Contourites and associated sediments controlled by deep-water circulation processes: State-of-the-art and future considerations

doi:10.1016/J.MARGEO.2014.03.011

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Contourites and associated sediments controlled by deep-water circulation processes: State-of-the-art and future considerations

Journal Article•DOI•

Contourites and associated sediments controlled by deep-water circulation processes: State-of-the-art and future considerations

Michele Rebesco, F. Javier Hernández-Molina¹, David Van Rooij², Anna Wåhlin³•Institutions (3)

Royal Holloway, University of London¹, Ghent University², University of Gothenburg³

01 Jun 2014-Marine Geology (Elsevier)-Vol. 352, pp 111-154

TL;DR: The contourite paradigm was conceived a few decades ago, yet there remains a need to establish a sound connection between contourites, basin evolution and oceanographic processes.

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About: This article is published in Marine Geology.The article was published on 2014-06-01 and is currently open access. It has received 600 citations till now. The article focuses on the topics: Contourite.

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Journal Article•DOI•

Seafloor microplastic hotspots controlled by deep-sea circulation.

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Ian A. Kane¹, Michael A. Clare², Elda Miramontes³, Roy A. Wogelius¹, James J. Rothwell¹, Pierre Garreau⁴, Florian Pohl⁵ - Show less +3 more•Institutions (5)

University of Manchester¹, National Oceanography Centre², University of Bremen³, IFREMER⁴, Durham University⁵

30 Apr 2020-Science

TL;DR: It is demonstrated that thermohaline-driven currents can control the distribution of microplastics by creating hotspots of accumulation, analogous to their role in causing focused areas of seafloor sediment deposition.

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Abstract: Although microplastics are known to pervade the global seafloor, the processes that control their dispersal and concentration in the deep sea remain largely unknown. Here, we show that thermohaline-driven currents, which build extensive seafloor sediment accumulations, can control the distribution of microplastics and create hotspots with the highest concentrations reported for any seafloor setting (190 pieces per 50 grams). Previous studies propose that microplastics are transported to the seafloor by vertical settling from surface accumulations; here, we demonstrate that the spatial distribution and ultimate fate of microplastics are strongly controlled by near-bed thermohaline currents (bottom currents). These currents are known to supply oxygen and nutrients to deep-sea benthos, suggesting that deep-sea biodiversity hotspots are also likely to be microplastic hotspots.

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369 citations

Journal Article•DOI•

Dispersion, Accumulation, and the Ultimate Fate of Microplastics in Deep-Marine Environments: A Review and Future Directions

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Ian A. Kane¹, Michael A. Clare²•Institutions (2)

University of Manchester¹, National Oceanography Centre²

30 Apr 2019-Frontiers in Earth Science

TL;DR: In this article, the authors synthesize existing knowledge of seafloor microplastic distribution, and integrate this with process-based sedimentological models of particle transport, to provide new insights, and critically, to identify future research challenges.

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Abstract: An estimated 8.3 billion tonnes of non-biodegradable plastic has been produced over the last 65 years. Much of this is not recycled or disposed of ‘properly’, has a long environmental residence time and accumulates in sedimentary systems worldwide, posing a threat to important ecosystems and potentially human health. We synthesise existing knowledge of seafloor microplastic distribution, and integrate this with process-based sedimentological models of particle transport, to provide new insights, and critically, to identify future research challenges. Compilation of published data shows that microplastics pervade the global seafloor, from abyssal plains to submarine canyons and deep-sea trenches. However, few studies relate microplastic accumulation to sediment transport and deposition. Microplastics may enter directly into the sea as marine litter from shipping and fishing, or indirectly via fluvial and aeolian systems from terrestrial environments. The nature of the entry-point is critical to how terrestrially-sourced microplastics are transferred to offshore sedimentary systems. We present models for physiographic shelf connection types related to the tectono-sedimentary regime of the margin. Beyond the shelf, the principal agents for microplastic transport are: i) gravity-driven transport in sediment-laden flows; ii) settling, or conveyance through biological processes, of material that was formerly floating on the surface or suspended in the water column; iii) transport by thermohaline currents, either during settling or by reworking of deposited microplastics. We compare microplastic settling velocities to natural sediments to understand how appropriate existing sediment transport models are for explaining microplastic dispersal. Based on this analysis, and the relatively well-known behaviour or deep-marine flow types, we explore the expected distribution of microplastic particles, both in individual sedimentary event deposits and within deep-marine depositional systems. Residence time within certain deposit types and depositional environments is anticipated to be variable, which has implications for the likelihood of ingestion and incorporation into the food chain, further transport, or deeper burial. We conclude that integration of process-based sedimentological and stratigraphic knowledge with insights from modern sedimentary systems, and biological activity within them, will provide essential constraints on the transfer of microplastics to deep-marine environments, their distribution and ultimate fate, and the implications that these have for benthic ecosystems.

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234 citations

Cites background from "Contourites and associated sediment..."

...Thermohaline stratification can create nepheloid layers that inhibit fall-out and promote the lateral advection of fine sediments, while bottomhugging contour currents can be agents of sediment deposition, bypass and reworking, and can develop very large accumulations of fine-grained sediment, known collectively as drift deposits (e.g., Stow and Lovell, 1979; Rebesco et al., 2014)....
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...The exceedingly thick and stratigraphically continuous drift deposits preserved offshore east and west Africa, east of South America (e.g., Faugères et al., 1993; Rebesco et al., 2014), and elsewhere, demonstrate the high preservation potential of these features....
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...This suggests that microplastics delivered to the basin floor by gravity currents may be prone to erosion and transport by bottom currents, and eventually be sequestered within drift deposits (Rebesco et al., 2014)....
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Journal Article•DOI•

GlobSed: Updated total sediment thickness in the World’s oceans

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Eivind Olavson Straume¹, Carmen Gaina¹, Sergei Medvedev¹, Katharina Hochmuth², Karsten Gohl², Joanne M. Whittaker³, R. Abdul Fattah, J.C. Doornenbal, John R. Hopper⁴ - Show less +5 more•Institutions (4)

University of Oslo¹, Alfred Wegener Institute for Polar and Marine Research², University of Tasmania³, Geological Survey of Denmark and Greenland⁴

01 Apr 2019-Geochemistry Geophysics Geosystems

TL;DR: In this article, a new global 5 arc-minute total sediment thickness grid for the world's oceans and marginal seas is presented, GlobSed, which provides a much needed update of the sediment thickness distribution of the world oceans and delivers a model for sedimentation rates on oceanic crust through time that agrees well with selected drill data used for comparison.

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Abstract: We present GlobSed, a new global 5‐arc‐minute total sediment thickness grid for the world's oceans and marginal seas. GlobSed covers a larger area than previously published global grids and incorporates updates for the NE Atlantic, Arctic, Southern Ocean, and Mediterranean regions, which results in a 29.7% increase in estimated total oceanic sediment volume. We use this new global grid and a revised global oceanic lithospheric age grid to assess the relationship between the total sediment thickness and age of the underlying oceanic lithosphere and its latitude. An analytical approximation model is used to mathematically describe sedimentation trends in major oceanic basins and to allow paleobathymetric reconstructions at any given geological time. This study provides a much‐needed update of the sediment thickness distribution of the world oceans and delivers a model for sedimentation rates on oceanic crust through time that agrees well with selected drill data used for comparison.

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207 citations

Cites background from "Contourites and associated sediment..."

...These anomalous large‐scale bathymetric features are known to control ocean currents directions and induce contourite drift deposits and erosion (e.g., Dutkiewicz, Müller, et al., 2016; Rebesco et al., 2014), yielding anomalous sediment thickness compared to normal seafloor....
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Journal Article•DOI•

Transport and Burial of Microplastics in Deep-Marine Sediments by Turbidity Currents

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Florian Pohl¹, Joris T. Eggenhuisen¹, Ian A. Kane², Michael A. Clare³•Institutions (3)

Utrecht University¹, University of Manchester², National Oceanography Centre³

07 Apr 2020-Environmental Science & Technology

TL;DR: It is shown that microplastic fragments become relatively concentrated within the base of turbidity currents, whereas fibers are more homogeneously distributed throughout the flow, and the resultant deposits show an opposing trend, as they are enriched with fibers, rather than fragments.

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Abstract: The threat posed by plastic pollution to marine ecosystems and human health is under increasing scrutiny. Much of the macro- and microplastic in the ocean ends up on the seafloor, with some of the highest concentrations reported in submarine canyons that intersect the continental shelf and directly connect to terrestrial plastic sources. Gravity-driven avalanches, known as turbidity currents, are the primary process for delivering terrestrial sediment and organic carbon to the deep sea through submarine canyons. However, the ability of turbidity currents to transport and bury plastics is essentially unstudied. Using flume experiments, we investigate how turbidity currents transport microplastics, and their role in differential burial of microplastic fragments and fibers. We show that microplastic fragments become relatively concentrated within the base of turbidity currents, whereas fibers are more homogeneously distributed throughout the flow. Surprisingly, the resultant deposits show an opposing trend, as they are enriched with fibers, rather than fragments. We explain this apparent contradiction by a depositional mechanism whereby fibers are preferentially removed from suspension and buried in the deposits as they are trapped between settling sand-grains. Our results suggest that turbidity currents potentially distribute and bury large quantities of microplastics in seafloor sediments.

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151 citations

Journal Article•DOI•

Deciphering bottom current velocity and paleoclimate signals from contourite deposits in the Gulf of Cádiz during the last 140 kyr: An inorganic geochemical approach

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André Bahr¹, Francisco J. Jiménez-Espejo², Nada Kolasinac¹, Patrick Grunert³, F. Javier Hernández-Molina, Ursula Röhl⁴, Antje H L Voelker⁵, Carlota Escutia⁶, Dorrik A. V. Stow⁷, David A. Hodell⁸, Carlos A. Alvarez-Zarikian⁹ - Show less +7 more•Institutions (9)

Goethe University Frankfurt¹, Japan Agency for Marine-Earth Science and Technology², University of Graz³, University of Bremen⁴, Instituto Português do Mar e da Atmosfera⁵, Spanish National Research Council⁶, Heriot-Watt University⁷, University of Cambridge⁸, Texas A&M University⁹

01 Aug 2014-Geochemistry Geophysics Geosystems

TL;DR: This article investigated the potential of geochemical data obtained by XRF scanning to decipher bottom current processes and paleoclimatic evolution at two different sites drilled during IODP Expedition 339 through contourites in the northern Gulf of Cadiz (GC).

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Abstract: Contourites in the Gulf of Cadiz (GC) preserve a unique archive of Mediterranean Outflow Water (MOW) variability over the past 5.3 Ma. In our study, we investigate the potential of geochemical data obtained by XRF scanning to decipher bottom current processes and paleoclimatic evolution at two different sites drilled during IODP Expedition 339 through contourites in the northern GC: Site U1387, which is bathed by the upper MOW core, and Site U1389, located more proximal to the Strait of Gibraltar. The lack of major downslope transport during the Pleistocene makes both locations ideally suited for our study. The results indicate that the Zr/Al ratio, representing the relative enrichment of heavy minerals (zircon) over less dense alumnosilicates under fast bottom current flow, is the most useful indicator for a semiquantitative assessment of current velocity. Although most elements are biased by current-related processes, the bromine (Br) record, representing organic content, preserves the most pristine climate signal rather independent of grain-size changes. Hence, Br can be used for chronostratigraphy and site-to-site correlation in addition to stable isotope stratigraphy. Based on these findings, we reconstructed MOW variability for Marine Isotope Stages (MIS) 1–5 using the Zr/Al ratio from Site U1387. The results reveal abrupt, millennial-scale variations of MOW strength during Greenland Stadials (GS) and Interstadials (GI) with strong MOW during GS and glacial Terminations and a complex behavior during Heinrich Stadials. Millennial-scale variability persisting during periods of poorly expressed GS/GI cyclicities implies a strong internal oscillation of the Mediterranean/North Atlantic climate system.

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115 citations

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References

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Buoyancy Effects in Fluids

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J. S. Turner

23 Feb 1973

TL;DR: In this article, the authors introduce linear internal waves and herar flows in a stratified fluid and double-diffusive convection in stably stratified fluids, and show that the shear flows can produce turbulence.

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Abstract: Preface 1. Introduction and preliminaries 2. Linear internal waves 3. Finite amplitude motions in stably stratified fluids 4. Instability and the production of turbulence 5. Turbulent shear flows in a stratified fluid 6. Buoyant convection from isolated sources 7. Convection from heated surfaces 8. Double-diffusive convection 9. Mixing across density interfaces 10. Internal mixing processes Bibliography and author index Recent publications Subject index.

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2,722 citations

"Contourites and associated sediment..." refers background in this paper

...Laboratory experiments (see, for example: Ellison and Turner, 1959; Turner, 1973; Cenedese et al., 2004) have shown that if the speed of the dense water exceeds the phase speed of a long internal wave, then the flow becomes unstable and starts to overturn....
[...]
...Laboratory experim ents (see, for example: Ellison and Turner, 1959; Turner, 1973; Cenedese e t al„ 2004) have shown that if the speed of the dense water exceeds the phase speed of a long inter nal wave, then the flow becomes unstable and starts to overturn....
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Journal Article•DOI•

Abyssal recipes II: energetics of tidal and wind mixing

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Walter Munk¹, Carl Wunsch²•Institutions (2)

University of California, San Diego¹, Massachusetts Institute of Technology²

01 Dec 1998-Deep Sea Research

TL;DR: Using the Levitus climatology, the authors showed that 2.1 TW (terawatts) is required to maintain the global abyssal density distribution against 30 Sverdrups of deep water formation.

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"Contourites and associated sediment..." refers background in this paper

...The distribution of salt and heat in the deep ocean is strongly related to these dense currents and to the rates at which they descend to greater depths and subse quently mix w ith ambient fluid (Munk and Wunsch, 1998; Wells and W ettlaufer, 2005; W áhlin and Cenedese, 2006; Legg et al„ 2009; Akimova et al„ 2011)....
[...]
...…of salt and heat in the deep ocean is strongly related to these dense currents and to the rates at which they descend to greater depths and subsequently mix with ambient fluid (Munk and Wunsch, 1998; Wells and Wettlaufer, 2005; Wåhlin and Cenedese, 2006; Legg et al., 2009; Akimova et al., 2011)....
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...This mechanism provides a substantial part of the ocean mixing that is required for sustaining the global meridional overturning circulation (Munk and Wunsch, 1998)....
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Journal Article•DOI•

The Great Ocean Conveyor

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Wallace Broeker

01 Jan 1991-Oceanography

TL;DR: The ocean's conveyor appears to be driven by the salt left behind as the result of water-vapor transport through the atmosphere from the Atlantic to the Pacific basin this paper.

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Abstract: A DIAGRAM DEPICTING the ocean's \"conveyor belt\" has been widely adopted as a logo for the Global Change Research Initiative. This diagram (Fig. 1) first appeared as an illustration in an article about the Younger Dryas event that was published in the November 1987 issue of Natural History. It was designed as a cartoon to help the largely lay readership of this magazine to comprehend one of the elements of the deep sea's circulation system. Had I suspected that it would be widely adopted as a logo, I would have tried to \"improve\" its accuracy. In hindsight such repairs would likely have ruined the diagram both for the readers of Natural History and for use as a logo. The lure of this logo is that it symbolizes the importance of linkages between realms of the Earth's climate system. The ocean's conveyor appears to be driven by the salt left behind as the result of water-vapor transport through the atmosphere from the Atlantic to the Pacific basin. A byproduct of its operation is the heat that maintains the anomolously warm winter air temperatures enjoyed by northern Europe. A millennium of very cold conditions known as the Young Dryas appears to have been the result of a temporary shutdown of the conveyor. Thus the conveyor logo portrays the concern that led to the launching of the Global Change Research Initiatives: that complex interconnections among the elements of our Earth's climate system will greatly complicate our task of predicting the consequences of global pollution. Most of the concepts involved in this story have roots that extend well back in time. The most important feature of the conveyor is the production of deep water in the northern Atlantic. This aspect of the ocean's thermohaline circulation was thoroughly described by Wrist (1935) and Wrist and Defant (1936) more than 50 years ago. In 1906 Chamberlain explored the importance of freshwater transport to ocean circulation. He raised the question as to whether changes in the pattern of deep circulation could be responsible for the climate changes of glacial time. My contribution

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1,148 citations

Journal Article•DOI•

Turbulent entrainment in stratified flows

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T. H. Ellison¹, J. S. Turner¹•Institutions (1)

University of Manchester¹

01 Oct 1959-Journal of Fluid Mechanics

TL;DR: In this article, it is assumed that the entrainment is proportional to the velocity of the layer multiplied by an empirical function, E(Ri), of the overall Richardson number for the layer defined by Ri = g(ρa - ρ) h/ρa V2.

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Abstract: When a fluid which is lighter than its surroundings is emitted by a source under a sloping roof (or a heavier fluid from a source on a sloping floor), it may flow as a relatively thin turbulent layer. The motion of this layer is governed by the rate at which it entrains the ambient fluid. A theory is presented in which it is assumed that the entrainment is proportional to the velocity of the layer multiplied by an empirical function, E(Ri), of the overall Richardson number for the layer defined by Ri = g(ρa - ρ) h/ρa V2. This theory predicts that in most practical cases the layer will rapidly attain an equilibrium state in which Ri does not vary with distance downstream, and the gravitational force on the layer is just balanced by the drag due to entrainment together with friction on the floor or roof.Two series of laboratory experiments are described from which E(Ri) can be determined. In the first, the spread of a surface jet of fluid lighter than that over which it is flowing is measured; in the second, a study is made of the flow of a heavy liquid down the sloping floor of a channel. These experiments show that E falls off rapidly as Ri increases and is probably negligible when Ri is more than about 0·8.The theoretical and experimental results allow predictions to be made of flow velocities once the rate of supply of density difference is known. An estimate is also given of the uniform velocity which the ambient fluid must possess in order to cause the motion of the layer to be reversed.

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999 citations

"Contourites and associated sediment..." refers background in this paper

...Laboratory experiments (see, for example: Ellison and Turner, 1959; Turner, 1973; Cenedese et al., 2004) have shown that if the speed of the dense water exceeds the phase speed of a long internal wave, then the flow becomes unstable and starts to overturn....
[...]

Journal Article•DOI•

Circulation, mixing, and production of Antarctic Bottom Water

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Alejandro H. Orsi¹, Gregory C. Johnson², John L. Bullister²•Institutions (2)

University of Washington¹, Pacific Marine Environmental Laboratory²

01 Jan 1999-Progress in Oceanography

TL;DR: In this article, the authors make use of the available high-quality station data in the Southern Ocean to construct bottom maps of neutral density and mean property maps, including Chlorofluorocarbon (CFC), for the abyssal layer underneath a selected neutral density surface.

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933 citations

"Contourites and associated sediment..." refers background in this paper

...12 and 14) can be found in various areas, such as the Denmark Strait (e.g. Smith, 1975; Girton and Sanford, 2003; Käse et al., 2003; Karcher et al., 2011); Faeroe-Bank channel (Borenäs and Lundberg, 2004; Mauritzen et al., 2005; Riemenschneider and Legg, 2007; Darelius et al., 2011); Gulf of Cádiz (Smith, 1975; Borenäs et al., 2002; Johnson et al., 2002); Red Sea (Peters et al., 2005; Matt and Johns, 2007), the South China Sea (Gong et al., 2013); Weddell Sea (Orsi et al., 1999; Naveira Garabato et al., 2002a,b, 2003; Foldvik et al., 2004; Nicholls et al., 2009); and Ross Sea (Carter et al., 2008; Capello et al., 2009; Muench et al., 2009a,b)....
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...…et al., 2002; Johnson et al., 2002); Red Sea (Peters et al., 2005; Matt and Johns, 2007), the South China Sea (Gong et al., 2013); Weddell Sea (Orsi et al., 1999; Naveira Garabato et al., 2002a,b, 2003; Foldvik et al., 2004; Nicholls et al., 2009); and Ross Sea (Carter et al., 2008; Capello…...
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