Ocean Motion

The polar regions are important drivers of the world’s climate. Ocean currents redistribute heat around the world via thermohaline circulation (also called the Global Ocean Conveyor). One reason water in the Global Ocean Conveyor circulates is because of differences in water density. Differences in temperature and salinity are the cause of changes to water density. The colder the water the denser it becomes. Same with salt, the saltier the water the denser it becomes.

The greater the density difference between separate layers in the water column, the greater the mixing and circulation. Water heated near the equator travels at the surface towards the poles where it becomes cooler. As the water cools, it becomes denser and sinks into the deep ocean, driving the deep ocean currents. When salt water freezes the salt is excluded. When water freezes at the poles the surrounding water becomes saltier and sinks, this also contributes to ocean circulation.

Melting of polar ice could cause dramatic changes to the Global Ocean Conveyor. As the earth continues to warm and arctic ice melts, freshwater is released from melting ice, making seawater at high latitudes less salty, therefore less dense. The less dense water will not be able to sink and circulate through the deep ocean as it currently does. Therefore this melting of arctic ice has the potential to disrupt and slow the Global Ocean Conveyor. The warmth from the warm surface currents carried away from the tropics is lost to the atmosphere.  The slowing of this ocean circulation could lead to a cooling in places where this warmth is currently lost into the atmosphere.

So why does this matter for the small island of Utila? When fresh water flows into the sea it changes ocean currents, which changes living conditions for marine organisms. These changes will be noticed everywhere around the world. Many marine animals depend on these currents for migration. They depend on these currents to find food and for breeding purposes. A change in ocean currents could change the distribution of phytoplankton, which would change migration patterns of larger organisms that depend on such distributions. A change in heat distribution could cause problems as well. The warmer less nutrient dense water will stay concentrated in the tropics, which will cause further changes to the marine organisms found here.