Palaeoenvironmental monitoring; Sea-level change; Sediment geochemistry
• ISSN: 0921-8181; 1872-6364
• DOI: 10.1016/j.gloplacha.2021.103623

Marine influence on low-salinity environments can trigger aquatic ecosystem shifts, including biodiversity turnovers. High-resolution palaeoenvironmental records of marine connection events are particularly valuable, as they provide natural laboratories to understand analogous oceanographic and biodiversity turnover events in present-day climate- and anthropogenically-induced incursions. One such incursion event occurred across the Plio-Pleistocene transition when water from the open ocean spilled into the Eurasian continental interior, inundating the Caspian area. Here we record the so-called Akchagylian marine incursion using well-dated palynological and geochemical records of the Lokbatan section (Azerbaijan). Immediately prior to the intensification of northern hemisphere glaciations (~2.75 Ma), fresh-brackish peri-Paratethyan dinocyst assemblages were replaced by monospecific assemblages of the marine dinocyst, Operculodinium centrocarpum sensu Wall and Dale (1966). This indicates that the Caspian Sea experienced a marine incursion during a period of global high sea level. The marine incursion also registered in the geochemical record as a peak in excess‑strontium and carbonate content. Marine influence on the Caspian ceased after ~2.46 Ma and a second biological turnover took place, with low-salinity tolerant peri-Paratethyan dinoflagellate communities replacing the marine assemblages. The large-scale Akchagylian marine incursion episode shows the extreme degree of biodiversity change that marine influence on fresh-brackish water basins could trigger. Similar processes are increasingly relevant to present-day marginal and landlocked basins, which face ever-greater incursions from marine species and water due to both climate-mediated sea-level rise and human-made infrastructure projects. •Marine water entered the Caspian Sea at the end of the Pliocene (2.75 Ma).•Geochemical shifts occurred, with complete biotic turnover in algal communities.•Biotic turnovers were most likely associated with changes in salinity.•Current sea-level change may drive similar events today and in the near future.•Human-made shipping canals may drive hydrological imbalance in seas worldwide.