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ArticleTesting the physical oceanographic implications of the suggested sudden Black Sea infill 8400 years ago(American Geophysical Union, 2004-03-17) Siddall, M. ; Pratt, Lawrence J. ; Helfrich, Karl R. ; Giosan, LiviuWe apply a shock-capturing numerical model based on the single-layer shallow water equations to an idealized geometry of the Black Sea and the Sea of Marmara in order to test the implications of a suggested sudden Black Sea infill 8400 years ago. The model resolves the two-dimensional flow upstream and downstream of the hydraulic jump provoked by the cascade of water from the Sea of Marmara into the Black Sea, which would occur during a sudden Black Sea infill. The modeled flow downstream of the hydraulic jump in the Black Sea would consist of a jet that is in part constrained by bathymetric contours. Guided by the Bosporus Canyon, the modeled jet reaches depths of up to 2000 m and could explain the origin of the sediment waves observed at this depth. At a late stage of the infill the modeled jet is attached to the coast and might account for the course of a submerged channel at the mouth of the Bosporus. The preservation of continuous barrier-washover-lagoonal fill systems occurring on the Black Sea shelf is, however, not easily reconcilable with the large flows over the southwest Black Sea shelf predicted by the model. Intensified flow in the upstream basin (Sea of Marmara) is restricted to the immediate vicinity of the Bosporus, suggesting that a sudden reconnection need not have disturbed sediments in the wider Sea of Marmara.
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PreprintA cartographical perspective to the engineering works at the Sulina mouth, the Danube Delta( 2009-06-19) Constantinescu, Stefan ; Giosan, Liviu ; Vespremeanu-Stroe, A.From 1856 to 1939, the European Commission of the Danube (ECD), was responsible for technical surveys at the mouth of Sulina arm. During this period, ECD prepared general maps of Danube Delta as well as detailed charts for all the Danube mouths: Chilia, Sulina and Sf. Gheorghe (St. George) that were published in various reports or atlases. ECD used a local grid network benchmarked at Sulina, divided in 500 feet units. The reference point was the old lighthouse located on the right bank of Danube. After the Second World War, the Romanian authorities elaborated new cartographical products using the Gauss‐Kruger projection or Stereo‐70 like national grid. Our goal is to generate a cartographical background database necessary for refining the coastal evolution model of the Sulina mouth. To handle the large number of available maps, we chose GeoNetwork like a solution for catalog service, indexing and defining metadata. The service is operating at geo‐spatial.org.
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PreprintSinking deltas due to human activities( 2008-12-26) Syvitski, James P. M. ; Kettner, Albert J. ; Overeem, Irina ; Hutton, Eric W. H. ; Hannon, Mark T. ; Brakenridge, G. Robert ; Day, John W. ; Vorosmarty, Charles J. ; Saito, Yoshiki ; Giosan, Liviu ; Nicholls, Robert J.The world’s population living on low-lying deltas is increasingly vulnerable to flooding, whether from intense rainfall, rivers or from hurricane-induced storm surges. High-resolution SRTM and MODIS satellite data along with geo-referenced historical map analysis allows quantification of the extent of low-lying delta areas and the role of humans in contributing to their vulnerability. Thirty-three major deltas collectively include ~26,000 km2 of area below local mean sea level and ~96,000 km2 of vulnerable area below 2 m a.s.l. The vulnerable areas may increase by 50% under projected 21st Century eustatic sea level rise, a conservative estimate given the current trends in the reduction in sedimentary deposits forming on the surface of these deltas. Analysis of river sediment load and delta topographical data show that these densely populated, intensively farmed landforms, that often host key economic structures, have been destabilized by human-induced accelerated sediment compaction from water, oil and gas mining, by reduction of incoming sediment from upstream dams and reservoirs, and from floodplain engineering.
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PreprintThe last reconnection of the Marmara Sea (Turkey) to the World Ocean : A paleoceanographic and paleoclimatic perspective( 2008-07) McHugh, Cecilia M. G. ; Gurung, Damayanti ; Giosan, Liviu ; Ryan, William B. F. ; Mart, Yossi ; Sancar, Ummuhan ; Burckle, Lloyd H. ; Cagatay, M. NamikDuring the late glacial, marine isotope Stage 2, the Marmara Sea transformed into a brackish lake as global sea level fell below the sill in the Dardanelles Strait. A record of the basin’s reconnection to the global ocean is preserved in its sediments permitting the extraction of the paleoceanographic and paleoclimatic history of the region. The goal of this study is to develop a high-resolution record of the lacustrine to marine transition of Marmara Sea in order to reconstruct regional and global climatic events at 24 a millennial scale. For this purpose, we mapped the paleoshorelines of Marmara Sea along the northern, eastern, and southern shelves at Çekmece, Prince Islands, and Imrali, using data from multibeam bathymetry, high-resolution subbottom profiling (chirp) and ten sediment cores. Detailed sedimentologic, biostratigraphic (foraminifers, mollusk, diatoms), X-ray fluorescence geochemical scanning, and oxygen and carbon stable isotope analyses correlated to a calibrated radiocarbon chronology provided evidence for cold and dry conditions prior to 15 ka BP, warm conditions of the Bolling-Allerod from ~15 to 13 ka BP, a rapid marine incursion at 12 ka BP, still stand of Marmara Sea and sediment reworking of the paleoshorelines during the Younger Dryas at ~11.5 to 10.5 ka BP, and development of strong stratification and influx of nutrients as Black Sea waters spilled into Marmara Sea at 9.2 ka BP. Stable environmental conditions developed in Marmara Sea after 6.0 ka BP as sea-level reached its present shoreline and the basin floors filled with sediments achieving their present configuration.