C1-C5 hydrocarbons from core gas pockets at DSDP Leg 56 Holes

C1-C5 hydrocarbons from DSDP Legs 56 and 57 sediment gas pockets were analyzed on board ship. Results suggest that the C2-C5 hydrocarbons accompanied biogenic methane and were generated at low temperatures - less than 50° C - either by microorganisms or by low-temperature chemical reactions. Neopentane, a rare constituent of petroleum, is the major C5 component (about 80%) in much of the sediment at Site 438. This compound, which appeared in smaller amounts at Sites 434, 439, 440, and 441, seems to correlate with either fractured or coarse-grained sediments. Scatter in C4 and C5 isomer ratios and generally good correlation between C3, C4 and C5 components suggest local sources for these molecules.

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.