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

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

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.

Bottom shear stress, Erosion, Oceanic circulation, Sediment drift
0169-555X
43-60
Miramontes, Elda
46306494-7ab5-42c9-beda-f89fb7d19a65
Garreau, Pierre
544e5a5a-d2e5-4f94-a0b5-947cd35ce3f1
Caillaud, Matthieu
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Jouet, Gwenael
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Pellen, Romain
c0c6d1dd-7fb6-453f-aea6-fe9075d8fd26
Hernández-Molina, F. Javier
256ca467-a4e8-4f24-9ff1-23bd2ab8d28d
Clare, Michael A.
b26da858-9c08-4784-aaa9-7092efcd94bd
Cattaneo, Antonio
ca00590a-440f-4c59-b9bb-f801f109f66c
Miramontes, Elda
46306494-7ab5-42c9-beda-f89fb7d19a65
Garreau, Pierre
544e5a5a-d2e5-4f94-a0b5-947cd35ce3f1
Caillaud, Matthieu
70cf8e78-ef2e-461a-97c0-563c789512f3
Jouet, Gwenael
7f9fe9f0-3b0e-4bbb-b6b6-e69de4ebb257
Pellen, Romain
c0c6d1dd-7fb6-453f-aea6-fe9075d8fd26
Hernández-Molina, F. Javier
256ca467-a4e8-4f24-9ff1-23bd2ab8d28d
Clare, Michael A.
b26da858-9c08-4784-aaa9-7092efcd94bd
Cattaneo, Antonio
ca00590a-440f-4c59-b9bb-f801f109f66c

Miramontes, Elda, Garreau, Pierre, Caillaud, Matthieu, Jouet, Gwenael, Pellen, Romain, Hernández-Molina, F. Javier, Clare, Michael A. and Cattaneo, Antonio (2019) Contourite distribution and bottom currents in the NW Mediterranean Sea: Coupling seafloor geomorphology and hydrodynamic modelling. Geomorphology, 333, 43-60. (doi:10.1016/j.geomorph.2019.02.030).

Record type: Article

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_etal_manuscript_Geomorphology3 - Accepted Manuscript
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Accepted/In Press date: 22 February 2019
e-pub ahead of print date: 23 February 2019
Published date: 15 May 2019
Keywords: Bottom shear stress, Erosion, Oceanic circulation, Sediment drift

Identifiers

Local EPrints ID: 429478
URI: http://eprints.soton.ac.uk/id/eprint/429478
ISSN: 0169-555X
PURE UUID: ab2d5287-89e2-4481-aa5b-0f1ccd00827f

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Date deposited: 27 Mar 2019 17:30
Last modified: 28 Apr 2022 06:17

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Contributors

Author: Elda Miramontes
Author: Pierre Garreau
Author: Matthieu Caillaud
Author: Gwenael Jouet
Author: Romain Pellen
Author: F. Javier Hernández-Molina
Author: Michael A. Clare
Author: Antonio Cattaneo

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