On the interpretation of century–millennium-scale variations of the Black Sea level during the first quarter of the Holocene

Abstract

Analysis and synthesis of different paleo evidence has enabled a qualitatively new outline of the Holocene history of the Black Sea (BS). In the early Holocene, the sea level rise was complicated by a series of transgressions and regressions. The question of their origin remains open because there are no clear, stable links of the BS level anomalies and palaeohydrological phases with the calendar of climatic anomalies. Tectonically induced vertical motions may also be a source of discrepancies of different eustatic curves.Neglecting the water exchange via the Bosphorus Strait at the beginning of the Holocene, we can propose the mechanism of occurrence of large transgressive/regressive stages of the BS. The model of the BS level dynamics is interpreted as stochastic; from this perspective, it is a Langevin equation that incorporates the action of river runoff, precipitation and evaporation as random white noise. Under these conditions, the fast anomalies of the water regime are accumulated by the BS undergoing random walk. This mechanism could be responsible for the appearance of secular-millennium-scale large, irregular fluctuations of the BS level that do not correlate with known climatic events.However, such hypothetical BS level anomalies could not have occurred in the presence of a large water discharge value via the Bosphorus Strait because intensive water exchange between the BS and the Sea of Marmara was a very effective spin-down process, destroying BS level anomalies and prohibiting the development of large-scale anomalies lasting a few centuries or, furthermore, a few thousand years.Therefore, the theoretical analysis showed that the empirical data are controversial; observed BS level fluctuations during the first quarter of the Holocene and large water discharge value via the Bosphorus Sill could not occur simultaneously. The magnitude and occurrence of BS level fluctuations and features of the BS–Sea of Marmara interaction require further specification based on geological and geochronological evidence.