Currents & Gyres Notes
Current A river of water flowing in the ocean. 2 Types of Currents Surface Currents wind-driven currents that occur in the top 100m or less Deep Currents density-driven currents that result from differences in salinity & temperature Produce very slow flows in deeper waters.
Surface Currents Surface currents transport heat from the tropics or cold water from the poles.
Ben Franklin & the Gulf Stream In the 1750s, when Postmaster for the American Colonies, Ben Franklin and Capt. Timothy Folger created the first map of the Gulf Stream to help speed up delivery of mail to & from Great Britain.
Matthew Fontaine Maury Did the first systematic Study of currents based on logbooks from the US Navy. His charts and Physical Geography of the Sea assisted navigators worldwide.
Winds and Surface Water Rule: the Coriolis effect is more pronounced the slower an object moves. 1. Wind blows only on the surface water layer (but it moves slower than the wind). 2. This layer of water will also drag the underlying water, but with less force (even slower). 3. This proceeds lower & lower (each layer is even slower). 4. This is an Ekman Spiral.
Ekman Spiral A spiraling pattern of water direction caused b/c slower substances are more greatly influenced by the Coriolis effect.
Ekman Spiral Nansen & other Arctic explorers noticed that ice & surface currents move at an angle to the wind direction. Ekman first explained the mathematics of this phenomena, and why it decreases with depth to produce the spiral pattern.
Ekman Transport Says that the overall movement of a current is 90 to the right or left of the global wind direction.
Surface Current Formation 2 1 2 5 3 4
Gyres A circular pattern formed by the connection of several surface currents. Northern Hemisphere 2 gyres - clockwise rotation Southern Hemisphere 3 gyres counter-clockwise rotation Gyres are named for the ocean & hemisphere they are found in.
Parts of a Gyre Western Boundary Currents 1. Form on the western sides of oceans. 2. Fast, deep, narrow currents that form eddies. 3. Warm currents b/c they flow from the equator. 5 Main WBCs: Gulf Stream largest Japan Current (aka Kuroshio c.) Brazil Current Agulhas Current East Australian Current
Parts of a Gyre Eastern Boundary Currents 1. Form on the eastern sides of oceans. 2. Slow, shallow, broad currents with no eddies. 3. Cold currents b/c they flow from the poles. 5 Main EBCs: Canary Current California Current Peru Current Benguela Current West Australian Current
Currents going towards the equator (away from the poles) are cold water currents. Current going towards the poles (away from the equator) are warm water currents.
Currents Lab N. Pacific N. Equatorial N. Equatorial S. Equatorial Equatorial Counter S. Equatorial Equatorial S. Equatorial West Wind Drift West Wind Drift West Wind Drift
Density-Driven Ocean Circulation Cold, dense water sinks below warmer water. Salty, dense water sinks below less salty water. Just like air, water will move to areas of lesser concentration. There are different density layers found in the ocean.
Water Masses Bodies of water that are fairly uniform in their densities. Identifiable from their temperature, salinity and other characteristics.
Mixed/Surface Layer The top few hundred meters. Here the water is mixed around by wind, waves & surface currents. Has a relatively uniform temp. & salinity throughout.
Intermediate Layer Immediately below the mixed layer. It is more dense than the mixed layer due to temp. and/or salinity.
North Atlantic Deep Water (NADW) From below the intermediate water to the ocean bottom. Very cold water w/ higher salinity than the above layers.
Antarctic Bottom Water (AABW) In contact w/ the seafloor. Extremely cold water. Typically nutrient rich. Can travel around the globe for years.
Great Ocean Conveyor Belt Combination of deep ocean currents & surface currents