lecture note 8

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Department
Biological Sciences
Course
BIOC50H3
Professor
Herbert Kronzucker
Semester
Winter

Description
LECTURE 8: - The Coriolis force also governs the major ocean currents (the ocean gyres); they, as a consequence, run clockwise in the N. hemisphere and counterclockwise in the S. hemisphere, and have major climate implications (e.g. the Gulf Stream in the Atlantic carries warm waters from the Caribbean, moderating temperatures from the US east coast to Scandinavia; the Gulf of California carries cold waters from Alaska to California’s coast: diving in California is a nippier affair than one would expect!!) - The Earth’s tilted axis (23.50) causes unequal distribution of incoming solar radiation across the planet’s surface, and with it creates the seasons. The Earth, in its revolutions around the sun, “wobbles” between 23.50 N. (Tropic of Cancer) and S. latitude (Tropic of Capricorn). For the part of the year when the Earth is closest to 23.50 N. latitude, the N. hemisphere enjoys summer (summer solstice: the longest day of the year in the N. hemisphere, on June 21), when it is closest to 23.50 S. latitude, the N. hemisphere has winter (winter solstice: the shortest day of the year, on Dec. 21), and vice versa. During the vernal (spring) and autumnal (fall) equinoxes (March 21, and Sept. 23), the sun is closer to the equator, and both hemispheres have identical daylengths. Areas between the Tropics of Cancer and Capricorn have a fairly steady input of solar radiation, and thus experience relatively little seasonal variation – this area is thus known as the Tropics - During the winter solstice in the N. hemisphere, points north of the Arctic Circle (66.50 N.) experience 24-h darkness, points south of the Antarctic Circle (66.50 S.) experience 24-h daylight (during the summer solstice, this situation is reversed); this creates dramatic physiological challenges for the organisms living in these areas www.notesolution.com - Older systems of classification of ecosystem types relied on animal diversity, and were known as biogeographical realms (the six realms: Nearctic, Neotropical, Palaearctic, Ethiopian, Oriental, Australian) - However, the now almost universally accepted classification system for Earth’s ecosystems is that of biomes; biomes are distinguished by their predominant vegetation and are associated with particular climates - Ecologists differ in how many biomes they recognize (typically five to fourteen); however, there is considerable consensus that a distinction of nine biomes is the most reasonable and useful - The nine terrestrial biomes covered in class (and in the textbook) are: - tropical rainforest - tropical dry forest (also known as seasonal or monsoon forest) - tropical savanna - desert - temperate woodland/shrubland - temperate grassland - temperate forest - boreal forest - tundra - These biomes are largely defined by their latitudinal positioning; however, important modifiers are: - proximity to oceans (central continental areas are significantly drier than coastal ones, e.g. “continental deserts”, such as the Gobi desert are created www.notesolution.com largely by their distance from the ocean; likewise, cold or warm ocean currents can significantly influence local terrestrial climates along shorelines) - presence and direction of mountain chains (e.g. N. America’s major mountain chains run from North to South; they produce wet climates on western slopes and dry, “rainshadow” climates on eastern slopes; interior of British Columbia, Californian deserts) - The best way to describe biomes is by means of climate diagrams (introduced by H. Walter, 1985; diagrams for the nine biomes discussed in class are provided in detail in the textbook); climate diagrams depict monthly (months are plotted on the x-axis) and yearly averages of temperatures (in ºC, plotted on the left y-axis) and precipitation (in mm, plotted on the right y-axis); 10ºC intervals correspond to 20-mm increments in precipitation (or 200 mm, in cases where average precipitation is above 100 mm): where the precipitation line lies above the temperature line, evapotranspiration from the ecosystem is compensated for by enough precipitation to allow for plant growth; where this line is below the temperature line, most plants are unable to conduct physiological activity (however, in most environments, there are extremist species with specialized adaptations that defy this definition of limitations); most biomes have easily recognizable climate diagram types – study these in the book! www.notesolution.comLECTURE 8: - The Coriolis force also governs the major ocean currents (the ocean gyres); they, as a consequence, run clockwise in the N. hemisphere and counterclockwise in the S. hemisphere, and have major climate implications (e.g. the Gulf Stream in the Atlantic carries warm waters from the Caribbean, moderating temperatures from the US east coast to Scandinavia; the Gulf of California carries cold waters from Alaska to Californias coast: diving in California is a nippier affair than one would expect!!) 0 - The Earths tilted axis (23.5 ) causes unequal distribution of incoming solar radiation across the planets surface, and with it creates the seasons. The Earth, in its revolutions 0 around the sun, wobbles between 23.5 N. (Tropic of Cancer) and S. latitude (Tropic of Capricorn). For the part of the year when the Earth is closest to 23.5 N. latitude, the N. hemisphere enjoys summer (summer solstice: the longest day of the year in the
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