When WHOI geologist Liviu Giosan first reconstructed the history of how the Danube River built its delta, he was presented with a puzzle.
In the delta's early stages of development, the river deposited its sediment within a protected bay. As the delta expanded onto the Black Sea shelf in the late Holocene and was exposed to greater waves and currents, rather than seeing the decline in sediment storage that he expected, Giosan found the opposite. The delta continued to grow. In fact, it has tripled its storage rate.
If an increase in river runoff was responsible for the unusual rapid build up of sediment in the delta, says Giosan, the question is, "Was this extraordinary event in the Danube delta felt in the entire Black Sea basin? And if so, what caused it?"
In answering those questions, Giosan and an international team of collaborators including environmental engineers, modelers, paleogeographers, and paleobiologists pieced together a unique history of the region that ultimately provides evidence for a transformative impact of humans on the Black Sea over hundreds, if not thousands of years. The study was published on August 30 in Scientific Reports, a new online journal of the Nature Publishing Group.
The largest and longest river in the European Union, the Danube is the source of over 60 percent of the freshwater running into the Black Sea, and therefore is a dominant factor in the biogeochemistry of this basin. Because the Black Sea is nearly enclosed, changes in its hinterland provoked by climate or people should be readily reflected there.
The research team reconstructed a 9000-year record of the delta's growth, and through various scientific techniques, developed and mapped against it a record of changes in the Black Sea's salinity, nutrients, and relative abundance of its ecosystem's major phytoplankton groups. Finally, they also examined the history of land use in the greater Danube watershed.
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Woods Hole Oceanographic Institution