Ch4 Variation in the Environment6.pdf

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Spencer Barrett

 water temp. don’t fall below 4°C  therefore, lake doesn’t stratify in winter and there is only one mixing event per year (after summer stratification)  some tropical lakes with uniform temperature profile have deep vertical mixing caused by surface winds  brings oxygen to depths and minerals to surface, supporting high overall productivity  in temperate zones, deep lakes are permanently stratified and are very unproductive  global warming may create a thermocline in tropical lakes  increase in surface temp. (increase temp. diff. btn surface and depths)  impair vertical mixing, therefore reduce lake production ex. in Lake Tanganyika, East Africa Unpredictable Changes in Climate and Weather  extreme conditions occur infrequently, but affect ecological systems disproportionately  Peru Current consists of cold, nutrient-rich waters which provide abundance of fish  flows north along west coast of South America and veers offshore at Ecuador towards the west  north of this, warm, tropical inshore waters exist along the coast  each year, a warm countercurrent, El NEl Niñoves down the coast towards Peru  sometimes flows strongly and far enough south to force Peru Current offshore  normally, the cool waters of the Peru Current warm up as they move westward along the equatorial Pacific Ocean  ∴ temp. increases from east to west  the temp. diff. creates a steady surface wind blowing in the same direction  from an area of h
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