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lecture note 8


Biological Sciences
Course Code
Herbert Kronzucker

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- 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
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