Ocean CurrentsOcean Currents

Huge Rivers in the OceanOcean currents are huge rivers flowing within the ocean. Each current has its own temperature and its own saltiness (salinity). For example the Gulf Stream current carries 30 million cubic metres of water per second as it travels at about 2 m/s. The current is strong enough to push some sailboats backwards even when they have a good wind in their sails.

The Gulf Stream Climate InfluenceThe warmer waters of the Gulf Stream have a moderating effect on Europe’s climate which would be much colder if the Gulf Stream were not flowing by its western side.

The Difference the Gulf Stream MakesIn-land cities at the same latitude have much colder temperatures than coastal cities that are warmed by the Gulf Stream.

The Effect of a Warm Current on Coastal ClimateCoastal Eastern Australia receives a warm ocean current which produces lush growth with much moisture. Warmer currents typically generate low pressure regions as evaporated water rises and condenses to form rain clouds.

The Effect of a Cool Current on Coastal ClimateCoastal Namib on the Southwest of Africa receives the cool Benguela current which causes the land to dry into a desert. Cooler currents typically produce high pressure regions and drier conditions.

The Dimensional Aspect of Ocean CurrentsOcean currents can be surface currents if they are lighter or less dense (warmer) or if they may flow deeper down in the ocean if they are colder and denser because they are more saline (salty).

GyresCircular ocean currents are called gyres. Human garbage (plastics) that is deposited in the ocean collects towards the centres of the gyres.

The Effects of Ocean CurrentsWarmer ocean currents typically increase the precipitation and temperature of the land they flow past. Cooler ocean currents typically keep the land they pass cooler and drier. This is because air over cooler waters becomes cooler. This cooler air is more stable supporting high pressure. Warmer currents affect the air above them by evaporating water into them and giving rise to low pressure regions which bring rain. Warmer air holds more water than cold air so it precipitates this water as rain when it cools. Cooler air which has less water has a drying effect when it is warmed over land since its relative humidity drops.

Relation Between Global Ocean Currents and Global WindsIn general there is a similarity between global ocean currents and global winds.

Comparing Ocean Currents and Wind CurrentsWhere are the places where ocean currents and wind currents do not flow the same general way?

Comparing Wind and Ocean Currents (Continued)Where might air currents and ocean currents be different in direction?

Upwelling due to Ocean CurrentsWhen winds displace surface waters, deeper water laden with nutrients is drawn to the surface. These nutrient rich waters stimulate microscopic phytoplankton which become food for zooplankton and eventually feed fish. The world’s fisheries are located in regions of upwelling.

(c) McGraw Hill Ryerson 2007

Waters near the coast of Peru undergo irregular cyclic warming and cooling irregularly from as little as a 9 month cycle to much as a 5 year cycle. The warming occurs around December and is named for “El Nino”, a reference to the Christ child. The warming is followed by a cooling period called la nina (the girl child). Both of these water changes are accompanied by pressure changes that change climates worldwide on a seasonal basis.

See pages 471 - 473

(c) McGraw Hill Ryerson 2007

An El Nino event causes Northwestern and Northeastern North America to have a warmer and drier winter. It also causes Southeastern US to have a wetter, cooler winter and it causes Northeastern Australia to be drier along with Indonesia. Japan and Korea also have warmer and drier winters with an El Nino event.– El Niño has reverse effects from La Nina; warmer water on the surface of the

Pacific» This results in warm winters in the Pacific Northwest, and in Eastern Canada

See pages 471 - 473

La NinaDuring a La Nina event, strong easterlies carry warm water to Indonesia and northwestern Australia which brings much precipitation. Upwelling is strong in Peru which brings nutrients to surface waters which in turn feed algae, plankton and fish. In Northwestern and Northeastern North America it is cooler and wetter. In Southeastern and Southwestern US it is warmer and drier.

El Nino and la NinaWhile there is a cycling between El Nino and La Nina, it is not on a regular or predictable basis and El Nino events tend to happen more frequently than La Nina events.

(c) McGraw Hill Ryerson 2007

During an El Nino year, California often gets much more rain than normal, leading to ground subsidence. During a La Nina year, the South of the US often experiences drought conditions.

Normal Walker Circulation

An El Nino Year

La Nina

End of Presentation