Jökull - 01.12.1966, Page 21

GUNNAR BODVARSSON1:
Heat Transfer and Temperature
Microstructure at the Ocean Floor
ABSTRACT
The stability of the temperature field at the
ocean floor depends on the regime of floio in
the bottom boundary layer. Both convective
and dynarnical instabilities can cause fluctua-
tions. Eddy diffusion of heat and rnomentum
enliance greatly the stability against free con-
vection. A feio estimates are given of the eddy
diffusioh coefficient in the Pacific deep cur-
rent, and it is shoion that these estimates are
not inconsistent wit.h the existence of measure-
able superadiabatic temperature lapse rates
above the ocean floor. On the other hand, it
does not appear that conv'ective instabilities
can cause appreciable temperature fluctuations.
The influence of the terrestrial heat floiu on
the regional temperature field i?i tlre bottom
boundary layer is studied. and it is concluded
that heat floiu anomalies on a relatively small
spatial scale could cause measurable tempera-
ture anomalies in the water.
(1) INTRODUCTION
The ílow of heat from the earth’s interior
up through the ocean floor has been studied
extensively during the past decade. The ob-
servational technique presupposes a stationary,
or a quasi-stationary, temperature at the solid-
water interface (see e.g. Von Herzen and Lang-
seth, 1965). The question as to the relevance
of this assumption has resulted in an enhanced
interest in the temporal and spatial character-
istics of the microstructure of the temperature
field at the ocean floor. Since the temperature
structure depends largely on the dvnamical
conditions in the boundary layer above the
ocean floor, the theory of the temperature field
will therefore have to draw heavily on fluid
dynamics, and on the dynamics of turbidence
in particular.
1) Department of Oceanography, Oregon
State University, Corvallis, Oregon.
This intetTelationship is also reciprocal. Im-
portant data on the dynamics of oceanic tur-
bulence can be obtained on the basis of the
temperature data. There is therefore a general
interest in the temperature field at the ocean
floor.
The present paper has been written for the
purpose of discussing a few questions relevant
to the above topic, mainly the influence of the
convective transport of lreat on the tempera-
ture field. Within this context it is of irnport-
ance to arrive at an understanding of the
superadiabatic temperature lapse rates at the
ocean floor which have been reported by Lubi-
rnova, Von Herzen and Udintsev (1965) as well
as by Bodvarsson, Berg and Mesecar (1967).
According to their observations in the Pacific,
there appears to be a number of locations
where there is a boundary layer of a few met-
ers with superadiabatic temperature lapse rates
of the order of 10~4 to 10~2 °C/m. In extreme
cases, the superadiabatic lapse rates appear to
extencl perhaps as far as 50 m above the ocean
floor.
In a recent paper, Lee and Cox (1966) discuss
the subject matter of the present paper. They
present temperature records from various
depths in the Pacific displaying noticeable fluc-
tuations. These are believed to result from
internal oscillations and the authors point out
that they may introduce errors in oceanic heat
flow data. On the other hand, Lee and Cox
(1966) come to the conclusion that free convec-
tive motions above the ocean floor are of little
importance. They apply the „similarity theory“
of Monin-Obukhov to the turbulent boundary
above the oceanic floor and conclude that
noticeable superadiabatic lapse rates are un-
likely to occur unless in combination with a
stabilizing density gradient. It is pointecl out
that other researchers have not been able to
confirm the observations of Lubimova et al.
(1965).
JÖKULL 175