Wimbledon, W. A. P., and Smith-Meyer, S. (eds.), 2012.
Geoheritage in Europe and its conservation. Oslo: ProGEO,
Norway. 405 pp.
Cross-references
Moraines
Reefs (Biogenic)
Seamounts
Submarine Canyons
MARINE HEAT FLOW
John G. Sclater
1
, Derrick Hasterok
2
, Bruno Goutorbe
3
,
John Hillier
4 and Raquel Negrete
5
1
Scripps Institution of Oceanography, University of
California San Diego, La Jolla, CA, USA
2
Department of Geosciences, University of Adelaide,
Adelaide, Australia
3
Institute of Geosciences, State University Fluminense,
Niteroi, Brazil
4
Department of Geography, Loughborough University,
Leicestershire, UK
5
Ensenada Center for Scientific Research and Higher
Education, Department of Geology, CICESE, Zona
Playitas, Baja California, Mexico
Definition
Heat flow is a measure of the rate of thermal energy transferred (power) from one place to another normalized area,
commonly denoted q. The units of q are equivalent to
energy time
À1 area
À1
, which is W m
À2 in the System
International (SI) where a watt (W) is equivalent to a joule
second
À1 (J s
À1 ). Since the heat flow is typically small for
most Earth processes, we often report heat flow in mW
m
À2
, where 1 mW ¼ 10
À3 W. Heat flow is physically
defined by Fourier’s law, given by the product of the thermal conductivity, k, with a thermal gradient between two
points, DT/Dz, i.e., q ¼ k (DT/Dz). In marine geophysics
steady-state conductive heat flow is the measurement typically made. Thermal gradients are estimated by driving a
3–10 m long, thin steel probe into the soft marine sediments. The probe contains several thermistors, to measure
temperature (mK accuracy), distributed along the length at
known distances. Such measurements over the short
length of such a probe are possible because of the insulating effect of poorly mixed deep-sea water reservoirs. Thermal conductivity is more challenging to estimate but is
typically done by (1) modeling the decay of heat due to
insertion of the temperature probe or (2) performing measurements on retrieved sediment core. Very few heat flow
measurements have been made through or around bare
rock, and thus, inherently, the current measurements do
not account for the advective heat loss due to the circulation of water at the Earth’s surface (Louden and Wright,
1989).
Method of measurement
There are three principal methods of measuring seafloor
heat flow. One pioneered by Bullard (1954) (Figure 1a)
involves the use of a thin steel probe with the temperature
measuring devices located within the steel probe. The second developed by Ewing (Gerard et al., 1962) (Figure 1c)
uses a standard core tube and measures the temperature
gradient using thermistors within outriggers mounted on
the outside of the core tube. The third, the violin-bow
probe (Figure 1b), designed by Lister in 1967 but
described in Lister (1979), measures the temperature
within a thin tube attached to a very strong 3–5 mm diameter steel rod. In this method, the thermal conductivity is
determined in situ by pulsing heat into the tube and afterward examining the temperature decay with time from the
pulse. The other two instruments rely on known relations
between sediment properties and thermal conductivity
from a nearby sediment core. In addition to the above
methods, a number of measurements have been made
using temperatures measured in a core pushed ahead of
drill string in the Deep Sea Drilling and Ocean Drilling
Programs (Pribnow et al., 2000). Agreement between the
shallow measurements and the borehole observations is
generally good (Hyndman et al., 1984) and confirm that
bottom water temperature does not vary significantly in
the eastern north Pacific and the central and eastern
Atlantic. However, water temperature variations observed
offshore western North America, South Atlantic, and eastern Pacific affect measurements with shallow, <5 m, penetration (Davis et al., 2003).
The above techniques require sediments so that the
probe can penetrate below the surface. A thermal blanket
(Johnson and Hutnak, 1997), made of a thin (5 cm) urethane foam sheet with known thermal conductivity and
thermistors on either side, can be draped directly over a
rock outcrop. Thermal blankets have seen very little use
as they require placement by an ROV and must be left
for approximately 12 h to equilibrate.
Introduction and early work
Measurement of the flow of heat through the Earth is crucial because it is heat and temperature differences that primarily drive motion within the Earth. Heat flow is difficult
to measure because it involves measuring a gradient at or
near the boundary between two different substances: sediment and water for the oceans and rock/sediment and air
on land. Despite these difficulties heat flow measurements
have contributed to many major advances in the Earth sciences. This contribution is especially true of the measurements from the ocean floor, and it is these measurements
that are the subject of this review.
Essentially one man, Sir Edward Bullard, initiated
marine heat flow as a subdiscipline of geophysics at the
end of WWII. Given the controversy created by Lord Kelvin (1895) who used temperature gradients from mines on
land to compute the age of the Earth, it is truly surprising
that it took so long for heat flow measurements to be made
MARINE HEAT FLOW
449
Geoheritage in Europe and its conservation. Oslo: ProGEO,
Norway. 405 pp.
Cross-references
Moraines
Reefs (Biogenic)
Seamounts
Submarine Canyons
MARINE HEAT FLOW
John G. Sclater
1
, Derrick Hasterok
2
, Bruno Goutorbe
3
,
John Hillier
4 and Raquel Negrete
5
1
Scripps Institution of Oceanography, University of
California San Diego, La Jolla, CA, USA
2
Department of Geosciences, University of Adelaide,
Adelaide, Australia
3
Institute of Geosciences, State University Fluminense,
Niteroi, Brazil
4
Department of Geography, Loughborough University,
Leicestershire, UK
5
Ensenada Center for Scientific Research and Higher
Education, Department of Geology, CICESE, Zona
Playitas, Baja California, Mexico
Definition
Heat flow is a measure of the rate of thermal energy transferred (power) from one place to another normalized area,
commonly denoted q. The units of q are equivalent to
energy time
À1 area
À1
, which is W m
À2 in the System
International (SI) where a watt (W) is equivalent to a joule
second
À1 (J s
À1 ). Since the heat flow is typically small for
most Earth processes, we often report heat flow in mW
m
À2
, where 1 mW ¼ 10
À3 W. Heat flow is physically
defined by Fourier’s law, given by the product of the thermal conductivity, k, with a thermal gradient between two
points, DT/Dz, i.e., q ¼ k (DT/Dz). In marine geophysics
steady-state conductive heat flow is the measurement typically made. Thermal gradients are estimated by driving a
3–10 m long, thin steel probe into the soft marine sediments. The probe contains several thermistors, to measure
temperature (mK accuracy), distributed along the length at
known distances. Such measurements over the short
length of such a probe are possible because of the insulating effect of poorly mixed deep-sea water reservoirs. Thermal conductivity is more challenging to estimate but is
typically done by (1) modeling the decay of heat due to
insertion of the temperature probe or (2) performing measurements on retrieved sediment core. Very few heat flow
measurements have been made through or around bare
rock, and thus, inherently, the current measurements do
not account for the advective heat loss due to the circulation of water at the Earth’s surface (Louden and Wright,
1989).
Method of measurement
There are three principal methods of measuring seafloor
heat flow. One pioneered by Bullard (1954) (Figure 1a)
involves the use of a thin steel probe with the temperature
measuring devices located within the steel probe. The second developed by Ewing (Gerard et al., 1962) (Figure 1c)
uses a standard core tube and measures the temperature
gradient using thermistors within outriggers mounted on
the outside of the core tube. The third, the violin-bow
probe (Figure 1b), designed by Lister in 1967 but
described in Lister (1979), measures the temperature
within a thin tube attached to a very strong 3–5 mm diameter steel rod. In this method, the thermal conductivity is
determined in situ by pulsing heat into the tube and afterward examining the temperature decay with time from the
pulse. The other two instruments rely on known relations
between sediment properties and thermal conductivity
from a nearby sediment core. In addition to the above
methods, a number of measurements have been made
using temperatures measured in a core pushed ahead of
drill string in the Deep Sea Drilling and Ocean Drilling
Programs (Pribnow et al., 2000). Agreement between the
shallow measurements and the borehole observations is
generally good (Hyndman et al., 1984) and confirm that
bottom water temperature does not vary significantly in
the eastern north Pacific and the central and eastern
Atlantic. However, water temperature variations observed
offshore western North America, South Atlantic, and eastern Pacific affect measurements with shallow, <5 m, penetration (Davis et al., 2003).
The above techniques require sediments so that the
probe can penetrate below the surface. A thermal blanket
(Johnson and Hutnak, 1997), made of a thin (5 cm) urethane foam sheet with known thermal conductivity and
thermistors on either side, can be draped directly over a
rock outcrop. Thermal blankets have seen very little use
as they require placement by an ROV and must be left
for approximately 12 h to equilibrate.
Introduction and early work
Measurement of the flow of heat through the Earth is crucial because it is heat and temperature differences that primarily drive motion within the Earth. Heat flow is difficult
to measure because it involves measuring a gradient at or
near the boundary between two different substances: sediment and water for the oceans and rock/sediment and air
on land. Despite these difficulties heat flow measurements
have contributed to many major advances in the Earth sciences. This contribution is especially true of the measurements from the ocean floor, and it is these measurements
that are the subject of this review.
Essentially one man, Sir Edward Bullard, initiated
marine heat flow as a subdiscipline of geophysics at the
end of WWII. Given the controversy created by Lord Kelvin (1895) who used temperature gradients from mines on
land to compute the age of the Earth, it is truly surprising
that it took so long for heat flow measurements to be made
MARINE HEAT FLOW
449