Composition and fluxes of sinking particulate material and bottom sediments in the northeast Black Sea in 1998-1999

For the first time deep-sea mooring stations with sediment traps were deployed in the northeast Black Sea. One sediment trap for long-term studies was located at Station 1 (44°15'N, 37°43'E, deployment depth 1800 m, depth 1900 m). The trap collected sinking sedimentary material from January to May 1998. Material collectors were changed every 15 days. Other stations with sediment traps for short-term studies (September-October 1999) were located on the shelf: Station 2 (44°16'N, 38°37'E, deployment depth 45 m, depth 50 m) and on the bottom of the canyon: Station 3 (44°16'N, 38°22'E, deployment depth 1145 m, depth 1150 m), Station 4 (44°11'N, 38°21'E, deployment depths 200, 1550, 1650 m, depth 1670 m). Collected material indicates that vertical particle fluxes are controlled by seasonal changes of in situ production and by dynamics of terrigenous matter input. Higher vertical particle flux of carbonate and biogenic silica was in spring due to bloom of plankton organisms. Maximum of coccolith bloom is in April-May. Bloom of diatoms begins in March. In winter and autumn lithogenic material dominates in total flux. Its amount strongly depends on storms and river run-off. Suspended particle material differs from surface shelf sediments by finer particles (mainly clay fraction) and high content of clay minerals and biogenic silica. This material may form lateral fluxes with higher concentration of particles transported along the bottom of deep-sea canyons from the shelf to the deep basin within the nepheloid layer. In winter such transportation of sedimentary material is more intensive due to active vertical circulation of water masses.

La persuasión por el carácter como argumentum ad verecundiam en Aristóteles : Retórica II 23 1400ª30-37

Fil: Badenes, Andrés Ignacio. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Late Quaternary calcareous nannofossils in ODP Leg 139 holes

Upper Quaternary calcareous nannofossils contained in drill cores taken in the heavily sedimented Middle Valley of the northern Juan de Fuca Ridge in the northeast Pacific Ocean (Ocean Drilling Program Leg 139) are investigated. The host sediments have been subjected at depth to high temperatures and hot hydrothermal fluids that have altered or destroyed in part or in toto the nannofossil assemblages, thereby raising at several sites the level of the first (deepest) stratigraphic occurrence of nannofossils or of the important Emiliania huxleyi datum. The degree of alteration of the nannofossil assemblages is dependent on the intensity of the hydrothermal activity, which is indicated by paleotemperatures derived independently from studies of color alteration of palynomorphs and by vitrinite reflectance (Mao et al., this volume). State of preservation and the downhole level at which assemblages have been destroyed correlate well with the inferred paleotemperature estimates. Destruction of the assemblages appears to be species selective and follows in general the dissolution rankings determined independently by others for Recent nannofossils of the Pacific basin. More systematic correlation of these phenomena is hampered, however, by the fact that nannofossil preservation is already quite variable at the time of deposition because of the predominance of turbidite activity in the study area.