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 energy and other seawater components is ocean surface currents. Their strength and variability help form our weather over 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 and atmospheric 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 the wind (air in motion) to ocean depths of a few hundred meters. Winds are responsible for not only horizontal currents but also the vertical water motions within the surface layer (e.g., upwelling, to be discussed later)."
Adapted from DataStreme Ocean and
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 the evolution of ancient oceans. Using a combination of satellite sensors, floats, and acoustic Doppler profilers from the ship, scientist monitored temperature, salinity and dissolved oxygen. These data provided information about the mixing of deep and surface waters and the rates of circulation. While learning of the depth of the current reversal, scientists discovered that changes in circulation brought about by the monsoon winds were associated with a surprisingly high level of productivity, confirming findings from earlier expeditions and satellite surveillance.
Phytoplankton (microscopic, single-celled, photosynthetic organisms) provides the ultimate source of food for marine life. If upwelling of cold, nutrient-rich ocean water ceases (e.g., during El Niño, 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.