Seafloor morphology in the Mozambique Channel: evidence for long-term persistent bottom-current flow and deep-reaching e
- PDF / 24,995,633 Bytes
- 29 Pages / 595.276 x 790.866 pts Page_size
- 73 Downloads / 131 Views
ORIGINAL RESEARCH PAPER
Seafloor morphology in the Mozambique Channel: evidence for long-term persistent bottom-current flow and deep-reaching eddy activity Monika Breitzke1 · Errol Wiles2 · Ralf Krocker3 · Michael K. Watkeys2 · Wilfried Jokat3
Received: 10 August 2016 / Accepted: 24 May 2017 / Published online: 2 June 2017 © Springer Science+Business Media Dordrecht 2017
Abstract The Mozambique Channel plays a key role in the exchange of surface water masses between the Indian and Atlantic Oceans and forms a topographic barrier for meridional deep and bottom water circulation due to its northward shoaling water depths. New high-resolution bathymetry and sub-bottom profiler data show that due to these topographic constraints a peculiar seafloor morphology has evolved, which exhibits a large variety of current-controlled bedforms. The most spectacular bedforms are giant erosional scours in the southwest, where northward spreading Antarctic Bottom Water is topographically blocked to the north and deflected to the east forming furrows, channels and steep sediment waves along its flow path. Farther north, in the water depth range of North Atlantic Deep Water, the seafloor is strongly shaped by deep-reaching eddies. Steep, upslope migrating sediment waves in the west have formed beneath the southward flow of anticyclonic Mozambique Channel eddies (MCEs). Arcuate bedforms in the middle evolved through an interaction of the northward flow of MCEs with crevasse splays Electronic supplementary material The online version of this article (doi:10.1007/s11001-017-9322-7) contains supplementary material, which is available to authorized users. * Monika Breitzke Monika.Breitzke@uni‑bremen.de 1
Department of Geosciences, Universität Bremen, Klagenfurter Straße, D‑28359 Bremen, Germany
2
School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Private Bag X 54001, Durban 4000, Republic of South Africa
3
Alfred-Wegener-Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, D‑27568 Bremerhaven, Germany
from a breach in the western Zambezi Channel levee. Hummocky bedforms in the east result from an interplay of East Madagascar Current eddies with overspill deposits of the crevasse and Zambezi Channel. All bedforms are draped with sediments indicating that the present-day current velocities are not strong enough to erode sediments. Hence, it can be concluded that the seafloor morphology developed during earlier times, when bottom-current velocities were stronger. Assuming a sedimentation rate of 20 m/Ma and a drape of at least 50 m thickness the bedforms may have developed during the Pliocene Epoch or earlier. Keywords Seafloor morphology · Bedforms · Bottom currents · Deep-reaching mesoscale eddies · Mozambique Channel · SW Indian Ocean
Introduction Since the early publication of first seabed images showing current-induced features such as ripples, scours or current lineations on the deep-seafloor (Heezen and Hollister 1964, 1971; Heezen et al. 1966) numerous st
