Antarctic intermediate water in the South Pacific Ocean

187 Pages·2012·1.58 MB·English

AN ABSTRACT OF THE THESIS OF
Ronald Ernest Johnson for the Doctor of Philosoph
(Degree)
(Name)
presented on September 28, 1971
in Oceanography
(Date)
(Major)
Title: ANTARCTIC INTERMEDIATE WATER IN THE SOUTH
PACIFIC OCEAN
Redacted for Privacy
Abstract approved:
The distribution of Antarctic Intermediate Water in the South
Pacific has been examined using a model of horizontal advection,
along the Sigma-t surface 27. 10, with three point vertical mixing.
traced
The core of the A.ntarctic Intermediate Water mass was
The charts used to
from the Antarctic Convergence northward.
describe the distribution were those of core depth, salinity, per-
Thickness, and acceleration poten-
centage composition, Equivalent
tial. The percentage composition of Antarctic Intermediate Water
in the entire water column for all stations was computed and the
Intermediate water volume for
Equivalent Thickness determined.
the South Pacific was then calculated. North-South geostrophic
velocities and transports were computed for two zonal sections.
The model agreed quite well with the flow patterns reported by
The broad counterclockwise gyre in the central
other investigators.
South Pacific, the flow into the Tasman and Coral Seas, the localized
flow near New Zealand, and the suggestion of southward flow near
A pre-
the South American Coast are all indicated by the model.
viously unreported small, counterclockwise gyre in the southeast
South Pacific was detected. The circulation within the small gyre
is consistent wity flow over a variable bottom in the Southern Hemis-
phere. Antarctic Intermediate Water transport across selected
sections indicate a northward flow of 10 x 10 m sec. A low
salinity tongue was found on the salinity chart. This tongue extended
northward, then westward, into the northern Tasman Sea. The
salinity was over 34. 500/00 in the center of this counterclockwise
motion east of New Zealand. The isohalines in the southeast Pacific
suggest the presence of the small counterclockwise gyre. A 20
percent drop in core percentage composition was noted in the 10 de-
grees north of the Antarctic Convergence. A large uniform area
between 80 percent and 70 percent over the central portion of the
central South Pacific was bounded on the north by a 20 percent drop
near the equator, again supporting the general counterclockwise
circulation.
The Equivalent Thickness distribution showed a general lenticu-
lar shape, the thickest part lying in the center of the counterclock-
wise gyre east of New Zealand. The Equivalent Thickness distri-
bution, as well as the core percentage, supported the hypothesis of
little or no flow into the Tasman Sea from the south. The volume of
intermediate water obtained from surface area integration of the
Equivalent Thickness distribution was 59. 44 x 106 km3. This is
approximately 16% of the water volume in the South Pacific.
1971
RONALD ERNEST JOHNSON
ALL RIGHTS RESERVED
Antarctic Intermediate Water
in the South Pacific Ocean
by
Ronald Ernest Johnson
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Doctor of Philosophy
June l97Z
APPROVED:
Redacted for Privacy
Profelsor of Oceanography
In Charge of Major
Redacted for Privacy
Chaiiman of Departmnt of Oceanography
Redacted for Privacy
Dean of Graduate School
Date thesis is presented September 8, 1971
Typed by Marcia Griffin for Ronald Ernest Johnson
ACKNOWLEDGEMENTS
I wish to thank my wife, Roberta, Miss Margaret Poole, and
Miss Deecee Davenport who typed the first drafts; and Messrs.
Dennis Barstow, Zvi Weinman, William Weiss, and Paul Moersdorf
for the drafting of all thesis figures and charts. I also wish to thank
Dr. June Pattullo for suggesting the thesis topic; Mr. Joe Reid for
providing the opportunity to participate on a data collection cruise
in the study area; and Mrs. Marcia Griffin who typed the thesis on
short notice.
The funding for the basic calculations was provided by a
Bureau of Commercial Fisheries fellowship in ocean engineering and
an Office of Naval Research Assistantship, Nonr 1286(1).
TABLE OF CONTENTS
Page
INTRODUCTION 1
LITERATURE SURVEY 5
Introduction 5
Formation Zone S
Distribution 9
Volume Determinations 17
MODEL AND DATA 26
Model 26
Introduction 26
Isentropic Analysis 29
Three Point Vertical Mixing 31
Data 47
ANTARCTIC INTERMEDIATE WATER DISTRIBUTION 49
Core Characteristics 49
Formation Position 49
Depth 49
Salinity 51
Percent Composition 52
Equivalent Thickness 56
Percent Composition With Depth 56
Equivalent Thickness Distribution 62
AAIW Volume 64
Volume Calculations 64
Volume Distribution 68
Page
72
L)YNAMIC CALCJLAT1ONS
Geostrophic Velocities 72
Level of No Motion 72
Dynamic-Height Anomalies 73
Flow Direction 74
Velocity Magnitude Estimates 76
Geostrophic Transport 78
Section Locations 78
Relation to Percent AAIW Composition 79
82
SUMMARY AND CONCLUSIONS
84
RELATED PROBLEMS
Movement of AAIW 84
Other Models 86
BIBLIOGRAPHY
Literature Sources 89
Data Sources 99
APPENDICES 103
Sources of Oceanographic Stations 104
I
Isentropic Analysis 110
II lii
Derivation
A.
Example Acceleration Potential Calculation 116
B.
Example Geostrophic Velocity Calculation 117
C.
Ill Three-Point Mixing 120
Derivation 121
A.
Example AAIW Percentages Calculation 123
B.
Graphical Solution 124
C.
Data Reduction Summary, Acceleration 126
IV
Potential 127
Page
137
APPENDICES (Cont.)
Data Reduction Summary, Percent Composition
V
and Equivalent Thickness 138
Vi Data Reduction Summary 148
Volume Calculations 149
Equivalent Thickness Modifiers 166