Lesson 8: Currents Physical Oceanography

Last class we learned about ocean layers What are the three main ocean layers? How does temperature change with depth in the thermocline? How does it change below the thermocline? Teacher’s Notes: Three main layers are surface (mixed) layer, thermocline, deep ocean In the thermocline, temperature changes rapidly with depth Below the thermocline, temperature is relatively constant

Today we’re going to explore ocean currents An ocean current is a regular movement of large amounts of water along defined paths. There are two primary types of ocean currents: Surface Currents (to a depth of about 400 m) Driving factor: Wind Deep Currents (entirely below the effect of wind) Driving factor: Density differences Thermohaline circulation: Ocean circulation driven by differences in density caused by temperature (“thermo”) and salinity (“haline”) variations Deep-ocean currents are driven by differences in the water’s density, which is controlled by temperature (thermo) and salinity (haline). This process is known as thermohaline circulation.

Why are currents so important? Photo: NOAA Influence world climate and weather Ocean navigation and transportation Support marine life (transport mechanism, food source) Transport of materials (both helpful and harmful) and energy to different regions and depths of the ocean Teacher’s Note: Below are additional examples of currents supporting marine life: -The eel uses the Gulf Stream to get to the Sargasso Sea where spawning occurs. -Upwelling off the coast of Peru supports one of the most productive fishing areas in the world – nutrients brought to the surface attract large populations of anchovy. Photo: http://www.nmfs.noaa.gov/pr/species/mammals/cetaceans/rightwhale_southern.htm; Accessed: November 2010 Marine organisms like the Southern right whale (above) depend upon currents to circulate the nutrients that support their food sources

An important ‘current’ event: Thermohaline Circulation (THC) THC creates a world wide current system called the “global conveyor belt" The global conveyor belt begins with sinking of cold, dense water near the North Pole in North Atlantic Cold temps + Sea ice = cold, salty, dense water that sinks Then water moves south and circulates around Antarctica, where cold salty conditions “recharge” it The water then moves northward to the Indian, Pacific and Atlantic ocean basins It can take around 1,000 years for water to complete one cycle of the entire global conveyor belt! Teacher’s Note: Sea ice formation increases salinity because, the salt is left behind in the water as the sea ice forms. As the cold, salty dense water sinks, surface water moves in to replace it thereby starting a current. When water reaches Antarctica, the cold, salty conditions lead to more sinking, thus “recharging the current”.

A map of the global conveyor belt Photo: NASA Photo: http://www.jpl.nasa.gov/news/news.cfm?release=2010-101; Accessed: November 2010

What drives ocean currents? Density gradients (differences) drive deep ocean currents Upwelling brings cold, nutrient-rich water from the depths up to the surface Wind is one of the primary drivers of surface currents

Student activity In today’s activity, we will play a game to learn the names and locations of the ocean’s currents