66
GORDON A. RILEY
lacking on dissolved organic carbon. The ordinary method for determining organic carbon by wet oxidation is not precise enough to provide
useful information on some of the small changes that are involved here,
and as indicated earlier there is considerable doubt as to whether all
of the organic carbon is oxidized. Methods for carbon determination
by dry combustion are under development in this laboratory by P. J.
Wangersky, but data are not yet available for incorporation in the
present account.
C. Sinking rates
1. Introduction to the problem
Various problems involving the biological and geochemical significance of non-living particulate matter require some knowledge of its
residence time in the ocean and its sinking rate. Thus far no direct
measurements of sinking rates have been published.
Riley et al. (1965) made an indirect calculation based upon estimated
food requirements and availability of assimilable organic matter in deep
water. The results implied an average residence time of four years and
an average sinking rate of 2 miday, with a general range in likely
estimates of 1-7 m/day. This estimate was of course dependent on the
validity of several assumptions about biological relationships. In
particular, recent work by Gordon (1970b) on enzymatic hydrolysis of
particulate organic matter suggests that the assimilable fraction may
be less than was assumed by Riley et al. (1965), and if this is so, the
sinking rate was over estimated.
I n contrast with these estimates Menzel and Goering (1966) postulated that the particulate matter below a depth of about 200m is
unassimilable and neutrally buoyant. Some experiments were described
in which water samples were filtered, and the filter pads were inoculated
with surface water. No significant decrease in carbon was found after
90 days’ storage. The further postulate that the particles are neutrally
buoyant was not supported by data but was regarded by these authors
as the simplest explanation for observed patterns of distribution.
Hobson (1967) used a Coulter Counter to measure the size-frequency
distribution of deep water particulate matter, and with certain assumptions about the specific gravity of the particles he was able to calculate
sinking rates, using a modified version of the Stokes equation. He
concluded that most of the rates should be within the general range of
0-1-10 m/day. This large range resulted from a variety of assumptions
about specific gravity ; there was no certainty about the correct value
to be used, and the range was too large to be very useful.
GORDON A. RILEY
lacking on dissolved organic carbon. The ordinary method for determining organic carbon by wet oxidation is not precise enough to provide
useful information on some of the small changes that are involved here,
and as indicated earlier there is considerable doubt as to whether all
of the organic carbon is oxidized. Methods for carbon determination
by dry combustion are under development in this laboratory by P. J.
Wangersky, but data are not yet available for incorporation in the
present account.
C. Sinking rates
1. Introduction to the problem
Various problems involving the biological and geochemical significance of non-living particulate matter require some knowledge of its
residence time in the ocean and its sinking rate. Thus far no direct
measurements of sinking rates have been published.
Riley et al. (1965) made an indirect calculation based upon estimated
food requirements and availability of assimilable organic matter in deep
water. The results implied an average residence time of four years and
an average sinking rate of 2 miday, with a general range in likely
estimates of 1-7 m/day. This estimate was of course dependent on the
validity of several assumptions about biological relationships. In
particular, recent work by Gordon (1970b) on enzymatic hydrolysis of
particulate organic matter suggests that the assimilable fraction may
be less than was assumed by Riley et al. (1965), and if this is so, the
sinking rate was over estimated.
I n contrast with these estimates Menzel and Goering (1966) postulated that the particulate matter below a depth of about 200m is
unassimilable and neutrally buoyant. Some experiments were described
in which water samples were filtered, and the filter pads were inoculated
with surface water. No significant decrease in carbon was found after
90 days’ storage. The further postulate that the particles are neutrally
buoyant was not supported by data but was regarded by these authors
as the simplest explanation for observed patterns of distribution.
Hobson (1967) used a Coulter Counter to measure the size-frequency
distribution of deep water particulate matter, and with certain assumptions about the specific gravity of the particles he was able to calculate
sinking rates, using a modified version of the Stokes equation. He
concluded that most of the rates should be within the general range of
0-1-10 m/day. This large range resulted from a variety of assumptions
about specific gravity ; there was no certainty about the correct value
to be used, and the range was too large to be very useful.