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| Titel |
Internal Waves and Mixing Near the Yermak Plateau, Arctic Ocean |
| VerfasserIn |
Ilker Fer |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250035677
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| Zusammenfassung |
| Recent findings show that i) moderate mixing levels typical of mid-latitude can erode or even
remove the Arctic cold halocline layer, and ii) internal wave induced mixing is
enhanced in the absence of sea ice. In the prospect of a seasonally ice-free Arctic
Ocean, mixing levels sufficient to remove the cold halocline layer, can be anticipated
as a result of wind energy input over large areas of open water. The ice is then
easily exposed to the relatively warm Atlantic water, possibly leading to a strong
positive feedback. The Yermak Plateau, located in the Marginal Ice Zone northwest of
Svalbard, where the West Spitsbergen Current (WSC) carries the warm Atlantic Water
into the Arctic Ocean, is a site where insight can be gained. Earlier studies have
identified the Yermak Plateau as a region of enhanced tidal variability, internal
wave activity and turbulent mixing. Here we report on observations of oceanic
currents, hydrography and microstructure made in the southern Yermak Plateau
in summer 2007 on both sides of the Arctic Front. Time series of approximately
one-day duration from five stations (upper 520 m) and eight-day duration from a
mooring are analyzed to describe the characteristics of internal waves and turbulent
mixing.
Internal waves generated in response to the tidal flow over this topographic feature locally
contribute to mixing and remove heat from the Atlantic Water. The spectral composition of
internal wave field over the southern Yermak Plateau is 0.1-0.3 times the mid-latitude levels
and compares with the most energetic levels in the central Arctic. Dissipation rate and eddy
diffusivity below the pycnocline increase from the noise level on the cold side of the front by
one order of magnitude on the warm side. Here, 100-m thick layers with average
diffusivity of 5Ã10-5 m2 s-1 lead to heat loss from the Atlantic Water of 2-4 W
m-2. Dissipation in the upper 150 m is well above the noise level at all stations,
but strong stratification at the cold side of the front prohibits mixing across the
pycnocline. Close to the shelf, at the core of the WSC, diffusivity increases by
another factor of 3 to 6. Here, near-bottom mixing removes 15 W m-2 of heat
from the Atlantic layer. Internal wave activity and mixing vary spatially, thus the
path of WSC will affect the cooling and freshening of the Atlantic inflow. When
generalized to the Arctic Ocean, diapycnal mixing away from abyssal plains can
be significant for the heat budget. Around the Yermak Plateau, it is of sufficient
magnitude to influence heat anomaly pulses entering the Arctic Ocean, however,
diapycnal mixing alone is unlikely to have regional significance in cooling of WSC. |
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