El Niño and La Niña are opposite phases of a natural climate pattern across the tropical Pacific Ocean that swings back and forth every 3-7 years on average. Together, they are called ENSO (pronounced “en-so”), which is short for El Niño-Southern Oscillation. In this activity, you will examine provided information to determine the changes that occur during these phases and the resulting impacts.
Examine the graph above. Complete the following sentence.
As ocean depth decreases, temperatures
Identify the source of the heat in the ocean.
The thermocline is the layer of the ocean where there is a rapid change in temperature. On the graph, there are two horizontal lines that represent the upper and lower depth of the thermocline. Notice the drastic shift between 1000 and 400 ft below sea level.
Upwelling will cause the temperature of the surface water to
Dead marine organisms decay and fall to the ocean floor, resulting in nutrient rich sediments. Upwelling can bring these nutrients to the surface, leading to high productivity that supports the upper levels of the food chain. Explain one benefit of this increase in nutrients and productivity to humans.
According to Model 2 shown above, identify the winds in the tropics (latitudes near the equator).
Identify the direction the winds in the prior question are directed.
Based on the information from Model 1 combined with model 2, identify which side of the southern Pacific ocean upwelling would be expected to occur under normal conditions.
El Niño and La Niña are opposite phases of what is known as the El Niño-Southern Oscillation (ENSO) cycle. The ENSO cycle is a scientific term that describes the fluctuations in temperature between the ocean and atmosphere in the east-central Equatorial Pacific. During El Niño the surface winds across the entire tropical Pacific are weaker than usual, and can sometimes even reverse
Explain how the weakening of the trade winds will affect the upwelling that typically occurs, and how this will affect the sea surface temperatures (SST) in the tropical Pacific Ocean.
Recall that El Niño shows WEAK tradewinds. Think about which directions the tradewinds blow. Identify the year in which the colored map shows El Niño conditions.
Identify the year in which the colored map shows “normal” conditions.
During La Niña the trade winds blow in the same direction as normal, but with greater intensity. Describe how the upwelling off the coast of South America will change during a La Niña event.
Describe the water temperature of the coast of South America during a La Niña event.
Think back to model 1 and the impact of upwelling on marine food chains. Predict what is likely to happen to the fisheries in the eastern Pacific during an El Niño event.
The deviations from normal surface ocean temperatures that occur during ENSO events can have large-scale impacts not only on ocean processes, but also on global weather and climate. The global winds examined in Model 2 are caused by convection - land near the equator is warmed by direct sunlight which in turn warms the air above it, which rises. Warm water will also warm the air above, resulting in rising air and low pressure. Warm water also evaporates more easily than cool water, leading to higher humidity levels in this air. Once the air reaches the upper troposphere, it cools and can no longer hold as much moisture, resulting in storms and rainfall.
On the map of normal sea surface temperatures below, add a large L to indicate the most likely location of this rising, moist air.
Under normal conditions, identify which part of the South Pacific is likely to receive significant rainfall.
On the El Niño map below, add a large L to indicate the most likely location of this rising, moist air.
Describe the impact El Niño is likely to have on the amount of precipitation that occurs on each side of the Pacific ocean.
On the La Niña map below, add a large L to indicate the most likely location of this rising, moist air.
Given what you know about stronger tradewinds during a La Niña event, predict what will happen to precipitation on the Eastern coast of Australia.
As shown in the diagram, upwelling is the process by which deep water is brought to the surface, and downwelling is the process by which surface water is forced deeper. Based on the diagrams, what causes upwelling? (hint- look at the direction of the arrows)
What causes downwelling? (hint- look at the direction of the arrows)
The drawing below shows a colorcoded Pacific Ocean in 1988, indicating the color of the surface water. On the diagram provided, use the same color code, and fill in the June 1987 diagram. Start by coloring inside the 30°C with the purple. Using the next color in your color key, follow the same procedure for the next lower temperature band that ranges between 30°C and 28°C. Continue this process for all the temperature ranges in your color key.
