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| Titel |
A Lagrangian study of the influence of a canyon on an alongslope current |
| VerfasserIn |
Jaimie Cross, Andrew Dale, Phil Hosegood |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250110695
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| Publikation (Nr.) |
 EGU/EGU2015-10722.pdf |
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| Zusammenfassung |
| The European slope current is a poleward flow which traces the shelf edge from the Bay of
Biscay to the Faeroe-Shetland Channel and beyond. Along its path, this current encounters a
variety of bathymetric environments, differentiated by slope steepness and level of
topographic complexity, in particular due to indentation by canyons. In one region, the Malin
shelf to the north of Ireland and west of Scotland, persistent intrusions of oceanic water occur
onto the shelf. It has been suggested that these intrusions result from a tendency for
the slope current to depart from the slope, and that the reason for this departure is
bathymetric. The slope in this region is relatively smooth, however it changes in
orientation and is indented by two significant canyons near to the source of the
intrusions. The response of the slope current to these topographic features is considered
here.
A purely geostrophic flow must follow isobaths. When the curvature of the topography is
too great, flow becomes ageostrophic and may cross isobaths, stretching the water column
vertically and inducing cyclonic vorticity. In this study, a Lagrangian approach was taken, in
which a dye tracer, fluorescein, was injected into the slope current upstream of the canyons
and used to track the behaviour of a tagged water column as it encountered the topography in
its path. The dye injection was mid-slope, at a depth of 181 m in a water depth of 625 m, and
10 km upstream of the southernmost canyon. Dye was followed for 4 days as it
advected alongslope at a mean speed of 0.13 ms-1, a relatively weak flow for this site,
while repeated transects were made across it using a free-fall turbulence profiler.
Rather than following isobaths around the heads of the canyons, the dye-tagged
water took a more direct route across them. The dye-laden part of the water column
stretched by around 50%, comparable to the proportional change in bottom depth,
but this stretching was in large part reversed downstream and the dye resumed its
alongslope flow. It appears that the weak slope current was able to pass over this pair of
canyons and resume its alongslope trajectory without significant disruption to its
path. |
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