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| Titel |
North Atlantic Current variability and associated mixing at the Mid-Atlantic Ridge |
| VerfasserIn |
M. Walter, C. Mertens, M. Dengler, M. Rhein |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250064910
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| Zusammenfassung |
| Observational evidence for enhanced turbulent energy dissipation at sites of
topography-mesoscale flow interaction indicates the possible role of fronts and eddies
as energy source for mixing. In consequence, changes in the (upper ocean) flow
field must have an impact on stratification and circulation in the deep ocean as
patterns of mixing and water mass transformation may be altered by changing the
locations of flow-topography interactions. In the North Atlantic, the North Atlantic
Current (NAC) that crosses the Mid-Atlantic Ridge (MAR) between 48° and 54° N is
known to shift its position and develop different branch modes in response to the
prevalent wind field. Strength and positioning of the branches is modulated by the
slowly varying eddy field and corresponds to the gaps in the MAR: the northern
branch, also known as subpolar front (SPF) crosses the ridge at the latitude of the
Charlie–Gibbs Fracture Zone (CGFZ), the southern branches are less restricted
and more eddy dominated, but tend to align with the Faraday or Maxwell Fracture
Zones.
We use repeated observations of hydrography and currents at the SPF west of the
Mid-Atlantic Ridge to investigate the temporal variability of the spatial distribution of
finescale variance, vertical mixing and their relation to the position of the NAC. The CTD and
lowered ADCP observations were carried out during three (summer) cruises in
2008, 2010, and 2011. During the 2008 cruise, additional microstructure data were
collected at three stations, used to validate dissipation rates from a shear/strain
parameterization in the upper 1200Â m. The orientation of the repeat section is roughly in
southeast–northwest direction, starting at about 48° N and ending near the western exit of
the CGFZ. The position of the NAC shows considerable differences between the
three observations. During the 2008 and 2010 transects, a single branch mode was
observed, with the SPF between 50 and 51° N in 2008 and farther north at 52° N
in 2010. In contrast, a two branch mode was observed in 2011, with a (stronger)
southern front at 49° N, and a weaker northern front north of 50° N. The highest
shear variance as well as elevated mixing was found in the vicinity of the front at
mid-depth for all cruises, indicating the generation of finestructure variability by the
front. |
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