Jökull - 01.12.1966, Side 27

higher velocities in the Atlantic, and may pos-
sibly indicate a significant difference between
the two oceans.
Very little is known about the vertical varia-
tion of the eddy diffusivity az in the ocean.
There is no doubt that the behavior of this
quantity is quite complex, and it will depend
heavily on the local stability of the water masses.
On the other hand, it is not inconceivable
that there is a certain resemblance with the
eddy diffusivity in the lower atmosphere. It is
well known that the eddy diffusivitv of the
lower atmosphere increases with the height over
the ground and it appears to reach a maximum
at heights of the order of a few hundred meters.
The values found in the lowest part of the
surface boundary layer are generally substanti-
ally lower than the values at a higher level.
A similar behavior of the diffusivity in the
deep oceanic currents would imply relatively
low values in the bottom boundary layer. As a
matter of fact, this trend seems to be indicated
bv the relatively low value of the estimate given
above for the lowest section of the Pacific deep
current. Hence, if the average for the deep
Pacific current is az = 10~4 m2/sec., the values
in the lowest section may be one or two orders
of magnitude smaller. The thickness of this low
diffusivity layer cannot be inferred on the basis
of the above data, but it is of interest to point
out that Koczy (1950) has on the basis of chemi-
cal investigations of samples taken from the
bottom boundary layer in the Atlantic come to
the conclusion that there is a boundary layer
of 20 to 50 m with an apparently very low dif-
fusivity.
Although the speculative character of these
results has to be underlined, it is rather evident
that they appear to be consistent with the
superadiabatic lapse rates which Lubimova et
al. (1965) claim to have observed in the bottom
boundary layer in some locations in the deep
Pacific.
Based on the similarity theory of Monin and
Obukhov, Lee and Cox (1966) have computed
a typical boundary layer profile of the mean
horizontal velocity ú(z) ancl potential tempera-
ture 0(z) for a current with a main velocity of
u = 10-2 m/sec. Their results implv a rela-
tively very thin boundarv layer with rather high
values of the eddv diffusivity. At elevations of
z = 1 and 10 m values of az = 2 X 10~5 and
and 1.5 x 10-4 m2/sec., respectively, are im-
plied. On the basis of their temperature data,
Lee and Cox (1966) question the validity of the
observations of Lubimova et al. (1965) They
claim that the observed superadiabatic lapse
rates are unlikely to exist for much over 1 m
above the sea floor, unless there is a stabilizing
density gradient. At least as far as the Pacific
Ocean is concerned, this view is not supported
by the present investigation.
(5) HEAT FLOW ANOMALIES
AND THE TEMPERATURE
ABOVE THE OCEAN FLOOR
The above considerations appear to indicate
a rather interesting possibility as to the detec-
tion of terrestrial heat flow anomalies on the
basis of their influence on the temperature of
the water just above the ocean floor.
The data given by Knauss (1962) indicate
that the terrestrial heat flow raises the tem-
perature of the bottom current in the Pacific
by about 0.1° C along the initial 1,800 km
of flow. If this interpretation is correct, then
we may, on the basis of equation (10), infer
that an anomalous temperature rise of 0.02° C
would be obtained when the current flows
across an elongated heat flow anomaly of 100
km width and having an excess heat flow of
0.06 watts/m2.
Hence, it appears possible that relatively
small areas of anomalous terrestrial heat flow
may have a noticeable effect on the tempera-
ture of the bottom water. As stated above,
Knauss (1962) has already pointed out that an
anomaly of this kind appears to exist in the
neighborhood of the East Pacific Rise.
An accurate study of the spatial variations of
the bottom temperature of the deep oceans may
therefore be of value for the detection of local
heat flow anomalies. As a matter of course, the
instrumental precision has to be quite great,
and interpretational difficulties will, no doubt,
be encountered in areas of uneven topography
and complex currents. But an attempt in this
direction appears worthwhile.
(6) TEMPERATURE FLUCTUATIONS
AT THE OCEAN FLOOR
It is possible to list a number of phenomena
that could cause temperature fluctuations at
the floor of the deep oceans. These factors
JÖKULL 181