Jökull - 01.12.1966, Blaðsíða 28

include (1) large scale temperature variations
of climatic origin, (2) oscillatory motions due
to internal and planetarv waves, (3) turbulence
and other dynamic instabilities, (4) convective
instabilities and (5) morphological factors such
as turbidity currents and earthquakes.
The climatic factors are beyond the scope
of the present discussion. Lee and Cox (1966)
have discussed the case of the oscillatory mo-
tions and come to the conclusions that they
may cause some minor temperature fluctuations
at the sea floor.
Temperature fluctuations due to turbulence
and dynamic instabilities are very difficult to
handle from the theoretical point of view. The
scale of turbulence iii the oceans varies within
wide limits. Small scale relatively high frequ-
ency temperature fluctuations in the bottom
boundary laver have a very small amplitude
and are of no importance within the present
context. The other end of the spectrum, that
is, instabilities of current systems, are more
interesting but very little is known about this
subject. The possibilities for such fluctuations
appear to be enhanced by the oscillatory un-
rest in the oceans which is now more apparent
on the basis of recent observations. However
since the temperature environment at the floor
of the deep oceans is laterally rather homo-
geneous, it appears somewhat doubtful that
these phenomena could cause fluctuations which
could interfere greatly with the studies of the
terrestrial heat flow through the ocean floor.
But it should be emphasized that practically
no experimental data are available on this
subject.
Due to the tliermal inertia of the bottom
sediments, temperature fluctuations resulting
from current instabilities would cause local
transitory changes of the temperature lapse
rate. Deviations of this nature can be both posi-
tive ancl negative, and the quantitative aspects
involved can possibly be investigated on the
basis of the diffusion type models discussed in
section (3).
As to the convective instabilities, the discus-
sion in section (2) appears to imply that, al-
though superadiabatic temperature lapse rates
of the order of 10-3 to 10-2 °C/m could
possibly be built up at favorable conditions,
such rates may be rather unstable. A change
in the state of the turbulence could leacl to
instabilities in the boundary layer and to the
formation of “thermals”. Similar to the situa-
tion in the atmosphere, “bubbles” of water
could break away from the bottom and rise
into the boundary layer. Temperature fluctua-
tions ot the orcler of 10 ~2 °C could possiblv
be caused by such “thermals”. On the other
hand, their frequency may be such that they
are of little practical importance for the heat
flow studies. As a matter of course, at this
juncture, this is purely speculative.
The morphological factors are probably of
little or no importance except in certain re-
stricted active areas. However, it is to be realiz-
ed that major earthquakes can cause consider-
able local disturbances at the ocean floor. The
uppermost section of the sediments becomes
mixed with the bottom waters. The equalizing
of the resulting temperature disturbance may
possibly take years.
A CKNO WLED GEMEN T
This work was supported by the National
Science Foundation under Grant GP-4642. The
author is also indebted to various members of
the Department of Oceanography, Oregon St.ate
University, Corvallis, Oregon, for their helpful
comments on t.he manuscript.
REFEREN CES
Bodvarsson, G., Berg, J. and Mesecar, R. 1967.
Vertical temperature gradient and eddy dif-
fusivity above the ocean floor in an area
west of the coast of Oregon. J. Geophys.
Res. 72: 2693-2694.
Carslaw, H. S., and Jaeger, J. C. 1959. Conduc-
tion of heat in solids, 2nd ed. Oxford Uni-
versity Press, London.
Isaacs, J. D., Reid, J. R. Jr., Schick, G. B. and
Schwartzlose, R. A. 1966. Near bottom cur-
rents measured in four kilometers depth
off the Baja California coast. J. Geophys.
Res. 71: 4297-4303.
Jefíreys, Sir Harold. 1926. Tlie stability of a
layer of fluid heated from below. Phil.
Mag., 2, Ser. 7: 833-844.
- 1928. Some causes of instability in fluicl
motion. Proc. Royal Soc., London, Series A,
118: 152-208.
182 JÖKULL