Oceanography and marine biology. : volume 26 an annual review

552 Pages·1988·7.9 MB·English

by  Barnes

OCEANOGRAPHY AND MARINE BIOLOGY
AN ANNUAL REVIEW
Volume 26
OCEANOGRAPHY AND MARINE
BIOLOGY
AN ANNUAL REVIEW
Volume 26
HAROLD BARNES, Founder Editor
MARGARET BARNES, Editor
The Dunstaffnage Marine Research Laboratory
Oban, Argyll, Scotland
Assistant Editors
A.D.Ansell
R.N.Gibson
T.H.Pearson
FIRST PUBLISHED IN 1988
This edition published in the Taylor & Francis e-Library, 2005.
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© Aberdeen University Press 1988
British Library Cataloguing in Publication Data
Oceanography and marine biology: an annual
review.—Vol. 26
1. Oceanography—Serials
2. Marine biology—Serials
551.46′005
ISBN 0-203-02079-0 Master e-book ISBN
ISBN 0-203-19129-3 (Adobe eReader Format)
ISBN 0-08-036397-0 (Print Edition)
ISSN 0075-3218
ABERDEEN UNIVERSITY PRESS
PREFACE
The completion of the twenty-fifth volume of these Annual Reviews seemed an appropriate time to
introduce some editorial help so that the continuity of the Series is ensured. From Volume 26 onwards my
colleagues Drs A.D. Ansell, R.N.Gibson, and T.H.Pearson join me as assistant editors. In this way the
immense amount of editorial work will be shared and not fall too heavily on any particular person. It is a
pleasure to have them with me.
As usual we have had excellent co-operation from all the contributors to the present volume. Our thanks
are due to them for acceding to our requests and to the publishers for maintaining the regular appearance of
these Annual Reviews.
CONTENTS
PREFACE iv
Numerical Simulation of Oceanographic Processes in the Waters between Vancouver Island and 1
the Mainland
P.B.CREAN, T.S.MURTY and J.A.STRONACH
Carbon Flow in Fjords 1 18
DAVID C.BURRELL
Seasonality in the Deep Sea 1 92
P.A.TYLER
Structure of the Cell Walls of Marine Algae: Ecophysiological Functions of the Matrix 2 21
Polysaccharides
B.KLOAREGR and S.QUATRANO
Comparative Oceanic Ecology of the Plankton Communities of the Subarctic Atlantic and Pacific 2 73
Oceans
T.R.PARSONS and C.M.LALLI
Diel Vertical Migration: Zooplankton Photobiology and Behaviour 3 11
RICHARD B.FORWARD JR.
The Benguela Ecosystem. Part V. The Coastal Zone 3 41
G.M.BRANCH and C.L.GRIFFITHS
The Replenishment of Coral Reef Fish Populations 4 22
PETER J.DOHERTY and DAVID McB.WILLIAMS
Are Cetacea Ecologically Important? 4 79
STEVEN KATONA and HAL WHITEHEAD
AUTHOR INDEX 493
SYSTEMATIC INDEX 5 23
SUBJECT INDEX 5 32
Oceanogr. Mar. Biol Annu. Rev., 1988, 26, 11–142
Margaret Barnes, Ed.
Aberdeen University Press
NUMERICAL SIMULATION OF OCEANOGRAPHIC
PROCESSES IN THE WATERS BETWEEN VANCOUVER
ISLAND AND THE MAINLAND
P.B.CREAN and T.S.MURTY
Department of Fisheries and Oceans, P.O. Box 6000, Sidney, British Columbia, Canada
V8L 4B2
and
J.A.STRONACH
Pacific Ocean Sciences Limited, 301A–3700 Gilmore Way, Burnaby, British Columbia,
Canada V5G 4M1
ABSTRACT The estuarine circulation in the waters (Strait of Georgia and Juan de Fuca Strait)
between Vancouver Island and the mainland is superimposed on the interactions of strong tides
of the mixed type with highly complex topography which result in the formation of eddies and
associated residual circulation. The major source of fresh water (Fraser River) forms a tidally
and seasonally modulated (1000–10000 m3/s) buoyant jet which interacts with the strongly
divergent lateral tidal streams in the Strait of Georgia. Vertical mixing by the strong tidal streams
in the constricted channels leading seaward from the Strait of Georgia strongly influences the
nature of the estuarine circulation. The system is subject to a further major annual modulation
as deep mixed water in the system is displaced by intruding ocean water from the adjacent
continental shelf. Basic features of these processes have been systematically investigated with
an evolving sequence of one-, two-, and three-dimensional models. The results are shown to be
consistent with field data, either existing or acquired for the purpose.
INTRODUCTION
The waters between Vancouver Island and the mainland coasts of British Columbia and the state of
Washington constitute a deep, topographically complex and strongly tidal estuarine system. Contiguous to
the main population centres, Vancouver and Seattle, they are characterized by high traffic density, both
commercial and recreational, and, in addition, support major fisheries. Pressing questions involve the
effects of commercial and domestic effluent, provision of data for biological research programmes, and
2 P.B.CREAN, T.S.MURTY AND J.A.STRONACH
shore and underwater coastal engineering installations. An excellent general account of the physical
oceanography of the region may be found in Thomson (1981).
This review is primarily concerned with the numerical modelling studies undertaken to achieve an
understanding of elements controlling the basic circulation in the system, starting from features that stand
out clearly against the background of less systematic variability. The approach is based on the development
of several numerical models in which external forcing and bathymetry are well resolved, and the turbulent
momentum and mass flux terms in the governing equations are adequately approximated. Extensive use is
made of field data, in many instances specifically obtained in light of features of the circulation predicted by
the models. Thus, emphasis has been placed on understanding salient aspects of the physics of the system
using finite-difference numerical schemes found satisfactory in other applications.
The basic geographical features of the region (Fig. 1) consist essentially of an outer strait (Juan de Fuca)
140 km long and surface area of 3700 km2, and an inner strait (Georgia) 200 km long with widths 20–40 km
and surface area about 7000 km2. The major axes of both straits are approximately parallel, joined by a
180° bend containing a complex of islands (San Juan Islands) which lie at the head of a major system of
side channels (Puget Sound) having an area about 2600 km2. The bottom topography of the inner and outer
straits (Fig. 2) illustrates the complex nature of the two major conveying channels between the mentioned
straits. Haro Strait (Figs 1 and 2) contains a deep trench with depths 180–250 m and a shallow irregular sill,
about 60 m deep, at its northern end which contains a short (0.5 km), narrow (0.5 km), and deep (250 m)
passage (Boundary Passage). This strait plays a major rôle in the fresh- and salt-water exchanges in the
flushing of the inner basin. The other major conveying channel through the islands, Rosario Strait, is
shallower (60–70 m) and hence is limited in its capacity to replenish deep saline water in the inner basin.
The inner strait is connected to the open sea at its northern end through a series of narrow channels
(referred to later as the northern passages) containing relatively shallow sills 30–100 m deep where tidal
velocities can exceed 6 m/s. In the aggregate, the associated cross-sectional areas constitute less than 7% of
the comparable cross sectional area available to the south in Haro and Rosario Straits, and thus limit
seaward egress of fresh water northward. A number of fjords with sills at their mouths and with interior
depths of up to 800 m open into the system from the mainland coast. The Fraser River which drains the
largest watershed in the province of British Columbia (230 000 km2), constitutes by far the largest single
source of fresh water entering the system and accounts for 70–80% of total freshwater input.
Winds in the northeastern Pacific Ocean are dominated by two major atmospheric pressure systems, the
North Pacific high and the Aleutian low. Variations in location and intensity of these systems strongly
influence the prevailing winds over the offshore waters, the high tending to dominate the region in summer,
the low during the winter. Thus, from October to March, cyclonic winds associated with the Aleutian low
result in a dominance of southeasterlies whereas in summer weaker winds from the west or northwest,
associated with the anticyclonic North Pacific high, tend to prevail (Kendrew & Kerr, 1955).
Winds over the waters between Vancouver Island and the mainland are strongly influenced by
mountainous terrain. In Juan de Fuca Strait, the cyclonic winds over the water tend to be associated with
easterlies. In summer inward-blowing westerlies are likely to accompany anticyclonic systems. Over the
southern part of the Strait of Georgia and the San Juan Islands, funnelling effects of Juan de Fuca Strait,
Puget Sound, and the Fraser Valley (which opens out onto the Vancouver lower mainland area) play an
important rôle, favouring a closed anticlockwise wind pattern during the winter. In summer the winds are
lighter with a less regular pattern, but still tend to dominate from the southeast and southwest. Over the
northern part of the Strait of Georgia there is a closer approximation to the offshore seasonal wind patterns,
southeasterlies again dominating in winter, northwesterlies in summer. Further complications of these basic
patterns tend to result from differential heating of land and sea during fine weather and from outbreaks of
NUMERICAL SIMULATION OF OCEANOGRAPHIC PROCESSES 3
Fig. 1.—Location map of the study area for British Columbia and Washington waters. Inset indicates the site locations
referred to in the text. The dashed line from A to B denotes the locations of the hydrographie stations used in the
represented contoured vertical sections of salinity and temperature (Figs 3 and 4).
polar continental air that stream down the valleys and inlets leading from the interior of British Columbia to
the coast in winter.
The oceanic tide is of the mixed type and moves northward past the mouth of the outer strait and the
western coast of Vancouver Island. Tidal cooscillations within the system result in the semi-diurnal
constituents having degenerate amphidromes in the inner part of the outer strait while diurnal amplitudes
and phases increase monotonically up to the northern end of the inner strait. The passage of the semi-
diurnal tides along the seaward coast of Vancouver Island takes approximately 20 min while the same tide
takes about 5 h to traverse the shallower confines of the outer and inner straits, leading to significant
differences in tidal elevations through the narrow channels that link the northern end of the inner strait to
4 P.B.CREAN, T.S.MURTY AND J.A.STRONACH
Fig. 2.—Bathymetry of the Strait of Georgia, San Juan Islands region, and Juan de Fuca Strait.

the open sea. As a consequence, the largest tidal streams in the world are to be found associated with
constrictions in these channels.
In the system, density is primarily determined by salinity although temperature may have an appreciable
dynamical effect under unusually cold winter conditions when saline stratification tends to be least. The