Oceanography and marine biology. : volume 26 an annual review PDF
Preview Oceanography and marine biology. : volume 26 an annual review
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. “To purchase your own copy of this or any of Taylor & Francis or Routledge’s collection of thousands of eBooks please go to www.eBookstore.tandf.co.uk.” This book is copyright under the Berne Convention. All rights reserved. Apart from any fair dealing for the purpose of private study, research, criticism or review, as permitted under the Copyright Act, 1956, no part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, electrical, chemical, mechanical, optical, photocopying, recording or otherwise, without the prior permission of the copyright owner. Enquiries should be addressed to the Publishers. © 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
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