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Biology 2483A
Mark Moscicki

Ecology: Lecture 2 Sept 17 2013 Climatic Variation & Salmon Abundance: A Case Study  Salmon are anadromous. They are born in streams and then they move out into the oceans where they spend the majority of their lives. They then return to the streams to lay their eggs  Successful reproduction depends on the health of the streams in which they spawn. Therefore, damn construction, sediment from logging operations, overharvesting and water pollution may be blamed for the salmon declines  A 1994 study claimed that the real problem is in the oceans, where salmon spend the majority of their lives. Fish harvest records were studied, and it was found that there were periods of high and low production associated with climate variation in the North Pacific. The nature and cause of these climate shifts is unclear  It was also found that high salmon production in Alaska corresponded to low salmon production in Oregon & Washington  Correlation between salmon production shifts and changes in sea surface temperatures in the North Pacific. Cool ocean water is caused by upwellings. Upwelling involves the wind driven motion of dense, cooler and nutrient rich water towards the ocean surface, replacing the warmer usually nutrient depleted surface water. This attracts salmon because they have an increase in their food source. Warm water lacks these nutrients, so we see less salmon Physical Environment  Key determinant to where organisms can live, which resources are available to them, and the rates at which their populations can grow  Includes climate, the chemical environment, and the soil in which microorganisms, plants and animals live  Must be characterized by variability over time, not just average conditions. Extreme conditions can change the resources available, and the organisms that can survive there. Climate  Climate: Long term (decades) trends in temperature, wind and precipitation at a given location. Based on averages and variation measured over decades  Weather: Short term (current temp, humidity, precipitation, wind and cloud cover)  Climatic Variation: Daily & seasonal cycles associated with changes in solar radiation as the Earth rotates on its axis and orbits the sun. It also includes yearly and decadal cycles  Climate changes as a result of the intensity/distribution of solar radiation hitting the earth's surface and the changing concentrations of gases in the earth's atmosphere (CO2 and other gases from global warming)  Climate determines where organisms live, and how they function  Climate is characterized by average conditions (long term conditions organisms must face if they are to survive there), but extreme conditions are also important because they can contribute to mortality (Ex: drought kills forest trees) What Drives Climate Patterns?  Solar radiation  1/2 of this radiation is Climate - Earth's energy balance absorbed by the earth (land and water). The other 1/2 is either absorbed or bounces back into the atmosphere. About 1/3 of this half is reflected back out into the atmosphere by clouds, aerosols (fine atmospheric particles) and the earth's surface. Another fifth is absorbed by ozone, clouds, and water vapour in the atmosphere.  If Earth's temperature is to remain the same, these energy gains from solar radiation must be offset by energy losses. Much of the radiation that is absorbed by the Earth's surface is emitted to the atmosphere as infrared long wave radiation. The Earth's surface also loses energy when water evaporates. Changes in phase from solid to liquid to gas require energy to be absorbed from earth's surface. This leads to cooling of the earths surroundings. Latent heat flux is the heat loss due to evaporation. Sensible heat is the energy transfer from the warm air immediately above earth's surface to the cooler atmosphere by convection and conduction.  Earth's surface actually releases more energy than it receives by direct solar radiation. However, a lot of the long wave radiation emitted by Earth is absorbed and reradiated back to Earth's surface. This is done by greenhouse gases such as H20, CO2, CH4, N2O. Everyone talks about greenhouse gases being bad, but they are crucial! Without them , the Earth would be 33 degrees cooler. Latitudinal Differences in Solar Radiation at Earth's Surface  Near the equator, the sun's rays strike Earth's surface perpendicularly Latitudinal Differences in Solar Radiation  At the poles (N & S), the sun's rays at Earth’s Surface are spread over a larger area and take a longer path through the atmosphere.  In addition, the amount of atmosphere the rays must pass through increases toward the poles so more radiation is reflected and absorbed before it reaches the surface. As a result, the tropics receive a lot more energy than the poles. Surface Heating & Uplift of Air  When solar radiation heats Earth's surface, the surface warms and emits infrared radiation to the atmosphere, warming the air above it.  Warm air is less dense than cool air, so the air above the warm surface rises (uplift). This is a low pressure system. As the warm air Differential solar heating of Earth's surface rises it expands and cools. Eventually the air cools enough for condensation to occur so that we get clouds and thus precipitation. This is why we have rainforests at the equator. The tropics receive the most precipitation of any area on earth because they receive the most solar radiation and thus experience the greatest amount of surface heating, uplift of air, and cloud formation.  The uplift of air causes a system of low Tropical Heating and Atmospheric Circulation Cells pressure relative to the north and south (tropics are low pressure and poles are high pressure)  The clouds reach the boundary between the troposphere (atmospheric layer above earth's surface) and the stratosphere (next atmospheric layer above troposphere)This boundary is marked by a transition from cooler temperatures to warmer temperatures.  Once the warm air reaches the warm air of the stratosphere it stops rising. At this point it begins to flow toward the poles. This air will begin to cool as it meets cooler air moving from the poles toward the equator. Once the air reaches a temperature similar to the rest of the atmosphere, it begins to descend toward the earth's surface. This is known as subsidence and it creates regions of high atmospheric pressure at latitudes 30 degrees north and south, which inhibits cloud formation. (where major deserts of world are located)  This tropical uplift of air creates a large scale pattern of atmospheric circulation in each hemisphere (N & S) known as a Hadley cell.  Additional atmospheric circulation cells are formed at higher latitudes. The Polar cell occurs at the north and south poles. Cold, dense air subsides at the poles and moves towards the equator when it reaches the earth's surface. The descending air at the poles is replaced by air moving through the upper atmosphere from lower latitudes (exchange of energy between tropical and polar air masses at the polar front)  Intermediate Ferrell cells exist at mid-latitudes between the Hadley and Polar cells. The Ferrell cell is driven by the movement of the Hadley and Polar cells and by exchange of energy between tropical and polar air masses in an area known as the polar front.  Tropical: Between 30 degrees N & S  Temperate: Between 30 degrees and 60 degrees N & S  Polar: Above 60 degrees N & S Global Atmospheric Circulation Cells and Climatic Zones These three cells result in the three major climatic zones in each hemisphere— tropical, temperate, and polar zones. Wind Patterns  Winds flow from areas of high pressure to areas of low pressure.  Atmospheric circulation cells create surface wind patterns known as prevailing winds.  The direction of the wind can be explained by the Coriolis effect.  The Coriolis effect results from the earth's rotation. It is defined as the apparent deflection of air or water currents when viewed from a rotating reference such as earth's surface. (air is actually stationary-rotation of earth on its axis makes path of wind appear curved)  Surface winds blowing toward the equator from the high pressure systems at 30 degrees N & S appear to be deflected to the west. These are called trade winds. Winds blowing toward the poles from those zones of high pressure, called westerlies, are deflected to the east. Winds blowing toward the poles from 60 degrees N & S are called easterlies, and are deflected to the west. The Coriolis Effect on Global Wind Patterns Prevailing Wind Patterns (July) Wind Patterns  The presence of continental land masses interspersed with oceans complicates the above idealized depiction of prevailing winds. Prevailing Wind Patterns (January)  Water has a higher heat capacity than land-it can absorb and store more energy without its temperature changing than land can.  As a result, solar radiation heats the land surface more than the ocean water in the summer, but the oceans retain more heat and remain warmer in winter than land at the same latitude. As a result, seasonal temperature changes over oceans are smaller than those on land.  In summer, air over the oceans is cooler and denser than that over land. As a result, semi permanent zones of high pressure (high pressure cells) form over the oceans. There is a low pressure cell over land.  In winter, air over continents is cooler and denser than that over oceans, so high pressure cells
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