Hydrography of the East Shetland Basin in relation to decadal North Sea variability

Turrell, W.R.; Slesser, G.; Payne, R.; Adams, R. D.; Gillibrand, Phil

doi:10.1006/jmsc.1996.0112

Cited by 56 publications

(43 citation statements)

References 18 publications

(30 reference statements)

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“…At slightly lesser depths (about 150 m) the current turns clockwise around the Shetlands, forming the East Scotland Atlantic Inflow, which flows south along the bathymetry. At 100 meter depth, the Fair Isle Current (FIC) separates from the Slope Current (Turrell et al, 1996) and enters the northern part of the North Sea between the Orkney and Shetland Islands and follows the 100-m isobaths, in the process passing by the 22/4b site ( Figure 1). The FIC strength displays seasonal variability and has an average velocity of about 0.1 m/s (ICES, 2005;Turrell et al, 1990) and is directed approximately to the north at the 22/4b site following the bathymetry.…”

Section: Circulation In the Northern North Seamentioning

confidence: 99%

Bubble momentum plume as a possible mechanism for an early breakdown of the seasonal stratification in the northern North Sea

Nauw

Линке

Leifer

2015

Marine and Petroleum Geology

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The presence of a seasonal thermocline likely plays a key role in restraining methane released from a seabed source in the deeper water column, thereby inhibiting exchange to the atmosphere. The bubble plume itself, however, generates an upward motion of fluid, e.g. upwelling and may thereby be partially responsible for an early breakdown of the seasonal thermocline. Measurements at site 22/4b, located at (57 o 55'N, 1 o 38'E) in the UK Central North Sea, 200 km east of the Scottish mainland, where gas is still being released since a blow out in 1990, have been used to identify the generation of the seasonal thermocline, and thus, the depth of the upper mixed layer and its breakdown in autumn. Data derived from two landers, containing an Acoustic Doppler Current Profiler and a Conductivity Temperature Depth recorder, were used to determine the mixed layer depth and the breakdown of the thermocline. Mixing of upper layer fluid into the lower layer has been inferred from large amplitude variations in the near-bottom temperature. The ADCPs estimate velocity profiles in four beam directions using Doppler shifted frequency from acoustic pings sent out and received by four different transducers in a specific configuration. Besides that, the intensity of the backscattered sound per transducer is also recorded. Bubbles from the nearby plume contaminate the signal during part of the tidal cycle, but in bubble free periods, the mixed layer depth can be estimated using the acoustic backscatter signal as local maxima. Results show that the thermocline broke down between mid-October and early November, several weeks earlier than the breakdown of the thermocline in nearby/comparable areas, likely caused by bubble-induced downwelling at the site. The early breakdown of the thermocline was accompanied by multiple occurrence of a strong jet-like structure, associated with the seasonal tidal mixing front. 2

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Section: Circulation In the Northern North Seamentioning

confidence: 99%

Bubble momentum plume as a possible mechanism for an early breakdown of the seasonal stratification in the northern North Sea

Nauw

Линке

Leifer

2015

Marine and Petroleum Geology

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“…1) crosses the combined path of the two western Atlantic inflows into the north-western North Sea: the FIC and the East Shetland Atlantic Inflow (ESAI; Fig. 1; Turrell et al, 1996). Bathymetry along the section varies between 69 and 143 m, deepening eastward.…”

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“…1) is present in the north-western North Sea to the west of 1 • W (Turrell et al, 1996;Sheehan et al, 2017). The front is bottom-intensified and frequently has only a limited surface signature (Hughes, 2014;Sheehan et al, 2017).…”

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“…The front is bottom-intensified and frequently has only a limited surface signature (Hughes, 2014;Sheehan et al, 2017). Consequently, the front may be more readily observed from subsurface observations collected from a (Turrell et al, 1996) are shown. The area shown in Figs.…”

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confidence: 99%

“…3. (Turrell et al, 1996). Occupations took between 3 and 11 days, depending on how much of the section was sampled.…”

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Shelf sea tidal currents and mixing fronts determined from ocean glider observations

et al. 2018

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Abstract. Tides and tidal mixing fronts are of fundamental importance to understanding shelf sea dynamics and ecosystems. Ocean gliders enable the observation of fronts and tidedominated flows at high resolution. We use dive-average currents from a 2-month (12 October-2 December 2013) glider deployment along a zonal hydrographic section in the northwestern North Sea to accurately determine M 2 and S 2 tidal velocities. The results of the glider-based method agree well with tidal velocities measured by current meters and with velocities extracted from the TPXO tide model. The method enhances the utility of gliders as an ocean-observing platform, particularly in regions where tide models are known to be limited. We then use the glider-derived tidal velocities to investigate tidal controls on the location of a front repeatedly observed by the glider. The front moves offshore at a rate of 0.51 km day −1 . During the first part of the deployment (from mid-October until mid-November), results of a onedimensional model suggest that the balance between surface heat fluxes and tidal stirring is the primary control on frontal location: as heat is lost to the atmosphere, full-depth mixing is able to occur in progressively deeper water. In the latter half of the deployment (mid-November to early December), a front controlled solely by heat fluxes and tidal stirring is not predicted to exist, yet a front persists in the observations. We analyse hydrographic observations collected by the glider to attribute the persistence of the front to the boundary between different water masses, in particular to the presence of cold, saline, Atlantic-origin water in the deeper portion of the section. We combine these results to propose that the front is a hybrid front: one controlled in summer by the local balance between heat fluxes and mixing and which in winter exists as the boundary between water masses advected to the north-western North Sea from diverse source regions. The glider observations capture the period when the front makes the transition from its summertime to wintertime state. Fronts in other shelf sea regions with oceanic influence may exhibit similar behaviour, with controlling processes and locations changing over an annual cycle. These results have implications for the thermohaline circulation of shelf seas.Copyright statement. The works published in this journal are distributed under the Creative Commons Attribution 4.0 License. This license does not affect the Crown copyright work, which is re-usable under the Open Government Licence (OGL). The Creative Commons Attribution 4.0 License and the OGL are interoperable and do not conflict with, reduce or limit each other.

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Sea surface temperature changes in the North Sea and their causes

Becker

1996

ICES Journal of Marine Science

112

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Hydrography of the East Shetland Basin in relation to decadal North Sea variability

Cited by 56 publications

References 18 publications

Bubble momentum plume as a possible mechanism for an early breakdown of the seasonal stratification in the northern North Sea

Bubble momentum plume as a possible mechanism for an early breakdown of the seasonal stratification in the northern North Sea

Shelf sea tidal currents and mixing fronts determined from ocean glider observations

Sea surface temperature changes in the North Sea and their causes

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