Patterns of
Circulation
Vertical
Structure
Ocean in
Motion:
The Forces
Wind-Driven
Currents and
Ekman
Transport
Geostrophic
Flow
Wind-Driven
Surface
Currents
Gyres
Equatorial
Currents
Western
Boundary
Currents
Rings
Upwelling and
Downwelling
Deep
Circulation
Monitoring the
Deep Ocean
Water Masses
Ocean
Conveyer
Belt
Conclusions
Ocean and atmospheric circulation play an essential role in sustaining life by moderating climate over much of Earth's surface. An important part of the circulation of heat and freshwater and other seawater components are ocean surface currents. Their strength and variability help form our weather in short and long time scales, impacting climate, and environments for all life on Earth. What causes the ocean to circulate?Energy and matter are continually exchanged between the ocean and atmosphere, and these processes drive the ocean circulation. Evaporation, precipitation, plus heating and cooling bring about changes in the temperature and salinity of surface waters. Density changes that accompany changes in temperature and salinity can cause water to sink or rise in the ocean. Kinetic energy (energy of motion) is transferred from near-surface winds to the ocean's surface layer, driving the currents that dominate the motion of the upper few hundred meters of the ocean. Winds are responsible for not only horizontal currents but also vertical water motions within the surface layer. |
One example of the importance of ocean-atmospheric circulation is the asian monsoon. The image, above left, shows monsoon wind patterns over the Indian ocean. The two ocean color satellite images, right, compare phytoplankton productivity in the pre-monsoonal calm in May-June, top, with strong summer southwesterly monsoon winds which generate upwelling of nutrient-rich waters, leading to development of bloom conditions in September-October, bottom. Analysis of data collected on two scientific cruises of RRS Charles Darwin in the Indian Ocean is leading to a new understanding of the role of the monsoon in ocean productivity and global climate and of the evolution of ancient oceans. Using a combination of satellites and acoustic tracked floats and acoustic Doppler profiling from the ship. Their measurements of temperature, salinity and oxygen provided information about the mixing of deep and surface waters and the rates of circulation. In addition to their discovery of the depth of the current reversal, they found that changes in circulation brought about by the monsoon winds were responsible for a surprising amount of productivity (blossoming phytoplankton). Phytoplankton, microscopic, single-celled ocean plants provide the ultimate source of food for marine life. If the upwellings cease the blooms of brown and green phytoplankton diminish and so do the fish, and with them the sea birds. This has a severe impact on the fishing industry. |