Bathymetry and structure of the Arctic Ocean

221 Pages·2012·12.15 MB·English

AN ABSTRACT OF THE THESIS OF
MIAH ALLAN BEAL for the Doctor of Philosophy
(Name) (Degree)
in Oceanography presented on August 12. 1968
(Major) (Date)
Title: Batymety and_Strictuof_thp..4rctic_Ocean
Redacted for Privacy
Abstract approved:
John V.
The history of the explordtion of the Central Arctic Ocean is
reviewed. It has been only within the last 15 years that any signifi-
cant number of depth-sounding data have been collected. The present
study uses seven million echo soundings collected by U. S. Navy
nuclear submarines along nearly 40, 000 km of track to construct,
for the first time, a reasonably complete picture of the physiography
of the basin of the Arctic Ocean. The use of nuclear submarines as
under-ice survey ships is discussed.
The physiography of the entire Arctic basin and of each of the
major features in the basin are described, illustrated and named.
The dominant ocean floor features are three mountain ranges,
generally paralleling each other and the 40°E. 140°W. meridian.
From the Pacific- side of the Arctic basin toward the Atlantic, they
are: The Alpha Cordillera; The Lomonosov Ridge; and The Nansen
Cordillera.
The Alpha Cordillera is the widest of the three mountain
ranges. It abuts the continental slopes off the Canadian Archipelago
and off Asia across more than 550 of longitude on each slope. Its
minimum width of about 300 km is located midway between North
America and Asia. In cross section, the Alpha Cordillera is a
broad arch rising about two km, above the floor of the basin. The
arch is marked by volcanoes and regions of "high fractured plateau,
and by scarps 500 to 1000 meters high. The small number of data
from seismology, heat flow, magnetics and gravity studies are
reviewed. The Alpha Cordillera is interpreted to be an inactive
mid-ocean ridge which has undergone some subsidence.
The Lomonosov Ridge is a narrow mountain range which extends
from the continental slope off the Lincoln Sea to the Eurasian slope
off the New Siberian Islands. In the middle of the basin, the
Lomonosov Ridge is only 40 to 75 km wide. It becomes broader at
the continental margins, where it merges with the Alpha Cordillera.
In cross section, the Ridge has side slopes convex upward to a
rounded crest. The minimum water depth on the Lomonosov
Ridge is about 750 meters. It has a relief of about 3,200 meters
above the floor of the basin. Aeromagnetic data indicates that the
Ridge is not of volcanic rock and earthquake distribution data show
that it is aseismic. The Lomonosov Ridge is interpreted to be a
continental outlier in the Arctic basin.
The Nansen Cordillera is an extension of the Mid-Atlantic
Ridge across the Arctic basin. It extends from the passage between
Greenland and Svalbard (The Lena Trough) to the Eurasian continental
slope off the Lena River. Its axis lies on a great circle between
these two points. In cross section, the Nansen Cordillera is about
200 km wide. It is made up of volcanoes or ridges standing about
1500 meters above the basin floor. There are V-shaped rifts in
the Cordillera which are 1500 meters deeper than the basin floor (to
5500 meters water depth). Earthquake study shows that essentially
all epicenters in the Arctic basin are in the Nansen Cordillera.
Aeromagnetic data indicate that its rocks are only weakly magnetic.
The Nansen Cordillera is interpreted to be an 'embryonic" mid-
ocean ridge. The basin floor is being rifted, but no uplift has
occurred as yet.
The three mountain ranges divide the Arctic basin into four
sub-basins, each floored by a plain. From the Pacific-side of the
Arctic basin these are: 1) The Canada Basin, bounded by the conti-
nental slopes of Alaska and Siberia and the Alpha Cordillera and
floored by Canada Plain; 2) The Makarov Basin, bounded by the Alpha
Cordillera and the Lomonosov Ridge and floored by Fletcher Plain;
3) The Fram Basin, bounded by the Lomonosov Ridge and the Nansen
Cordillera and floored by Hakkel' Plain; and, 4) the Nautilus Basin,
bounded by the Nansen Cordillera and the continental slope of Europe
and floored by the Sverdrup Plain. Each of these plains is close to
4000 meters deep. Echograms show that they have slopes of only
about 1:4000, but minor 'bumps" and swales of some ten meters
relief are also shown.
There are three regions of a few hundred meters depth on the
margin of the Arctic basin. These are called the Arctic Rises. The
largest of these is the Chukchi Rise, which appears to be an exten-
sion of the Continental Shelf between Alaska and Siberia. The other
two rises flank the Lena Trough. The Morris Jesup Rise, north of
Greenland, appears to be a part of the Lomonosov Ridge. The
Yermak Rise is an extension of the continent north of Svalbard.
Two plains at intermediate depth (2000 to 3000 meters) are
located on the flanks of the Alpha Cordillera at its intersection with
the continental slope of Eurasia. These are named the Chukchi
Plain and the Wrangel Plain. Each appears to be ponded sediment.
The Lomonosov Ridge is taken as a boundary to divide the
Arctic basin into two major sub-basins. The Fram and Nautilus
Basins together make up the Eurasia Basin. The Makarov and
Canada Basins together form the Amerasia Basin.
The continental slopes and rises around the margins of the
Arctic basin are described and illustrated. The slopes generally
are steep and broken and the rise poorly developed except for the
section off the Mackenzie River and north of Alaska.
Geophysical data from the Arctic basin are few and do not
provide good geographical coverage. The data are reviewed and
related to the physiography of the basin. It is hypothesized that the
entire floor of the Arctic basin formed on the Alpha Cordillera
following fracturing of a continent by mantle upwelling. Following
formation of the basin by sea floor spreading, the cell centered
beneath the Alpha Cordillera ceased to convect and is now in a cooling
phase. A new phase of mantle convection is now thought to be begin-
ning beneath the Nansen Cordillera.
The geographical arrangement of the ocean floor features in
the Arctic basin is discussed. It is suggested that the Arctic Rises
and the Lomonosov Ridge are composed of fragments of the Arctic
Paleozoic Fold Belts. This in turn indicates that the continental
block was fractured in the Paleozoic Fold Belts rather than in the
Precambrian Shields.
Possible former extensions of the mantle convection cell,
which is thought to have existed beneath the Arctic basin, are
discussed. Evidence is presented for a "circular" termination of the
cell at the Eurasian end of the Alpha Cordillera. Toward the Atlantic,
the axis of the former convection cell is traced through Baffin Bay
and into the Labrador Sea. A farther extension to an intersection
with the Mid-Atlantic Ridge at 28° N. Lat. is suggested. The
possible size and extent of the former convection cell is discussed
and the name Wegener Rise proposed for its manifestation in the
Earth's crust. The time of the formation of the Arctic basin is
considered, although there are no unique data for age dating avail-
able from the basin itself.
Bathymetry and Structure of the Arctic Ocean
by
Miah Allan Beal
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Doctor of Philosophy
June 1969

APPROVED:
Redacted for Privacy
Professo\ of Oceanography
in charge of mjOr
\
Redacted for Privacy
Chairm n of the Departme of Ocean?py
Redacted for Privacy
Dean clf graduate School
Date thesis is presented August 12, 1968
Typed by Marion F. Palmateer for Miah Allan Beal
AC KNOW LE DGEME NT
I am deeply indebted to many people for assistance in the col-
lection of the data upon which this study is based. Above all, great
credit must be given to the officers and ratings of the nuclear sub-
marines: The men who probed into the unknown regions beneath the
ice pack to gather knowledge where none had existed before.
A debt to Dr. Waldo K. Lyon, Civilian Research Director for
the Arctic submarine expeditions is gratefully acknowledged. It was
due to his careful planning that a reonaissance of all parts of the
Arctic basin was accomplished. Mr. Arthur Molloy participated in
most of the submarine cruises and in the processing of the echo-
grams. His contribution to this study cannot be over emphasized.
I have profited greatly from discussions with Dr. Ned A.
Ostenso, Dr. Arthur Lachenbruch and Dr. Kenneth Hunkins, three of
the foremost students of the Arctic basin. Each has been generous
with his thoughts and with the unpublished data referenced in this
study. The interpretation of these data is, of course, entirely my
responsibility.
Dr. John V. Byrne has guided this research and has had con-
siderable influence on its content. Under his guidance, I have been
encouraged to avoid the easy way and to enter controversial regions
at the forefront of geological knowledge in the data interpretation.
This freedom and encouragement are much appreciated, but it is
even more incumbent than usual on the writer to stress that he is
solely responsible for any errors in judgement in the study.
Finally, I am privileged to acknowledge the debt that I owe to
my wife, Phyllis, for her support and encouragement. She has as
cheerfully lived with me on the shore of the Arctic Ocean as in San
Diego, and has struggled alone with home and hearth while I was on
board icebreakers and submarines for months at a time in carrying
out my studies.