Distribution of euphausiids (Crustacea) at the Great Meteor seamount, Atlantic Ocean

In the course of the voyages 9a and 9c (1967) and 19 (1970) of the RV "Meteor" samples of plankton and neuston have been taken in the area of the Great Meteor Seamount. The euphausiids of this material have been examined quantitatively as well as qualitatively in order to study the influence of the Great and Small Meteor Seamount on a vertically migrating group of plankton. 20 species could be identified. All stem from the surrounding deep water and belong to the tropical and subtropical fauna. On the plateau of the Great Meteor Seamount no indigenous species have been encountered and also the typical neritic species from the west coast off Africa are lacking. As for the euphausiids no relationships exist between the Great Meteor Seamount and the shelf area of West Africa. The dominant species around the Meteor Seamount were Euphausia brevii, Stylocheiron suhmii, E. hemigibba, S. longicorne and Thysanopoda subaequalis. Using the index of diversity (Simpson) distinct differences in the composition of species could be shown to exist between the plateau area of the Meteor Seamount and the surrounding sea. On the plateau of the Great Meteor Seamount the number of species was only 7, E. brevis and S. suhmii dominated. None of the species occurred in great numbers and none is adapted to the specific environmental conditions of the plateau of the Meteor Seamount. The fauna of the plateau is a depauperate one as compared with that of the surrounding sea. This can be explained by the fact that adult euphausiids require for their existence greater water depths than are found above the plateau of the Meteor Seamount.

Description and chemical composition of ferromanganese encrustations and deposits in the Atlantic Ocean from R/V Atlantis II cruises 20, 42, 60, 85; R/V Chain cruise 35; R/V Knorr cruise 61 and RRS Shackleton cruise 75/1 stations

Chemical and mineralogical compositions of ferromanganese oxide coatings on rocks dredged from the New England Seamounts, the Sierra Leone Rise and the Mid-Atlantic Ridge near the Equator have been determined in an investigation of regional differences in Atlantic ferromanganese deposits. Most encrustations are clearly of hydrogenous origin, consisting mainly of todorokite and delta MnO2, but several recovered from the equatorial fracture zones may be hydrothermal accumulations. Differences in the chemistry of the water column and in growth rates of the ferromanganese coatings may be important in producing this regional contrast in composition. Fine-scale changes in element abundances within the encrustations indicate that the nature of the substrate has little influence on compositional variations.

Cretaceous radiolarians of the North Atlantic Ocean

Radiolarians form a remarkable part of the fossil plankton for Cretaceous sediments of the North Atlantic. Selected sites with long-term sedimentary successions of deep facies were studied (ODP Leg 103 and DSDP Site 398 off northwest Spain and DSDP Site 603 off the east coast of the United States). Preservation of the radiolarian faunas is generally poor, and the faunal abundance and diversity reflect the diagenetic history of the host sediment rather than the original faunal productivity. Several exceptions include abundant and some well-preserved radiolarian faunas from lower Campanian, Cenomanian/Turonian boundary, upper Albian, lower Albian, and Barremian sediments. These increases in radiolarian abundance and preservation coincide with well-established Cretaceous oceanic events in the North Atlantic. Typical faunal associations of these sections are described, and faunal associations from the Cenomanian/Turonian Boundary Event are documented for the first time in the North Atlantic. The relationship of the radiolarian blooms with coeval oceanic events in the North Atlantic is also discussed.

Geochemistry of surface sediment samples from the South Atlantic Ocean

The aim of the present study is an evaluation of the applicability of biogenic barium as a proxy for productivity. For this purpose, 190 surface sediment samples from the South Atlantic Ocean were analysed for their barium and aluminium concentrations. Biogenic barium is estimated by subtracting the calculated terrigenous barium (obtained from the terrigenous Ba/Al ratio and the amount of Al in the sample) from the total Ba content in the sample. Based on the accumulation rates of biogenic barium, export production is estimated using three different algorithms proposed by [Paleoceanography 7 (1992) 163, doi:10.1029/92PA00181; Global Biogeochem. Cycles 9 (1995) 289, doi:10.1029/95GB00021; Geomar. Report 38 (1995) 105]. Primary productivity was calculated from these different export productions and compared with measurements of recent primary productivity in the overlying surface waters. Only the primary productions calculated on the basis of the algorithm of [Paleoceanography 7 (1992) 163, doi:10.1029/92PA00181] yield productivity values comparable to those existing in ocean surface waters. This study further reveals that it is not sufficient to use a constant, generally applicable organic carbon/biogenic barium ratio, as is postulated by [Global Biogeochem. Cycles 9 (1995) 289, doi:10.1029/95GB00021]. This ratio has to be assessed regionally. For the sediments of the Cape Basin in the eastern South Atlantic Ocean, a new algorithm is developed which gives plausible primary productivities for the overlying surface waters.