The Cadiz Contourite Channel: Sandy contourites, bedforms and dynamic current interaction

D.A.V. Stow; F.J. Hernández-Molina; E. Llave; M. Bruno; M. García; V. Díaz del Rio; L. Somoza; R.E. Brackenridge

doi:10.1016/j.margeo.2013.06.013

The Cadiz Contourite Channel: Sandy contourites, bedforms and dynamic current interaction

D.A.V. Stow^*, F.J. Hernández-Molina^*, E. Llave, M. Bruno, M. García, V. Díaz del Rio, L. Somoza, R.E. Brackenridge

^*Corresponding author for this work

Geology and Geophysics

Research output: Contribution to journal › Article › peer-review

103 Citations (Scopus)

Abstract

The Cadiz Contourite Channel is the largest and most prominent contourite channel in the middle slope of the Gulf of Cadiz, and is known to channelise the southern branch of the Lower Core of Mediterranean Outflow Water (MOW) as it flows westwards from the Gibraltar Gateway. The channel lies in water depth between 650 and 1500 m, is 150 km long, 2–12 km wide, up to 120 m deep, and broadly s-shaped in plan view. It has several associated subparallel marginal channels and shorter spillover channel segments. Its geometry is controlled by the interaction of a strong bottom current with the seafloor morphology, affected by neotectonic deformation and diapiric intrusion. Bottom photographs and dredge hauls reveal a channel floor shaped by high-energy flow, in places with bare rock, boulders and gravel, and elsewhere covered with sandy contourites. The rocky substrate and derived clasts are formed of authigenic iron-rich carbonates, testifying the high degree of fluid escape from adjacent diapiric ridges and mud volcanoes. The sandy substrate shows a wide range of current-induced bedforms including small, straight-crested ripples, large sinuous sand waves and dunes (wavelength 3.5–5 m, height 0.3–0.9 m), weak surface lineation on sands, and aligned gravel stringers and deep erosive scours around large boulders. Bedform orientation indicates flows directed to the south/south-west (main channel) and west (spillover channel), which can be related to MOW bottom currents, and current velocities that vary between about 0.2 and 0.8 m s− 1, even in the same channel location. However, current vane orientation was clearly responding, at least in part, to tidal effects and periodicity in the Gulf of Cadiz at the time the photographs were taken. Maximum current velocities are achieved by a combination of barotropic and internal tides (probably generated at the continental slope) that reinforce the normal MOW flow. In addition, meteorologically-induced internal waves with periods shorter than tidal ones may exert an even greater influence on current intensity, especially when they occur at times of sudden changes of meteorological forcing. This effect further influences MOW variability. In all cases, the funnelling effect of the Cadiz Channel amplifies tidal or meteorologically-induced bottom currents.

Original language	English
Pages (from-to)	99-114
Number of pages	16
Journal	Marine Geology
Volume	343
Early online date	26 Jun 2013
DOIs	https://doi.org/10.1016/j.margeo.2013.06.013
Publication status	Published - 1 Sept 2013

Bibliographical note

Acknowledgements

DAV Stow acknowledges receipt of a ‘Mobility Award’ from the Spanish Ministry of Education and Science (ref: SAB2005-0182) during which time he was working at the Instituto Español de Oceanografia (IEO, Malaga) during 2006. This work has been also carried out during research stages of FJ Hernández-Molina at National Oceanographic Centre of Southampton, NOCS (UK) at 2007 funded by the Secretaría de Estado de Educación y Universidades (PR2006-0275) and at Heriot Watt University during 2009–2010 (PR2009-0343) and during the sabbatical year 2013. Thanks are due to the captain and crew of R/V Cornide de Saavedra (IEO). The Spanish “Comisión Interministerial de Ciencia y Tecnología” supports this research through the Projects MAR-98-0209 (TASYO); CTM 2008-06399-C04/MAR (CONTOURIBER) and CTM2012-39599-C03-01 (MOWER). R Brackenridge is supported by an EPSRC DTA PhD scholarship. The authors would like to thank Dr. V. Hanquiez (Univ. Bordeaux, France) for sending us his original figure with good resolution used here as the Fig. 3B. Photographic operations were carried out by Francisco Gonzalez. Initial interpretation of the photographic evidence was by Jo Rolf at Southampton University. Finally, we also thank David Van Rooij, Thierry Mulder, one anonymous reviewer and David Piper for their interest and suggestions, which have helped us to improve the final version of our manuscript.

Keywords

Gulf of Cadiz
bottom currents
contourite channel
sandy contourites
internal tides/waves

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title = "The Cadiz Contourite Channel: Sandy contourites, bedforms and dynamic current interaction",

abstract = "The Cadiz Contourite Channel is the largest and most prominent contourite channel in the middle slope of the Gulf of Cadiz, and is known to channelise the southern branch of the Lower Core of Mediterranean Outflow Water (MOW) as it flows westwards from the Gibraltar Gateway. The channel lies in water depth between 650 and 1500 m, is 150 km long, 2–12 km wide, up to 120 m deep, and broadly s-shaped in plan view. It has several associated subparallel marginal channels and shorter spillover channel segments. Its geometry is controlled by the interaction of a strong bottom current with the seafloor morphology, affected by neotectonic deformation and diapiric intrusion. Bottom photographs and dredge hauls reveal a channel floor shaped by high-energy flow, in places with bare rock, boulders and gravel, and elsewhere covered with sandy contourites. The rocky substrate and derived clasts are formed of authigenic iron-rich carbonates, testifying the high degree of fluid escape from adjacent diapiric ridges and mud volcanoes. The sandy substrate shows a wide range of current-induced bedforms including small, straight-crested ripples, large sinuous sand waves and dunes (wavelength 3.5–5 m, height 0.3–0.9 m), weak surface lineation on sands, and aligned gravel stringers and deep erosive scours around large boulders. Bedform orientation indicates flows directed to the south/south-west (main channel) and west (spillover channel), which can be related to MOW bottom currents, and current velocities that vary between about 0.2 and 0.8 m s− 1, even in the same channel location. However, current vane orientation was clearly responding, at least in part, to tidal effects and periodicity in the Gulf of Cadiz at the time the photographs were taken. Maximum current velocities are achieved by a combination of barotropic and internal tides (probably generated at the continental slope) that reinforce the normal MOW flow. In addition, meteorologically-induced internal waves with periods shorter than tidal ones may exert an even greater influence on current intensity, especially when they occur at times of sudden changes of meteorological forcing. This effect further influences MOW variability. In all cases, the funnelling effect of the Cadiz Channel amplifies tidal or meteorologically-induced bottom currents.",

keywords = "Gulf of Cadiz, bottom currents, contourite channel, sandy contourites, internal tides/waves",

author = "D.A.V. Stow and F.J. Hern{\'a}ndez-Molina and E. Llave and M. Bruno and M. Garc{\'i}a and {D{\'i}az del Rio}, V. and L. Somoza and R.E. Brackenridge",

note = "Acknowledgements DAV Stow acknowledges receipt of a {\textquoteleft}Mobility Award{\textquoteright} from the Spanish Ministry of Education and Science (ref: SAB2005-0182) during which time he was working at the Instituto Espa{\~n}ol de Oceanografia (IEO, Malaga) during 2006. This work has been also carried out during research stages of FJ Hern{\'a}ndez-Molina at National Oceanographic Centre of Southampton, NOCS (UK) at 2007 funded by the Secretar{\'i}a de Estado de Educaci{\'o}n y Universidades (PR2006-0275) and at Heriot Watt University during 2009–2010 (PR2009-0343) and during the sabbatical year 2013. Thanks are due to the captain and crew of R/V Cornide de Saavedra (IEO). The Spanish “Comisi{\'o}n Interministerial de Ciencia y Tecnolog{\'i}a” supports this research through the Projects MAR-98-0209 (TASYO); CTM 2008-06399-C04/MAR (CONTOURIBER) and CTM2012-39599-C03-01 (MOWER). R Brackenridge is supported by an EPSRC DTA PhD scholarship. The authors would like to thank Dr. V. Hanquiez (Univ. Bordeaux, France) for sending us his original figure with good resolution used here as the Fig. 3B. Photographic operations were carried out by Francisco Gonzalez. Initial interpretation of the photographic evidence was by Jo Rolf at Southampton University. Finally, we also thank David Van Rooij, Thierry Mulder, one anonymous reviewer and David Piper for their interest and suggestions, which have helped us to improve the final version of our manuscript.",

year = "2013",

month = sep,

day = "1",

doi = "10.1016/j.margeo.2013.06.013",

language = "English",

volume = "343",

pages = "99--114",

journal = "Marine Geology",

issn = "0025-3227",

publisher = "ELSEVIER SCIENCE BV",

}

TY - JOUR

T1 - The Cadiz Contourite Channel

T2 - Sandy contourites, bedforms and dynamic current interaction

AU - Stow, D.A.V.

AU - Hernández-Molina, F.J.

AU - Llave, E.

AU - Bruno, M.

AU - García, M.

AU - Díaz del Rio, V.

AU - Somoza, L.

AU - Brackenridge, R.E.

N1 - Acknowledgements DAV Stow acknowledges receipt of a ‘Mobility Award’ from the Spanish Ministry of Education and Science (ref: SAB2005-0182) during which time he was working at the Instituto Español de Oceanografia (IEO, Malaga) during 2006. This work has been also carried out during research stages of FJ Hernández-Molina at National Oceanographic Centre of Southampton, NOCS (UK) at 2007 funded by the Secretaría de Estado de Educación y Universidades (PR2006-0275) and at Heriot Watt University during 2009–2010 (PR2009-0343) and during the sabbatical year 2013. Thanks are due to the captain and crew of R/V Cornide de Saavedra (IEO). The Spanish “Comisión Interministerial de Ciencia y Tecnología” supports this research through the Projects MAR-98-0209 (TASYO); CTM 2008-06399-C04/MAR (CONTOURIBER) and CTM2012-39599-C03-01 (MOWER). R Brackenridge is supported by an EPSRC DTA PhD scholarship. The authors would like to thank Dr. V. Hanquiez (Univ. Bordeaux, France) for sending us his original figure with good resolution used here as the Fig. 3B. Photographic operations were carried out by Francisco Gonzalez. Initial interpretation of the photographic evidence was by Jo Rolf at Southampton University. Finally, we also thank David Van Rooij, Thierry Mulder, one anonymous reviewer and David Piper for their interest and suggestions, which have helped us to improve the final version of our manuscript.

PY - 2013/9/1

Y1 - 2013/9/1

N2 - The Cadiz Contourite Channel is the largest and most prominent contourite channel in the middle slope of the Gulf of Cadiz, and is known to channelise the southern branch of the Lower Core of Mediterranean Outflow Water (MOW) as it flows westwards from the Gibraltar Gateway. The channel lies in water depth between 650 and 1500 m, is 150 km long, 2–12 km wide, up to 120 m deep, and broadly s-shaped in plan view. It has several associated subparallel marginal channels and shorter spillover channel segments. Its geometry is controlled by the interaction of a strong bottom current with the seafloor morphology, affected by neotectonic deformation and diapiric intrusion. Bottom photographs and dredge hauls reveal a channel floor shaped by high-energy flow, in places with bare rock, boulders and gravel, and elsewhere covered with sandy contourites. The rocky substrate and derived clasts are formed of authigenic iron-rich carbonates, testifying the high degree of fluid escape from adjacent diapiric ridges and mud volcanoes. The sandy substrate shows a wide range of current-induced bedforms including small, straight-crested ripples, large sinuous sand waves and dunes (wavelength 3.5–5 m, height 0.3–0.9 m), weak surface lineation on sands, and aligned gravel stringers and deep erosive scours around large boulders. Bedform orientation indicates flows directed to the south/south-west (main channel) and west (spillover channel), which can be related to MOW bottom currents, and current velocities that vary between about 0.2 and 0.8 m s− 1, even in the same channel location. However, current vane orientation was clearly responding, at least in part, to tidal effects and periodicity in the Gulf of Cadiz at the time the photographs were taken. Maximum current velocities are achieved by a combination of barotropic and internal tides (probably generated at the continental slope) that reinforce the normal MOW flow. In addition, meteorologically-induced internal waves with periods shorter than tidal ones may exert an even greater influence on current intensity, especially when they occur at times of sudden changes of meteorological forcing. This effect further influences MOW variability. In all cases, the funnelling effect of the Cadiz Channel amplifies tidal or meteorologically-induced bottom currents.

AB - The Cadiz Contourite Channel is the largest and most prominent contourite channel in the middle slope of the Gulf of Cadiz, and is known to channelise the southern branch of the Lower Core of Mediterranean Outflow Water (MOW) as it flows westwards from the Gibraltar Gateway. The channel lies in water depth between 650 and 1500 m, is 150 km long, 2–12 km wide, up to 120 m deep, and broadly s-shaped in plan view. It has several associated subparallel marginal channels and shorter spillover channel segments. Its geometry is controlled by the interaction of a strong bottom current with the seafloor morphology, affected by neotectonic deformation and diapiric intrusion. Bottom photographs and dredge hauls reveal a channel floor shaped by high-energy flow, in places with bare rock, boulders and gravel, and elsewhere covered with sandy contourites. The rocky substrate and derived clasts are formed of authigenic iron-rich carbonates, testifying the high degree of fluid escape from adjacent diapiric ridges and mud volcanoes. The sandy substrate shows a wide range of current-induced bedforms including small, straight-crested ripples, large sinuous sand waves and dunes (wavelength 3.5–5 m, height 0.3–0.9 m), weak surface lineation on sands, and aligned gravel stringers and deep erosive scours around large boulders. Bedform orientation indicates flows directed to the south/south-west (main channel) and west (spillover channel), which can be related to MOW bottom currents, and current velocities that vary between about 0.2 and 0.8 m s− 1, even in the same channel location. However, current vane orientation was clearly responding, at least in part, to tidal effects and periodicity in the Gulf of Cadiz at the time the photographs were taken. Maximum current velocities are achieved by a combination of barotropic and internal tides (probably generated at the continental slope) that reinforce the normal MOW flow. In addition, meteorologically-induced internal waves with periods shorter than tidal ones may exert an even greater influence on current intensity, especially when they occur at times of sudden changes of meteorological forcing. This effect further influences MOW variability. In all cases, the funnelling effect of the Cadiz Channel amplifies tidal or meteorologically-induced bottom currents.

KW - Gulf of Cadiz

KW - bottom currents

KW - contourite channel

KW - sandy contourites

KW - internal tides/waves

UR - https://www.sciencedirect.com/science/article/pii/S0025322713001345

U2 - 10.1016/j.margeo.2013.06.013

DO - 10.1016/j.margeo.2013.06.013

M3 - Article

SN - 0025-3227

VL - 343

SP - 99

EP - 114

JO - Marine Geology

JF - Marine Geology

ER -

The Cadiz Contourite Channel: Sandy contourites, bedforms and dynamic current interaction

Abstract

Bibliographical note

Keywords

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