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| Titel |
On the fate of the lower North Atlantic Deep Water at the equator. |
| VerfasserIn |
M. Dengler, P. Brandt, C. Eden, J. Toole |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250029648
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| Zusammenfassung |
| The Deep Western Boundary Current (DWBC) transports North Atlantic Deep Water
(NADW) into the South Atlantic. It forms along the continental slope east of Greenland and
carries dense and cold water masses from the Denmark Strait overflow (lower North Atlantic
Deep Water, lNADW), the Iceland - Scotland sills (middle NADW) and the Labrador Sea
(upper NADW). In the equatorial zone, our knowledge of the DWBC continuation is
incomplete. Due to topographical constraints at about 8°N the DWBC splits into a
shallow (2500m) branch. At 35°W, the deep branch is found to be attached to the
Parnaiba Ridge slightly north of 2°S carrying about 7 Sv of mNADW and 5 Sv of
lNADW. A large part but not all of the NADW arriving at 35°W appears to continue
southward at the western boundary. The DWBC is reestablished at 5°S having a
velocity core at about 2000m depth. Its southward transport there is confined to the
uNADW and mNADW layers and amounts to about 20 Sv, which is comparable to
the eastward transports within the same two layers at 35°W. There is, however,
no net southward transport in the lNADW layer at the western boundary in the
tropical Atlantic south of the equator. Fritz Schott formulated the problem as follows:
“The fate of the lNADW is one of the major oceanographic questions remaining
today which may involve circuitous zonal routes into the interior of the basin and
interactions with topography of the Mid-Atlantic Ridge" (Schott et al., 2005). In this
contribution, we investigate possible processes contributing to the fate of the lNADW
in the equatorial Atlantic. In previous invers studies, abyssal upwelling through
diapycnal mixing has been invoked to explain the deep equatorial circulation. However,
microstructure data from the equator at 13°W indicate very low mixing rate that account for
small abyssal upwelling transports. Similarly, repeat sections at 23°W suggest little
eastward transport of lNADW in the equatorial region. Recent model studies have
suggested that the equatorial deep jets are forced in the western and central part of the
equatorial basins by instability of intraseasonal equatorial waves. These jets are
capable of advecting water mass properties zonally on long time scales and their
generation and maintenance may enhance diapycnal water mass transformation. |
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