Adjustment of the basin-scale circulation at 26 N to variations in Gulf Stream, deep western boundary current and Ekman transports as observed by the Rapid array


Bryden, H.L., Mujahid, A., Cunningham, S.A. and Kanzow, T. (2009) Adjustment of the basin-scale circulation at 26 N to variations in Gulf Stream, deep western boundary current and Ekman transports as observed by the Rapid array. Ocean Science, 5, (4), 421-433.

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Description/Abstract

The Rapid instrument array across the Atlantic
Ocean along 26 N provides unprecedented monitoring of the
basin-scale circulation. A unique feature of the Rapid array
is the combination of full-depth moorings with instruments
measuring temperature, salinity, pressure time series at many
depths with co-located bottom pressure measurements so that
dynamic pressure can be measured from surface to bottom.
Bottom pressure measurements show a zonally uniform rise
(and fall) of bottom pressure of 0.015 dbar on a 5 to 10 day
time scale, suggesting that the Atlantic basin is filling and
draining on a short time scale. After removing the zonally
uniform bottom pressure fluctuations, bottom pressure variations
at 4000m depth against the western boundary compensate
instantaneously for baroclinic fluctuations in the strength
and structure of the deep western boundary current so there
is no basin-scale mass imbalance resulting from variations
in the deep western boundary current. After removing the
mass compensating bottom pressure, residual bottom pressure
fluctuations at the western boundary just east of the Bahamas
balance variations in Gulf Stream transport. Again the
compensation appears to be especially confined close to the
western boundary. Thus, fluctuations in either Gulf Stream
or deep western boundary current transports are compensated
in a depth independent (barotropic) manner very close to the
continental slope off the Bahamas. In contrast, compensation
for variations in wind-driven surface Ekman transport
appears to involve fluctuations in both western basin and
eastern basin bottom pressures, though the bottom pressure
difference fluctuations appear to be a factor of 3 too large,
perhaps due to an inability to resolve small bottom pressure
fluctuations after removal of larger zonal average, baroclinic, and Gulf Stream pressure components. For 4 tall moorings
where time series dynamic height (geostrophic pressure) profiles
can be estimated from sea surface to ocean bottom and
bottom pressure can be added, there is no general correlation
between surface dynamic height and bottom pressure. Dynamic
height on each mooring is strongly correlated with sea
surface height from satellite observations and the variability
in both dynamic height and satellite sea surface height decrease
sharply as the western boundary is approached.

Item Type: Article
ISSNs: 1812-0792 (print)
Related URLs:
Subjects: G Geography. Anthropology. Recreation > GC Oceanography
Divisions: University Structure - Pre August 2011 > School of Ocean & Earth Science (SOC/SOES)
University Structure - Pre August 2011 > National Oceanography Centre (NERC)
ePrint ID: 73042
Date Deposited: 25 Feb 2010
Last Modified: 27 Mar 2014 18:52
URI: http://eprints.soton.ac.uk/id/eprint/73042

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