Carol A. Stein- Hydrothermal Circulation Research page

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Hydrothermal circulation is one of the primary ways the solid earth
interacts with the ocean/atmosphere system and is a consequence of
plate tectonics. Early in the development of plate tectonics,
the large difference between the observed heat flow
and the higher heat flow predicted from cooling lithospheric models was
recognized to be a consequence of heat transfer by water flow in
the crust. The required heat transfer implies
that the equivalent of the volume of the whole ocean cycles through
the oceanic crust every few million years. The interaction between the sea water
and the oceanic crust significantly affects the chemistry of the
oceans and the atmosphere. 


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Figure 1: Schematic illustration of estimation of
hydrothermal flux from the heat flow anomaly. The anomaly, or
difference between the heat flow predicted by a
lithospheric cooling model and that observed (shaded)
is presumably transported by water flux. The flux is thought
to be divided into a near-ridge, high temperature, "active" flow and
an off-ridge, low temperature, "passive" flow. At a sealing age,
the observed and predicted heat flow approximately coincide. The data
can be presented either in raw form
(top) or as the fraction
of the predicted heat flow that is observed (bottom).















I have used the global heat flow data set to better
constrain the amount of hydrothermal heat loss and water circulation,
and find several important results [Stein and Stein, 1992; Stein et al., 1995].


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First, about 2/3 of the hydrothermal heat loss
occurs by off-ridge and presumably low-temperature flow in crust
older than 1 Myr.  Because the water temperature for near-ridge
flow exceeds that for off-ridge flow, the near-ridge water
flow should be even a smaller fraction of the total water flow.
Hence in estimating fluxes from geochemical data,
use of the high water temperatures appropriate for the ridge axis
may significantly overestimate the heat flux for
an assumed water flux, or underestimate the water flux for an
assumed heat flux. 
Second, the ratio
of observed to predicted heat flow increases with age until
about 65 Myr, but
shows little dependence on the sediment thickness at the sites.
In particular, contrary to earlier suggestions, about 100-200 m
of sediment is generally neither necessary nor sufficient to bring
heat flow to the value predicted by lithospheric cooling models.
The most straightforward inference from these observations is
that the fraction of
heat transported by hydrothermal flow varies primarily with crustal age
and at most secondarily with the sediment thickness.
Third, although heat flow in young lithosphere is
highly variable, due presumably to local hydrologic complexities,
the average heat flow
decreases approximately linearly from near the axis to about
20 Myr and then is roughly constant to about 50 Myr. 





Figure 2:
Top: Cumulative predicted, observed, and inferred hydrothermal heat fluxes
as a function of age. The lines connect
the points whose values were computed. For clarity, the 1 Ma point
is not plotted, and the observed values are offset.
Error bars are one standard deviation of the data.
Bottom: Cumulative inferred hydrothermal heat flux for 0-65 Ma.









Recently Hofmeister and Criss [2005] have suggested that 
the total global heat flow is about 30 TW, about 25% less than previously 
estimated by Pollack et al. [1993]. The main difference between the two 
estimates is whether oceanic heat flow values are based on the predicted
from conductive lithospheric cooling models or the
lower measured values, reflecting the additional near-surface
heat transfer by hydrothermal circulation.
While hydrothermal circulation is spectacularly displayed
at hot springs at midocean 
ridges (see photographs at the top of this web page)
detailed heat flow measurements and pore water chemistry do
show that significant amounts of water flow near the top
of the basaltic oceanic crust and transfer heat 
within off-axis regions. 


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Often water is discharged at
basement highs and outcrops associated with high heat flow. However,
the lower surrounding areas are ofen associated with significantly lower heat
heat flow where heat has been removed by hydrothermal circulation. 
Since most heat flow measurements in younger crust
are made in basement lows with sufficient sediment for the
heat flow equipment to penetrate, measured heat flow is
biased towards lower values and underpredicts the 
total heat flow. For more detailed discussion see
Pollack et al. [2005].


This effect of high heat flow on basement
highs due to water discharge
and lower heat flow due to removal of heat by hydrothermal
circulation in the surrounding lower
region is discussed in Stein and Stein [1997].
Detailed heat flow measurements made near basement highs
are shown below.











Figure 3: Smoothed surface plot of heat flow data for the eastern portion of
the FlankFlux area (top) and Galapagos Spreading Center (bottom).
Data are shown as heat flow fraction, the
ratio of the observed value to that predicted by a model
without hydrothermal cooling.
Except near basement highs, most measurements have
heat flow fractions less than one, indicating significant
lateral heat transport by hydrothermal flow.
Heat flow data from Davis et al. [1992] and Green et al. [1981].





















References:


Davis, E., D. Chapman, M. Mottl, W. Bentkowski, K. Dadey, C. Forster, R. Harris,
S. Nagihara, K. Rohr, G. Wheat, and M. Whiticar,
FlankFlux: nature of hydrothermal circulation in young oceanic crust,

Can. J. Earth Sci., 29,

925-952, 1992.  




Green, K. E., R. P. Von Herzen, and D. L. Williams,
The Galapagos Spreading Center at 86 degrees W: A detailed geothermal field
study,

J. Geophys. Res., 86,

979-986, 1981.  




Hofmeister, A. M., and R. E. Criss, Earth's heat flux revised and linked to
chemistry, 

Tectonophysics, 395, 

159-177, 2005.




Pollack, H. N., S. J. Hurter, and J. R. Johnston,
Heat loss from the earth's interior: analysis of the global data set,

Rev. Geophys., 31,

267-280, 1993.  




Stein, C. A., and S. Stein, Constraints on hydrothermal heat
flux through the oceanic lithosphere from global heat flow,

J. Geophys. Res., 99, 

3081-3095, 1994. 
 For pdf click here




Stein, C., and S. Stein,
Estimation of lateral hydrothermal flow distance from
spatial variations in oceanic heat flow,

Geophys. Res. Lett., 24,

2323-2326, 1997.
 For pdf click here




Stein, C., S. Stein, and A. Pelayo,
Heat flow and hydrothermal circulation,
in: Physical, chemical, biological
and geological interactions within
hydrothermal systems,
AGU Mono.,
edited by Humphris, S., L. Mullineaux, R. Zierenberg and R. Thomson,
Am. Geophys. Un.,
Washington, D.C., 425-445,
1995. 
 For pdf click here





Von Herzen, D. P., E. E. Davis, A. Fisher, C. A. Stein, and H. N. Pollack,
Comments on "Earth's heat flux revised and linked to chemistry" by A. M.
Hofmeister and R. E. Criss, 

Tectonophysics, 409,

193-198, 2005. 
 For pdf click here