Effect of Ridges and Gaps
409
flow structure occurring in the experiment, but it is plausible that the dipolar
flow predicted here had become unstable.
The recirculations produced by the sources driven by the pumping out of
the abyss can also be found when the source is produced by the flow drawn
through a gap in the eastern boundary of a subregion of the oceanic basin. This
is the subject of the next section.
7.5 Effect of Ridges and Gaps
As described in Section 7.1, the ocean basins at depth are actually divided into
subbasins by the enormous subsurface mountain ranges produced by the
geological processes of seafloor spreading. The midocean ridge systems are
found in all oceans, and the peaks of the ridges rise to within 2 km of the ocean
surface. If the ridge systems were unbroken, they would represent impenetrable
barriers to the abyssal circulation and divide the basin into sets of subplanetary
scale vessels in each of which the Stommel-Arons theory could be applied
separately. However, the ridges are fractured at many places along the length
of the ridge and these deep gaps offer passage for the water of one subbasin to
communicate with the neighboring subbasin. The restriction of the interbasin
deep flow to these gaps can be expected to have a significant influence on the
circulation patterns constructed using the Stommel-Arons theory. To examine
this in more detail, consider the model shown in Fig. 7.5.1. To simplify matters
to their essentials a cartesian coordinate system is used.The discussion follows
that of Pedlosky (1994b).
An abyssal basin with eastern and western boundaries at Xe and xw,
respectively, is divided in two by a north-south ridge system at x = x1• The
basin lies between latitudes of Yn and Ys to the north and south where the basin
is also closed by solid boundaries although this is not necessary to complete the
solution. The ridge is broken, here for illustration, into three segments. The
latitude interval for the jth segment is y 1 • :::;; y :::;; YJn, for j = 1, 2, 3. There are
two gaps between the three segments through which the fluid can leak from one
basin to the next as well as gaps between the northern extent of the ridge and
the northern basin boundary and the southern limit of the ridge and the
southern boundary. These last two gaps can also be thought of as representing
gaps in a more prolonged ridge system.
The flow is on the fJ plane and governed by the equation for the
geostrophic streamfunction:
"' = ____!!__ Polo
(7.5.1)
Because of the relatively small scales that are produced in the circulation by the
presence of the ridges and gaps, a quasi-geostrophic theory is applied in which
409
flow structure occurring in the experiment, but it is plausible that the dipolar
flow predicted here had become unstable.
The recirculations produced by the sources driven by the pumping out of
the abyss can also be found when the source is produced by the flow drawn
through a gap in the eastern boundary of a subregion of the oceanic basin. This
is the subject of the next section.
7.5 Effect of Ridges and Gaps
As described in Section 7.1, the ocean basins at depth are actually divided into
subbasins by the enormous subsurface mountain ranges produced by the
geological processes of seafloor spreading. The midocean ridge systems are
found in all oceans, and the peaks of the ridges rise to within 2 km of the ocean
surface. If the ridge systems were unbroken, they would represent impenetrable
barriers to the abyssal circulation and divide the basin into sets of subplanetary
scale vessels in each of which the Stommel-Arons theory could be applied
separately. However, the ridges are fractured at many places along the length
of the ridge and these deep gaps offer passage for the water of one subbasin to
communicate with the neighboring subbasin. The restriction of the interbasin
deep flow to these gaps can be expected to have a significant influence on the
circulation patterns constructed using the Stommel-Arons theory. To examine
this in more detail, consider the model shown in Fig. 7.5.1. To simplify matters
to their essentials a cartesian coordinate system is used.The discussion follows
that of Pedlosky (1994b).
An abyssal basin with eastern and western boundaries at Xe and xw,
respectively, is divided in two by a north-south ridge system at x = x1• The
basin lies between latitudes of Yn and Ys to the north and south where the basin
is also closed by solid boundaries although this is not necessary to complete the
solution. The ridge is broken, here for illustration, into three segments. The
latitude interval for the jth segment is y 1 • :::;; y :::;; YJn, for j = 1, 2, 3. There are
two gaps between the three segments through which the fluid can leak from one
basin to the next as well as gaps between the northern extent of the ridge and
the northern basin boundary and the southern limit of the ridge and the
southern boundary. These last two gaps can also be thought of as representing
gaps in a more prolonged ridge system.
The flow is on the fJ plane and governed by the equation for the
geostrophic streamfunction:
"' = ____!!__ Polo
(7.5.1)
Because of the relatively small scales that are produced in the circulation by the
presence of the ridges and gaps, a quasi-geostrophic theory is applied in which