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 world’s 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 world’s 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 Earth’s 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 1990’s 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 ocean’s 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 world’s 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.