4.11.08 - Exam #2

4.11.08 - Exam #2 - Light in the Ocean "VISIBLE...

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Light in the Ocean “VISIBLE LIGHT” (0.38 – 0.76 µm): Tiny fraction of total wave spectrum. 47% of solar radiation arriving at Earth’s surface. LIGHT STRIKES THE OCEAN , some reflected, some absorbed. DEEP OCEAN : Utterly dark. WATER WITH SUSPENDED PARTICLES : murky. WHAT HAPPENS TO LIGHT IN THE WATER? Two possibilities for light hitting a water molecule or a suspended particle: (1) Absorption Photons “disappear”: E turns into heat, or used for chemical reactions (e.g. photosynthesis). (2) Scattering Photons “bounce off”: change direction, but do not disappear. May go up, down, or sideways. LIGHT ABSORPTION If you go 1 m. down into ocean, only 45% remains of light that was at surface. If you go 10 m. down into ocean, only 16% remains of light that was at surface. If you go 100 m. down into ocean, only 1% remains of light that was at surface. NO LIGHT PENETRATES BELOW 1000 m. Longer ג (wavelength) absorbed first. Shorter ג absorbed later. PHOTIC ZONE Sufficient light energy for photosynthesis. LIGHT SCATTERING Direction of travel of photons interrupted by particles. More particles, more scattering. Scattering makes objects blurry underwater. Suspended particles reduce overall light penetration. Increased absorption. Increased scattering (including back out of water). LIGHT PENETRATION AFFECTS: (1) Photosynthesis Biological structure of the ocean (2) Upper ocean temperature Large-scale climate effect
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SOUND TRANSMISSIONS IN THE OCEAN Sound travels farther and faster in water than in air. An explosion heard for 1 km in air can be heard 160 km. away in water. Velocity of sound in dry air (at 20 C): 334 m/sec Velocity of sound in water (at 20 C and .35% salinity): 1450 m/sec Sound velocity in water increases: o + 4.5 m/se per 1 C increase in temperature (+1.3 m/sec per 0.1% in salinity) o + 1.7 m/sec per 100 m increase in depth (pressure) Result: Velocity-minimum zone in the ocean 1. Temperature decrease ( p increasing): Net V decrease 2. Temperature stable ( p increasing): Net V increase 3-LAYER VERTICAL STRUCTURE OF THE OCEAN Surface layer: Warm, mixed, most life, fast currents. Zone of changing properties Deep ocean: Dark, cold, sparse life, slow currents. TEMPERATURE GENERALIZED: some parts of the ocean will differ. Called the thermocline for the change from warm to cold water. Equator: 28 C Tropics: 16 C High Latitudes: 2 C SALINITY Called the halocline for the change in salinity from warm to cold water. o Significant in: Estuaries/river mouths Polar oceans In a few locations : rare, but oceanographically important o It is more salty in the warm water and less salty in cold water. Significant in:
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4.11.08 - Exam #2 - Light in the Ocean "VISIBLE...

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