Persistent Holocene outflow from the Black Sea to the eastern Mediterranean Sea still contradicts the Noah's Flood Hypothesis: A review of 1997–2021 evidence and a regional paleoceanographic synthesis for the latest Pleistocene–Holocene

Abstract

This review and synthesis weaves various multiproxy data into a single coherent narrative for the latest Pleistocene–Holocene paleoclimatic and paleoceanographic evolution of the Black Sea, Marmara Sea and the Aegean Sea. This narrative, referred to as the “Outflow Hypothesis” rests on several key observations and interpretations which are incompatible with the suggestion that the post-LGM reconnection of the Black Sea basin to the global ocean occurred as a catastrophic flood. The widespread occurrence of sub-storm-wavebase uppermost Pleistocene to lower Holocene sediments across the southwestern Black Sea shelf at elevations as shallow as −78 m shows that the level of the Neoeuxine Lake (today's Black Sea) between 12.3 cal ka and 9.5 cal ka was high enough to spill outward into the Marmara Sea over the shallow sill in the southern Strait of Bosphorus (−37 m today). Southwest-prograded clinoforms immediately south of the strait in the northeastern Marmara Sea record the development of an early Holocene (11.1–10.2 cal ka) mid-shelf delta (Δ1) showing ~3.3 km of aggressive progradation while its topset-to-foreset break climbed 8–9 m into a rising Marmara Sea. A streamlined south-prograded barform in the throat of the strait and giant megaflutes along its thalweg confirm the vigorous outflow from the early Holocene Neoeuxine Lake required to explain the climbing Δ1 lobe. Multiproxy data from the northeastern Marmara Sea and southwestern Black Sea shelves indicate that the post-Last Glacial Maximum (LGM) reconnection of the Black Sea with the eastern Mediterranean occurred in a gradual fashion: first, at ~10.2 cal ka, a salt wedge lifted the brackish outflow off the floor of the Strait of Bosphorus terminating Δ1 progradation; second, a more persistent density underflow introduced enough seawater strontium into the Black Sea to be taken up in mollusc shells by ~9.5 cal ka, and finally a range of euryhaline marine organisms replaced lacustrine faunas when salinity levels became favourable by ~7.5 cal ka. The onset of sapropel M1 deposition across the Marmara Sea followed the breach of the Strait of Dardanelles at 13.8 cal ka when, as originally suggested by other researchers, nutrient-rich highly saline Mediterranean waters forced lower density relict lacustrine waters to the surface and then out through the Strait of Dardanelles, initiating water-column stratification. Once the low-salinity cap was expelled, the deep waters of the fully saline Marmara Sea remained stagnant and sapropel accumulation continued. The onset of outflow from the Neoeuxine Lake at 11.1 cal ka re-established water-column stratification, induced effective deep circulation across the Marmara Sea, and created a low salinity lid across the northern Aegean Sea, initiating sapropel S1 deposition in that area.