Distribution and biomass of seston in the East Atlantic

Biomass of seston in the surface layers of coastal waters off Namibia reaches 1 g/m**2 and decreases with distance from the shore. Two regions of high seston biomass, one northern and one southern, are distinguished. A subsurface maximum of seston biomass, presumably coinciding with the stream of compensating countercurrent, is identified in the 200-500 m layer. Similar vertical distribution of plankton is known in upwelling areas of the eastern shores of the Atlantic and Pacific Oceans and in several other ocean areas, such as the area of the Kuril-Kamchatka Trench. This fact probably indicates that life cycles of pelagic animal forms of various taxonomic groups that inhabit them and phases of their ontogenic migrations are similar.

Radio-echo sounding investigation of the western Dronning Maud Land and north-eastern Coats Land, East Antarctica (Scale 1:2 500 000)

During two Antarctic field seasons, western Dronning Maud Land and eastern Coats Land were covered by airborne radio-echo sounding surveys, conducted in combination with magnetic and gravity measurements along the 50 NW-SE-directed tracks, totaling about 11200 km and spaced 20 km apart. The data were collected in analogue form and then processed to compile ice surface, ice thickness and bedrock topography maps in I : 2 500 000 scale which gave a new and/or more detailed information on the region than previous compilations. The maps show that western Dronning Maud Land is dominated by a large mountainous area with altitudes up to 2800 m including rock outcrops of Annandagstoppane, Borgmassivet, Kirwanveggen and Heimefrontfjella. Upland terrains of Vestfjella and Mannefallknausane have an isolated position and are surrounded by a plain with bedrock depressions of 600 m deep below sea level. A narrow strip of north-eastern Coats Land studied by radio-echo soundings exhibits a smooth subice relief with altitudes close to sea level. The structural style of bedrock topography was mostly determined by extensional tectonics.

Part of the global DOC versus AOU (dissolved organic carbon/apparent oxygen utilization) data compilation, Azores-I

Temperate, transitional and subtropical waters of the remote Azores Front region east of Azores (24-40°N, 22-32°W) were sampled during three cruises conducted under increasing stratification conditions (April 1999, May 1997 and August 1998). Despite the temporal increase of surface temperature (by 5 °C) and stratification (by 2.1 1/min**2), as well as the thermocline shoaling (by ~15 m), dissolved organic carbon (DOC) and nitrogen (DON) in the surface layer were not significantly different for the early spring, late spring and summer periods, with average concentrations of 69±2 µM-C and 5.2±0.4 µM-N, respectively. The surface excess of semi-labile DOC, compared with the baseline DOC concentration in the deep ocean (47±2 µM-C), represents 33% of the bulk DOC concentration and as much as 85% of the TOC (=POC+DOC) excess. When compared with the winter baseline (56±2 µM-C), the seasonal surface DOC excess is 20% of the bulk DOC concentration and 87% of the seasonal TOC excess. These results confirm the major role played by DOC in the carbon cycle of surface waters of the Azores Front region. The total amount of bioreactive DOC transported from the temperate to the subtropical North Atlantic by the Ekman flux between March and December represents only ~15% of the average annual primary production, and ~15% and ~30% of the measured sinking POC flux+vertical DOC eddy diffusion during early spring and summer, respectively. Vertical eddy diffusion is 35% and 2% of the spring and summer sinking POC flux, respectively. On the other hand, DOC only contributes 13% to the local oxidation of organic matter in subsurface waters (between the pycnocline and 500 m) of the study region.

Geochemistry of hydrothermal solutions, ores, and biota from hydrothermal fields at the East Pacific Rise axis near 9°50'N

Hydrothermal solutions were examined in a circulation system that started to develop after the 1991 volcanic eruption in the axial segment of the EPR between 9°45'N and 9°52'N. Within twelve years after this eruption, diffusion outflow of hot fluid from fractures in basaltic lavas gave way to focused seeps of hot solutions through channels of hydrothermal sulfide edifices. An example of the field Q demonstrates that from 1991 to 2003 H2S concentrations decreased from 86 to 1 mM/kg, and the Fe/H2S ratio simultaneously increased by factor 1.7. This fact can explain disappearance of microbial mats that were widespread within the fields before 1991. S isotopic composition of H2S does not depend on H2S concentration. This fact testifies rapid evolution of the hydrothermal system in the early years of its evolution. Carbon in CH4 from hot fluid sampled in 2003 is richer in 12C isotope than carbon in fluid from the hydrothermal field at 21°N EPR. It suggests that methane comes to the Q field from more than one source. Composition of particulate matter in hydrothermal solutions indicates that it was contributed by biological material. Experimental solutions with labeled substrates (t<70°C) show evidence of active processes of methane oxidation and sulfate reduction. Our results indicate that, during 12-year evolution of the hydrothermal system, composition of its solutions evolved and approached compositions of solutions in mature hydrothermal systems of the EPR.

Sulfur compounds in bottom sediments and interstitial waters of the Pacific Ocean to the east of Japan

In near-shore Pacific bottom sediments to the east of Japan unusually high content of free H2S ocurs. H2S resulting from bacterial reduction of sulfates from interstitial waters has a number of derivatives; pyrite dominates among them. Contents of other derivatives of H2S: sulfide sulfur and organic sulfur do not exceed 0,01%, content of organic sulfur does not exceed 0.1%. Due to reduction content of sulfates can reduce to 0,03% S. Capacity of the process of sulfate reduction, estimated by sum of all reduced forms of S - derivatives of H2S, is a function of organic matter content in sediments. Ability of bottom sediments to accumulate free H2S depends on content of reactive forms of Fe. Spatial distribution of reduced forms of S in the studied sediments is considered.