ALBERT

Beschreibung: Sediment transport processes in the northern North Atlantic have been investigated on the basis of various numerical models. A general circulation model has been used to investigate large-scale particle transport, a reduced gravity plume model has been used to investigate particle transport by cascading from the shelves into the deep basins, an ocean slice model has been used to investigate particle exchange processes between a bottom current and the ambient water mass, and a Bottom Boundary Layer model has been used to investigate particle interactions influencing the settling behavior of suspended particles. In this paper, the various processes investigated in these models are described (i) schematically, (ii) on the basis of field data, if available, and (iii) by employing results from numerical simulations. In a first attempt the northern North Atlantic will be divided into separate process defined areas, which can be used in carbon budgeting, for example.

Beschreibung: To date, work on the Great Bahama Bank’s western, leeward margin has centred chiefly on seismic-scale expressions of carbonate sequences and systems tracts. However, periplatform, slope sediments also exhibit very well developed cyclicity on scales of decimetres to several metres. It is these small-scale, high-frequency cycles within the larger-scale facies successions of the Quaternary which form the main topic of this paper. Previous studies have shown that the small-scale cycles correlate to the orbitally forced, high-frequency sea-level changes. Therefore these cycles should indicate how sea level has affected the slope development and thus platform-margin evolution during this period. Through detailed, high-resolution sequence stratigraphy of the Great Bahama Bank’s leeward margin, obtained via δ18O isotope and mineralogical (XRD) analyses, confined by U/Th dating and nannofossil bioevents, a greater understanding of the bedding geometries within the Pleistocene–Holocene seismic sequences and clues as to the nature of the slope development has been achieved. The high-resolution seismic profiles indicate that since the Plio–Pleistocene change in geometry, in which the Great Bahama Bank developed into a rimmed platform, continued steepening and subsequent progradation of the leeward margin has typified slope development during the Quaternary, which is described as an accretionary slope. However, on the basis of our observations we conclude that only the early to lower middle Pleistocene section (isotope stages 45–20) and the Holocene (isotope stage 1) of the leeward margin is accretionary. This indicates that a degree of erosion and/or by-passing has occurred on the leeward margin since the lower middle Pleistocene (isotope stage 19). During the first part of this period (isotope stages 19–12) erosion and/or by-passing occurred in the middle to lower slope regions and toe-of-slope. By the end of the upper middle to late Pleistocene phase (isotope stages 11–2) erosion also occurred on the upper slope. This erosion by currents at the toe-of-slope and oversteepening of the upper and middle slopes have led to back-cutting upslope and resulted in the progressive retreat of the toe-of-slope towards the platform to the east. However, the rise in sea level since the Last Glacial Maximum to its present-day level has allowed high productivity on the platform top during the Holocene and the deposition of a thick sediment wedge on the slope and sedimentation across the entire leeward flanks. This has led to the redevelopment of an accretionary slope and continued westward progradation of the Great Bahama Bank’s western, leeward margin.

Beschreibung: In 3 successive years (1998 to 2000), the winter migration of rockhopper penguins Eudyptes chrysocome from 3 separate breeding colonies on the Falkland Islands was monitored using satellite transmitters. After their moult, 34 penguins were followed for a mean transmission period of 81 ± 21 d. While there were substantial spatial and temporal variations in migration patterns, we identified several foraging areas where food availability is presumably higher than elsewhere. Coastal areas of the Falkland Islands and South America appeared to provide a sufficient food supply, and many penguins commuted between these 2 areas, which are about 600 km apart. Rockhopper penguins from northern breeding colonies also used areas along the slope of the Patagonian Shelf up to 39°S, about 1400 km northwards. By contrast, only a few birds from the southern breeding colony migrated to the Burdwood Bank, which is situated about 250 km to the south of the Falkland Islands, and adjacent oceanic waters. None of the penguins in this study left the maritime zone of the Falkland Islands in an easterly direction to forage in oceanic waters. The mean distances covered per day by individual birds varied greatly, depending on the phase of the foraging trip. The overall mean travelling speed was 26 km d-1 (range: 13 to 45 km d-1). Inter-annual variation was evident both in the use of different foraging areas, and also in the time at which the winter migration began. In 1998 and 2000, penguins from Seal Bay and Sea Lion Island left their breeding colony within 1 wk after being equipped with transmitters and did not return, whereas in 1999 most penguins made short foraging trips and returned repeatedly to their colonies for periods of up to 100 d. Potential threats to the rockhopper penguins during their winter migration, resulting from human activities such as fishing and oil pollution within the Falkland Islands maritime zone and the Argentine Exclusive Economic Zone, are discussed.