Contourite distribution and bottom currents in the NW Mediterranean Sea: Coupling seafloor geomorphology and hydrodynamic modelling

Type Article
Date 2019-05
Language English
Author(s) Miramontes Garcia Elda1, 4, Garreau PierreORCID2, Caillaud Matthieu3, Jouet Gwenael1, Pellen Romain1, 4, Hernández-Molina F. Javier5, Clare Michael A.6, Cattaneo AntonioORCID1
Affiliation(s) 1 : IFREMER, Géosciences Marines, Plouzané 29280, France
2 : UMR 6523 CNRS, IFREMER, IRD, UBO, Laboratoire d'Océanographie Physique et Spatiale, Plouzané 29280, France
3 : IFREMER, Dynamiques des Ecosystèmes Côtiers, Plouzané 29280, France
4 : UMR6538 CNRS-UBO, IUEM, Laboratoire Géosciences Océan, 29280 Plouzané, France
5 : Dept. Earth Sciences, Royal Holloway Univ. London, Egham, Surrey TW20 0EX, United Kingdom
6 : National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton SO14 3ZH, United Kingdom
Source Geomorphology (0169-555X) (Elsevier BV), 2019-05 , Vol. 333 , P. 43-60
DOI 10.1016/j.geomorph.2019.02.030
WOS© Times Cited 8
Keyword(s) Sediment drift, Erosion, Oceanic circulation, Bottom shear stress
Abstract

Contourites are common morphological features along continental margins where currents encounter the seafloor. They can provide long-term archives of palaeoceanography, may be prone to sediment instability, and can have a great potential for hydrocarbon exploration. Despite their importance and increasingly recognised ubiquitous occurrence worldwide, the link between oceanographic processes and contourite features is poorly constrained. In particular, it is unclear under which specific conditions sediments are mobilised, modified and deposited by bottom currents. Here, we aim to determine key bottom current characteristics (velocity and bottom shear stress) affecting contourite deposition, by assuming that recent oceanographic regimes may be extended back in time over the past glacial-interglacial cycles, with strong winter circulation assumed similar to glacial conditions and weak summer circulation to interglacials. We present an integrated study from the NW Mediterranean Sea that couples results of the MARS3D hydrodynamic model with high-resolution sedimentological and geophysical data (piston cores, multibeam bathymetry and high resolution seismic data). Near bottom circulation was modelled during winter and summer 2013 as representative of past periods of high and low current intensity, respectively. Model results match well with the extent of contourite depositional systems and their different localised morphologic elements. We deduce that higher intensity events control the formation of erosional features such as moats and abraded surfaces. The heterogeneous distribution of bottom-current intensity on slopes explains the development of different types of contourite drifts. Plastered drifts form in zones of low bottom-current velocities constrained upslope and downslope by higher current velocities. Separated elongated mounded drifts develop where fast bottom-currents decelerate at foot of the slope. In contrast, no mounded contourite morphologies develop when the current velocity is homogeneous across the slope, especially in margins prone to downslope sediment transport processes. In confined basins, gyres may transport sediment in suspension from a margin with a high sediment supply to an adjacent starved margin, favouring the development of fine-grained contourites in the latter. Our results provide new insights into how detailed bottom-circulation modelling and seafloor geomorphological analyses can improve the understanding of palaeoflow-regimes, at least over time spans when the overall paleogeography and the distribution of contourite drifts is comparable to present-day conditions. The approach of coupled hydrodynamic models and geomorphological interpretations proposed here for depositional, erosional and mixed contourite features may be used to understand other areas affected by bottom currents, and for a better conceptual understanding of bottom-current processes and their interactions with the seafloor.

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Miramontes Garcia Elda, Garreau Pierre, Caillaud Matthieu, Jouet Gwenael, Pellen Romain, Hernández-Molina F. Javier, Clare Michael A., Cattaneo Antonio (2019). Contourite distribution and bottom currents in the NW Mediterranean Sea: Coupling seafloor geomorphology and hydrodynamic modelling. Geomorphology, 333, 43-60. Publisher's official version : https://doi.org/10.1016/j.geomorph.2019.02.030 , Open Access version : https://archimer.ifremer.fr/doc/00483/59426/