David ?V, Menzel and John J. Goering

THE
DISTRIBUTION
OF ORGANIC
IN THE OCEAN1
DETRITUS
David ?V, Menzel
Woods 1101~ Oceanographic
Institution,
Woods Hole, Massachusetts
02543
and
John J. Goering
Institute
of Marine
Scicncc, University
of Alaska, College
99735
ABSTRACT
Decomposition
expcrimcnts
on particulate
matter from surface and deep Atlantic waters
are described.
Changes in carbon in surface water were related to the initial biomass of
phytoplankton,
the residue representing
refractory
detritus.
No changes could be induced
in deep-water samples. The distribution
of particulate
organic carbon in water below 200 m
is remarkably
constant in time, space, and depth. It is postulated that all of this material
is uniformly
resistant to decomposition.
Surface waters contain living matter which is
supcrimposcd
upon levels of detrital carbon remarkably
similar to those in deep water.
It has been observed generally that the
concentration of particulate carbon is higher
in the cuphotic zone of the ocean than in
the underlying water. But because of relatively large concentrations of detritus, attempts to correlate organic carbon with
plant biomass have been indirect and the
validity of the necessary assumptions is suspcct. Steele and Baird (1961, 1962, 1965)
and Menzel and Ryther (1964) used the
regression of chlorophyll
(as an index of
plant biomass) on carbon to statistically
separate living plant carbon from detritus,
assuming that the intcrccpt on the carbon
axis provided an estimate of the average
amount of dead material (detrital carbon).
This approach has the weakness that reprcscntative ranges of values for both carbon
and chlorophyll
concentrations are ncccssary to clearly establish the slope of the rcgression. These ranges are not commonly
found in the open ocean. The approach
also assumes that the level of detrital carbon is constant from sample to sample. The
l Contribution
No. 1731 from
Woods
Hole
Oceanographic
Institution
and No, 10 from the
Institute of Marine Science. Supported in part by
National Science Foundation
Grants GB 1525 and
GB 2678; by Office of Naval Research Contract
Nonr 2196 and U.S. Atomic Energy Commission
Contract AT( 30-l ) -19,18 ( ref. NY0 1918-128 ) ,
assumption of Ryther and Menzel (1965)
that an assigned carbon : chlorophyll ratio
(in their cast 35 : 1) can bc used to estimate the fraction of plant carbon is equally
indirect and subject to error.
Interest has been gcncrated recently in
the distribution and mechanisms of formation of organic detritus in deep oceanic
water (Sutcliffc, Baylor, and Menzel 1963;
Riley 1963; Riley, Wangersky, and Van
IIemcrt 1964; Dal Pont and Newell 1963;
and earlier work which has been summarized by Parsons 1963). It has been postulatcd (Sutcliffc
et al. 1963; Riley ct al.
1964, 1965) that organic aggregates may be
formed near the surface through the action
of bubbles. The bubbles presumably serve
as sites for the concentration of dissolved
organic matter which, upon collapse of the
bubble, is compressed and solidified.
If
this were so, it is logical to expect a gcncral
decrease in the amount of detritus with
depth because, as solid organic matter, it
would be subject to predation and bacterial
consumption as it sinks into deep water. In
fact, no such dccrcase has been observed,
as will bc shown later (see also Riley et al.
1965), and vertical changes in carbon below the euphotic zone are gcncrally small
or nonexistent. The adsorption of dissolved
matter from the water onto settling particlcs was proposed as a mechanism that
333
334
1. Initial
TABLE
day decomposition
Station
649
650
651
652
653
654
655
656
657
658
659
660
661
662
DAVID
W.
MENZEL
AND
JOIIN
J,
GOERING
control (IPC) and partic&te
carbon concentrations
(j4g C/liter)
remaini7tg after
expertients
(FPC) along with estimates of living (A) and detrital carbon (FPC).
samples from. 1 m. RV Chain Cruise 48: 5-20”N lat, 50-6O”W long
IPC
PPC
63
37
44
34
55
86
74
67
79
34
45
40
74
56
30
31
27
22
33
56
52
29
38
21
28
21
53
42
A
33
6
17
12
23
30
22
38
41
13
17
19
21
14
would help preserve the equilibrium nccessary to explain this discrepancy (Riley et al.
1965)) but Jerlov ( 1959 ) and Dal Pont and
Newell ( 1963) have chosen to attribute
particle clistribution to horizontal transport
from regions of deep-water formation. None
of these authors has tried to separate these
two viewpoints completely, and both mechanisms are probably active. For particles
to remain in suspension for the considerable times required for their transport over
long distances, and to maintain their integrity, deep, oceanic detrital particles must
be relatively refractory to decomposition
and neutrally buoyant. The s?me refractory
characteristic is a prerequisite for particles
settling through 5,000 m of water.
The observations reported in this paper
were collected on Cruise 14 of the Atlantis
II and Cruises 24 and 48 of the RV Chain
in the Atlantic Ocean. The purpose was
threefold:
1) to determine possible relationships between the distribution
of particulate carbon and plant biomass, 2) to
characterize surface and deep oceanic detritus in terms of its relative stability to
heterotrophic decomposition, and 3) to detcrmine the distribution of detritus in deep
oceanic waters over widely separated areas.
Initial
chlorophyll
( ,wOter )
A
Chlorophyll
0.378
0.083
0.206
0.130
0.270
0.340
0.253
0.349
0.405
0.146
0.226
-
87
72
82
92
85
88
87
109
101
90
75
0.208
-
101
-
Detrital
(%I
90All
C
48
84
61
65
60
65
70
43
48
62
62
49
72
75
METIIODS
Samples for the measurement of particulate carbon were collected with a 16-liter
bottle constructed
entirely of polyvinyl
chloride. Generally, 2 liters of water were
concentrated on precombusted glass-fiber
filters using a vacuum not exceeding 25 cm
Hg. The carbon subsequently was determined by the method of Menzel and Vaccare ( 1964). The error of this method does
not exceed -I- 10 pg C (absolute).
Experiments to determine oxidizable carbon were carried out as follows:
Eight
liters of water were filtered onto precombusted 4.5-cm diameter glass-fiber filters.
The filter was then divided into two fractions. One fraction was dried under vacuum for preservation and the second placed
in a plastic petri dish containing 3 ml of
unfiltered surface water. The dishes, with
perforated tops, were sealed in a plastic
box containing water in the base (to maintain a saturated atmosphere) and stored
in the dark at 20C for 90 days. These filters
were then analyzed for carbon by the
method described above. The purpose of
adding surface water to the filters was to
provide an inoculum of bacteria and other
microorganisms
capable of oxidizing
the
ORGANIC
DETRITUS
particulate matter in the sample. Any particulatc carbon ingcstcd (i.e., infusoria) or
oxidized is presumably lost to the system as
COa, and it is assumed that the method
provides an index of utilizable
organic
matter.
Chlorophyll
was determined
by the
method of Yentsch and Menzel (1963) using the same type of glass filter for its
concentration
as in the determination
of
carbon.
RESULTS
It appears that the level of carbon at any
given location is influcnccd by factors other
than the amount of phytoplankton.
The
simplest explanation is attributing
this to
varying levels of organic detritus. Macroscopic zooplankton, if encountered, have
routinely been removed from filters before
analysis, and it is assumed that bacteria
contribute an insignificant
amount of carbon compared to the amount of detritus.
If the detritus is refractory and not easily
oxidized chemically or biologically or both,
relatively large concentrations may result
through accumulation over long periods of
time. To test this hypothesis, dccomposition cxperimcnts were conducted on RV
Chain Cruise 48 in the western tropical Atlantic Ocean by the technique described
above. Table 1 gives the original carbon
content of surface water and the residue
after a go-day incubation period. Residual
carbon ranged from 43 to 84% of that originally present. These values represent refractory detritus while the difference bctwecn the initial and final value represents
labile matter, assuming that all of the latter was oxidized during the go-day incubation period. A relatively constant ratio
of labile carbon to the initial chlorophyll
concentrations
was observed ( Table 1))
and the intercept of a plot of thcsc variables against each other was at the origin.
Thus, labile carbon appears to provide a
reasonably good estimate of living plant
matter. The average carbon : chlorophyll
ratio of 87 : 1, by weight, rcprcsents a maximum value because some refractory carbon
must arise from the decomposition of the
living plants.
Similar experiments
con-
IN
TI-IE
335
OCEAN
control
(IPC) and particulate
TAULE 2. Initial
carbon concentration
(pg C/liter)
remaining
after
a go-clay decomposition
period
(FPC).
Water
samples from indicated depths. RV Chain Cruise
48: 5-20”N lat, SO-6O”W long
Station
649
650
651
652
653
654
656
657
658
659
660
661
662
663
664
200 in
1,000 m
IPA
FPC
A
28
20
27
24
25
28
20
24
25
20
25
24
-
24
21
26
25
25
26
22
22
20
21
24
24
-
4
+l
-6
+1
0
-2
3-2
2
+l
-1
0
-
IPC
FPC
A
26
23
25
26
19
20
26
26
-7
-3
+l
0
27
24
22
19
19
24
24
28
20
24
18
15
20
24
24
31
-7
0
4
4
+1
0
0
+3
ductcd with Skeletonema costatum, in the
laboratory,
indicated
that approximately
75% of the initial carbon was oxidized
within 40 days and that no further change
occurred during an additional 200 days.
It can bc further postulated that if organic detritus is refractory, deep oceanic
water should contain only stable fractions
because this material presumably
takes
considerable time to settle to depth or to
be transported horizontally to a given location. Table 2 gives the results of decomposition experiments conducted on water
from various depths below the euphotic
zone. These data show clearly that no carbon ( within the analytical error ) was oxidized and that essentially all the organic
matter was refractory.
Fig. 1 represents the distribution of particulatc organic carbon at depths below 200
m in the Atlantic Ocean and Caribbean
Sea, with the range, mean, and number of
samples obtained at each depth. In general, the range indicated is within the presumcd absolute analytical error of 4 10 pg
C. Since 2 liters of water were filtered in
each cast, the error was reduced to 4 5
pg C/liter. These data illustrate a remarkable consistency throughout the water col-
336
DAVID
W.
MENZEL
I
AND
I
El
x-
x9
x-
,I
X17
x
:
x5
x- --x,2
D
2
x-
,I,
-x2
x
x12
*
-r 6
IO
PARTICULATE
CARBON
20
#
30
(,ug/d?iterl
distribution
of particulate
FIG. 1. The vertical
carbon
in the central
North
Atlantic
organic
Ocean. Numbers at each depth indicate the numbcr of samples the range (x) and mean ( l ) arc
based upon. A. Caribbean Sea. 13”35’N lat, 6,7”
04’W long. Atlantis II, Cruise 14, November 1964.
B. Tropical
Atlantic
Ocean. 5-20”N
lat, 50-60”
W long. Mantis II, Cruise 14, October-November
1964. C. Subtropical
Atlantic
Ocean. 22-36”N
lat, 65”W long. RV Chain, Cruise 24, April 1962.
D. Tropical Atlantic Ocean. 5-20”N lat, 50-6O”W
long. RV Chain, Cruise 48, May-June
1965.
umn in both time and space. In addition,
within relatively small limits (a factor of
two) all values are remarkably similar to
those obtained for residual detritus from
surface experiments ( Table 1) .
DISCUSSION
On the basis of the cvidcnce given above,
the following postulates can be advanced:
1) Living labile carbon represents a variable fraction of the total organic particulate matter present in surface waters. Superimposed on this is detrital carbon which
is refractory to decomposition.
Most carbon in water below 200 m is uniformly resistant to decomposition.
2) The level of
particulate
carbon in the North Atlantic
Ocean ( 5-36”N lat ) is remarkably uniform
JOIIN
J.
GOERING
with respect to time, depth, and location.
3) The level of detritus in both surface
and deep water is the same within a factor
of two.
Dal Pont and Newell ( 1963) and Menzel
( 1964) have pointed out that total particulate organic carbon in a vertical section
far exceeds the annual rate of production
in a water column. On this basis, Menzel
( 1964) postulated that deep-water carbon
in both dissolved and particulate fractions
is exceedingly stable and subject to only
limited changes by biological action. Evidence supporting this contention is given
above. To the authors’ knoqwledgc this is
the first attempt to demonstrate the stability of these compounds experimentally.
Our observations arc consistent with the
data of Riley et al. (1965) that show the
uniformity of detrital carbon in a vertical
section. Various hypotheses were advanced
by Riley ct al. (1965) to explain this phcnomenon, because if the particles are utilized by animals or bacteria in deep water,
it would be logical to expect their concentration to decrease with depth. If, on the
other hand, they arc refractory and undigestible, no such explanation is necessary.
Although Riley ct al. (1965) were able
to detect seasonal changes below 500 m
at a given station in the Sargasso Sea, no
such variation is evident in our data (Fig.
2, B and D) even though they encompassed two diffcrcnt seasons at a lower latitudc. The mechanism producing a seasonal
change of the order reported by Riley ( lo40 ,~g C/liter)
over a depth of 3,000 m at
Bermuda would represent the production
of approximately 90 g of C/m? -more than
the net annual rate of primary production
at that location (Menzel and Ryther 1960).
On the other hand, if physical phenomena
at the surface)
(for example, bubbling
cause the precipitation of dissolved organic
matter such an increase might be explained
( Riley et al. 1965). The problem of how
particles so produced could distribute thcmsclvcs equally through the entire water
column
in so short a period of time remains.
Alternatively,
if horizontal transport from
other regions produce such changes, it is
ORGANIC
DETRITl
unlikely that it would bc reflected in the
entire water column. One would cxpcct
horizontal transport to be sclcctively manifcst at the levels occupied by intruding
water masses.
Dal Pont and Newell (1964) po,stulatcd
that vertical differences in the conccntration of particulate carbon could bc corrclatcd with hydrographic
features in the
Tasman Sea and obtained values
in deep
water varying by a factor of five. Parsons
and Strickland ( 1962) and Menzel ( 1964)
obtained considerably less scatter (21-53
,ug C/liter) below 1,000 m at three stations
in the northeastern Pacific Ocean and in
two stations in the Arabian Sea, respectively. It is therefore, at present, impossible to evaluate the applicability of our data,
which suggest the relative uniformity
of
particulate carbon in deep waters, to the
world’s oceans, but it is likely that the
amount of variation is small,
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distribution
of particles in the sea. Deep-Sea
Res., 5: 173-184.
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of dissolved organic carbon in the Western Indian
Ocean. Deep-Sea Res., 11: 757-765.
-,
AND J. II. RYTHER. 1960. The annual
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production
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