Convergent margin processes play an important role in the distribution of t
errestrial volatile species. During subduction processes volatiles are filt
ered from the subducting package and are restricted to return to the mantle
. Water is the most abundant volatile and plays an important role in these
processes. There is a number of geochemical investigations to determine the
subduction, regassing, and recycling fluxes as well as the regassing ratio
of water. The latter describes the partition of subducting water by water
that is regassed into the mantle and water that is returned to the surface
in arc magmas. Here we present a geophysical-based modelling approach for t
he calculation of such fluxes and ratios in order to compare them with the
geochemical data. In order to assess the recent values and the evolution of
the subduction, regassing, and the recycling flux a simple parameterized t
hermal convection model with a water-dependent rheology and a constant cont
inental growth model is applied. To test the sensitivity of the results dif
ferent continental growth models were applied and the total amount of water
in the system was varied as well as the initial distribution of water in t
he reservoirs. According to our estimations a value of 0.31 for the time in
dependent regassing ratio of water, R-H2O, is an acceptable upper bound. Lo
wer values of R-H2O give larger water reservoirs on the surface compared to
the recent situation. Larger values of R-H2O suggest smaller surface reser
voirs of water and, therefore. seem to be unlikely. The model results show
a relatively stable value for the regassing ratio of 0.31 by varying the in
itial conditions of the water distribution in the reservoirs (which are pre
tty much unknown at the present moment). But R-H2O is very sensitive toward
s the total amount of water in the system. Altering the value of four ocean
masses to ten we get values for the regassing ratio from 0.31 to 0.89. Nev
ertheless, as a result of all numerical experiments the recent subduction f
lux is stable and equal to 1.02x10(15) g/a. The influence of the continenta
l growth model on the results could be neglected. The calculated value for
the recent subduction water flux fits the modern geochemical data very well
while our value for R-H2O is smaller, One possible reason could be that in
our experiments R-H2O remains constant and, therefore, represents an avera
ge value over Earth's history. In order to check this assumption we apply a
simple exponential time dependence of R-H2O. Here, the modern regassing ra
tio increases to 0.41. Therefore, based on a geophysical modelling approach
in contrast to the geochemical investigations we suggest a smaller value f
or the modern regassing ratio of about 0.3 to 0.4. (C) 2001 Elsevier Scienc
e Ltd. All rights reserved.