Bulgarian Academy of Sciences

About: Bulgarian Academy of Sciences is a government organization based out in Sofia, Bulgaria. It is known for research contribution in the topics: Coupling constant & Catalysis. The organization has 17989 authors who have published 36276 publications receiving 642820 citations. The organization is also known as: Bulgarian Academy of Sciences，簡稱：BAS & Balgarska Akademiya na Naukite.

Nutrient and phytoplankton trends on the western Black Sea shelf in response to cultural eutrophication and climate changes

Abstract: Long-term trends (1960se1990s) in surface winter nutrients and summer oxygen concentration of the euphotic zone, as well as seasonal and interannual variability in surface chlorophyll a (chl a) and Secchi depth (Zd) were investigated for different shelf regions (depth <50 m) of the western Black Sea. Increasing phosphate and nitrate levels and changes in the summer oxygen concentration on the shelf before the mid-1980s corresponded well with the increase in riverine nutrient inputs. At the same time, decreasing silicate levels resulted almost equally from enhanced diatom stripping and trapping of silicate in the numerous dams constructed on the Danube River. The associated decrease in the Si:N ratio caused a shift towards more non-siliceous phytoplankton blooms. A decoupling of winter nutrient levels and summer oxygen concentration on the shelf after the mid-1980s suggests that other sources of inputs, such as regenerated nutrients from shelf sediments and/or upwelling, may have increased substantially. Large variations in the regional climate during the 1980s and 1990s could potentially account for increases from either or both of these sources and the resulting high summer primary production despite decreasing winter nutrients. The seasonal pattern in chl a within the Ukrainian NW shelf is similar to the open Black Sea, with low chl a in summer and high concentrations in cold months. The seasonal chl a variations on the Romanian and Bulgarian shelves also show high concentrations in May/June, most likely related to the Danube River maximum discharge during spring. As a result, chl a annual means in these two regions are significantly higher than e in the Ukrainian NW shelf. 2007 Elsevier Ltd. All rights reserved.

Bridging onshore and offshore present-day kinematics of central and eastern Méditerranean: Implications for crustal dynamics and mantle flow

Abstract: We present a new kinematic and strain model of an area encompassing the Calabrian and Hellenic subduction zones, western Anatolia and the Balkans. Using Haines and Holt's (1993) method, we derive continuous velocity and strain rate fields by interpolating geodetic velocities, including recent GPS data in the Balkans. Relative motion between stable Eurasia and the western Aegean Sea is gradually accommodated by distributed N-S extension from Southern Balkans to the Eastern Corinth Gulf, so that the westward propagation of the North Anatolian Fault (NAF) throughout continental Greece or Peloponnesus is not required. We thus propose that the NAF terminates in north Aegean and that N-S extension localized in the Corinth Gulf and distributed in Southern Balkans is due to the retreat of the Hellenic slab. The motion of the Hyblean plateau, Apulia Peninsula, south Adriatic Sea, Ionian Basin and Sirte plain can be minimized by a single rigid rotation around a pole located in the Sirte plain, compatible with the opening the Pelagian rifts (2–2.5 mm/yr) and seismotectonics in Libya. We interpret the trenchward ultraslow motion of the Calabrian arc (2–2.5 mm/yr) as pure collapse, the Calabrian subduction being now inactive. In the absolute plate motion reference frame, our modeled velocity field depicts two toroidal crustal patterns located at both ends of the Hellenic subduction zone, clockwise in NW Greece and counter-clockwise in western Anatolia. We suggest the NW Greece toroidal pattern is the surface expression of a slab tear and consequent toroidal asthenospheric flow.