Project study areas
The EUROSTRATAFORM project will study four different areas around the European continental margin. These areas have been carefully selected to give comprehensive cover of the varied sedimentary systems that characterise the European continental shelf and slope.
Study of these four areas will allow us to compare:
- Shelf and slope areas with and without a major river input
- Areas with strong and weak tidal and/or storm influence
- Smooth continental slopes with those cut by deep canyons
- Areas where sediment accumulates at the shelf edge with areas where sediment bypasses the slope and moves rapidly to the deep sea
- Glaciated with non-glaciated continental margins
The Portuguese Margin
The western Iberian margin is characterised by a narrow shelf adjacent to a steep iregular slope, with intense wind-induced summer upwelling occurring at the shelf edge. It is dissected by steep canyons, including the Porto, Aveiro, Nazare and Lisbon/Setubal canyons. Along the continental slope, all Portuguese margins interact with a northward-flowing bottom current derived from the Mediterranean. The largest canyons (Nazare, Setubal) intersect the entire continental shelf, allowing them to intercept sediment carried over the shelf and upper slope by alongshore currents and providing a direct conduit of particles from the upper shelf to the deep sea. In addition, both these canyons reach close to the coastline, or have a direct connection to a river mouth (Setubal), while others, such as the Porto Canyon, begin only at the shelf edge.
The Lisbon/Setubal canyon is closely related to the large riverine sediment source formed by the Tagus River, a feature absent from the vicinity of the Nazare Canyon. Recent studies have shown that fast sedimentation occurs in the Nazare canyon system, and that areas of enhanced sediment accumulation occur. The Nazare canyon may well act as a temporary catchment area and sediment trap for material which is transported over the shelf until it is flushed to the deep sea.
In contrast, the Porto Canyon terminates at the shelf edge and plays only a minor role in interception of shelf material at the present-day sea level. All canyons were probably more active at times of low sea level than at present, although this remains to be proven. The Iberian margin is the site of frequent and sometimes very large earthquakes, many of which may trigger large scale slope failure and transport of sediment to the adjacent abyssal plains.
The Gulf of Lions
The Gulf of Lions is a perfect example of a temperate, deltaic margin dissected by numerous canyons. The Gulf receives water and sediment from the River Rhone (the largest river input into the Mediterranean Sea) as well as from some smaller rivers. This characteristic allows us to compare a large season-dominated system (the Rhone River and its prodelta, at the entrance to the Gulf) with a small, event-dominated system (the Tet River and its prodelta, at the exit). In both areas, occasional floods may contribute more sediment than the whole of the contribution from the rest of the year.
The Adriatic Sea
The primary fluvial dispersal system in the Adriatic is the Po River, with additional contributions from many smaller Apennine rivers. Sediment is deposited on the Po delta with some distribution towards the south along the shelf. Eventually the Bari Canyon intercepts this transport pathway, and sediment is transferred directly to the deep water Adriatic Basin. During low sea level stands the shelf area was much reduced and sediment moved more directly to the deeper water entering the Adriatic Basin from the north.
The Norwegian Margin
The Andøya Canyon is located on the continental slope of northern Norway where the shelf is very narrow, and it is deeply incised into the continental shelf and slope. The head of the Andøya Canyon is located only 10km away from the present day coastline, while the canyon terminates in a water depth of just over 3000m. The development of the Andøya Canyon (and the associated Lofoten Basin Channel) is believed to have been driven by sediment erosion from ice sheets and melt water, since no fluvial river system is connected to the canyon. Holcene sediments from eithin the channel indicate that the channel may not be active today, but that it acts as a trap for sediment carried by the northward-directed Norwegian current. During glacial times, ice sheets may have brought large amount of sediment to the cayon head. These sediments may have been remobilised during changing sea level conditions due to continental uplift and sea level rise. The role of this remobilisation in canyon slope stability is relatively unknown and not well constrained. It is intended to use the Andøya Canyon study results for comparison of forcing conditions and processes governing margin structure in a glaciated margin setting with those in a non-glaciated margin setting.
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