Observations
of the ocean
Ocean
planet
Earth
is an ocean planet 70% of its surface is covered by ocean.
The ocean plays a critical role in establishing global climate and
is inextricably linked to the atmosphere in creating the natural
fluctuations of our climate system:
- the
ocean is the heat engine of the planet global
ocean circulation, together with the atmosphere, constitutes the
mechanism by which solar energy received in the tropics is re-distributed
to the entire planet;
- the
state of the ocean influences climate and the energy and water
cycles, and thereby affects agriculture, and water and energy
supplies;
-
the ocean also affects the intensity of hurricanes and tropical
cyclones, which can cause billions of dollars in property damage
and alter the economic fortunes of peoples in affected areas;
- the
El Niño/La Niña phenomenon of the tropical Pacific
widely impacts normal weather patterns in many regions and can
have profound economic consequences (some bad, some good);
- the
ocean, through atmospheric exchange, plays an important part in
the global carbon cycle and is therefore inextricably linked
to global change processes.
The
ocean has always been critical to the success of human civilisation;
some 30% of the worlds population now live within 100 km of
the coasts, and humans have depended on the ocean for food and economic
growth for hundreds of years:
- in
the technically developed Group of Seven countries, marine resources
and services contribute, on average, 5% of GNP or about $600 billion
per annum (1991);
- the
world fish catch is 80-90 million tonnes/year (worth approximately
$70 billion), and provides about 20 % of the world protein supply.
For large parts of the world population, particularly in East
and Southeast Asia, fish constitute the most important source
of animal protein;
- ocean
transport is the most inexpensive way of trading bulk goods. The
result is that about 90% of the worlds trade involves transit
via the ocean and the volume is expected to double over
the next decade.
World
production of offshore oil and gas was worth $135 billion in 1990,
amounting to 20% of world hydrocarbon production. Operations continue
to venture into deeper waters at depths of up to 2000 metres.
Ocean
observations
In
the coming years, the need to understand and forecast the oceans
and their resources is going to increase significantly and
on time-scales that permit relevant and effective management decision-making.
Scientists will require a range of data for assimilation into numerical
models to provide analyses of a range of ocean phenomena and climate-related
processes:
- understanding
the dynamics of ocean circulation will require systematic measurements
of ocean currents at least weekly, but also spanning decades,
commensurate with the characteristic time scales of anomalies
such as El Niño, The North Atlantic Oscillation, and the
Pacific Decadal Oscillation;
- global,
precise, long-term measurements of ocean temperature are of key
importance for studies of the Earths energy balance, for
understanding how the ocean regulates weather and climate, and
for the provision of indicators of the El Niño event;
- the
mean level of the oceans must be monitored precisely for decades
to come, for use in climate models which have suggested
a future rise in ocean levels due to global change and
to allow mitigation planning by low-lying countries;
- more
accurate information is needed on the concentration, position,
extent, and thickness of sea ice for monitoring of changes in
the polar regions, which have a strong relationship to global
climate;
- the
ocean is the largest mobile reservoir of carbon on decadal to
millennial time-scales, and is estimated to absorb between 30-40%
of the CO2 added to the atmosphere. Assessments of the effectiveness
of any measures taken to reduce carbon emissions will ultimately
be judged by their long-term effect on atmospheric CO2 levels,
which in turn requires a understanding and monitoring the ocean
carbon cycle and long-term storage changes;
- a
suite of biological, chemical, and physical parameters must be
monitored to understand, predict and manage potential climate
change effects on the abundance, diversity, and productivity of
marine populations, including fisheries.
The
continued migration of people to coastal communities, the increasing
volume of commodities transported by sea, the exploitation of sea-based
mineral and oil reserves in deeper water, the creation of offshore
facilities, rising sea-levels threatening to overwhelm present coastal
protection systems, increasing pollution of coastal waters caused
by increased use of nitrogen-based fertilisers, national security,
and the need to sustain and protect marine fisheries will also force
us to pay much more attention to the open ocean and coastal seas
over the next century. Minimising loss of life and property, and
avoiding environmental degradation and disasters requires significant
improvements in the ocean information which is available to decision-makers
in addressing issues of public concern such as:
- frequency
and intensity of hurricanes and storm surges;
- pollution
(e.g. nitrates, oil, and industrial chemicals from land affecting
water quality and public health);
- oil
spills and other marine accidents;
- dumping
and waste disposal, including radioactive waste;
- loss
of amenities due to coastal development, and urbanisation;
- coastal
erosion and loss of coastal ecosystems;
- degradation
of coral reefs and mangrove forests;
- increases
in toxic algal blooms;
- exhaustion
of fish stocks, degradation of biodiversity in the ocean, and
wildlife conservation;
- safety
of passenger and cargo ships, ferries and offshore operators.
Recognition
of the increasing need for comprehensive measurements in the marine
environment led in the 1990s to the formation of the Global
Ocean Observing System (GOOS) a permanent global system for
observations, modelling and analysis of marine and ocean variables
to support operational ocean services worldwide. The vision guiding
the development of GOOS is one of a world where the information
needed by governments, industry, science and the public to deal
with marine related issues, including the effects of the ocean upon
climate, is supported by a unified global network to systematically
acquire, integrate and distribute oceanic observations, and to generate
analyses, forecasts and other useful products.
GOOS
capitalises on a range of existing ocean observing systems, including
meteorological stations on land, remote sensing from space, a mixture
of fixed and floating data-gathering instrument arrays, and observations
from ships.
The
importance of Earth observation satellites
Satellite
remote sensing has revolutionised observation of the oceans in many
ways, providing synoptic views of a range of key parameters. Some
of the most significant achievements and their applications are:
- the
provision of long term sea surface temperature data to the high
accuracy required for climate studies (the same data is also used
on a daily basis to assist the management of fishing fleet operations);
satellite remote sensing provides the only practical means of
developing such a dataset in-situ data are extremely limited
in coverage and predominantly confined to shipping lanes whereas
satellites offer the potential for surveying the entire ocean
surface in just a few days;
- satellite
altimetry is the main source of data being used to monitor large
scale changes in ocean circulation and the mean level of the oceans
such as those related to El Niño; on a local scale,
topographic information from satellites is used in support of
off-shore exploration for resources and for optimising cable and
pipeline routing on the sea floor;
- sea
surface winds: satellites now acquire all-weather, high-resolution
measurements of near-surface winds over global oceans: this information
is used to improve weather forecast models and climate applications,
and is particularly valuable for short-term severe weather warnings
and for ship-routing;
- ocean
biology: ocean colour data from satellites is now being collected
for every square kilometre of cloud-free ocean every 48 hours;
this data provides information on concentrations of types and
quantities of marine phytoplankton (microscopic marine plants)
and will help develop understanding of the oceans' role in the
global carbon cycle, as well as other biogeochemical cycles.
Future
challenges
Ocean
observing systems must rise to a number of challenges in the 21st
century in order to keep pace with the demand for information on
the oceans role in climate change, and on parameters to assist
its sustainable management for use in transportation, resource exploration,
recreation, and fisheries.
These
challenges include organisational and institutional issues related
to: coordinating efforts among providers/users of ocean/climate
services; developing applications and infrastructure to deliver
them to users; delivering information products for decision-making
that are responsive to user needs.
Part
III of this document summarises the various plans of the worlds
space agencies over the coming decades in providing satellite missions
for critical ocean observations. To be effective, improved techniques
for assimilation of data from these missions will be necessary.
Satellite data will also have to be integrated better with in-situ
observations; in-situ sensors provide invaluable validation information
for satellites, as well as measurements deep below the ocean surface,
which satellites cannot.
Future
plans for next generation Earth observation satellites include:
- maintaining
crucial continuity and calibration of key measurements
such as sea surface temperature, ocean winds, and ocean colour
over long timescales in support of climate studies;
- development
and proving of remote sensing technologies to provide measurements
of the depth of the ocean mixing layer, and of sea surface salinity
- a key variable in determining ocean density, which drives ocean
circulation and thus impacts climate;
- provision
of improved measurements on sea ice extent, type, and thickness
allowing scientists to determine the mass balance of the
polar ice sheets and their contributions to global sea level change;
- missions
for accurate global and high-resolution determination of the Earth's
gravity field which is prerequisite for better understanding
of ocean surface currents and heat transport.
These
developments, and others, have been determined as priorities for
the way ahead by the Ocean Theme studies of the IGOS Partnership.
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