Lecture 4

Lecture 4 - Reminder: Week 1 online reading assignment\...

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Unformatted text preview: Reminder: Week 1 online reading assignment\ Reminder: www.physicalgeography.net/fundamentals/chapter8.html OPTIONAL Study Aid for this reading will be posted on lab website OPTIONAL • Where are the cold currents? the warm currents? • Which are linked to major ocean upwelling zones persistent on eastern boundaries of the Atlantic, Pacific & Indian Oceans? ( *California, Peru, Canary, Benguela & W. Australia currents) Fig. 8q-1 some of the major surface ocean currents Fig. Light in water: lecture slides plus take-home study aid slides Light Homework: Read On-line web pages (links therein are optional) “What is hydrologic optics” http://www.serc.si.edu/labs/phytoplankton/primer/hydrops.jsp http://www.serc.si.edu/labs/phytoplankton/primer/hydrops. “The Color of the Ocean” http://science.hq.nasa.gov/oceans/living/color.html “The Homework: Chapter 10 in your reader: Light Homework: Light QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. Tropical species show great shapes QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. Review: Light travels as waves of energy (hv), Light energy is quantified in Watts or Joules, terms used in heat budgets Light 1. Waves of light have different wavelengths (λ ), 1. wavelengths expressed as nanometers (nm) or Angstroms (A) 1 nm = 10 A nm Photosynthetically Available Radiation = PAR 2. Purple and blue light waves have short λ . Red light has a longer λ 3. Short λ carry more energy than Long λ . 3. 4. When the λ of light matches the distance 4. of spacing in a chemical bond, then the of energy (hv) of the light is transferred to the energy of the chemical = Absorption energy Absorption 5. All molecules absorb light energy.. 5. Most dissipate the absorbed energy as heat Most e.g. H2O, CO2 Light also acts like a Stream of Particles, called Photons or Quanta (hv). Photons Quanta Most important to study of biology (photosynthesis, photochemistry, bio-optics) • Light is absorbed in packets of energy • Each packet = 1 photon =1 quantum Each • Energy content of a photon varies inversely with wavelength Energy • Measurements of rate of incoming photons are usually expressed in units of moles of photons/area/time = Photon Density Flux (PDF) = Irradiance (I) Photon Conceptualization of a photon of of chemical bonds Because of their dual nature as particles and waves, photons are often shown as squiggly lines. squiggly Absorbed photon increases Absorbed the resonance energy of the resonance chemical , pushing electron to higher excited state. to That “extra” resonance energy can That resonance transferred between chemicals (e.g. pigments) in packets called excitons. excitons Energy transduction Energy Light Absorption & Resonance Energy Transduction are 1st steps in Photosynthesis Solar radiation (sunlight) at the ocean surface QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. PAR (400-700 nm) = photosynthetically available radiation (400-700 = λ s absorbed by photosynthetics pigments Sum of all ‘colors’ of light energies of PAR = white light PAR, with flux Q = QPAR white with For a narrow waveband of PAR (e.g. blue light) = spectral PAR, with flux Q = QPAR(λ ) For spectral with Define UVR = ultraviolet radiation (280- 400 nm), with flux Q = QUVR UVR < 295 nm do not the ocean surface; < 300 nm do not penetrate in oceans/lakes UVR 295 Environmentally Relevant UVR = (300-400 nm)= most energetic light reaching earth most UVR excitation energy breaks chemical bonds.. Esp. those of DNA, RNA & proteins Light in water: PURE WATER ABSORPTION & ATTENUATION ARE OPTICAL CONSTANTS PURE Light Note this is a log Plot of attenuation rate Maximum depth penetration (in meters) of different wavelengths (colors) of QPAR into clear waters (colors) clear QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. Attenuation of UVR and PAR by pure water Incident Light, Io = QPARo Io UnderWater Light (UWL) is absorbed by WATER, cDOM & phytos Absorbed + Scattered Light Absorption due to Absorption colored DOM = cDOM colored Attenuated Light, Iz = QPARz Iz Short wavelength UV and violet/blue light are in Short fact scattered about twice as strongly as red light. scattered twice For wavelengths in the visible light range, selective scattering causes us to see the blue color. Scattering is why light below a few meters is said to be ‘diffuse’.. Bouncing in all directions. to ’.. Phytos Absorption See readings for review and added details Phytoplankton pigmentation evolved to absorb different types of UWL fields. Phytoplankton (cDOM) (particles) Spectral properties of UWL vary widely Spectral Case I: Open Ocean Case II: Coastal and Inland waters In coastal waters the depth of the euphotic zone decreases and ocean color shifts from blue to green as phytoplankton biomass, cDOM and particle load increases. Euphotic zone = depths where phytoplankton grow ~1% of surface Io Euphotic depths • Over the day the depth of the euphotic zone deepens and shallow as sun rises and sets. Over the • For intercomparison purposes, UWL field properties are reported as measurements For UWL made at solar noon unless otherwise specified. at • Why would scientists take care to also report the time of year & the sky conditions when presenting UWL data? presenting Calculating Attenuation Coefficients for “white light” Qpar In the water column, light (e.g. QPAR) is absorbed exponentially with depth is Beer-Lambert law describes the Beer-Lambert exponential decrease in irradiance with depth exponential Io Iz = I0.eIo .z • Iz is irradiance at a given depth • I0 is irradiance at the surface Iz • kd is the diffuse attenuation coefficient attenuation 1% Io See Fig. 10-8 in readings Absorption of UVR and PAR by pure water • z is depth in meters. When plotted as depth vs log % surface When irradiance (Io), the line is straight irradiance Kd for QPAR indicate transparency but do not indicate possible color difference in UWL. Kd not To recognize color differences, would need to measure spectral attenuation coefficients for Kd (λ ), Kd looking at narrow bandwidths of visible spectrum at a time, e.g. QPAR(λ ) QPAR( Examples of Water Color Images Examples This aerial photograph the spatial variability high concentrations of phytoplankton and suspended matter change water color in the coastal zone . Example is typical of Santa Barbara Channel after major storm events. Case II waters This true color satellite image of SW coast of Florida shows patch of intense phytoplankton biomass (bloom). Study Aid: after completing your readings on Light Properties, consider the following image of sunlight on a story day shining down on a shallow sandy water column. sunlight note the 2 arrows note A B QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. 1. What might account for the difference in color at A & B? the 2. How might the following play a role in explaining the difference? role sandy bottom, sun with broken clouds depth 3. What is the equation that What describes the 3 spectral components that account for the spectral attenuation of light in natural waters? natural 5. What color is your favorite swimming place? Why? 4. What color is pure water? What makes it whiter?, What greener?, redder? Do these waters appear to have abundant phytoplankton biomass? Do you think there is much cDOM? Why or why not? cDOM? Study Aid: 1. Which side of this lake suffers from eutrophication (nutrient pollution)? 2. How can you tell? Color change is 2. obvious but what does it mean? 3. If you were to see this event with an uninformed friend, what would you tell them to explain this remarkable site? site? Consider how nutrients affect Consider phytoplankton growth and absorption; how biomass can clump and form particles that scatter light; how cDOM might be come into play and affect spectral light attenuation (color) in the water column. water Study Aid: Reading of Chapter 10 on “Light” Pay close attention to this chapter as info is considered fundamental; consider forming study groups early. . How does light regulate aquatic ecology? (eg. photosynthesis, vision, heat budgets, etc) (eg. consider making a list and be as specific as you can; refer and revise this list as other lectures and readings are completed. and 2. Study Fig. 10.1 closely (seasonal changes in solar light as a function of latitude) & thoughtfully Note solar radiation highest in N. Hemisphere summer & S. Hemisphere “austral summer”, the later Note occurring at time of N. Hemisphere winter; what happens near the equator? Since unused radiation dissipates to heat, this figure also shows how the earth is heated by the sun during different seasons. Consider this uneven heating when upcoming lectures discuss the forces that drive winds and, in turn, how wind drives currents. For a review of major currents, see online reading assignment for week 1. Bonus: how might a change this heat distribution (eg. uneven global warming) affect dessert formation, precipitation, winds, currents? Clearly a case where biology (us) change atmospheric chemistry, resulting in heat budget changes that affect fundamental physics of the planet and, in turn, have huge biological effects. have . Learn to recognize names, wavelengths & units of measure of light color and intensity Learn the better you know, the easier your understanding of light attenuation, absorption, utilization, etc. the Don’t need to know Conversions between units but understand that different units do exist . Generalities of how light is measured with different instruments should be understood. Generalities if you are taking the accompanying lab to this course, a deeper understanding of these methodologies (as described in the reading) should help you in your laboratory/field studies. (as . Eqs. 10.1 and 10.2 are fundamental equations from which other useful equations are derived. Eqs. Why is blue light more energetic than red light? Of UV radiation, PAR and IR, which has most/least E? What is light attenuation in the water column? Why does it get dark at depth? Where does the attenuated light energy go? attenuated Study Aid: Self Test of Chapter 10 on “Light” . What is the lowest wavelength of light entering the water column? Is this wavelength in the UV, PAR or IR? . What units are used when measuring the ENERGY of incoming solar radiation? What units are used when measuring the NUMBER of PHOTONS (quanta) of incoming radiation? . Some light instruments (photometers) measure the INTENSITY (photon flux) of all PAR light (e.g. “white light”) t once; others (spectroradiometers) measure the INTENSITY of narrow wavebands of PAR light (e.g. “spectral ight). How does the attenuation of ‘white’ PAR and spectral PAR compare as a function of depth? Thought uestion: What are the possible differences in the uses of ‘white light’ and ‘spectral’ data in studies of bio-optics f phytoplankton ecology? . What percent of total sunlight reaching the ocean surface is PAR? What percent is UV radiation? IR? . Clouds/fog can reduce incident radiation (Io, sunlight reaching earth surface) by how much? What about effects f natural local topography?.. Eg. mountains, trees, ice (with and without air bubbles), snow, sand? What about nnatural effects, e.g. buildings, pavement, windows, greenhouses, oil slicks? What others can you think of? ook around as you walk campus or go to the beach and ask yourself why the light is variable in different places nd how frequently does it change.. Minutes, hours (dawn, noon, dusk), daily, seasonally, yearly. . Light scatters differently at different wavelengths. Of red vs blue vs UV radiation, which scatters more? What is e formula that calculates by how much a specific wavelength of light will scatter? Which of the variables in 5) bove tend to scatter light rather than absorb it? Eg. Under cloudy skies are incoming photons absorbed and/or cattered? . What color of light penetrates deepest in oligotrophic water columns? As more DOM is present, what happens oth to the depth of penetration and the color of light that penetrates deepest? Why? What is the effect of articles? Of phytoplankton (and their pigments)? . How do the light penetration (transparency) of lakes, coastal oceans and oligotrophic central gyres compare? ...
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