I . SOME ASPECTS of the OPTICAL TURBIDITY OF

SOME ASPECTS OF THE OPTICAL TURBIDITY OF BRITISH COLUMBIA INLET WATERS

LAURENCE FRANK GIOVANDO B.A., University of B.C., 1946. M.A., University of B.C., 1948.

A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

in the Department of PHYSICS

We accept this thesis as conforming to the required standard

THE UNIVERSITY OF BRITISH COLUMBIA October, 1959 ABSTRACT

A light-scattering method has been utilized to determine the seasonal and geographical variation of optical turbidity in the waters of the major inlets of the southern British Columbia coast. (The optical turbidity is here defined as the fractional decrease in light intensity per meter due to the presence of suspended material in the water.) The major contribution to the turbidity in the inlets is the minerogenic material brought into the inlet by rivers at or near the head. The inlets whose rivers are primarily glacier-fed possess the highest turbidity values and exhibit the most marked seasonal variation of turbidity. The net outflow of water in the shallow layers-which is a prominent feature of the circulation in the inlets-ds the basic mechanism by which the material introduced by rivers is distributed throughout the length of the inlet. The surface values of turbidity range from about 0.5 to over 30 meters * (m *) in the summer and from about 0.1 to 1 m-^ in the winter. The values decrease from head to mouth, the effect being especially marked in the summer. The main body of water in the inlets usually possesses uniform tur• bidity at any time of the year, values ranging from 0.1 to 0.7 m"1. A marked increase in turbidity occurs, in the bottom layers of water, in all inlets. In the shallower inlets, this increase appears to be due primarily to tidal scouring of bottom material. In the deep inlets, it is presumably due to two causes: intermittent intrusion of deep water from outside the inlet, and, to a more prominent degree, turbidity currents originating at the inlet head. Evidence suggests that these currents are slow and possess a frequency of occurrence of the order of weeks. The contribution of material of biological origin to the turbidity is confined primarily to the inlets with small runoff. Little or no dissolved coloured matter is present in inlet waters. Size analysis by microscope indicates that the suspended material averages somewhat below 10/c in the major portion of an inlet; average sizes of up to 17/6 occur near the head of inlets during large runoff. There is little material below \JL in size. Light-scattering measurements indicate that the suspended material is preponderantly anisotropic in nature. The concentration of material varies from less than 1 to over 100 parts per million by volume. By means of the turbidity and concentration values obtained, it has been estimated that the rate of sedimenta• tion in the inlets ranges from about 35 cms to about 650 cms per 100 years, the value increasing from mouth to head of the inlet. The following relation between the Secchi disc reading 3> and the average turbidity Z over the distance 3) has been found: 7 = JJL J)L'Z Faculty of Graduate Studies

, PROGRAMME OF THE

FINAL ORAL EXAMINATION FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

L. F. GIOVANDO B. A., University of British Columbia, 1946 M. A., University of British Columbia, 1948

IN ROOM 301 PHYSICS BUILDING

TUESDAY, JULY 14th, 1959 at 10:30 A. M.

COMMITTEE IN CHARGE DEAN G. M. SHRUM: Chairman G. L. PICKARD K. C MANN R. W. STEWART R. D. RUSSELL J. A. JACOBS V. J. OKULITCH A. M. CROOKER C. K. SMITH External Examiner: Dr. W. V. BURT Oregon State College, Corvallis SOME ASPECTS OF THE OPTICAL TURBIDITY OF

BRITISH COLUMBIA INLET WATERS

ABSTRACT

A light-scattering method has been utilized to determine the sea• sonal and geographical variation of optical turbidity in the waters of the major inlets of the southern British Columbia coast. (The optical turbid• ity is here defined as the fractional decrease in light intensity per meter due to the presence of suspended and/or dissolved material in the water.)

The major contribution to the turbidity in the inlets is the minerogenic material brought into the inlet by rivers at or near the head. The inlets whose rivers are primarily glacier-fed possess the highest turbidity values and exhibit the most marked seasonal variation of turbidity. The net outflow of water in the shallow layers—which is a prominent feature of the circulation in the inlets--is the basic mechanism by which the mat• erial introduced by rivers is distributed throughout the length of the inle^. The ^surface values of turbidity range from about 0^. 5 to over 30 meters (m ) in the summer and from about 0. 1 to 1 m in the winter. The values decrease from head to mouth, the effect being especially marked in the summer. The main body of water in the inlets usually possesses uniform,turbidity at any time of the year, values ranging from0 . 1 to 0.7 m" .

A marked increase in turbidity occurs, in the bottom layers of water, in all inlets; In the shallower inlets, this increase appears to be due primarily to tidal scouring of bottom material. In the deep inlets, it is presumably due to two causes; intermittent intrusion of deep water from outside the inlet, and, to a more prominent degree, turbidity cur• rents originating at the inlet head. Evidence suggests that these currents are slow and possess a frequency of occurrence of the order of weeks.

The contribution of material of biological origin to the turbidity is confined primarily to the inlets with small runoff. Little or no dissolved coloured matter is present in inlet waters.

Size analysis by microscope indicates that the suspended material averages somewhat below 10// in the major portion of an inlet*, average sizes of up to 17/4 occur near the head of inlets during large runoff. There is little material below 1/i in size. Light-scattering measure• ments indicate that the suspended material is preponderantly anisotropic in nature. The concentration of material varies from less than 1 to over 100 parts per million by volume. By mass of the turbidity and concen• tration values obtained, it.has been estimated that the rate of sediment• ation in the inlets ranges from about 35 cms to about 650 cms per 1000 years, the value increasing from mouth to head of the inlet. The followingjrelation between the Secchi disc reading D and the average turbidity T over the distance D has been founds T = JL_

Dl. 2 GRADUATE STUDIES

Field of Study: Oceanography

Synoptic Oceanography.. . . W. M. Cameron

Oceanographic Methods Staff

Oceanographic Seminar Staff

Dynamic Oceanography G. L. Pickard

Fluid Mechanics GIL. Pickard

Waves and Tides G. L. Pickard

Turbulence R. W. Stewart

Int. Chemical Oceanography M. Kirsch

Int. Biological Oceanography...... W. M. Cameron

Other Studie s :

Electromagnetic Theory , J.R.H. Dempster

Theory of Measurements ...... A.M. Crooker In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I ..further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my

Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.

Department ACKNOWLEDGMENTS

The author wishes to express his gratitude to Dr* G.L. Pickard under whose direction and encouragement this study was carried out. The author is indebted to the officers and men of the various oceanographic research vessels for wholehearted cooperation in the field. Thanks are due to the Water Resources Branch, Department of Northern Affairs and Natural Resources for permission to use unpublished material. Appreciation is due T.H. Killam, L, Regan and G.K, Rodgers for their assistance in the field, and T.H. Killam and F.A. Payne for help in the preparation of the figures. The author also wishes to thank members of the staff and fellow graduate students at the Institute of Oceanography for their interest and comments during the preparation of this work. V.

-TABLE OP CONTENTS Page

I. INTRODUCTION 1.

II. ORIGIN OF THE LIGHT-ATTENUATING MATERIAL FOUND IN NATURAL WATERS 3.

III. THE BRITISH COLUMBIA MAINLAND INLETS 5.

A. Basic Oceanographic and Morphological Features 5. B. Features of the Individual Inlets Involved in this Study 8, a) Bute and Toba Inlets and Adjacent

Channels 8e b) Jervis Inlet 9» c) Knight Inlet 10. d) Loughborough Inlet 11. e) Call Creek 11.

IV. SUMMARY OF THE THEORY OF THE ATTENUATION OF LIGHT IN MATERIAL MEDIA 12.

A. The Definition of Turbidity 12.

B. The Mie Theory 14. (l) Underlying Assumptions 14. 2) General Results 15. ! 3) General Features of the Scattering from Non-absorbing Material (m real) 18. (4) Details of the Scattering Exhibited by (non-absorbing) Particles of Various Sizes 19. (a) Sizes very much smaller than the incident wavelength 20. (b) Sizes about equal to the incident wavelength 21© (c) Sizes larger than the incident wavelength 22. vi.

Page 5. Depolarization of the Scattered Light 24.

C. Polydisperse Suspensions 26»

V. INSTRUMENTATION 27.

A. Instrumentation in Previous Work 27.

(1) Transmission Method 27. (2) Scattering Method 29. B. Instrumentation in the Present Work 31. (1) Description of the Instrument 31. (2) Calibration of the Instrument 35.

VI. COLLECTION AND TREATMENT OF DATA 39•

VII. RESULTS 44.

A. Distribution of Turbidity in the Inlets 44* 1. Bute and Toba Inlets and Adjacent Channels (the Bute Inlet System) 44. Winter (February, 1958) 45. Summer (June, 1958) 47«, Late Spring (May, 1957) 50. Summer (July, 1957) 50. Summer (September, 1957) 51. Autumn (November, 1957) 52. Winter (March, 1958) 53.

2. Jervis Inlet 55e Winter (February, 1958) 55. Summer (June, 1958) 56. Late Spring (May, 1957) 57. Autumn (November, 1957) 58. vii

Page 3. Knight Inlet 59. Late Summer (September, 1957) 59• Early Summer (June, 1958) 60,

4. Loughborough Inlet 62. Late Summer (September, 1957) 62©

5. Call Creek 63. Late Summer (September, 1957) 63. B. The Nature of the Suspended Material In the Inlets 64. (a) Polar Diagrams of the Scattered Light 64. (b) Measurements of Depolarization 66. (c) Results of Size-Analysis of the Suspended Material 67. Size Range of the Suspended Material 67. Concentration of the Suspended Material 69. C. Calibration of the Photometer 71.

D. Present Rates of Sedimentation in the Inlets 74. E. The Relationship between Secchi Disc Readings and Turbidity 78.

VIII. DISCUSSION 79.

A. The Turbidity Distribution in the Inlets 79« 1. Sources of the Suspended Material 79. (a) Large-Runoff Inlets 79. (b) Small-Runoff Inlets 85. 2. The More Prominent Features of the Turbidity Distribution in the Inlets 87, (a) Vertical Stratification of Turbidity 87. Page

(b) Turbidity of the Main Water Mass in the Various Inlets and Channels ^ 88. (c) Isolated Turbidity Maxima Throughout the Entire Water

Column 92B (d) The Turbidity Maximum in the Deep Water 94. ( i) Tidal Currents 94. ( ii) Advective Intrusion of Deep Water 98. (iii) Turbidity Currents 104.

B» Characteristics of the Light-attenuating Material in the Inlets 110. C. Brief Evaluation of the Light-Scattering Method 117.

IX. SUMMARY AND CONCLUSIONS 118.

A. General Features of the Turbidity Distribution in Southern British Columbia Mainland Inlets 118.

Bo The Nature of the Light-Attenuating Material in Southern British Columbia Inlet Waters 119.

REFERENCES 123. IX

LIST OF TABLES

Table

I» Catalogue of the surveys during the period May, 1957 to June 1958*

II* Size of the material in suspension in Bute Inlet, and a comparison with suspended material present in other localities.

III. Relationships between the turbidity and the concentration of suspended material. x.

LIST OP FIGURES

Figure 1. Southern British Columbia Mainland Inlets,

2. Bute and Toba Inlets and Adjacent Channels. .3, Jervis Inlet. 4. Knight and Loughborough Inlets and Call Creek.

5. Effective Area Coefficient for Scattering -

Ks-as a Function of y = 2P(m -1), M = 1.15.

AM 6. Optical System of the American Instrument Company Light-scattering Photometer. 7. Butj Inlet, Sutil Channel. Distribution of Z (m~ ) in Longitudinal Section. February 1958. 8. Homfray Channel, Toba Inlet. Distribution of Z in Longitudinal Section, February, 1958, 9. Bute Inlet, Sutil Channel. Distribution of S (o/OO) in Longitudinal Section. February 1958. 10. Homfray Channel, Toba Inlet. Distribution of S (o/OO) in Longitudinal Section. February 1958. 11. Bute Inlet, Sutil Channel. Distribution of T ( C) in Longitudinal Section. February 1958.

12. Homfray Channel, Toba Inlet. Distribution of T ( C) in Longitudinal Section. February 1958,

13. Bute Inlet, Sutil Channel. Distribution of Density (

Density ( (tt) in Longitudinal Section. February 1958, 15. Bute Inlet, Sutil Channel. Distribution of Og (mg/liter) in Longitudinal Section. February 1958. xi.

Figure

16. Homfray Channel, Toba Inlet. Distribution of 0^ (mg/liter) in Longitudinal Section. February, 1958. 17. Bute Inlet, Sutil Channel. Distribution of Z (m""*) in Longitudinal Section. June, 1958.

18. Homfray Channel, Toba Inlet. Distribution of Z(wT^) in Longitudinal Section. June, 1958.

19. Bute Inlet, Sutil Channel. Distribution of S (o/OO) in Longitudinal Section. June, 1958. 20. Homfray Channel, Toba Inlet. Distribution of S (o/OO) in Longitudinal Section. June, 1958.

21. Bute Inlet, Sutil Channel. Distribution of T (°C) in Longitudinal Section. June, 1958.

22. Hgmfray Channel, Toba Inlet. Distribution of T ( C) in Longitudinal Section. June, 1958. 23. Bute Inlet, Sutil Channel. Distribution of Density

( 0~t) in Longitudinal Section, June, 1958. 24. Homfray Channel, Toba Inlet, Distribution of

Density (0~t) in Longitudinal Section, June, 1958.

25. Bute Inlet, Sutil Channel. Distribution of 02 (mg. /' liter) in Longitudinal Section. June, 1958. 26. Homfray Channel, Toba Inlet. Distribution of 0 (mg. / liter) in Longitudinal Section. June, 1958. 27. Bute Inlet. Distribution of Z(wT^) in Longitudinal Section. May, 1957»

28. Bute Inlet, Sutil Channel. Distribution of Z (m"1) in Longitudinal Section. July, 1957. 29. Homfray Channel. Distribution of £(m~*) in Longitudinal Section. July 1957. xii. Figure

30. Bute Inlet. Distribution of Z (nf^) in Longi• tudinal Section. September, 1957.

31. Homjray Channel, Toba Inlet. Distribution of Z (m~ ) in Longitudinal Section. September, 1957.

32. Bute Inlet, Sutil Channel. Distribution of Z (m~ ) in Longitudinal Section. November, 1957.

33. Homfray Channel. Distribution of Z (m""^) in Longitudinal Section. November, 1957.

34. Bute Inlet, Sutil Channel. Distribution of Z (m~ ) in Longitudinal Section. March, 1958.

35. Homfray Channel. Distribution of Z (m"~^) in Longitudinal Section. March, 1958.

36. Jervis Inlet. Distribution of Z (m-*) in Longi• tudinal Section. February, 1958.

37. Jervis Inlet. Distribution of S (o/OO) in Longi• tudinal Section. February, 1958.

38. Jervis Inlet. Distribution of T (°C) in Longi• tudinal Section. February, 1958.

39. Jervis Inlet. Distribution of Density (0~) in Longitudinal Section. February, 1958. *

40. Jervis Inlet. Distribution of 02 (mg/liter) in Longitudinal Section. February, 1958.

41. Jervis Inlet. Distribution of Z (m~^) in Longi• tudinal Section. June, 1958.

42. Jervis Inlet. Distribution of S (o/OO) in Longi• tudinal Section. June, 1958.

43. Jervis Inlet. Distribution of T (°C) in Longi• tudinal Section. June, 1958. xiii.

Figure

44. Jervis Inlet. Distribution of Density ( (Tt) in Longitudinal Section. June, 1958. 45. Jervis Inlet. Distribution of (mg/liter) in Longitudinal Section. June, 1958,

46. Jervis Inlet. Distribution of T(m ) in 47. LongitudinaJervis Inletl . SectionDistributio. May,n 1957of K. (m~^) in Longitudinal Section. November, 1957.

48. Knight Inlet. Longitudinal Distribution of Properties. September, 1957.

49. Loughborough Inlet. Longitudinal Distribution of Properties. September, 1957.

50. Call Creek. Longitudinal Distribution of Properties. September, 1957. 51. Polar Diagrams of the Scattering Exhibited by Inlet Waters. 52. Relationship between Turbidity and Weight-Concentra• tion. 53. Monthly Mean Discharge Values. Homathko River, May 1957-June 1958.

54. Seasonal Variation of Turbidity in Bute Inlet. May 1957-June, 1958. 1.

I. INTRODUCTION

In recent years, appreciable progress has been made in determining the circulation pattern in British Columbia inlets by means of direct measurements with current meters. Theoretical considerations of the dynamics of the circulation indicate that the currents in the deep water should generally be small, and what direct measurements have been made tend to confirm that such is actually the case. However, it requires considerable time and effort to obtain significant quantitative data at even a single "deep-water" location. Por a general qualitative description of circulation patterns, time-series studies of the classic oceanographic variables, such as salinity, temperature and dissolved oxygen content, are often useful. Lately another characteristic of natural waters, their light-attenuating property, has been found to be of great value in many phases of oceanographic and limnological research. In studies of water-mass movement, of mixing processes, and of phytoplankton productivity, to name but a few instances, light-attenuation measurements have not only provided new information but also aided in the corroboration of information obtained by other means. In view of the demonstrated value of such results, a time-series study of the light attenuation in the waters of a number of British Columbia inlets has been undertaken. The purposes of this study are threefold:

(1) To investigate the general features of the areal and seasonal distribution of the suspended material in the inlets. (2) To investigate the possibility of using the suspended and/or the dissolved material as a water charac• teristic to help determine the basic features both of the circulation in the deeper waters of the inlets and of the exchange between the inlets and the neighboring waters* (3) To discover to what extent the nature of the suspended material can be determined by measurement of light attenuating properties« This investigation forms a part of the detailed study of the mainland inlets which is being carried out by the Institute of Oceanography of the University of British Columbia, the study having been underway since 1951« The investigation was conducted, in main part, during the period from May 1957 to June 1958 inclusive. 3.

II. ORIGIN OP THE LIGHT-ATTENUATING MATERIAL FOUND IN NATURAL WATERS

The attenuation of light in natural waters (and more particularly for the purpose of this investigation, seawater) is produced by the water itself, by suspended material, and by dissolved material. The suspended and the dissolved material in the sea has many sources. Plant organisms (in particular, the phytoplankton) contribute a considerable proportion of the suspended particles in the upper, well-illuminated strata. The animal plankton (zooplankton) population can be present in varying density to very much greater depths. The presence of living matter is more marked in fertile coastal waters, especially during the spring and summer months. Both the organic, and inorganic remains of dead plankton (the former being termed detrital material or detritus) are present in varying quantity throughout the whole water column} the distribution is intimately connected to many factors, such as water temperature and both turbulent and advective motions of the water. The remains are present both in coastal water and in the deep ocean, although generally to a lesser degree in the latter. The minerogenic inorganic material in suspension in the sea is perhaps more diversified in origin. It may enter the sea in river or stream waters. Material can be brought into suspension by turbidity currents or as a result of bottom currents or possibly of the deeper internal waves. The absolute and relative effects of the last two agencies are, with few exceptions, unknown in the case of the deep oceans. Wind-blown terrigenous dust may, especially in regions where prolonged dry periods occur, contribute significantly to the inorganic material in suspension, A notable feature of many coastal waters is the dis• solved material known as "yellow substance" (Kalle 1938, 1949.i Jerlov, 1953). Its exact nature is still uncertain but the substance (or substances) are probably stable oxidation products of marine or terrestrial plant life (Strickland, 1958)? they absorb strongly in the blue and ultra-violet regions of the spectrum. The content of suspended and dissolved material, arising from many different sources, is of interest to all phases of marine science. The marine biologist, for example, is primarily interested in the content of the illuminated zone, as a measure of productivity; the physical oceano— grapher usually is concerned more with the distribution of material throughout the whole water column, as a possible means of characterizing both the extent of water masses and the features of their movements. 5.

III. THE BRITISH COLUMBIA MAINLAND INLETS

As previously mentioned, the British Columbia mainland inlets have been under study for several years. A general description of the basic oceanographic and morphological features of these inlets has been given by Pickard (1955, 1956). In Section A below is given a summary of the findings reported in those papers. The present study has been con* centrated on several inlets of the southern coast, namely Bute, Jervis, Knight, Loughborough, and Call Creek. The general locale of these inlets is depicted in Eig.l. More detailed descriptions of the individual inlets follow in Section B.

A. Basic Oceanographic and Morphological Features

The mainland inlets are elongated indentations of the coastline lying substantially transverse to that coastline. They range in length from about 4 to about 60 (nautical) miles. They open to the sea at their western end and generally have rivers at the other. They possess steep- sided basins of appreciable depth; the average mid-channel depth is about 330 metres (180 fathoms), while the greatest sounding recorded is about 730 metres (400 fathoms). The inlets, presumably formed by both glacial action and by structural changes in the earth's crust, resemble closely the Norwegian fiords; the most striking dissimilarity is the presence in the latter of very shallow sills of only about 4 metres depth, near the mouth (Sverdrup, Johnson and Fleming, 1942; p. 1028). Such extreme sills are not. present in the major mainland inlets of.British Columbia, and are possessed by only a few of the minor ones. The shallowest "major inlet sill" is about 30 metres (17 fathoms), while most are over 200 metres (110 fathoms). Thus the deeper 6. water in most major inlets has free communication with the coastal waters, although in all cases the depth between the deep inlet basins and the open ocean decreases to less than 180 metres (100 fathoms). The majority of the inlets, especially those having a large river at the head, possess a main basin that is relatively flat and level and is composed of mud. The bottom deposits are usually grey in colour; their predominant components appear to be quartz, potash and soda-lime feld• spars, and mica (Toombs, 1956). Some inlets, however, (for example, Jervis) possess an extremely irregular basin floor. Oceanographically the inlets can be classified as estuaries since they contain fresh water measurably diluted by sea water (Pritchard, 1952). They are, by definition, "positive" in the sense that precipitation and fresh-water drainage exceed evaporation. The fresh water entering the inlets overrides the heavier salt water and flows seaward, entraining salt water from below as it does so; superposed upon this flow are the effects of wind and of the recipro• cating tidal currents. The net motion in the upper layer, however, is toward the inlet mouth. This layer, the so- called "shallow zone", has a depth of from 4 to 13 metres* Below this zone, there is a slower, net up-inlet, flow to compensate for the loss of salt water by entrainment. The depths to which this flow occurs, and whether it is unidirectional at all depths of occurrence, has not yet been determined with certainty; however, it too appears to be influenced, in some degree at least, by the tidal currents (Bodgers, 1958). 7.

As will be noted, even the shallowest sill depths found in the inlets are considerably greater than the depth of the shallow zone; as a result stagnant conditions, such as are found in many Norwegian fiords, are uncommon in British Columbia inlets* On the basis of salinity distribution, the inlets can be divided into two groups, those with a large river discharge at the head during the spring and summer run-off period, and those with a small discharge* The distinction between the two groups is most marked in the shallow zone. In the first class, typified by Bute Inlet, the surface water at the inlet head is substantially fresh during the run-off period. Below the upper 2 to 9 metres there appears a transition zone of about 6 to 9 metres depth (the halo— cline), in which the salinity increases rapidly* The halocline becomes less apparent toward the inlet mouth. The surface salinity values at the mouth correspond approximately to the surface salinities of the surrounding coastal waters* In the.second group, typified by Jervis"Inlet, the surface salinity at the head is much greater during the run-off period than in the first group; also, the change in salinity at the halocline is nowhere as sharp* During the period of minimum run-off, the halocline becomes much less marked in both groups of inlets. The deeper water of both types exhibits a slow monotonic increase of salinity with depth in all seasons. During the summer months, the surface water in the inlets is usually the warmest, and the brackish layer is nearly isothermal. The temperature increases from head to mouth, as a result of absorption of heat from sun and atmosphere. Below the brackish layer occurs a rapid decrease 8. in temperature within a short depth (the thermocline); the temperature then usually decreases slowly with depth until a minimum is reached at about 60-90 metres depth. This minimum gradually dissipates, and has usually become imperceptible by the following winter. This minimum temperature layer is apparently winter-cooled water which either has sunk or has been overrun by warmer water in the following spring and summer. The conditions thus indicate that seasonal warming and cooling penetrate only to a depth of about 100 metres. In the winter, the surface water is the coldest in the water column; the temperature decreases from head to mouth indicative of a net loss of heat to the atmosphere. The temperature increases with depth to a maximum at about 100 metres? it then usually decreases gradually to the bottom," although at times there may be a slight increase. In contrast to many open ocean areas, temperature plays only a minor part in the density distribution in the inlets. Therefore, during most of the year the density is, to a good degree of approximation, directly determined by the salinity.

B. Features of the Individual Inlets Involved in the Study

a) Bute and Toba Inlets and adjacent channels The features of this region are shown in Fig. 2. Bute Inlet proper is about 40 (nautical) miles in length, averages about 2 miles in width, and is sinuous in plan form. It possesses a deep sill (about 340 metres) at its mouth; its greatest depth (about 670 metres) is located about 10 miles from the mouth. The inlet communicates 9. with the waters of Cordero Channel through both Xuculta Rapids and Arran Rapids* It is connected to the Strait of Georgia, through Calm Channel, by two approaches: Sutil Channel (the more direct) and Pryce-to-Homfray Channels (hereafter referred to as Homfray Channel). Homfray is also in contact with Toba Inlet, which is about 20 miles in length. Communication at depth between Homfray and the Strait of Georgia is restricted to Baker Passage (of depth about 135 metres) and the passage (of depth about 85 metres) between Savary Island and the mainland* Two rivers drain into the head of Bute Inlet, the Homathko from the north, and the much smaller Southgate from the east* Midway along the inlet a river, of modest 1 size, the Oxford, enters the inlet. Three rivers drain into the head of Toba Inlet, none of these, however, being as large as the Homathko. b) Jervis Inlet Jervis (Fig. 3), a major inlet of the "low- runoff" type, is about 40 miles in length, averages about 1.5 miles in width and is extremely sinuous in plan form* The waters of the inlet are in contact with those of the Strait of Georgia, both through a main channel and through the narrower Agamemnon Channel, the two passages being separated by Nelson Island. The latter channel, averaging about 0.5 mile in width, varies in depth from about 35 to 250 metres. At the entrance to the main channel a broad sili of depth about 300 metres is present. Along most of the inlet the depth is generally between about 500 and 600 metres, the bottom contour being extremely irregular. The maximum depth, about 730 metres, is located about 8 miles from the main entrance. About 10 miles from the head, another sill is present; it is about 250 metres deep compared with the depths of about 350 and 500 metres occurring at its inner and outer sides respectively. Inside this sill the 10. bottom is much more level, both in longitudinal and in transverse section, than in the rest of the inlet* A river of modest size, the Skwawka, enters the inlet at the head, and a comparable one, the Deserted, enters about 12 miles from the head. No quantitative measurements of flow, are available. Numerous small streams discharge into the inlet along its length. Two smaller inlets, Sechelt and Princess Louisa, connect with Jervis; the larger, Sechelt (about 20 miles long), has its entrance about 12 miles from the mouth of Jervis, while Princess Louisa (about 5 miles long) is located about 6 miles from the head. Both possess very- shallow entrance sills. c) Knight Inlet This inlet (Fig* 4) is about 55 miles long and has an average width of about 1.5 miles. It is connected with Queen Charlotte Strait both through a main channel and through Tribune Channel. The outer half of the inlet is straight, and the inner half sinuous, in plan form. The aver-» age mid-inlet depth is about 420 metres, and the maximum depth is about 550 metres. The inlet possesses two sills; the outer one, about 70 metres deep,is about 59 nautical miles from the head, the inner one, about 65 metres deep, about 40 miles from the head. The outer basin between the two sills possesses an irregular bottom topography but does not exceed about 200 metres in depth. The bottom in the inner basin (between the inner sill and the head) is more regular in nature. The fresh water is supplied largely by runoff from the Klinakini River situated at the head; this river is apparently comparable in size to the Homathko. 11.

d) Loughborough Inlet Loughborough (Pig. 4) is about 18 miles in length and averages about 0.9 miles in width. It connects with Johnstone Strait through Chancellor Channel. In the inlet the bottom slopes down from the mouth (where there is a sill having a depth of 110 metres); the greatest depth about 240 metres, occurs midway along the inlet. It is believed that a deep sill (~140 metres) exists near the head. Two small rivers enter the inlet at the head. e) Call Creek Call Creek (Fig. 4) is about 11 miles long and averages 0.8 miles in width. The inlet possesses an entrance sill having a depth of about 35 metres; the greatest depth, about 225 metres, occurs near the head. The inlet is straight and possesses no significant year- round river runoff at the head. 12.

IV. SUMMARY OF THE THEORY OF THE ATTENUATION OF LIGHT IN MATERIAL MEDIA

The results of a study such as the present one primarily involve:; the optical effects produced by suspensions of material in natural waters. It is the object in this section both to bring together and to discuss briefly the salient relationships which could be needed in the evalua• tion of such results. As these relationships are scattered throughout the literature, it was deemed justifiable to consolidate them for more easy reference during the course of this work.

A. The Definition of Turbidity

The attenuation of light in natural waters can as in all material media, be described by means of the Bouguer-Lambert Law. This law states that when a parallel beam of monochromatic light passes through any isotropic medium, the incident intensity is decreased according to the relation:

I (1) where: the incident energy per unit projected area per unit time I the energy per unit projected area per unit time of the light after it has traversed a distance 1_ in .the medium e the base of natural logarithms = 2.71828... 2 a constant having the dimensions of reciprocal length T ( Z SL) = a dimensibnless quantity referred to as the optical thickness.

In the general ease, two processes are instrumental in 13. diminishing the incident light intensity. One is that of absorption, in which the light energy as such actually disappears, undergoing conversion into heat or chemical energy in the material. The other, that of scattering,, occurs because of the presence of inhomogenieties in the medium. (in the case of particles suspended in a liquid, for example, scattering will arise both because of the inhomogenieties represented by the particles themselves, and, usually to a much lesser degree, because of the effect of random statistical fluctuations in the density of the liquid.) In the scattering process, the oscillating electric field associated with the incident radiation can be con• sidered as producing forced vibrations of the electric charges constituting the medium; the vibrating charges then radiate secondary waves. As a rule, this secondary radiation, the scattered light, is of the same frequency as the incident light. (Such processes as fluorescence or Raman scattering, which involve a frequency change between incident and scattered radiation, will not be considered here.) In the general case, the constant Z' of equation (1) is termed the attenuation coefficient. If the suspending medium is a liquid, X' signifies the loss in intensity-* from a parallel beam-due to absorption and scattering by both the suspended and the dissolved material, and also by the medium itself. The turbidity (denoted hereafter by Z ) will in this thesis denote the effect due to suspended material only, this effect being the characteristic with which this study will be most concerned. The dimensionless quantity T = Z'/ (or ZJ) is termed the optical thickness of the material. 14.

B. The Mie Theory x

(1) Underlying Assumptions The most general theoretical treatment of the processes effecting the attenuation of light utilizes electromagnetic field theory and was first presented in a comprehensive form in this century (Mie, 1908).. The theory treats the case of a spherical particle, of any size and optical properties, immersed in a medium effectively infinite in extent. The major assumptions underlying the Mie theory are the following: (i) The optical properties of the sphere are assumed completely specified by the relative refractive index m , defined as the ratio of the real or complex index of refraction of the particle to the real refractive index of the surrounding medium. The complex index takes into account absorption by the sphere and is usually written:

m = n(l-ik) where: n = the real relative refractive index i = J-l k = K "X = the absorption index 4 T K = the absorption coefficient of wave-length in the material of the sphere; it has the dimensions of a reciprocal length. (ii) The theory considers a single particle only; because of this limitation two effects are disregarded. The first of these is coherence in the scattering by a number of spheres. Estimates have shown that in practice such coherence can be neglected in a suspension if the mutual distance of the scattering particles (spheres) is about 3 times the radius of the spheres. The effect will then be one of independent scattering (Van de Hulst, 1957; page 5). 15.

The theory also presupposes that multiple scattering can be disregarded. This fact implies that every particle of the suspension is illuminated only by the incident radiation, and not by radiation scattered by other particles, (Multiple scattering, however, need not vitiate the condition of independent scattering.) A sensitive criterion for the presence of multiple scattering has been given by Van de Hulst, 1957$ p. 6) and involves the optical thickness T. For T < 0.1, single scattering only prevails, for 0.1< T< 0.3, a correction for double scattering may be necessary, and for T > 0.3 the complete theory of multiple scattering must be applied. The mathematical theory of this scattering ("radiative transfer" theory) is extremely involved, however, and will not be discussed here. (iii) Both the particle and the embedding medium are assumed to be homogeneous and isotropic. (iv) Both the light source and the "observer" are assumed positioned, effectively at infinite distances from the scattering particle. Under these assumptions, the theory reduces to the mathe• matical problem of solving the Maxwell field equations with the appropriate boundary conditions. The total radiation field due to the scattering sphere is represented by the effect of an infinite series of electric and magnetic multipoles (dipoles, quadrupoles, etc.) having the centre of the sphere as their origin. Solutions for the amplitudes and phases of the contributions of the various multipoles can be derived explicit^ (Born, 1933; Stratton, 1941). (2) General Results The results of the Mie theory are usually expressed in terms of the "effective area coefficient" K. This is defined, for a single particle, as the ratio of the energy absorbed by, and scattered by, the particle per unit time to the energy geometrically incident on the particle per unit time. K is thus a dimensionless quantity. Gorrespondingly, partial extinction coefficients K and K £L S can be designated for the separate processes of absorption and scattering respectively. For a uniform dilute suspension of N identical spheres per unit volume, each having a projected area A:

Z = NAK + Zv = NA(Kg + Ka) + Zv (2) Zj> referring to the effect of any dissolved material but not, by definition, to that of the suspending medium itself. If the suspension contains particles of more than one size and/or material, Z will involve the sum of the products K^ • A^ • N^, suitably weighted, for each size and material present, the size-frequency distribution of the particles being assumed known. The values of the effective area coefficients obtained from the general Mie theory are exceedingly complicated functions of the relative refractive index in and the dimensionless parameter «< = where D is the particle

diameter and AM is the wave length of the incident light in the suspending medium. The applicability of these functions to various particle sizes is often expressed in terms of another dimensionless parameter T = —r—*— ' — 2 representing the phase lag suffered by a light wave passing along a diametral path of the sphere. As will be discussed more fully later, measurement of the intensity of the light scattered at one angle with, or at a series of angles with, the direction of the incident light are at times very informative in light attenuation measurements. The angular scattering 1(e) of a single particle is defined as the ratio of the energy scattered per unit solid angle in the direction 0 per unit time, to the energy gemetrically incident ran that particle, per unit time. The angle 9 is henceforth taken with respect to the 17. forward diredbliioo, i.e. the direction of travel of the incident light. Like the effective area coefficient K, the angular scattering is a dimensionless quantity. It also varies with 81 and <* , generally in an even more complicated manner than do the K*s. The integral of 1(9) over all Q will give the total scattering by a particle. The scattering due to a suspension is sometimes termed the Tyndall Effect, after the physicist who first intensively studied the pheno• menon (1869). Evaluation of 1(0) and the various K*s becomes extremely tedious for particles as large as, or larger than, the wavelength of the incident light. Needed here are the terms of the Mie series solution which involve the multipoles of higher order. Only in recent years, with the advent of high-speed computers, has the exact calculation; of useful numbers of such terms become feasible. Por example, calculations permitting the determination of diagrams of polar scattering ( I[Q) vs © ) for the simplest possible case (that of non-absorbing spheres) have upto 1958, been completed only for oi. 4 40, corresponding in the maximum case to a sphere diameter of about 5for visible light in water (Pangonis, Heller e,nd Jacobsen, 1957). In view of such complexities, only particles exhibiting pure scattering will be considered further. The justification for this action, as regards the present study, will be discussed on page 19 • The Mie theory, as also previously noted, applies only to suspended particles that are spherical in form; however, those occurring in natural suspensions are generally both non-spherical and <|uite.r varied in shape. The theory of non-spherical scatterers has been discussed, in terms of electromagnetic field theory, for relatively few cases (v.,e.g., Van de Hulst, 1957,; Chapters 15 and 16), However, both 18.

Van de Hulst and Penndorf (1953) indicate that for values of the relative refractive index U less than about 1.5, the results of the Mie theory can be applied to non-spherical material without appreciable error. (3) General Features of the Scattering from Non-Absorbing Material (M real). The theory indicates that, in the general case, the scattering from non-absorbing spherical particles consists of two parts, one due to reflection and refraction, and another due to diffraction. In the case of the first part, both the angular distribution of, and the state of polarization of, the scattered light are greatly dependent upon the composition and size of the scattering particle, and also upon the nature of its surface. On the other hand, the angular distribution.of the intensity arising from diffraction effects is independent of the composition and nature of the scatterer. The diff• raction light is unchanged, in state of polarization, with respect to the incident light, and the diffraction pattern is independent of the incident polarization. This portion of the scattering arises from the effect of the incomplete wavefront, which is represented by the original wavefront minus the area defined by the geometric shadow of the particle. As both source and viewer are, in all practical cases, effectively at an infinite distance from the scatterer, only plane wavefronts are considered and therefore only Fraunhofer diffraction is involved. The significant effect of diffraction is restricted to a narrow cone in the directly forward direction. The angular width of this cone is that of the first Fraunhofer maximum, this maximum becoming increasingly narrow as the particle size increases with respect to the incident wavelength XM . The salient results of the Mie theory for a spherical particle exhibiting scattering only are depicted in Fig. 5.

Here the effective area coefficient per particle, Kg, is plotted against the dimensionless "phase-shift" parameter T = 2 TTP(tf-1), where D is the particle diameter* The ~W - relative refractive index ni is taken to be 1.15, this value being representative of the particulate material most commonly encountered in suspensions in natural waters. It is possessed both by most material of minerogenic origin and by protein, the primary constituent of organic matter (Oster, 1948j p. 331). Since in differs but little from i, this curve depicts, without appreciable error, the scattering for non-spherical particles also (pagel8 )• (The size of a non-spherical particle will be considered represented by the greatest dimension of the particle.) The relationship depicted in Fig. 5 can be expressed by the following equation (Van de Hulst, 1957j p. 176)

Ks = 2 " I sin T + ^2 (1-cosT) (3)

Equation (3) is valid not only forjM close to i (in either the positive or negative sense) but also for values of M as large as 2. The successive maxima (the "Mie maxima") of Fig. 5 arise from constructive interference of the trans• mitted (refracted) and the diffracted light, the minima ("Mie minima"), from destructive interference* (4) Details of the Scattering Exhibited by (Non-Absorbing) Particles of Various Sizes For the case of isotropic particles, one can present the more prominent features of the scattering exhibited by monodisperse suspensions. Such suspensions will be composed effectively of particles of a single size* (The effect due to the suspending medium itself will be 20. neglected; thus the total scattering will, by definition, represent the turbidity.) Three general particle sizee ranges will be considered: those encompassing, respectively, sizes very much smaller than-, about equal to, and larger than, the wavelength of the incident light. (a) Sizes very much smaller than the inci• dent wavelength. In this case, the scattered intensity at any angle Q to the forward direction is given by:

3 2 1(6) = B1C0) (l+cos 9 ) (4)' where: C = the concentration of the suspended material D = the common diameter of the particles (less than about AM in this case.) 10 = a factor involving the optical properties of the material (i.e. the relative refractive index D_);

it varies only slightly with the wavelength XM and will be treated here as a constant.

AM = the wavelength of the incident light in the suspending medium. By integration over all 9 we obtain the total scattering due to the particles (i.e. the turbidity Z ):

3 > = B0CP

AM %2 being another constant. In (4) the two terms in parenthesis refer to the two plane-polarized components of the scattered light, the first to the vertically polarized component and the second to the horizontally polarized component. (Light will hereafter be considered horizontally polarized when the electric vector vibrates in the plane defined by the source, the scattering 21. centre, and the point of observation. Vertically polarized light will have its electric vector vibrating perpendicu• larly to this plane.) The scattering is seen both to be isotropic about the perpendicular to the forward direction ( 0 = TC_) and to be completely plane-polarized at that 2 position. Equations (4) and (5) present the salient features of the scattering law first enunciated by Lord Rayleigh (e.g. 1881) and reveal the strong, (inverse fourth—power) dependence of the scattering on the incident wavelength. The range of validity of the Rayleigh law is given in Fig.

5 by the portion of the Kg - T curve very near the origin. In this case, separation of the scattered light into refracted, reflected and diffracted components has little physical significance. The law may be noted, holds also for a polydisperse suspension (one containing more than one particle size) provided that all sizes are < AMj it is also valid To" for values of frf that are large, provided that the condition BkTTJ) *- 0 is satisfied. *M (b) Sizes about equal to the incident wave• length. For a dilute suspension of particles of size larger than "Rayleigh" particles but not much greater than the incident wavelength, the following expression for

the total scattering 4 (turbidity) is found to be valid: I = B3D = B4CD (6) AM2 AM2 and B^ are again optical constants, and the other symbols are as in (4) and (5). For a given concentration, (6) shows that the scattering at any wavelength increases linearly with the particle diameter. This condition holds (theoretically) up to a maximum value of the diameter and is represented in Fig. 5 by the linear portion of the 22.

K - Y curve preceding the "first Mie maximum". The high S scattering at this maximum occurs for particles of diameter about 4 times the incident wavelength (i.e.. for Y = 2 and M = 1*15, D « 4 AM). Beyond this maximum the total scattering will (for a fixed wavelength) decrease over a considerable range of increase in the particle size. (c) Sizes larger than the incident wavelength For even larger values of Y it is seen that Kg passes through succeeding maxima and minima and approaches (in an oscillatory fashion) the value 2« Thus, for a particle large compared to the incident wavelength, the total scattering is effectively constant, and is twice that expected from a particle of the given (projected) geometrical area* For a dilute suspension of such large scatterers, the turbidity should therefore be linear with respect to the total surface of the suspended material or, linear with respect to concentration and inversely proportional to the scattering particle size. Therefore, for a monodisperse suspension of N particles per unit volume,

2 I = BgND = B6C/p (7)

B^ and Bg are again optical constants of the suspended material. The validity of (7) has been established for monodisperse suspensions of minerdgenic material in water- in *» 1.15- by-Jerfev and Kullenberg (1953). The relationship has also, on the basis of field studies byJ.er]ow (1951, 1953a, 1953b, 1955), assumed considerable importance in oceanographic studies. In the case of large scatterers, the portion of the scattering due to refraction and/or reflection, and that due to diffraction, can be sharply differentiated. 23.

Por large non-absorbing transparent particles (having ^ close to 1) the non-diffractive portion of the scattering . will be due mainly to light that has undergone two refractions in the scattering particle. This light will form a forward- directed lobe ( 9<5), which will be narrower the nearer M is to 1 . It may be noted that the maximum deviation for scattering by refraction, involving no internal reflections in the material is, for quartz (_l«1.15)j about 60°. To obtain the total scattering pattern the portion due to diffraction must be added. Por large particles having M near i , the polarization of the scattered light will not be complete at 6 B % as is the case for Rayleigh scattering. A marked polarization maximum (i.e. a scattering minimum) will still, however, be present in the general case, but it will be shifted into the backward direction ( 0 >IT). z For large non-absorbing- material having W not only real but much larger than 1 , the non-diffracted part of the scattering will be effectively "total reflection". Two " cases for such reflection can be characterized. If the . particle is spherical and smooth, the reflection will be specular in nature. In this case the scattering will be isotropic in direction. Natural incident light will give natural scattered light. These conditions hold also for all non-spherical scatters that are convex in form and are randomly oriented. The concept of whiteness in which the reflection is total, but diffuse rather than specular, is, of course, relevant only for the case of a "large" particle. Here, the surface brightness is the same in all directions, irrespective of the direction in which the particle is illu• minated. The light scattered by reflection is unpolarized, regardless of the incident polarization. 24.

Thus in general the characteristics of the scattering pattern for large non-absorbing particles consist of a very strong, directly-forward component due to diffrac• tion, and a less intense radiation, into all directions, due to refraction or reflection* (5) Depolarization of the Scattered light As previously noted, the polarization characteristics of the scattered light vary not only with size of the scattering particle, but also with its optical nature* In the case of a suspension, there can also be a dependence of the polarization in the concen• tration of the suspended material; this, however, will be ignored in this study, for the reasons given on page 112. It is known that most materials commonly encountered in natural suspensions are anisotropic in nature* Theory indicates that the polarization characteristics of the scattered light can be used to describe qualitatively the size and nature of the scattering material. The method most generally employed involves the determination of the depolarization. This quantity is, in effect, a measurement of the deviation, from complete polarization, of the light scattered at 6 = . For unpolarized (u) incident light, the depolarization is defined by:

pu = Hu where Hu represents the horizontally ' Vu polarized component scattered at 0= ^— and Vu the corres• ponding vertically polarized component* (The definitions of horizontal and of vertical polarization adopted here were given on page 20). Corresponding definitions for vertically (v) and horizontally (h) polarized incident light are given, by = and ph = gjj respectively. the "inversion" occurring in the last definition should be noted. It is seen that P ii is also equal to Hh + Hv. 1 Vh + Vv 25. The following general relationships (Oster, 1948j pp. 345^.346) are found to hold true for a suspension in which multiple scattering is negligible: (a) For small isotropic particles: pv — o, = 1 and ^>u =0. (b) For small anisotropic particles pv o, ph = 1 and p\i £ 0. (8) (c) For large isotropic particles: = o, ph = 0 and p\x = 1. (d) For large anisotropic particles: r t o, * 0 and pu +.0* In all four cases, Hv = Vh. Thus, by determination of the various p's, a qualitative measure both of the size of, and of the nature of, the suspended material can in theory be quickly obtained. If the suspended particles are randomly oriented . and (".l their number is large (but not large enough to bring about multiple scattering) a relationship of the following form exists between the various depolarization ratios: 1 pu = 1 + /?H (9)

1 +k By this relationship, the third ratio can be obtained if the other two are known; a check can also be made, by this equation, for internal consistency if all three have been obtained. It may also be noted that a simple check for multiple scattering exists,involving the P's. large (relative) values of pu and pv, and a small value of ph, occur if multiple scattering is present, irres• pective of the size, shape or degree of anisotropy of the suspended material. 26.

G. Polydispefse Suspensions . Thus far, in general only monodisperse sus• pensions have been discussed; however, only polydisperse suspensions occur in nature. Various researchers (v. Axford et al; 1948) have confirmed the important fact that the size-frequency distribution of particles in polydisperse systems of fine sediments, dusts and smokes can be represented in general by the log-normal relation• ship, given by:

n = N exp ( -(logP-log *>o )2) (10) ( 2 log*

log 0j = J 2(n(logJ>- log Dj)2 ) = log-goimetrie standard deviation; this gives a measure of the dispersion about the mean. (In particular, such a curve will usually describe a dispersion of inorganic material obtained from such processes as milling, grinding or crushing.) In conclusion, it may be noted that Burt (1956) has prepared a very useful light-scattering diagram. In it, the effective area coefficient for scattering K s can be readily obtained as a function of the quantities

J) m and XM* The range of these quantities encompasses the values possessed by the preponderance of the parti• culate material in suspension in natural waters. 27. V. INSTRUMENTATION

A. Instrumentation in Previous Work

The light attenuation of natural waters can be measured by the use of either daylight or artificial light. The former type of illumination has several basic disad• vantages. Its use is restricted, especially in oceano• graphic work, both to daytime and to exceedingly favorable weather conditions. Also in the more turbid waters, obser• vations can be made to minor depths only. In oceanographic investigations, therefore, preference should be given to attenuation measurements involving artificial light, 1, Transmission Method The most direct method of measuring light attenuation is by the determination of the quantities IQ I and £ of Equation (l), and the application of this equation to find X • Measurements on natural waters by this "transmission" method are of either the in situ or the in vitro type. The former type involves an instrument which is used in the water itself. One form, the generically-termed "transparency meter" consists essentially of a light source and a detector (each enclosed in a water-tight container) held a fixed distance apart. This intervening distance, ranging from about } to 2 meters, in the various forms of the instrument so far constructed, represents the path length This type of meter wa$ pioneered by Pettersson (1934); recently, more refined versions have been constructed and utilized (Pukuda et aL, 1954, 1958; Jones and.Wills, 1956j Sasaki et al, 1958; and others listed by Strickland, 1958.) With such an instrument, one can make a fairly detailed study of the continuous change of attenuation with depth and thus detect any microstratification tha^ might be present. 28. If absolute, rather than relative, turbidity values are desired, the instrument must be calibrated by some means. This type of apparatus does not permit the possibility of distinguishing between the effect of the suspended material and that of the water itself. Also, the problems always present in the handling of submerged equipment have, so far, generally limited the operation of this form of instrument to depths of less than about 100 meters; however, a con• tinuously-recording apparatus, giving simultaneous readings of transparency and temperature, has been used down to 200 meters and shows promise of use at even greater depths (Joseph, 1955). The in vitro type of transmission measurement was first utilized extensively during the study of selective absorption by lake waters (James and Birge, 1938). The technique involves a laboratory determination of the attenuation, light passing through a sample contained in a cell of known dimensions (path length). James and Birge analyzed the transmitted light by means of a prism. More recently, the Beckman Model DU Quartz Prism Spectrophotometer has been adapted for shipboard laboratory use; this instrument, Which provides a continuous measure• ment of attenuation over the entire visible spectrum, has been utilized both in coastal waters (Burt, 1952, 1953, 1955a, 1955b) and in tropical ocean waters (Burt, 1958)* The transmission-type measurement possesses one major inherent disadvantage. It cannot be used with confidence in the case of very feebly attenuating systems, involving small values of Z , because Equation (l) reduces in this instance to:

z * - T> upon series expansion of the exponential term. Thus the medium under study must be turbid enough so that incident and transmitted intensities differ by an amount large enough 29. for the numerator in the above expression to be determined accurately; the effect of instrumental fluctuations may prevent such accuracy from being obtained, and may even, in extreme cases, prevent significant readings from being obtained at all. Another inherent disadvantage of the transmission- type measurement involves the fact that no presently—known type of light-measuring device can measure the intensity of only the undisturbed portion of the incident light, to the complete exclusion of the forward-scattered radiation* This latter effect will be most marked for the case of large particles in suspension; here the energy which is scattered by diffraction is concentrated within a relatively small cone in the forward direction and for a dilute solution, will make the turbidity value recorded too low* Jones and Wills (1956) have given a mathematical treatment which provides a measure of the factor necessary to correct for the effect of the forward^scattered light* They cal• culated that the reading of transmitted intensity obtained with their instrument was about 1.3 times larger than the true valuej they believed that the error in this factor would be unlikely to exceed + 20fo if the material in: suspension was 5or greater in size. 2. Scattering Method The second major method of determing the turbidity involves the measurement of the intensity of light scattered at an angle away from the forward direction. Calibration of such an instrument involves relating the value of this intensity to that of the total scattering (the turbidity). Here the disadvantages inherent in the transmission-type measurement are to a large extent overcome. For accurate work, an in vitro method is again indicated* 30. The same limitations as previously mentioned (page 28 ) apply to the use of submerged equipment. Recently, however, a submersible light-scattering "bathy-photometer" has been used at depths as great as 1000 meters (iKetchum and Shonting; 1958). This instrument incorporates a photomultiplier tube as a detector (page 32)j the scattering at 90° to the incident beam is used as a measure of the turbidity. The light source is "chopped", to permit more easy differentia• tion between the light scattered by the material in sus• pension and the light from other sources such as biolumin- escence. A continuous recording of turbidity with depth has not yet proved feasible, however. The major work utilizing the"scattering method" of turbidity measurements has been accomplished by Jerlov (1951, 1953, 1955). In the original studies (on the extent and motion of water masses in the equatorial regions) a Pulfrich photometer was utilized to measure visually the scattering, at 45° to the forward direction, of the light from a carbon arc. In later investigations, a photomul• tiplier tube was used to increase the sensitivity of the method. Each 45° scattering value obtained was related to the corresponding total scattering (and, it was assumed, to the turbidity) by the experimental demonstration that the ratio of the two values was effectively a constant for all readings, at any wavelength. Atkins and Poole (1952) have constructed an apparatus by which the angular distribution of scattering between 9 (nearly) = 0° (the forward direction) and 0 s* 150° could be determined. It consisted, in part, of .a photomultiplier tube which could be moved,in a horizontal plane, about the sample cell, through the above-mentioned angular range. A spherical sample cell was used, in order to mini• mize instrumental errors arising from refraction effects in the cell (page 34). Such an instrument has a distinct 31. advantage over a "one-angle scattering" apparatus. The polar diagrams of scattered intensity obtainable can usually be used to provide a qualitative indication of the size of particulate material in suspension.

B. Instrumentation in the Present Work

(l) Description of the Instrument The apparatus employed in the present study is a commercially produced light-scattering photometer. * The instrument is based on that described by Oster (1953) and is similar in nature (for the case of scattering measure• ments) to that employed by Atkins and Poole (1952). With it the intensity of angular scattering from nearly 0° to 150° (with respect to the forward direction) can be deter• mined. The apparatus is rugged, compact (26x10x12 inches high), and relatively light (50 lbs.); thus it can be easily handled and transported. The details of the optical system of the photometer are shown in Pig. 6. Preliminary tests conducted at sea (after a few minor troubles in the circuitry had been overcome) confirmed the suitability of the instrument for shipboard use. The photometer possesses the following essential elements: (a) a system for producing a parallel beam of monochromatic light, (b) a sensitive light detector, and (c) a sample cell. As the scattered light from very clear natural water can be of an exceedingly low level of intensity, a powerful source of illumination is desirable for general work. High or medium pressure mercury arcs are the most commonly used, sources, since much of their very intense output is con• centrated in the blue, yellow, and green spectral lines, which can be easi.iy isolated by filters. The present source is a General Electric AH4 125-watt medium pressure mercury

* Manufactured by the American Instrument Company, Inc., Silver Spring, Maryland, U.S.A. 32. lamp., which takes about 10 minutes to reach maximum in• tensity. It is provided with a ballast transformer which allows for alterations in current for starting the lamp and also aids in the stabilization of the lamp output; -this output was found to vary by not more than 2$ during the greatest line voltage fluctuations (+ 10$) encountered in this study. The light from the lamp is rich in the following spectral lines: 3650 A° (Near ultra-violet), 4050 A° (violet), 4360 A° (blue), 5460 A (green) and 5780 A° (yellow), (Note: 1 A° = 1 Angstrom Unit = lO"-^ meter = 10""^/t .) These lines are isolated by means of the. appropriate glass filters. The requirement that the incident light beam should be parallel is met by the use of a lens and a series of slits. The narrowness of the incident beam used (1 mm.) permits the measurement of scattering (effectively undisturbed by the effect of transmitted light) down to very small angles from the forward direction; it also permits a better definition of the scattering volume. The detector is a nine-stage photomultiplier tube, examples being RCA Type 931A or Type 1P21. These types have cesium- oxide sensitive surfaces and employ up to 100 volts per stage. Their maximum sensitivity is in the blue-violet region of the spectrum, being about 1/10 that of the dark adapted eye. The photomultiplier voltage is supplied, from a stabilized source, through a chain of highly stable resistors. The output current is, in the present form of the instrument, amplified with an electrometer tube and recorded on a microammeter, The response of the photo• multiplier is linear with light intensity over the entire range of sensitivity of the instrument. This linearity was confirmed by comparison of readings obtained for various combinations of neutral density filters placed in the 33. incident light beam. The sensitivity can be varied over a 10,000-fold range accurately in steps of ten. On the least sensitive scale, full meter deflection occurs for a 10-microammeter photomultiplier current, A neutral filter of density -4- is automatically moved into position to protect the photomultiplier from high intensities at or near the forward direction; this filter can be removed or other filters added, as the necessity arises. The detector is also view-collimated by a series of slits. Both the detector and the sample cell are positioned in a light- tight chamber which is lined with black rayon flocking to absorb any stray reflected light. Two main types of sample cell have been used with this instrument, one rectangular, of path length 2,4. cms., the other cylindrical, of diametral path length 4*0 cms. The latter cell has been utilized more extensively in the present work, with it, light scattered at any angle in the horizontal plane is effectively perpendicular to the cell face, the narrowness of the beam used minimizing distortion arising from the curvature of the cell faces. This condition con• siderably simplifies the calculation of reflection effects at those faces. The meter-drift and dark-current charac• teristics of the apparatus are excellent. In addition, any reading arising from meter drift, dark current, or fluctuations in the incident light, can be zeroed out before each reading of scattered intensity is made. Any dark current increase arising from the humidity of the surround• ings can quickly be rendered negligible by placing a dessicating agent, such as silica gel, in the light-tight chamber. When not in use, the instrument is. kept covered to minimize the effect of dust or moisture upon the optical system. More detailed descriptions of the microphotometer have been given by Oster (1953) and by Oster and Pollister (1955). 34. The values of turbidity obtained with any instrument require possible corrections for optical effects associated with that instrument. Without such corrections, only relative measurements are possible. The three major "optical corrections" to be considered are the following: (a) The refractive index correction (b) The volume correction (c) The Fresnel correction. In the present experimental arrangement, as in most, the scattered light emerges from the suspension under study into air on the way to the photomultiplier tube. If the detector's aperture is an appreciable distance from the sample cell face, the light reaching the detector will be reduced as a consequence of refraction at the interface between sample and air. In this case the aperture is very near the cell face (less than 1 mm. away), calculations based on formulae developed by Carr and Zimm (1950) indicate that the connection arising from the above cause (the refractive index correction) is negligible in this case. Correction (b) arises because there occurs, again owing to the refractive index change between sample and surround• ings, an increase in the effective volume of the suspension serving as a source of light to the photomultiplier tube (Carr and Zimm; 1950). This correction is also negligible, for the same reason as in the preceding case. The Fresnel correction takes into account the reflection losses suffered by the incident beam as it passes through the sample cell. Such losses occur at the four interfaces separating media of different refractive indices; two interfaces are air-gLass, and two water-glass, in nature. Normal incidence at all interfaces can be assumed for light scattered at any angle, provided that the cylindrical cell is utilized and that narrow portions of the incident and 35. scattered beams are used. In these circumstances, the reflection losses add up to an 8.5$ diminution of the incident intensity (Oster and Pollister; 1955). Thus all readings obtained in this study were multiplied by the factor 1.09 to correct for the effect.

(2) Calibration of the Instrument The photometer can be quickly calibrated for use with suspensions exhibiting effectively pure Rayleigh scattering. Such calibration relates directly the turbidity and the intensity of scattering at a single angle, and therefore permits an easy and rapid determination of the turbidity. If the standard suspension used in the calibra• tion is stable over a long period of time, one can also quickly check for day-to-day variations in the performance of the apparatus. The standard suspension should, in addition, exhibit both high scattering power and negligible absorpti on. For the most accurate calibration, the standard should possess neither depolarization (page 24 ) nor dis- symetry (this latter characteristic being defined by the scattering ratio 1(0) / l(TC-©) ). Ludox * a commercially available aqueous colloidal suspension of small silica spheres (having a radius of about 0.02^/i i.e., about 200 A0) was found to be, after careful filtration, an excellent standard suspension. The procedure entailed in calibrating the photometer has been described in detail by Oster (1952), who used a 3$ concentration of Ludox* The double-distilled water used in this comparator-type method was found, by examination of the angular distribution of scattered intensity, to be Rayleigh-scattering in nature; this fact indicated that

* Manufactured by E.I. Du Pont de Nemouus and Co., Wil• mington, Delaware, U.S.A. 36. the effect of any dissolved or suspended material in the water was negligible, to the limit of accuracy of the photo• meter. In addition, it demonstrated not only that stray-s• light effects in the scattering chamber were negligible, but also that, under ordinary circumstances of operation, any dust present in the chamber had no effect upon the scattering at any angle. The scattering by optically dense particles such as those of Ludox is, however, so great that the turbidity values found are considerably higher, at a 3$ concentration, than are the true values (Maron and Lou; 1954). The dis• crepancy is caused both by the loss in intensity (due to scattering) of the incident light before it reaches the centre of the sample cell, and by the corresponding loss in the scattered light on the way out of the cell* It was indicated that the turbidities obtained would be too large by a factor of the order of gT/2 (where T is the optical thickness - page 12). However, this effect appeared to be offset somewhat by the reinforcement of the two beams by multiple scattering (the presence of such scattering being indicated by the optical thickness criteria given on page 12). Ludox diluted to a concentration of about 0.3$ rendered these effects negligible in the photometer used in this study. •The calibration of the present photometer, for use with.suspensions containing the "large" minerogenic material found to predominate in the inlets (page 68), was accomplished by making use of results obtained by Julov and Kullenberg (1953), who determined the turbidity produced by mono-- disperse suspensions of such minerogenic material in distilled water (jgji ^ 1.15). The use of these results was believed justified as the effect of dissolved material was found to be negligible in this study (page 110 ) .Jerlov and 37. Kullenberg used particle sizes ranging from 1 to 12ju> They found, for any particle size, a linear relationship between the turbidity and the concentration of suspended material. Burt (1954) compared the experimental results with those predicted, for similar circumstances, by the Mie theory (pagel4 ), and found striking agreement for the range of particle sizes used. It appears that discrepancies between theory and experiment occur at sizes below about J/J. (Burt, 1954); however, in the present work, the governing size of the suspended material never attained values below JJL. • A linear relationship was found, for the present apparatus, between the value of the . scattered intensity at 0 = 45o and the concentration of suspended material (page 71). After the effect due to the water had been sub• tracted, the relationship was compared with that of Julov and Kullenberg; thus the scattering at a single angle was again related to the turbidity. The numerical form of the relationship is derived on page 72. As just mentioned, one must, to obtain the turbidity of a suspension, take the effect of the suspending medium (seawater in the present study) into account. The scattering both from pure artificial seawater and from Berkefeld- filtered seawater has been found to be almost identical with that from double-distilled water (Clarke and James; 1939). The Berkefeld.filter will retain all material larger than about 0.75in size. (it has been shown in recent work (Lenoble, 1956) that the ions of dissolved salts do not absorb significantly at wavelengths greater than about 3400A0, which value is in the ultra-violet.) In general, the.separate effects due to scattering and absorption by any suspended or dissolved material in double-distilled water are too small to be differentiated. Values for the attenuation of the double-distilled water used in this study were determined to be: for 4360A°, 0.036 + 0.006 meters-1 and for 5460A°, 0.024 + 0.003 meters"1. These values, representing the results of about 100 determinations, agree closely with those given by Sawyer (1931); they were sub• tracted from the relevant values of the total scattering exhibited by each suspension. The effect of (uncoloured) seawater attained significance, in the present study, in the majority of the. work done during the winter period* the attenuation; of the water represented up to 30$ of the total effect exhibited by the clearest samples obtained at this.time. 39*

VI. COLLECTION AND TREATMENT OF DATA

The data available for this study were obtained in seven separate oceanographic surveys conducted by the Institute of Oceanography of the University of British Columbia during the period May 1957 to June 1958 inclusive* A catalogue of these surveys is given in Table I; the nominal positions of the principal hydrographic stations occupied in the individual inlets are shown in Figs* 2,

3, and 4* Samples for the determination of surface turbidity and salinity were obtained by bucket just before the ship stopped, this procedure being adopted in order to avoid contamination from the ship* The bucket, before being used for sampling, was thoroughly flushed out three times with sea water, the flashings being disposed of on the opposite side of the ship* The sub-surface samples for determination of turbidity, salinity, and dissolved oxygen content, were drawn from the Atlas-type reversing water bottles (made of brass and bronze and coated with nickel) which were secured to the hydrographic wire at the desired intervals* All turbidity samples were collected in well- rinsed non-wettable polyethylene bottles, these containers being chosen because of their chemical inertness* Surface temperatures were obtained by an ordinary mercury thermometer immersed in a sample of water drawn from the surface in the bucket. Subsurface temperatures were obtained by reversing thermometers attached to the Atlas bottles and by bathy thermographs. The dissolved oxygen content for each water sample was determined on shipboard by the standard Winkler method. The salinities were determined ashore by the Mohr method, using silver nitrate standaxdLzed against Copenhagen sea. water0 40. The inside of each Atlas bottle was coated in an effort to minimize contamination of the turbidity samples by corrosion products from the bottle. Tiro coatings were initially tried: an epoxy resin, and Ceresin, a paraffin wax. The presence of either coating made a significant difference in the turbidity of samples, drawn simultaneous• ly from the same depth, only if the readings were of the order of 0.5 meter""1 (to-1) or less. Values in these cases were found to be from 10 to 25$ lower than those ef samples from untreated bottles. The Ceresin coating was adopted throughout this investigation, it being possible to apply a thicker coating with a single applica• tion than in the case of the resin. However, the central spring of the Atlas bottle was found to require re-coating after about two months' use at sea, the paraffin being unable to withstand the repeated tensing and slackening of the spring without breaking up and flaking away. Care was taken to avoid the introduction of dust into the samples, especially during work in the laboratory. Dust was not as acute a problem during the winter months, because of the general prevailing dampness. The sample cell, when filled and placed in the light-tight chamber, was kept covered at all times. This both minimized the effect of dust and reduced leakage currents"in the photo• meter-brought about by moisture evaporating from the sample. The sample cell itself was kept free from grease and dirt by frequent washing with an organic solvent such as carbon tetrachloride. No samples were stored for more than two hours before being analysed; this procedure was followed in order to minimize the possible effects both of biochemical action and of flocculation. When living material is present to an appreciable degree in a water sample, bio• chemical action can materially increase the attenuation, especially if the sample is exposed to natural light* Also, flocculation or "clumping" of minerogenic material can increase the average particle size ;{ }; the total "projected area" for a given amount of such material will, however, usually decrease as the particle size increases, Flocculation occurs if the suspending medium is saline, and is most marked in very turbid waters contain• ing an appreciable portion of inorganic material of colloidal clay size (involving sizes ranging from about 0.001/^to 4yU)* The clay or colloidal particles have large surface areas relative to their bulk. In fresh water, they are dispersed as individual particles largely because the unsatisfied valence bonds of the surface ions attract negatively charged ions such as 0" and OH" and thus tend to prevent one particle from coming in contact with another. If the particles enter saline water, with its abundant positive ions such as Na+, the surface shells of attracted ions are stripped away and the particles can more readily come into contact with, and adhere to, one another (Gilluly, Waters and Woodford; 1951). Measurements of the intensity of the scattering at 45° to the forward direction ( 0 = 45°) were made on all raw samples drawn, using green light of wavelength 5460A0 (4095A0). (The "double-value" notation for wave• length will be adopted throughout the remainder of this discussion; the first value refers to the wavelength in air, the second to that in water, i.e0 to AM in this case.) For every second sample, the "45 scattering" 42* was also determined for blue light of wavelength 4360A0 (3270A0), and for yellow light, of wavelength 5780A0 (4335A0). For various depths at several stations, measure• ments of the scattered intensity were made, at 10° intervals from 10° to 150° for all three wavelengths- For a single wavelength, five readings were taken, at 10-second intervals, and averaged to give a final result* Further repeated readings on samples chosen at random showed that fluctuations of the individual readings were effic- tively random about the average value so obtained* During the course of the seven surveys, light-scattering measure• ments were conducted on over 3000 samples* In addition, a measure of the turbidity of the surface layers was also obtained, at various stations, by means of the Secchi disk* 3 Portions (of volume 50 cm.) of several samples were treated with a combined fixing and staining solution which contained both the organic stain "fast green" and 10$ formalin, the ratio being 7s 3 respectively by volume* 3 Ten cm. of this solution was added to each portion* In the shore laboratory, each of these samples was filtered, under reduced pressure, through a hydrosol HA Millipore filter of pore size 0*5y- (1/^ = 10~ meter •=• 10 cm.)* The filter-retained material was washed with distilled water and then treated with four serial dilutions of alcohol/water in order to dehydrate the organisms* T «» The filter was then rendered transparent by means of four serial dilutions of cedar oil/alcohol, and mounted on a microscope slide (Goldberg, Baker and Fox; 1952). The material retained by each filter was then examined with a 43. microscope| using an oil—immersion objective giving a total magnification of 970. Examination was made on several microscope "fields" (of area 17,660/6 each) chosen at random from the total filter area averaging 2 about 2.4 cm. for the Millipore filters employed. In this manner an estimate could be made both of the number of, and of the size distribution of, particles greater than about 0,5y« in size. Several other samples were treated with a solution of 10$ formalin only, about 3 3 5 cm. being added to a 75 cm. sample* This was done to inhibit any further biochemical action after drawing. Ashore some of these samples were filtered in the same manner as previously described; they were then measured for light scattering in order to give some estimate of the effect of "filter-passing" material (that less than about 0.5/^ in size) on the scattering. Other samples were subjected to qualitative microscope examination which permitted a rough check to be made upon the relative amounts of material of minerogenic and of biological origin. Por every inlet, a longitudinal section for each oceanographic variable was plotted. The variables concerned were: turbidity (Z)t salinity (S), tempera• ture^!), dissolved oxygen content (Og) and density anomaly (<£). ( <7£ = (yj -1) x IC? where J>t is the density of the seawater at the temperature at which it was collected.) The turbidity values plotted were those obtained by the scattering of green light 5460A°(4095A°), the reason for choosing this particular wavelength is discussed on page 111 • 44.

VII. RESULTS

A. DISTRIBUTION OP TURBIDITY IN THE INLETS

1. Bute and Toba Inlets and Adjacent Channels (the Bute Inlet System). This region will be considered first, as it was the one most intensively examined during this study. The results of seven synoptic surveys are available (Table I.). The turbidity values given are absolute, and were obtained from the measurements of scattering of green light 5460A (4095A ). The reasons for the choice of this wavelength are discussed on page 111. Calibration of the instrument was accomplished in this study by obtaining a measure both of the size and of the concentra• tion of the suspended particulate material. The distribu• tions of absolute turbidity found constituted the basis of the studyj these are therefore described immediately.; Both the calibration, and the information upon which it is based, are given later (pages 71 and 73). (N.B. In the following sections, any numerical values of the turbidity above about 8 meters-*(m~*) should be treated with some caution. Although these values can be considered as being generally indicative of the "optical" conditions prevailing, they are somewhat in error because of effects arising from the large concentrations of suspended material associated with such values. This point is discussed more fully on page 116 .) It was observed that turbidity values in general were highest in summer and lowest in winter0 Values occurring at times of other surveys were intermediate between these extremes. Results obtained in February and in June of 1958 have been selected as typical of 45. of winter and summer conditions respectively, and are discussed in some detail. It has been found (Pickard; 1955) that the general distributions of oceanographic properties (S, T, and 0^ page 6 ) may, in inlets possessing runoff at or near the head, be divided into two main groups. One group occurs at periods of small river runoff (effectively the winter months) and the other at periods of large runoff (effec• tively the summer months). The most marked differences between the conditions characteristic of the two periods occur in the case of salinity; these differences occur primarily in about the uppermost 20 meters. Lesser variations occur in temperature (primarily in about the upper 100 meters) and in dissolved oxygen content. Longitudinal sections for S, T, and 0^ are therefore also given, for such inlets, to demonstrate the order of the range of these variables throughout the year. (a) Winter (February 1958) - Figs* 7 and 8.

The surface values of turbidity in the inlet proper varied from about 0.' 7 meters —1( m*» 1) at the head-the largest value found in the system at this time-to about 0.2 m"*1 at the mouth. The values were virtually the same along the outer third of the inlet length. At this time, no significant effect on the mid• stream turbidities was contributed by water introduced, from Cordero Channel, through Arran Rapids. A marked surface turbocline was present near the inlet head. (The term "turbocline" is coined to signify a transition zone, occurring in the surface layers, in which the turbidity decreases sharply with depth.) Slight thermo- and haloclines also existed. A vertical stratification of turbidity was present in the inner portion of the inlet, being most pronounced near the head. The main body 46* of inlet water (between about 100 and 550 meters depth) possessed uniform turbidity of about 0.12 m *. The deepest water* that between a depth of about 550 meters and the bottom.(~650 meters), increased in turbidity with respect to the "uniform" water above. The highest value attained was 0.4 m""1; the values were generally greater the nearer the bottom and the nearer the head. In Sutil Channel, the sux&ce values of Z averaged about 0.2 m~*; in the upper meters or so, the.water was effectively homogeneous in both the horizontal and vertical directions. In the southern half of the.channel, values in the intermediate and deep water averaged about 0.23 m~*. Near the bottom at the inner end of the channel, the turbidity reached 0.36 m~*. ., In Homfray Channel, the surface values of ?Taveraged about 0.12 m~*. The surface layers were characterized by uniformity of all properties in both the horizontal and vertical directions. The main mass of intermediate water (at depths between about 100 and 400 meters) possessed in general the lowest average turbidity encountered,in this study, about 0.06 m""*, (This value is only about 3 times that, for visible light, of double-distilled water or of filtered seawater.) The turbidity increased somewhat in the very deep water. A localized maximum of about 0.2 m""* occurred near the relatively' deep bottom slope at the outer end of the channel* The region in-the vicinity of Savary Island possessed higher turbidity values than did the adjoining waters; Z reached 0.46 m""* at the- surface, decreased to 0.3 m-* at 50 meters depth, and then increased to 0.38 m~* at about 85 meters, which is the depth of the sill between Savary Island and the mainland. 47. There was present at this time a well-defined region of (relatively) high turbidity centered in Calm Channel and extending somewhat into Homfray Channel. It extended vertically from a depth of about 50 meters to the bottom (~500 meters). Z was uniform throughout most of the region at about 0*3 m""1. A "core," between the depths of 150 and 300 meters, had a maximum value of 0.45 m"1. Qualitative microscope analysis revealed that the suspended material in the region was predominantly minerogenic in origin except in the core* where about one-quarter appeared to consist of organisms in an advanced state of decomposition. (The maximum had disappeared within a month, not being found in a survey of the region conducted in March, 1958.) A sharp vertical discontinuity existed at all depths between the main low-turbidity Homfray water (Z = 0.06 m"*1) and the main body of water in Toba Inlet (of average about 0.2 m"*1). Surface values in Toba ranged monotoni• cally from 0.64 m"1 at the head to 0.23 m~* at the mouth. No marked longitudinal stratification of turbidity was present at the head of Bute at this time* The longitudinal distributions of salinity, tempera• ture, density and dissolved oxygen content present at this time are depicted in Pigs. 9 to 16* (b) Summer (June, 1958) - Pigs. 17 and 18 Considering first Bute Inlet proper, surface values of turbidity at this time were found to decrease monotonically from about 36 nf"1 at the head to 7 m""1 at the mouth. The surface halocline, which is especially marked at the head, was closely paralleled in position by a turbocline in which the turbidity decreased by a factor of from 3.5 at the head to about 2 at the mouth. 48. Again, no significant effect appeared to arise from the presence, of Arran Rapids. The decrease in Z at the surface was much less rapid at the outer end of the inlet, being only about 1 m""1 along the outer third of the inlet length. A vertical stratification was present throughout the entire inner half of the inlet, again being most pronounced near the head. In the outer half of the inlet there existed, between depths of about 100 and 500 meters, a region of uniform turbidity of about 0.6 ra""1. The deepest water in the inlet, that.below about 550 meters, increased in turbidity to at least 1.5 to 2 times that of the uniform-? water above, values reaching 1.5 a"1. In Sutil Channel, the surface turbidity averaged about 2.5 m"1. A maximum appeared, at between 2.and 5 meters depth, along the entire length of the channel* A pronounced stratification with depth was present in the main body of the channel* Water between 100 and-150 meters depth was continuous in turbidity (at 0.6 m"1) with the main "isoturbid" Bute water. Values reached almost 1.15 m"1 near the bottom. In Homfray Channel, the surface was quite isoturbid, values averaging about 3.5 m"*1. No maximum was present just below the surface, this condition being in sharp contrast to that occurring in Sutil at this time* The intermediate water had a uniform value of about 0*8 m-1 in the major part of the channel. In the deepest water in the channel, that at depths greater than about 200 to 600 meters (according to location), the turbidity increased to about 1.5 to 2.5 times that of the water above* Near Savary Island the turbidity was again larger than that in the main part of Homfray Channel* Surface values 49. reached 4.0 m~*; sub-surface values averaged about 1.2 m"1 down to the depth of the Savary "sill" (~85 meters). A sharply-defined region of higher turbidity was present at this time also, in Calm Channel, in the same general vicinity as the one in February 1958} the turbidity was uniform (at about 1.3 m""''') between the depths of about 100 and 400 meters. Qualitative micros• cope analysis revealed that a considerable portion of the suspended matter at all depths in this region was bio• logical in origin} this condition was in sharp contrast to that prevailing in the maximum present during part of the preceding winter. In the deepest water, X values in the "region of maximum" reached 1.7 m-*. The waters at the mouth of Toba Inlet showed , continuity at all depths with the contiguous water of Homfray Channel. Toba itself, having at this time,an appreciable river inflow at the head, presented a turbidity picture essentially similar to that in Bute Inlet. ,Surface values ranged from 32 m"1 at the head to 8.5 m"1 at the mouth. A marked vertical stratification of turbidity appeared- in the inner quarter of the inlet. In the intermediate water showed a slight tendency to increase somewhat with depth, averaging, however, about 0.8 m~*. In the bottom 100 meters (i.e. at depths between 400 and 500 meters) Z attained values up to 1.6 m""*. , The longitudinal distribution present in the Bute Inlet system at this time, for the regular oceanographic variables, are depicted in Figs. 19 to 26. A brief description follows of the salient features of the turbidity distributions present in the Bute Inlet system during the other surveys conducted (Table I). The distributions will be discussed in chronological order. 50. Late Spring (May, 1957) - Fig. 27

Only Bute Inlet proper was surveyed at this time. The surface values of turbidity decreased monotonically from about 22 nf1 at the head (the maximum value found in this survey) to about 4 m""1 at the mouth. Both turbocline and halocline were well developed, especially near the head. A pronounced vertical stratification of turbidity existed in the northern part of the inlet. In the southern half, the main body of water (that at depths between 50 and 400 meters) was almost uniform in turbidity at about 0.6 m"1. A sharp increase, with. respect to the water above, occurred below about.450 meters, Z values reaching 1.7 nf*1 near the base of the i H II entrance sill. The isoturbs in the deeper water near the sill tended to follow the bottom contour quite markedly; this feature was also displayed by the deep isopleths of temperatures and salinity. No significant effect seemed attributable to the presence of Arran Rapids.

Summer (July, 1957) - Figs. 28 and 29

At this time, the entire inlet system, with the exceptionof Toba Inlet, was surveyed. The maximum value found (about 34 m"1) occurred at the head of Bute Inlet. The surface turbidity then decreased monotonically to about 8 m""1 at the mouth of the inlet; a shallow turbocline was present at about the same depth as the halocline. A vertical stratification of turbidity occurred near the head and a uniform value of £ , of about 0.7 m*"1, occurred in the main mass of inlet water away from the head. Z increased in the deepest water- that below about 550 meters-and attained values as high as 1.4 m-1. 51. In Sutil Channel, the surface turbidity values ranged monotonically from 1.15 m""* at the northern end to about 0.67 at the southern, the latter value being the smallest encountered in the Bute Inlet system during this survey. A marked maximum was present, at about 5 metes depth, along the entire length of the channel. The intermediate water (that at depths less than about 200 meters) averaged slightly over 0.6' in turbidity. At the southern end of the channel, values in water below about 200 meters depth increased to 1.2 m*"1. In Homfray Channel, the surface turbidity values averaged about 3 m~*. Throughout the main body of .water Z was uniform at about 0.75m"" . Values of 1 to 1.5 m"* were recorded at the outer end of the channel and in the deeper water. Two isolated turbidity maxima were present at the northern end of Homfray Channel. The one in shallower water, centered at about 100 meters depth, possessed a "core" value of 1.35 m~* and extended into both Calm and Sutil Channels. The other extended as a column from about 200 meters depth to the bottom (here at about 500 meters); the core value was 1.25 m""*0

Summer (September, 1957) - Figs. 30 and 31 In Bute Inlet, surface values ranged monotonically in this survey from about 30 m"~* at the head to 6 m~* at the mouth, both the halocline and the corresponding turbocline being quite sharp. The longitudinal strati• fication was again in evidence at the head. In the main body of the inlet water, the value of Z averaged about 0.75 m"~*. Values in the very deepest water increased to 1.9 a"1. 52. In Homfray Channel, surface values varied from 5 to 7 m"~\ with an isolated maximum, of value about 11 m"*1, occurring about half-way along the channel. In the main water mass, Z averaged about 0.8 m_1. Values present below about 500 meters depth increased markedly, reaching 1.25 m"1 in one instance. Although Sutil Channel was not visited in this survey, the 1.0 m""1 isoturb appeared to follow the bottom contour quite faithfully at the mouth of Bute and to move into Sutil* A similar feature charac• terized both the deep isotherms and the deep isopyenals at this time* In Calm Channel, a turbidity maximum was again present from near the surface to a depth of about 200 meters. The value in this maximum was generally about 1.1 m"1, however in two cores one, between about,25 and 50 meters depth and the other between about 75 and 200 meters, values reached 1.75 m"*1 and 1.4 rn""1 respectively. Values in Toba were continuous at all depths with those of the contiguous waters in Homfray Channel. _ Surface values ranged from about 22.6 m"1 at the head to 10*2 m"1 at the mouth and were accompanied by a.well- developed turbocline* The main water mass above a.depth of 400 meters was uniform in turbidity at 0*8 nCi, .A vertical stratification existed in the inner part of the inlet, and below about 400 meters, the turbidity rose in value to about 1.$ m""1.

Autumn (November, 1957) - Figs. 32 and 33

Surface values in Bute Inlet proper decreased monotonically from over 11 m"1 at the head to 0.65 m""1 at the mouth. Vertical stratification occurred near the inlet head. In the main mass of inlet water, the turbidity 53. was uniform at about 0.25 m"1. Near the bottom £ increased somewhat, attaining a value of about 0.5 m~* along the entire length of the inlet. Near the mouth, the turbidity in the main body of water increased in a longitudinal direction, values throughout the water column at the mouth averaged 0.35 m""*. In Sutil Channel, the surface turbidity values varied irregularly, ranging from about 0.45 m~* to about 0.9 m~*. Beneath the surface, the turbidity exhibited essentially horizontal stratification right to the bottom. The value of Z averaged about 0.25 m~* down to a depth of about 150 meters. The value in the water in the next 50 to 100 meters depth was continuous with the value throughout most of the water column at the entrance to Bute (at about 0.35 m-*). The deepest water in the** channel,that in the bottom 50 meters or so, possessed a value of between 0.4 and 0.5 m""*. In Homfray Channel, surface values varied little, ranging only from about 0.6 to 0.7m~*. In the main body of water, Rvalues were relatively constant .averaging about 0.35 m~\ this water also being continuous in tur• bidity with that at the entrance to Bute Inlet. A cloud of higher turbidity, with a maximum value of about . 0.55 m~* was present at the northern end of Homfray, between depths of about 150 and 390 meters. Values in the deepest water that below about 450 meters, rose in value to between 0.4 and 0.5 m~*.

Late Winter (March 1958) - Figs. 34 and 35

In Bute Inlet, surface values varied monotonically from 0.85 m~* at the head to 0.35 m~* at the mouth. 54. A weak vertical stratification was present at the,head. The water between a depth of 50 to 400 meters was uniform in 7s , at about 0.12 m~*. In the deepest water, values rose to 0.30 m""*. In Sutil Channel, surface values dxcreased mono• tonically from 0.27 m"* at the inner end to 0,17 m~* at the outer. The main body of water averaged about 0.12 BT^ also. Below about 200 meters, the turbidity increased-to about 0.2 m~*. In Homfray Channel, surface values decreased from 0,90 m~* at the inner end to 0.43 m"* at the outer* Values in the main body of water averaged 0.0.9 m"**. At the outer end, the turbidity at depths between 100 and 300 meters was considerably higher, values up to 0,30 ra~* being recorded. An isolated maximum of "core" value about 0.5 m"*, was present between 50 and 200 meters depth in the northern part of the channel, and extended into Toba Inlet, Surface values of turbidity in Toba itself varied irregularly with distance from the head, ranging from 0,67 nf* to 0,23 m~*. The water at sub-surface depths was continuous in turbidity with the adjoining waters of Homfray, averaging about 0.12 m""*j no vertical stra• tification was present near the head. An isolated maximum, of highest value 0.28 m""1 was present near the bottom. 55. 2. Jervis.Inlet

Jervis was the major "low-runoff" inlet studied in the present work; there were, however, fewer surveys conducted in this inlet (4) than in Bute (7). On the basis of the available-data, it appears that, in this inlet also, the smallest values of turbidity occur in the winter and the largest-in the summer. The longitudinal distributions of S, T, Ct and O2 for these periods have also been depicted (page 7 )• (a) Winter (February, 1958) - Fig. 36 — ._. Generally low turbidities prevailed at this time. The surface value at the head was 0.85 m-1, the largest value found in the inlet, 0.94 m-1, occurred off, and was directly attributable to, the Deserted River. The surface value of Z" then decreased slowly downinlet to about- 0.14* m— at the mouth. A rather diffuse turbocline existed near the head. Away from the head, a maximum occurred at about 2-5 meters depth. Below this, and throughout the main body of inlet water above 300 meters, (about the entrance, sill depth), the turbidity was uniform, averaging about 0.1 m""1. Z values near the inlet mouth were generally higher than this average. An isolated "cell" of higher turbidity, having a maximum value of about 0.5 m"1 and centered at about 25 meters depth, appeared to be largely organic in origin, as did a somewhat less turbid cell having a maximum value of about 0.3 m*"1 and centered between 200 and 300 meters. At about sill depth,and greater (300 meters and deeper), values reached 0.3 m"1. No significant increases in the very deepest water were noted. In the inner basin however, Z values reached ~ 0.45 m-1 near the bottom. 56.

The longitudinal distributions of salinity, tem• perature, density and dissolved oxygen content for this period (winter) are depicted in Pigs, 37 and 40, (b) Summer (June, 1958) - Fig. 41. At this time, surface turbidities in the inlet ranged from 2 to 12.8 m-1, the larger values again occurring near the head. A value of about 11 m~* was recorded at the head, the value 12.8 m"*, the largest found in the inlet during this study occurred at this time off the Deserted River. The surface turbidities were generally about one-third as large as those occurring in Bute Inlet proper at about the same time. A turbocline was present at this time, and was as sharp, relative to the values concerned, as was that in Bute. This fact was in contrast to the lesser degree of sharpness of the halocline. In water at depths from about 50 to 300 meters, the turbidity varied in value along the inlet. The largest average value between these depths (about 1.5 m~*) occurred near the head, where a vertical strati• fication (much less marked than that in Bute Inlet) occurred. The average then decreased down-inlet to 0.6 m~*, then rose again to 0.9 m~* at about 25 miles from the inlet mouth. It remained essentially constant along the rest of the inlet. Qualitative microscope analysis revealed that this "constant" z" region contained a considerable amount of biological material. The region appeared also to be marked in general by a temperature maximum. In the inner basin, Z attained values of about 3m* near the bottom. Seaward of the inner sill, the 57. turbidity increased somewhat below 300 meters (about the outer sill depth). In the main body of the inlet it averaged about 1 m~*; near the outer sill it reached about 1.25 m~*. Several of the readings at depths below about 400 meters were obtained near the base of some of the more prominent bottom ridges; there the turbidity averaged about 1.3 m"1, the highest value. 2.5 m~*, being obtained near a ridge in the deepest part of the inlet* Also noteworthy was the presence of higher turbidities near the tops of the ridges, a value of 2.2 nf"1 being recorded in one such instance. Distributions for the regular oceanographic .variables for this period (summer) are depicted in Figs. 42.to 45* The main features both of the turbidity distribution present in late spring (May 1957) and of that present in autumn (November, 1957) will also be discussed briefly. (c) Late Spring (May 1957) - Fig. 46 _ At this time, surface values ranged from about 11 m"~* to 2,5 m~*, the largest value again occurring off the Deserted River, A surface value.of 9.5 m~* was found at the head. A turbocline was present, being most marked at the head, and a vertical stratifi• cation occurred in the inner inlet. The intermediate water, that between the depths of 50 and 300 meters, possessed uniform turbidity at about 1.2 m*~*, except, at the mouth. At sill depth, and below this depth inside the sill, Z was somewhat higher, averaging about 1.45 m~*. In the deep water, the turbidity averaged about 1 m~*. Near bottom ridges, values were again markedly higher than in the water above, becoming as large as 1,85 m"1. In-the inner basin,-? increased, in the deeper water; a value of 2,5 m~* was present near the bottom. 58, In May 1957, the bottom water in Jervis was sampled, in detail, at four of the regular hydrographic stations in the vicinity of the inner sill. The stations are denoted by the suffix 3 in Fig. 46. Three of the stations were taken at or about low water slack, the fourth? station 9, of the inner sill-was taken at the full ebb tide. Uniformity (to within the limits of experimental accuracy) occurred for both temperature and salinity, and thus for (TT, in the bottom 30 to 40 meters. At all four stations, uniformity of turbidity also prevailed except in the deepest 2 meters. Above these 2 meters, the most extreme difference-at any station-from the average deep- water turbidity was less than 5$ of that average. At the very bottom, significant increases (of about 25$ of the average values) were found to occur. These might have been due to bottom sediment brought into suspension by the dragging of the sounding weight, a slight ship drift being in evidence during all four stations. (d) Autumn (November, 1957) - Fig. 47 ' At this time, surface values varied from 1.1 to 0.35 m~\ the former value occurring off the Deserted River. The value at the head was 0.95 m^y the surface turbocline was very weakly developed. Theinter- mediate water possessed uniform turbidity at 0.15 m"1, no longitudinal stratification being present at the head. At the mouth, values at sill depth and deeper averaged 0.4 m"1. In the main body of deep water, a uniform turbidity of 0.2 m""1 existed. No significant increases were noted in the vicinity of bottom ridges. In. the inner —1 basin, 6 reached 0.65 m near the bottom. It should be noted that neither Sechelt nor Princess Louisa Inlets appeared to affect significantly the long• itudinal (mid-stream) turbidity distributions encountered in Jervis during this study. 59. 3. Knight Inlet

In this inlet, the longitudinal turbidity distribution was determined both in September 1957 and in June 1958, both times being representative, effectively, of high-runoff conditions. (a) Late Summer (September 1957)-Fig. 48(a) The survey conducted at this time was the more complete; the results will therefore be discussed in some detail. The-longitudinal distributions of the regular oceano• graphic variables encountered in this survey are displayed in Fig. 48(b) to (e). Surface values in the inlet decreased monotonically from about 30 m™1 at the head to about 1.85 m"1 just inside the outer sill; there was an abrupt increase at this sill to 2.36 m"*1. In the inner basin, the turbocline in the surface layers was well developed; in it, the turbidity dropped by a factor of from 4.5 to 3. The turbocline was accompanied by a sharp halocline. A well-developed vertical stratifica• tion was present near the head of the inlet. The main .body of water in the inner basin-that between depths of 50,to 400 meters-was effectively isoturbid) possessing a value of of about 1.25 m""1; there was a tendency for the turbidity to increase somewhat below 400 meters. Jusir inside the inner sill, a sharp vertical stratification of turbidity was . present. Z decreased rapidly, values as low as 0.65 m-1 being reached. Adjoining the sill was an isoturbid column of water having Zslightly higher than this (about 0.7 m""1), In the outer basin, the turbo-and haloclines were both less extreme than inthe inner one. Intermediate water in this basin-that between about 25 and 100 meters depth- possessed an average turbidity of about 0.7 m-1. This water 60. was continuous in turbidity both with that present in the 40 meters above the inner sill (of depth about 70 meters) and with the isourbid column inside the inner sill. X values at the seaward end of the outer basin were markedly higher than those in the intermediate water, as were those in the deeper layers. At the seaward end, the values aver• aged about 2 m~* in the upper 50 meters, with an increase to 2.4 m"~* just above the bottom (60 meters), "Z in the deep -1 -1 water averaged about 1,4 m and reached 4m in one isolated instance. The deep isoturbs followed the bottom contour quite accurately up to the inner sill. , ., It will be noted (Fig. 48) that water in the inner basin, between the depths of about 100 to 300 meters, possessed effectively the same density value as that in a narrow "intermediate11 region in the outer basin. The isopleths of dissolved oxygen content also appear to follow the same pattern, in the vicinity of the inner sill, as do the isoturbs. (b) Early Summer (June, 1958) Surface turbidities decreased monotonically from about 34 at the head to 1.34 m"~* at the inner sill and then rose to about 1.7 m~* at the outer sill. The general features of the turbidity pattern in the inner basin were effectively the same as those encountered in the previous summer, with one exception: no column of clearer water was present inside the inner sill at this time. The water mass between 50 and 400 meters depth was lonitudinally isoturbial (atr= 1.3 m~*) from the inner sill to the inner third of the basin, where a vertical stratification was present. The turbidity in the outer basin was in general markedly higher than in the earlier cruise. The main body of water possessed an average Z of about 1.2 m"1; values in the deeper 61.

water rose markedly, 3.4 m being recorded near the base of the inner sill. The turbidity in the water column above the inner sill was relatively high,averaging 1.5 m"1. No continuity of isopleths, such as was remarked upon for the previous summer's survey, occurred at this time. (The distribution of turbidity has not been depicted for this survey.) 62. 4. Loughborough Inlet-Late Summer (September 1957)-Fig. 49 Both this inlet and Call Creek (see next section) were surveyed only once in this study, the survey being carried out in the late summer of 1957* The longitudinal distribution of turbidity, salinity, temperature, density anomaly and dissolved oxygen content present in Loughborough at that time are depicted in Pig. 49. The surface turbidity exhibited a monotonic decrease in the-down-inlet direction, values ranging from 4.7 m"* at the head to about 1.9 m~* at the mouth. A relatively sharp turbocline existed in the surface layers, values decreasing by a factor of 2 or 3 in about the first 10 meters. In the main body of water, a vertical stratification of turbidity prevailed near the inlet head. Elsewhere, in this water body, the turbidity was almost uniform,averaging about 0.6 m~*. In the deepest water, that below a depth of about 100 meters, Z increased from about 1.15 m""* at the mouth to a value of 1.26 m~* in the deepest part of,the., inlet ( 270 meters). The largest value found in the inlet, 2.26 nf*, secured at the outer base of the inner sill.(near the head). At the head itself, Z reached 1.9 m~* near the bottom. A noticeable feature of the turbidity distribu• tion in this inlet was the following of the bottom contour by the deep isoturbs; the effect was especially marked near the head. 63

5* Call Creek-Late Summer (September 1957)- Fig. 50 The longitudinal distribution (of both the turbidity and the regular oceanographic variables) present at this time are depicted in Fig. 50. At this time, the surface turbidity in Call rose from 0.52 m*"1 at the head to 1.15 m"1 at mid-inlet and then fell again to 0.69 m"1 at the mouth. A marked surface turbocline was present only below the mid-inlet maximum, values dropping by a factor of 3 in the upper 10 meters. No vertical stratification of turbidity occurred near the head in this inlet; values below the surface layers averaged about 0.2 m"1. At the head, Z reached values of 0.32 m"1 near the bottom. „....„.... A tongue of water, more turbid than its surroundings and centered at about 50 meters depth, was present along the major portion of the inlet length. The tongue .. . , possessed an average turbidity of about 0.36 m"1; it was characterized also by a temperature maximum and by a slight but significant minimum of dissolved oxygen. In the. deeper water in the outer half of the inlet, Z rose markedly. Near the mouth (at a depth of about 115 meters) the turbidi• ty reached 1.6 m-1. The deep values then decreased in an up-inlet direction, having dropped to about 0.6 nf1 at mid-inlet. 64.

B. THE NATURE OF THE SUSPENDED MATERIAL IN THE INLETS

Another purpose of this study has been to discover to what extent the nature of the suspended and the dissol• ved material in B.C. inlet waters can be determined from light-scattering measurements. Information was sought from two sources: the "polar scattering" diagram, and the measurement of depolarization. (a) Polar Diagrams of the Scattered Light Polar diagrams ( 1(9) vs 6) representative of those obtained from all raw (unfiltered and untreated) samples are shown in Fig. 51. Values for the angular scattering 1(e) were obtained at 10° intervals; the directly forward direction (0=0) has not been included because of the impossibility of separating the effects of the undis• turbed and of the forward-scattered light (page 29 ). Several salient features appeared in all polar, diagrams. For every wavelength, the scattered intensity in the forward direction ( A 36 aT1, Bute Inlet, June 1958), while 51(b) represents that for one of the clearest samples

1 ( t=0.17 nT , Jervis Inlet, February, 1958). Also noticeable was the uniformity of the results obtained, at any angle, for the three wavelengths employed. 65,

Mean values for either blue or yellow light never deviated by more than + 4$ from the corresponding value for green light. (Por clarity, therefore, polar diagrams for only one wavelength, that of green light 5460A°(4G95A°) have been depicted in Fig. 51. Reasons for the choice of this particular wavelength are given on pagelll) The polar scattering diagrams obtained from several Millipore-filtered samples, (That had not been originally treated with the "staining-fixing" solution) were also examined. The samples were drawn from the shallow,zone in several of the large-runoff inlets, the salinity of any sample never exceeding about 3$$. thus any very fine material present would not have been affected to any significant degree by flocculation. The scattering for any filtered sample never exceeded by more than about 10$ the value, at the corresponding wavelength, for double-distilled, water (page 38). "* The phytoplankton are known to constitute the only, significant amount of coloured organic particulate material present in natural waters. The vast majority of these . organisms are greater in size than about 0.5/1 ; thus the presence of their scattering effect would, in the present work, be limited primarily to unfiltered, rather than to filtered samples. The most abundant pigment of the phyto• plankton population is believed to be Chlorophyll-A, the concentration of which is widely used as an indicator of biomass density. This pigment possesses a strong spectral absorption band centered at 4300A°(3225A°), (Smith et al.f 1951); the presence of this band was amenable to measure• ment, by the "Aminco" Microphotometer, at wavelength 4360A°(3270A°). No markedly lower scattering (i.e. higher absorbing) values were recorded, at this wavelength, for any sample tested. 66.

(b) Measurements of Depolarization

Measurements of the various depolarization ratios (p's) defined on page 25 were made for 20 samples obtained in Bute, Knight, and Jervis Inlets in June 1958. All the samples had turbidity values less than about 2.5 m-1; such samples were chosen in order to eliminate effects arising from large concentrations of suspended material (page 112). However, the turbidities were large enough that instrumental fluctuations were small compared to the mean "signal11; thus accurate determinations of the various ^>'s could be made. The average values obtained were:

pu- 0.055 + 0.005, pH = 0.34 + 0.009 and^s 0.015 + 0.004. These values of the p's,when compared with the value ranges listed on page 112, indicate that the suspended material is predominently both large and anisotropic. For several very clear samples also, non-zero values for all p*swere indicated, again suggesting the presence of large aniso• tropic particles in suspension. However, in such samples, exact values for the were almost impossible to obtain; the relatively weak mean "signal" was markedly affected by fluctuations arising from the light-scattering exhibi• ted by any (relatively) very large particles passing through the incident beam. 67.

(e) Results of Size-analysis of the Suspended Material For the purpose of determining the correct• ness (or otherwise) of the qualitative information obtained- by light-scattering measurements-about the particulate material in suspension, a microscope analysis (page 42 ) was conducted on the "filter-retained" material from several samples.

Size Range of the Suspended Material Eleven of the samples, possessing the highest tur• bidity values encountered during this study, were obtained near the head of several inlets in June, 1958, i.e» during the large-runoff period. The samples were drawn from the shallow-zone (of salinity less than 3^, at depths down to 5 meters. For every sample, the particles visible in each of 10 microscope fields were counted. The projected length, along a unique direction, was measured for each particle; this quantity was considered to represent a "statistical diameter" d, since the particles were assumed randomly oriented. The measurements were accurate to within about + 0.2 JUL . In six of the eleven samples, three "10-field" counts were made in order to obtain some estimate of the variation in the observer's measurements of the number of particles. Each size-distribution of particles obtained was assumed typical of the entire relevant sample. The filler-retained particles from each sample were found to follow closely a log-normal size-frequency distri• bution. Each distribution curve was sharply peaked, but was truncated on the "large-particle" side. The geometric— 68 mean diameter ^ was found to be, for example, in the most turbid case about 17.3/6, with a standarddeviation of about 1.5JJ. • (The geometric mean is considered to be the best index of the governing particle size, as it will be less influenced by extreme values than other forms of the mean.) The maximum particle "size" d found in the 11 samples was 49/£ , the minimum size, about 0,75yt . The arithmetic mean of 3>g for the samples was 16.7+1yx • The amount of material of biological origin was negligible, being less, in every sample, than 0.5% by volume of the total suspended material. Quantitative size-analyses were also conducted in the particulate material present in several further sets of samples drawn from the Bute Inlet system. The results are given in Table II; also listed, for purposes of comparison, are the median particle sizes found by analysis of surficial sediments in Bute Inlet. The size of the suspended particulate material present in Chesapeake Bay, a coastal-plain estuary (Burt, 1955a, 1955b) and in the Eastern Tropical Pacific Ocean (Burt 1958) are also noted; in both cases, the general sizes were determined by means of transmission-type measurements of turbidity. In addition, the size (determined by microscope) of material believed representative of that present in suspension in Swedish fiords (Jerlov, 1955) is given. (It appears that the material in suspension in the southern British Columbia inlets is preponderantly in the "silt" size-range (from about 4 to 62/*.) ,-Twenhofel, 1939; p. 293). The mean sizes of the suspended particles found 69. at various locations in Bute Inlet compare closely with median particle sizes present in bottom sediments in the same general locations« In all samples, the inorganic material was predominan• tly angular in shape; the material of biological origin varied widely in shape with the species of organism and also (if the organism was dead at the time of drawing of the sample in which it was present) with the degree of decomposition of the detrital material. Concentration of the Suspended Material The volume concentration C^ of the suspended material, i.e. the volume of material per unit volume of suspension, can be determined by means of the following relationship:

3 Cv = N*VDV where N = the total number of particles per unit volume of suspension. .

oCv = the "volume shape-factor" of the particles, e.g. for spheres, (volume = E D ), = — = 0,523. Here<*was taken to be 0.14, the value obtained for crushed quartz-having sizes between 1 and 70JJL. -by Hatch and Choate (1929). (The material in suspension in the inlets is found to be predominantly in this size range (page 68), and is produced primarily by glacial abrasion of granitic material (page80).) ' - 3 3 J) = Snd = 2nd is the "statistical volume diameter" Zn N (Dalla Valle, 1948; p. 65) where n is the number of particles per unit volume, possessing- the statistical diameter d ( is also related to the geometric-mean diameter by the equation: 3 3 2 log X>v = log +10.36 log cr- ) 70.

For the most turbid sample found in this study-occurring at the surface near the head of Bute Inlet—the volume- concentration Cy was calculated to be about 105 parts per million (ppm). The values for the remainder of the group of 11 very turbid samples whose material was size-analysed ranged down to 30 ppm. Assuming a mean density of 2.65 3 grams per cm . for this predominantly granitic material, the corresponding weight-concentrations C^., in milligrams per liter (mg per liter) ranged from about 280 to 80 respectively. Concentrations present in other "size- analysed" samples are shown in Table III. ,

The volume of suspended material Cy present in the surface layers at the head of Bute Inlet can be considered as roughly representative of that occurring in the Homathko River near its mouth. (The values will presumably be,some• what smaller than the actual ones, as the heavier material, which would settle out immediately the river waters enter the inlet (page 80) would not be included in the determina• tions* For the Homathko, Cv was found to range from about 10 to about 105 ppm. over the course of a year; by comparison, in the Fraser River, which is just south of Vancouver, the suspended load has been found to vary from about 10 to 230 ppm. over a year (Johnston, 1921). 71

C. CALIBRATION OP THE PHOTOMETER

As previously mentioned (page 22'), Jerlov and Kullenberg (1953) have demonstrated the validity of the relationship

Z = B6Gw (7, page 22) D for monodisperse minerogenic suspensions prepared in the laboratory. (Their results were utilized to calibrate the photometer used in the present study, and thus to permit an estimate to be made of the absolute values of the turbidities encountered (page 44 ))• In the 12 clearest samples, whose suspended material was size-analysed, the range of concentration present was about the same as that used by Jerlov and Kullenberg*, (in Fig. 52 are depicted, for these samples, the values of

Cw obtained and the corresponding values of 1(45°), the value of the scattered intensity at 45° to the forward direction. The results treated here are for light of wavelength 5460A°(4095A°)-page 111. By least squares analysis, the following linear relationship was obtained between 1(45°) and C^.:

1(45°) = 35 Cw + 10 (11) where 1(45°) is the photometer reading in scale units (referred to the most sensitive scale of the instru• ment), and Cw is in milligrams per liter.

The values plotted for the variables are (where possible, in the case of the concentrations) the arithmetic means obtained. The ranges in value are represented by the individual values furthest removed from the mean. The correlation coefficient was + 0.65. 72.

In the work of Jerlov and Kullenberg, it was indicated that the value of constant of equation (7) was very- near 0.75, if Z is measured in meters-*, D in microns

and Cw in milligrams per liter. The particle sizes chara• cterizing the laboratory-prepared suspensions were 1, 3, 7, 9 and 12respectively. The incident light possessed a wavelength of 4700A0(3525A0). The particle sizes were large enough, however, to permit selective scattering to be ignored; it was therefore assumed that the results could be extrapolated to other wavelengths of (visible) incident light (selective absorption being assumed negligible). As the suspended7material in the present study was primarily minerogenic in origin, it was assumed that the turbidities of the 12 "natural!'' samples could be related to the corresponding C '-S by an expression similar to (7), namely:

Z - B6Cw " °-75 Cw <12) The arithmetic mean of -D^ for the 12 samples was chosen as being the most representative measure of the particle sizes in the samples; it equalled 7.3/^-(Table JJJ). The combina• tion of (11) and (12) indicated the following relationship between 1(45°) and Z t

X = 0.003 1(45°) - 0.03 (13) The units for the variables having been defined previously in this section. In Fig. 52 is also given the scale for the turbidities obtained by means of (13). The equation (13) is strictly valid only for the

concentration range 0

(governing) particle sizes much greater than those charac• terizing the samples just discussed. The procedure adopted was the following:

1(45°)" Cw relationships were obtained, again by- least squares analysis, for the two groups. Then (13) was substituted into each relationship to obtainZ- C^. equations. If the laboratory results obtained can be assumed to hold at concentrations greater than those used, the Z equations obtained should agree closely with the.value of Equation (7) for the relevant (governing) particle size. The results are compared in Table III: it is seen that the calibration equation (13) holds well at least up to turbi• dities of about 3 m"1, However, for turbidities above, —1 ~- about 8 m , the 6- C_ relationship, while effectively W linear, has deviated markedly from that obtained- by extra• polation from the laboratory results. Therefore it appears that, as mentioned on page 44, the greatest numerical, values of the turbidity obtained in this study should be treated with caution. The foregoing results should not be basically altered by the presence of organic matter (if absorption effects can be neglected); the optical proper• ties of such material with respect to water (m = 1.15) are effectively the same as those of minerogenic material. 74.

D* PRESENT RATES OP SEDIMENTATION IN THE INLETS

Determination of sedimentation rates in the B.C. inlets by application of stratigraphic methods to bottom cores has not been successful because of the absence of "varves". (Varves, thin laminae consisting of both a coarae and a fine layer-each pair representing the deposit of one year-are often found in the bottom sediments of bodies of water influenced by the inflow of melt-water from glaciers. The larger material transported by rivers (fed wholly or in part by such melt-water) during the high- runoff period)sinks first and forms the coarse (summer) layer. This material is then buried by successively finer deposits which settle out during the succeeding low-runoff (winter)period]' and form the fine layer, (if an appreciable amount of biological material is either produced in, or transported into, such a body of water, the "winter" portion of the varve may be considerably darker than the "summer" one. The darkness will be due to the presence of organic material that also has settled out of the overlying.water•) However, from information obtained about the size of the suspended material throughout the water column, some estimates can be made,of the rate of deposition,by a form of the "supply method". Rates have been calculated both for the mouth of, and for the head of, Bute Inlet. The general procedure utilized, together with the underlying assumptions, follows; the numerical values refer to the mouth of the inlet: . , (i) The particle size was assumed constant, over the year, throughout the water column. This constant value is taken to be the average of the values of X>j obtained for the suspended material, in 75.

summer and in winter (about 8 and IJL , respectively- Table II.) i.e., about 1.5/J. • (ii) The relationship (12) page 72, was utilized to provide (and thus C^) values corresponding to the turbidity values occurring at the depths at which the "particle-sizing" samples were drawn.

The average, of the Cy values so determined, was considered to be the volume concentration re• presentative of the entire water column at the mouth of Bute Inlet, (iii) The Stokes* settling law, which holds for tranquil settling of particles up to about 60_/£ in size, is assumed valid for the material in suspension in inlet waters. Values for Stokesian settling velocities, in distilled water, of quartz particles (p = 2.65 grams per cm ) of various sizes are given by Sverdrup et aL, (1942; p. 957), (These values will, of course, be somewhat in error in the present case, because of non-tranquil con• ditions occurring in nature.) The Stokesian velocities have been multiplied by the factor 0.7; this affords a measure of the reduction in sinking speed brought about by the difference between the (molecular) viscosity at the tempera• ture quoted by Sverdrup e t al. (20°C) and that at the temperature of the deeper inlet waters (about 8°C). (The decrease in sinking velocity due to the density difference between distilled- and seawater is negligible for granitic material

such as quartz0 It will affect significantly, of course, any particles containing an appreciable fraction of organic material; however, in Bute Inlet,which will be used as a basis for this discussion, the amount of such particles is apparently small and will not be considered further in this treatment.) The governing particle size in the deep water at the mouth of Bute appeared to be almost uniform, averaging about 7,5 Jl over the year (page75). The "settling distance" D for granitic material of this size was found to be, by interpolation from data in Sverdrup et al. (1942; p, 957), about 300 cms, per day. (iv) It will also be assumed that, below the shallow zone, transport of material by horizontal currents is neg• ligible. The amount of material accumulating daily on o each cm. of the bottom will then, from (3) and (4), be 2 that contained in a volume 1cm by 300 cms, (v) The "depth-average C " for any two successive cruises can be averaged to give a "time-depth average Cv" for the period between these cruises. Then the material M 2 deposited per year on 1 cm. of the bottom is, under the assumptions made: ^

M = I Ti(Cv). where: i = N-l is the number of periods between N oceanographic surveys. N >s 2; the simple case of a single cruise not being included here* T^ = number of days in the i-th period.

(Cy)^ = the "time-depth average" volume concentration for the i-th period,

Ds = the settling distance (assumed constant throughout the year), in this case about 300 cms, per day* Prom the results of the seven synoptic surveys conducted in this study, the rate of deposition near the entrance of 77. Bute Inlet was calculated to be, at the present time, about 35 cms. of solid material (page 114) per 1000 years. At the head of the inlet, there existed a great disparity between the governing particle size occurring in summer and that occurring in winter (~17 and ~10.5 respec• tively, Table II.). Therefore, the contributions to the yearly deposition rate occurring in the low-runoff period (October to April ) and in the high run-off period (May to September) were calculated separately. (Some error will be introduced, however, because of the uncertainty in the; determination of the higher values of turbidity (those above about 8 m~*)); these values are apparently somewhat larger than the true ones, (page 116);) The rate of deposition at the head was estimated to be, under the assumptions made, about 650 cms. per 1000 years. The calculated rates appear, in spite of the many assumptions made, to be of a reasonable order of magni• tude. Strom (1936) reports varves indicating a sedi• mentation rate of about 27 cms. of solid material per 1000 years in a fiord in southeastern Norway. This latter rate was calculated on the assumption that the water content of the superficial sediments was about 75$. All these rates are exceedingly small compared to that reported for the mouth of the Fraser River in southern British Columbia-about 600 cms. per year (Johnston, 1921). 78.

E. THE RELATIONSHIP BETWEEN SECCHI DISC READINGS AND TURBIDITY

The values of the Secchi disc reading D obtain• ed in this study ranged from about 0.1 to 13 meters ( D / being the depth at which the disc disappeared from view). The average turbidity Z over each depth J> was also cal• culated. If waters with Z greater than about 5 m~* were excluded, the relationship between Z and X>was found to be given very closely by:

This result can be compared with those obtained for English coastal waters: y 1.7 (Poole and Atkins, 1929) and X = 1>9 (Jones and Wills, 1956). Por the highest values of x encountered, the relationship became obscure. This condition was due primarily to the following reasons: uncertainty in the numerical values of the turbidity (page 1114), and the difficulty in obtaining accurate values of X> (the readings for D , being small - of the order of a few inches - for the highest turbidities would be maredly influenced by, for instance, the state of the sea surface). 79.

VIII. DISCUSSION

A. The Turbidity Distribution in the Inlets

la Sources of the Suspended Material (a) Large-Runoff Inlets

The Bute Inlet system will be discussed in some detail in this section. However, the discussion for Bute Inlet proper can be assumed generally to apply to other large-runoff inlets such as Knight. In Fig. 53 are depicted the monthly mean discharge values for the Homathko River during the period of this study. This river drains into the head of Bute Inlet, and was the only one metered in the region at the time of this study, flow-values being recorded at a point about 8 miles from the. mouth, (.toon,, 1957-58). The discharge reached values of about 17,000 cubic feet per second (cfs) both in the late spring and in the late summer of 1957, and about 22,000 cfs in the late spring of 1958. The values compare closely with those obtained by Pickard and Trites (1957) from heat budget analysis; the latter values, which represented the combined discharge of the Homathko and the much smaller Southgate, ranged up to 20,000 cfs. The minimum discharge of the period (about 2600 cfs) occurred in the late, winter, in February, 1958. Heat budget analysis indicated that the runoff in Toba Inlet is over one-half as large as that in

Butee The runoff is concentrated mainly at the head; the variation of salinity in the inlet throughout the year indicates that the runoff varies seasonally in the same manner as does that in Bute. 80.

Now, during the large-runoff period (the late spring and the summer) rivers at the head of Bute and Toba are fed primarily by melt-water from the glaciers and snowfields of the Coast Range. (In what follows, the terms "large-runoff period" and "summer period" will be considered equivalent.) At this time, the river waters contain great quantities of solid suspended material,which is known to consist in the main of quartz, mica, and various types of feldspar (Toombs; 1956). This material, produced primarily by glacial abrasion of the granitic rocks of the Coast Range, is released at the glacier front-when that front retreats because of melting induced by warm climatic conditions-and is finally discharged into the inlets by the rivers. That the suspended material near the head essentially obeys the.log-normal size-frequency distribution is consistent with its origin (page 26). Studies have indicated (Hjulstrom, in Sverdrup e,t aL, 1942; p. 961) that rivers possessing velocities of several knots-as does the Homathko in freshet, for example-can erode and transport solid material up to several millimeters in size. As the river waters enter the inlet they will at once be markedly slowed by frictional forces.. Therefore the very heaviest material will presumably settle out almost immedia• tely, contributing to the build-up of the mudbanks that front the head of most inlets. This fact will also account for the truncation, at the large-particle end, characterizing the size-frequency distribution of the suspended material near the inlet head (page 67 ). During the low-runoff ( winter) period the rivers are fed mainly by precipitation (rain and snow), the effect of glacial melt-water being at a minimum because of the colder climatic conditions generally prevalent at this time. 81

As was evident from microscope analysis of filter-retained suspended material (page 68), the material will, in the latter period, be both less in amount and finer in general size. This fact is a consequence of the reduced transport• ing and eroding ability of the rivers at this time. In Fig. 54 are depicted,on a logarithmic scale, the turbidity values found-during all cruises of this study- both at the surface and in deep water at Stations 1 and 8 in Bute Inlet. Also shown again (this time on a logarithmic scale) are the monthly mean discharge values of the Homathko River. The high correlation (throughout the year) between river runoff and turbidity, in both the surface layers and in the main body of water in the inlet, is strikingly evident. (Although the numerical values of the high turbidities are somewhat in error, the general results obtained are hot invalidated-page 116) The results, combined with those from microscope analysis (page 68), suggest that the-material in suspension throughout Bute Inlet (and presumably, through• out all large-runoff inlets) is primarily minerogenic in origin. The fresh river water with its suspended load is apparently not dense enough at any time to sink, as a well- defined current, through the saline water below (page 70 ). Much of the finer material, moreover, can be held in the upper (shallow) zone for a considerable time-in the high- runoff period, for example, by turbulence associatediboth with the down-inlet flow and with the mixing induced by up«» inlet winds which are prevalent during the summer months© The mixing will be confined at this time preimarily to the shallow zone, because of the large positive stability, associated with the rapid density increase with depth, occur• ring at the halocline. (By definition, the stability is 82. effectively proportional to the increase in density with depth.) The net seaward transport in a large-runoff inlet is appreciable during the summer period; transit times from head to mouth in Bute (~40 miles), for example, have been estimated to be of the order of 4 to 8 days (Tabata and Pickard*, 1957). Now, suspended particulate material averaging about 8/^ in size was found throughout the year in the shallow zone at the mouth of Bute (page 68)• Grani- tic material (density about 2.65 grams per cm. ) of this size is known to sink, in tranquil distilled water at 20°C, at the rate of about 5 meter's per day (Sverdrup, Johnson and Pleming; 1942} p. 957); the rate for such material in the shallow zone will be greatly lessened, primarily by the effect of turbulence, and, to a very minor degree, by the increase in molecular viscosity associated with the lower temperatures prevailing in the shallow zone (generally about 10 to 14°C in the high-runoff period). It thus appears possible that granitic particles, of size %ju. for example, could remain in the shallow zone long enough to be trans• ported from head to mouth of the inlet, and even beyond, before sinking into the more slowly-moving water beneatho The net seaward-moving flow in the shallow zone thus could act as a source of suspended material, in the case of the Bute Inlet system, at least for the entire inlet proper;, and presumably in some measure, for the approach channels also. When such material finally settled out of the shallow zone, it would contribute to the turbidity of the water beneath. 83.

Even during the low-runoff period, the surface-layer turbidities in both Bute and Toba were found to be signifi• cantly larger than those present in the deeper water. The down-inlet transport associated with runoff effects will, of course, be at a minimum at this time. However, an appre• ciable amount of the material discharged by rivers could move down-inlet a considerable distance before sinking out of the shallow zone. Such movement could occur because of runoff effects (generally small) or because of wind trans• port associated with the strong offshore gales or "Squamishes" which frequently occur in the British Columbia inlets in the winter months* The material was generally finer than that present in the summer, and therefore could be held in the surface layers for an appreciable period by turbulent mixing associated with the winds; such mixing can extend as deep as 20 meters or more at this time. (The halocline is much less marked during the winter; thus the stability associated with the accompanying density gradient would be much less pronounced.) The longitudinal distributions of turbidity presented in the previous section were based on values obtained in midstream in each inlet or channel. Material added by runoff from either streams or small rivers entering from the side did not significantly affect at any time these midstream values. In Bute Inlet, even the presence of Arran Rapids (Fig. 2) produced no noticeable effect. As for material of biological origin, phytoplankton blooms are known to occur along the British Columbia coast in spring and autumn, production at the former time generally being greater than at the latter (Hutchinson and Lucas; 1931). 84.

Attendant upon these blooms there will generally be a rapid increase in the amount of zooplankton, both in the surface layers (euphotic zone) and below. The exact effect of such material upon the turbidity distributions in the inlets could not be evaluated; specific detection of phytoplankton-by a colour effect-was not possible with the light-scattering photometer used (page 65). Because of the marked effect of both salinity and turbidity extremes upon phytoplankton production, the dynamics of the circulation in a region dominated by large runoff could profoundly effect the dis• tribution of biological material. For example, the evidence both of microscope analysis of the suspended material (page67) and of light-scattering measurements indicated that biolo• gical material was not an important contributor to the turbidity in Bute inlet proper but exerted considerable effect in the approaches to Bute. Evidence also indicated that such material could be significant in the turbidity distribution in low-runoff inlets (page 56 ). This material, because of its content of organic matter (having a density very near that of seawater) can in prin• ciple remain in suspension for a longer period than can minerogenic material, under similar conditions. When an organism dies, its organic material (detritus) commences to decompose. The decay of this lighter (organic) portion of the organism will lead both to a reduction in size and to an increase in the specific gravity. The former effect will lead to a decrease in the sinking rate, the latter to an increase. There will also be, generally, a retardation of the sinking rate-with depth-due to the increase, both in density and in viscosity, of the inlet waters. The possibi• lity exists that a temporary balance could be achieved 85. between the various factors, as a result of which remains of organisms could collect and remain at a restricted range of depths for a considerable period of time. This condition presumably represents the best explanation for any horizontal strata, characterized by a turbidity maxi• mum, present at depth in the main body of water of an inlet. The occurrence of such a condition appeared to be exempli• fied on some occasions during this study (Jervis Inlet, June 1958, page and Call Creek, September 1957, page 63 ). (It may be noted that the effect of wind-blown terri- geneous dust is not believed to be significant at any locality in the region in which this study was made.)

(b) Small-Runoff Inlets No exact figures were available-in the case of the low-runoff inlets surveyed-for runoff occurring during the period of this study. In the case of Jervis, the work of Pickard and Trites (1957) indicates not only that the total yearly runoff in the inlet is about two- thirds that in Bute, but that the greater part occurs at the sides rather than at the head. This fact is due in the main to drainage from Sechelt Inlet (Pig.3 ); however, a considerable portion of the "lateral" runoff is apparently due to rivers and streams. 1 The runoff into Loughborough, although much smaller than that into either the Bute system or Jervis, is apparently almost evenly divided between head and sides of the inlet. The longitudinal turbidity distributions in Jervis throughout the year indicate that the preponderance of the suspended minerogenic material in the inlet enters from rivers at or near the head, and that a "surface-layer" transport mechanism essentially similar to that in Bute is 86.

operative in this inlet. (A similar condition presumably exists in Loughborough, although the variations in turbidity with time of year were not determined in this case.) The longitudinal variation in the surface-layer turbidity values encountered in Jervis in February 1958 (page 55) indicated that the discharge from lateral streams can, however, affect- in the winter, at least-the turbidity pattern in this low- runoff inlet. It is also probable that phytoplankton produc• tion will be of greater importance in the genuine turbidity distributions in low-runoff inlets than in those in high- runoff inlets, the summer turbidity and salinity values being less extreme and thus less inhibiting to such pro• duction. In Call Creek, which possesses no significant continuous runoff at the head, summer turbidity values appear to be very much less, in the corresponding period than those present in other inlets. Most of the suspended material in such an inlet will presumably be due either to sources outside the inlet or to biological production in the inlet itself. In summary, it appears that in inlets with1appreciable continuous runoff at or near the head, the "background" of the longitudinal turbidity distribution is contributed by the inorganic material discharged by the rivers, especially in the summer period. Superposed on this background will be effects, especially marked in certain areas, due to other agencies such as biological production. Much of the material introduced in the large-runoff period settles out during the following period of reduced runoff, at which time the effect of all sources of material is at a minimum. The turbidity in inlets with negligible river runoff at the head appear to 87.

be primarily due both to the effect of adjoining waters and to biological production in the inlet itself. 2, The More Prominent Features of the Turbidity Distribution in the Inlets (a) Vertical Stratification of Turbidity

A pronounced vertical stratification of turbidity was present in the subsurface water near the inlet head in all of the large-runoff inlets studies, being espe• cially evident during the period of high runoff. In the low- runoff inlets such as Jervis, the stratification was present during summer, although more weakly developed, and was not present during the winter. It apparently did not occur at all in inlets such as Call, which possessed insignificant continuous runoff at the head. The feature is attributed primarily to the progressive settling out, by size, of the minerogenic material introduced by the rivers-both that originally large and any that had become enlarged by floe— culation (page 41). Flocculation would be attendant upon the mixing of the salt-and the freshwater as the latter pro• gressed down the inlet. According to various studies, (Gripenberg; 1934) clay-size granitic material (that less than about 4^tt in size) suspended in sufficient concentra• tion in saline water tends to form particles between 5 and 15in size; this process, if originally present would presumably continue until all the finer material had disappear• ed or until flocculation was inhibited by the increased dilution of the suspension. The weakness of, or lack of, the stratification in the low-runoff inlets was presumably due to the decreased eroding and transporting power associated with the lower river speeds present in these cases. 88.

(b) Turbidity of the Main Water Mass in the Various Inlets and Channels The chief characteristic of the main water mass (i.e. excluding the surface and the bottom layers) both of the large-runoff inlets, and of approach channels influenced by them, was relative uniformity of turbidity. Results in Bute indicated that the governing particle size in suspension near the mouth of Bute (about 8/^) varied little with either depth or time of year (page68). This condition indicated that a lower general size limit for the suspended particles had been attained in the outer part of the inlet itself, and presumably beyond. Size-analysis of material in the bottom surficial sedi• ments of Bute Inlet was carried out by Toombs (1956). From the head to mid—inlet, the governing particle size was found to decrease approximately linearly with distance. From mid-inlet to the mouth, the material was more uniform, the average size being between 5 and 10JJ- • These results were consistent with the surface-layer mechanism of trans• port, of the suspended material, already postulated (page82). The linear decrease in size with distance from the head was consistent with the progressive settling-out, by size, of material being moved down-inlet in the shallow zone (giving rise to the vertical stratification near the head)© The relative uniformity of size of the material present in the superficial sediments in the outer part of the inlet is in agreement with the uniformity, both of turbidity and of particle size, present in the main mass of water in this region. 89.

In small-runoff inlets such as Jervis, the main water mass also displayed uniform "background" turbidity in both summer and winter. This background was again attributed to the minerogenic material, introduced into the inlet prima• rily at or near the head, and transported downinlet, in the shallow zone, in the same manner as in large-runoff inlets* However, in the low-runoff case, the material transported appreciable distances down-inlet will presumably be finer both because of the generally lesser eroding ability of the entrant rivers and because of the smaller speed of net out• flow in the shallow zone, especially in summer. In June 1958, a "tongue" of higher turbidity, centered at about 200 meters depth, extended for a considerable distance along Jervis Inlet (Fig.41); the general region of the tongue was also marked by a pronounced temperature maximum (Fig.43). The suspended material in the tongue was subjected to qualitative microscope analysis and roughly one-third was found to be of biological origin; this figure could be interpreted as representing approximately the difference between the characteristic turbidity of the tongue and of the background turbidity in the inlet* It appeared that the layers of water characterized by the temperature maximum possessed approximately the density temporarily attained by the biological material in the layers. However, no dissolved oxygen minimum appeared in the vicinity of the more turbid layer; this fact indicated that biological material had not been present long enough for a significant deple• tion of oxygen to occur due to oxygen demand of decomposition processes. A similar temperature maximum was present about 90.

four months previously, in February 1958 (Figs 38 ); it seems highly improbable that conditions at the two times represent two different temperature maxima. It appears more likely that the turbidity maximum represented not a recent intrusion of warmer water (bearing organic material) from outside the inlet, but a temporary entrapment at depth of the sinking remains of phytoplankton from a spring bloom in the inlet-biological production presumably being more important in this low-runoff inlet than in an inlet where large-runoff prevails (page 86). An example of a turbidity maximum at more moderate depths occurred in Call Creek in September, 1957. The maximum, centered at about 50 meters depth, was also chara• cterized not only by a temperature maximum but by a sig• nificant oxygen minimum. The material was again probably of biological origin, although no microscope analysis of the suspended material in the region of the tongue was conducted to confirm or disprove this surmise. The results of only one survey were available; thus no statement can be made as to whether the material in the tongue, if biological, had sunk into the layer from the surface strata in the inlet itself, or whether the material had been carried into the inlet by an intrusion of warm water from outside» The presence of the oxygen minimum would tend to indicate that the material had been present at the general depth of the temperature minimum for some time; this in turn would suggest that the material could have been carried for some distance, if the temperature maximum re• presented a characteristic of an intruding tongue of water. 91.

In the Bute Inlet system, the summer turbidities both in the surface layers and in the main water mass were found, generally, to be larger in Homfray Channel than in Sutil; in winter, the reverse state obtained. In both July 1957 and June 1958, the turbidity at about 2 to 5 meters depth showed a distinct maximum in Sutil; a like condition did not prevail in Homfray. A qualitative microscope analysis of the suspended material in the maximum present in June 1958, indicated that about one-half of the material was biological in origin. The material in suspension near the surface in Homfray was found to be predominantly minerogenic, in character. Another difference between the surface layers of Homfray and of Sutil was the lower salinity present in the former, the effect being especially marked in the summer period. These facts indicate that the surface water from Bute Inlet tends to accumulate in Homfray rather than in Sutil. The effect due to Bute water would be enhanced by the runoff-influenced surface water entering Homfray from Toba Inlet. The fresher, more turbid, water in Homfray would tend to inhibit biological production there. Such production would be more favored by the clearer, more saline, water of the surface layers in Sutil, and could account for the surface layer maximum in Sutil (page 48 ). Therefore the higher turbidities general in Homfray during the summer (high-runoff)• period could be explained by the preponderance of more quickly sinking (because more dense) minerogenic material originally present in the surface layers. The reverse state present in winter could be accoun• ted for, in part at least, by the presence of more slowly settling remains of organisms from the previous summers' biological production, which would be expected to be larger in Sutil than in Bute. 92.

(c) Isolated Turbidity Maxima Throughout the Entire Water Column The turbidity maximum which occurred effectively throughout the entire water column in Calm Channel was a notable feature of the turbidity distribution in the Bute Inlet system. The maximum was present during every survey except that of March 1958. Suspended material in this maximum was examined qualitatively (by microscope) in both February and June of 1958. At the former time* the material was predominantly minerogenic, except at the core (page 47 )« while at the latter time, an appreciable amount of biological material was present throughout the maximum. Longitudinal distribution of the various oceanographic variables revealed that the water in the region was not, at any time, either is isohaline or isothermal. Thus intense vertical mixing, which could conceivably distribute particulate material, from either surface or bottom* throughout the water column could not have occurred. No appreciable river flow, which might account, by direct- runoff effects, at least for the February 1958 maximum, is known to occur in the vicinity at any time. It has been observed that the tide floods southward from Cordero Channel through Yuculta Rapids, which are north of Calm Channel; it also floods northward through the passages from the Strait of Georgia, which is south of the latter channel. It is possible that the frequently-occurring turbidity maximum throughout the water column in Calm demarcates the region of convergence of these tides from north and south and that in general there is little aett flow through this region. At such a place, therefore, 93

there could occur accumulations of material (of minerogenic and/or of biological origin) that could remain in a relatively restricted longitudinal zone for an appreciable period. The time could be long enough, for example, for the slowly-sinking biological material to reach the greatest depths present in the region of the maximum (over 400 meters); such appeared to be the case in June, 1958, It is not to be expected that the location of the convergence will be fixed geographically; it is probable that meteorological effects (such as wind stress) might cause it to move. Such effects might also give rise to differential movement, between surface and deep water, which would cause the suspended particulate material to be carried away from time to time (as apparently occurred between February and March of 1958), A turbidity maximum throughout the water column also occurred, at most times, in the region of Savary Island, near the mouth of Homfray Channel (Fig.2 )• It is likely that this latter maximum might be due in part to scouring of the extensive sand-and mudflats in the region of the island. Such scouring could result in part from wind effects, which would arise either from wave action or from wind driven currents generated in the shallow-water around the island. Scouring could also be due in part to tidal effects, which would likely occur in the narrow passage between Savary Island and the mainland. 94.

(d) The Turbidity Maximum in the Seep Water

A feature that appeared to be present, to a greater or lesser degree, in the main portion of every inlet or approach channel, was the marked increase in turbidity occurring in the bottom layers of water. The region of high turbidity varied both in extent and form in the individual inlets. It occurred locally - at the inlet entrance or along a restricted length of the inlet (as in Jervis) or along the entire length of the inlet (as in Bute Inlet proper). There are three main possibilities as to the origin of such turbidity maxima: the scouring effect of tidal currents, non-tidal advective inflow of more turbid water into an inlet or inlet system, and turbidity currents. Each of these possibilities will be discussed briefly in turn.

(i) Tidal currents Scouring by tidal action is the agency that most readily comes to mind. Jerlov (1953b), in his study of the turbidity distribution present in a shallow Norwegian fiord (about 100 meters in depth) expresses the belief that the turbidity maximum found near the bottom of the fiord was due primarily to tidal effects. Observations of the effects of river flow (Hjulstax>m„ in Sverdrup et al., 1942$ p. 961) indicates that water having speeds of about 0.4 knot (20 cms. per second) can both erode and transport granitic material of size between about 100 and 500JJ* . Particles in this size range are the easiest to erode; higher speeds are necessary to bring finer material into suspension, although it should be noted that water having a speed of 95. only 0.1 cm. per second can transport (but not erode) material up to about 15/£ in size. A bottom turbidity maximum, similar to that found by Jerlov is seen to occur in the shallower inlets surveyed in this study, i.e. Loughborough and Call Creek; each of these inlets possesses a maximum depth of about 200 meters. The entrance-sill depth in Loughborough is about 100 meters; that in Call about 35 meters; both inlets open into Johnstone Strait. While no information is present regard• ing the variation of current with depth in this region, it is probable that tidal scouring of bottom material in the shallower part (near the entrance sill) is the primary cause of the bottom turbidity maximum present at the outer end of each of these inlets. The deep maximum present very near the head of Loughborough is more likely due to the effect of turbidity currents (page 104) ^horizontal tidal velocities would, in this locality* likely be ;too small to possess scouring ability, although they would possibly be large enough to transport material into this region. The question of the existence of tidal currents avery close to the bottom in the deepest B.C. inlets is still open. No current measurements have as yet (1959) been made in the deep waters of Bute or Jervis Inlets. (It may be noted that in Knight Inlet tidal currents of a few centimeters per second have been found within 50 meters of the bottom (at a depth of about 300 meters) behind the inner sill (Rodgers, 1958).) 96.

The characteristics of the turbidity distribution in Jervis, however, indicate that tidal effects, in this inlet at least, may be important to depths of at lea-st 450 meters (about 150 meters below entrance-sill level) and also well along the inlet length. In the Strait of Georgia (into which both Jervis Inlet and the southern ends of the main approach channels to Bute Inlet open-Pig. 1) bottom currents, tidal in character and having appreciable speeds, are known to occur. In the southern part of the Strait such currents possess mean speeds of about 0.25 knot (12 cms. per second)-and attain maximum speeds of about 0.8 knot (40 cms. per second)- at a depth of about 200 meters (Pickard, 1956). The values of bottom currents elsewhere in the Strait are not known; however, it is probable that they would be less than those quoted. The results of a few turbidity measurements off the mouth of Jervis Inlet (which is about halfway along the Strait) revealed that a significant turbidity maximum was present in about the bottom 30 meters (at,depths of up to about 300 meters); thus currents of sufficient strength to scour the mud and sand predominant at the bottom in that locality are apparently present. (N.B. The effect of any non-tidal motion in the Strait has been ignored, because of the speeds-of the order of 1 mile per day (2 cms. per second) which apparently occur-page 100. Such speeds would possess negligible scouring ability.) It is therefore possible that the turbidity maximum near the entrance sill of Jervis is due to the scouring of material (and perhaps some transport of such material over the sill) by tidal currents. (it is also possible that tidal effects may similarly be responsible for the turbidity maximum occur- 97. ring near the bottom at the seaward end of Homfray Channel* However, this latter maximum may also be due in part to turbidity currents (page 104) produced by some disturbance (e.g. of tidal origin) of the bottom deposits present near the entrance sill of the channel.) The curvature of the isoturbs (the isopleths of turbidity) in the region of the inner sill in Jervis (Pigs. 41 and46 ) appear to indicate that significant horizontal motion, presumably of tidal origin, is present in this region also. Another charac• teristic of the longitudinal turbidity distribution in this inlet was the increase occurring both at the peak and at the. base of the more pronounced ricges present at the bottom of the outer basin. This increase was noted only in the summer period, A possible explanation is that suspended material settles out, of the overlying water, onto the ridges, thereby contributing to the high turbidity readings at the top of the ridges; the sinking of such material could contribute to the larger values of turbidity present also at the base of the ridges. This explanation thus implies again the existence of appreciable horizontal motion, the most likely explana• tion for such motion being tidal action. The material sett• ling out during the winter period could presumably be generally much smaller, both in size and in quantity; thus scouring effects would be less likely to give rise at this time to significantly higher turbidity readings in the vicinity of a ridge. The effect migh extend some vertical distance from the ridge because of the effects of turbu• lence associated with flow over the ridge. 98.

(ii) Advective Intrusion of Deep Water In the circulation of positive estuaries, the conservation of salt demands that a compensating net up— inlet flow be present* below the shallow zone, to balance the salt removed by entrainment of more saline water into that zone (page 6). The extent in depth of such inflow has not yet been determined in detail in the British Colum• bia inlets; one object of the present study was to seek information as to the nature (e.g. the spatial and temporal characteristics) of the inflow. The dissolved oxygen content indicates that stagnation does not occur at anytime in the deep water of the inlets; the content, throughout the period of this study, was never less than about 2,5 mg. per liter in the main basin of any inlet surveyed. Thus renewal of the deep water must occur in some fashion,, as any bio• logical processes occurring below the euphotic zone must lead to a consumption of oxygen. The evidence for advective renewal rests mainly on results from the Bute Inlet system, both because of the more complete coverage, with respect to time, obtained for this region and because of the measu• rable variation in temperature occurring in the deep water. Although no data for the approaches to Bute Inlet were available in May 1957, both the deep isotherms and isopycnals appeared to indicate a movement of colder water (of temperature less than about 7,7°C) over the entrance sill into the deep basin of the inlet; the temperature of the water displaced was somewhat over 8°C; the flow had, however, not penetrated along the entire length of the main basin of the inlet at this time. 99

In September 1957, a similar situation appeared to be revealed by the distribution of both density and tempera• ture. Here the inflowing water again was colder (7.8_7.9°C vs 8.-8,15°C) than the water already present. No inflow appeared to be present during the time of other surveys. In both May and September of 1957, the deep isoturbs (isopleths of turbidity) at the mouth of Bute Inlet not only indicated an increase in turbidity toward the bottom, but also displayed the same tendency to follow the bottom contour as did the isotherms and isopycnals. In other surveys, the lack of continuity in the deep water turbidity between Bute Inlet and its approach channels was markedly evident. These intrusions of water into the greatest depths of the inlet will be termed advective in the sense that they represent a net transport of water over, a period long compared to a tidal cycle. Water must enter the Bute Inlet system either from Cordero Channel-by way of Yuculta Rapids and Arran Rapids-or from the Strait of Georgia-by way of Sutil and Homfray Channels. In the former case, horizontal movement is restricted to depths of less than about 50 meters, because of the topography of the region. The distribution of oceanographic variables indicated that this water from Cordero Channel possesses at all times a density1 equal,to that of the water at corresponding depths in the Bute . system, this (common) density, is however, markedly differ• ent at all times from that in the deep water of Bute Inlet. Thus it would appear that the Strait of Georgia must supply deep water to the approach channels and thus to Bute Inlet itself. Prom the topographical point of view, the most likely avenue of renewal would appear to be Sutil Channel. Here the shallowest depth, which occurs in the outer part of the channel appears to be about 250 meters, a value not much 100. less than that typical of the neighboring region of the Strait of Georgia. If the density of the deep water in the Strait (and thus in Sutil) becomes greater than that of the deep water in Bute Inlet, there would be an advec• tive flow into the inlet. As for Homfray Channel, horizontal movement in Baker Passage, at the entrance to Homfray, is restricted to depths of less than about 150 meters (the sill depth at the passage). At this depth the density was found during every survey to be considerably smaller than that in the deepest . water of Bute Inlet. Thus renewal of such water through this channel appears unlikely. However the stability (which by definition is effectively proportional to the vertical gradient of density-and thus of 0"t ) although positive, is small at the sill depth. Thus it is possible that a relatively minor disturbance at, or reaching to, about sill depth, could result in advective intrusion into the inlet system-at depths considerably greater than the level of the sill. Now it has been determined that the deep water in the Strait of Georgia undergoes replacement effectively twice annually (Waldichuk, 1957). During each winter, deep water is formed in the southern strait; both increased- salinity, due to inflow at the southern end, and surface cooling- generate a water mass of temperature between 7 and 8°C, This water flows north along the bottom, gradually diffusing upward. Generally the flow commences about December, and reaches the northern end of the Strait in early summer. Also, during late summer, an intrusion of high-salinity water occurs at the southern entrance of the Strait of Georgia; a warm intermediate water mass is formed. This water is characterized by a slightly higher salinity and 101. higher temperature (between 8 and 9°C) than that of the existing deep water, because of the mixing-in of the warm surface water with more saline deep water. Diffusion and/or advection of this water occurs both upward and downward until most of the colder water is displaced, usually by late autumn. Although no data were obtained for either Sutil or Homfray Channel in May 1957, the survey conducted two months later (July, 1957) indicated that cold (<8°C) deep water was present as far north as the inner end of Sutil Channel. (This water presumably originated in the southern Strait of Georgia during the previous winter.) The likelihood exists therefore that displacement of deep Bute water occurred, primarily through this Channel, in the previous May. No data were obtained for Sutil Channel in the survey of September, 1957. However, conditions present near the entrance to Homfray and at depths corresponding to those representative of the outer end of Sutil, indicate again the replacement of warmer deep water (up to 8.15°C) in Bute by colder water (<8°C) from Sutil. (The effect of the previous cold intrusion had apparently completely disappear• ed, presumably by vertical turbulent mixing, associated both with the intrusion itself and with turbidity currents (page10t), and by lateral mixing.) It may be noted that such colder deep water was not present in Bute Inlet in June 1958, also, the temperature of the water at the greatest depths in both Sutil Channel and the neighboring region of the Strait of Georgia was still relatively high (~ 8.5°C). This state of affairs was presumably due to the mild conditions prevailing generally during the winter of 1957-58, and a consequent decrease in the intensity of, and an increase in the time scale of, the (winter) formation of cold (< 8°C) deep water. 102. The increase in turbidity-in the water apparently contributing to advective renewal in the system-could have arisen in various ways. The most likely would be that the content of suspended material was increased by the scouring action of the tidal currents near the bottom in the Strait of Georgia (page 96) and that water moving into the Bute Inlet system transported this added material with it. There is also a possibility that the increase could have been caused, to some degree at least, by scouring effects associ• ated with the velocity of such inflow itself, especially if the flow were of the sudden "pulsed" variety. The penetration of warmer deep water (of temperature considerably in excess of 8°C) into the approach channels of the Bute Inlet system was indicated by data obtained in November 1957. Primarily because of its higher temperature, such water was found to be in general considerably less dense than the deepest water in Bute Inlet. This fact was consistent with the lack of evidence for deep advective intrusion into the system during the winter months; movement of such water would be in general restricted to intermedi• ate depths. In Jervis Inlet, no indication of advective inflow could be inferred from the data on distribution of either turbidity or of the regular oceanographic variables. The vertical distribution of density encountered, at entrance sill depth, during the surveys conducted, indicated that no renewal occurred during the time of these surveys. The presence of renewal is, however, necessary to account for the non-stagnant conditions present in this inlet also. The generally lower values of dissolved oxygen content in 103. the main basin, as compared with those in Bute, indicate the possibility of less frequent renewal there than is the case in Bute Inlet. The values appeared to become pro• gressively smaller from November 1957 through June 1958 indicating a small rate of renewal during this periods In this inlet, the variations in temperature, between the cruises made, were too minute to be of use in determining the characteristics of deep-water circulation. The variation in dissolved oxygen content is apparently consistent, however, with the pattern of deep-water circu• lation prevailing in the Strait of Georgia. By November, the warm deep water formed in late summer would be present effectively throughout the entire Strait (page 100). Re• placement of this water by newer (and presumably more highly-oxygenated) deep water formed in the following winter (of 1957-58) had not occurred in the Strait by June 1958, in all likelihood because of the mildness of that winter. Thus the possibility of any extensive renewal (during the period from November 1957 to June 1958) of the deepest water in Jervis would have been greatly lessened. It would therefore appear that what evidence of deep- water renewal was found during this study is basically consistent with the gross seasonal features of the deep circulation present in the Strait of Georgia. It appeared also that, during the period of this study at least, the increase in deep—water turbidity could be utilized as a tracer to confirm the presence of deep-water renewal sugges• ted by the distributions of other oceanographic variables«, 104.

(iii) Turbidity Currents Another possible explanation for the deep-water turbidity maximum present in various inlets involves the presence of turbidity currents. These currents are avalanches of water whose density has been increased, by the presence of suspended material, to a value above that of the deepest water in the region* They can flow, under the influence of gravity down a sloping bottom and can attain considerable speeds on steep slopes. The increase in density due to the load of suspended material-of river water entering the inlets was not found to be sufficient to make the fresh water denser than the saline water already present in the inlet (page 70 ); thus turbidity currents would not be formed by river water directly. In the deeper water of the inlets, however, the density changes little with depth, in Bute Inlet, for example the change in (= ( pt -1)10~" ) between about 100 and 500 meters is, at any time, only from about 24.0 to about 24.4. It is also known that a considerable portion of the (larger) material brought down by rivers at or near the head of an inlet is deposited on the mudbanks fronting the head (page 80 )• The superficial layers of sediment on such banks would generally be inherently unstable, and it is very probable that slides could occur on these banks from time to time at some depth, or range of depths, below the halocline (i.e. below about 5 to 10 meters). (It is believed that such slides can occur even when the bottom slope is only about 1° (Sverdrup, Johnson and Fleming, 1942; p. 960); the mean slope at the head of such inlets as Bute and Jervis has approximately this value, while "local" slopes are certainly greater.) These slides could bring into suspension enough material to increase the density of the bottom water at this location to a value 105. greater than that of the water in the deepest part of the inlet; this more turbid water would then flow down the bottom slope. The slides could result, for instance, from the effect of water motions upon the unstable superficial deposits (v., e.g., page 109). They could also arise (presumably infrequently only in the British Columbia inlets, however) from seismic disturbances. The turbidity currents formed would move down-inlet until their energy was dissi• pated by friction or until halted by a sill structure. (It is to be noted that the turbidity increase in advective renewal could increase the density of the deep water in a similar fashion. However, the distinction made here is that, in the case of turbidity currents, the density increase is due primarily to the presence of the suspended material; in intermittent intrusion, a distur• bance has provided water whose density is more often greater primarily because of its temperature and salinity characteristics.) Now it is known that the general size of the material present in the bottom sediments is not as great at the mouth as it is at the head (Table II.). Such sorting, due to progressive settling-by size-of the suspended material, is inherent in the postulated mechanism for the surface- layer transport of the material away from the head (page 81). If this mechanism is correct, the material transported downinlet by turbidity currents should also be subjected to such sorting. If swift turbidity currents were pre• dominant, the greater turbulance associated with such currents would tend to hold in suspension, for a longer time, the material being transported. Appreciable amounts of the larger material could, under these circumstances, be transported far down-inlet, even to the mouth; this 106. condition would give rise to a distinctly different varia• tion with position, of the particle sizes in the bottom sediments, than that actually found. These considerations indicate that the currents are slow in nature. (The relatively gentle mean slope of the bottom also militates against the presence of swift currents.) Indirect means also permit some estimate to be made of the frequency of occurrence of the turbidity currents. If a measure of the governing size of the particulate material in suspension in the deep-water turbidity maximum is obtained, one can calculate approximately the time for such particles to settle out. If the turbidity current has ceased, and variations, in the turbidity maximum, due to such agencies as advective intrusion (page 98 ) can be neglected, Stoke's law for tranquil settling should give a reasonable value of this time-at which the maximum will effectively have disappeared,, (Thus only the "back• ground" turbidity, arising from material presumably supplied, from the surface layers in the inlet (page81 ), will remain.) This period can then be compared with the periods between the successive surveys. If the calculated period is, in the most extreme case, not much longer than the others, the presence during several successive surveys of a turbidity maximum which either remains constant or increases in intensity would indicate that material (giving rise to the maximum) which had settled out had been re• placed by that carried by one or more turbidity currents occurring between surveys. Information obtained in Bute Inlet can now be con• sidered. It was found that, near the mouth of the inlet, the governing particle size in the turbidity maximum averaged about 8/t throughout the year. Minerogenic 107. material of such size will sink in (tranquil) water at a rate of somewhat over 300 cms. per day. under the condi• tions prevailing in the deep inlet water (page 76). A marked increase in turbidity-with respect to the background- occurred in about the bottom 75 meters or so in Bute Inlet in February, 1958 (Fig. 7). In the absence of other factors influencing the turbidity, the maximum should have disappeared in a period of about 25 to 30 days. However, one month later, the maximum was found to be relatively unchanged (Fig. 34). About three months later again (June 1958), the bottom turbidity maximum had increased in strength (Fig. 17). Thus the indications are that during the four-month period several turbidity currents had occurred and supplied further suspended material to replace that which had settled out. (Conditions were found to militate strongly against the presence of any advective intrusion i.—an\& the attendant turbidity increase V' ; ^ }- during this period (pagel02).) The time-scale of the frequency of such currents appears therefore to be of the order of a few days or weeks rather than of years. The fact that the bottom turbidity maximum possesses greater absolute intensity, with respect to the background, in summer than in winter is presumably due both to the effect of advective intrustions and, more importantly, to the likelihood that turbidity currents are more frequent in summer. The probability of "clumping" (i.e., the formation of local concentrations of settling material) would be largest, at the head, in the summer (the time of year at which the greatest rates of deposition would be expected to occur). The even greater degree of instability introduced into the bottom deposits by such clumping would therefore be expected to increase the likelihood of forma• tion of turbidity currents during the summer period. 108.

Further evidence for the presence of such currents appears to exist in the morphology of the inlets themselves* In some large inlets, such as Bute, the bottom near the entrance sill is remarkably level, both in longitudinal and in transverse section, while in others, such as Jervis, a level floor occurs only in an inner basin (Pickard, 1956)• In the former inlet, the level floor can be accounted for primarily both by the settling of material from the shallow- zone source (page 82) and by the settling of material trans• ported the entire length of the inlet by turbidity currents and intercepted by the entrance sill. In Jervis, both the feature just described, and the marfedly lower values of the bottom-water turbidity outside the inner basin, suggest the entrapment (by the inner sill) of the major portion of the material transported by turbidity currents originating at the head. There will be a contribution by any inflow of more turbid deep water into an inlet. However, such inflow is apparently intermittent (pp. 98-103); also its load of suspended material must be spread over the distance of in• flow. Much of this settling material will presumably be carried back to the mouth, by the more frequent turbidity currents, after the inflow has ceased. The results in Jervis also offer evidence that significant turbidity cur• rents do not originate elsewhere than at the head of an inlet, (with, apparently, one exception, an example of which is mentioned on page 97: currents brought about by disturbances of the sediment at shallow entrance sills.) Thus it appears likely that turbidity currents, charac• terized by low speeds-and a frequency of occurrence of the order of weeks rather than, say, years, are the primary cause of the increase of turbidity present in the bottom water of the inlets. 109. It is suggested that turbulent mixing brought about by advective intrusions, and, to an apparently greater degree, by the (more frequent) turbidity currents is the principal means by which the presumably originally density- stratified deep water in the inlets was mixed effectively to homogeniety. (The homogeniety would, of course, be preserved during succeeding time by recurrences of such intrusions:, and currents.) Internal waves have been reported in several of the British Columbia inlets, notably Bute and Knight (Pickard,, 1955)• The magnitude of water motions associated with such waves should be examined in the light of their possible effect in generating turbidity currents. The shallow internal waves occur at the depth of the halocline (3- 15 meters), they have a period of a few minutes, a length of between 50 and 100 meters, and a height of up to 10 meters. The deeper internal waves are present between 30 and 120 meters, and possibly deeper; evidence suggests that in Bute Inlet, this latter type is a standing wave with possibly two nodes, the mouth of the inlet being an antinodal point; it is of tidal period and has an ampli• tude of about 30 meters. The horizontal particle velocities associated with a travelling internal wave can be readily calculated (Sverdrup et al, 1942; p. 589). It is assumed that for standing waves possessing the same dimensions, velocities will be of the same order of magnitude. Calcu• lations indicate that the horizontal particle velocities -associated with either type of wave are of the order of 1 cm. per second. This result indicates that the eroding ability-of such waves-on the bottom deposits in the inlets will be effectively negligible; however disturbance of un• stable local conglomerations of material near the head might be produced. 110. B. Characteristics of the Light-attenuating Material in the Inlets

1. Size and Nature of the Material The effect of both the absorption and the scattering arising from filter-passing material (i.e. from that less than about Q,5yuu in largest dimension) appeared at all times to be negligible with respect to the turbid• ity of the filter-retained material. In addition, the insignificance of the effect for all wavelengths utilized indicated that dissolved coloured matter ("yellow-substance") was effectively absent in the inlets during the period of this study. An absence of dissolved coloured matter has also been noted in the waters of Chesapeake Bay (Burt, 1955a). The results obtained both in this study and in that of Burt are in marked contrast to those obtained by Jerlov (1953), who was able to use "yellow-substance" as an effective delineator of water masses in Swedish coastal waters. The absence of markedly lower scattering (i.e. higher absorption) values, for the blue spectral line 4360A0 (3270A0), in all raw samples indicates that the presence of organic material (and thus of material of biological origin) could not be specifically detected, with the photometer used, by effects due to the pigment Chloro- phyll-A, at least at any of the in situ concentrations encountered during this study. The inlets surveyed differed markedly in this respect from Chesapeake Bayj in the latter estuary the presence of phytoplankton was, during spring, made quite evident by absorption effects due to Chlorophyll-A. HI. The high values of the scattering, in the forward direction (0<^), exhibited at all wavelengths by the raw samples indicated that the particulate material in suspension is predominantly "large" (more explicitly, greater than about 1 ju. in size-page 37 ), The position of the minimum of scattered intensity presumably represents the position of most pronounced polarization of the scat• tered light. The shift of this minimum into the back• ward direction ( ©>^) also is suggestive of the presence of larger material. The large range of particle sizes generally present in suspension presumably accounts for the broadness of the minimum found in all polar diagrams of scattering. The distribution of scattered intensity also indicated that most of the particles in suspension are relatively transparent, thus exhibiting a relative refractive index m (with respect to water) near to 1. Because of the equivalence of the angular distribu• tion of scattered intensity for each of the three wave• lengths used in this study, it appears that light of any of these wavelengths can be considered as representative of the total amount of suspended material present. For this study, scattering values obtained with green light 5460A°(4095A°) were used. The green light was of greater intensity, in the mercury lamp utilized, than was the yellow; thus the former would give more accurate results for weakly-scattering suspensions. Green light would also be less affected by any degree of concenuation of coloured organic material present than would blue light. 112. Size-analysis of the suspended material also indi• cated that the condition for independent scattering (page 14 ) was satisfied at all times. Calculations for the sample containing the greatest concentration of suspended material found indicated that the average distance between particles (if they were assumed uniformly dispersed) was about 10 times the size d of the largest particle found, and about 25 times the geanetrie-mean diameter of all the particles. The numerical values obtained for the depolarization ratios and given on page 66 , indicate by a comparison with the relationships (8), page 25 , that the scattering material is predominantly large with respect to the incident wavelength and anisotropic in nature. The values are seen by (9) to be consistent among themselves; they also appear to be generally consistent with those obtained by Hoover et al. (1942) for bentonite suspensions having comparable concentration and governing particle sizes large with respect to the incident wavelength. (Bentonite is a mixture of silicates of aluminum and magnesium and is anisotropic in nature.) The depolarization ratios are known to depend not only upon the size and the degree of anisotropy of the suspended particulate material, but also upon its concen• tration. However, Hoover et al. found this last-mentioned dependence to be negligible for weight-concentrations less _3 than about 10 . The highest weight-concentration present in samples for which numerical values of the ratios were -4 obtained in this study was less than 10 . Thus in these samples the dependence of the depolarization on concen• tration could be neglected. 113. It is seen (Table II) that size-analysis of the suspended particulate material bears out the general conclusion, drawn from the results of light-scattering measurements, that the material is in general larger than the wavelength of the incident (visible) light. Optical anisotropy, also suggested by the results of relatively simple light-scattering measurements as being a feature of the suspended material in general, is known to be a characteristic of the quartz, mica and various feldspars comprising the bulk of the inorganic (and thus of the total) material in suspension (Toombs, 195.6). The grey color revealed by visual examination of bot• tom sediments indicates that in general some absorption is present, as would be expected. The absorption is, however, non-selective, confirming another deduction from observa• tion of light scattering. The main water mass in the outer half of Bute Inlet was marked both by uniformity of turbidity during any survey and by near-uniformity of governing particle size throughout apparently the entire year (Table II). These facts indicate that material predominantly between about 5 and 10JUL in size may generally comprise a quasi-per• manent "background" suspension, in the Bute Inlet system at least. This assumption appears to be borne out by the restricted range of median particle sizes found in the bottom sediments in the southern half of Bute Inlet (Toombs, 1956). Uniform turbidity was also noted in the (fewer) surveys conducted in other inlets. Although no size-analysis of the suspended material was conducted in any inlet other than Bute, it appears likely that a similar background suspension exists in these inlets also. 114.

The rates of sedimentation calculated refer, as previously mentioned (page 77), only to deposition of a solid (or "dry") layer of material. No account has been taken of the volume increase arising from the presence of water entrapped in the sediments-especially that present in the superficial layers. However such water will presumably not be significant with respect to the approximations made for the purposes of calculation. (It has been estimated that, in Bute Inlet, the volume shrinkage, in the super• ficial sediments, resulting from drying varies from about 7 to about 30$ (Toombs, 1956).) The actual amount of material remaining at the bottom at the head of the inlet would probably be considerably lower than the calculated amount if turbidity currents were of frequent occurrence. Material sufficient to provide the increase (or any appreciable part of the increase) in the turbidity in the deep water would presu• mably be removed from only a relatively short length of bottom near the inlet head. The action of burrowing organisms such as worms would tend to obliterate, stratification in bottom sediments. However, the occurrence of such organisms is uncommon in the bottom material of the inlets (Pickard, 1956). It is to be expected that flocculation effects would be of some importance in reducing the amount of the very finest mat• erial originally present in the river-transported sediment (page 41), thus contributing to the lack of varves . .., •• in the British Columbia mainland inlets. 115. However, the results of the present work in Bute have provided evidence for other possible factors contribu• ting to the absence. The relative uniformity of particle size, throughout the year, at the inlet mouth (page 74 ) could account for the lack of distinct stratification in the bottom sediments of that region. The fact that dis• tinct varves are not found at the head of Bute appears to offer further indirect evidence of the presence of turbidity currents (page 104)j both the disturbance of the unstable bottom sediments, and the transportation of material away from the head, by such currents would account for the absence of any marked stratification at that locality. The lack of darker layers in the sediments in Bute Inlet is consistent with the paucity of organic matter reported for those sediments by Toombs (1956). In Bute, biological production is presumably low because of the influence, in the upper layers of runoff. In addition it is to be expected, both because of the great depth of the inlet and because of the high oxygen content of the inlet waters, that much of the detrital material present would be decomposed, either by oxidation or by the action of aerobic bacteria, before reaching the bottom. While conditions for biological production appear to be more favorable in low-runoff inlets such as Jervis the great depth and a high oxygen supply would again appear to militate against a large proportion of the detrital material reaching the bottom. The essential agreement, up to turbidities of at least 3 m~*, between the turbidity-concentration relationships (both actual and extrapolated) obtained for laboratory- prepared monodisperse dilute suspensions and those obtained 116. for natural suspensions possessing comparable governing particle sizes, establishes confidence in the procedures followed in both instances. There is, however, a marked lack of such agreement at higher turbidities, above at least about 8 m~* (Table III), the values obtained in the present study being considerably greater. The divergence is presu• mably due primarily to the presence in the latter case of effects similar to those found for high concentrations of Ludox (page 36). A quantitative evaluation of these effects has not been given here. The mathematical complications are considerable; in addition, such effects are signifi• cant for only a very small fraction (about 1/20) of the turbidities determined in this study, this fraction in turn representing only about yfo of the inlet waters involved. The high values occurred primarily in the shallow zone of the high-runoff inlets during the summer period, and were never present in the intermediate or deep waters of any inlet. It may be noted that Z was also determined, for several of the more turbid samples, by means of "transmission-type" measurements (page 27 )• Even when a correction factor- for the directly-forward scattered light-of the same order as that obtained by Jones and Wills (v.p,29, this work) was applied to these Z values, such values were still-above 8 m~*-only about one-half as large, on the average, as the corresponding ones obtained by scattering measurements; they were therefore much more in accord with what would be expected (from extrapolation of laboratory results) if secondary effects due to the high concentration were not present. Therefore the numerical values, of the high tur• bidities, obtained by scattering should be treated with caution, they will, however, still be basically representa• tive of the prevailing optical conditions. 117.

C. Brief Evaluation of the Light-Scattering Method

The chief virtue of the light-scattering method is the ease and rapidity with which the relative turbidities can be obtained, the determination for three wavelengths taking only about five minutes. When measurements of the scattered intensity can be made at several angles to the direction of the incident light, a qualitative estimate can quickly be given for the size of the suspended (particu• late) material, i.e. whether it is large or small compared to the wavelength of the incident light. Measurements at a single angle (0 = 90°) of polarization effects produced by the material not only give an idea of the size but also reveal whether it is isotropic or anisotropic in nature. However, if the suspension is polydisperse, no quantitative information as to the size-frequency distribution can be obtained. The light-scattering method is most useful for obtaining both relative and absolute turbidities if the suspensions are dilute and contain particulate material which is large compared to the incident wavelength. In the transmission method the most accurate values of absolute turbidity should be those obtained from samples containing either dissolved material or material exhibiting Rayleigh scattering. For suspensions of high concentrations of large material, the scattering method appears to give values for absolute turbidity that are higher than the true ones, whereas the transmission method gives values that are lower. The "scattering" values are believed to be high by a factor of about two. 118.

IX. SUMMARY AND CONCLUSIONS

A. General Features of the Turbidity Distribution in Southern British Columbia Mainland Inlets. The turbidity distribution possesses the same general features in both high and low-runoff inlets. The values of turbidity are (relatively) high in the shallow zone, i.e. in the top 2 to 15 meters. The highest values present in the inlet at any time are found at or near the inlet head in this zone; values then generally decrease steadily to the mouth. The main body of water in each inlet is usually marked by a distinct vertical stratifi• cation in the inner part of the inlet and by uniform turbidity in the outer part. The stratification is less well developed, however, in the low-runoff inlets. The bottom water in most inlets shows a decided increase in turbidity (by a factor of up to 2) with respect to that in the main body of water above. The turbidity shows a marked seasonal variation in both large and small-runoff inlets. The highest values throughout the inlet occur in the late spring and the summer and the lowest in winter. In high-runoff inlets, values in the shallow zone range from about 4 meters""* to about 30 meters in the summer, and from about 1 to 0.2 meters ~* in the winter. In small-runoff inlets, the ranges in shallow-zone values are from about 2 to 12 meters in summer, and from about 0.15 to 1 meters ~* in the winter In the main mass of water, the characteristic turbidity possesses values of from 0.6 to 1,3 meters "** in the summer and from 0.06 to 0.2 meters in the winter© 119.

In inlets with no runoff the surface layers do not appear to be characterized by (relatively) high values of turbidity. The values in the main body of water are smaller, in the summer at least, by a factor of about 2 with respect to corresponding values in other inlets* The listed turbidity values above about 8 m"1 are believed to be somewhat higher than the true values* B. The Nature of the Light-attenuating Material in Southern British Columbia Inlet Waters

1* The preponderance of the particulate material is composed of relatively transparent colourless minerogenic particles which are greater than about 1JJL in size and possess a refractive index near that of water. 2. Size-analysis (by microscope) of the particulate material indicates that both the concentration and the size-distribution of the material vary consider• ably in both time and space. (a) The volume concentrations ranges from less than 1 to about 1,05 ppm by volume, and the corresponding weight concentrations from about 1 to 280 mg per liter. (b) The suspended material ranges in size from about §.5JJL %O 49yu. • The size range in the high- runoff period is from 0.75/^ to 49y" > that in the low- runoff period from 0,5^"- to 15/<: • The largest particles are found near the head, in the high-runoff period* 3. The effect of filter-passing material (smaller than about 0.5in size) is negligible. 4. The bulk of the particulate material is anisotropic in nature. 5. Material of biological origin could not be detected by selective absorption-at the in situ concentrations of such material encountered-with the 120, apparatus used in this study. However, microscope analysis indicated that biological material was present, in some degree, in most of the inlets and that turbidity maxima encountered at a short distance below the surface, and/or at intermediate depths, in various localities could be primarily attributed to such material. Biological activity appears to be low in large-runoff inlets, presumably because of the inhibiting effect, upon production, of the low salinity and high turbidity (associated with high-runoff conditions) occurring in the surface layers, 6, The suspensions exhibiting the highest turbidity values encountered were still dilute enough to permit the assumption of independent scattering. 7. Dissolved coloured matter ("yellow-substance") was not detected in the inlets surveyed during this study,

C. Deductions from the Results 1, In the inlets possessing substantial year- round river runoff at or near the head, the longitudinal turbidity distribution is determined primarily by the effect of minerogenic material carried into the inlets by the rivers, 2, The net outflow which takes place in the upper (shallow) zone is apparently the chief mechanism by which the river-introduced material is distributed throughout the inlet or inlet system, 3, In some instances, the distribution of turbidity tends to confirm the suggestion-obtained original• ly from the distribution of the regular oceanographic variables-that renewal of the deep water in the inlets occurs, in part at least, by advective intrusion which is intermittent in nature. .121.

4. There appear to be three possible causes for the turbidity increase occurring in the bottom water of the inlets: stirring by tidal currents, the effect of advective intrusion of deep water, and turbidity currents. It is pro• bable that tidal effects, involving the scouring of bottom material, account in great part for the increase in the shallower inlets (those of maximum depth less than about 200 meters). An increase also appears to be associated with any advective intrusion. Strong evidence exists, however, that the increase in the deeper inlets is primarily attributable to turbidity currents originating at the inlet head. The currents appear to be slow and the time scale of their frequency of occurrence appears to be of the order of a few weeks or less. The existence of such currents would appear to be a likely explanation for the level floor found in many cases on the up-inlet side of a sill structure. Turbulent mixing associated with turbidity currents and, to a lesser degree, with (the presumably less frequent) advective intru• sion is suggested as the principal means by which homogeniety of the deep water in the large inlets has been attained. 5. In the inlets, the turbidity can be employed as an indicator of water-mass movement, with some limitation. The value of turbidity as a tracer appears, in the inlets, to be greatest in the bottom water. 6. Both microscope analysis and turbidity measure• ments have indicated possible explanations for the lack of varves, in Bute Inlet at least. At the mouth, the relative uniformity of particle size with time of year is a factor. At the head, the effect of turbidity currents could be a 122 a major factor in destroying any stratification originally present in the bottom sediments. The lack of organic material in suspension at any time, and the resultant paucity of such material in the bottom deposits, would obviate the possibility of a colour stratification occur• ring in those deposits. 7. By use of a form of the supply method, the rate of sedimentation in Bute Inlet was estimated to be, at the present time, between about 35 and 650 cms. per 1000 years. The larger rate occurs at the inlet head, and the smaller-which is presumably more representative of the rate present generally throughout the inlet-occurs at the mouth. 8. In the inlet waters studied, the relationship between the Secchi disc reading J) and the average turbidity over the distance -D was given by the expression

T = (valid for Z up to about 5 m"1). 123. REFERENCES

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Burt, W.V, (1956). A light-scattering diagram. Jf, Mar. Res., 15: 76-80. Burt, W.V, (1958). Selective transmission of light in tropical Pacific waters. Deep-Sea Research, 5j_ 51-61. Carr, C.I., and B.H. Zimm (1950). Absolute intensity of light scattered from pure liquids and solutions. J. Chem. Phys., 18: 1616-1632. 124

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Fukuda, M., N. Inoue, and S. Nishizawa, (1958). A new turbidity meter. Bull. Fac. Fish., Hokkaido Univ. 9 (2)

Gilluly, J., A.C. Waters and A.O. Woodford (1951). Prin• ciples of Geology. W.H. Freeman and Co., San Francisco 631 pp. Goldberg, E., M. Baker, and D.L. Fox (1952). Microfiltration in oceanographic research. I. Marine Sampling. J. Mar. Res. YU 194-204.

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Hoover, C.R., F.W. Putnam, and E.G. Wittenberg (1942). Depolarization of the Tyndall-scattered light of bentonite and ferric oxide sols. J. Phys. Chem., 46: 81-92.

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Jerlov, N.G. (1951). Optical measurement of particle distribution in the sea. Tellus,3j^ 122-128. 125 Jerlov, N.G. (1953a). Particle distribution in the ocean* Rept. Swedish Deep-Sea Expd. 1947-48, 2i 71-97. Elanders Boktryckeri Aktiebolag, Goteborg, Sweden.

Jerlov, N.G. (1953b) Influence of suspended and dissolved.1 matter in the transparency of sea water. Tellus, 5j_ 59-65. Jerlov, N.G* (1955) The particulate matter in the sea as determined by means of the Tyndall meter. Tellus, 7: 218-225. Jerlov, N.G. and B. Kullenberg. (1953). The Tyndall effect of uniform minerogenic suspensions. Tellus,5: 306-307.

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TABLE I. Catalogue of the surveys during the period May, 1957 to June, 1958.

Cruise Date Inlets No. of Hydro- Cruise No. Prom To Surveyed graphic Stations

7 18 Bute 20 57/4 May 1957 Jervis 17

18 30 Bute Inlet System 23 57/9 July 1957 Jervis 9

11 25 Bute Inlet System 30 57/12 September Loughborough 6 1957 Call 4 Knight 19

13 23 Bute Inlet System 23 57/15 November Jervis Inlet 8 1957

11 20 Bute Inlet System 25 58/3 February Jervis Inlet 12 1958

20 27 58/5 March 1958 Bute Inlet System 24

9 17 Bute Inlet System 21 58/11 June 1958 Jervis Inlet 8 Knight Inlet 6 130. TABLE II. Size of the material in suspension in Bute Inlet, and a 1 comparison with Suspended Material Present in Other Localities.

Location and Depth at which Size of the Particle Sizes Size of the Suspended Time of Drawing Samples Drawn Suspended Bute Inlet Material Found in Remarks of Samples (meters) Material (Toombs| 1956) * Several Other Localities (Microns-^) (Microns-^)

JL1 Samples. 0, 2 and 5 Max.d=4$4 22 Chesapeake Bay. Particle size- In any sample suspended material Head of Bute, Min.d=0.75>^ 18 distribution highly skewed to• of biological origin<0.5$ (by Toba, and Average Geome• ward particles with average volume) of the total suspended Knight Inlets. tric-Mean Dia• diameters l/t clearer samples (those below 400 meters) had material of 8 Samples. 20, 50, 75 Max.d = 21/t 11 diameters < 0.4p. Marine organisms accounted, in Bute Inlet, 100, 200, Min.d = 0.5/x (Burt 1958). all samples for between 3 and Station 4. 300, 400 Average 9$ by volume of total material September 500 =12.3 ±+ 1.2/. and possessed sizes between 5A 1957. English Coastal Waters: and 10/t.Governing particle Most scattering caused by size effectively constant with articles > 1^ depth. ?Atkins and Poole, 1952).

12 Samples Max.d s 15AC Gullmar Fiord, Sweden: Marine organisms accounted in Calm & Homfray Min.d = 0.5yx About 50$ of the particles any sample for between 5 and Channels, Surface Average Da less than 2ji in diameter; 10$ by valume of the suspended Mouth of Bute = 7.3 + 1.5/* about 30$ between 2 and 4/t material; the great majority Inlet. about 12$ between 4 and of the organisms was between February 1958 10 ju. ; about 6$ between 3 and 6// in size. 10 and 20yu (Jerlov, 1955). These results were utilized to Head of Feb. 25,50,75 estimate rates of sedimentation Bute 1958 100 10.5 + 1.5/4 Inlet in Bute Inlet; samples in the June 25,50,75 Average 3.= shallow zone "source" of the 1958 100 17 suspended material were not ± V* considered. At both the head Mouth Feb. 100, 200, 300 Average Ja = and the mouth, uniformity of of 1958 400, 500 7.1 + \1%JJL governing particle size occur• Bute red throughout the water column Inlet June 100, 200, 300 Average D» - in both winter (Feb. 1958) and 1958 400, 500 8.0 + \ji summer (June 1958).

* Median Particles Sizes Found in Bottom Sediments at Corresponding Locations in Bute Inlet 131 TABLE III. Relationships between the turbidity and the concentration of suspended material.

Parti• Turbidity-Concentration Range of culars (Z -C^) relationships Variables _^ of Samples ( Z in meters"" Present Jerlov and C in mg.per Remarks Work Kullenberg (1953) liter

Cy in ppm ;

12 I(45°)=35C +10 ?=o.ic o

8 I(45)=20C + 26 f=0.06C 0.5

11 I(45)=41C + 445 r=0.75 C Z>& Marked Discre*- Samples. (Correlation _> „ w 80

Head of e n 83)= 0 c the twoZrC r Ti1r +li' ^ " 30

N.B. The values utilized for the volume "shape-factor" (0.14) and for the density (2.65 grams per cm ) of the suspended material were those for the minerogenic material pre- dominent in all cases. —, 1 —— 1

,27ow I25«W I23°W

Fig. 1. Southern British Columbia Mainland Inlets. Pig. 2. Bute and Toba Inlets and Adjacent Channels.

126° 30' W 126° W 125° 30' W KLINAKLINI RIVER

- 51° N 51° N " 0 5 10 NAUTICAL MILES

• STATION POSITIONS

Fig. 4. Knight and Loughborough Inlets and Call Creek. A Fig. 5. Effective Area Coefficient for Scattering-K -as a function of I=|HM- ). m = 1.15, -291mm —— mmm— - 73 mm - 85 mm 70** — rt-ZERO DE6REE -FILTER POSITIONS TT/—SHUTTER N NEUTRAL FILTER NO. 5 86

-FILTER POSITION NO. I (COL. LENS)

AM-4 LAMP- -LIGHT TRAP

-PHOTOMULTIPLIER TUBE

-REMOVABLE LIGHT FILTER INCIDENT SLITS (-RECEIVER NOSE PIECE STOP POSITION NO. 2 WITH 5 MOUNTS INCIDENT NOSE PIECE

Fig. 6. Optical System of the American Instrument Company Light-Scattering Photometer. NAUTICAL MILES

Fi'g.7.Bute Inlet, Sutil Channel. Distribution of Z(m"-) in Longitudinal Section. Feb. 1958. GEORGIA HOMFRAY CHANNEL CALM HOMFRAY ' TOBA INLET STRAIT >, CHANNEL CHANNEL f 4 3 1 2

V7777777P JUNCTION JUNCTION WITH WITH NAUTICAL MILES TOBA CALM INLET CHANNEL

Fig. 8.Homfray Channel, Toba Inlet .Distribution of T(m=^") in Longitudinal Section. Feb. 1958. 700 L NAUTICAL MILES

Pig.9.Bute Inlet.Sutil Channel.Distribution of S ( / do)in Longitudinal Section. Feb. 1958. .nomrray unannei,iooa miex.uistrxDuxion or s \

Y- YUCULTA RAPIDS A- ARRAN RAPIDS

CHANNEL

/ i 1 1 >777777777? 0 5 10 700 NAUTICAL MILES Pig.11.Bute Inlet.Sutil Channel.Distribution of T ( C) in Longitudinal Section. Feb. 1958. HOMFRAY CHANNEL CALM HOMFRAY TOBA INLET

Pig.12.Homfray Channel,Toba Inlet.Distribution of T (°C) in Longitudinal Section. Feb. 1958. GEORGIA SUTIL CHANNEL CALM Y BUTE INLET STRAIT * :—\ CHANNEL /- I 2 3 0 ,

IOO -

200

300

UJ Q

400

500 Y- YUCULTA RAPIDS A- ARRAN RAPIDS

600

0 5 10 700 NAUTICAL MILES

Fig.13.Bute Inlet.Sutil Channel .Distribution of Density (CTt)in Longitudinal Section. Feb. 1958. GEORGIA HOMFRAY CHANNEL CALM HOMFRAY TOBA INLET STRAIT y ' ^ CHANNEL CHANNEL Y ^

Pig.14.Homfray Channel,Toba Inlet.Distribution of Density (

JUNCTION Y- YUCULTA RAPIDS WITH A- ARRAN RAPIDS HOMFRAY CHANNEL

$7777777777^ 0 5 10 700 NAUTICAL MILES

Fig.15.Bute Inlet.Sutil Channel .Distribution of $2 lite? )in Longitudinal Section Feb. 1958. GEORGIA HOMFRAY CHANNEL CALM HOMFRAY TOBA INLET

Fig.l6.Honifray Channel,Toba Inlet.Distribution of 02(mg I liter) in Longitudinal Section.Feb.1958

Fig.18.Homfray Channel,Toba Inlet. Distribution of Z (m ) in Longitudinal Section. June 1958, GEORGIA SUTIL CHANNEL CALM BUTE INLET STRAIT 8 HEAD

100

200 -

300 •>

a. ui a

400

500 Y- YUCULTA RAPIDS A- ARRAN RAPIDS

600

$7777777777^ 0 5 10 700 L NAUTICAL MILES Fig.19.Bute Inlet.Sutil Channel.Distribution of S ( / oo)in Longitudinal Section.June 1958. Fig.20.Homfray Channel,Toba Inlet.Distrintion of StV'o.-o) in Longitudinal Section.June 1958. GEORGIA SUTIL CHANNEL CALM Y BUTE INLET STRAIT "\ CHANNEL 2 3 . .0 8 HEAD'

100 h

200

cr UJ t- UJ 2 300 k

a. UJ a 400

500 h YUCULTA RAPIDS ARRAN RAPIDS

600

$7777777777^ 0 5 10 700 NAUTICAL MILES

Pig.21.Bute Inlet,Sutil Channel.Distribution of T (°C) in Longitudinal Section. June 1958. GEORGIA HOMFRAY CHANNEL CALM HOMFRAY TOBA INLET

Pig.22.Homfray Channel,Toba Inlet'.Distribution of T (°C) in Longitudinal Section. June 1958. GEORGIA SUTIL CHANNEL BUTE INLET STRAIT HEAD

Y- YUCULTA RAPIDS A- ARRAN RAPIDS

/ r >777777777T^ 0 5 10 TOO NAUTICAL MILES

Fig.23.Bute Inlet,Sutil Channel.Distribution of Density (Ct) in Longitudinal Section.June 1958 ;'ig. 24.Homfray Channel,Toba InletvDrstribution of Density \trt) in Longitudinal Section.June 1958. Fig.25.Bute Inlet,Sutil Channel.Distribution of 0>,(mg.7 liter)in Longitudinal Section.June 1958. GEORGIA HOMFRAY CHANNEL ^ CALM . HOMFRAY TOBA INLET

Figv26.Homfray Channel.Toba.Inlet.Distribution of 0 (mg/liter) in Longitudinal Section. June 1958 .27.Bute Inlet.Distribution of ZiaT1) in Longitudinal Section. May 1957. GEORGIA SUTIL CHANNEL CALM Y BUTE INLET STRAIT -\ CHANNEL /-] 3 0 8 HEAD

JUNCTION Y- YUCULTA RAPIDS WITH A- ARRAN RAPIDS HOMFRAY CHANNEL \ 1.4 0 5 10 700 L NAUTICAL MILES

Fig.28.Bute Inlet,Sutil Channel.Distribution of Z (m^) in Longitudinal Section. July 1957. GEORGIA HOMFRAY CHANNEL CALM HOMFRAY TOBA INLET

Pig, 29. Homfray Channel. Distribution*of Z (m~ ) in Lbngitudinal Section. July 1957. Pig.30.Bute Inlet.Distribution of Z(m~ ) in Longitudinal Section. Sept. 1957. GEORGIA HOMFRAY CHANNEL CALM HOMFRAY TOBA INLET STRAIT '/ ' CHANNEL CHANNEL /• * ^

Fig. 31. Homfray Channel, Toba Inlet. Distribution of Z (m~ ) in Longitudinal Section.Sept.1957. GEORGIA SUTIL CHANNEL CALM Y BUTE INLET STRAIT -\ CHANNEL /*\ 3 JL. 0 6 7 8 HEAD

Y- YUCULTA RAPIDS A- ARRAN RAPIDS

CHANNEL

^7777777777^ 0 5 10 700 NAUTICAL MILES I : • ,r —. Fig.32.Bute Inlet,Sutil Channel.Distribution of 2T(m ) in Longitudinal Section. Nov. 1957. GEORGIA HOMFRAY CHANNEL CALM HOMFRAY TOBA INLET

Pig. 33.Homfray Channel.Distribution of Z(m~x) in Longitudinal Section. Nov. 1957. j.

GEORGIA SUTIL CHANNEL CALM Y A BUTE INLET GEORGIA HOMFRAY CHANNEL CALM HOMFRAY TOBA INLET STRAIT >, CHANNEL CHANNEL f 4 3 I "0123

V77777777' JUNCTION JUNCTION WITH WITH NAUTICAL MILES TOBA ^@flsM*% INLET CHANNEL

Pig. 35. Homfray Channel. Distribution of Z (m"1) in Longitudinal Section, March 1958. Pig.36.Jervis Inlet.Distribution of Z(m~ ) in Longitudinal Section. Feb. 1958. STATION HEAD

Q- 400 UJ Q

D- DESERTED RIVER PL- PRINCESS LOUISA INLET

0 5 10 NAUTICAL MILES

Fig.37.Jervis Inlet.Distribution of S( /• oo) in Longitudinal Section. Feb. 1958. Fig.38.Jervis Inlet.Distribution of T (°C) in Longitudinal Section. Feb. 1958. STATION r* 0 I 2 3 4 5 6 7 Bj 9j 10 - HEAD

Pig. 39. Jervis inlet. Dis^trxbtrfeicrir af^l^Ha^fcy '^(T^i±n- -Longitudinal Section. Feb. 1958. STATION

Fig, 40,Jervis Inlet.Distribution of 00(mg,/liter)in Longitudinal Section. Feb, 1958,

STATION STATION HEAD

D— DESERTED RIVER PL- PRINCESS LOUISA INLET

0 5 NAUTICAL MILES

Pig.43.Jervis Inlet.Distribution of T ( C)in Longitudinal Section. June 1958 D PL

Fig.44iJervis Inlet.Distribution of Density in Longitudinal Section. June 1958. Pig.45.Jervis Inlet.Distribution: .of • 02(mg-./liter) in Longitudinal Section. June 1958. STATION D PL

Fig.4£. Jervis Inlet. Distribution of Z(m~ ) in Longitudinal Section. May 1957. Pig.47.Jervis Inlet.Distribution of\ X (m~ ) in Longitudinal Section. November 1957. o io 20 NAUTICAL WULES

77777777,

Pig.48.Knight Inlet.Longitudinal Distribution of Properties. Sept. 1957. 1 1 1 0 5 10 NAUTICAL MILES

Pig.49. Loughborough Inlet. Longitudinal Distribution of Properties Sept. 1957. o 5 ib NAUTICAL MILES

10.7 I2J> 167

Fig.50. Call Creek. Longitudinal Distribution of Properties. Sept. 1957. \

0 30 60 90 120 150 01 0 30 60 90 120 150 SCATTERING ANGLE 0 (•) Pig. 51. Polar Diagrams of the Scattering Exhibited by Inlet Waters. Fig.52.Relationship between Turbidity and Weight-Concentration. I I I I I I I I 1 I 1 1 1 MJJ ASOND JFMAMJ | 1957 1 1958 Pig.53. Monthly Mean Discharge Values, Homathko River. May 1957-June 1958. 100

Head of Bute Inlet Mouth of Bute Inlet Station 8= Depth~l50m Station h Depth ~ 580 m o 9 uoi 0 meters

o s o'

ui ^ < t

X Q

Q 3

>- _l X o 2

j i i i i i i i i i i 0.1M J JASONDJFMAMJJMJ JASO NDJ FMAMJJ

1 III ii II ll i i I i CRUISE NO. 57/4 57/9 57/12 57/15 58/3 58/5 58/11 57/4 57/9 57/12 57/15 58/3 58/5 58/11 Pig.54. Seasonal Variation of Turbidity in Bute Inlet. May 1957-June 1958.