7th Training-through-Research Cruise

The seventh Training-through-Research international cruise of the R/V Professor Logachev was carried out in the northeast Atlantic in July - August 1997. As in previous years the cruise was conducted within the UNESCO/IOC "Floating University" Programme but this year in co-operation with the CORSAIRES and ENAM programmes of the European Commission. The expedition aimed to solve some outstanding problems in the field of geological processes on a passive continental margin and particularly to shed light on the nature and ecology of carbonate mounds recently discovered west off Ireland, which were thought to be due to hydrocarbons migrating upward.

Modern analogues of hydrocarbon reservoirs were the other important objective of the cruise. A well developed system of tributary channels that runs from the margin south of Ireland to the Porcupine Abyssal Plain, and the potential area of sandy contourites lying to the west of the Faeroe Bank Channel were considered to be of interest as such analogues. Comprehensive investigations resulted in the realisation that there are huge quantities of carbonate within cold water carbonate mounds. They are of enormous size (up to 400 m high, 5 km long) and have great diversity of shape. Over 150 mounds were mapped on just a small portion of the slopes of the Rockall Trough and Porcupine Seabight. Advances in understanding why carbonate mounds occur came from the biological, geochemical and sedimentological studies. The importance of fast flowing currents to the growth of cold water corals, the main growth builder of the mounds, was clearly demonstrated. Moulding of mounds by prevailing currents was also seen.

Contour currents are one of the main ways that slopes in the region are fashioned. In spite of the fact that sandy contourites are rarely recognised in studies of either ancient or modern sediments they were shown to be very significant in this part of the Atlantic. Sidescan sonar proved the most effective way to map the pathways of strong currents. By this method, a hitherto unknown, strong northward directed current was discovered in the Porcupine Seabight. Strong currents were also sweeping sands along the upper slope east of Rockall Bank and along the slope west of Porcupine Bank. Complex, sand filled channels shaped by the cold, salty overflow water from the Norwegian Sea were mapped in the Iceland Basin.

The deep sea turbidite channel system in the Porcupine Seabight was shown to be inactive during the Holocene.

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cruise report
post-cruise meeting abstracts