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1. Carter, L., Burnett, D., Drew, S., Hagadorn, L., Marle, G., Bartlett-McNeil, D., Irvine, N., 2009. Submarine Cables and the Oceans- connecting the world. UNEP-WCMC Biodiversity Series 31. ICPC/UNEP/UNEP-WCMC, 64pp. ISBN 978-0-9563387-2-3 Available http://www.iscpc.org/publications/icpc-unep_report.pdf

Authors:
Submarine cables and the oceans:
connecting the world
DRAFT
Submarine cables and the oceans:
connecting the world
UNEP World Conservation Monitoring Centre
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Cambridge, CB3 0DL
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The United Nations Environment Programme World
Con servation Monitoring Centre (UNEP-WCMC) is the
biodiversity assess ment and biodiversity policy support
arm of the United Nations Environment Programme
(UNEP), the world’s foremost inter governmental envi ron -
mental organization. The Centre has been in operation for
over 25 years, combining scientific research with prac -
tical policy advice.
©ICPC Ltd/UNEP/UNEP-WCMC, 2009
ISBN: 978-0-9563387-2-3
AUTHORS
Lionel Carter (Introduction and Chapters 3, 5, 6, 8),
Victoria University, Wellington, New Zealand.
lionel.carter@vuw.ac.nz
Douglas Burnett (Chapter 4), Squire, Sanders & Dempsey
L.L.P, New York, USA. dburnett@ssd.com
Stephen Drew (Chapter 7), Tyco Telecommunications,
New Jersey, USA. scdrew@tycotelecom.com
Graham Marle (Introduction), Qualtrack Ltd, Lymington,
UK. graham.marle@qualtrack.com
Lonnie Hagadorn (Chapters 2, 3), formerly Flag Telecom,
USA. lhagadorn@earthlink.net
Deborah Bartlett-McNeil (Chapter 1), formerly Global
Marine Systems Limited, Chelmsford, Essex, UK.
debsmcneil@yahoo.co.uk
Nigel Irvine (Chapter 5), Verizon, Reading, UK.
nigel.irvine@uk.verizonbusiness.com
DISCLAIMER
The contents of this report do not necessarily reflect the views or policies
of ICPC, UNEP or contributory organizations. The designations employed
and the presentations do not imply the expressions of any opinion
whatsoever on the part of ICPC, UNEP or contributory organizations
concerning the legal status of any country, territory, city or area and its
authority, or concerning the delimitation of its frontiers or boundaries.
International Cable Protection Committee Ltd (ICPC)
PO Box 150
Lymington, SO41 6WA
United Kingdom
Tel: +44 (0) 1590 681673
Fax: +44 (0) 870 432 7761
Email: secretary@iscpc.org
Website: www.iscpc.org
The International Cable Protection Committee Ltd (ICPC)
is a non-profit organization that facilitates the exchange of
technical, legal and environmental information con-
cern ing submarine cable installation, maintenance and
protection. It has over 100 members representing tele com -
muni cation and power companies, government agen cies
and scientific organizations from more than 50 countries,
and encourages cooperation with other users of the seabed.
CITATION
Carter L., Burnett D., Drew S., Marle G., Hagadorn L.,
Bartlett-McNeil D., and Irvine N. (2009).
Submarine Cables
and the Oceans – Connecting the World
. UNEP-WCMC
Biodiversity Series No. 31. ICPC/UNEP/UNEP-WCMC.
URLs
http://www.unep-wcmc.org/resources/publications/
UNEP_WCMC_bio_series/31.aspx
http://www.iscpc.org/publications/icpc-unep_report.pdf
For all correspondence relating to this report please contact:
info@unep-wcmc.org or secretary@iscpc.org
A Banson production
Design and layout Banson
Printed in the UK by The Lavenham Press
UNEP promotes
environmentally sound
practices, globally and in its own
activities. This report is printed on FSC
paper, using vegetable-based inks and
other eco-friendly practices. Our
distribution policy aims to reduce
UNEP’s carbon footprint.
3
There are many things and services in our everyday life
that we take for granted, and telecommunications is
one of them. We surf the internet, send emails to
friends and colleagues abroad, talk to family members in
foreign countries over the phone, book airline seats and
make banking transactions without actually realizing and
appreciating the sophisticated technology that enables us
to do so.
There is a common misconception that nowadays most
international communications are routed via satellites, when
in fact well over 95 per cent of this traffic is actually routed
via submarine fibre-optic cables. Data and voice transfer via
these cables is not only cheaper, but also much quicker than
via satellite.
The first submarine cable – a copper-based telegraph
cable – was laid across the Channel between the United
Kingdom and France in 1850. Today, more than a million
kilometres of state-of-the-art submarine fibre-optic cables
span the oceans, connecting continents, islands and
countries around the world. Arguably, the international sub -
marine cable network provides one of the most important
infra structural foundations for the development of whole
socie ties and nations within a truly global economy.
At the beginning of the submarine cable era, there was
a widely held belief that the riches of the ocean were too
vast ever to be affected by humans. Apart from shipping and
regional fishing, there were few other uses of the sea and
most of the marine environment (the little that was known)
was still relatively pristine.
Today, the situation is vastly different. Human activities,
directly or indirectly, have affected and altered all environ -
ments world-wide, including the 71 per cent of the planet
that is ocean. The number and the intensity of mari time uses
have increased dramatically and will continue to do so in the
future, stretching the capacity of the oceans and their finite
space and resources to the limit – or even beyond. In the
light of the actual and potential pressures and impacts this
creates on marine biodiversity and ecosystems (including
the services and functions they pro vide for humankind and
life on Earth), governments and international organizations
have recognized that there is an urgent need for wise
conservation and protection in concert with the sustainable
management and use of the oceans and their resources.
Even the placement and operation of submarine tele -
communications cables, as one of the oldest and arguably
one of the most important uses of the sea, has to be
considered in this process. In order to focus and guide these
deliberations and decision making, an objective, factual
description of this industry and the interaction of submarine
telecommunications cables with the marine environment is
needed: information that the reader will find in this report.
We hope that this report will contribute to and streng -
then the ongoing exchange of information, mutual edu -
cation and cooperation between all stakeholders, so that,
despite increasing technological change and environmental
pressures, we can continue to share the seabed in harmony
for the benefit of all.
Ibrahim Thiaw
Director, Division of Environmental Policy
Implementation, UNEP
Jon Hutton
Director, UNEP World Conservation Monitoring Centre
Mick Green
Chairman, International Cable Protection Committee
Foreword
4
The authors are indebted to Stefan Hain for his encour -
agement, expertise and general advice. Without that
contribution, this novel project would not have happened.
The authors gratefully acknowledge the external reviewers,
Robert Beckman, David Billet, Kristina Gjerde, Malcolm
Gilberd, Alan Green, Michelle Dow, Don Hussong, Jihyun
Lee, Claus Nielsen, Myron Nordquist, Alain Polloni, Neil
Rondorf, John Tibbles, Dean Veverka, Bob Wargo, Robin
Warner, Nigel Weaver and Ian Wright, whose expert com -
mentaries and critiques improved the manuscript versions
of this report. We are also indebted to those individuals,
companies and institutions who generously contributed
images, each of which is attributed to the contributor in the
caption text. Those photographs and graphics are a
fundamental part of the report. Finally, we acknowledge
UNEP and ICPC for providing the opportunity for this col -
laborative venture. Although from different cultures, both
organizations recog nize the value of providing an evidence-
based synopsis of the interactions between the marine
environment and the submarine cable network. In that
context, this report could be viewed as the first step towards
a knowledge base to guide future management and use
of the marine environment. The views presented in this
report, together with any errors or inconsistencies, are the
responsibility of the authors.
Acknowledgements
5
FOREWORD.................................................................................................................................................................................3
ACRONYMS AND ABBREVIATIONS............................................................................................................................................7
INTRODUCTION ..........................................................................................................................................................................8
CHAPTER 1: A HISTORY OF SUBMARINE CABLES .................................................................................................................11
Telegraph era......................................................................................................................................................................................11
Telephonic era................................................................................................................................................................................... 14
Fibre-optic era....................................................................................................................................................................................15
CHAPTER 2: INSIDE SUBMARINE CABLES.............................................................................................................................17
Designed for the deep....................................................................................................................................................................17
Analogue cables arrive .................................................................................................................................................................18
The digital light wave revolution ...................................................................................................................................................18
Conclusions .......................................................................................................................................................................................19
CHAPTER 3: SURVEY, LAY AND MAINTAIN CABLES ......................................................................................................21
Route selection ..............................................................................................................................................................................21
Route survey ..................................................................................................................................................................................21
Cable deployment .........................................................................................................................................................................22
From coast down to c.1,000–1,500 m water depth: the need for protection .............................................................................23
Below c.1,500 m water depth........................................................................................................................................................24
Cable recovery ...............................................................................................................................................................................24
Best practice ..................................................................................................................................................................................25
CHAPTER 4: INTERNATIONAL LAW.........................................................................................................................................26
International conventions..............................................................................................................................................................26
Cables as critical infrastructure ...................................................................................................................................................28
CHAPTER 5: ENVIRONMENTAL IMPACTS ...............................................................................................................................29
Environmental impact assessments............................................................................................................................................29
Cables on the seabed ....................................................................................................................................................................30
Cables into the seabed ..................................................................................................................................................................33
Cable placement and ecologically significant areas ...................................................................................................................36
Cable protection zones and marine reserves ..............................................................................................................................37
CHAPTER 6: NATURAL HAZARDS............................................................................................................................................38
Leaving their mark on the seabed ...................................................................................................................................................38
Impacts on submarine cables ..........................................................................................................................................................39
Climate change .................................................................................................................................................................................41
Contents
6
Submarine cables and the oceans
CHAPTER 7: SUBMARINE CABLES AND OTHER MARITIME ACTIVITIES........................................................................43
Introduction.....................................................................................................................................................................................43
Cable damage.................................................................................................................................................................................43
Numbers and causes of cable faults............................................................................................................................................44
Maritime activities and cable faults..............................................................................................................................................45
Fishing/cable interactions.............................................................................................................................................................45
Risks to fishermen and vessels....................................................................................................................................................47
Other causes of cable damage .....................................................................................................................................................47
Mitigating fishing and cable interactions .....................................................................................................................................47
CHAPTER 8: THE CHANGING FACE OF THE DEEP: A GLIMPSE INTO THE FUTURE......................................................49
Human activities.................................................................................................................................................................................49
Concluding comments.......................................................................................................................................................................53
GLOSSARY.................................................................................................................................................................................55
REFERENCES ...........................................................................................................................................................................59
7
ACC Antarctic Circumpolar Current
ACMA Australian Communications and Media Authority
AT&T American Telephone and Telegraph Company
ATOC Acoustic Thermometry of Ocean Climate
CANTAT Canadian Trans-Atlantic Telephone cable
CBD Convention on Biological Diversity
CPZ Cable protection zone
DTS Desktop study
EEZ Exclusive economic zone
EIA Environmental impact assessment
ENSO El Niño-Southern Oscillation
ESONET European Seafloor Observatory Network
FAD Fish aggregating devices
FAO Food and Agriculture Organization of the United Nations
GCCS Geneva Convention on the Continental Shelf
GCHS Geneva Convention on the High Seas
GISS Goddard Institute for Space Studies, NASA
GPS Global positioning system
ICES International Council for the Exploration of the Sea
ICPC International Cable Protection Committee
IEEE Institute of Electrical and Electronic Engineers, USA
IPCC Intergovernmental Panel on Climate Change
ITLOS International Tribunal for the Law of the Sea
MBARI Monterey Bay Aquarium Research Institute, USA
NASA National Aeronautics and Space Administration, USA
NEPTUNE North-East Pacific Time-series Undersea Networked Experiments
NIWA National Institute of Water and Atmospheric Research, New Zealand
NOAA National Oceanic and Atmospheric Administration, USA
OFCC Oregon Fishermen’s Cable Committee
OOI Ocean Observatories Initiative
OSPAR Oslo and Paris Convention for the Protection of the Marine Environment of the North-East Atlantic
ROV Remotely operated vehicle
SCIG Submarine Cable Improvement Group
TAT-1 Trans-Atlantic Telephone, first trans-ocean telephone cable
UKCPC United Kingdom Cable Protection Committee
UNCLOS United Nations Convention on the Law of the Sea
UNEP United Nations Environment Programme
UNESCO United Nations Educational, Scientific and Cultural Organization
UV-B Ultra-violet light, type B
WCMC World Conservation Monitoring Centre (of UNEP)
Acronyms and abbreviations
Introduction
8
This report results from collaboration between the
United Nations Environment Programme (UNEP)
and the International Cable Protection Committee
(ICPC), which represents the majority of ocean users
within the submarine telecommunications cable industry.
Why is such a report required? The last 20 years have seen
expo nen tial growth of and increasing reliance on the
internet for commu nication, commerce, finance, enter -
tainment and education. That remarkable development has
been accompanied by rapid growth in international tele -
phone communications. Whether sending an email,
making an airline booking or simply telephoning overseas,
there is more than a 95 per cent probability that those
actions will involve the international submarine cable
network. In recognition of its importance as the backbone
of the internet, govern ments now view the submarine tele -
com muni cations cable network as
critical infrastructure
that deserves a high level of protection (e.g. ACMA, 2007).
The communications revolution has occurred against
a backdrop of greater pressure on the ocean from increased
human activities, which range from the exploitation of re -
sources to anthropogenic global warming (e.g., UNEP-
WCMC, 2009; IPCC, 2007). In response to concerns about
potential and actual impacts on the marine environment,
govern ments and international organizations have stepped
up their efforts to ensure the conservation, protection and
sustainable management/use of coastal seas and deep
offshore waters. In the light of recent scientific discoveries
(e.g. Masson
et al.
, 2002; Freiwald
et al.
, 2004), discussions
about the risks to vulnerable and threatened marine
ecosystems and biodiversity in areas beyond national
jurisdiction have emerged. It was this increased inter -
national awareness and interest in the deep and high seas
environments that led UNEP and the ICPC to collaborate
in the preparation of this report in 2004, with the shared
objective of providing a factual context for discussions
involv ing submarine fibre-optic cables and the environment.
As such, it allows for more informed decision making,
especially when weighing the benefit of an activity against
any potential negative environmental impact (e.g. UNEP,
2007). It should be noted that
Submarine Cables and the
Oceans – Connecting the World
focuses exclusively on
fibre-optic telecommunications cables, and hence does not
address submarine power cables.
The opening chapters of this report are a com -
pendium of information that starts with a history of
submarine telecommunications cables. The first trans-
oceanic cable came into full operation in 1866, when a link
was established between Ireland and Newfoundland that
allowed trans mission of seven words per minute via
telegraph. Today, a modern fibre-optic cable can transport
vast amounts of data and is capable of handling literally
millions of simul taneous telephone calls. Even so, deep-
ocean fibre-optic cables are no larger than 17–21 mm
diameter – about the size of a domestic garden hose.
Closer to shore (in water depths shallower than about
1,500 m), a cable’s diameter may increase to 40–50 mm
due to the addition of protective wire armouring. Chapter 3
focuses on submarine cable operations and presents an
insight into the technology that permits accurate place -
ment of a cable on or into the seabed. Modern seabed
mapping systems such as multibeam side-scan sonar and
high-definition seismic profilers, used in conjunction with
satellite navigation equipment, permit submarine cables to
be installed with unprecedented precision. Thus, hazardous
zones and eco lo gically sensitive locations, such as volcanic
areas and cold-water coral communities, can be avoided.
All cables eventually come ashore, and it is in these
shallow coastal waters that they are at most risk from
human activities, especially ships’ anchoring and bottom
trawl fishing, which are together responsible for most
submarine cable faults. As a result, special protective
measures are needed that typically include the addition of
steel armour to the cable exterior and, where possible,
burial into the seabed. Cable deployment within the waters
of a coastal state generally requires some form of environ -
mental impact assessment (EIA) covering the potential
effects of the survey and laying oper ations on the local
en vironment, other seabed users and underwater cultural
heritage sites.
The success and very existence of international sub -
marine cable systems owe much to the treaties that the
nations of the world have introduced into customary inter -
national law since 1884. These international norms are
widely accepted and followed by the cable industry as well
as the global community. They are an excellent example
of international law working at its best in balancing
competing uses in the ocean. Chapter 4 provides a basic
restatement of the current international legal regime that
underpins the world's undersea communications network.
Open-file information from environmental agencies,
together with published studies, forms the basis of
Chapter 5, which examines the environmental impacts of
modern submarine cables and associated operations. The
main threats to cables are found in water depths shallower
than about 1,500 m, the present limit of most bottom trawl
fishing, although some boats are extending that limit to
2,000 m depth. In these conti nental shelf and slope areas,
cables require some form of protection. This may be
achieved through legislation for the creation of protection
zones (e.g. ACMA, 2007), or by physical means such as
burial beneath the seabed. In the case of designated and
controlled protection zones, there may be no need to bury
cables, in which case they are exposed to waves, currents
and the marine biota. How a cable interacts with the
environment depends on the many influences and factors
that shape the ocean. However, the small physical size of a
telecommunications cable implies that its environmental
footprint is likely to be small and local; a suggestion that is
borne out by several studies, e.g. Kogan
et al.
(2006). Using
a combination of sediment samples and direct obser va -
tions made with a remotely operated vehicle (ROV), Kogan
et al.
con cluded that a telecommunications cable off
Monterey Bay, California, had minimal to no impact on the
fauna living in or on the surrounding seabed, with the
exception that the cable locally provided a firm substrate
for some organisms that otherwise would not have grown
on the mainly soft seafloor sediments. These results
contrast with the findings of an earlier study by Heezen
(1957), who documented a significant impact on marine
life, namely the entanglement of whales with old telegraph
cables. However, such distressing occurrences were
restricted to the telegraph era (1850s to c.1950s). With
improved design, laying and maintenance techniques,
which developed with the first coaxial submarine cables in
the 1950s and continued into the fibre-optic era beginning
in the 1980s, no further entanglements with marine
mammals have been recorded (Wood and Carter, 2008).
The remainder of Chapter 5 considers the environmental
effects of cable burial and recovery as well as broader
issues concerning the relationship between cables and
ecologically sensitive areas, and the potential use of cable
protection zones as
de facto
marine sanctuaries.
The December 2006 earthquake off southern Taiwan
focused the world’s attention not only on the human
tragedy, but also on the impact of natural hazards on the
sub marine cable network. The magnitude 7.0 earthquake
trig gered submarine landslides and dense sediment-laden
flows (turbidity currents), which passed rapidly down to
the +4,000 m-deep ocean floor, breaking nine fibre-optic
submarine cables en route (Figure 1). Southeast Asia’s
regional and global telecommunications links were severely
disrupted, affecting telephone calls, the internet and data
traffic related to commerce and the financial markets.
As outlined in Chapter 6, such natural hazards generate
less than 10 per cent of all cable faults, but fault occur -
rence rises to around 30 per cent for cables in water deeper
9
Figure 1: On 26 December 2006, a magnitude 7.0
earthquake and after shocks (pink stars) set off several
submarine land slides off southern Taiwan. These slides
transformed into fast-flowing mud-laden currents that
sped down Kao-ping sub marine canyon (red dashes) into a
deep-ocean trench: a distance of over 300 km. Nine cables
were broken en route, disrupting international commu -
nications for up to seven weeks.
Source: Professor C.S. Liu,
Institute of Oceanography, National Taiwan University.
Introduction
10
Submarine cables and the oceans
than c.1,500 m, i.e. beyond the main zone of human off -
shore activities. And, as seen off Taiwan in 2006 and
Newfoundland in 1929, the consequences of major hazards
can be profound. Seismically triggered submarine land -
slides and tur bidity currents, along with major storms, wave
and current action, and even river floods, pose the largest
natural threat to cables, with volcanic eruptions and iceberg
scour playing very minor roles. Furthermore, cables are
unlikely to be exempt from the anticipated changes in the
ocean resulting from human-influenced climate change.
High on the list of potential hazards are rising sea level and
more powerful storms, which together are likely to threaten
the shallow and coastal reaches of cable routes. Regional
changes in wind patterns, precipitation and ocean currents
are also likely to have an effect.
Integrating cable activities with other seabed uses is
the theme of Chapter 7. Mid-water to bottom trawl fishing,
dredging, ships’ anchoring and some recreational activities
threaten underwater communications. Because it is the
most significant cause of cable faults, Chapter 7 concen -
trates on fishing, presenting an over view of fishing gear and
practices, risks to cables, fishing ves sels and crew, and
means of reducing those risks. Risk reduction is achieved
through close consultation between cable engineers and
fishermen so that there is a full under standing of their res -
pective equipment and operations, e.g. know ledge of the
type of trawl gear deployed allows engin eers to identify a
suitable burial depth for a cable. Other miti gation measures
may involve cable routing, armouring, clear identification of
cable routes on marine charts, educational material and
stakeholder working groups consisting of fishing and cable
representatives.
The report ends with a discussion of future activities in
the ocean based on present trends in offshore con servation,
renewable energy development and resource exploitation.
There is no doubt that the oceans, and especially the
coastal seas, are under increas ing pressure from a growing
range of human activities. The past decade has witnessed
an expansion of offshore renewable energy schemes (in
particular wind turbine farms) as nations seek to lower
emissions of greenhouse gases and establish secure
supplies of energy. Fishing activities are changing due to
reduced stocks in coastal seas. Trawling is now moving into
deeper waters, although this may be tempered by the
increased costs of operating further offshore, lower
biomass in more distant, deeper waters and rapid stock
depletion because of fish life-history characteristics (e.g.
Clark
et al.
, 2000; Pauly
et al.
, 2003). As China, India and
other nations develop their industrial sectors, the import of
raw mater ials and export of manufactured goods have
expanded. Shipping routes, traffic volumes and vessel size
have all undergone major adjustments brought about by
profound shifts in the global economy. Offshore exploration
and production of hydro carbons are also set to extend into
deeper water, with operations taking place at depths of
3,000 m and beyond. Deep-sea mining for minerals has
recently attrac ted increased interest, with commercial
operations planned for the near future. Furthermore, the
science community is estab lishing long-term ocean obser -
vatories (e.g. Ocean Sites, 2009) to determine how the deep
ocean and seabed function, to discover what biodiversity
and ecosystems they harbour, and to detect natural hazards
and responses to climate change.
As a consequence of these pressures, nations and
international groups are seeking to preserve ocean
ecosystems through the formation of marine protected
areas and similar devices (e.g. OSPAR Commission, 2009).
In the face of increasing human activities in the marine
environment, it has become vital for relevant parties and
stakeholders to communicate and cooperate. In this
manner, harmonious development and conservation of the
71 per cent of Earth’s surface found beneath the oceans
can be realized. This is far from an idle sentiment: it is
founded on the extensive experience of the collaborators
of
Submarine Cables and the Oceans – Connecting the
World,
actively working with other seabed users.
TELEGRAPH ERA
Submarine cables were born around the 1820s. Baron
Schilling von Canstatt, an attaché with the Russian Embassy
in Munich, successfully exploded gunpowder mines using
insulated wires laid across the River Neva, near St
Petersburg (Ash
et al.
, 2000). His interest moved to the
electric telegraph, which he integrated with another earlier
device known as Schweigger’s ’Multiplier‘, in order to im -
prove the sensitivity of a compass needle. Once combined,
‘Schilling’s Telegraph’ was able to communicate messages
through a directed needle that moved across black and white
paper disks representing letters of the alphabet and
numbers (Stumpers, 1884; Ash
et al.
, 2000).
Inventions involving telegraphy escalated through the
19th century. In 1836, English chemist and inventor, Edward
Davey, came close to completing a practical telegraph
system. He envisioned an electric telegraph that could
be insulated for protection and placed underwater with
relay-type ‘repeaters’ to boost weak signals along the
cable. This was the forerunner of the submarine telegraph
cable. Close to success, Davey unexpectedly departed for
Australia, leaving his main competitors, William Cooke
and Charles Wheatstone, to complete an operational tele -
graph (Stumpers, 1884; Ash
et al.
, 2000). Their system was
patented in 1837 and involved the identification of alphabetic
letters by deflections of magnetic needles. At about the
same time, Samuel Morse patented a telegraph based on an
electromagnetic system that marked lines on a paper strip.
The technique came into commercial reality in 1844 when a
communications link was made between Baltimore and
Washington, DC.
The concept of insulating submarine telegraph cables
to make them durable, waterproof and sufficiently strong
to withstand waves and currents, fostered several trials
with different materials. In 1843, Samuel Morse produced a
prototype by coating a hemp-covered cable in tar and pitch;
1. A history of submarine cables
11
Undersea communications cables
Undersea communications cables, 2009.
Source: Tyco Telecommunications (US) Inc.
12
Submarine cables and the oceans
insulation provided by a layer of rubber also gave the cable
strength and durability (Ash
et al.
, 2000). By the late 1840s,
the basic technology existed to manufacture submarine
cables, and in 1848 the Gutta Percha Company received its
first order for wire insulated with a newly discovered natural
polymer from Malaya – gutta percha (Figure 1.1) (Kimberlin,
1994; Gordon, 2002; ICPC, 2007).
An English merchant family, headed by the brothers
James and John Brett, financed a submarine cable across
the English Channel from Dover to Calais. Constructed
from copper wire and gutta percha without any form of
protection, the cable was laid by the tug
Goliath
on 28
August 1850 (Figure 1.2) (Kimberlin, 1994; Ash
et al.
, 2000;
Gordon, 2002). The cable lasted for just a few messages
before it suc cumbed to vigorous waves and currents. A year
later it was replaced by a more robust design comprising
four copper conductors, each double coated with gutta
percha, bound with hemp and heavily armoured with iron
wires. This improved version extended the cables’ working
life to a decade. After installation, John Brett sent a special
message to soon-to-be Emperor of France, Napoleon III –
an act that symbolically marked the day that submarine
telecom munications became an industry. By 1852, cables
also con nected England to the Netherlands and Germany,
with other links between Denmark and Sweden, Italy and
Corsica, and Sardinia and Africa.
Submarine cables of that time were far from perfect.
Figure 1.1: Tapping gutta percha, a natural polymer used
for insulating early submarine cables.
Source: Bright (1898);
courtesy of archives of BT Heritage.
Figure 1.2: The steam tug,
Goliath
, laying the first
international submarine cable between Dover and Calais,
28 August 1850. The vessel was accompanied by HMS
Widgeon
.
Source: Bright (1898).
13
A history of submarine cables
The copper used for the conductors tended to be hard, brittle
and poorly conductive, while the gutta percha insulation was
sometimes lumpy and only moderately flexible. There was a
need to improve cable design and materials as the emerging
communications industry looked to the Atlantic Ocean as the
next great challenge (Figure 1.3). Such a communications
link would allow British and American busi nesses to develop
trade – particularly the British cotton industry.
In 1854, Cyrus Field, a wealthy American paper
merchant, became interested in laying a telegraph cable
across the Atlantic Ocean (Gordon, 2002). Along with John
Brett and Sir Charles Bright, he founded the Atlantic
Telegraph Company in 1856 (Ash
et al.
, 2000). Its board
members included William Thomson, the eminent physicist
who later became Lord Kelvin. After an unsuccessful
attempt in 1857, the company laid the first trans-Atlantic
cable in 1858, when Ireland was linked to Newfoundland
(Figure 1.4). However, success was short lived, and after 26
days of operation the cable failed. Following three other
attempts, a new and improved cable was laid in 1866 from
the
Great Eastern
cable ship by the Telegraph Construction
& Maintenance Company (TELCON) – a merger of the Gutta
Percha Company and Glass, Elliot & Company (Figure 1.5).
The new and more durable cable provided reasonably
reliable communication at around 12 words per minute
across the Atlantic. On its return journey to England, the
Great Eastern
recovered the cable lost the year before. A
repair was made and connection with Newfoundland com -
pleted to provide a second trans-Atlantic cable link (Ash
et
al.
, 2000; Gordon, 2002).
As telegraph technology and laying techniques
improved, the submarine network expanded greatly. To
facilitate government and trade, cables linked the United
Kingdom with the many outposts of its empire. By the early
20th century, much of the world was connected by a network
that enabled rapid communication and dissemination of
information for government, commerce and the public.
The durability and performance of telegraph cables
improved with new conducting, strengthening and insulat -
ing materials. Alloy tapes and wires, such as the iron-
nickel, permalloy, and the copper-iron-nickel, mu-metal,
were used to increase cable performance (particularly the
speed of signalling) in the 1920s. Staff employed to send
and receive telegraphic messages at relay stations were
grad ually replaced by electro-mechanical signallers.
Transmis sion speeds increased progressively, and by the
late 1920s speeds exceeding 200 words per minute became
the norm.
By the 1930s there were just two cable manufactu -
rers in Britain, TELCON and Siemens Brothers. The Great
Depression and competition from radio-based communi -
cations made business difficult. As a result, TELCON
merged with the submarine communications cable section
of Siemens Brothers to form Submarine Cables Limited.
Despite the technological advances of the telegraph, the
developing radio industry could do something that the
telegraph could not – namely produce intercontinental voice
communications. Marconi’s company, Imperial, owned the
patent to radio communication; it joined forces with the
cable industry after they were encouraged to merge by
the UK government. And so, in 1934, Cable & Wireless was
born. The new partnership enabled even more rapid com -
munications, which came into their own during the Second
World War. Radio was used for communicating with troops,
Figure 1.3: Loading gutta percha insulated cable for the
Great Eastern
cable ship.
Source: courtesy of archives of BT
Heritage.
Figure 1.4: HMS
Agamemnon
laying the first Atlantic
cable in 1858.
Source: ARC photographs from archives of BT
Heritage.
14
Submarine cables and the oceans
and submarine cables provided secure networks that could
not be intercepted easily.
TELEPHONIC ERA
Following Alexander Graham Bell’s invention of the tele -
phone in 1875, it was only a matter of time before phone
lines linked continents by submarine cables. Initial attempts
in the United States and United Kingdom met with limited
success. The British Post Office laid a telephone cable
across the English Channel, but inherent deficiencies of the
gutta percha insu lation meant that sig nals were limited
to short distances before they became distorted. The dis -
covery of polyethylene in 1933 made trans-oceanic telephony
possible. In 1938, a polyethylene-encased cable was devel -
oped with a copper coaxial core capable of carrying a num -
ber of voice channels (Chapter 2). That innovation, along
with the use of repeat ers to boost the signals, meant that a
trans-oceanic cable with multiple voice channels was
achievable. Thus in 1955–1956, two cables were laid between
Scotland and Newfoundland as a joint venture between the
British Post Office, American Telephone and Telegraph
(AT&T) and the Canadian Overseas Telecommunications
Corporation. The system, named TAT-1, came into service on
25 September 1956, and in the first day of operation carried
707 calls between London and North America. The era of
submarine coaxial telephone communications had begun.
With it came a suite of tech nological developments relating
to the design of signal-boosting repeaters, new methods of
Figure 1.5: The first trans-Atlantic cables were promoted
as the Eighth Wonder of the World by Cyrus Field and his
colleagues, who emphasized cooperation between the
United Kingdom and the United States.
Source: Kimmel and
Foster (1866). Lithograph, Library of Congress.
15
A history of submarine cables
cable laying and im proved methods of strengthening cables,
especially in deep water where as much as 6 km of cable
could be sus pended through the water as it was laid on the
ocean floor from a cable ship.
In the 1970s and early 1980s, these relatively low-
bandwidth cables were only cost-effective on high-density
communication routes, with the bulk of global trans-oceanic
traffic carried by satellites. The last coaxial system across
the Atlantic Ocean was TAT-7, which had a capacity of 4,000
telephone channels. However, to achieve this repeaters had
to be installed at 9 km intervals, which made the technology
very expensive. A more cost-effective solution was needed
to meet the increasing demand for more capacity at reason -
able cost. The race to develop fibre-optic technology for
appli cation in submarine cables began in the mid-1970s,
thus heralding the dawn of another technological revolution
in submarine communications.
FIBRE-OPTIC ERA
Glass fibres could carry 12,000 channels, compared
to 5,500 for the most advanced coaxial cable. Furthermore,
the quality of fibre-optic communication was superior.
However, at this stage it was difficult to envisage that fibre-
optic cables would form a global network. Over the next
decade, scientists continued to improve and refine fibre-
optic technology. The world’s first trial of a submarine
fibre-optic cable was in Loch Fyne in 1979 (Ash
et al.
, 2000).
The trials proved that the cable could withstand the
mechanical stresses involved in laying, as well as retaining
the required stability of transmission characteristics. By
1986, the first international system was installed across the
Figure 1.6: CS
Long Lines
which, together with cable ships
from France and the United Kingdom, laid the first trans-
Atlantic fibre-optic cable (TAT-8).
Source: AT&T Inc.
16
Submarine cables and the oceans
English Channel to link the United Kingdom and Belgium. In
1988, the first trans-oceanic fibre-optic cable was installed,
which marked the transition when sub marine cables started
to outperform satellites in terms of the volume, speed and
economics of data and voice communications. TAT-8 linked
the United States, United Kingdom and France and allowed
for a large increase in capacity (Figures 1.6 and 1.7). At about
that time, the internet began to take shape. As newer and
higher-capacity cable systems evolved, they had large
bandwidth at suf ficiently low cost to provide the necessary
economic base to allow the internet to grow. In essence, the
two tech nologies complemented each other perfectly:
cables carried large volumes of voice and data traffic with
speed and security; the internet made that data and infor -
mation accessible and usable for a multitude of purposes.
As a result, communications, business, commerce, edu -
cation and entertainment underwent radical change.
Despite the success of submarine telecommuni -
cations, satellite transmission remains a necessary adjunct.
Satellites provide global broadcasts and communications
for sparsely populated regions not served by cables. They
also form a strategic back-up for disaster-prone regions. By
comparison, submarine cables securely and consistently
deliver very high-capacity communications between popu -
lation centres. Such links are also cost-effective, and the
advantages of low cost and high bandwidth are becoming
attractive to governments with low population densities.
The amount of modern submarine fibre-optic cables laid in
the world’s oceans has exceeded a million kilometres and
under pins the international internet. Almost all trans-
oceanic telecommunications are now routed via the sub -
marine cable network instead of satellite.
Figure 1.7: A section of TAT-8, the first trans-oceanic fibre-
optic cable which, together with a developing internet,
heralded a new age of communications.
Source: AT&T Inc.
17
DESIGNED FOR THE DEEP
A submarine cable is designed to protect its information-
carrying parts from water, pressure, waves, currents
and other natural forces that affect the seabed and over -
lying waters. Most of these forces change with depth.
Temperatures become colder, pressure increases and
wave effects lessen, but strong current action can occur at
any depth. There are also the impacts of human activities,
most notably fishing and shipping.
Designing cables to meet such challenges has been
a quest for more than 160 years. In 1842, for instance, a
telegraph cable laid across the East River, New York, by
Samuel Morse, was soon damaged by a ship’s anchor.
Designing cables to cope with such mishaps progressed
rapidly. Redesigning the first cables across the English
Channel in 1851 and the first trans-Atlantic link in 1858
allowed these pioneering systems, which had failed on
their first deployments, to operate successfully (Chapter
1). Nevertheless, the fundamental design of telegraph
cables changed little for the next 100 years (Figure 2.1;
Haigh, 1968).
Telegraphy involved the transmission of coded elec -
trical impulses through a conductor, which in a submarine
cable was a stranded copper wire with gutta percha
insulation wrapped in brass or jute tape (Figure 2.1). This
construction, however, had insufficient strength to with -
stand deployment or recovery from any appreciable water
depth. As a result, a sheathing of wires or
armour
was
added to provide strength. Armour also protected the
cable, and various wire types and layers were devised to
meet different seabed conditions. Two-layered or double
armour helped protect against anchors and fishing gear,
as well as abrasion under wave and current action in
coastal seas. Heavy single-armoured cable was designed
2. Inside submarine cables
Stranded
copper
conductor
Gutta percha
insulation
Brass tape
Jute
I
n
n
e
r
a
r
m
o
u
r
w
i
r
e
s
T
a
r
-
s
o
a
k
e
d
j
u
t
e
O
u
t
e
r
a
r
m
o
u
r
Figure 2.1: Submarine telegraph cables from the early
1900s, with the inner copper conductor for transmitting
messages, an insulating layer of the tree resin, gutta
percha, and one or more outer layers of iron wire for
strengthening and protecting the whole assembly.
Source:
Lonnie Hagadorn.
Figure 2.2: Cables of the coaxial telephonic era, with a core
of steel wires for strength, an inner copper sheath, which
also acted as the conductor, encased in polyethylene
dielectric, and an outer conductor. The assembly was
coated with black polyethylene which, in shallow water,
was armoured for protection.
Source: Lonnie Hagadorn.
Intermediate depth
coaxial telephone
design,
c. mid-1950s
Deep-water coaxial telephone designs
Stranded
steel strength
member
Copper inner
conductor
c. 1976
c. 1970
c. 1963
C
o
p
p
e
r
o
u
t
e
r
c
o
n
d
u
c
t
o
r
P
o
l
y
e
t
h
y
l
e
n
e
d
i
e
l
e
c
t
r
i
c
P
o
l
y
e
t
h
y
l
e
n
e
s
h
e
a
t
h
18
for intermediate water depths beyond the reach of anchors
and most trawl fishing gear. Light single armour was a
deep-water design that allowed cables to be laid in full
ocean depths (Haigh, 1968).
ANALOGUE CABLES ARRIVE
Coaxial or analogue cables came into use in the 1950s and
continued for the next 40 years and more. They differed
from telegraph cables in three key ways:
1. Instead of gutta percha, polyethylene was used
exclusively as the insulator or dielectric. It also
formed the outer sheath of deep-ocean designs
(Figure 2.2).
2. The cable core had a coaxial structure consisting of
an inner and outer conductor of copper separated
by polyethylene insulation material.
3. The first trans-Atlantic analogue cable (TAT-1) used
traditional armour for strength. However, later
cables used fine-stranded, high tensile strength
steel wires encased in the central conductor. As a
result, deep-ocean systems did not require armour,
although cables in shallow seas still needed a
strong outer casing for protection (Figure 2.2).
TAT-1 had about 36 individual voice channels, and used two
cables, one for each direction of transmission. In addition,
electrically powered amplifiers or repeaters were needed to
boost the transmission, and these were inserted into the
cable at spacings of c.68 km in deep water (Bell, 1957).
Analogue cable and repeater technology improved
rapidly through the 1960s and 1970s, allowing a cable to
carry up to 5,000 telephone calls. However, this increase in
bandwidth was accompanied by an increase in cable size
and repeater numbers, whose spacing was reduced to
6–9 km in the highest capacity systems. This made it
extremely expensive to install trans-oceanic communi ca -
tion systems (Bell, 1957, 1964, 1970, 1978).
THE DIGITAL LIGHT-WAVE REVOLUTION
During the late 1970s and early 1980s, development focused
on fibre-optic submarine cables that relied on a special
property of pure glass fibres, namely to transmit light by
internal reflection. By coding information as light pulses,
data could be sent rapidly around the world. In 1985, the first
deep-water repeatered design was laid off the Canary
Islands. By 1988, the first trans-Atlantic fibre-optic cable
(TAT-8) had been installed, followed several months later by
Figure 2.3: Shallow- to deep-water (left to right) fibre-optic cables, with a core supporting pairs of hair-like optical fibres
surrounded by a layer of wire to provide strength, a copper conductor to power the repeaters or amplifiers that process the
light signal, and a case of polyethylene dielectric. Wire armour is added for protection.
Source: Lonnie Hagadorn.
Unified fibre
structure
Stranded steel
strength member
Copper power
conductor
Tar-soaked
jute or nylon
I
n
n
e
r
a
r
m
o
u
r
O
u
t
e
r
a
r
m
o
u
r
l
a
y
e
r
l
a
y
e
r
21 mm
cable
17 mm
cable
Submarine cables and the oceans
19
Inside submarine cables
the first trans-Pacific system. Such cables usually had two
or more pairs of glass fibres. Originally, a pair could transmit
three to four times more than the most modern analogue
system. Today, a cable with multiple fibre-optic pairs has
the capacity for over 1 million telephone calls. Despite this
greatly enhanced capacity, modern cables are actually much
smaller than analogue predecessors. Deep-ocean types are
about the size of a garden hose (17–20 mm diameter), and
shallow-water armoured varieties can reach up to 50 mm
diameter (Figures 2.3 and 2.4). This means that instead of
making four or five ship voyages to load and lay an analogue
cable across the Atlantic, only one or two voyages are now
required for fibre-optic types. It also means that the footprint
of the cable on the seabed is reduced (AT&T, 1995).
Modern repeaters
With the digital light-wave revolution came major changes
in the design of repeaters (Figure 2.5). Light signals still
required amplification, and initially electronic regenerators
were placed along a cable to boost signals. New systems,
however, rely on optical amplifiers – glass strands con tain -
ing the element erbium. Strands are spliced at intervals
along a cable and then energized by lasers that cause the
erbium-doped fibres to ‘lase’ and amplify optical signals.
The typical spacing for this type of repeater is 70 km.
Fibre design changes
Since the advent of fibre-optic systems, major advances
have been made in the manufacturing technology of the
actual fibres. Various impurities or
dopants
are now added
or removed from the glass to change its light-transmitting
properties. The result is that the speed at which light
passes along a glass fibre can be adjusted and controlled.
This allows customized cables to be built to meet the
specific traffic and engineering requirements of a route.
This spe cialist use has increased the need for specialized
repair services. The correct spare cable and fibre type must
be used, which means that a comprehensive stock has to
be carried by the cable repair authority. Repairs typically
require removal of the damaged section followed by the
splicing or jointing of the replacement section. During the
telegraph and analogue eras, a single repair joint was a
relatively quick (3–6 hours) and simple operation. It has now
become a lengthy (10–24 hour), very specialized task that
requires expensive and sensitive equipment. Hair-thin
optical fibres must be aligned and spliced perfectly,
followed by full testing before making the mechanical joint
to give the repair strength and protection (AT&T, 1995).
CONCLUSIONS
The progress made in submarine cable design over the
last 50-plus years has been remarkable. The world has
Figure 2.4: Modern fibre-optic cables (life-size), ranging
from the typically used deep-ocean types (top two) leading
to the shallow-water armoured varieties, which in many
instances are now laid and buried into the seabed for
additional protection.
Source: Lonnie Hagadorn.
Insulating sheath
ø 17 mm
Steel wires
strand
Composite
conductor
ø 7.8 mm
External sheath
ø 22.5 mm
ø 28 mm
ø 46 mm
ø 31 mm
Layers of black
PP yarn
Layers of compound
Single armour (SA)
Double armour (DA)
Galvanized
steel wires
Single armour light (SAL)
Light-weight protected (LWP)
Light-weight (LW)
Optical
fibres
Thixotropic
jelly
Steel tube
ø 2.3 mm
Metal
sheath
gone from single-circuit telegraph cables to fibre-optic
systems with almost unlimited voice and data carrying
capacities. The physical size of the cable itself has shrunk
dramatically, and the reliability of the submarine com -
ponents is down to just a few failures over the entire life
of a long-distance system, which is typically 15–20 years.
One can only wonder what progress the next 50 years
will bring!
20
Submarine cables and the oceans
Figure 2.5: Representative repeaters from different manufacturers. The housings can accommodate as many as eight
individual regenerators, or more recently, optical amplifiers.
Source: Lonnie Hagadorn.
Amplifier section variable, 0.7-1.47 m (28-58”)
Flexible
coupling
(Armadillo)
Bend
limiter Splice case
Amplifier
section
Flexible
coupling
Flexible
coupling
Bend limiter/buffer Bend limiter/buffer
270 mm (10.5”)
314 mm (12.36”)
Approx. 3 m (10’)
Max. approx. 4.4 m (14.5’)
Modern fibre-optic joint box and repeaters (roughly to scale)
A
B
C
Approx. 1.8 m (6’)
21
ROUTE SELECTION
A key part of route selection is the identification and under -
stand ing of marine geopolitical boundaries that a proposed
route may encounter. Access to databases such as Global
Maritime Boundaries (NASA, 2009) can prevent unnecessary
passage through areas where geopolitical constraints could
affect the application or permit to place and maintain a cable
on the seabed.
Definition of these maritime boundaries is provided
by the United Nations Convention on the Law of the Sea
(UNCLOS) (Chapter 4). The extent to which any coastal state
controls cable-related activities within its territorial seas
and exclusive economic zone varies, and depends on the
nature and geographical jurisdiction of federal, state and/or
local regulations that enact the provisions of UNCLOS in
domestic legislation. For countries that have not ratified
UNCLOS, the focus is on existing domestic legislation.
ROUTE SURVEY
Following the identification of potential cable landings that
are to be connected, it is most effective to conduct a full
review of pertinent available information in order to define
the most efficient and secure route that will then be fully
surveyed. This preliminary engineering, commonly referred
to as a desktop study (DTS), is generally conducted by
marine geologists with cable engineering experience who
assemble all available hydrographic and geologic infor ma -
tion about the pertinent region, commission fisheries and
permitting reports if appropriate, consi der the location and
history of existing nearby cables and other obstructions,
and then design an optimal route to be surveyed. The DTS
will also generally include visits to the landings to determine
where the cable crosses the beach and links to the cable
terminal. Visiting landing sites also provides an opportunity
to consult with local officials about possible cable hazards,
environmentally sensitive areas, requirements to gain a
permit to operate, fisheries, development plans and land
access, amongst other factors. A comprehensive DTS will
provide an optimal route design that can then be surveyed in
the most cost-effective manner.
Based on the DTS, an efficient survey can then be
designed along an optimized route to fully characterize that
route and to avoid hazards and/or environmentally signi fi -
cant zones that may not have been identified from existing
information. Surveys include water depth and seabed
topography, sediment type and thickness, marine faunal/
floral communities, and potential natural or human-made
hazards. Where appropriate, measurements of currents,
tides and waves may be needed to evaluate the stabi lity of
the seabed, movement of sediment and ocean conditions
that may affect cable-laying and maintenance operations.
A route survey commonly covers a swath of seabed
c.1 km wide in water depths down to about 1,500 m, re -
flecting the need to bury cables for protection according to
local conditions. The width of the survey corridor can be
adjusted largely in consideration of the expected complexity
of the seabed, and the depth to which these complete
surveys are conducted will be based on local hazards,
particularly bottom trawl fishing and shipping activities,
which may require the cable to be buried. Water depth is
traditionally measured by echo-sounding, which has now
developed into seabed mapping or
multibeam
systems.
Whereas con ven tional echo-sounders measure a single
profile of water depth directly under the ship, multibeam
systems provide full depth coverage of a swath of seabed
with a width that is three to five times the water depth
(Figure 3.1). Thus, in deep water, a single multibeam track
can be up to 20 km wide. As a result, sectors of the seabed
are fully covered by a dense network of depth soundings
that yield highly accur ate images and charts (Figure 3.2).
As multibeam data are collected, side-scan sonar
systems may be deployed to produce photographic-like
images of the seabed surface. Termed
sonographs
, the
images are used to identify zones of rock, gravel and sand,
structures such as sand waves, and human-made objects
ranging from shipwrecks to other cables. These images,
together with multibeam data and seabed photography,
have also been used successfully to map benthic habitats
and communities (e.g. Pickrill and Todd, 2003). If cable burial
is required, seismic sub-bottom profilers are deployed to
measure the type and thickness of sediment below the
seabed as well as possible natural hazards (Chapter 6). Like
echo-sounders, the seismic profilers direct acoustic energy
from the ship to the seabed. However, instead of just echo -
ing off the seabed surface, the energy also penetrates
through the substrate and reflects off layers of sediment to
produce records of their thickness and structure. Sediment
coring and other geotechnical testing of the seabed are
also generally conducted to help determine its stability and
suitability for cable burial.
3. Survey, lay and maintain
cables
22
For depths where burial is not required, a single track
of a vessel using multibeam bathymetry will generally
suffice. The data acquired during such surveys are cons -
tantly monitored so that if an unexpected hazard, cable
obstruction or benthic community is identified, the surveyors
can immediately adjust the planned route and detour around
any hazardous or ecologically sensitive areas.
Ultimately, the desktop and field surveys will define
a viable cable route and identify the natural and human
activities that could impinge on the cable. This infor mation
guides the cable design so that it meets the specific con -
ditions of the route.
CABLE DEPLOYMENT
As a cable enters the water, its path to the bottom is
affected by the marine conditions and any variation in the
operations of the laying vessel (Roden
et al.
, 1964). These
can be distilled into three key parameters, which are: the
ship’s speed over the ground, the speed of the cable as
payed out
from the cable ship, and water depth (other less
important factors are not covered here). Initially, a cable
must be payed out slowly, with the vessel moving ‘slow
ahead’ until the cable reaches the seabed. This is the
touch-down point
. Then the ship can increase its laying
speed up to a practical maximum of about 11–15 km/hr
(6–8 knots), periodically slowing down to pass repeaters
or amplifiers through the cable-handling machinery that
controls cable tension and pay-out speed. Once a steady
state is achieved, the cable pay-out speed should approxi -
mate ship’s speed plus 2–3 per cent, assuming the seabed
topography is fairly constant. In this steady state, the
catenary of the cable will be minimized in the water column.
Laying up-slope, however, requires the pay-out speed to be
less than the ship’s speed because the water becomes
shallower. The opposite is true when laying down-slope,
because as water depth increases, more cable is needed to
Figure 3.1: ‘Mowing the lawn’: a survey ship, equipped with a multibeam mapping system and guided by satellite
navigation, charts the seabed to provide total coverage with depth soundings along a swath of seabed that can be 20 km
wide.
Source: NIWA.
Figure 3.2: A detailed multibeam image of a rocky reef,
fractured by faults and joints, and surrounded by a zone
of fine gravel that is overlain by a 1 m-thick layer of
mobile sand. Ideally, a cable would be buried below the
sand and gravel along a route designed to avoid the rocky
reef.
Source: NIWA.
Submarine cables and the oceans
23
Survey, lay and maintain
reach the seabed at the engineered touch-down point,
assuming the ship’s speed remains constant.
Laying operations on a modern vessel undergo
constant and accurate monitoring. The ship’s position and
speed over the ground are measured by the satellite-based
differential global positioning system, and the water depth
by precision echo-sounders and seabed mapping systems
(see
Route survey
), whereas cable pay-out speed and
length are recorded by a
rotometer
. Onboard, the cable
engi neer scrutinizes laying progress with constant ref -
erence to the engineered route plan, making ad just ments if
necessary. In addition, there may be computerized tracking
of the entire laying operation that includes detection of
external factors such as winds and ocean currents, plus the
means to correct for such influences.
Once laid, the cable comes ashore and is connected to
the terminal or cable station, which assumes full manage -
ment of the telecommunications system (Figure 3.3).
FROM COAST DOWN TO c.1,000–1,500 m WATER DEPTH:
THE NEED FOR PROTECTION
Cables that extend across the continental shelf (typically
0–130 m deep) to a depth range of c.1,000–1,500 m, are
commonly buried below the seabed to protect them from
damage by other seabed users (Chapter 7). The most
effective method of burial is by
sea plough
(Figure 3.4). As a
cable approaches the seabed, it is fed through the plough,
which inserts the cable into a narrow furrow. Different
plough designs are available to suit various bottom
conditions, e.g. the traditional plough-share is well suited
for muddy substrates, whereas sandy sediments may
require a plough equipped with a water jet to cut a trench
into which the cable is placed. Burial disturbs the seabed
along the narrow path of the cable, and this is discussed in
Chapter 5.
When towing a sea plough, the ship carefully controls
its operations so that cable slack is kept to a practical
minimum as it enters the plough. The aim is to lay the cable
with near-zero slack, but with enough looseness to fall into
the furrow. In areas where the cable crosses another cable
or a pipeline, the plough must be either recovered or ‘flown’
over the crossed section and then re-deployed on the oppo -
site side. These skipped sections may be buried later, either
by divers or by a remotely operated vehicle (ROV) fitted with
trenching and burial tools as well as video and navi gational
aids (Figure 3.5).
Even with the latest sea plough and ROV technology,
there are areas of seabed where burial is either impracti -
cal or impossible, e.g. rugged, rocky zones (Figure 3.2). In
such areas, cable pay-out must be regulated to minimize
suspensions between rock ridges. At the same time,
slack cannot be excessive because heavy, stiff armoured
Cable
station
Repeater or
amplifier
Unarmoured deep-
ocean cable
Armoured cable
Terminal equipment
Management
network
Figure 3.3: Summary diagram of a submarine cable system.
Source: UK Cable Protection Committee.
cables (necessary for such rugged areas) may form loops if
pay-out tension is allowed to approach zero at the touch-
down point.
Cable deployment may be followed by a post-lay
inspection to ensure that the cable is emplaced correctly
either on or into the seabed (Figure 3.6). In shallow water
down to c.40 m depth, inspections may be carried out by
divers, whereas deeper-water inspections are usually made
by an ROV equipped with video and digital cameras whose
images are viewed on the surface control vessel in real time
(Figure 3.5).
Some areas of the shallow-water seabed are un -
suitable for burial and where possible are avoided. However,
where rocky areas or zones of high sediment mobility, e.g.
surf zone, cannot be avoided, other forms of protection are
avail able and include protective covers of rocks, concrete
‘mattresses’ and steel or plastic conduits, the choice of
which will be dictated by operational and environmental
considerations.
BELOW c.1,500 m WATER DEPTH
Below a depth range of c.1,000–1,500 m, cables are
deployed mainly on the seabed, although in rare instances
burial may extend into deeper water (Chapter 7). This depth
limit is presently the extent of modern bottom trawlers, but
their forays into deeper water may necessitate burial in
even greater water depths.
Typically, cable size and weight decrease with depth as
the requirement for protective armour diminishes to zero.
Such lightweight cables are easier to handle than armoured
varieties, but cable slack must still be controlled carefully so
that the cable follows the seabed contours. This may involve
engineering 2–3 per cent slack into the laying procedure.
CABLE RECOVERY
Cables are retrieved from the seabed for repairs, replace -
ment or removal (Alcatel-Lucent, 2008). Recovery may
result from damage by human activities or natural events
(Chapters 6 and 7), failure of components, cable age (design
life is typically 20–25 years), or a need to clear congested
routes. Recovery generally entails:
location of the cable and, if a repair is required,
identi fication of the faulted section;
retrieval of the cable with specially designed
grapnels deployed from the repair vessel;
lifting to the surface for removal or repair.
During the haul-up process – sometimes from 1–3 m below
the seabed – the strain on the cable is substantial. Thus
recovery, like laying, is a complex process that takes into
account a wide range of variables:
the speed and angle of recovery;
24
Submarine cables and the oceans
Figure 3.5: TRITON ST-214 remotely operated vehicle
(ROV), which is designed to assist burial of cables in areas
inaccessible to a sea plough. It also performs cable
inspections and recovery operations.
Source: Lonnie
Hagadorn.
Figure 3.4: A sea plough about to be deployed from a cable
ship. The fibre-optic cable (yellow arrows) is fed into a
furrow cut by the plough-share (black arrow), which is
towed across the seabed on skids (red arrow).
Source:
Alcatel Submarine Network (ASN) now Alcatel-Lucent.
25
Survey, lay and maintain
the ship’s track along the cable route;
the drag of the cable, which may have increased
due to biological growth on the cable’s exterior;
water depth, current velocity, wave effects on vessel
motion, and any natural or human-made objects,
such as ship wrecks, that could potentially snag the
ascending cable.
To aid this difficult process, manufacturers provide recovery
tension tables that describe the maximum recommended
recovery speed in a given water depth and at a given
recovery angle for each cable type manufactured.
BEST PRACTICE
Most of the larger companies operating in the submarine
cable industry typically work to standards and quality
management systems set by the International Organization
for Standards under the ISO 9000 and ISO 9001 schemes. In
addition, the International Cable Protection Committee
(ICPC) publishes recommendations on key issues such as
cable routing, cable protection and cable recovery that are
available to anyone on request. Although their observance is
not mandatory, these recommendations are designed to
facilitate quality improvement and are often cited by third
parties as examples of best practice in the industry (ICPC,
2009). Guidelines relating to submarine cable activities are
also published by the Submarine Cable Improvement Group
(SCIG, 2009) and the UK Cable Protection Committee
(UKCPC, 2009).
Figure 3.6: Image of a surface-laid cable taken during a
post-lay inspection by an ROV. This image reveals the cable
in the throes of burial by mobile gravel.
Source: Transpower
New Zealand and Seaworks.
INTERNATIONAL CONVENTIONS
The invention of the submarine telegraph cable, and its
successful use to span oceans and link nations, was imme -
diately recognized as ‘necessary to maintain the vitality of
our modern international State system’ and ‘an interest of
the highest order to States’ (Twiss, 1880). The international
community responded to this recognition with the
International Convention for the Protection of Submarine
Cables (1884) (Box 4.1).
This Cable Convention was the foundation of modern
international law for submarine cables as contained in the
Geneva Conventions on the High Seas 1958 (Articles 26–30)
and Continental Shelf 1958 (Article 4) and, most recently, in
the United Nations Convention on the Law of the Sea (1982)
(UNCLOS). UNCLOS establishes the rights and duties of all
states, balancing the interests of coastal states in offshore
zones with the interests of all states in using the oceans.
Coastal states exercise sovereign rights and jurisdiction in
the exclusive economic zone (EEZ) and on the continental
shelf for the purpose of exploring and exploiting their natural
resources, but other states enjoy the freedom to lay and
maintain submarine cables in the EEZ and on the conti -
nental shelf (Figure 4.1). In archipelagic waters and in the
territorial sea, coastal states exercise sovereignty and may
establish conditions for cables or pipelines entering these
zones (UNCLOS, Article 79(4)). At the same time, the lay ing
and maintenance of submarine cables are considered
reasonable uses of the sea and coastal states benefit from
them. Outside of the territorial sea, the core legal prin ciples
applying to international cables can be summarized as
follows (UNCLOS, Articles 21, 58, 71, 79, 87, 112-115 and
297(1)(a)):
the freedoms to lay, maintain and repair cables
outside of territorial seas, including cable route
surveys incident to cable laying (the term laying
refers to new cables while the term maintaining
relates to both new and existing cables and includes
repair) (Nordquist
et al.
, 1993, p. 915);
the requirement that parties apply domestic laws
to prosecute persons who endanger or damage
cables wilfully or through culpable negligence
(Box 4.2);
the requirement that vessels, unless saving lives or
ships, avoid actions likely to injure cables;
the requirement that vessels must sacrifice their
anchors or fishing gear to avoid injury to cables;
the requirement that cable owners must indemnify
vessel owners for lawful sacrifices of their anchors
or fishing gear;
26
4. International law
BOX 4.1: INTERNATIONAL CONVENTION FOR THE
PROTECTION OF SUBMARINE CABLES, 1884
The Cable Convention continues to be widely used in the
cable industry. While its essential terms are included in
the United Nations Convention on the Law of the Sea
(UNCLOS), the Cable Convention remains the only treaty
that provides the detailed procedures necessary to
implement them. See:
Article 5 special lights and day shapes displayed by
cable ships; minimum distances ships are required to
be from cable ships;
Article 6 minimum distance ships are required to be
from cable buoys;
Article 7 procedures for sacrificed anchor and gear
claims;
• Article 8 competency of national courts for infractions;
Article 10 procedures for boarding vessels suspected
of injuring cables and obtaining evidence of infractions.
Article 311(2) of UNCLOS recognizes the continued use
of these provisions, which are compatible with and
supplement UNCLOS.
BOX 4.2: CULPABLE NEGLIGENCE
The origin of the term ‘culpable negligence’ is found in
Renault (1882), where reference is made to two early
English cases:
Submarine Cable Company v. Dixon
, The
Law Times, Reports-Vol. X, N.S. at 32 (5 March 1864) and
The Clara Killian
, Vol. III L.R. Adm. and Eccl. at 161
(1870). These cases hold that culpable negligence
involves a failure to use ordinary nautical skill that would
have been used by a prudent seaman facing the situation
that caused the cable fault. Since the term ‘culpable
negligence’ was adopted in UNCLOS without discussion,
it is reasonable to assume that the same standard
applies under UNCLOS.
27
the requirement that the owner of a cable or pipe -
line, who in laying or repairing that cable or pipe line
causes injury to a prior laid cable or pipeline, indem -
nify the owner of the first laid cable or pipeline for
the repair costs;
the requirement that coastal states along with pipe -
line and cable owners shall not take actions which
prejudice the repair and maintenance of existing
cables.
These traditional rights and obligations were carefully
codified by the UNCLOS drafters who were familiar with
the historical state practice of cables. Parts IV to VII of
UNCLOS set out the rights and obligations in the following
UNCLOS designated zones: archipelagic waters, the EEZ,
the continental shelf and the high seas (Figure 4.1). UNCLOS
treats all cables the same, whether they are used for tele -
com mu ni cations or power transmission or for commercial,
military or scientific purposes.
While natural occurrences such as submarine land -
slides or turbidity currents occasionally damage submarine
cables, the most common threat to cables is other human
activities, especially bottom fishing (Chapter 7). In many
countries, care ful route planning helps to avoid damage to
cables and to cultural seabed features (Wagner, 1995). With
respect to potential adverse impacts caused by submarine
cables, UNCLOS indirectly takes into account their potential
environmental impact by distinguishing cables from sub -
marine pipelines, i.e. on the continental shelf it allows a
coastal state to delineate a route for a pipeline but not for
a cable (Article 79(3)). The reason for this distinction is
that there is clearly a need to prevent, reduce and control
any pollution that may result from pipeline damage. By
comparison, damage to a submarine telecommunications
cable is unlikely to involve pollution (Nordquist
et al.
, 1993,
p 915), but may significantly disrupt international commu -
nications and data traffic.
More generally, UNCLOS, in its preamble, recognizes
the desirability of establishing ‘a legal order for the seas and
oceans which will facilitate international communication,
and will promote the peaceful uses of the oceans and seas,
the equitable and efficient utilization of their resources, the
conservation of their living resources, and the study, pro -
tection and preservation of the marine environment’.
3
nautical
miles
12
nautical
miles
24
nautical
miles
200
nautical
miles
Territorial
sea
Contiguous
zone
Exclusive economic zone UNCLOS (58, 113-115)
UNCLOS (3) UNCLOS (33) UNCLOS (57)
UNCLOS
(87, 112-115)
GCHS (26-30) High seas
High seas
Depth
(metres)
0
1,000
2,000
3,000
4,000
5,000
Shelf
edge
OCEAN
Geological
slope
Base of
slope Geological
rise
Oceanic crust (basalt)
Continental crust (granite)
LAND UNCLOS (79, 113-115)
GCCS (4)
Figure 4.1: Legal boundaries of the ocean from territorial sea to exclusive economic zone and onto the high seas (figures in
parenthesis refer to treaty articles).
Source: D. Burnett.
International law
Submarine cables clearly facilitate international com muni -
cation, along with freedoms of navigation and overflight.
Part XII of UNCLOS establishes the legal duty of all states to
protect and preserve the marine environment (Article 192).
It establishes a general legal framework for this purpose,
which balances economic and environmental interests in
general as well as the interests of coastal states in pro -
tecting their environment and natural resources and the
rights and duties of other states. To flesh out the framework,
it requires states to adopt more detailed mea sures to ensure
that pollution from activities under their control does not
cause environmental damage to other states or areas
be yond national jurisdiction. States shall, consistent with
the rights of other states, endea vour to observe, measure,
evalu ate and analyse, by recog nized scientific methods, the
risks or effects of pollu tion of the marine environment
(Article 204).
CABLES AS CRITICAL INFRASTRUCTURE
An emerging trend is for states to treat international cables
in national maritime zones as critical infrastructure that
deserves strong protection to complement traditional
international cable law. In that vein, Australia, consistent
with international law, has legislated to protect its vital cable
links by creating seabed protection zones that extend out
to 2,000 m water depth. Bottom trawling and other poten -
tially destructive fishing practices, as well as anchoring, are
pro hi bited inside these zones. Three international cables
carry around 99 per cent of Australia's voice and data traffic
and in 2002 were worth more than AU$5 billion a year to
the country's economy (Telecommunications and Other
Legislation Amendment (Protection of Submarine Cables
and Other Measures) Act 2005; proposed regulations for
sub marine cables off Sydney, New South Wales (August
2006)). New Zealand has also enacted legislation that estab -
lished no-fishing and no-anchoring zones around cables
(Submarine Cable and Pipeline Protection Act (1966)). The
trend is expected to continue because most nations depend
on cables for participating in the global economy and for
national security, e.g. the United States relies on cables for
over 95 per cent of its inter national voice and data traffic,
only 7 per cent of which could be carried by satellites if the
cables were disrupted (Burnett, 2006). These developments
sometimes go hand in hand with conservation, as restric -
tions on trawl ing to prevent cable damage can also provide
direct benefits for bio diversity by protecting vulnerable
seabed ecosystems and species such as corals and sponges
(CBD, 2003).
Since UNCLOS, the parties to the UNESCO Convention
on Underwater Cultural Heritage (2001) agreed to exempt
cables from that treaty because of the specific provisions
of UNCLOS and the agreement of the parties that cable
laying and maintenance posed no threat to underwater cul -
tural heritage.
There are numerous international conventions that
build on the UNCLOS framework to further specify require -
ments for ocean uses such as international shipping or
fisheries, but not for submarine cables. Other treaties elabo -
rate on what states should generally do to protect and
preserve the marine environment and, as embodied in the
1992 Convention on Biological Diversity (CBD), to conserve
and sustainably use marine biodiversity. All of these
conventions function in accordance with the UNCLOS
framework, both within and beyond national jurisdiction.
However, there are no conventions that further elaborate the
legal framework for cables established by UNCLOS and the
earlier Cable Convention.
The laying and maintenance of telecommunications
cables is a reasonable use of the sea, and in 159 years of
use, there has been no irreversible environmental impact.
UNCLOS and state practice have provided adequate gover -
nance for inter national cables outside of national waters,
and state practice increasingly recognizes the import ance of
protecting cables from activities that could damage them.
The corresponding benefits of cable pro tection zones for
biodiversity conser vation have also been recognized. Yet
increasing use of the oceans and seabed is likely to result in
more conflicts between users (Figure 4.2). This may require
future changes in the existing international legal regime.
Careful planning may also be necessary to avoid adverse
impacts on vul nerable seafloor ecosystems and biodiversity.
Consistent with past practice and recog nizing the import -
ance of cables to the world's infra structure, any change to
the existing international law requires express provisions in
an international treaty.
28
Submarine cables and the oceans
Figure 4.2: Rights and obligations relating to submarine
cables in the world's oceans can be enforced in national
courts or in the International Tribunal for the Law of the
Sea, shown in session in Hamburg, Germany.
Source:
Stephan Wallocha.
29
The total length of fibre-optic cables in the world’s oceans is
c.1 million km (J. Annals, Global Marine Systems Ltd, pers.
comm., 2007). In terms of physical size, a modern cable is
small (Chapter 2). The deep-ocean type has a diameter of
17–20 mm and its counterpart on the continental shelf
and adjacent upper slope is typically 28–50 mm diameter
because of the addition of protective armouring. Despite this
small footprint, fibre-optic cables may still interact with the
benthic environment. This chapter begins with an overview
of the procedures for evaluating those interactions via the
environmental impact assessment (EIA) process. This is fol -
lowed by a synopsis of those environmental interactions of
cables laid on and into the seabed, using the peer-reviewed
science litera ture supported by open-file and published
reports. The chapter concludes with some general con sider -
ations regarding cables and the environment.
ENVIRONMENTAL IMPACT ASSESSMENTS
For some countries, domestic law and regulations require
an analysis of the project’s effects on the natural
environment. The report that is subsequently produced is
commonly referred to as an environmental impact assess -
ment (EIA). The breadth of content, level of detail and time
required to undertake an EIA in relation to a proposed
submarine cable project varies considerably from country to
country. Nevertheless, the principle of assessing a project’s
effect on the environment is well established in Europe,
Australasia, North America and parts of Asia and Africa.
The purpose of an assessment is to ensure that any
environmental effects of cable laying and maintenance are
taken into account before authorization is provided to lay
a cable on the seabed (e.g. Hong Kong Environmental
Protection Department, 2002; Monterey Bay National Marine
Sanctuary, 2005; North American Submarine Cable
Association, 2008). However, the extent to which a permit
application requires an EIA depends on the regulatory
process. It can range from the provision of relevant technical
information and a statement of compliance with environ -
mental accreditation, to a brief environmental review, to a
comprehensive analysis that includes formal public and/or
governmental consultation. Schedules for completing an
assessment range from a few weeks to a year or longer. This
depends on the quantity and quality of data needed, the level
of documentation and consultation required, and the
presence of sensitive environmental resources within the
project’s bounds.
5. Environmental impacts
Figure 5.1: Telecommunications and power cables laid on the seabed surface of Cook Strait, New Zealand, because the
presence of rock and the constant movement of sediment by powerful tidal flows make it impractical to bury them.
Protection is afforded by a legal cable protection zone (boundaries are grey lines on multibeam image). Even so, fibre-
optic cables were displaced (arrows) by illegal fishing prior to full-time boat patrols of the zone, when such incidents
ceased.
Source: Transpower New Zealand, Seaworks and NIWA.
A formal EIA typically has five components:
1. description of the proposed operation;
2. description of the receiving environment (covering
all relevant physical, geological, biological and
anthro pogenic/socio-economic factors);
3. evaluation of potential effects on the environment;
4. assessment of mitigating measures needed to
reduce any effects to an environmentally accep t -
able level (i.e. spatial or temporal limitations,
replacement, re-establishment or restoration of
affected environments);
5. assessment of any monitoring measures needed to
ensure that the extent of an effect (mitigated or
other wise) is maintained at an acceptable level.
This documentation is usually followed by a non-technical
summary, which is a ‘reader-friendly’ synopsis for general
circulation in a consultation process. As well as evaluation of
existing data, an EIA may require field surveys that involve
seabed mapping and sampling of sediments, rocks, fauna,
flora and biochemistry (Chapter 3).
EIAs for cable operations are rare and are generally
limited to a coastal state’s territorial sea. The European
Union EIA Directive currently does not explicitly impose an
EIA requirement on cable-laying projects. That, of course,
does not discount the possibility of an EIA being required as
a result of a submarine cable planning application. Indeed,
such applications are most likely to be routinely reviewed by
the appropriate authority.
CABLES ON THE SEABED
Modern cables are usually buried into the seabed at water
depths down to c.1,500 m as a protective measure against
human activities (Chapters 3 and 7). However, some
shallow-water cables may be placed on the seabed in areas
unsuitable for burial, e.g. rock or highly mobile sand (Figure
5.1). For water depths greater than c.1,500 m, deployment
on the seabed is the preferred option (Chapter 3).
Surveys
Cable route surveys rely primarily on acoustics-based echo-
sounding, sonar and seismic systems. These focus on the
seabed surface and, where burial is concerned, the few
metres of sediment below the seabed. Accordingly, high-
frequency low-energy acoustic systems are used to pro vide
the necessary precision and detail to define a suitable route.
Given our incomplete knowledge of the different responses
of marine animals to different sources of noise (National
Research Council, 2003), cable survey equipment is
regarded as posing only a minor risk to the environment
(SCAR, 2002) compared to prolonged high-energy mid-
range sonar systems, which may be associated with strand -
ings of some whale species (Fernandez
et al.
, 2005) and are
the subject of ongoing research (Claridge, 2007).
Physical interactions
Surface-laid cables may physically interact with the seabed
under natural or human influences. Continental shelves
are typically exposed to wave and current action, including
tidal flows that move sediment and result in the burial,
exposure or even undermining of a cable (Figure 5.1; Carter
and Lewis, 1995; Carter
et al.
, 1991). Where undermining is
significant, the suspended cable can vibrate or strum under
the water motions. Such actions may abrade the rocks
supporting the suspension and the cable itself. Observed
suspensions off California indicate that rock abrasion
occurs mainly in the zone of frequent wave activity in water
depths of less than c.20 m (Kogan
et al.
, 2003, 2006);
abrasion marks ranged from 6 to 45 cm wide. Where the
suspensions are long lived, they can be colonized by
encrusting marine biota (Figure 5.2) that can biologically
cement the cable to the rock suspension points.
Cables undergo self-burial that is either temporary
or permanent. Where routes traverse fields of mobile sand
waves, burial takes place as the sand-wave crest passes
across the cable. Exhumation may follow with the passage
of the sand-wave trough (Allan, 2000). Temporary burial
30
Submarine cables and the oceans
Figure 5.2: Surface-laid submarine cable, which has served as a substrate for the growth of epifauna.
Source: Nigel Irvine.
also occurs nearshore, where ‘fair-weather’ accumulation
of sand may be interrupted by storm-forced waves and
currents that erode the substrate to expose a previously
buried cable (Carter and Lewis, 1995). In zones of high
sediment accumulation, cables can be rapidly buried by
depositing sediment or simply settle into a soft substrate.
Off California, for example, about half of a 95 km-long
scien tific coaxial cable was covered by sediment in the eight
years following its surface installation (Kogan
et al.
, 2003).
Bottom trawl fishing and ships’ anchoring can
displace and/or damage cables (NOAA, 2005). To protect
against such mishaps, cables are routinely buried beneath
the seabed (Chapters 3 and 7). Where burial is impractical,
a cable protection zone may be enforced whereby all
potentially damaging human activities are prohibited
(Figure 5.1; e.g. ACMA, 2007; Transpower and Ministry of
Transport, 2008). Such measures are only as good as their
enforcement, which may entail constant surveillance,
including vessel patrols and electronic monitoring of all
ship movements. Dialogue with other seabed users, along
with public education regarding the importance of sub -
marine cables, is also an effective protection measure
(Chapter 7).
Benthic biota
Any interaction of cables with seabed life may be evaluated
by assessing and monitoring the biota before and after
cable installation (Andrulewicz
et al.
, 2003) or, in the case of
installed cables, by comparing the biota at sites near and
distant from a cable (Grannis, 2001; Kogan
et al.
, 2003). In
addition, there are reports of epifauna and epiflora that live
on the cables themselves (Figure 5.2; Ralph and Squires,
1962; Levings and McDaniel, 1974).
Overall, those studies demonstrate that cables have
no or minimal impact on the resident biota. On the basis
of 42 hours of video footage, the comprehensive study of
Kogan
et al.
(2003, 2006) showed no statistical difference in
the abundance and distribution of 17 animal groups living
on the seabed within 1 m and 100 m of a surface-laid
coaxial scientific cable. Likewise, 138 sediment cores with
an infauna of mainly polychaete worms, nematodes and
amphipods showed that the infauna was statistically
indistinguishable whether near or distant from the cable.
The main difference associated with the cable was that it
provided a hard substrate for the attachment of anemones
(Actiniaria). These organisms were abundant where the
cable traversed soft sediment that normally would be
unsuitable for such animals (Figure 5.3). Fishes, especially
flat fishes, were more common close to the cable at two
observational sites where small patches of shell-rich
sediment had formed, probably in response to localized
turbulence produced by current flow over the cable.
Marine mammals and fish
Records extending from 1877 to 1955 reveal that 16 faults in
submarine telegraph cables were caused by whales
(Heezen, 1957; Heezen and Johnson, 1969). Thirteen of the
faults were attributed to sperm whales, which were
identified from their remains entwined in the cables. The
remaining faults were caused by a humpback, killer and an
unknown whale species. In most instances, entanglements
occurred at sites where cables had been repaired at the
edge of the continental shelf or on the adjacent continental
slope in water depths down to 1,135 m. However, whale
entangle ments have nowadays ceased completely. In a
recent review of 5,740 cable faults recorded for the period
1959 to 2006 (Wood and Carter, 2008), not one whale
entangle ment was noted (Figure 5.4). This cessation
occurred in the mid-1950s during the transition from tele -
graph to coaxial cables, which was followed in the 1980s by
the change to fibre-optic systems.
The absence of entanglements since the telegraph era
reflects the following developments in cable design and
laying:
advances in design, especially the achievement of
torsional balance, lessened the tendency of coaxial
and fibre-optic cables to self-coil on the seabed;
accurate seabed surveys, coupled with improved
vessel handling and laying techniques, reduced
suspensions and loops by laying cables under
tension while following the seabed topography and
avoiding excessively rough rocky substrates;
31
Environmental impacts
Figure 5.3: The exposed ATOC/Pioneer Seamount cable
with attached anemones (
Metridium farcimen
) at c.140 m
water depth. The cable provides a hard substrate on an
otherwise soft seabed. The thin, erect organisms are sea
pens (
Halipteris
sp.), and the mollusc
Pleurobranchaea
californica
is next to the 3.2 cm wide cable.
Source: Monterey
Bay Aquarium Research Institute (MBARI).
burial of cables into the seabed on the continental
shelf and slope down to c.1,500 m water depth,
which is the typical maximum diving limit of sperm
whales (Watkins
et al.
, 2002);
fault repair techniques that are designed to mini -
mize slack cable and, if the repaired section is on
the continental shelf or slope, burial beneath the
seabed, usually with the assistance of an ROV.
Is the cessation of whale entanglements since 1959 possibly
a consequence of non-reporting? This is unlikely because:
whale entanglements prior to 1959 were reported in
the scientific literature (Heezen, 1957; Heezen and
Johnson, 1969);
interactions with other marine animals since 1959
have been reported (ICPC, 1988; Marra, 1989);
cable repairs are undertaken by a few specialized
maintenance groups contracted to many cable
owners and operators, and are therefore required to
operate at high standards, which would reduce the
chance of non-reporting;
an event such as a whale capture is unlikely to
escape media attention when electronic communi -
cation is so freely available, even at sea.
Fish, including sharks, have a long history of biting cables as
identified from teeth embedded in cable sheathings (Figures
5.4 and 5.5). Barracuda, shallow- and deep-water sharks
and others have been identified as causes of cable failure
(ICPC, 1988; Marra, 1989). Bites tend to penetrate the cable
insulation, allowing the power conductor to ground with
seawater. Attacks on telegraph cables took place mainly
on the continental shelf and continued into the coaxial era
until c.1964. Thereafter, attacks occurred at greater depths,
presumably in response to the burial of coaxial and fibre-
optic cables on the shelf and slope. Coaxial and fibre-optic
cables have attracted the attention of sharks and other fish.
The best-documented case comes from the Canary Islands
(Marra, 1989), where the first deep-ocean fibre-optic cable
failed on four occasions as a result of shark attacks in water
depths of 1,060–1,900 m (Figure 5.5). Reasons for the
attacks are uncertain, but sharks may be encouraged by
electro magnetic fields from a suspended cable strumming
in currents. However, when tested at sea and in the
laboratory, no clear link between attacks, elec tro magnetic
fields and strumming could be established. This lack of
correlation may reflect differences between the behaviour
of the deep-water sharks responsible for the bites and
that of the shallow-water species used in the experiments.
Whatever the cause, cables have been redesigned to im -
prove their protection against fish biting.
Leaching from cables
Modern deep-water fibre-optic cables are composed of
several pairs of hair-like glass fibres, a copper power
conductor and steel wire strength member, which are all
32
Submarine cables and the oceans
1860
1870
1880
1890
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
Persian Gulf
Gulf of Suez
Prince William
Sound, Alaska
? Pakistan
South American
west coast
Rio de Janeiro,
Brazil
Cabot Strait Channel
New York, USA
Brazil
185 0
First international telegraph cable
(English Channel)
First trans-Atlantic telegraph cable
First coaxial submarine cable
First trans-Atlantic coaxial cable
Cable burial (ploughing) begins
First fibre-optic telephone developed
First trans-Atlantic fibre-
optic cable
? Valparaiso, Chile
Esmeraldas, Ecuador
Chorrillos, Peru
El Salvador
Peru
Peru
Chorrillos, Peru
Paita, Peru and
Colombia
Alaska
? cable system
Alaska
? cable system
Telegraph cable era
Coaxial cable era
Fibre-optic cable era
Whale entanglements
Unspecified whale damage
Fish bites
Date uncertain
?
Figure 5.4: Interaction of whales and fish with submarine cables over time. The cessation of whale entanglements coincided
with the improved design and laying techniques of the coaxial and fibre-optic eras. In contrast, fish bites (including those of
sharks) have continued.
Source: Wood and Carter (2008) and IEEE Journal of Oceanic Engineering.
33
Environmental impacts
sheathed in high-density polyethylene. Where extra
protection is required, as for areas of rocky seabed or
strong wave and current action, additional steel wire
armour is added (Chapter 2). No anti-fouling agents are
used (Emu Ltd, 2004). Of these materials, cable-grade
polyethylene is essentially inert in the ocean. Processes
such as oxidation, hydrolysis (chemical breakdown in
water) and mineralization are extremely slow; the total
conversion of polyethylene to carbon dioxide and water will
take centuries (Andrady, 2000). The effects of ultraviolet
light (UV-B), the main cause of degradation in most
plastics, are minimized through the use of light-stabilized
materials, burial into the seabed and the natural reduction
in light penetration through the upper ocean, where the
photic zone rarely extends beyond 150 m depth. Any
mechanical breakdown of a cable’s plastic sheathing to
fine-grained particles on the energetic continental shelf –
a potential hazard for marine life (Allsop
et al.
, 2006 and
references therein) – is minimized by armouring and
burial.
With respect to other cable components, data on their
behaviour in seawater are sparse, with the exception of a
study under way at Southampton University, UK (Collins,
2007). Various types of fibre-optic cable were immersed
in containers with 5 litres of seawater, which was tested
for copper, iron and zinc – potential leachates from the
conductors and galvanized steel armour. Of these ele ments
only zinc passed into the seawater, yielding concentrations
of less than 6 parts per million (ppm) for intact cables and
less than 11 ppm for cut cables with exposed wire armour
ends. The amount of leaching declined after c.10 days.
Bearing in mind that tests were carried out in a small, finite
volume of seawater, zinc leachate in the natural environ -
ment would be less due to dilution by large volumes of
moving seawater. Furthermore, zinc is a naturally occurring
element in the ocean, with concentrations in fish and shell -
fish ranging from 3 to 900 ppm (Lenntech, 2007).
CABLES INTO THE SEABED
Installation of cables into the seabed can disturb the
benthic environment. Compared to other offshore acti vities
such as bottom trawling, ship anchoring and dredging,
disturbance related to cable burial is limited in its extent,
and is a non-repetitive procedure, unless a cable is damaged
(Chapter 3). The decommissioning and recovery of a buried
system may also result in benthic disturbance, but again
it is of limited extent and relatively infrequent, reflecting the
20–25 year design life of a fibre-optic cable. The following
discussion examines the type and extent of seabed dis -
turbance associated with cable installation, maintenance
and decommissioning, followed by a brief overview of seabed
recovery after disturbance.
Seabed disturbance
Route clearance
Prior to installation, any debris is cleared from a cable route
by deployment of a ship-towed grapnel (NOAA, 2005; NSR
Environmental Consultants, 2002). This tool penetrates
0.5–1.0 m into soft sediment and is generally not used in
rocky areas. In accord with modern practice, the location of
the grapnel is carefully monitored to ensure that burial
follows the grapnel route as closely as possible so that the
cable is installed in a debris-free zone.
Ploughing
As a plough passes across the seabed, the share opens a
furrow, inserts the cable and allows sediment to fall back,
thereby filling the fissure (Allan, 1998). However, the precise
nature of this disturbance will vary with substrate type,
depth of burial and plough type (Hoshina and Featherstone,
2001; Jonkergrouw, 2001; Mole
et al.
, 1997; Turner
et al.
,
2005). In nearshore zones including tidal flats, special
ploughs are available to lessen disturbance to, for example,
eelgrass and seagrass beds (Ecoplan, 2003). Disturbance is
also minimized by drilling conduits through which a cable
may pass beneath biologically sensitive coastal areas (Austin
et al.
, 2004). On the continental shelf, burial to c.1 m depth
in soft to firm sediment typically leaves a ploughed strip,
c.0.3 m wide, in which the cable is entirely covered. However,
burial in consolidated substrates may result in only partial
closure of the furrow, with displaced sediment deposited
at the furrow margins (NOAA, 2005). The skids that support
the plough can also leave their footprint on the seabed,
particularly in zones of soft sediment (Chapter 3). Potential
effects are increased sediment compaction and the
disruption of marine fauna. Overall, the disturbance strip
produced by the plough-share and skids in direct contact
with the seabed ranges from c.2 m to c.8 m wide, depending
on plough size.
Figure 5.5: The crocodile shark (
Pseudocarcharias
kamoharai
) is a small species that grows to just over
1 m long. On the basis of teeth embedded in the Canary
Islands fibre-optic cable, it was found to be a main
instigator of the bite-related faults.
Source: National Marine
Fisheries Service, NOAA.
Jetting
This method is used to bury cables that are already laid.
Some systems use a combination of ploughing and jetting
for burial but, in general, jetting is favoured for deep parts
of a route where steep slopes or very soft sediment are
unfavourable for ploughing (Hoshina and Featherstone,
2001; Jonkergrouw, 2001). It is also used to rebury repaired
sections. Modern post-lay burial relies on an ROV that is
equipped with jets to liquefy the sediment below the cable,
allowing it to sink to a specified depth (Chapter 3). The width
of disturbance zones associated with jetting (liquefaction
and coarse sediment redeposition) is typically about 5 m
(Ecology and Environment, 2001), but fine-grained silt and
clay may be dispersed further afield in plumes of turbid
water. Organisms directly within the zone of liquefaction can
be damaged or displaced, whereas biota near the jetting
zone may receive the resuspended sediment (NOAA, 2005).
Any effect on and recovery of the biota will depend on a suite
of variables including the amount and particle size of the
suspended sediment, ambient current and wave conditions,
seabed topography, the nature of the benthic biota and the
frequency of natural disturbances (see
Seabed recovery
).
Cable repairs
Around 70 per cent of all cable failures associated with
external aggression are caused by fish ing and shipping acti -
vities in water depths shallower than 200 m (Kordahi and
Shapiro, 2004). Accordingly, cables are buried for protection,
an action which, together with an increased awareness of
cables by other seabed users, has produced a marked
fall in the number of faults per 1,000 km of cable. Faults re -
lated to component failure have also decreased in response
to improved cable system design (Featherstone
et al.
, 2001).
Nevertheless, faults still occur and require repair. For buried
cables, the repair procedure relies on towing a grapnel
across the path of the cable, cutting the cable and retrieving
both ends. Onboard the repair ship, a new section may be
inserted or ‘spliced’ to replace the damaged cable. The
repaired section is re-laid on the seabed at right angles to
the original route so as to minimize slack produced by
insertion of the splice (Drew and Hopper, 1996). The repair is
then reburied by a jet-equipped ROV (e.g. Mole
et al.
, 1997).
Where water depths permit, ROVs may also be used to
retrieve damaged cables both on and below the seabed. As
this technique is likely to require no or few grapnel runs,
seabed disturbance is reduced.
Cable removal
As cables reach the end of their design life or become
redundant due to technological advances, their removal
from the seabed may be considered. In the case of a buried
cable, its removal may result in disturbance, the extent of
which has been assessed for offshore UK by Emu Ltd (2004).
In essence, as a cable is pulled from the seabed it disturbs
the sediments and associated benthic fauna. The degree of
disturbance is closely related to the type of substrate, with
soft sandy and muddy sediments suffering little or no
impact, whereas consolidated substrates, such as stiff clay
and chalk, may create fine-scale rough topography from
frag ments of consolidated material ejected during cable
extraction. For bedrock, a cable is usually laid on the rocky
surface if outcrops cannot be avoided. In that context, the
cable may support an epifauna which would be lost during a
recovery procedure. It may then be deemed prudent to leave
the cable in place in order to preserve the epifauna.
How much do submarine cables affect the environment?
A sense of context
Disturbances and impacts caused by cable laying and
repairs must be viewed in the context of the frequency and
extent of these activities. Clearance of debris from a path
proposed for cable burial is usually followed within days to
weeks by actual burial. Unless a cable fault develops, the
seabed may not be disturbed again within the system’s
design life. Furthermore, the one-off disturbance asso ciated
with cable placement is restricted mainly to a strip of seabed
less than 5–8 m wide. For comparison, bottom trawl and
dredge fishing operations are repetitive and more extensive
(e.g. National Research Council, 2002; UNEP, 2006). A single
bottom trawl can be tens of metres wide, sweep substantial
areas of seabed in a single operation and is likely to be
repeated over a year at the same site. As noted by NOAA
(2005), a single impact, such as a cable burial, is preferred to
continuous, multiple or recurring impacts.
Seabed recovery
Seabed disturbance related to cable operations most
commonly occurs in the burial zone from 0 to c.1,500 m
water depth. This is also the main range of disturbance
resulting from human activities as well as natural forces
such as storm waves and currents, etc. (UNEP, 2006;
Nittrouer
et al.
, 2007). The time taken for the seabed to
recover depends on the natural dynamics of the various
environments and the type of disturbance. Much of our
knowledge of seabed recovery is based on studies of areas
disturbed by fishing or large natural perturbations (e.g.
National Research Council, 2002; Kroeger
et al.
, 2006 and
references therein) with additional information provided by
several cable-specific studies (e.g. Andrulewicz
et al.
, 2003;
Grannis, 2001; NOAA, 2005).
Coastal zone
For coastal wetlands and inter-tidal zones, the use of
various techniques to meet different environmental
34
Submarine cables and the oceans
35
Environmental impacts
conditions has helped to reduce disturbance. A specially
designed, low-impact vibrating plough was used to bury a
cable through salt marshes along the Frisian coast,
Germany. A post-lay monitoring survey recorded the re-
establishment of salt marsh vegetation within one to two
years and full recovery at most monitoring sites within
five years (Ecoplan, 2003). In Australia, cables crossing
seagrass beds were placed in narrow slit trenches (40 cm
wide) that were later replanted with seagrass removed from
the route prior to installation (Molino-Stewart Consultancy,
2007). A similar technique was used for eelgrass beds in
Puget Sound where cables were also installed in conduits
drilled under the beds to minimize disturbance (Austin
et al.
,
2004). Soft sediment communities in artificially disturbed
muddy mangrove flats recovered in two to seven months
depending on the intensity of the disturbance (Dernie
et
al.
, 2003). With respect to high-energy sandy coasts, any
physical disturbance is usually removed within days to
weeks through natural wave and current action (e.g. CEE,
2006; Carter and Lewis, 1995).
Continental shelf and slope
The continental shelf has a range of substrates and habitats
that reflect:
the amount of sediment discharged from rivers and
produced directly in the ocean and seabed through
biological growth;
wave and current action that erodes, disperses and
deposits sediment;
the local geology (e.g. Nittrouer
et al.
, 2007).
Of course, these influences are themselves ultimately
controlled by the climate, regional oceanography and tec -
tonic framework. With respect to unconsolidated sediment,
the amount of wave energy required to mobilize it decreases
with water depth. Thus, on the inner continental shelf
(typically less than 30 m deep), sand is frequently moved by
swell in the presence of local currents. Sediment movement
is less frequent on the middle shelf (c.30 to 70 m depth),
occurring mainly during storms when swell and current
activity intensifies. Finally, sediment movement on the
outer shelf (c.70 m to the shelf edge at an average depth of
c.130 m) is infrequent, being controlled mainly by the pas -
sage of major storms. However, move ment may be more
frequent at the shelf edge
per se
, where the steepened
topography intensifies local currents and causes internal
waves (i.e. waves formed along density surfaces under the
ocean surface) to break like a normal wave on a beach.
This generalized picture of shelf behaviour is in -
fluenced and sometimes over-ridden by local conditions.
For instance, the powerful tides in the North Sea, Straits of
Messina, Bass Strait and Cook Strait, frequently move
sediment at most shelf depths. Whatever the forcing
mechanism, physical restoration of the seabed is most rapid
on those shelves with a substantial supply of sedi ment and
moderate to high wave or current action. Thus any cable-
related disturbance of sandy substrates on the inner shelf is
usually rectified within days to months (CEE, 2006; DeAlteris
et al.
, 1999; NOAA, 2007). Likewise, the benthic communities
also recover quickly because they have natural adaptive
behaviours gained from an environment subject to frequent
change. Bolam and Rees (2003), for instance, show that ben -
thic macrofaunal communities in energetic zones recovered
within nine months following the dumping of dredge spoil.
Where possible, cable routes avoid zones of rocky reef
because of operational difficulties in protecting cables on
hard substrates and potential disturbance of reef eco -
systems (e.g. Ecology and Environment, 2001; Science
Applications International, 2000).
On the middle shelf (c.30–70 m depth), zones of dis -
turbance are likely to remain longer due to less frequent
wave and current activity (e.g. NOAA, 2005). However, if local
currents are active, sediment movement will restore
equilibrium, as observed in the Baltic Sea where a cable
trench collected sand to the point that, one year after laying,
any physical dislocation of the seabed was erased
(Andrulewicz
et al.
, 2003). Furthermore, the post-lay inspec -
tion failed to detect significant changes in the composition,
abundance and biomass of benthic animals. In the case of
muddy substrates, cable-related disturbances may persist
longer than in mobile sand settings. In Stellwagen National
Marine Sanctuary off Massachusetts, USA, slow sedi -
mentation had not completely infilled a cable trench one
year after ploughing (Grannis, 2001). However, there was no
detectable effect on the epifauna, which appears to have
recovered in the one-year period. Where the cable trench
passed through an area of active bottom fishing grounds, the
epifauna was more abundant within the trench; a feature
that was attributed to fishing-induced resuspen sion of fine
sediment within the trench to expose gravel fragments that
provided substrates for epifaunal colonization. A similar
response was noted in a cable trench in Olympic National
Marine Sanctuary off Washington State, USA (NOAA, 2005),
where exposed con solidated sediment attracted an epifauna
which, in this case, differed from the benthos in undisturbed
sediment.
The speed at which a trench infills depends on:
its depth of incision;
the sediment supply and wave or current action to
carry the material to the trench, which tends to act
as a sediment sink;
the degree of sediment consolidation, with soft
sediments tending to respond readily to wave and
current action whereas consolidated materials will
be more resistant.
Continental shelves receiving large amounts of river mud
and sand, such as those bordering the Pacific Ocean
(Milliman and Syvitski, 1992), can expect several milli metres
to centimetres of sediment to deposit each year. This
appears to be the case on the Californian shelf, where
repeated surveys of a cable trench have shown persistent
accumulation and burial over four years (California Coastal
Commission 2005, 2007).
On the outer shelf and upper slope (more than 70 m
deep), increasing water depth and distance from shore
mean that burial disturbance remains longer due to reduced
water movements and sediment supply, also bearing in
mind that trenches in resistant sediments will persist longer
than those in unconsolidated materials (NOAA, 2005). The
exceptions are very narrow shelves, where river discharges
can extend over much of the shelf, and the continental shelf
edge, where tidal and other currents may intensify to actively
move sediment. Thus similar principles apply: mobile sedi -
ments and associated faunas will recover more rapidly than
counterparts in quiet, stable settings.
CABLE PLACEMENT AND ECOLOGICALLY SIGNIFICANT
AREAS
The last 15 years have witnessed substantial advances
in our knowledge and understanding of deep-ocean
ecosystems. International research initiatives are reveal -
ing hitherto unknown or poorly known habitats and
ecosystems (Ausubel, 1999; Freiwald
et al.
, 2004; UNEP,
2005, 2006). Currently under the spotlight are seamounts,
cold-water coral communities, hydrothermal vents such as
those found along the volcanic mid-ocean ridges, deep-
ocean trenches, submarine canyons and the lower con -
tinental slope, amongst others.
To gain an insight into the nature, role and importance
of these habitats and ecosystems, deep-sea or cold-water
corals are instructive as they were recently the subject of a
major review (Freiwald
et al.
, 2004). Located in water depths
of 40–1,000 m or more, cold-water corals occur in all the
major oceans. To date, most have been found in the North
Atlantic – a feature that probably reflects the intensive
research and exploration efforts in that region rather than it
being a preferred habitat. While their full extent is unknown,
recent studies suggest that the area occupied by cold-water
corals may rival or exceed the coverage of tropical reefs. Off
Norway alone, cold-water reefs cover c.2,000 km2, and on
Blake Plateau, southeast of the United States, an estimated
40,000 reefs may be present (Paull
et al.
, 2000). Compared to
tropical coral reefs with their massive structures and mul -
tiple species composition (up to c.800), cold-water reefs are
created by only a few species (c.6), and their so-called ‘reef’
structure is often in the form of dense thickets that develop
on rocky outcrops, sediment mounds and even coral debris
(Figure 5.6). Furthermore, they are slow growing, with rates
of 4–25 mm per year compared to rates of up to 150 mm per
year for tropical forms.
While a full appreciation and understanding of the
ecological role of these ‘reef’ communities has yet to be
realized, they are known to provide habitats and nursery
grounds for fish and other marine organisms. As a result,
reefs are targets for bottom trawl fishing that can cause
substantial damage. In order to conserve cold-water corals
and other potentially vulnerable deep-water habitats, many
countries have created (or are in the process of establishing)
protected areas or closures where trawls and other bottom-
contact fishing gear are prohibited (Hourigan, 2008). When
extensive trawl damage was documented for the Darwin
Mounds off northwest Scotland (Masson
et al.
, 2002;
Wheeler
et al.
, 2004), the European Commission imposed
an emergency measure in 2003 and one year later per -
manently prohibited the use of bottom fishing trawls and
gear on the Mounds and across 1,380 km2of the surround -
ing seabed. The Darwin Mounds are now designated as
an offshore marine protected area, the first in the United
Kingdom and part of a developing network that is planned
to extend throughout the marine waters of the European
Union. The need for more research and (in parallel) for more
management and protection is also reflected in the
recurring themes at International Deep-sea Coral Symposia
(ISDCS, 2008). These included:
improved identification and understanding of cold-
water coral reefs and the need for nationally con -
sistent management plans;
recognition and accommodation of seabed users,
36
Submarine cables and the oceans
Figure 5.6: Deep-water coral thicket on Chatham Rise,
New Zealand.
Source: Dr M. Clark, National Institute of Water
and Atmosphere (NIWA).
37
Environmental impacts
including implementation of effective policing of
marine protected areas;
management decisions and policy for corals,
conservation and human impacts.
In general terms, these themes highlight the need to use
and protect the marine environment sustainably, especially
in international waters beyond the jurisdiction of coastal
states. In the case of submarine cables, the United Nations
Convention on the Law of the Sea (UNCLOS) prescribes the
freedom to lay, maintain and repair cables outside territorial
seas, but these are not necessarily inconsistent with the
need to protect deep-ocean habitats and ecosystems, which
is also reflected in UNCLOS:
cable deployment in the deep ocean, i.e. laying of
a 17–20 mm diameter tube on the surface of the
ocean floor, has a minor if not negligible one-off
impact;
cable repairs can result in substrate disturbance.
However, cable failures in deep water are relatively
rare and are mainly caused by major natural events
such as the 2006 Taiwan earthquake and submarine
landslide (Introduction). Cable repairs resulting
from human and natural agents in water depths
greater than 1,200 m are c.5 per cent and c.7 per
cent respectively of all repairs (Featherstone
et al.
,
2001; Kordahi and Shapiro, 2004).
In addition, the submarine cable industry, together with
environmental regulators, attempts to reduce or avoid any
impact on vulnerable deep-water ecosystems by:
utilizing modern seabed mapping and navigation
systems that allow identification of benthic habitats
in unprecedented detail and accuracy (e.g. Masson
et al.
, 2002; Pickrill and Todd, 2003). Together with
modern cable-laying techniques, it is now possible
to deploy cables to avoid ecologically and bio logically
sensitive areas;
avoiding the deployment of cables on or through
habitats such as seamounts, submarine canyons
and hydrothermal vents, which are also unsuitable
as cable routes due to the risk of natural hazards
(Chapter 6). For example, canyons are often swept
by powerful currents that may abrade or break
cables (Krause
et al.
, 1970; Shepherd and Marshall,
1969); seamounts can be volcanically active and
subject to landslides and hydrothermal venting.
CABLE PROTECTION ZONES AND MARINE RESERVES
As coastal states increase protection of their submarine
cable infrastructure, it has been mooted that designated
cable protection zones may act as
de facto
marine reserves
or sanctuaries (Froude and Smith, 2004). To gauge the
reserve potential of such zones, a pilot study was made of
exploitable fish species inside and outside the Southern
Cross cable pro tection zone off New Zealand (Figure 5.7;
Shears and Usmar, 2006). The authors found no statistical
difference in species in or out of the zone, a result that was
attributed to the short existence of the zone (four years) and
illegal fishing. Furthermore, a zone must offer favourable
habitats for marine species. In the case of the fish
populations in or near the Southern Cross protection zone,
fish preferred reef habitats rather than soft sediment
substrates. Although results were inconclusive, the success
of estab lished marine reserves and sanctuaries suggests
that cable protection zones with suitable habitats may help
to maintain and improve biodiversity and species abundance,
but this concept has yet to be proven.
Figure 5.7: Cable protection zone for the New Zealand
terminal of the Southern Cross and other international
submarine cables. Such protection zones have the
potential to act as
de facto
marine reserves.
Source:
Telecom New Zealand.
38
LEAVING THEIR MARK ON THE SEABED
The ocean encompasses a suite of dynamic environments
that extend from the coast to the abyss. All are exposed
to natural hazards, which are defined here as
naturally
occurring physical phenomena caused by rapid- or slow-
onset events, influenced by atmospheric, oceanic and
geological forces that operate on timescales of hours to
millennia
(modified from UNESCO, 2006). Such phenomena
include weather-related disturbances, earthquakes, vol -
canic eruptions and, in the longer term, climate change.
And all may directly or indirectly affect the safety of
submarine cables.
The continental shelf and coast have a higher
incidence of natural hazards due to the frequency of
meteorological disturbances, as well as less frequent
events such as tsunamis and earthquakes, all of which are
overprinted on longer-term effects associated with tecto -
nic and climatic change (e.g. Nittrouer, 1999; Gomez
et al.
,
2004). As a result, coasts are exposed to flooding and
erosion by surging seas and waves. The adjoining seabed
may be scoured by currents and waves, or inundated by
sediment as in the case of shelves fed by major rivers
(Nittrouer
et al.
, 2007). Some disturbances of the seabed
can occur daily, as in tide-dominated settings (e.g. Carter
and Lewis, 1995), or with the frequency of severe storms,
which may strike once or more per year depending on
the effects of climatic cycles such as the 3–8 year El Niño-
Southern Oscillation or the 20–40 year Atlantic Multi -
decadal Oscillation (NOAA, 2006).
The continental slope connects the shelf edge
(average depth c.130 m) with the deep ocean at 1,000 m or
more (Figure 6.1). Because of the slope’s depth, the influ -
ence of storms is generally less than on the shelf. However,
the slope is prone to gravitational forces. Sediment destabil -
ized by earthquakes, tsunamis or severe storms moves
down-slope as landslides that range from frequent small-
volume (less than 1 km3) displacements to rare giant slides
of up to 20,000 km3(Figure 6.2; also Hampton
et al.
, 1996;
Collot
et al.
, 2001). En route, slides may transform into more
fluid debris flows or turbidity currents capable of travelling
hundreds to thousands of kilometres (e.g. Krause
et al.
,
1970; Piper
et al.
, 1999).
Such catastrophic events leave their imprint in the
form of landslide scars, zones of jumbled sediment masses,
rough seabed topography (Figure 6.2) and, where turbidity
currents are active, steep-sided submarine canyons. As well
as down-slope movement of sediment, the continental slope
acts as a boundary that guides currents and sediment along
its flank.
The slope descends to the deep ocean – a nondescript
term that belies a diversity of landforms and associated
environments, including seamounts (many of which are
6. Natural hazards
LST
Alongshelf currents
Bioturbation
Plume
Overbank
deposits
Internal
waves
Boundary
currents
Gravity
currents
Flood plain Continental
shelf
Continental
slope
Continental
rise
LST
HST
AVALANCHE
DEBRIS