http://www.dailymail.co.uk/news/article-5106689/Missing-Argentine-submarine-located-Navy.html

Geomorphology

Volume 128, Issues 3–4, 15 May 2011, Pages 116-136

Submarine canyon formation and evolution in the Argentine Continental Margin between 44°30’S and 48°S

Author links open overlay panel G.LastrasabJ.AcostabA.MuñozcM.Canalsa

a

GRC Geociències Marines, Universitat de Barcelona, E-08028, Spain

b

Instituto Español de Oceanografía, E-28002, Madrid, Spain

c

TRAGSA – Secretaría General del Mar, E-28006, Madrid, Spain

Received 4 May 2010, Revised 23 November 2010, Accepted 24 December 2010, Available online 3 January 2011.

https://doi.org/10.1016/j.geomorph.2010.12.027Get rights and content

Abstract

In the framework of the Vulnerable Marine Ecosystems (VME) of the High Seas of the South West Atlantic, large areas of the Argentine Continental Margin (ACM) between 44°30’S and 48°S have been swath-mapped for the first time, obtaining full data coverage of the seafloor in this region between the outermost continental shelf and the middle slope down to 1600 m water depth.

https://ars.els-cdn.com/content/image/1-s2.0-S0169555X10005714-gr16.jpg

 

 

The slope is characterized by the presence of smooth terraces (Nagera, Perito Moreno and Piedra Buena) that widen towards the south, limited by morphological steps with evident signs of erosion in the form of scours. These terraces form part of the Argentine contourite depositional systems, generated by the interaction of the northwards flowing Antarctic water masses with the seafloor. Within the studied area, seven canyons and their multiple branches dissect the upper and middle continental slopes, from west to east, across the terraces and the steps.

 

These canyons, which belong to the Patagonia submarine canyon system and are collected at a depth of ~ 3.5 km by a slope-parallel, SSW–NNE-oriented channel known as the Almirante Brown transverse canyon, display a large variety of morphologies. These include incisions from just a dozen of metres to 650 m, straight to highly meandering sections with sharp bends, well-developed levees and walls that reach 35° in slope gradient, hanging branches, conspicuous axial incisions and multiple knickpoints. Only the northernmost canyon indents in the continental shelf, whereas the others start at the limit between the upper and middle slopes, and are often fed by small, straight, leveed gullies.

The action of both across-slope processes represented by submarine canyons and along-slope processes represented by terracing and scouring conform the ACM as a peculiar mixed margin, with the presence of both contour and gravity currents at the same place at the same time. We propose that at present, along-slope erosion and transport mainly occurs along the Perito Moreno terrace, whereas across-slope processes are much more dominant in the Nagera terrace. Erosive bedforms such as crescent scours, generated by contour currents, contribute to the progressive bottom-up erosion of the Nagera terrace and act as an initial collector of across-slope transported sediment, that later, due to flow focusing and recurrence, incise and interconnect creating definitive canyons that progress upslope by retrogressive erosion until their head indents the shelf break.

Changes in the balance between across-slope and along-slope transport would imply a disequilibrium in the combination of processes leading to canyon formation, producing canyon abandonment, and partial or total filling. These changes could be produced by a variation in the depth of the main interfaces of Antarctic water masses leading to either an increase or a decrease in the erosion and transport capacity of contour currents, and/or by an enhancement of across-slope transport related to an increase of sediment availability.

Keywords

Submarine canyon

Contourite depositional system

Argentina Continental Margin

Gullies

Canyon formation

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