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Topic: Currents and Ocean Circulation

Theme: Measurement

Key Concepts:

Measurement Challenge

  • To develop a comprehensive theory of ocean structure and dynamics, a wide variety of measurements--including water temperature, salinity, sea level, wind speed, and ocean current speed--must be made in many places at many times.
  • Quantitative measurements form the foundation of modern science.
  • Monitoring the dynamics of the oceans helps us to discover how they interact with and affect landmasses and the atmosphere.

Sea Surface Measurements

  • Earth-orbiting satellites--such as TOPEX/Poseidon (and soon to be launched JASON)--have revolutionized our ability to collect ocean surface data over large areas of Earth's surface at one time.
    • TOPEX/Poseidon measures the height of the sea surface almost everywhere every 10 days.
      • Slopes of sea level are used to compute ocean currents.
    • Satellites measure sea surface temperature by monitoring infrared wavelengths emitted by the oceans.
    • Satellites can measure the amount of phytoplankton (a significant link to the ocean food chair) in our oceans by observing the color of the water.
    • Satellites can measure wind speed and direction using a scatterometer, which measures the roughness of the sea. The stronger the wind, the rougher the surface.
  • Surface measurements made from ships and buoys are extremely important for ocean science, but are very limited in space and time.

Within the Ocean Measurements

  • Science research ships and buoys continue to play an important role in understanding oceans because they can observe what is happening below the sea surface.
  • New drifting buoys sink to a depth of 1 km, float for a month (collecting data on currents at that depth), pop up to report their position (via satellite), then sink again. They last for several years.

Below the Ocean Floor

  • The Glomar Challenger, a global-ranging vessel managed by the Scripps Oceanographic Institute and part of the Deep Sea Drilling Project, explored what lay beneath the ocean's floor. It featured a deep-sea drilling rig for obtaining core samples from beneath the ocean floor at depths up to six kilometers.
  • The Ocean Drilling Program (ODP) is currently the largest and most successful multinational Earth science project.
  • The JOIDES Resolution took over the ocean drilling activities of the retired Glomar Challenger.
    • Deep-sea cores have shown changes in climate over the last few million years, including changes in the thermohaline circulation and its relationship to ice ages.
    • Deep-sea cores have measured the places where old turbidity currents flowed.
  • ODP scientists have recovered from cores, fragments of the oldest remaining seafloor. The sample is about 175 million years old, a relic of the Middle Jurassic period when the continents were still one large landmass.