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CHAPTER 14. APPLICATIONS TO PHYSICAL OCEANOGRAPHY

CHAPTER 14. APPLICATIONS TO PHYSICAL OCEANOGRAPHY

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156



APPLICATIONS TO PHYSICAL OCEANOGRAPHY



that the observed, nearly Gaussian distribution of slopes is consistent

with a continuous wave spectrum of arbitrary width or with a large

number of discrete frequencies.

The refracted glitter is also dependent on wave action. SCHENCK

(1957) has studied the phenomenon of bright bands of light moving

across a shallow sea bottom at the same velocity as the waves. The

intensification of radiance is ascribed to lens action by the waves.

In this context, it may be mentioned that the heights of water waves

produced in a laboratory tank can be observed by fluctuations in the

absorption of light passing vertically through the water (FALLER,

1958).

DISTRIBUTION OF PARTICLES



Scattering measurements



There is adequate ground for treating separately the oceanographic

application of scattering observations, since they provide the most

sensitive means of exploring the particle distribution as was first

demonstrated by KALLE(1939a). Some conspicuous results indicate

that the particle content may be considered to be an inherent property

of the water mass. An example of clear identification is given in

Fig.G6. The Pacific water present below 1,000 m depth has passed

several sills before reaching the deep Flores Basin. In spite of the

long duration of this transport, it has apparently maintained its



30



Scattering coefficient (krn''1

LO

50

60

70



80



90



rn

1000



3,000

4000



spoo

Fig.66. Particle stratification in the Flores Basin, showing the inflow of clear

Pacific water between 800 and 1,400 m. (After JERLOV, 1959.)



D I S T R I B U T I O N OF P A R T I C L E S



157



integrity and remained unaffected by the turbid water in the surface

layers. At present, definite conclusions can be drawn neither about

the refractory character of particulate matter which is transported

over long &stances nor about the rate of continual supply of particles

from above to a spreading water mass.

An important aspect of the particle problem is the formation of

optical scattering layers frequently encountered at various levels in the

sea. RILEYet al. (1949) have considered theoretically the distribution

of phytoplankton in an uppermost layer of the ocean with a constant

eddy diffusion, and found that a maximum is developed near the lower

limit of the photic zone. WYRTKI

(1950) has discussed the significant

role of the vertical gradient of the eddy diffusion in forming the

particle distribution pattern. Below the photic zone, the mechanism

at which a maximum is developed requires not only that the eddy

diffusion increases with depth but also that the sinking rate of the

particles be reduced, i.e., their buoyancy be improved (JERLOV,

1959).

The necessary conditions are generally fulfilled for a discontinuity

layer which shows high vertical stability. NEWMINand SOROKINA

(1964) and PARAMONOV

(1965) have thoroughly investigated the

relation between stability and distribution of particles. They found

that in the upper layers down to 150 m the predicted distribution

does not invariably correlate with stability, on account of migrations

of living organisms. Vertical movements of water occurring at

upwellings or at divergences and convergences are generally indicated by the particle content, as they lead to salient changes of the

productivity of the sea (see Fig.82).

The spreading of water masses in the deep sea is often reflected

in particle diagrams. A conspicuous situation in Fig.67 demonstrates

that the tongue of high-salinity water from the subtropical convergence in the Pacific is fairly rich in particles. The intruding water mass

as a rule has higher particle content than the surrounding water.

It is difficult to judge to what extent this is an inherent property

of the water mass originating from surface levels or an effect of the

turbulence created by the flow of the water masses. The occurrence

of strata of such high particle concentration as that extending at the

6" level in Fig.67 is in many cases associated with a defined water

mass. In other instances one fails to find any relationship. The

initial scattering data obtained by KALLE(1939a) in deep Atlantic

water indicate that particle maxima are strong and numerous (Fig.68).



158



APPLICATIONS

52.



25



0'



TO P H Y S I C A L O C E A N O G R A P H Y

N2*



25-30



4'



6'



8'



10'



12'



14'



30-40



Fig.67. Stratum with high-particle concentration in the salinity minimum. Tongue

of high-salinity water from the subtropical convergence rich in particles. Meridional section near longitude 150"W in the Pacific. (After JERLOV, 1959.)



Fig.68. Particle maxima in a west-east vertical section near the Tropic of Cancer

in the Atlantic. (After KALLE,1939a.)



159



D I S T R I B U T I O N O F PARTICLES



30



50



Scattering coefficient (km-1)

50

50



50



50



50



I

\East Pacific West. P'ocific East Indian



East Atlantic



West Atlantic



Fig.69. Depth profiles of scatteringin the oceans, indicating spreading of Antarctic

Intermediate (A.I.) and Antarctic Bottom water (A.B.). (After JERLOV, 1959.)



This circumstance is supported by JERLOV'S

(1953a) measurements

in the equatorial region. Several problems in marine chemistry and

geology must be treated with due regard to the particle component.

In that connection, some guidance about average or typical vertical

distributions as derived from scattering observations is obtainable

from Fig.69. The profiles which represent exclusively the equatorial

regions indicate that at great depths the western Atlantic has the

highest relative particle concentration, whereas minimal amounts

are encountered in the western Pacific.

The spreading in the sea of turbid river water or other freshwater

discharge is readily studied by scattering measurements. KETCHUM

and SHONTING

(1958) have traced the flow of the turbid Orinoco

water in the Cariaco Trench. Another example of particle distribution

from off the Po River proves the existence of a deep countercurrent

which flows against the turbid surface water (JERLOV,1958).

Beam transmittance measurements

The beam transmittance meter has developed into a powerful tool

for identifying water masses, as evidenced by a great number of

investigations (JOSEPH,1955, 1959, 1961; NISHIZAWA

et al., 1959;

WYRTKI,1960; PAVLOV,1961; SCHEMAINDA,1962; DERA,1963;



Fig.70. Distribution of beam transmittance in a meridional section near

longitude 171" W i n the Pacific. (After KOZLYANINOV,

1960.)

0



m



x,



010 0.l5

~



i

>'0.75



Fig.71. Turbidity layer associated with the thennodine. Section from the Nomegian to the Scottish coast.

(After JOSEPH, 1955.)



DISTRIBUTION OF PARTICLES



161



NEWMIN

al.,~1964;

~

BALL^^^ LAFOND,1964; and MALMBERG,

1964).

Beam transmittance, if recorded in the red, is a measure of the particle

content, though it is a less sensitive parameter than scatterance. Its

relation to dynamics is analogous to that of scatterance.

A section of vertical particle distribution in Fig.70 serves to

illustrate the usefulness of beam transmittance as an oceanographic

parameter. Note that the prominent features of the section in Fig.67

are only vaguely indicated in Fig.70, which is situated farther to

the west. Instead, attention is drawn to the huge stratum of turbid

water present at 2,000-2,500 m. It is interesting to note that the

profiles in Fig.69 display similar maxima. Both JERLOV (1959) and

KOZLYANINOV

(1960) think that they result from the flow of Antarctic

water. Furthermore, a large-scale comparison between dynamic

sections and distributions of beam transmittance made by KOZLYANINOV and OVCHINNIKOV

(1961) shows correlations between the structure of the current pattern and the broad outlines of the beam

transmittances.

Convincing proof of the capability of the beam transmittance

meter to detect the discontinuity layer and record its movements is

furnished first and foremost by JOSEPH (1955). A section between the

Scottish and the Norwegian coast (Fig.71) shows that the thermocline is associated with a layer rich in particles. This is not split up

until over the deep Norwegian trench where the Baltic current

influences the structure of the surface water. On the basis of beam

transmittance measurements, JOSEPH and SENDNER (1958) have

elaborated a new approach to the problem of horizontal diffusion in

the sea and have induced a fruitful development in this domain.

VOITOV

(1964) has utilized the transmittance method to measure

vertical eddy diffusion as a function of depth.

Particle di.rtribution near tbe bottom

The turbulence effected by bottom currents generally leads to an

increase of particle content towards the bottom. Only if currents

vanish, or if the bottom is uncovered, is the bottom layer uniform in

particles. The existing turbulence is obviously much influenced by

topographic features. Tn a systematic study of oceanic particle

distribution, JERLOV (1953a) has shown that clouds of particles are

frequently encountered at levels 10-50 m above the bottom. This is



162



APPLICATIONS TO PHYSICAL O C E A N O G R A P H Y

Scattering coefficient (km-')

20 LO 60 80 100 120 140 160



3700-



I



I



8



I



a



I



I



I



-



3800



3858



Fig.72. Example of particle cloud above the bottom. (After JERLOV, 1953a.)



1936



Fig.73. Particle accumulation in the high-salinity water near the bottom of the

Red Sea. (After JBRLOV, 1953a.)



20



50



100 200



500 mb



Fig.74. Logarithmic increase o f particle content toward bottom in the Baltic and

in the Adriatic Sea. (After JERLOV, 1955a, 1958.)



163



DISTRIBUTION OF PARTICLES



06h



15.3.53



lZh



re.”



00‘



16.3



06’



Fig.75. Periodic rising and sinking of sediment in the North Sea caused by tidal

currents. (After JOSEPH,1955.)



interpreted as an effect of lateral transport from adjacent topographic

heights (Fig.72). It is a matter of particular interest that the highsalinity water found at the greatest depths in the Red Sea is rich in

particles (Fig.73).

In shallow waters a logarithmic increase towards the bottom is

evidenced in some cases (Fig.74). The distribution in the Bothnian

Gulf indicates slow settling of organic material under the influence of

horizontal flow (JERLOV,

1955a; FUKUDA,

1960). Similar distributions

in the North Sea (Fig.75; JOSEPH, 1955) and in the Adriatic Sea

(Fig.74; JERLOV,1958) are attributed to periodic rising and sinking

of sediment for which the tidal currents are the chief agency. Other

observations do not suggest any systematic change of the particle

content, e.g., IVANOFF’S

(1960b) data from 50 to 600 m depth off

Monaco. PICKARD

and G I O V A N D O (have

~ ~ ~pointed

~)

out the role of

turbidity currents as the cause of particle abundance near the bottom.

Pollution research

Extensive applications of scatterance and beam transmittance

meters are found in pollution research. The method rests on the



164



APPLICATIONS TO PHYSICAL OCEANOGRAPHY



finding that for a given type of particulate matter the attenuation

coefficient is proportional to the particle concentration expressed

as mass per unit volume (WYRTKI,1953; JOSEPH, 1955; JONES and

WILLS,1956; OCHAKOVSKY,

1966a).



D I S T R I B U T I O N OF YELLOW SUBSTANCE



Yellow substance may be treated as a semi-conservative concentration which is readily determined by means of beam transmittance

measurements. The analysis presumes its presence in fairly high

concentrations such as are generally encountered in coastal waters.

Original experiments in the Baltic conducted by KALLE(1949) and

corroborated by JERLOV (1955a) prove that diagrams of the content

of yellow substance plotted against salinity yield exceUent information

about the water masses and the mixing between them (Fig.76). The

very first scattering and beam transmittance measurements made by

PETTERSSON

(1936) showed that the Baltic water flowing northwards

along the west coast of Sweden is clearly identified by its colour due

to yellow substance. It is evident from Fig.77 which represents these



ul



A



0



1



2



3 I



6 7

Salinity



5



8



9 10 11%



Fig.76. Relationship between salinity and amount of yellow substance in the

Baltic. A. After KALLE

(1949). B. After JERLOV (1955a).



D I S T R I B U T I O N OF F L U O R E S C E N C E



20



60



I00



LO



80



165



120



Fig.77. Comparison of scatterance and beam transmittance (in the blue) for water

off the Swedish west coast indicating stronger absorption in the top layer of

partly Baltic water than in the underlying Skagerrak water. (After PETTERSSON,

1936.)



results, that the upper layer of water of partly Baltic origin absorbs

more strongly in the blue than does the underlying Skagerrak water

of higher salinity; an accumulation of particles occurs at the boundary

between the two water masses.



DISTRIBUTION OF FLUORESCENCE



The use of fluorescent dyes as tracers in order to study diffusion in

the sea is another beautiful example of an optical method applied

to a significant dynamical problem. Rhodamine B is generally selected

as a suitable dye on account of its relatively low cost, high detectability and relatively good stability.

The method aims at exciting rhodamine B, preferably by the green

mercury line which can be isolated, e.g., by an interference filter.

The exciting light is filtered from the emitted path by an orange

Schott filter OG 2, so that light scattered by particles is eliminated.

Tests are usually made by means of a laboratory meter o n collected

water samples or on water brought up under positive pressure with

the aid of a pumping system. More adequate in situ measurement is

hampered by the superposed effect of ambient natural light. This

difficulty is overcome for a meter which is provided with two measuring units; both of them face downwards but with only one receiv-



166



APPLICATIONS TO PHYSICAL OCEANOGRAPHY



J



R C



0



1



2



3



L



5

6

Salinity



?



8



9%.



Fig.78. Relationship between salinity and ratio of amount of fluorescent matter

to amount of yellow substance in the Baltic. (After KALLE,1949.)



ing the fluorescent light (KULLENBERG,

1967a). It may also be expedient to use a chopped light source in the fluorimeter.

It follows from Chapter 3 that natural fluorescence is a characteristic property of the same utility as yellow substance. KALLE

(1949)

has proved that in coastal waters the ratio of fluorescent substance

to yellow substance is a suitable parameter to be plotted against

salinity (Fig.78).



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CHAPTER 14. APPLICATIONS TO PHYSICAL OCEANOGRAPHY

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