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ENVIRONMENT: Surface Temperature, Subsurface Temperature, and Wind Data Surface Temperature is a measure of the relative "hotness" or "coldness" of the uppermost waters of the ocean. This is different from measuring the amount of heat that the oceans hold. A candle may burn at a higher temperature than a forest fire, but a forest fire produces far more heat. Similarly, the vastness and depth of our oceans enable them to hold a tremendous amount of heat, even though temperatures vary from near freezing to moderately warm. The two Pacific Ocean study areas – "Coastal California" and "Tropical Pacific" – have different patterns of sea surface temperature, mostly because of their positions relative to the equator. Situated greater than 35° north of the equator, sea surface temperatures in the "Coastal California" study area are relatively cool – ranging from 10°C to 16°C (50°F to 61°F; see color coded bar at left). On the other hand, "Tropical Pacific" ocean waters are exposed to intense sunlight throughout the year. This leads to warm sea surface temperatures – ranging from 19°C to 31°C (66°F to 88°F; see color coded bar at right). Subsurface Temperature is a measure of the relative "hotness" or "coldness" of deeper waters of the ocean. Whereas surface temperature data are displayed as maps, subsurface data are displayed as "profiles" with shallower waters at top and deeper waters at bottom. When analyzing subsurface data, an important piece of information is its location. For example, the easternmost extent of all "Coastal California" profiles is Monterey Bay (as shown in the map at left). The westernmost extent of this profile is about 300 km (~180 mi) offshore. From the surface to 200 m (~650 ft) depth, the range of subsurface temperatures in this area is 8°C to 16°C (46°F to 61°F; see color coded bar at right). For the "Tropical Pacific" study area, subsurface data were taken along the equator over 85° of longitude, an extent of 9,450 km (5,870 mi). From the surface to about 500 m (1640 ft) depth, subsurface temperatures in PHYTOPIA - UPWELLING ZONES - ENVIRONMENT OVERVIEW - PAGE 1 the "Tropical Pacific" study area range from just above freezing to 32°C (90°F; see color coded bar, at right). Subsurface temperature data are important because they give clues about the types of oceanographic processes occurring in a region. For example, cool temperatures through the water column may indicate that nutrient-rich waters are moving vertically from depth to the surface. Where this type of "upwelling" occurs, phytoplankton populations can grow dramatically to fuel the marine food web. On the other hand, warm temperatures deep within the water column may reveal unusual patterns of heat storage – for example, abnormal heat transfer from the tropical Pacific Ocean to the overlying atmosphere that drives "El Niño weather." Wind Data show the movement of air near the sea surface. Winds can drive ocean currents and mix ocean waters, bringing colder, nutrient-rich waters to the surface, aiding productivity. Wind data are displayed as "vectors" – their lengths show relative speed and arrows indicate the wind direction. In the "Coastal California" example at right, all data vectors are shorter than the reference arrow shown at far right – thus all winds shown in this figure are weaker than 10 meters per second (36 kilometers per hour or 22 miles per hour). The vectors' directions indicate winds that predominantly blow out of the northwest, parallel to the coast. Tropical wind patterns are dominated by "trade winds" – steady winds that blow from east-towest, located north and south of the equator. As these easterly winds converge, moist air is forced upward. This causes water vapor to condense, or be "squeezed" out, as the air cools and rises, resulting in a band of heavy precipitation around the globe. This band of clouds and rain – the "Intertropical Convergence Zone" – moves seasonally, always drawn toward the area of most intense solar heating, or warmest ocean temperatures. PHYTOPIA - UPWELLING ZONES - ENVIRONMENT OVERVIEW - PAGE 2