Light Absorption in Sea Water

Transcription

1 Light Absorption in Sea Water Atmospheric and Oceanographic Sciences Library 33 Bogdan Woźniak Jerzy Dera

2 Light Absorption in Sea Water

3 ATMOSPHERIC AND OCEANOGRAPHIC SCIENCES LIBRARY VOLUME 33 Editors Lawrence A. Mysak, Department of Atmospheric and Oceanographic Sciences, McGill University, Montreal, Canada Kevin Hamilton, International Pacific Research Center, University of Hawaii, Honolulu, HI, U.S.A. Editorial Advisory Board L. Bengtsson Max-Planck-Institut für Meteorologie, Hamburg, Germany A. Berger Université Catholique, Louvain, Belgium P.J. Crutzen Max-Planck-Institut für Chemie, Mainz, Germany J.R. Garratt CSIRO, Aspendale, Victoria, Australia G. Geernaert DMU-FOLU, Roskilde, Denmark J. Hansen MIT, Cambridge, MA, U.S.A. M. Hantel Universität Wien, Austria A. Hollingsworth European Centre for Medium Range Weather Forecasts, Reading, UK H. Kelder KNMI (Royal Netherlands Meteorological Institute), De Bilt, The Netherlands T.N. Krishnamurti The Florida State University, Tallahassee, FL, U.S.A. P. Lemke Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany P. Malanotte-Rizzoli MIT, Cambridge, MA, U.S.A. S.G.H. Philander Princeton University, NJ, U.S.A. D. Randall Colorado State University, Fort Collins, CO, U.S.A. J.-L. Redelsperger METEO-FRANCE, Centre National de Recherches Météorologiques, Toulouse, France A. Robock Rutgers University, New Brunswick, NJ, U.S.A. S.H. Schneider Stanford University, CA, U.S.A. F. Schott Universität Kiel, Kiel, Germany G.E. Swaters University of Alberta, Edmonton, Canada J.C. Wyngaard Pennsylvania State University, University Park, PA, U.S.A. The titles published in this series are listed at the end of this volume.

4 Light Absorption in Sea Water Bogdan Woźniak 1,2 and Jerzy Dera 1 1 Institute of Oceanology Polish Academy of Science Powstańców Warszawy Sopot, Poland 2 Institute of Physics Pomeranian Academy Arciszewskiego S lupsk, Poland

5 Bogdan Woźniak Institute of Oceanology Polish Academy of Sciences Powstańców Warszawy Sopot, Poland and Institute of Physics Pomeranian Academy Arciszewskiego S lupsk, Poland Jerzy Dera Institute of Oceanology Polish Academy of Sciences Powstańców Warszawy Sopot, Poland Library of Congress Control Number: ISBN-10: eisbn-10: ISBN-13: eisbn-13: Printed on acid-free paper Springer Science+Business Media, LLC All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights springer.com

6 Contents 1 Introduction: Absorption of Sunlight in the Ocean Inflow and Absorption of Sunlight in the Ocean Case 1 and Case 2 Waters The Light Absorption Coefficient and its Components in Sea Water Light Absorption by Water Molecules and Inorganic Substances Dissolved in Sea Water Light Absorption Spectra of Small Molecules Such as Water: Physical Principles Vibrational-Rotational Absorption Spectra Electronic Absorption Spectra The Absorption of Light and Other Electromagnetic Radiation in Pure Liquid Water and Ice Physical Mechanisms of Absorption The Absorption of Electromagnetic Radiation in Pure Liquid Water The Absorption of Electromagnetic Radiation in Ice Light Absorption by Atoms, Sea-Salt Ions and Other Inorganic Substances Dissolved in Sea Water Dissolved Gases Salts Inorganic Complex Ions The Interaction of Light with Organic Molecules Present in Sea Water: Physical Principles The Characteristic Absorption Properties of Simple Chromophores in Organic Molecules The Absorption Properties of Complex Organic Molecules with Conjugated p-electrons v

7 vi Contents Linear Polyenes Cyclic Polyenes Mixed Conjugations (p- and n-electron) and Photosynthetic Pigments The Influence of Auxochromic Groups and Complexes on the Optical Properties of Organic Compounds in the Sea Intramolecular Interactions The Solvent Effect Organometallic Complexes Charge-Transfer Complexes Light Absorption by Dissolved Organic Matter (DOM) in Sea Water Classification, Origin and General Characteristics of Light Absorption by the Principal Groups of Organic Absorbers in Sea Water Occurrence and Origin of Organic Matter in the Ocean Principal Organic Absorbers of Light in the Ocean Analysis of the Conditions Governing UV-VIS Absorption by the Principal Organic Absorbers in the Sea Amino acids and their Derivatives Peptides and Proteins Purines, Pyrimidines and Nucleic Acids Lignins Colored Dissolved Organic Matter (CDOM) The Total Absorption of UV-VIS Radiation by All Organic Substances Dissolved in Sea Water Fine Spectral Structure Absolute Magnitudes of Absorption Coefficients The Slopes of Absorption Spectra Light Absorption by Suspended Particulate Matter (SPM) in Sea Water The Optical Properties of Dispersing Media: Theoretical Principles The Packaging Effect: What is it and How Does it Manifest Itself? Light Absorption in Polydispersing Media: A Quantum-Mechanical Electrodynamic Description Elements of Mie Theory Some Theoretical Optical Characteristics of Suspended Particles

8 Contents vii 5.2 Suspended Particulate Matter in the Sea: Nature, Origins, Chemical, and Physical Properties Suspended Particulate Matter in the Sea: Main Types, Origins, and Resources The Chemical Composition and Optical Constants of Mineral Particles The Chemical Composition and Optical Constants of the Planktonic Components of Organic Particles The Chemical Composition and Optical Constants of Organic Detritus Sizes and Shapes of Particles Light Absorption Properties of Nonalgal Particles: Results of Empirical Studies Light Absorption Spectra of All Suspended Particulate Matter (SPM) and Nonalgal Particles: General Characteristics Spectra of the Mass-Specific Light Absorption Coefficients of Nonalgal Particles Parameterization of the Particulate Matter Spectra for Oceanic Case 1 Waters Light Absorption by Phytoplankton in the Sea Abiotic Factors Governing Light Absorption by Phytoplankton in the Sea The Trophicity of Marine Basins: A Factor Governing The Resources of Algae and Light Absorption The Light Field: A Factor Governing the Composition of Light-Absorbing Pigments in Cells Phytoplankton Pigments and their Electronic Absorption Spectra in the Visible Region The Role of Phytoplankton and the Main Types of Phytoplankton Pigments The Chemical Structure of Pigments The Individual Absorption Properties of Pigment Extracts The Individual Absorption Properties of Pigments in Vivo The Native Forms of Chlorophyll Pigments Phytoplankton Resources and Chlorophyll a Concentrations in Oceans and Seas The Principal Natural Factors Governing Phytoplankton Resources in the World Ocean The Distribution of Chlorophyll in the World Ocean

9 viii Contents Vertical Distributions of Chlorophyll a in the Sea Statistical Formulas Describing the Vertical Distributions of Chlorophyll Concentration The Composition of Chlorophyll a and Accessory Pigments in Marine Algae Pigment Compositions Characteristic of Various Classes of Phytoplankton Pigment Compositions in Natural Plant Communities, in Different Types of Sea and at Different Depths Photoadaptation and Chromatic Adaptation; Model Descriptions of Pigment Concentrations in Different Seas The Packaging Effect of Pigments in Marine Phytoplankton Cell An Approximate Formal Description of the Packaging Effect for Marine Phytoplankton The Product C chl D for Phytoplankton in Different Types of Seas: A Preliminary Statistical Description Total Light Absorption by Marine Algae: Results of Empirical Studies Methodological Problems Light Absorption Spectra of Phytoplankton: A General Outline Light Absorption Spectra of Phytoplankton: Fine Structure Absolute Values of Total and Specific Absorption Coefficients Model Descriptions of the Absorption Properties of Marine Phytoplankton: A Review The Principal Model Descriptions of Light Absorption by Phytoplankton Classical Models Single-Component, Nonhomogeneous Models The Multicomponent, Homogeneous Model The Multicomponent, Nonhomogeneous Model Complex Utilitarian Models Modeled Absorption Properties of Algae in Different Types of Sea References Subject Index List of Symbols and Abbreviations

10 1 Introduction: Absorption of Sunlight in the Ocean 1.1 Inflow and Absorption of Sunlight in the Ocean The absorption of light by the oceans is a fundamental process in the Earth s harvesting of the vast resources of solar radiation and its conversion into other forms of energy. Of course, light is also absorbed by the atmosphere and the continents, but the scale of the process there is very much smaller than in the oceans, inasmuch as the absorption capability of the atmosphere is lower and the surface area of the land is only about one-third of that of the oceans. At any instant, half the Earth s surface is illuminated by a beam of solar rays (Figure 1.1) which, at this distance from the sun and given the comparative size of the Earth, are practically parallel. Their angle of divergence is that through which we see the Sun from the Earth; that is, Dj radians, or c of a degree. Taking into consideration the daily cycles of the Earth s revolutions about its axis and the unevenness of its surface, the mean insolation of the Earth amounts to c. 342 W m 2, that is, around one quarter of the solar constant (S = 1365 W m 2 ; Wilson (1993)), because the surface area of the Earth is four times as large as its cross-section (Schneider 1992). If we allow for a 26% loss of this radiation due to reflection in the atmosphere and a further 19% due to absorption in the atmosphere (Harrison et al. 1993, Trenberth 1992), the mean insolation of the ocean is 55% of the original value, or c.188 W m 2. In other words, this is the time- and space-averaged downward irradiance of the sea surface. Furthermore, if we bear in mind that c. 6% of the light reaching the sea is reflected from the surface and within the water itself this is the mean albedo of the sea (Payne 1979) we have an average flux of radiant energy equal to c. 177 W that is constantly being absorbed in the water column beneath every square meter of the sea surface and converted to other forms of energy. If we take the World Ocean to have a total surface area of 361 million km 2, it is unceasingly absorbing a solar radiation flux of c MW. This energy is consumed in warming and evaporating the waters of the ocean, warming the atmosphere by conduction, the latent heat of evaporation, and 1

11 2 1. Introduction: Absorption of Sunlight in the Ocean FIGURE 1.1. Solar light fluxes and the Earth. Solar constant: the mean solar radiation flux incident on a plane at right angles to the radiation reaching the top of the atmosphere; insolation of the Earth: the average component at the top of the atmosphere of the above flux (solar constant) perpendicularly incident at every spot on the Earth s surface during the day; insolation of the ocean (and land areas, i.e., the combined surface area of the ocean and land): the insolation of the Earth minus the averaged amount of radiation lost in the atmosphere. (Adapted from Dera (2003).) the thermal radiation of the sea surface, as well as setting (and maintaining) the masses of water in motion. Finally, less than 1% of this energy drives the photosynthesis of organic matter and photochemical reactions in the sea water (e.g., Dera 2003). From the point of view of quantum mechanics, this flux of absorbed energy means that an average of collisions between photons and the component molecules of sea water and the absorption of the former by the latter takes place under every single square meter of ocean during every single second. The effect of every elementary collision of a photon with a particle of matter is strictly dependent on the energy of a photon E v = hn (where h = Js, Planck s constant and n is the frequency of vibrations of a photon, equal to the reciprocal of the period of vibrations T = 1/n, which is linked to the wavelength of the light l and its velocity c by the relationship c = nl). The most likely effects of these collisions, during which photons of the appropriate energy are absorbed, are shown in Table 1.1. We see in the table how very different the energies of photons are from different frequency bands of the light spectrum and also how large the extent to which the effects of their absorption vary, from the ionization of atoms by the far ultraviolet (UV) to the translation motions induced by the far infrared (IR). It thus becomes essential to know what the spectrum of light incident on the sea is and the changes it is subject to as it penetrates ever deeper into

12 1.1 Inflow and Absorption of Sunlight in the Ocean 3 TABLE 1.1. Relationships between the length of an electromagnetic wave l (in a vacuum), the frequency of vibrations n, the energy of a photon E n, the color of the light, and the probable effect of the absorption of a photon. Probable Number of effect of the Wave- Frequency of Energy of Energy of photons per J Color of absorption length vibrations a photon a photon of energy light (type of a photon l [nm] n [Hz] E n [10 19 J] E n [ev] [10 18 J 1 ] of waves) by a molecule Ionization, Far electronic ultraviolet excitation Ultraviolet Violet Blue Green Greenish- Vibrational Yellow rotational excitation Orange Red , Infrared 2, , , Far infrared 10, Rotational 20, excitation, 50, translations Adapted from Dera (2003). the water. Spectra of the irradiance of the sea surface by sunlight and the changes it undergoes with increasing depth in different seas are illustrated in Figure 1.2. Numerous studies have shown that, under average conditions, c. 50% of the sunlight incident on the sea surface consists of IR bands, some 45% of visible radiation and only around 5% of UV. The figure also shows how quickly the visible light spectrum narrows down with depth in the sea: bluish-green light (l 450 nm) penetrates the farthest in optically clear oceanic waters, whereas greenish-yellow light (l 550 nm) is the most penetrating in sea waters containing large amounts of organic substances. We can also see from Figure 1.2a that light reaching a depth of barely one meter contains practically no more IR, which means that IR radiation is very strongly absorbed by sea water and that all its energy entering the sea is absorbed in the very thin surface layer.

13 4 1. Introduction: Absorption of Sunlight in the Ocean FIGURE 1.2. Spectra of daily downward irradiance in sea waters at various depths: (a) in the ocean over a broad spectral range (Jerlov 1976); (b) in the Ezcurra Inlet, Antarctica, at around noon in January (from measurements by Woźniak et al. during the second Antarctic Expedition of the Polish Academy of Sciences (Dera 1980); (c) in the clear oligotrophic waters of the Sargasso Sea; (d) in the eutrophic waters of the Baltic Sea (drawn on the basis of data from IO PAN Sopot.) Reproduced from J. Dera, Marine Physics, 2nd ed., updated and supplemented, 2003 (in Polish), with the kind permission of PWN, Warszawa. Water molecules play the most important part in the absorption of solar light energy in the ocean, not only because of their amount (>96% of all the molecules contained in sea water), but also because of their absorption properties: light in the IR band is very strongly absorbed (Chapter 2). Even so,

14 1.1 Inflow and Absorption of Sunlight in the Ocean 5 there is a multitude of other substances in sea water that are also capable of absorbing this energy. The complexity of sea water as a substance means that its optical properties are essentially different from those of pure water. Sea water contains numerous dissolved mineral salts and organic substances, suspensions of solid organic and inorganic particles, including various live microorganisms, and also gas bubbles and oil droplets. Many of these components participate directly in the interactions with solar radiation in that they absorb or scatter photons. Many also participate indirectly by fulfilling diverse geochemical and biological functions, for instance, in photosynthesis, which regulates the circulation of matter in marine ecosystems, and in doing so, affects the concentrations of most of the optically active components of sea water. The resources and the concentrations of the most important sea water components of the World Ocean are listed in Table 2.17, which also gives the principal optical and biological functions of these components. The occurrence in sea water of suspended particles as well as other inhomogeneities, such as gas bubbles, oil droplets, and turbulence, means that from the optical standpoint it is a turbid medium, a light absorber and scatterer, the optical properties of which vary together with changes in the composition and concentration of the components and depend on the physical conditions prevailing at any given time (Jerlov 1976, Morel and Prieur 1977, Shifrin 1983b,1988, Højerslev 1986, Kirk 1994, Spinard et al. 1994, Mobley 1994, Stramski et al. 2001, Dera 1992, 2003). Because of this powerful interaction between the molecules and the large number of components in sea water, we observe in the optical spectrum not discrete spectral absorption lines but broad absorption bands. Overlapping to various degrees and in different regions of the spectrum, the absorption bands actually form an absorption continuum with local maxima and minima. The absolute principal minimum of electromagnetic wave absorption in sea water lies in the visible region, as is the case with pure water (Figures 1.3 and 2.11). As we see in Figure 1.3, there is a great variety for different seas (e.g., a large absorption for the Baltic). The huge number of sea water components and the continuous nature of its absorption spectrum preclude any meaningful discussion of the optical properties of each component in turn. Nevertheless, it is possible to distinguish groups of components that are especially actively involved in the absorption of the solar radiation entering the sea water. Generally speaking, we have to examine the following groups of components, which differ distinctly in their optical properties: water molecules and their associated forms, sea salt ions, dissolved organic matter (DOM), live phytoplankton and suspended phytoplanktonlike particles, and other particulate organic matter (POM; organic detritus, zooplankton, and zooplanktonlike particles), suspended mineral particles, and other components such as oil droplets and gas bubbles. It is thus the aim of the present volume to describe and assess the current state of knowledge of the absorption properties of these optically significant substances and the part they play in the interaction with light in sea water.