The Malin cascade in winter 1996

Hill, Anthony Edward; Souza, Alejandro J.; Jones, Ken; Simpson, John H.; Shapiro, Georgy; McCandliss, R.R; Wilson, Hilary; Leftley, John W.

doi:10.1357/002224098321836127

Cited by 59 publications

(33 citation statements)

References 29 publications

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“…These geohydrological structures provide conduits for the transport of sediment from the shelf to the abyssal plain and over-bank turbidity currents, which deposit on the intervening terraces and spurs [4], but they also accumulate high amounts of sediments and OM, making them important in budgeting carbon sinks and sources [5], [6]. In addition, at the Celtic Margin cascading of dense water masses down the slope is likely to occur [7] and may entrain fresh chlorophyll material rapidly down slope, as reported by Hill et al [8]. These observations all imply the presence of enhanced levels of OM and phytodetrital material in canyons and channel systems in this area, which will have implications for the trophic conditions, the biogeochemical processes and ultimately the benthic fauna.…”

Section: Introductionmentioning

confidence: 76%

Meiofauna in the Gollum Channels and the Whittard Canyon, Celtic Margin—How Local Environmental Conditions Shape Nematode Structure and Function

2011

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The Gollum Channels and Whittard Canyon (NE Atlantic) are two areas that receive high input of organic matter and phytodetritus from euphotic layers, but they are typified by different trophic and hydrodynamic conditions. Sediment biogeochemistry was analysed in conjunction with structure and diversity of the nematode community and differences were tested between study areas, water depths (700 m vs 1000 m), stations, and sediment layers. The Gollum Channels and Whittard Canyon harboured high meiofauna abundances (1054–1426 ind. 10 cm−2) and high nematode diversity (total of 181 genera). Next to enhanced meiofauna abundance and nematode biomass, there were signs of high levels of organic matter deposition leading to reduced sedimentary conditions, which in turn structured the nematode community. Striking in this respect was the presence of large numbers of ‘chemosynthetic’ Astomonema nematodes (Astomonema southwardorum, Order Monhysterida, Family Siphonolaimidae). This genus lacks a mouth, buccal cavity and pharynx and possesses a rudimentary gut containing internal, symbiotic prokaryotes which have been recognised as sulphur-oxidising bacteria. Dominance of Astomonema may indicate the presence of reduced environments in the study areas, which is partially confirmed by the local biogeochemical environment. The nematode communities were mostly affected by sediment layer differences and concomitant trophic conditions rather than other spatial gradients related to study area, water depth or station differences, pointing to small-scale heterogeneity as the main source of variation in nematode structure and function. Furthermore, the positive relation between nematode standing stocks, and quantity and quality of the organic matter was stronger when hydrodynamic disturbance was greater. Analogically, this study also suggests that structural diversity can be positively correlated with trophic conditions and that this relation is tighter when hydrodynamic disturbance is greater.

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Section: Introductionmentioning

confidence: 76%

Meiofauna in the Gollum Channels and the Whittard Canyon, Celtic Margin—How Local Environmental Conditions Shape Nematode Structure and Function

2011

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“…Under the slope current, turbid down-slope Ekman flow on the outer slope of Porcupine Bank (Dickson and McCave, 1986) again suggests a route for sediment transport off the shelf. There is evidence of cascading at the north end of Porcupine Bank (Hill et al, 1998b). River input of freshwater exceeds rainfall-evaporation, but large ocean-shelf exchange implies only a small salinity reduction, except in the coastal current.…”

Section: Western Ireland Shelfmentioning

confidence: 99%

Deep ocean exchange with west-European shelf seas

2009

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Abstract. We review mechanisms and studies of exchange between the north-east Atlantic and the adjacent shelf seas. Well-developed summer upwelling and associated filaments off Portugal and north-west Spain give exchange O(3 m 2 /s per unit length of shelf). Prevailing westerly winds further north drive exchange O(1 m 2 /s). Poleward flow along most of the upper slope has associated secondary circulation O(1 m 2 /s), meanders and eddies. Eddies are shed from slope waters into the Bay of Biscay, and local exchanges occur at shelf spurs and depressions or canyons (e.g. dense-water cascading of order 1 m 2 /s). Tidal transports are larger, but their reversal every six hours makes exchange largely ineffective except where internal tides are large and non-linear, as in the Celtic Sea where solitons carry water with exchange O(1 m 2 /s). These various physical exchanges amount to an estimated 2-3 m 2 /s per unit length of shelf, between ocean and shelf. A numerical model estimate is comparable: 2.5×10 6 m 3 /s onto and off the shelf from Brittany to Norway. Mixing controls the seasonal thermocline, affecting primary production and hence fluxes and fate of organic matter. Specifically, CO 2 take-up by primary production, settling below the thermocline before respiration, and then off-shelf transport, make an effective shelf-sea "pump" (for CO 2 from the atmosphere to the deep ocean). However, knowledge of biogeochemical fluxes is generally sparse, giving scope for more measurements, model validation and estimates from models.

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“…Dense shelf water cascading contributes to the ventilation of intermediate and deep waters of the oceans and has a significant impact on biogeochemical cycles by entraining significant quantities of minerals and organic material both dissolved and particulate (Hill et al, 1998;Niemann et al, 2004;Canals et al, 2009;Vilibic and Santic, 2008).…”

Section: Formation Of Dense Water On Shelvesmentioning

confidence: 99%

A review of the role of submarine canyons in deep-ocean exchange with the shelf

2009

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Abstract. Cross shelf-break exchange is limited by the tendency of geostrophic flow to follow bathymetric contours, not cross them. However, small scale topography, such as canyons, can reduce the local lengthscale of the flow and increase the local Rossby number. These higher Rossby numbers mean the flow is no longer purely geostrophic and significant cross-isobath flow can occur. This cross-isobath flow includes both upwelling and downwelling due to wind-driven shelf currents and the strong cascading flows of dense shelfwater into the ocean. Tidal currents usually run primarily parallel to the shelf-break topography. Canyons cut across these flows and thus are often regions of generation of strong baroclinic tides and internal waves. Canyons can also focus internal waves. Both processes lead to greatly elevated levels of mixing. Thus, through both advection and mixing processes, canyons can enhance Deep Ocean Shelf Exchange. Here we review the state of the science describing the dynamics of the flows and suggest further areas of research, particularly into quantifying fluxes of nutrients and carbon as well as heat and salt through canyons.

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The Malin cascade in winter 1996

Cited by 59 publications

References 29 publications

Meiofauna in the Gollum Channels and the Whittard Canyon, Celtic Margin—How Local Environmental Conditions Shape Nematode Structure and Function

Meiofauna in the Gollum Channels and the Whittard Canyon, Celtic Margin—How Local Environmental Conditions Shape Nematode Structure and Function

Deep ocean exchange with west-European shelf seas

A review of the role of submarine canyons in deep-ocean exchange with the shelf

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