Sediment Trap Technology and Sampling in Surface Waters
Edited by Wilford D. Gardner
Department of Oceanography
Texas A&M University
College Station, TX 77843-3146
There is a wide range of possible trap designs and environmental conditions
for their use. Protocols for the use of traps have been outlined twice
(U.S. GOFS Report No. 10, 1989; IOC Manual and Guides No. 29, 1994),
but have not always been followed because of differing opinions and
our inability to devise unequivocally accurate calibration schemes
that can be routinely followed for surface waters. Thus, we have not
progressed to the point of the CO2 measurements in establishing
fixed, widely accepted and adhered to protocols.
The objective of this report is to assess the present status of particle
trapping in the upper water column and suggest plans on how to:
- Estimate the magnitude of errors in trap and trap-related measurements;
- Resolve differences in fluxes measured by different methods
in the upper 200 m;
- Establish which ancillary measurements are needed in future
trapping experiments; and
- Verify which protocols should be used for traps.
To accomplish this objective, we list and discuss some of the potential
causes of biases in using traps in surface waters and estimate the
magnitude of their importance. We acknowledge disagreement in this
assessment because we have not been able to adequately quantify the
errors under all conditions. While many of the issues in this report
were discussed in the U.S. GOFS Report No. 10 (1989), half of the
references in this report were published after the GOFS report and
they demonstrate substantial progress. This report is an update of
the major issues with a narrow focus on using and calibrating traps
in the upper 200 m of the water column.
As a unifying theme, the discussion centers around the potential impact
of each parameter on the carbon imbalance reported by Michaels et
al. (1994) at the Bermuda Atlantic Time-Series station (BATS), and
to a lesser extent some comparable carbon budgets made at the Hawaii
time-series station (HOT). The format of this report is mostly in
the less orthodox form of an outline rather than straight prose in
an attempt to cut to the heart of each issue.
BATS carbon imbalance: At BATS a one-dimensional (vertical)
mass balance was constructed for carbon during the April-December
period when sediment traps were deeper than the mixed layer depth.
The time-course of total suspended carbon (DIC+DOC+POC) was compared
with the balance of all vertical fluxes (measured or estimated). The
carbon changes in the water were 3 times greater than the balance
of the fluxes. If the discrepancy were entirely due to undertrapping,
the traps would have had to collect 6 times as much material. Alternately,
advection or vertical migration of zooplankton could account for some
of the difference.
HOT carbon balance: At HOT, two different 1-D models predict
a carbon export from the upper ocean of approximately the same rate
as the measured carbon flux in traps (without accounting for sample
dissolution). Not included in this mass balance was an estimate of
the carbon flux due to vertical migration of swimmers or the fluxes
of DOC. Thus modifications of our sense of trap accuracy to bring
the trap estimate more towards addressing the imbalance at BATS might
create a disagreement between carbon fluxes and model estimates at
In constructing a carbon balance, we must remember that carbon can
be removed from surface waters by several processes; gravitational
settling of particles, vertical migration of zooplankton, vertical
mixing of DOC, DIC and POC, advective transport that creates a horizontal
gradient, and gas exchange of CO2 with the atmosphere.
Traps are intended to collect only the settling particles. Sources
of errors in trap measurements include; swimmers, solubilization of
carbon within the trap and hydrodynamic effects that include trap
geometry, flow, wave-induced trap motion, tilt, and the effects of
brine inside the trap.
The central question is whether differences in carbon budgets arise
because we don't understand the behavior of the instruments we are
using (traps and in-situ filtration systems) or because we don't understand
the dynamics of the system (particle fluxes and dynamics in surface
waters, radionuclide distributions and interactions with a wide range
of particle types, spatial scales etc.) or both?
For each issue there are comments made at the meeting or in response
to the draft report, notes on the magnitude of the problem, and recommendations
of what to do in the future. Names in parentheses indicate the person
responsible for the comment.
I. Possible Trap Biases
Magnitude of problem
- Protocols for picking swimmers have been established (IOC Manual
and Guides, 1994)
- Keep in mind that some swimmers may be part of the signal (Knauer,
Jim Murray; Silver et al., 1984)
- Swimmers have low Th content (Coale, 1990; Buesseler et al.,
- Swimmer-avoidance traps
- Coale (1990) - A cylindrical trap with internal funnels
and collars designed to separate the active swimmers from
the trap sample. It was used in VERTEX as a cod end on Soutar
cone traps. It is commercially available, but the only published
report of its use appears to be Lee et al., 1988. It removed
25-70% of the swimmers from the sample based on amino acid
content, but there were no comparisons made simultaneously
with other traps.
- Peterson et al. (1993) - A cylinder/cone trap with an indented
rotating sphere (IRS) separating upper and lower trap segments.
The device is designed to eliminate swimmers from lower regions
of the trap and to isolate the sample. On average, the flux
of material >850 µm was reduced by 88% relative to
identical control traps without the sphere. At the same time,
the flux of material < 850 µm decreased to 59-97%
(ave 84%) of the flux in identically-shaped control traps
without spheres. The C/N ratio of material in the IRS traps
was about 10, whereas it was about 8 in the control traps
suggesting some differentiation in the type of material passing
around the sphere. During the JOGFS EqPac program the IRS
traps collected much less material than the cylindrical traps
of Murray et al (submitted) when they were surface tethered,
but the moored IRS trap fluxes were more similar to the fluxes
measured with other moored traps (Cindy Lee).
- Hansel and Newton (1994) - A variation of the Coale trap,
it relies on random motion of swimmers to trap them away from
the sample chamber. It had a 70% exclusion efficiency for
copepods in coastal waters, but only 37-72% efficiency for
copepods in open ocean waters. Hansell suggests some modification
before these traps are used in the ocean. This trap has been
used to determine that only 7% of the trapped organic carbon
was remineralized to DOC in Monterrey Bay in 1.7 days.
- In the Mediterranean, pteropods are regularly and abundantly
found in the traps (Miquel et al., 1992, 1994, 1995). In principle,
shells with the animal inside do not belong to the trap flux whereas
empty shells do contribute to the passive vertical flux. (See
Harbison and Gilmer, 1986). Most of the shells are "full"
at upper depths (200 m) but deeper (1000 m), a good fraction (sometimes
up to 1/2) are empty. On the other hand, if the empty shells are
left in the flux, their contribution to the carbonate flux will
mask any other qualitative and quantitative change on carbon fluxes
with seasons or years. So far, we have considered the pteropods
as swimmers and we have a numerical estimate of their importance
in the traps, but we are looking for better approaches if they
exist (Juan Carlos Miquel).
Effect on BATS/HOT carbon imbalance/balance
- Decreases with depth (Lee et al., 1988).
- Even after manual removal of zooplankton under a strong dissecting
microscope, much of the remaining carbon in very shallow traps
is still swimmer or swimmer derived particles. This cryptic swimmer
problem is described in Michaels et al. (1990); it averaged about
50% of the collected carbon, with a maximum value of 96% of the
carbon in a shallow, picked trap, but the problem decreases rapidly
below 200 m.
- Are these data available from the VERTEX project? (Richard
Some are available (Michaels).
- Karl and Knauer (1989) attempted to circumvent the swimmer problem
by using combinations of screened and unscreened traps to calculate
a swimmer-free flux.
- See US GOFS Report (1989).
- A preliminary comparison of picking methods between HOT and
BATS found a 50-100% difference in total carbon. The screening
technique used at HOT was employed on replicates of the BATS traps
and the resulting carbon estimate with the HOT technique was higher
than the traditional BATS technique.
- Swimmer errors in poisoned traps usually bias traps towards
higher fluxes. If more swimmers were picked, trap fluxes would
be even lower and the BATS imbalance larger. Could some of the
organisms classified as swimmers actually be part of the true
flux? Could swimmers in traps be compensating for traps missing
the vertical migration flux (Michaels).
- Removing swimmers also removes attached non-swimmer mass which
tends to underestimate true fluxes. There is a cross-over point
somewhere: no swimmer removal overestimates flux, complete swimmer
removal and the attached particles underestimates flux. The "null"
point will vary with size spectrum and, perhaps, species present.
A most difficult problem indeed. (Dave Karl)
- If HOT traps were processed like BATS traps, the flux estimate
would likely be somewhat lower, creating a difference with the
modelled fluxes (Michaels)
- If some of the residual carbon in traps at either location
is due to swimmers, the fluxes are still further from the independent
measurements of flux.
- Could swimmers be eating and leaving?
- Not likely to be significant if the trap contains poison.
- Lee et al. (1987) found a 43% loss of carbon in unpoisoned
traps at 3 m in a shallow lake and attributed the loss to
zooplankton feeding in the traps. The loss was only 1-3% at
8-10 m depth.
- All investigators should report how swimmers were removed and
quantify their abundance.
- Some intercomparisons of swimmer removal techniques is feasible
and should be done.
B. Solubilization of particulate matter in the trap
- Organic carbon is lost with time (Lee and Cronin, 1982; Gardner
et al., 1983; Knauer et al., 1984; Lee et al., 1992), but decay
components can be retained in the brine. Knauer et al. (1984)
argued that the quantification of these components (e.g. phosphate)
can be used to estimate carbon loss. Dennis Hansell points out,
however, that this is true only if the decay products are unique
to the sinking particles. If these decay products are also found
in herniating swimmers, then the source cannot be identified uniquely.
One would also have to know the percentage of DOC release per
unit POC from swimmers and sinking particles.
- Peterson and Dam (1990) demonstrated that the addition of brine
to a trap will cause zooplankton to herniate. Hansell and Newton
(1994) found a factor of 10 difference in DOM accumulation between
brine and brine-free trap solutions, which they attributed to
herniation of swimmers. In deployments of a swimmer-segregating
trap (1.7 days), the quantity of DOC released caused only a 7%
decrease in the total POC flux compared with standard PITS traps
(Hansell and Newton, 1994).
- Lee et al. (unpublished data) measured DOC in their EQPAC IRS
traps that have reduced swimmer content. It appeared to make up
10-20% of the C flux. This may still a problem, but probably more
for those interested in specific organic compounds (Cindy Lee).
- Measurements of DOC and DIC in sediment traps obviously have
not found a wide acceptance and only very few examples of DOC
measurements have been published (Hansell & Newton, 1994). DIC
measurements in sediment trap samples have not been carried out
or published at all to our knowledge. Besides the additional work
burden, theoretical considerations restrict the completeness of
any DOC+DIC correction of POC flux measurements. Degradation of
POC to DIC in sediment traps would increase the pCO2.
This increase would give rise to loss of DIC from the sample prior
to the DIC analysis. Excess DIC (above ambient values) would thus
be a minimum estimate of carbon lost from the POC sample to the
water of the sediment trap cups. The problem of the origin of
this excess DIC (sinking particles vs. swimmers) will be similar
to that of excess DOC (Section I.B.1). For routine measurements
of DOC additional problems arise for those samples poisoned with
formaldehyde (the poison most recommended from the JGOFS-protocols;
IOC- manual, 1994). The DOC introduced by formaldehyde appears
to be a very large background signal, that will not allow detection
of excess DOC at a reliable level. (Wolfgang Koeve)
- The `Kiel Particle Flux Group' suggests furthermore that not
only should the measurement of DOC and DIC in sediment trap cups
be optimized, but one should also be aware of possible dissolution
of other components. Excess phosphate has been observed frequently
(Bodungen et al., 1991) and should be monitored like other constituents
of interest to the respective program (e.g. trace metals, amino
acids, fatty acids). (As a caveat, see comment 1. above.) If we
believe that excess DIC is a significant source of error for our
POC flux estimates, dissolved excess Ca also should be monitored
to control our estimates of PIC fluxes. It will depend on the
precautions carried out to control or even increase the buffer
capacity of the seawater in the sediment trap cups (examine effects
of different poisons: buffered formaldehyde vs. HgCl2,
sodium azide etc., Lee et al., 1992) whether or not dissolution
of POC to DIC and the subsequent increase of the pCO2
in the sample give rise to the dissolution of PIC for a given
sample. Furthermore, without monitoring excess Ca in the sediment
trap cups one would not be able to decide whether any excess DIC
should be added to the POC or PIC flux estimate. (Wolfgang Koeve)
- Obviously, reliable detection of excess DOC and DIC in sediment
trap samples relies on
- improving the swimmer avoidance
- using other poisons than formaldehyde
- control the whole carbonate system in the trap samples
- measure and understand the artificial losses of dissolved
tracers from sediment trap cups and
- model the loss of DOC, DIC and other related dissolved components
from sediment trap cups (Wolfgang Koeve)
- Experimental lab and field tests carried out showed that losses
of dissolved compounds are small for the `Kiel Sediment Traps'.
Investigation of losses of the supernatant sodium azide concentration,
used as poison during these experiments, was carried out in a
series of 11 sediment traps (up to 20 samples each) from moorings
deployed over recent years in the North East Atlantic. Deployment
period was one year. On average, blank bottles which were not
exposed to the open funnel showed losses of 7.5% of the initial
value of the poison. Higher loss values (up to 20%) occurred in
the sample bottles, which were exposed to the funnel for 8 to
28 days. These higher losses can be explained by means of reaction
of the poison with particles, diffusion, swimmer activity and
probably turbulent mixing events (Lundgreen et al., in prep).
This source of uncertainty needs to be evaluated also for other
sediment trap designs (VERTEX, Soutar, Honjo-traps, etc.). Since
it will highly depend on the hydrodynamic environment of the sediment
trap for a given experiment or field study, regular measurements
are recommended. Tracers other than the poison sodium azide need
to be discussed, Kremling and Schuessler from Kiel recently used
22Na as a tracer in another study. (Wolfgang Koeve
& Ulrich Lundgreen)
- Brines also "purge" interstitial fluids of particles that could
contain substantial amounts of nutrients (Karl et al. 1984) and
biogenic gas (Karl and Tilbrook, 1994).
- The VERTEX group found that dense NaCl brines cause CaCO3
to dissolve (Honjo et al., 1992), so they switched to a NaCl,
MgCl2, CaCl2, KCl mix in making their brine.
- Sample cups in a JGOFS trap mooring with funnel traps lost
20% of the original sodium azide. The loss was believed to have
resulted from swimmer activity rather that diffusion or currents
(Ulrich Lundgreen). Dissolved components would have been lost
- Jim Murray didn't see a DOC difference in a two day trap deployment.,
but Dennis Hansell and Jan Newton report measuring large DOC signals
in numerous trap deployments in Monterey Bay. If traps are deployed
without brine, DOC could easily diffuse from the trap and would
not be detected.
- If C, N, P, etc. are lost due to herniation, maybe we should
redefine the whole biogeochemical cycle in terms of Si, which
has a much smaller magnitude problem with swimmers. If the carbon
imbalance problem finally falls on swimmers, perhaps this is a
viable solution, or at least a test of the hypothesis (Dave Karl).
Magnitude of problem
- Depends on length of deployment and what poisons/preservatives
- Lorenzen et al. (1981) reported a 7% loss per day for 5 days
using sediment trap material. Iturriaga (1979) reported an 8%
loss per day for zooplankton and 3% lost per day for phytoplankton
in 15°C water. Gardner et al. (1983) measured daily losses
of 0.1% to 1% per day extended over 106 days in deep traps, and
showed that if carbon losses were much greater than 1% per day
for long-term, multiple cup trap experiments, seasonal cycles
would not be discernable. In the upper water column carbon losses
were about 7% in 1.7 days (Hansell and Newton, 1994).
- In some earlier studies, carbon fluxes were increased by a
factor of 2.23 to "correct" for the presumed dissolution in traps.
This is no longer done.
Effect on BATS/HOT carbon imbalance/balance
- The herniating of swimmers would increase carbon in the supernatant
even if they are picked out.
- Hansell and Newton (1994) found only a 7% difference between
total organic carbon and particulate organic carbon after a 1.7
day deployment in Monterey Bay.
- This isn't large enough to solve the carbon imbalance (Michaels),
though some of the more extreme correction factors (e.g. the 2.23
fold VERTEX correction) would move the measured flux much closer
to the required export.
- Several measurements indicate that the carbon loss by solubilization
is at most a few percent a day in unpoisoned traps. Unless swimmers
are prevented from entering the trap, most of any excess DOC signal
in trap supernatant water is derived from herniating swimmers.
If trap samples are well-picked for swimmers, the apparent magnitude
of the solubilization problem appears to be smaller than previously
C. Hydrodynamic biases
- One of the major approaches in evaluating the efficiency of
sediment traps has been to calibrate small models of traps in
flumes or tanks where the conditions of sedimentation can be controlled
and measured (Hargrave and Burns, 1979; Gardner, 1980a; Butman,
1986). The experimentally confirmed assumption has been that in
the absence of any current, cylindrical traps accurately intercept
the material settling out of the water above the trap. In the
presence of velocities up to about 10 cm/sec, cylindrical traps
still collect particles at the rate predicted ±30-50%. The predicted
rate is determined from the loss of particles above the trap (Hargrave
and Burns, 1979; Gardner, 1980a) or the measured settling velocity
of the particles used in the calibration (Butman, 1986). In some
flume experiments conducted by Gust et al. (in press), VERTEX
style cylinders show significant increases in flux between velocities
of 5 and 10 cm/s. However, several reviewers versed in fluid dynamics
argue that their methods are flawed because they inject particles
into the trap through a tube rather than allowing particles to
be intercepted by the trap and collected naturally. It is difficult
to test traps in flumes at velocities much higher than about 10
cm/sec because settled material is resuspended from the flume
bottom and has a second chance to enter the trap.
- Moving to the field, one continues to make the reasonable assumption
that cylindrical traps still accurately intercept the material
settling out of the water above the trap if there is no movement
past the trap, though independent verification of this assumption
would certainly be desirable. (See section III below on INDEPENDENT
MEASURES OF VERTICAL FLUX.) The effects of large-scale turbulence,
internal waves, tilt and mooring line motions that are not present
in the flume have unknown effects on the comparison of flume and
field data. Comparisons have then been made between cylindrical
traps and traps of other designs such as funnels that are deployed
simultaneously (Honjo et al., 1992). Comparisons of fluxes measured
with drifting and moored traps of the same design at the same
location can also be used to determine the efficiency of traps
under different flow conditions. Baker et al. (1988) have done
precisely that experiment.
- Baker et al (1988). show that relative trap efficiency in moored,
cylindrical traps with a steep inner funnel in the field drops
to 20-25% efficiency somewhere in the velocity range of 12-30
cm/sec compared to the same design of trap when it is drifting
with the water in the same place over the same time. The corresponding
trap Reynolds numbers (Rt = (velocity*trap diameter)/viscosity)
for the 20 cm diameter Baker trap are 24,000-60,000. The Rt
or range of Rt over which the flux decreases is unknown.
The composition of particles was also very different at higher
Reynolds numbers. Field experiments by Gardner et al. (submitted)
showed no decrease in trapping efficiency up to a Reynolds number
of 43,000 in cylindrical traps with an interior funnel moored
at 4500 m. If Reynolds number is the controlling parameter in
trap efficiency, this suggests there should be no decrease in
relative trapping efficiency for the 7.6 cm diameter BATS traps
up to a velocity of 32-57 cm/sec, which is faster than any of
the velocities reported for those traps in the BATS area by Gust
et al. (1992, 1994). However, based on personal observations of
flow within model traps at just 20 cm/sec, it is hard to believe
that the collection efficiency of traps is not affected at velocities
above 20 cm/sec (Gardner). We must remind ourselves that although
we can scale the dynamics of flow between models and full-scale
traps using dimensional analysis, we may not be able to predict
the dynamics of natural marine particles at different scales.
Furthermore, in the dynamic region of the upper ocean one must
consider whether other factors such as large-scale flow, tilt
and mooring dynamics are more important than Reynolds number in
applying these results to regions like BATS and HOT (Gardner).
- Neutrally buoyant traps have been recommended (U.S. GOFS, 1989)
and tested (Honjo, personal communication, 1980; Diercks and Asper,
1994), but have not been widely used due to engineering difficulties.
Neutrally buoyant traps are not practical for all environments,
but they are well-suited to near-surface deployments in the open
ocean. Their use could significantly reduce questions about hydrodynamic
effects on trapping efficiency. One must also have information
about how tightly coupled a neutrally-buoyant trap is to the surrounding
water. Jim Price and Jim Valdes (WHOI) are making a neutrally
buoyant trap based on the RAFOS drifting float design and hope
to test it at BATS by the end of 1995. This should minimize the
hydrodynamic questions, but leaves the swimmer, solubilization,
and migration transport questions to be quantified simultaneously.
- For further discussion of trap dynamics see Hargrave and Burns
(1979), Gardner (1980a,b; 1985), Blomqvist and Kofoed (1981),
Butman (1986), Butman et al. (1986) and Hawley (1988).
- Gust et al. (1992) show a factor of two increase in flux with
a doubling of velocity (in the 10-30 cm/sec range) past large
funnel traps during one-day deployments at the BATS site.
- Is this simply a velocity effect?
- Could this be a tilt effect? -Tilted cylinder traps collect
more than upright traps - 25% at 5 degrees, up to 200-250%
at 30 degrees (Gardner, 1985).
- Tilts measured by Gust et al. (1992) were less than 5°,
but tilt effects on funnel efficiencies have not been tested.
- Michaels et al. (unpublished data) have measured velocities
at the 150 m trap for nearly 4 years of the BATS program and for
many of those samples looked in detail at the particle composition
of the traps. When all the data are considered together, there
is no significant trend with velocity. However, if high (>350
mgC/m2/day) and low (<350 mgC/m2/day) productivity
stations are considered separately, there is an apparent pattern
in collection of carbon with velocity. The collection differences
are 2-3 fold higher with increased velocity over the range of
4-14 cm/sec approach velocities. In examining the major components
of the carbon flux, there is no velocity pattern with the dominant
particle type, marine snow (assuming this can be adequately identified
in the trap). There is a strong velocity dependence for fecal
pellets (10-fold differences in collection over the velocity range).
Thus, the hydrodynamic effects on aggregates may be very different
than more solid particles. Alternately, fecal pellets in traps
could be due to swimmers and swimmer collection might well be
a function of approach velocity (and hence the amount of water
that passes through the trap mouth).
- One area that has received little to no attention is the behavior
and integrity of aggregates in the eddies and flow generated in
and around traps. It is also necessary to study how aggregates
cross a dense brine interface inside traps. One of the difficulties
is in being able to identify aggregates once they are collected
in a trap. Jannasch et al. (1980) attempted to preserve aggregates
by adding a polyacrylamide gel in the sample collection area so
that they could be thin-sectioned and studied, but the viscosity
of the gel was so large that aggregates rolled up like dust balls
before they sank into the gel. (Jannasch, personal communication
and observation, 1979).
- To minimize vertical motion use a spar for the first or only
surface float. (Tony Michaels)
- A spar buoy is effective, but the VERTEX solution of using a
string of small floats achieves the same purpose and is easier
to handle. The intent of a spar buoy is to minimize water displacement
per vertical displacement or to minimize the waterline area. The
string of small floats has a small waterline area and functions
like a "flexible spar buoy." (Vernon Asper)
- Gust et al., (1994) have measured significant vertical motion
and wave energy on floating arrays of the VERTEX design that had
a stretchable member.
- The VERTEX surface-tethered trap array has a stretchable member
to dampen out waves. It is important to be sure that there is
enough sub-surface flotation to prevent the stretchable member
from ever becoming fully extended or the surface-wave energy and
motion will be transmitted to the traps and may affect their efficiency.
- The installation of a horizontal drag plate below the trap
or at the bottom of the array can act as an effective sea anchor
to reduce upward motion of floating traps (Gardner et al., 1985).
- Most of the drag on a trap array is from the mooring line itself.
This can be minimized using very thin wire (Tony Michaels),
- To minimize flow past the trap, position the floats below the
Ekman layer to maximize the drag in the vicinity of the traps.
- Traps at multiple depths make it difficult to minimize the
flow past traps.
- Maybe we're too greedy. Perhaps we should use just a single
trap per mooring. (Tony Knap)
- One trap per floating array is the approach used by scientists
from the Kiel group in recent years. (Wolfgang Koeve)
- We keep making recommendations but is anyone listening? How
can these be widely accepted and practiced? What is the penalty
for non-compliance? (Dave Karl)
Magnitude of problem
- Up to a factor of 4-5 based on Baker et al. (1988) data,
but potentially only at very high velocities (Rt).
Potentially 2-3 fold biases at lower velocities based on field
Effect on BATS carbon imbalance/balance
- This could account for the entire effect, but there is still
significant uncertainty about flow effects where floating
traps are deployed. If the Reynolds number arguments are relevant
in surface waters, then flow effects should be small except
at high velocities. The unpublished Michaels et al. data show
a difference of a factor of two-three that may be attributed
to velocity effects at lower velocities.
- Approach velocities are likely to be in the same approximate
range at HOT as at BATS based on similar drift patterns, array
configurations and horizontal velocities. Thus, any ad hoc
explanation for the BATS imbalance that involves a flow-based
explanation should have the opposite impact on the comparison
of the HOT data with the models at that site.
- Develop a neutrally buoyant drifting sediment trap (U.S.
GOFS Report No. 10, 1989; Diercks and Asper, 1994).
- More experiments of the type performed by Baker et al. (1988)
should be made. The velocity bins need to be more narrowly
limited, especially between 12 and 30 cm/sec (Rt
= 24,000-60,000) since that is where the trapping efficiency
decreased markedly in their study. Use Reynolds numbers when
planning experiments and interpreting their results. One should
also test funnel traps in this mode since they are one of
the most widely used designs because they offer the advantage
of large collection area and sample concentration.
- Field experiments at the JGOFS sites should be done to compare
arrays drogued to have different approach velocities to see
if there are collection differences as traps are actually
used in the field. Although this will only establish a relative
accuracy pattern, it will allow a determination of flow impacts
in the regime in which these experiments are conducted.
- Minimize the flow past the traps.
- Measure flux at a single depth per array and measure
- Use thin lines to minimize drag.
- Put the maximum drag near the trap depth.
- Continue to decouple the trap from surface wave motion.
- Continue to use a stretchable segment of mooring
line above the trap and be sure it has a rapid response
and is never fully extended.
- Use a spar buoy as the surface float as this removes
a lot of the short period wave motion from the array.
- Use a horizontal drag plate below the trap to reduce
upward motion (Gardner et al., 1985).
- Measure the velocity past traps on all deployments.
D. Effect of adding brine to traps
- A 50 psu excess brine creates a much larger density difference
than the 10-4 - 10-5 density units difference
from seawater that exists for aggregates in the ocean (Alldredge
and Gotschalk, 1988). Macintyre et al. (1995) have observed
aggregates accumulating at density gradients in the water
column and report that it can take from hundreds of seconds
up to 3 hours for the pore water to exchange in the aggregates.
- Flume experiments show that the addition of brine to traps
decreases the collection rate (Gardner and Zhang, in press).
- Brine was 5 psu above ambient compared with a 50 psu
excess brine used in BATS and HOT traps.
- Undertrapping decreased as velocity increased. Efficiency
was 54% at 5 cm/sec and 75% at 15 cm/sec.
- Length of deployment and the sequence of velocities
to which traps are exposed may be important in determining
the magnitude of the effect. A high velocity at the beginning
of the trap deployment could wash out the brine early
on so it doesn't inhibit the collection rate as much.
- Three BATS field experiments showed 0, 25 and 60% higher
carbon fluxes in traps without brine, but showed both increases
and decreases in the flux of specific components of the flux.
- Scott Nodder (New Zealand) tested cylindrical traps (ID
= 9 cm, aspect ratio = 10.6) on frames 3 m above the harbor
floor for 24 hours filled with a 50 psu excess brine and found
that they collected 2-3 times less material compared with
traps that were partially filled with the same brine (equivalent
to 1 or 3 trap diameters of brine).
- A change in any of the protocols at the JGOFS time-series
station needs substantial justification that the new measurement
will lead to an increase in the absolute accuracy and it would
require an extensive period of simultaneous measurements using
both the old and new techniques (e.g. simultaneous brine/no-brine
experiments overlapping for a year to test for seasonal differences
in hydrography and particle types). Thus, operators of the
time-series stations are reluctant to modify one facet of
the method (brine) before there is an independent method to
determine that the new collection techniques actually result
in a flux estimate that is accurate on some absolute standard.
It is not considered worth the risk to go through the extensive
extra effort of switching one facet to find that the new method
without brine is still very inaccurate but for a very different
reason than the brine effect (e.g. flow, large-scale turbulence
or something else that is not adequately considered now) (Michaels).
- Two groups have discussed this issue (US GOFS, 1989, and
IOC Manual and Guides, 1994) and recommended that traps be
deployed with no more than a 5 psu excess brine only in the
sample collection region of a trap (equivalent to one trap
diameter in cylinders). Trapping programs should adopt this
and the other JGOFS recommendations.
Magnitude of the problem
- Flume experiments with a 5 psu brine show up to a factor
of 2 loss in the flux measured.
- Field tests with and without a 50 psu brine in cylindrical
traps have shown decreases in flux anywhere from 0% to
a factor of 2-3. The increases in flux with floating traps
in surface waters without brine have been 0-60% higher
than with brine-filled traps.
Effect on BATS/HOT carbon imbalance/balance
- A brine effect could increase trap fluxes at BATS but
given the brine experiments at the BATS site, the effect
is large enough to account for about 10% of the carbon
imbalance, or 20% of the projected undertrapping. However,
experiments in flumes and field experiments at other locations
find brine effects of as much as a factor of 2-3. If these
experiments are relevant to BATS, they could account for
about half of the carbon imbalance, or up to all of the
projected undertrapping. The magnitude of the brine effect
decreases with increasing velocity and with increased
exposure time. The HOT traps use the same protocol and
they report no carbon imbalance in their measurements.
Any effect of brine on the carbon budget at one site (BATS)
must be applied to other sites (e.g. HOT) assuming hydrodynamic
conditions are similar.
- Follow the published protocols which call for a 5 psu
brine only in the bottom one diameter equivalent of a
- Make necessary tests to convert the BATS/HOT trap protocols
to brine only in the bottom. These comparisons need to
be done in the context of experiments to determine the
absolute accuracy of sediment traps if they are going
to be useful for causing a change in protocols at a time-series
III. System Dynamics Questions
A. Vertical flux by zooplankton migration
- The role of particle transport by vertically migrating
organisms and respiration has been discussed for many
years with little quantification because it is a difficult
task Angel (1989).
- Traps are not designed to measure the effect of migrant
transport. Other methods must be employed to quantify
- The question of migrant transport does not directly
affect the efficiency of traps, but it is an essential
component when constructing mass balances in the upper
water column for assessing the accuracy of floating traps.
One must understand the dynamics of particles within the
upper water column as well as the dynamics of sediment
Magnitude of the problem
- Migrant transport measured in the North Atlantic by
Longhurst et al. (1988) was 8-28% of the flux measured
by BATS traps.
- Migrant transport measured at the BATS site by Dam
et al. (1995) was 18-70% of the carbon flux measured concurrently
by floating traps.
- Walsh et al. (1988) noted a recurring deep (>1000 m)
particle flux maximum in MANOP annual sediment trap profiles.
They concluded that as much as 50% of the flux measured
in traps at 1500-1900 m bypassed or was produced below
their shallower traps 500-1000 m. This is well below the
zone of interest in this discussion, but suggests migrant
transport is not isolated to surface waters. One would
expect migrant transport to be largest in surface waters,
where diel migration is well-documented.
Effect on BATS/HOT carbon imbalance/balance
- The migrant flux was included in the carbon balance
at BATS. If the true migrant flux is much higher than
that estimate, this could explain some of the imbalance.
The larger the magnitude of migrant transport, the smaller
the carbon imbalance at BATS.
- Recent measurements suggest transport by migrating
zooplankton is more important than previously measured.
- Carbon imbalance was not implied by the comparison between
the carbon budget and the particle fluxes at HOT, so external
transport mechanisms like migrant transport are not needed
to balance carbon budgets. If vertical migrant fluxes
occur at HOT, then that system is again out of balance
with the carbon budget. Longhurst and Harrison estimated
that migrant fluxes in the oligotrophic Pacific were 0.8-2.5
mg N/m2/d, comparable to an annual carbon flux
of 0.2-0.6 moles C/m2/y. This would increase
the HOT annual flux by 22-66%. Is migrant transport less
important at HOT than BATS, or are the measurements of
migrant transport more likely to be on the low end of
the range measured by Dam et al. (1995)? How does migrant
transport vary seasonally?
B. Mixed-layer (ML) depth or mixed-layer pumping
- Turbulent mixing in the mixed layer keeps particles
in suspension so fluxes cannot be accurately measured
with traps until you are below that depth (Gardner and
- Nocturnal increases in the mixed-layer depth can quickly
move particles downward where they are isolated and allowed
to settle in non-turbulent flow when the mixed layer thins
during the day. (Woods and Onken, 1982; Gardner et al.,
1995). Conversely, nutrients, pCO2 or any component
whose concentration increases with depth will be mixed
Magnitude of problem
- Shouldn't be an issue as long as you deploy traps below
Effect on BATS/HOT carbon imbalance/balance
- Trap fluxes in BATS were examined only when ML depth
was < trap depth, so there should be no direct influence.
- At HOT the trap depths were always greater than the
mixed layer depths.
- Total carbon increases with depth, so ML pumping would
increase carbon in the surface, not decrease it.
- Traps should be deployed below the maximum mixed-layer
depth during the time of deployment.
- The dynamics of 234Th and exchange out of
the mixed layer needs to be examined in the context of
ML pumping and the types of particles to which 234Th
C. Spatial inhomogeneity
- What is the spatial inhomogeneity of vertical fluxes?
- Just put out a lot of trap arrays and test for homogeneity!
- This would require extensive planning about where,
when, the number of arrays required and space and time
scales (Dave Karl).
- While this would provide information about spatial
homogeneity, it does not answer the question of accuracy.
- Time-series traps could average out some of the local
inhomogeneity if the time scales were chosen appropriately
- As discussed below in independent measures of vertical
flux, mass balances based on oxygen production match the
trap carbon fluxes at the HOT site, but not at the BATS
site. Perhaps this results from differences in the degree
of spatial inhomogeneity of the two sites.
- In Michaels et al. (1994) they analyzed the effect of
stochastic events on the carbon imbalance problem. Because
of the large number of measurements, it is statistically
very unlikely that rare, missed events could explain the
imbalance at BATS. With the frequency of sampling, there
is only a small number of events that could have occurred
and not been seen in the BATS sampling. However, these events
would have to account for the entire discrepancy and would
require an unreasonably large flux (more than the total
POC every day) to make up for the imbalance. Since the HOT
sampling is of similar frequency, the same conclusion can
be drawn at that site. The traps at the time-series stations
are not grossly inaccurate because they miss rare events.
- On the smaller scale of individual experiments or deployments,
we do not have enough data to see if a local event causes
a discrepancy between a trap measurement and a field experiment.
- For a regional study, we may not have enough measurements
to determine if the error lies in the traps or is a result
of large-scale advection. The advective field is not known.
Gradients in 234Th and carbon are small. Do we
need to know the 3-D flow field (Michaels)? Are three-D
experiments necessary for every place traps are deployed?
The question of the role of advection is much larger than
the trap accuracy issue and hits to the heart of the interpretation
of all JGOFS data (Michaels).
- Production variability - over what time scale?
- Traps from short-term deployments at multiple depths
each reflect the surface production history for different
time periods (Ian Walsh).
- Traps at multiple depths may also reflect the flux
from different source regions (Siegel et al., 1990).
Magnitude of problem
Effect on BATS/HOT carbon imbalance/balance
- Missing rare events likely cannot explain the annual
patterns. Advection may play an important role at each station.
- Consider deploying multiple trap arrays to test for homogeneity.
- Do control-volume experiments in JGOFS.
III. Independent Measures of Vertical Flux
- What is the accuracy of the trap measurements? Invoking
closure of mass balance can't be just a convenience when
testing for trap accuracy (Tony Michaels). Conservation
of mass must be maintained. Closure of mass balances provides
validity for other types of calibrations, but the time scales
of each measurement must be comparable. Closure should be
attempted whenever possible and when observations violate
this condition, it is a powerful constraint on the interpretation
- When we see disagreements between traps and other measurements,
other processes are often invoked as an explanation, but
if agreement is seen then the same questions aren't raised.
(Ken Buesseler) This is true of any endeavor in science.
We always seek closure of balance and when it is achieved,
we move on.
A. Thorium modeled and measured fluxes
(Moore et al., 1981; Coale and Bruland, 1985, 1987; Eppley
and Peterson, 1979; Buesseler, 1991; Buesseler et al., 1994).
- Measure 234Th deficiency (relative to 238U)
in surface waters.
- From the 234Th deficiency (half life is 24
days), one can predict the 234Th flux down to
the depth of disequilibrium. Given this and a 234Th
measurement in a trap, one can learn independently if the
trap is collecting 234Th-bearing particles in
a predictable (i.e. accurate) fashion (Buesseler et al.,
- The 234Th deficit is confined to the upper
70-200 m in the open ocean, so the method is restricted
to predicting the flux to the depth of the disequilibrium.
Other studies show that the flux of material decreases rapidly
with depth below the upper 50-150 m (VERTEX) or that at
least the material one would expect to make up the vertical
flux decreases rapidly with depth (Bishop et al., 1980).
- If the trap is not collecting particles bearing 234Th
in a predictable way, then there is no confidence that they
are collecting other particle types in an accurate fashion
(Ken Buesseler). However, surface area per unit mass is
greatest on the smallest particles, and the small particles
are not dominant in the vertical flux of mass.
- There is a 234Th deficit down to 1000 m off
Cape Hatteras due to scavenging along the continental margin
(Peter Santschi) so this method won't work in those regions.
- In a dynamic environment with strong currents, trap flux
estimates are very likely to be biased. As part of the French
KERFIX program in the Southern Ocean, we collected trap
data 60 NM SW of Kerguelen Island. Despite this distance
from the island, tidal currents are important not only in
upper waters but also at 1000 m depth. Under these conditions,
estimates of the surface flux from deeper traps was not
possible, nor was it possible to estimate flux based on
natural radionuclides measurements. At present, we conclude
that the site is not an appropriate one for estimates of
the flux from surface waters. (Juan Carlos Miquel)
- Murray et al. (submitted, DSR) measured the flux of organic
carbon from the central equatorial Pacific during EqPac
using floating traps at multiple depths and the 234Th
approach described above. In their calculations of 234Th
flux they included terms to account for upwelling and meridional
advection away from the equator. Zonal gradients in 234Th
were found to be small (Buesseler et al., 1995) and were
neglected. Comparison of the model 234Th fluxes
with the corrected 234Th fluxes shows that the
model fluxes shallower than 150 m were much less than the
trap fluxes. The fluxes at 150 and 200 m agreed to within
a factor of +/- 2 from 12°N to 12° S. Murray et
al. (submitted, DSR) argue that all drifting sediment trap
studies should be conducted as a function of depth and include
234Th analyses. This conflicts with the earlier
recommendation that traps be deployed at a single depth
and would thus require a large number of arrays deployed
- Swimmers have low 234Th (Jim Murray; Buesseler
et al., 1994).
- Error bars on data need to be included (Tony Michaels).
- How large are the Th error bars? (Gardner).
- See Buesseler et al., 1994
- What are the appropriate time scales (in terms of minimum
and maximum fractions or multiples of half-lives) on which
to make Th or other radionuclide measurements?
If you have only a single radionuclide profile, you need
to integrate particle fluxes over a comparable time scale
appropriate to the tracer activity. If 234Th
activities are decreasing with time (i.e. particle fluxes
are increasing) a single 234Th profile would
actually underestimate the net particle removal at the
time you took your sample. If you take a non-steady state
approach (Buesseler et al., 1994) and you measure 234Th
in a time-series (or better yet, 4D) manner, then you
can predict the 234Th export flux within the
measurement period, (i.e. within a 2-5 day period is OK,
as long as you have data to examine if the 234Th
activity is varying with time during this same period).
Magnitude of problem
- Buesseler (1990) showed that fluxes predicted based on
234Th-deficiency and trap-measured 234Th
fluxes often disagree by more than a factor of three, with
some experiments showing overtrapping and others showing
undertrapping by that amount.
- Time-series measurements of 234Th deficits
were made at BATS during trap deployments (Michaels et al.,
1994) and can account for much of the carbon imbalance based
on the 234Th calibration of the traps and the
measured range of C/Th ratios. Over the course of two years
of simultaneous 234Th profiles and 234Th
collections in traps, both undertrapping and overtrapping
have been observed at the BATS site.
- A previous study of this type at BATS showed that traps
on a single cruise tended to overcollect 234Th
(Buesseler et al., 1994). Their explanation of the variable
over/undertrapping was that their traps overcollected during
times of low flux and undercollected during times of high
flux, thus dampening out the seasonal signal of the total
Effect on BATS/HOT carbon imbalance/balance
- The difference between the predicted and measured 234Th
flux is of the same order as the carbon imbalance at BATS
(Michaels et al., 1994)
- In order for advection to account for this 234Th
difference, the magnitude of advection would have to be
large based on known gradients of [Th], and there would
have to be a seasonal trend to account for the flux imbalance.
Why should there be a seasonal trend in [Th] in the western
- If the 234Th deficiency is caused by scavenging
and if scavenging is related to the production and flux
of particles, how could there not be a seasonal trend in
[Th]? (Vernon Asper)
- 234Th measurements have not been made around
HOT because the scavenging of 234Th is generally
low in oligotrophic regions, making the Th disequilibrium
very small. When scavenging is low this means that the errors
can be large for this calculation (Ken Bruland).
- There are times when there is no 234Th deficiency
at BATS (Buesseler et al., 1994)
- See recommendations in section III. B below.
B. 234Th-derived estimates of particulate organic
- One can calculate a carbon flux by multiplying the 234Th
flux by the C/234Th ratio in sinking (trap- or
in-situ pump- collected) particles. This approach has its
own uncertainties including the time variability and transport
terms (Buesseler et al., 1992, 1994; Wei and Murray, 1992)
and the C/234Th ratio in sinking particles (Michaels
et al., 1994; Buesseler, 1995).
- Compare the carbon flux measured in the trap with the
carbon flux predicted based on the above calculation.
- To estimate the accuracy of traps at collecting carbon
by comparison with the thorium-derived calibration, however,
requires the assumption that the 234Th is distributed
similarly to organic C among the different types of sinking
particles (based on composition and settling velocity distribution)
that are responsible for the vertical flux of carbon in
the ocean. 234Th adsorption is a function of
surface area, and there is much greater surface area per
unit mass for small particles that may not be sinking rapidly.
How quickly do these small particles become incorporated
into larger particles and sink? C/Th ratios vary by particle
type, but by how much? The C/Th ratio varies between trap
and large-volume filtration samples. The C/Th ratio varied
as a function of time during the North Atlantic Bloom Experiment
by a factor of 2 and could vary between seasons (Buesseler).
Murray et al. (submitted to DSR) found a very different
C/Th ratio during two different cruises across the equator.
These changes must be adequately measured and incorporated
into the models (Buesseler et al., 1995). 234Th
on fragile, porous sinking aggregates may break up when
they encounter a sediment trap and broken-up pieces may
not be retained in the trap, or the aggregate may not be
able to penetrate the large density brine used in some traps,
thus decreasing the collection of both carbon and 234Th.
- Some have suggested that collections of profiles of thorium
deficit coupled to pump data on the C/Th ratio of large
particles could be used as an independent measure of carbon
flux (Buesseler et al., 1992; 1995). The biggest concern
is the assumption that the particles collected with in situ
pumps are representative of the local sinking particle pool.
If some class of exported particles exists that are not
sampled (or are masked by "suspended" material on the filter),
and it is a dominant fraction of the export flux, and it
has a different POC/Th ratio, then this empirical approach
fails. So far, the data look very encouraging (Ken Buesseler).
- Loss of POC due to vertical migrators would be accounted
for in the upper ocean 234Th balance, but not
- Swimmers have low 234Th relative to POC, hence
POC/Th ratios in traps may be elevated if swimmers are not
- The same concerns for 234Th alone (see section
A above) apply here to POC flux, i.e. if the predicted 234Th
flux is incorrect, then the POC fluxes would also be in
error (assuming the C/Th ratios have been measured and modeled
Effect on BATS/HOT carbon imbalance/balance
- Using the predicted 234Th fluxes and measured
POC/234Th on particles, the 234Th-derived
POC flux would account for up to 80% of the apparent carbon
imbalance at BATS (Michaels et al., 1994).
- 234Th is the best independent particle tracer
we have. Any JGOFS trap study should have Th measurements
made at the same time. (Jim Murray; Buesseler et al., 1994).
- Further studies are needed to examine the range of C/Th
ratios in sorted sediment trap and size-fractionated filtered
particle samples to determine if the 234Th-derived
trap calibration can be directly applied to POC.
- Further study of the U-Th system and its transfer between
dissolved, colloidal, particulate, and aggregate states
- In order to validate the Th-deficiency method for estimates
of carbon fluxes, design and conduct a trap/234Th
calibration experiment in the highest productivity, lowest
energy regime that is practical (i.e. low advection). Continental
margins should also be avoided because of the potential
of thorium scavenging in those regions (Wilf Gardner) This
experiment must include explicit consideration of non-steady
state and 3-D effects on the time-scale of the experiment
(Tony Michaels and Ken Buesseler).
C. Oxygen mass balance (Emerson)
- Carbon flux calculated from O2 mass balance
model: 3±1 mole C/m2/yr (Spitzer and Jenkins,
- Carbon flux from floating traps: 0.8±0.2 mole C/m2/yr
(Michaels et al., 1994)
- HOT station
- Carbon flux calculated from O2 mass balance
model: 1±0.5 mole C/m2/yr (Emerson et al.,
- Carbon flux from floating traps: 0.9±0.3 mole C/m2/yr
(Karl et al., 1995, DSR, in press)
- Carbon flux calculated from a mass balance of DIC
carbon and 13C-DIC in a 1-D model: 0.9±0.5
mole C/m2/yr (Paul Quay, unpublished data).
- About 25% of the carbon flux is carried as DOC (Emerson
et al. 1995).
Magnitude of error
- Errors given above.
- BATS - Factor of three difference between trap, 234Th
and carbon budget methods. Budget includes all vertical
processes, but not horizontal advection.
- HOT - Three methods (trap, oxygen and carbon isotope
budgets) agree within the accuracy of the data. They do
not include a number of other processes which may export
carbon (DOC, migrant fluxes). Does not include horizontal
- The methods show more agreement near Hawaii than Bermuda.
However, the comparisons do not include all of the same
processes at each of the two sites. Any changes in the BATS
flux as a result of a correction for an inferred source
of error tend to have the effect of creating an imbalance
- Some infer that the agreement at HOT means that traps
are accurate at that site. Perhaps there are fewer environmental
variables to contend with around Hawaii than Bermuda (e.g.
fronts passing the area, winter overturn, mode-water formation,
proximity to a major current like the Gulf Stream with its
attendant rings, general advection), so there is a better
chance of reaching closure for budgets of carbon, oxygen,
and 234Th for calibration with trap fluxes. However,
it is also possible that the agreement between one form
of carbon flux (traps) and the overall 1-D organic carbon
budget means that the trap is likely overcollecting since
the current comparison leaves no room for other processes
of transport and error like migrant fluxes, hydrodynamics
and solubilization of carbon.
- Continue to make mass balances of this sort where possible
whether or not other means of calibration are available.
- If possible use multiple independent strategies for comparison
D. Comparison with sediment accumulation rates
- Some trap fluxes have matched well with:
- accumulation rate of underlying sediments based on
radionuclide dating (Pennington, 1974 ; Soutar et al.,
1977; Dymond et al., 1981; Gardner et al., 1985);
- accumulation of radionuclides (Moore et al., 1981:
Anderson et al., 1983; Bacon et al., 1985; Biscaye et
al., 1988; Biscaye and Anderson, 1994; Colley et al.,
- accumulation above a known sediment horizon in lakes
- varves (Soutar et al., 1977; Brunskill, 1969 as discussed
in Gardner, 1980a; Hay et al., 1990).
- It is very difficult to use accumulation rates as a calibration
standard of the carbon flux for short-term near-surface
traps in the open ocean because so much degradation occurs
between the surface and seafloor. Even in shallow lakes
the time scales can also be orders of magnitude different
between trap deployments and accumulation rate measurements
(decades for 210Pb and 100-1000 years for 14C).
- The flux of inert components such as Al could be used
as a calibration standard with the assumption that trapping
efficiency for POC matched aluminosilicates. One must always
be aware of the possible "contamination" by lateral advection
of material resuspended from boundaries - both in traps
in in the sediments.
- The accumulation of short-lived radionuclides within
the water column (e.g 234Th) can be measured
on time scales close to the trap deployment time scales.
- Trap fluxes have been shown to have a seasonal cycle.
(Deuser and Ross, 1980; Honjo, 1982; Deuser, 1986, 1987)
- A seasonal cycle can exist without knowing the absolute
flux because the entire cycle or parts of the cycle could
be biased high or low depending on the dominant particle
type or sinking speed and hydrodynamic conditions.
- Buesseler et al. (1994) concluded that at the BATS site
floating traps overcollected during periods of low productivity
and undercollected during times of high productivity, thus
smoothing out the seasonal cycles, but resulting in an annual
F. Correlation with ocean color
- Mitchell et al. (in prep.) have compiled floating trap
data from numerous projects (RACER, ProMARE, NABE, HOT,
CABS, BATS, EqPac) and plotted the fluxes against an algorithm-derived
parameter based on sea surface temperature and a blue to
green water leaving radiance ratio. The 48 points have an
r-squared fit of 0.71 on a log-log plot. This is comparable
to the r-squared fit of 0.76 for the same number of points
fitting the data of Chl+Phaeopigments versus the blue to
green water leaving radiance ratio for the same sites.
- One must recognize that there could be a good correlation
between flux and the algorithm and still the traps could
all be too high or too low. There is also enough scatter
that some of them could be high and some could be low by
factors of 2-3 as seen in the data collated by Buesseler
(1991). Care must be exercised in selecting data for this
comparison (e.g. comparable by depth, etc.). Some of the
scatter may result from differences like these.
- The important, encouraging point is that there appears
to be a real correlation between ocean color and particle
flux. Such a relationship may seem intuitively obvious to
some, but others have questioned whether such a relationship
could be demonstrated. It is crucial to cover the entire
dynamic range of oceanic conditions to establish this relationship
rather than examining only a small portion of the entire
range, in which case the correlation might not be so obvious.
IV. Summary of the magnitude of possible errors
These tables are optimtized for use with Netscape 1.1 or
Here is a text version of the tables.
Traps are designed to collect only the settling particles.
Sources of errors in trap measurements include:
||Up to a factor of 2 depending on techniques
|Solubilization of carbon
||A few percent per day
|Hydrodynamic effects that include:
||Up to several multiples of change
||Zero to several multiples of change
|Wave induced trap motion
|Effects of brine in the trap
||0-300% (60% is max seen in surface waters)
|Vertical migration of zooplankton
||8-70% of trap flux
|Vertical mixing of DOC, DIC, and POC
||7-25% in two estimates
|Gas exchange of carbon dioxide with atmosphere
||2% in one estimate
Text Version of the Trap and System Error Tables
Traps are designed to collect only the settling particles.
Sources of errors in trap measurements include
- Up to a factor of 2 depending on techniques
- Solubilization of carbon
- Hydrodynamic effects that include
- Trap geometry
- Up to several multiples of change
- Zero to several multiples of change
- Wave-induced trap motion
- Effects of brine in the trap.
- 0-300% (60% is max seen in surface waters)
- Vertical migration of zooplankton
- Vertical mixing of DOC, DIC and POC
- Advective transport
- Gas exchange of CO2 with the atmosphere
V. Summary and Recommendations
Sediment traps have opened up a new era of investigation
of biogeochemical cycles in the ocean. They provided the first
proof that seasonal and episodic variations in surface water
productivity could result in variable fluxes at depth in the
ocean, thus triggering many new questions to pursue. The collection
of samples at various depths has allowed studies of the recycling
of oceanic particles and helped to elucidate where many processes
are occurring. In turn, this information is extremely important
in making comparisons with the small residue of biogenic material
which reaches the seafloor, and the even smaller residue that
is preserved in the sediments. This is critical to accurately
(albeit very imperfectly) interpret the paleo record from
sediment cores. It is equally important for understanding
correlations on short time scales between remotely sensed
ocean color data from satellites and processes that lead to
the export of carbon from surface waters.
Traps have proven to be valuable tools. Particle cycling
in the upper ocean is more complex that previously realized.
The lack of mass balance in some studies based on trap fluxes
is part of what has made us realize that complexity. That
does not mean a priori that traps don't (or do) work. We need
to make a more concerted effort to fully understand both traps
and the particle dynamics in the environments in which they
are used. Existing data clearly show there are trap designs
and regimes in which the results from traps cannot be used
in either quantitative (flux) or qualitative (composition)
analyses. There are studies using floating traps where the
carbon fluxes match well the macroscale carbon budgets derived
from oxygen budgets determined by completely independent measurements
(Emerson et al., 1995; Karl et al., 1995). Other studies show
mismatches of as much as a factor of three (Michaels et al.,
1994) Further studies are needed to understand why this discrepancy
exists. There needs to be some standard measurements that
can be made to verify or validate trap fluxes. One approach
has been to calibrate specific trap designs under known conditions
(e.g. velocity, Reynolds number, tilt) and then use those
traps in the field and accept only those data that are collected
within those acceptable physical parameters. A variation on
this approach is to compare fluxes between a trap moving with
the water and one that is not moving with the water to extend
the limits of acceptable hydrodynamic conditions. Only a limited
number of studies of this type have been made and the boundaries
of regimes where trap fluxes match still-water fluxes must
be better defined. The development of neutrally buoyant traps
would improve on this method significantly. A second approach
is to measure the loss of a radionuclide that is produced
in the water as an in-situ calibration for trap fluxes. A
third calibration scheme is to develop carbon budgets independent
of trap fluxes as a standard for trap carbon fluxes.
Ultimately, one of the prime JGOFS goals is to develop budgets
of carbon, carbonate, silica etc., not to determine a radionuclide
flux or trap accuracy. Each system may have a different portion
of material transported by vertical settling versus migrant
transport, DOM or other mechanisms (advection). From that
viewpoint it is a higher priority to develop a system that
can be used to predict the removal of carbon (by all pathways
combined) from the surface water than determine the absolute
accuracy of traps. If the 234Th method could be
shown unequivocally to accurately predict the flux of carbon
out of surface waters under all conditions, that is a very
important advancement for JGOFS, because traps probably don't
collect the material carried by vertical migrators and they
certainly can't collect DOC or colloidal material. At the
same time, trap samples afford the opportunity to examine
the composition of settling material if they are functioning
as we would like them to. That is what makes it worthwhile
to calibrate traps.
It is important to remember that comparisons between the
trap fluxes and 234Th fluxes apply only to the
depth over which particle scavenging creates a 234Th
depletion (the upper 70-200 m or so in the open ocean). Carbon
remineralization is rapid below the euphotic zone, so carbon
fluxes decrease rapidly. Still, a proven calibration scheme
for traps in this depth range is important for comparisons
with short-term processes in the euphotic zone and with satellite
data. With regard to long-term sequestration of carbon, fluxes
to the deep ocean and to the seafloor are far more significant
than carbon fluxes out of the upper 200 m. Agreement between
longer-lived radionuclides and trap fluxes at greater depths
has been much better, but that is beyond the scope of this
Why is there an apparent agreement between traps and independent
measurements at HOT and an apparent 3-fold disagreement at
BATS? One valid suggestion is to conduct a 4D-scale carbon
and 234Th calibration to verify the carbon and
234Th budget. If this is done at BATS, is this
a calibration of the trap methodology or a calibration of
the carbon dynamics around the around BATS region? 234Th
measurements have not been made around HOT because the scavenging
of 234Th is so low in oligotrophic regions that
the errors are large for this calculation. Buesseler generally
finds enough scavenging at BATS to make these measurements,
though there are times when there is no disequilibrium, which
means the predicted flux is zero.
What, then, is the calibration standard? Is it necessary
to measure 234Th depletion every time a trap measurements
is made in the upper 200 m to determine if it is accurate?
If we conduct a 4D-scale trap/234Th experiment
at a simple site, does that guarantee that similar trap measurements
conducted elsewhere can use the same correction factor or
scheme? Or do we take the hydrodynamics viewpoint and determine
the conditions under which traps match the flux determined
by an independent means such as 234Th depletion
or a carbon balance and then say that traps can be used under
those conditions and if the conditions are not met, the data
must be discarded?
We can make recommendations for JGOFS, but what is the penalty
for non-compliance? What about all the trap measurements made
outside of JGOFS? They probably constitute the majority of
trap measurements both now and in the future. What advice
do we give them? Most people who use traps don't have the
resources to measure either 234Th or currents.
Before NASA sends an instrument into space (except for the
Hubble space telescope) it is tested for responses in all
conditions it might experience. Many calibration and comparison
experiments have been made with sediment traps in both the
laboratory and field, but few calibration measurements have
been made in the upper 200 m of the water column. The only
calibration technique that has been suggested for calibrating
traps on short time scales in this region is 234Th.
If a 4D 234Th calibration of traps is done to answer
the question of trap efficiency, there should be an oversight
committee to ensure that all parameters are sufficiently characterized
and measured. Such a study would also have to include measurements
of vertical migrant and DOM transport.
Despite all the concern about fluxes measured with floating
sediment traps, Mitchell et al. have shown a correlation between
ocean color and particle flux when measured over the global
range of ocean color. While there is significant scatter in
the data and the precision is not known, it provides encouragement
that it is possible to develop even better algorithms to make
true Global calculations for the Joint Global Ocean Flux Study
using floating sediment traps.
VI. Major Recommendations
- Design and conduct a trap/234Th calibration
experiment in the highest productivity, lowest energy regime
that is practical. There should be community input to the
design of such an experiment even if only one or more groups
conduct the work. The C/Th ratio and Th cycling between
sinking and non-sinking particle pools is one of the crucial
points of such an experiment.
- Pending the outcome of the above experiment, measure
the 234Th deficiency during JGOFS trap studies.
- Develop and test neutrally buoyant traps.
- Minimize the flow past traps.
- Measure flux at a single depth per array. Measurements
at multiple depths are always desirable, but we must consider
the importance of one measurement in which we have confidence
versus several numbers that might be compromised because
of velocity effects.
- Decouple the trap from surface wave motion.
- Measure the velocity past traps.
- Deploy traps with 5 psu excess brine only in the bottom
of the trap. Make necessary tests to convert the BATS/HOT
trap protocols to brine only in the bottom.
- Carefully remove swimmers from samples.
- Put the JGOFS protocols on the Web so they can be accessed
- Fully report methods and errors in all publications.
- Make more experiments of the type of Baker et al. (1988).
- Alldredge, A. L. and C. Gotschalk, 1988. In situ settling
behavior of marine snow. Limnol. Oceanogr. 33:
- Anderson, R. F., M.P. Bacon, P.G. Brewer, 1983. Removal
of Th-230 and Pa-231 from the open ocean. Earth Planet.
Sci. Lett.. 62: 7-23.
- Angel, M. V., 1989. Does mesopelagic biology affect the
vertical flux? In: W. H. Berger, V. S. Smetacek, G. Wefer,
eds. Productivity of the Ocean: Present and Past.
John Wiley & Sons, 155-173.
- Bacon, M. P., C.A. Huh, A.P. Fleer, and W.G. Deuser, 1985.
Seasonality in the flux of natural radionuclides and Plutonium
in the deep Sargasso Sea. Deep-Sea Research.
- Baker, E. T., H. B. Milburn, and D. A. Tennant, 1988. Field
assessment of sediment trap efficiency under varying flow
conditions. J. Mar. Res. 46: 573-592.
- Biscaye, P. E. and R. F. Anderson, 1994. Fluxes of particulate
matter and on the slope of the southern Middle Atlantic Bight:
SEEP-II. Deep-Sea Res. II, 41: 459-509.
- Biscaye, P. E., R. F. Anderson, and B. L. Deck, 1988. Fluxes
of particles and constituents to the eastern United States
continental slope and rise: SEEP-I. Cont. Shelf Res.
- Bishop, J. K. B., R. W. Collier, D. R. Ketten and J. M.
Edmond, 1980. The chemistry, biology, and vertical flux of
particulate matter from the upper 1500 m of the Panama Basin
in the Equatorial Pacific Ocean. Deep-Sea. Res.
- Blomqvist, S. and C. Kofoed, 1981. Sediment trapping -
a subaquatic in situ experiment. Limnology and Oceanography.
- v. Bodungen, B. M. Wunsch, H. FŸrderer, 1991. Sampling and
analysis of suspended and sinking particles in the northern
North Atlantic. Geophys. Monogr. 63: 47-56.
- Brunskill, G. J., 1969. Fayetteville Green Lake, New York,
III. Precipitation and sedimentation of calcite in a meromictic
lake with laminated sediments. Limnol. Oceanogr..
- Buesseler, K. O., 1991. Do upper-ocean sediment traps provide
an accurate record of particle flux? Nature.
- Buesseler, K.O., J. K. Cochran, M. P. Bacon and H. D. Livingston,
1992. Carbon and nitrogen export during the JGOFS North Atlantic
Bloom Experiment estimated from 234Th:238U
disequilibria. Deep-Sea Res. I. 39: 1115-1137
- Buesseler, K. O., J.A. Andrews, M. C. Hartman, R. Belastock,
and F. Chai, 1995. Regional estimated of the export flux of
particulate organic carbon derived from thorium-234 during
the JGOFS EqPac program. Deep-Sea Res., 42:777-804.
- Buesseler, K. O., A. F. Michaels, D. A. Siegel, and A.
H. Knap, 1994. A three-dimensional time-dependent approach
to calibrating sediment trap fluxes. Glob. Biogeochem.
Cycles 8: 179-193.
- Butman, C. A., 1986. Sediment trap biases in turbulent
flows: results from a laboratory flume study. J. Mar.
Res. 44: 645-693.
- Butman, C. A., W. D. Grant, and K. D. Stolzenbach, 1986
a. Predictions of sediment trap biases in turbulent flows:
A theoretical analysis based on observations from the literature.
Journal of Marine Research 44: 601-644.
- Coale, K. H.,1990. Labyrinth of doom: a device to minimize
the "swimmer" component in sediment trap collections.
Limnol. Oceanogr. 35: 1376-1380.
- Coale, K. H. and K. W. Bruland, 1985. 234Th:238U disequilbria
within the California Current. Limnol. Oceanogr.
- Coale, K. H. and K. W. Bruland, 1987. Oceanic stratified
euphotic zone as elucidated by 234Th:238U disequilbria.
Limnol. Oceanogr. 32: 189-200.
- Colley, S., J. Thomson and P.P. Newton, 1995. Detailed
230Th, 232Th and 210Pb fluxes recorded by the 1989/90 BOFS
sediment trap time-series at 48¡N, 20¡W, Deep-Sea Res.
- Dam, H.G., M.R. Roman and M.J. Youngbluth, 1995. Downward
export of respiratory carbon and dissolved inorganic nitrogen
by diel-migrant mesozooplankton at the JGOFS Bermuda time-series
station. Deep-Sea Res. 42:1187-1197.
- Deuser, W. G., 1987. Seasonal variations in isotopic composition
and deep-water fluxes of the tests of perennially abundant
Planktonic Forminifera of the Sargasso sea: results from sediment-trap
collections and their Paleoceanographic significance. J.
Foram. Res.. 17: 14-27.
- Deuser, W. G. and E.H. Ross, 1980. Seasonal change in the
flux of organic carbon to the deep Sargasso Sea. Nature.
- Diercks, A. and V. Asper, 1994. Neutrally buoyant sediment
traps: The first designs. EOS, Transactions Amer. Geophys.
- DOE, 1994. Handbook of methods for the analysis of
the various parameters of the carbon dioxide system in sea
water; version 2. Dickson, A. G.; C. Goyet, Editors.
- Dymond, J., K. Fischer, M. Clauson, R. Cobler, W. Gardner,
M.J. Richardson, W. Berger, A Soutar, and R Dunbar, 1981.
A sediment trap intercomparison study in the Santa Barbara
Basin. Earth and Planetary Science Letters. 53:
- Emerson, S., P.D. Quay, C. Stump, D. Wilbur, and R.Schudlich,
1995. Chemical tracers of productivity and respiration in
the subtropical Pacific Ocean. J. Geophys. Res..
- Eppley, R. W. and B.J. Peterson, 1979. Particulate organic
matter flux and planktonic organic matter in the surfae layer
of the ocean. Deep-Sea Res., 30 (A): 311-323.
- Gardner, W. D., 1980a. Field calibration of sediment traps.
Journal of Marine Research 38: 41-52.
- Gardner, W.D., 1980b. Sediment trap dynamics and calibration:
a laboratory evaluation. Journal of Marine Research
- Gardner, W. D., 1985. The effect of tilt on sediment trap
efficiency. Deep-Sea Research 32: 349-361.
- Gardner, W. D., S. P. Chung, M. J. Richardson, and I. D.
Walsh, 1995, The oceanic mixed-layer pump. Deep-Sea
Res. II 42: 757-775.
- Gardner, W. D., P.E. Biscaye and M.J. Richardson, Sediment
Traps in the Vema Channel: Collectors of vertical or horizontal
particulate flux? Deep Sea Research (submitted)
- Gardner, W. D., K. R. Hinga, and J. Marra, 1983. Observations
on the degradation of biogenic material in the deep ocean
with implications on the accuracy of sediment trap fluxes.
J. Mar. Res. 41: 195-214.
- Gardner, W. D. and M.J. Richardson, 1992. Particle export
and resuspension fluxes in the western North Atlantic. In:
G.T. Rowe and V. Pariente, (eds.). Deep-Sea Food Chains
and the Global Carbon Cycle. Netherlands: Kluwer Academic
Publishers pp. 339-364.
- Gardner, W. D., J. B. Southard, and C. D. Hollister, 1985.
Sedimentation and resuspension in the western North Atlantic.
Mar. Geol. 65: 199-242.
- Gardner, W.D. and Y. Zhang, 1996. The effect of brine on
the collection efficiency of cylindrical particle traps, Deep
Sea Research (in press)
- Gust, G., W. Bowles, S. Giordano, and M. Huettel. Particle
accumulation processes in upright, flow-exposed cylindrical
sediment traps and proposed link to in-situ fluxes. Aquat.
Sci.. (in press).
- Gust, G., R.H. Byrne, R.E. Bernstein, P.R. Betzer, and
W. Bowles, 1992. Particle fluxes and moving fluids: experience
from synchronous trap collections in the Sargasso Sea. Deep-Sea
Res. 39: 1071-1083.
- Gust, G., A. F. Michaels, R. Johnson, W. G. Deuser, and
W. Bowles, 1994. Mooring line motions and sediment trap hydromechanics:
in situ intercomparison of three common deployment designs.
Deep-Sea Res. 41: 831-857.
- Harbison, G. R. and R. W. Gilmer, 1986. Effects of animal
behavior on sediment trap collections: implications for the
calculation of aragonite fluxes. Deep-Sea. Res.
- Hansel, D. A. and J. A. Newton, 1994. Design and evaluation
of a "swimmer"-segretating particle interceptor trap. Limnol.
Oceanogr. 39: 1487-1495.
- Hargrave, B. T. and N. M. Burns, 1979. Assessment of sediment
trap collection efficiency. Limnol. Oceanogr.
- Hawley, N., 1988. Flow in Cylindrical sediment traps. Journal
of Great Lakes Research 14: 76-88.
- Hay, B. J., S. Honjo, S. Kempe, V. A. Ittekkot, E. T. Degens,
T. Konuk, and E. Izdar, 1990. Interannual variability in particle
flux in the southwestern Black Sea. Deep-Sea Res.
- Honjo, S., 1982 Seasonality and interaction of biogenic
and lithogenic particulate flux at the Panama Basin. Science.
- Honjo, S., D. W. Spencer, and W. D. Gardner, 1992. A sediment
trap intercomparison experiment in the Panama Basin, 1979.
Deep-Sea Res. 39: 333-358. IOC Manual and Guides
No. 29, 1994. Protocols for the Joint Global Ocean Flux
Study (JGOFS) core measurements. UNESCO Scientific
Committee on Oceanic Research.
- Iturriaga, R., 1979. Bacterial activity related to sedimenting
particulate matter. Mar. Biol. 55: 157-169.
- Jannasch, H. W., O. C. Zafiriou, and J. W. Farrington, 1980.
A sequencing sediment trap for time-series studies of fragile
particles. Limnol. Oceanogr. 25: 939-943.
- Karl, D. M. and G. A. Knauer, 1989. Swimmers: a recapitulation
of the problem and a potential solution . Oceanography.
- Karl, D. M. and B.D. Tilbrook, 1994. Production and transport
of methane in oceanic particulate organic matter. Nature,
- Knauer, G. A., D. M. Karl, J.H. Martin, and C.N. Hunter,
C. N., 1984. In situ effects of selected preservatives on
total carbon, nitrogen and metals collected in sediment traps.
Journal of Marine Research. 42: 445-462.
- Lee, C. and C. Cronin, 1982 The vertical flux of particulate
organic nitrogen in the sea: Decomposition of amino acids
in the Peru upwelling area and the equatorial Atlantic. Journal
of Marine Research 40: 227-251.
- Lee, C., J. I. Hedges, S. G. Wakeham, and N. Zhu, 1992.
Effectiveness of various treatments in retarding microbial
activity in sediment trap material and their effects on the
collection of swimmers. Limnol. Oceanogr..37:
- Lee, C., J.A. McKenzie and M. Sturm, 1987. Carbon isotope
fractionation and changes in the flux and composition of particulate
matter resulting from biological activity during a sediment
trap experiment in Lake Greifen, Switzerland. Limnol.
Oceanogr. 32: 83-96.
- Lee, C., S. G. Wakeham, and J. I. Hedges, 1988. The measurement
of oceanic particles flux - are 'swimmers' a problem? (Review
and Comment). Oceanography. 1(2): 34-36.
- Longhurst, A. R. and W. G. Harrison, 1988. Vertical nitrogen
flux from the oceanic photic zone by diel migrant zooplankton
and nekton. Deep-Sea Res. 35: 881-889.
- Lorenzen, C. J., F.R. Shuman, and J.T. Bennett, 1981. In
situ calibration of a sediment trap. Limnology and Oceanography.
- Macintyre S., Alldredge AL, Gotschalk CC. 1995. Accumulation
of arine snow at density discontinuites in the water column.
Limnology & Oceanography 40:449-468
- Michaels, A.F., N. R. Bates, K. O. Buesseler, C. A. Carlson
and A. H Knap, 1994. Carbon-Cycle Imbalances in the Sargasso
Sea, Nature, 372: 537-540.
- Michaels, A. F., M.W. Silver, M.M. Gowing, and G.A. Knauer,
1990. Cryptic zooplankton "swimmers" in the upper
ocean sediment traps. Deep-Sea Res. 37: 1285-1296.
- Miquel, J.C., S.W. Fowler and J. La Rosa, 1992. Vertical
particulate carbon fluxes in the Ligurian Sea: a time-series
study. Rapport et Prochs Verbaux Commission Internationale
pour l'Exploration Scientifique de la Mer Miditerranie, 33:
- Miquel, J.C., S.W. Fowler, J. La Rosa and P. Buat-Menard,
1994. Dynamics of the downward flux of particles and carbon
in the open northwestern Mediterranean Sea. Deep Sea
Research 41, 243-261.
- Miquel, J.C., S.W. Fowler, B. Mostajir and J. La Rosa, 1995.
Long term study of particulate carbon flux in the open NW
Mediterranean Sea. In Tsunogai S., K. Iseki, I. Koike et T.
Oba (eds.), Global Fluxes of Carbon and its Related
Substances in the Coastal Sea-Ocean-Atmosphere System
(Proceedings of the 1994 Sapporo IGBP Symposium, 14-17 November
1994, Hokkaido University, Sapporo, Hokkaido, Japan), M&J
International, Yokohama, 353-359.
- Moore, W. S., K.W. Bruland, J. and Michel, 1981. Fluxes
of uranium and thorium series isotopes in the Santa Barbara
Basin. Earth and Planetary Science Letters. 53:
- Murray, J. W., J. N. Downs, S. Strom, C.-L. Wei, and H.
W. Jannasch. 1989. Nutrient assimilation, export production
and 234Th scavenging in the eastern equatorial Pacific. Deep-Sea
Res. 36: 1471-1489.
- Pennington, W. Seston and sediment formation in five Lake
District lakes. Jour. Ecol.. 1974; 62: 215-251
- Peterson, W. and H. G. Dam, 1990. The influence of copepod
"swimmers" on pigment fluxes in brine-filled vs.
ambient seawater-filled sediment traps. Limnol. Oceanogr.
- Peterson, M. L., P. J. Hernes, D. S. Thoreson, J. I. Hedges,
C. Lee, and S. G. Wakeham. Field evaluation of a valved sediment
trap. Limnol. Oceanogr.. 1993; 38: 1741-1761
- Siegel, D. A., T. C. Granata, A. F. Michaels, and T. D.
Dickey, 1990. Mesoscale eddy diffusion, particle sinking,
and the interpretation of sediment trap data. Jour.
Geophys. Res. 95: 5305-5311.
- Silver, M. W., M.M. Gowing, D.C. Brownlee, and J.O. Corliss,
1984. Ciliated protozoa associated with oceanic sinking detritus.
Nature, 309: 246-248.
- Soutar, A., S. A. Kling, P. A. Crill, E. Duffrin, and K.
W. Bruland, 1977. Monitoring the marine environment through
sedimentation. Nature, Lond. 266: 136-139.
- Spitzer, W. S. and W. J. Jenkins, 1989. Rates of vertical
mixing, gas exchange and new production: estimates from seasonal
gas cycles in the upper ocean near Bermuda. Jour. Mar.
Res. 47: 169-196.
- U.S. GOFS Report No. 10., 1989. Sediment Trap Technology
and Sampling. Available from U.S. JGOFS Planning Office,
Woods Hole Oceanographic Institution, Woods Hole, MA, 94 pp.
- Walsh, I., K. Fischer, D. Murray, and J. Dymond, 1988. Evidence
for resuspension of rebound particles from near-bottom sediment
traps. Deep-Sea. Res. 35: 59-70.
- Wei, C. -L. and J. W. Murray, 1992. Temporal variations
of 234Th activity in the water column of Dabob Bay: particle
scavenging. Limnol. Oceanogr. 37(2): 296-314.
Attendees at the Villefranche Trap Meeting
(Meeting was open to all who attended the JOGFS Symposium)
- Nicholas Bates (email@example.com)
- U. Bathmann (firstname.lastname@example.org)
- Ken Buesseler (email@example.com)
- Craig Carlson (firstname.lastname@example.org)
- Fei Chai (email@example.com)
- Andrew Dickson (firstname.lastname@example.org)
- Steve Emerson (email@example.com)
- Wilford Gardner (firstname.lastname@example.org)
- Julie Hall (email@example.com)
- Nobuhiko Handa (firstname.lastname@example.org)
- Roger Hanson (email@example.com)
- Dennis A. Hansell (firstname.lastname@example.org)
- Dale A. Kiefer (email@example.com)
- Tony Knap (firstname.lastname@example.org)
- Wolfgang Koeve (email@example.com)
- D. Lal (firstname.lastname@example.org)
- Richard Lampitt (email@example.com)
- K. K. Liu (firstname.lastname@example.org)
- Jim McCarthy (email@example.com)
- Nick McCave (firstname.lastname@example.org)
- Dennis McGillicuddy (email@example.com)
- Tony Michaels (firstname.lastname@example.org)
- J. Carlos Miquel (email@example.com)
- Jim Murray (firstname.lastname@example.org)
- Wajih Nagvi (email@example.com)
- Susanne Neuer (firstname.lastname@example.org)
- John Parslow (email@example.com)
- Don Rice (firstname.lastname@example.org)
- Javier Ruiz (email@example.com)
- T Saino (firstname.lastname@example.org)
- Jan Scholten (email@example.com)
- Ian Walsh (firstname.lastname@example.org) Rapporteur
Attendees without e-mail addresses (or incorrect addresses):
- Detlef Schulz-Bull IfM Kiel, Germany
- Ning Xiuren, 2nd Institute of Oceanography, SOA, 310012 Hangzhou,
- Jan Duinker email@example.com
- Ulrich Lundgreen IfM Kiel, Germany
- Andreas Irmisch PTBEO Meeresforschung FAX +4938151509
Invited participants who were not able to attend:
- Vernon Asper (firstname.lastname@example.org)
- Mike Bacon (email@example.com)
- Bodo Bodungen (firstname.lastname@example.org)
- Steve Calvert (email@example.com)
- Serge Heussner(firstname.lastname@example.org)
- Susumu Honjo (email@example.com)
- Cindy Lee (firstname.lastname@example.org>)
- Phil Newton (email@example.com)
- Paul Wassman (firstname.lastname@example.org)
- Graham Shimmield (G.Shimmield@edinburgh.ac.uk)
- Alexis Khripounoff (email@example.com)
Contributors of material and comments after the first draft:
- Tony Michaels
- Ken Buesseler
- Dave Karl
- Wolfgang Koeve
- Uli Lundgren
- Cindy Lee
- Vernon Asper
- Jim Murray
- Dennis Hansell
- Greg Mitchell
- Scott Nodder
- Juan Carlos Miquel
- Steve Emerson
- Ken Bruland
- Ken Coale