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| Titel |
New observations of eddies and boundary currents in the Red Sea |
| VerfasserIn |
Amy S. Bower, Stephen A. Swift, James H. Churchill, Daniel C. McCorkle, Yasser Abualnaja, Richard Limeburner, Ping Zhai |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250080945
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| Zusammenfassung |
| Physical oceanographic studies of the Red Sea have often focused on the large-scale
overturning circulation, in which water entering the sea from the Gulf of Aden becomes
cooler, saltier and more dense as it flows northward, due mainly to strong evaporation (~2
m/y), and then flows back southward and exits the sea as a dense overflow through Bab al
Mandeb. Less attention has been focused on the details of the horizontal circulation, in large
part due to the dearth of high-resolution observations of the three-dimensional structure of
water properties and currents. Two high-resolution hydrographic and current surveys were
recently carried out in the eastern Red Sea, in March 2010 and September-October 2011. Of
particular note are the continuous measurements of current velocity, taken along the cruise
tracks from the sea surface to 600 m with a hull-mounted Acoustic Doppler Current Profiler,
which revealed the presence and structure of several basin-scale eddies and eastern boundary
currents.
In March 2010, a strong, 200-km diameter anticyclonic eddy was found centered near
23oN, with peak azimuthal velocities of nearly 1 m/s, a transport of 6-7 Sv and eddy
currents extending to ~400 m depth. The eddy’s core was in solid body rotation, with
six-day rotation period and a relative vorticity of 0.5f (i.e., 1/2 the local Coriolis
parameter). Surface drifters deployed in the eddy core remained trapped for their entire
lifetimes (up to 5 months). An eddy was observed several times previously in this
location—20 years of satellite-derived altimetric measurements of sea level anomaly
indicate that it is a quasi-permanent feature of the Red Sea circulation and that
there is an annual cycle in its strength. This may be linked to the annual cycle in
buoyancy forcing and the strength of the cyclonic circulation in the northern Red
Sea.
In September 2011, cross-basin transects in the southern Red Sea (17-19oN) revealed a
layer of relatively cold, fresh, low-oxygen, high-nutrient Gulf of Aden Intermediate Water
(GAIW) being advected rapidly northward near the eastern boundary by a subsurface jet with
a transport of ~0.35 Sv, and with speeds of order 0.2 m/s in the depth range 35-100 m. The
GAIW layer overlapped with the euphotic zone and contributed to enhanced productivity in
the 35-75 m depth range. Most of the intrusion entered deep channels between coral reef
islands and shoals in the Farasan Bank region off Saudi Arabia, while a fraction was
advected into the basin interior by a mesoscale eddy. The shoreward intrusion of
GAIW could have significant implications for the coral reef ecosystems in the Red
Sea.
Numerical model results and some drifter trajectories from this and previous studies
suggest that major elements of the large-scale circulation in the Red Sea are located near the
western boundary, emphasizing the need for an international effort to survey the entire Red
Sea from coast to coast. |
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