Option B - Ocean - Atmospheric Conditions Flashcards
Surface Ocean Currents
Caused by the influence of prevailing winds blowing steadily across the sea. Main pattern is roughly circular flow clockwise in the northern hemisphere and anticlockwise in the southern hemisphere
Affect of temperature on currents
The effect of ocean currents depend on whether the current is cold or warm.
Warm currents : equatorial regions raise the temperatures of polar areas (with aid of prevailing winds). The effect only noticeable in winter eg the North Atlantic Drift raises the winter temp of north west Europe.
Cold currents : eg Labrador current off the north east coast of North America may reduce summer temperature but only if wind blows from sea to land
Upwelling Currents
many eastern oceans experience upwelling currents where the ocean current move cold water, rich in nutrients from the ocean floor to the surface. (eg coast of Peru, California and South west Africa) - nutrient rich water important for fisheries and disappears during El Nino events
El Nino
“Christ Child” is a reversal of the normal atmospheric circulation in the southern Pacific Ocean . Involves the warming of the eastern Pacific that occurs at intervals between two and ten years and last for up to 2 years.
La Nina
intermittent cold current that flows from the east across the equatorial Pacific Ocean, intensification of normal conditions whereby strong easterly winds push cold upwelling water off the coast of South America into the western pacific - linked to unusual rainfall patterns in the Sahel and in India (unusual temperature patterns in Canada)
Normal conditions in the Pacific Ocean
Walker circulation is the normal east-west circulation that occurs in low latitudes. Near South America - winds blow offshore causing upwelling of cold current, nutrient rich water. Warm surface water is pushed into the western Pacific and usual temperatures are over 28 degrees causing area of low pressure and producing high rainfall.
El Nino Conditions in the Pacific Ocean
During El Nino southern oscillation episodes, normal pattern of air circulation is reversed- water temperatures in the eastern pacific rise as warm water from the western pacific flows into the east pacific. Low pressure develops over the eastern Pacific whereas high pressure over the western paciifc- Heavy rainfall over South America
2015-2016 El Nino event
Most severe El Nino event :
- around 100 million people experienced food water and shortage
- southern africa experinced it’s driest years for 35 years
- Zimbabwe : food prices increased by over 50%
- heavy rains in South America enables the spread of Zika Virus (more stagnant water)
Managing the impacts of El Nino and La Nina
difficult to manage the impacts of these events : not predictable - now sensors over the Pacific that predict El Nino months in advance
problems remain:
- affect large parts of the globe
- some of the countries affected do not have resources to cope
- indirect impacts on other parts of the world through trade and aid
Hurricanes
intense low pressure systems that bring heavy rainfall strong winds and high waves and cause other hazards such as flooding and mudslides. enormous quantities of water due to their original over moist tropical seas. High intensity rainfall of up to 500mm in 24 hours invariably causes flooding - erratic path makes it hard to give warning = insufficient for proper evacuation measures
Hurricane structure
calm center area known as the eye - also has very strong winds that cause most of the damage in a belt up to 300 km wide. The whole hurricane may be up to 800 km wide.
Hurricane Movement
Hurricanes move excess heat from low latitudes to high latitudes - start as small scale depressions that is localized areas of low pressure that cause warm air to rise. only about 10% of tropical disturbances become true hurricanes (wind speeds above 74 mph).
Conditions for hurricane formation
sea temperature must be over 27 degrees
warm water needs to extend to a depth of 60 m
low pressure area has to be far enough away from the equator so that the Coriolis force creates rotation in the rising air mass
The Carbon Cycle
- Oceans are the largest co2 sink on earth - over geological time over 90% of the world’s carbon has settled in the ocean
- Photosynthesis turns carbon dioxide into organic material. Over time, organic carbon settles into the deep ocean - in a thermohaline circulation, carbon on the ocean floor could be lifted to the surface so the ocean could becomes a source rather than a sink
- Oceans plays a key role in the carbon cycle
- Photosynthesis by plankton generates organic compounds of carbon dioxide - some of this material passes through the food chain and sinks to the ocean flood where it is decomposed into sediments - eventually it is destroyed at subduction zones
- Carbon dioxide may be released during volcanic activity
- The transfer of carbon dioxide from ocean to atmosphere involves long time-scale.
Ocean acidification
caused by the anthropogenic sources such as carbon emissions from industrial plants, power stations and vehicle planes - more acidic oceans are beginning to kill off coral reefs and shellfish beds and threaten stocks of fish
Increasing acidification reduced calcification in coral, resulting in slower growth and weaker skeletons - now more 30% more acidic than they were last century. The great barrier reed the growth of some coral species has declines by 14% since 1990 due to combination of ocean acidification and temp stress
