Lateglacial and Holocene sea level changes in semi-enclosed seas of North Eurasia: examples from the contrasting Black and White Seas
Abstract A comparison of the Black and White Seas, which differ in their tectonic, glacial and climatic history but which share a strong dependence upon limited water exchange with the world ocean, represents an opportunity for the identification of major factors controlling sea level changes during the Lateglacial and Holocene and for the correlation of these changes. Existing data were critically analyzed and compared with the results of geological, geomorphological and palaeohydrological studies obtained by the present authors during the past two decades. We conclude that glacioeustatic processes played a major role in relative sea level changes on most coasts of both areas. However, along several coastlines, other factors overwhelm glacioeustasy during some time intervals. In the Black Sea, water level rose from its minimum position, −100–120 m, at 18–17 ka BP, to −20–30 m at nearly 9 ka BP. In the White Sea, the decreasing trend in relative sea level is well illustrated on the Kola Peninsula and in Karelia, subject to glacioisostatic emergence. A drastic sea level fall from +15 to −25 m occurred with the drainage of glacial lakes in the eastern White Sea (12.5–9.5 ka BP). The Black and White Sea histories changed drastically in the early Holocene or in the beginning of the middle Holocene (9.5–7.5 ka BP) due to the intrusion of water from the Mediterranean and the Barents seas, respectively. During this period, the White Sea developed under the strong influence of the formation of “ice shelves” and “dead ice” blocks, retreating glaciers, as well as of glacioisostatic and related processes. The Black Sea history, however, was determined by water exchange with the Mediterranean via the shallow Dardanelles and Bosporus straits (outflow from the Black Sea 10–9.5 ka BP and inflow from 9–7.5 ka BP according to various data), and, partially, by river discharge variations caused by climatic changes on the Russian Plain. The hypothesis of a catastrophic sea level rise from −120–150 to −15–20 m nearly 7550 calendar years BP is not supported by our data. Water intrusion from the Mediterranean was fast but not catastrophic. In the Black Sea, periods of high sea levels after the intrusion of Mediterranean waters are dated from four sedimentary complexes, Vityazevian, Kalamitian, Dzhemetian and Nymphaean, from nearly 7.5, 7–6, 5.5–4.5 and 2.2–1.7 ka BP, respectively. A fluctuating pattern of sea level change was established in the White Sea after the drainage of proglacial lakes and intrusion of ocean waters at the end of the early Holocene (nearly 8.5–8.2 ka BP). Major periods of sea level rise in the White Sea are dated from the late Boreal–early Atlantic (8.5–7.5 ka BP), late Atlantic (6.5–5.2 ka BP), middle Subboreal (4.5–4 ka BP) and middle Subatlantic (1.8–1.5 ka BP). Fluctuations of relative sea level during the middle and late Holocene were possibly on the order of several meters (from +2–3 to −2–3 m in the Black Sea and from +3–5 to −2–3 m in the White Sea). Lower estimates of regressive stages are principally derived from archaeological data on ancient settlements in tectonically submerging deltaic areas and cannot be regarded as reliable. Palaeohydrological analysis does not indicate that intensive (15–25 m or greater) sea level fluctuations were present in the Black Sea or in the White Sea during the middle and late Holocene. Instead, such analysis provides independent evidence to support the argument that significant differences in water level between the Black Sea and the Mediterranean could not be maintained for an extended period of time.