Deep-Sea Research, 1970, Vol. 17, pp. 175 to 185. Pergamon Press. Printed in Great Britain

A microscopic study of organic particles in the North Atlantic Ocean

DONALD C. GORDON, JR.*

(Received I1 June 1969)

Abstract---Organic particles greater than 5 t~ from 38 North Atlantic stations were examined using phase microscopy. Four morphological categories were evident: aggregates, flakes, fragments and unclassifiable particles. Judging from their reactions to histochemical stains, aggregates appear to be chiefly carbohydrate, flakes chiefly protein, and fragments completely carbohydrate. Total particle concentrations ranged from 32-253/mi in surface water and 12-27/ml in deep water. The abundance of aggregates was greatest in surface waters while that of flakes and fragments was generally constant with depth. Size-frequency measurements were made, and the suitability of particles as a food source and the factors affecting their distribution are discussed.

I N T R O D U C T I O N

MOST of our current knowledge of deep-sea non-living particles stems from particulate organic carbon data. However, since all particulate matter is lumped together, these data include living carbon and fail to provide any quantitative or qualitative infor- mation of the different particulate components. A more fruitful method of studying organic particles is microscopic observation (RILEY, 1963; RILEY, WANCERSKY and VAN HEYmRT, 1964; RILEY, VAN HEMERT and WANCERSKY, 1965; KANE, 1967; and JOHANNES, 1967). This method, coupled with histochemieal staining, has been used to study organic particles in the deep waters of the North Atlantic Ocean.

SHIPBOARD METHODS

Water for particle analysis was collected with 30-1. PVC Niskin samplers. At the start of each cruise, these were washed with isopropanol and distilled water, and since they were in daily use thereafter, further cleaning during a cruise was not thought necessary. Stations were widely distributed over the North Atlantic Ocean (Fig. 1). Surface water (1-2 m) was collected as soon as the ship arrived on station in order to minimize the chances of contamination. Usually eight deep water samples at approximately 500 m intervals were collected on a single east at each station, and their actual depths were interpolated from the computed depths of reversal of several accompanying Knudsen bottles. Subsamples for the particle analyses to be reported here were drawn immediately into 1-1. plastic bottles which were refrigerated until treatment (within a few hours).

A 10-1. glass-teflon sampler loaned by Dr. David Menzel and an in situ filtering device were used to check for possible particle contamination by the Niskin samplers. The latter, which could filter as much as 300 ml in surface waters, was identical to the

*Institute of Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada. Present address: Department of Oceanography, University of Hawaii, Honolulu, Hawaii, 96822, U.S.A.

175

176 DONALD C. GORDON, JR.

G R E E ~

5e e~ 12

A ~ eli • 4 ,7 ,I0

,,3 "8

• 2 -9 CANAD .I

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I

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o

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Fig. 1. Station locations in the North Atlantic Ocean. Stas. 1-12 were made with the C.S.S. Hudson, 23 April-12 May, 1966; Stas. 13-15 with the Panulirus, 13-17 January, 1967; Stas. 19-26 with the C.S.S. Baffin, 5 April-8 May, 1967; and Stas. 30--52 with the C.S.S. Hudson, 10 June-

19 July, 1967.

' ~ [ F ]0-cc PLASTIC SYRINGE

] ~,~q~ ~-25-mm GELMAN@EASY PRESSURE FILTER HOLDER

F . ' " ~ CONTAINING 12/~MILLIPORE® FILTER

~ --RUBBER STOPPER

~ FGuENLMA~25-ml POLYPROPYLENE fiLTER

,L:~;;;~ ---SAMPLE FILTER (1 2,u. MILLIPORE ® FILTER) 7~------- MILLIPORE ® PYREX MICROANALYS/S FilTER

[ : HOLDER BASE TO SUCTION PUMP

Fig. 2. Diagranl of filtering and staining apparatus depicting arrangement when a staining solution is being added. The funnel holding clamp has been omitted. Four identical units were mounted on a rack enabling replicate samples to be filtered and stained simultaneously. Staining solutions, distilled water and isopropanol were stored in 125-ml Erlenmeyer flasks and dispensed with syringes. The filter holder atop the funnel was removed only when seawater was filtered and its filter retained the particles occurring in the solutions added. These solutions were removed as necessary through the sample filter by gentle suction. Funnels were rinsed with 40-ml of iso-

propanol before each filtering.

A microscopic study of organic particles in the North Atlantic Ocean 177

device described by WATT (1965) except that a filter was placed between the intake and a 500-ml spherical flask.

The filtering and staining apparatus (Fig. 2) was designed to limit particle con- tamination under shipboard conditions to a low and predictable level and yet keep the methods as simple and easy to follow as possible. Two to four replicate volumes were filtered from each 1-1. seawater sample through 1.2/~ Millipore® filters using gentle suction (60-150 ml at Stas. 1-12 and 250 ml thereafter). Immediately following, just prior to staining, each sample filter was rinsed with 5 ml of distilled water to remove salts. After staining, each sample filter was removed from the apparatus, dried in a 60°C oven for 20 min, placed on a glass microslide, cleared with a few drops of Permount and covered with a glass coverslip. Slides prepared in this manner lasted indefinitely.

Frequent filter blanks for determining the extent of contamination by foreign particles were prepared using the same procedure outlined above except that 25 ml of distilled water were filtered, in place of seawater, to pick up any particles adhering to the inside wall of the funnel that could have contaminated a seawater sample.

Staining procedures specific for protein and carbohydrate were used. A procedure specific for neutral fats was used at Stas. 1-12, but it did not appear to stain anything and was discontinued in the later work. A mercuric bromphenol blue method (MAZIA, BREWER and ALVERT, 1953) was used to stain proteins, while carbohydrates were stained with the periodic acid-Schiff method (see PEARSE, 1960). These methods were selected because they were easily performed on Millipore® filters under ship- board working conditions and they are histochemicaUy sound.

L A B O R A T O R Y M E T H O D S

All microscopic observations were routinely made at 200 × magnification under phase illumination using a Zeiss Standard Universal microscope. Higher magni- fications were occasionally used for a closer examination of particles of special interest. For practical reasons, only particles having a greatest dimension exceeding 5/~ were studied.

Particles on all sample filters were counted by examining 49 ocular micrometer grids which were uniformly distributed and amounted to 1-8 ~ of the total filtered area. A Chi-square test, run on all counts made, demonstrated that particles were randomly distributed on sample filters. Particle counts were then blank corrected and multiplied by the appropriate conversion factor to express concentrations as part- icles/ml. Following the procedure of RILEY (1963), particle area as well as frequency was determined for samples from Stas. 1-12, but this practice was discontinued in light of an excellent correlation between area and frequency which indicated that it was unnecessary to measure both parameters. The size-frequency distributions of particles in selected samples were determined by measuring the greatest dimension of the first 100 particles encountered. Colour photomicrographs were taken using a conversion filter and Kodachrome X daylight colour film.

CHECKS AGAINST CONTAMINATION

Before the results obtained using these procedures were accepted as being rep- resentative of in situ particle conditions, various steps of the processing were examined to see if particle concentration or composition were being altered.

178 DONALD C. GORDON, JR.

Surface samples taken with the in situ sampler (Stas. 19-26) were compared with those taken simultaneously with a Niskin sampler. No differences were apparent indicating that Niskin samplers do not alter in situ particle conditions to any measure- able degree. Similar results were obtained when comparing deeper samples taken with Menzel's 10-1. glass-teflon sampler and a Niskin sampler.

The effect of storage time in 1-1. bottles was determined by comparing initial samples with those prepared at intervals of 12, 24, and 40 hr. The observed particle concentrations dropped (28-78 ~), roughly proportionally with time, but there was no obvious change in composition or mean particle size. This decrease is presumably due to particles settling or adhering to the inner surface of bottles. Particle samples must therefore be processed as soon as possible, but the rate of decrease appears to be such that samples stored for only a few hours, as in this study, are not seriously altered.

The concentrations of organic particles on blank filters were reasonably and dependably low, 3-12 particles/49 grids, rarely exceeding 10 ~ of the total number of particles counted on any sample filter. Their source is unknown; they could be natural particles from a prior sample which survive the isopropanol rinse between filterings or they could be of laboratory origin. It is interesting to note that particles occurred in the various filtered staining solutions plus the filtered distilled water and isopropanol, but they were retained on the filter atop the funnel (Fig. 2) when the fluids were added to sample filters.

PARTICLE MORPHOLOGY AND STAINING RESULTS

The term ' organic aggregate' (RILEY, 1963) has been so widely used that it is now applied to almost all organic particles, excluding detritus, in the sea. However, not all organic particles, particularly in deep water, look alike and many do not appear to be true aggregates. Striking morphological differences, some of which have been previously noted (RILEY, 1963; BOGDANOV, 1965; KAy, 1967; JOHANNES, 1967; and POMEROY and JOHANNES, 1968), were readily discernable in all samples examined. All particles counted were therefore assigned to one of four categories which were defined solely by morphological characteristics. The validity of this classification is supported by the compositional differences detected by staining.

Aggregates are amorphous particles composed of a variety of aggregated, yet distinctive, organic and inorganic sub-units of variable composition. Some may contain phytoplankton and bacteria plus recognizable mineral crystals (Fig. 3a) while others are mere blotches which are extremely difficult to quantify and are visible only after staining (Fig. 3b). Their outline is roughly circular and poorly defined. When suspended in seawater, they are almost spherical (RILEY, personal communi- cation), but this form is destroyed and particles are possibly broken apart during filtra- tion due to their friable nature. Carbohydrate staining of aggregates was generally intense (Fig. 3a, b) while protein staining was lighter, exhibiting a brownish green colour (Fig. 3c) not found with other particle categories. These results suggest that aggregates, as defined in this report, are composed principally of carbohydrate material and that the protein components might be different from those in other particles. Judging from descriptions by other authors, this category includes the amorphous, naturally occurring aggregates found in Long Island Sound (RILEY,

Fig. 3. Pho tomic rog raphs o f organic particles, a - -Aggrega t e , carbohydra te-s ta ined. Sta. 40, 90 m 70 x 85 tz field, b - - A g g r e g a t e s and unclassifiable particles, carbohydrate-s ta ined. Sta. 23, 1 m 175 x 212 ff field, c - -Aggrega t e s and flake, protein-stained. Sta. 25, 1 m 175 >( 212 ~ field. d C lump of flakes, protein-stained. Sta. 10, 1550 m 280 x 340 ff field, e - -F l akes , carbohydra te- stained. Sta. 26, 3950 m 70 × 85 t~ field, f - -F l akes , protein-stained. Sta. 52, 10 m 70 × 85 tz field, g - - F l a k e carbohydra te-s ta ined. Sta. 14, 1615m 28 × 34tz field, h - - F r a g m e n t ,

carbohydrate-s ta ined. Sta. 24, 1 m 280 >~ 340 ix field.

Lfacine p. 178]

A microscopic study of organic particles in the North Atlantic Ocean 179

1963), typical aggregates in the Ligurian Sea (KANE, 1967), and most of the particles in reef and lagoonal waters at Eniwetok Atoll (JOHANN,, 1967).

Flakes are thin, scale-like particles having a distinct margin and circular to elongate outline (Fig. 3d-g) with a varying number of small inclusions which appear to be mostly bacteria. Because of their persistent shape and structure, it is doubtful that they are deformed during filtration. They are occasionally clumped together (Fig. 3d); these groups may not occur naturally but be a consequence of filtering. Protein staining (Fig. 3d, f) was much more intense than that of aggregates, with colors ranging from blue to reddish blue, while carbohydrate staining (Fig. 3e) was less. These results suggest that flakes are predominantly proteinaceous. This category presumably includes films produced by experimental bubbling (RILEY, 1963), granular aggregates (KANE, 1967), and oceanic aggregates (JOHANNES, 1967).

Fragments are those particles obviously formed from the decay of organized tissue (detritus). They are almost exclusively chunks and fibers of cellulose as shown by their intense carbohydrate staining (Fig. 3h) and lack of protein staining.

Unclassifiable particles are those too small to be identified with certainty (5-10/z) or larger ones difficult to categorize. The staining behavior of this diverse assemblage of particles was naturally variable.

Amber and clear crystals not associated with organic material were frequently encountered in samples from all depths. Such inorganic particles plus fecal pellets and living organisms were not tabulated. Unicellular flagellates (cf. FOURNIER, 1966) were abundant in all samples. Copepods were occasionally captured in Niskin samplers, but never deeper than 1000 m.

According to this classification, the contaminating particles on filter blanks were mostly flakes and unclassifiable particles. Only a few aggregates and fragments were ever observed.

CONCENTRATION AND DISTRIBUTION OF ORGANIC PARTICLES

The replicates prepared from each sample were stained differently and those stained for carbohydrate had consistently higher particle counts than those stained for protein or unstained. This difference, which was greatest in surface samples, was due to the abundance of small particles (about 5-10/~) that were visible only when stained with the carbohydrate stain. Therefore, only the counts of stained particles in carbohydrate-stained replicates were used to calculate in situ concentrations of organic particles.

Particle concentrations were always greatest in surface and coastal waters (Table 1). The spacial distribution of particles in deeper water is illustrated by the con- centrations observed at Stas. 19-26 (Fig. 4). Most of the variability can be explained by the relatively large error inherent in the counting procedure. However, when analyzed with a Chi-square test for randomness, the deep particle concentrations of each separate cruise were non-randomly distributed suggesting that real variations do exist. Geographic variations become evident when the results of cruises to different areas are compared (Table 1). Daily variations, related to wind-speed, were observed in surface samples collected near Bermuda (Stas. 13-15).

These data indicate that there are some detectable variations in organic particle concentrations in the deep sea, but a more intensive investigation is needed to deter- mine their real magnitude and importance. Previous microscopic counts of particles

180 DONALD C. GORDON, JR.

Tab& 1. Summary oforganicpartic~data.

No./ml Depth of

Stations Location Date samples Number of X Range (m) samples

30, 41, 52 Nova Seotian Shelf June-July, 1967 1-150 I0 127 39-203 31, 32, 35 Nova Scotian and June-July, 1967 1-25 5 253 106-307 40, 43, 51 Nfld Slope 100-3000 20 23 8-38 13-15 Sargasso Sea January, 1967 1-5 3 32 19-48

170-2580 12 14 4-37 34, 45-50 June-July, 1967 1-15 3 91 78-101

450-4000 33 12 2-63 19-26 Temperate Nor th April-May, 1967 1-5 5 96 42-140

Atlantic 140-5360 56 22 3-104 1-12 Irminger Sea April-May, 1966 1-15 11 155 78-248

441-3269 58 27 9-70

PARTICLES / ml

O 50 I()0 150 0 I I I--TI~ T I I DI --T---- FT--- f i- i --Z~---

0 • 0 • 0 • N

5 0 0

I 0 0 0

1500

co 2000 w

2500 z

L 3000

3 5 0 0

4000

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0 AI3 o

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5500 ]1~ . t t ~ I~,. I z l E ± _ _ L _ _ L 0 50 IO0

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1 _ 1 J _

150

Fig. 4. Concentrations of organic particles in the temperate Nor th Atlantic Ocean observed on the C.S.S. Baffin cruise, 5 April-8 May, 1967.

A microscopic study of organic particles in the North Atlantic Ocean 18 l

Table 2. Average concentrations of various particle types.

No./ml

Station Location Depth of Number of Aggregates Flakes Fragments Unclassifiable samples (m) samples particles

41 Nova Scotian 1-150 4 71'9 11"8 3'5 64.5 shelf

11 Irminger Sea 1 1 124'2 32"8 1-4 58.5 542-2846 5 0'6 11 '5 0.2 12-8

25 Temperate 1 1 51"6 5"4 0'0 46.1 North Atlantic 140-4730 8 0-8 4-8 0-5 9.0

50 Sargasso Sea 1 1 51-6 1-3 0"4 25.4 450-3585 6 2-2 2"2 0"1 5'7

in deep water (RILEY, VAN HEMERT and WANGERSKY, 1965) were not detailed enough to provide much insight into particle distribution, but definite variations in the vertical distribution of particles have been observed in Tyndall data (JERLOV, 1959).

The organic particle concentrations reported in this study are higher than those from comparable locations and depths reported in the literature (RILEY, 1963; RILEY, WANGERSKY and VAN HEMERT, 1964; RILEY, VAN HEMERT and WANGERSKY, 1965; and KANE, 1967). This discrepancy is undoubtedly due to the fact that carbo- hydrate staining exposed particles which were not visible on the unstained filters examined by the above workers.

The relative abundances of the four particle categories were quite similar at all stations and only the data from four stations, three oceanic and one coastal, are presented (Table 2). Aggregate concentrations were greatest in surface samples, dropped sharply by several orders of magnitude within the euphotic zone, and rarely exceeded 1 aggregate/ml in deep water. In contrast, there were generally no pro- nounced vertical gradients in the concentration of flakes or fragments, not even within the euphoric zone. Except in surface samples, unclassifiable particles were the most abundant, usually amounting to more than half of the total number of particles counted.

SIZE-FREQUENCY DISTRIBUTION OF ORGANIC PARTICLES

Particle size data from all samples at Stas. 2, 20, 41 and 50 were amassed and the size-frequency distribution of each particle category plotted (Fig. 5). Three different kinds of distribution are apparent: the frequency of aggregates and unclassifiable particles decreases almost exponentially with increasing diameter, that of flakes is greatest near the center of their range, and that of fragments is irregular. Aggregates and fragments have the greatest size ranges; the larger flakes are actually clumps of smaller ones (Fig. 3d). By nature of their definition, most of the unclassifiable particles are small.

Two types of composite size-frequency distributions (Fig. 6) were evident at all stations. In surface samples, total particle frequency decreases almost exponentially with increasing diameter while in deep samples it has a characteristic peak or plateau in the 14-28/~ range. The difference is caused by changes in the relative abundance of the particle categories near the surface (Table 2). In surface samples, aggregates and unclassifiable particles are most abundant and their individual size-frequency

182 DONALD C. GORDON, JR.

Fig. 5.

70

60

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so LIJ

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2O

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14 28 42 56 70 GREATEST DIMENSION (/z)

u FLAKES (562) o AGGREGATES (512) .¢, FRAGMENTS (42) * UNCLASSIFiABLE PARTICLES(I084) '

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84 98 112 126

Size-frequency distributions of the four categories of organic particles. The numbers in parentheses indicate thelnumber of each particle type measured.

Fig. 6.

I I I I I I I I I I I I I I 1

6C o

5C

~ 4c 0 I m ( 1 0 0 )

u 140-5360m (700)

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o ~4 z8 42 66 70 e4 9~e

GREATEST DIMENSION, /z

Composite size-frequency distributions of all particles at Sta. 20. The numbers in parentheses indicate the number of particles measured.

A microscopic study of organic particles in the North Atlantic Ocean 183

distributions dominate the composite one. In deep samples however, flakes are proportionally abundant enough that their peak in the 21-28/z range affects the composite distribution.

The only particle size-frequency data in the literature gathered by microscopic examination are from Long Island Sound waters (RILEY, 1963), and they are quite similar to those reported here. The major difference is that in the former study the smaller and unidentifiable particles were not included in the measurements. Recently, Coulter counters have been used for size-frequency measurements of suspended particulate matter (SHELDON and PARSONS, 1967; SHELDON, EVELYN and PARSONS, 1967; and HOBSON, 1967). Unfortunately it is difficult to compare these data with microscopic measurements because the methods are quite different. Coulter counters measure particle volume, and to convert these units to both size and frequency one assumes all particles are spheres which may not be realistic in light of the variety of particle shapes (Fig. 3).

D I S C U S S I O N

The above information permits a re-examination of the possible role of organic particles as food for filtering-feeding organisms, particularly in deeper waters. Im- portant factors to consider are (1) particle concentration and distribution; (2) the ability of organisms to procure and handle particles; and (3) particle biochemical composition.

Organic particles are relatively abundant at all depths (Table 1, Fig. 4), more so than indicated by earlier studies (RILEY, VAN HEMERT and WANGERSI(V, 1965). Regarding their distribution, the poor sampling to date suggests significant variations in concentration over relatively large distances, but little is known about the small scale distribution of particles which is important to a filter-feeder seeking food.

What little information there is available indicates that filter-feeding zooplankton do occur and may even be abundant in deep water. RILEY, VAN HEM[RT and WANGERSI(Y (1965) list several species of bathypelagic zooplankton suited for filter- feeding in the Sargasso Sea, and HARDING (personal communication) observed that approximately 75 70 of the deep copepods in the Arctic Ocean are equipped with appendages capable of removing fine particles. Studies on the efficiency of particle retention by filter-feeders, reviewed by JORGENSEN (1966), indicate that the entire range of particles sizes occurring in seawater down to about 5 tz (Fig. 5) are easily filterable. Just how many particles an organism can gather in a given period is difficult to calculate since the filtration rates determined experimentally fluctuate widely.

Although most of the details remain obscure, all this evidence indicates that organic particles are being consumed in deep water. How much nourishment they provide depends upon their biochemical composition. Histochemical staining (Fig. 3) demonstrates that most particles contain substantial amounts of both protein and carbohydrate which, according to biochemical analyses (PARSONS and STRICK- LAND, 1962), are composed in part of a number of amino acids and sugars suitable as energy sources for most organisms. On the basis of this information, it is tempting to conclude that organic particles are an important food source. However, the possibility exists that the protein and carbohydrate compounds composing particles are not hydrolyzable by the enzyme systems of bathypelagic organisms and that they

184 DONALD C. GORDON, JR.

therefore are not assimilable even though ingested. Bacterial decomposition experi- ments (MENZEL and GOERIN6, 1966) suggested that this might be so, but it remains an open question which should be answered.

The distribution of organic particles in deep water is affected by advective processes and their settling rates. The only values of settling rates in the literature are indirect calculations: 1-7 m/day (RILEY, VAN HEMERT and WANGERSKY, 1965) and 0-14-12 m/day (HoBsoN, 1967). In this study, an attempt was made to measure settling rates directly by letting some full Niskin samplers sit upright undisturbed for periods of 12, 24 and 48 hours and then drawing samples from different depths for examination. Because of the various consequences of enclosing a seawater sample in a container, such as surface adsorption and bacterial growth, no conclusive results were obtained. However, rates in excess of 1 m/day should have been detected which indicates that the actual rates are in the lower range of the above calculations. The morphology of the particles (Fig. 3), particularly of the flakes, suggests low settling rates.

The importance of settling relative to advection remains obscure. Several workers (RILEY, VAN HEMERT and WANGERSKY, 1965 and WANGERSKY and GORDON, 1965) have observed that particulate organic carbon concentrations in deep water are roughly related to surface productivity which suggests that settling is important. More recently, however, it has been observed that high surface particulate matter concentrations do not affect the immediately underlying waters (MENZEL, 1967; and SHELDON, EVELYr~ and PARSONS, 1967), and HOBSON (1967) calculated that the settling rates are approximately three orders of magnitude less than rates of horizontal advection. These data suggest that advection is the dominant factor affecting particle distribution.

Both factors presumably are important: advection where advective rates are high and settling where they are low. Their relative importance should also vary in relation to particle size. Because of their low settling rates, small particles are probably distributed solely by advection, while settling becomes more important with pro- gressively larger particles.

No effort was made to determine the origins of the different categories of particles observed. Undoubtedly some of the particles were formed in the euphoric zone (aggregates and fragments) while others, particularly in deep water, presumably could have formed in situ from sub-particulate organics as proposed by RILEY, VAN HEMERT and WANGERSKY (1965) and SHELDON, EVELYN and PARSONS (1967). Recently there has been considerable interest in the potential role of bacteria in the production of particles (BARBER, 1966 and BATOOSINGH, RILEY and KESHWAR, 1969). At Stas. 1-12, counts of heterotrophic bacteria were made on all samples by Dr. Edward Batoosingh using a culture method (BAToOSINGFI, 1966). The counts were not significantly correlated with particle concentrations, despite large variations in each, suggesting that the relation between the two in deep water is not very direct. From these counts, it was calculated that there are 0-03-14.l heterotrophic bacteria/ particle which roughly agrees with the microscopic observations (Fig. 3).

Acknowledgements--The data discussed were part of my doctoral dissertation done under the able guidance of Dr. GORDON A. RaLEY. Dr. PETER J. WANGERSKY provided criticism and assistance throughout the work, and Dr. WALTON D. WATT assisted in designing the statistical procedures. In addition to the above, I wish to thank Drs. HAYDEN PRITCHARD and RONALD COWDEN for their advice in selecting the staining procedures, Dr. DAVID W. MENZEL for the loan of his sampler,

A microscopic study of organic particles in the North Atlantic Ocean 185

Dr. EDWARD BATOOSINGH for counting heterotrophic bacteria at Stas. 1-12, Mr. GARETH HARDING for his information on Arctic copepods, and finally MR. ROGER POCKLINOTON and Mr. ROBERT COOKE as well as the officers and crews of the vessels used for their able assistance in procuring the samples. Financial support was provided by NSF GS--2043.

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BATOOSINGH E. (1966). The distribution of heterotrophic bacteria in the western North Atlantic. Ph.D. Thesis, Dalhousie University, 102 pp.

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