Southern Transect Research Articles

Blake Escarpment Carbonate Platform Edge: Conclusions Based on Observations and Sampling from Research Submersible: ABSTRACT

Three continuous transects of the Blake Escarpment, east of Florida, were made during 10 dives in the submersible Alvin at depths from 1,400 to 4,000 m. We observed and sampled outcrops of horizontal strata known, from multichannel profiles across the dive sites, to extend westward beneath the Blake Plateau carbonate platform. The northern end of the Blake Escarpment, at the salient of the Blake Spur, is a nearly vertical limestone cliff, which is pitted and commonly fluted by vertical borings, coated by ferromanganese oxide, and heavily encrusted by organisms. Presumably, the cliff face is maintained by bioerosion and corrosion, and debris is removed by the strong turbulent currents (2 kn). Average slopes were less steep at transects 130 and 200 km south of the Blake Spu , but vertical cliffs as much as 450 m high exist. Talus slopes are common, and the large blocks and landward dips of beds suggest collapse of fragments at least several hundred meters across. On the southern transect are broad slopes of rippled pteropod sand between near-vertical outcrops; a vertical 160-m cliff of massive limestone at the top of the escarpment and rudists in talus blocks suggest the presence of a Mesozoic reef. Preliminary analysis of calcarenous nannofossils shows rocks as old as Early Cretaceous; identification of older rocks is anticipated. Sedimentary structures and components indicate deposition in shallow water. Thousands of meters of subsidence and extensive erosional retreat were required to create the escarpment's present configuration. End_of_Article - Last_Page 918------------

Estimation of Meridional Heat Flux in the North Atlantic by Inverse Methods

Hydrographic sections spanning the Atlantic Ocean at 24, 36 and 48°N are used to make an estimate of meridional heat flux in the ocean. An inverse method provides reference level velocities for geostrophic calculations, consistent with assumptions of conservation of mass and salt in a multilayered ocean. The heat-flux calculation is made on the total geostrophic velocity together with observed temperature. It is found that the dominant mechanism for heat transport in the North Atlantic is a meridional cell of northward flowing surface water balanced by deep southward flow. The strength of the meridional cell is determined best by the data at 24°N. This is attributed to higher information content and lower noise, from topographic roughness, in the southern transect. An ageostrophic correction to the heat flux is estimated, and the resulting total northward heat flux is 120×1013 W at 24°N and about 80×1013 W at 36°N. The heat flux was poorly determined at 48°N. It is concluded that the technique could be used to combine hydrographic data with other relevant measurements, such as air-sea heat exchange, to construct a heat budget for the world oceans.

Rankine memorial Movement

Sediment samples collected during expedition ARK XIII/2 in summer 1997 with the German ice-breaker R/V POLARSTERN were investigated to estimate benthic microbial activity and total biomass of the smallest sediment-inhabiting organisms (size range from bacteria to meiofauna) from the Yermak Plateau northwest of Spitsbergen and adjacent deep-sea areas. Stations covered water depths from about 500 m north of Svålbard and on top of the Yermak Plateau to 3250–4250 m in the Fram Strait and the Nansen Basin. The area of investigations is located in a region with permanent ice-coverage, but in summer 1997 stations along the southern transect crossing the Yermak Plateau at about 81°N lay 50–100 km from the ice-edge. The hydrography of the area is characterized by the inflow of relatively warm, nutrient-rich and particle-laden Atlantic Water into the Arctic Ocean. The input of organic matter from primary production was estimated by measuring concentrations of sediment-bound chloroplastic pigments. Benthic activities and biomasses were evaluated by analyzing a series of biogenic compounds (i.e. bacterial exoenzymes, total adenylates, phospholipids, particulate proteins) in the sediments. Bacterial numbers and biomasses, meiofauna abundances, and nematode biomasses were determined for direct comparison with biochemical parameters. Faunal and biochemical data suggest a high current-driven lateral input of particulate organic matter from the South associated with increased sedimentation rates along the western slope of the Yermak Plateau.