MICROLAYER
COLLECTION
FROM THE SEA SURFACE:
A NEW METHOD AND INITIAL
RESULmTS
George Mr. Harvey
Applied
Oceanography
University
Group, Scripps Institution
of California,
San Diego
of Oceanography,
92106
ABSTRACT
A newly constructed
collecting device can remove large quantities of a thin layer (approximately
60 P thick) from the sea surface. Samples obtained by means of this collector
indicate larger amounts of organic materials in the thin surface layer of the sea than in the
water at a depth of 10 cm. These organic materials include living nannoplankton
organisms, structural
comnoncnts of disintenratcd
organisms, surface-active
substances, chlorophyll,- and carotenoid- pigments.
INTRODUCTION
Although many aspects of the upper
layers of the sea have been investigated,
the submillimeter thick layer at the sea surface has received little attention. The water
at the surface appears to have properties
that differ from those of the underlying
water (Ewing and McAlister 1960; Kanwisher 1963). This layer and any associated surface films doubtlessly are affected
by winds, currents, solar radiation, humidity and temperature of the air, water temperature, and the presence of animals and
plants; hence, significant diurnal and other
short period variations in its characteristics
can be expected. Attempts were made to
apply existing methods of sampling to this
region.
The use of glass fabric as a surface collecting agent was suggested by D. L. Fox
(personal
communication).
Preliminary
work showed this to be excellent in most
respects, but the time required for processing large samples was excessive, and a sufficiently thin, unmixed layer could not be
selectively sampled. There also were serious difficulties arising from subsurface contamination of the surface layer by such objects as seaweeds, rope fragments, copepods,
and jellyfish.
The same problems were encountered
with monel-metal screens similar to those
used by Garrett (1965) and the stainless
steel screens used by Sieburth ( 1965).
-1 This work was supported by Office
Research Contract Nonr 2216( 13).
of Naval
The use of rising air bubbles (Sebba
1962) was not attempted at sea because
observations in experimental marine aquaria
indicated excessive mixing of the surface
layer with subsurface water and excessive
formation of new surfaces,
Studies to determine effective methods of
collection and observation have resulted in
improvements that save time, reduce the
serious problems of sample deterioration
and contamination, and allow the collection
of a layer, approximately 60 p thick, with a
minimum of vertical mixing.
DESCBIPTION
OF APPARATUS
The surface collector uses a smooth, rotating cylinder whose surface is readily wet
by water. A large neoprene blade is pressed
tightly to the surface of the cylinder to remove continuously the fiilm and water. The
cylinder,” 38 cm diameter and 60 cm long,
is of stainless steel, coated with a ceramic
material
designed for high-temperature
components, Rotation is accomplished by a
storage battery operated synchronous stepping motor with reducing gear. The speed,
usually 9 rpm, is controlled by a variablefrequency oscillator.
The advantages of
such a system are long battery life and accurate speed control. During the collecting
operation, the apparatus ( Fig. 1) is pushed
ahead of a small boat at a slow speed, only
slightly in excess of the surface speed of
the skimmer. The equipment is suitable for
2 Supplied
Department,
608
by Solar Aircraft
Company
San Diego, California.
Research
Frc. 1.
Photograph
of the surface skimmer.
USCin calm weather but cannot be used effectively in rough water.
A similar, larger
collector has been designed
to overcome
this difficulty.
The water, scraped off the drum, runs to
the end of the slightly slauted blade, thence
hy way of a plastic cup through a relatively
inert plastic hose into a 20.liter polyethylene bottle adjusted
to slightly
less than
atmospheric pressure (Fig. 2). Since there
is no pump in the liquid line, and since the
plastic is readily
replaced,
the system is
rasily kept clean.
The thickness of the water layer collected
by the drum depends on the speed of rotation and the water
temperature.
Layer
thickness was determined
by measuring
the
volume of water supporting
a monolayer
(marked by lycopodium
powder)
that was
picked up in 1 hr by the total swept surface.
ht 2OC, the layer collected is approximately
60 + thick. At 16C, the thickness of the recovered layer is increased
approximately
12% by the increased viscosity of the water.
This method results in the collection
of
a thinner, less disturbed
sample of surface
water than has been obtainable
with any of
the other methods investigated.
The samples can be collected more quickly with less
labor, less contamination,
and less degradation.
This allows the investigation
of
large areas of surface water (hundreds
of
square meters per hour), a great advantage
when only traces of surface active, radioactive, fluorescrnt,
or colorrd materials
are
present.
RESULTS
A sulfate film, liding
on the surface of
the water layer that adheres to the hydro-
philic cylinder, is picked up smoothly
(Fig.
2). In films composed of mixtures of substances having different
film pressures, it is
likely
that the higher
pressure
materials
would
be picked
up preferentially,
with
resulting fractionation,
as was demonstrated
by Blunk and LaMcr
(1957)
for films of
ethyl palmitate.
The same pressure relationships could result in nonuniform
distribution on natural surfaces of the sea. Although considerable
small-scale
turbulence
is developed
along the submerged
surface
of the cylinder
and at the emerging
area,
especially
in the presence
of ripples and
waves, the surface film does not appear to
bc seriously
disturbed.
Perhaps the thin,
structurally
coherent water layer at the surface (Kanwisher
1963) contributes
to the
surface stability
observed during operation
of the cylinder.
However, waves impinging
on the cylinder produce alternate compression and expansion of the film as it is picked
I,“.
.~r
All samples examined
under the microscope for particulate
material
were talefully studied for evidences of collapsed sur-
610
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~?IG. 4.
Optical transmission
curves of chloroform extracts of fresh bucket and skimmer samples
determined
by spectrophotometer.
Lower transmission indicates higher concentration
of organic
material.
FIG. 3. Abundance of living material found in
slicks off La Jolla in surface and subsurface water.
face film as described by Sutcliffe, Baylor,
and Menzel ( 1963)) Riley ( 1963)) and
Riley, Wangersky, and Van Hemert ( 1964)
for seawater, and by Goldacre (1949) for
rivers and ponds. There was no suggestion
of sheetlike aggregates (Riley 1963) in the
fresh untreated samples that were microscopically examined. A similar examination
of fresh 300-ml samples centrifuged
at
30,000 X g and 16C for 2 hr gave the same
negative results. Most of the organic aggregates appeared to be composed of living
bacteria, very small living algae, and small
living colorless flagellates in a matrix of
dead cells, expelled cell contents, cell walls,
diatom frustules, fibrous material, and occasional mineral grains, Small amounts of
filmlike material, resembling the cell walls
described by Lewin ( 195S), were found in
plankton blooms, but their origin could not
bc identified. In other cases, however, fragments of dinoflagellate cell walls could be
identified in various stages oE disintegration, those of Prorocentrum
micans and
other armored forms being especially noticeable.
Observations made by N. L. Jarvis (personal communication)
indicate that under
ordinary conditions there is no evidence of
the collapse of films on the sea surface. In
this investigation, samples from natural sea
surfaces, when tested in situ with Adam’s
( 1937) piston oils, also appeared to have
either no surface films or compressible
films. Upon very slight surface compression, film marked with powder was observed
always to flow between the ends of the
cylinder and the floats, indicating
little
possibility of fiIm collapse while sampling.
OBSERVATIONS
ON SAMPLES
Current studies of marine microorganisms
collected by the skimmer indicate some interesting differences between “skimmer”
surface samples and “bucket” samples taken
approximately
10 cm below the surface.
The volume of each type of sample was
about 20 liters, providing sufficient material
for the various types of analyses and minimizing changes in temperature, Examination of all samples began within 1 hr of
collection and without previous treatment.
In a few sparsely populated samples, larger
organisms were concentrated by slow rcmoval of water through 0.2-0.45~ membrane filters.
Generally, more bacteria were observed
in skimmer samples than in bucket samples,
most being found on or near dead or dying
dinoflagellates and diatoms, or less often,
closely associated in relatively large numbers with pieces of heterogeneous organic
aggregates, The greater numbers of bac-
MICROLAYER
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FIG. 5. Comparison of ripple-damping
values for skimmer and bucket samples
Per cent damping referred to clean distilled
water.
slick-forming
materials.
during
adsorption
of
612
GEORGE W. HARVEY
TABLE 1. Relatizje proportions,
numbers/liter,
of
hkg microorganisms in skimmer and bucket
samples in May 1964
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~-
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1,100
Ciliates
Diatoms
330
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teria found in water at the surface confirm
the observations of Sicburth ( 1965). Table
1 shows the relative proportions of living
organisms counted in a Sedgwick-Rafter
chamber in three samples taken about 11
km off La Jolla, California. The large differenccs in dinoflagellates arise mainly from
one species, Prorocentrum micans. Accompanying this dinoflagellate were large numbers of several species of small unidentified
flagellates.
Seasonal differences between skimmer
and bucket samples are indicated in Fig. 3,
showing total living material (5 to 1,000 p
in size) based on live counts. About 95%
of the visible (above 0.5 E,L)particulate organic material on 20 July was living Prorocentrum micans.
There are other striking differences between bucket samples taken at the lo-cm
depth and samples taken by the surface colIector. The optical transmission curves of
chloroform extracts of samples taken several miles west of the Scripps Institution of
Oceanography indicate a higher concentration of organic material in the thin surface
layer than at the IO-cm depth (Fig. 4). The
morning samples contained more organic
material, including chlorophyll
and carotenoid pigments, than did the afternoon
samples. Infrared transmission curves of
the same chloroform extracts obtained on a
spectrophotomctcr indicated similar concentrations of organic material.
Measurements carried out in a ripple
tank at a frequency of 120 cycle/see showed
differences in ripple-damping
comparable
to those in the spectrophotometric
records.
The method was similar to that employed
by Garrett and B&man
( 1963) in a tank
operating at 60 cycle/set, except that films
were allowed to form on the clean undisturbed water surface without compression
by movable barriers. Damping was estimated from high-speed flash photographs
of ripple-train
shadows projected on a
ground-glass screen.
The relationships between the skimmer
and bucket samples taken at different times
of the day on three different days are shown
in Fig. 5. In the 39 samples that have been
studied, in respect to the time of day and
type of sample, the higher quantities of
small plankton organisms were related to
much greater ripple-damping and to greater
absorption in the visible and infrared spectra. The large variations in plankton populations were associated with similar variations in ripple-damping
and spectral absorption,
The relationships among the surface film
responsible for ripple-damping,
the organic
substances and living populations in the upper 60 ,U of the sea surface, and oceanographic conditions such as water temperature, density, turbulence, wind velocity, and
light intensity are under investigation.
REFERENCES
N. K. 1937. A rapid method for detcrmining the lowering
of tension of exposed
water surfaces, with some observations on the
surface tension of the sea and of inland
waters.
Proc. Roy. Sot. London Ser. B., 122:
134-139.
BLANK, M., AND V. K. LAMER.
1957. The mechanism of transfer
of surface films.
Intern.
Congr. Surface Activity,
2nd, 1: 102-108.
Butterworth,
London.
EWING, C. C., AND E. D. MCALISTER.
1960. On
the thermal
boundary
layer of the ocean.
Science, 131: 1374-1376.
1965. Collection
of slick-formCARHETT,
W. D.
ing materials from the sea surface.
Limnol.
Occnnog., 10: 602-605.
AND J. D. BULTMAN.
1963. The damping of water waves by insoluble organic monolayers.
U. S. Naval Res. Lab. Rcpt. No. 6003.
18 p.
Surface Eilins on natural
GOLDACIUZ, R. 1. 1949.
bodies of water.
J. Animal Ecol., 18: 36-39.
1963. On the exchange of gases
KANWISIIICR,
J.
between the atmosphere and the sea. DeepSea Res., 10: 195-207.
1958. The ccl1 walls of PlalyLJEWIN, R. A.
J. Gen. Microbial.,
19: 87-90.
monas.
1963. Organic aggregates in seaRITXY,
C. A.
ADAM,
MICROLAYER
COLLECI’ION
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Limnol. Oceanog., 8: 372381.
-, I?. J. WANCERSKY, AND D. VAN IIEMERT.
1964. Organic
aggregates
in tropical
and
subtropical surface waters of the North Atlantic Ocean.
Limnol. Oceanog., 9 : 546-550.
SEDBA, F. 1962. Ion flotation.
Elsevicr,
New
York, N.Y. 154 p.
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TIIE
SEA
SURFACE
613
1965. Bacteriological
samSIEIUJ~TII, J. McN.
plcrs for air-water
and water-sediment
interfacts, p, 1064-1068.
In Trans. Joint Conf.
Ocean Sci. Ocean Eng., MTS-ASLO,
Washington, D.C.
SUTCLIBFE, W. II., JR., E. R. I~AYLOR, AND D. W.
MENZEL,
1963.
Sea surface chemistry and
Langmuir
circulation.
Deep-Sea
Rcs., 10 :
233-243.