R Majchrowski - Remote sensing of vertical phytoplankton pigment distributions in the baltic new mathematical expressions - страница 1

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Remote sensing of vertical phytoplankton pigment distributions in the Baltic: new mathematical expressions. Part 2: Accessory pigment distribution[1]

Baltic Sea

Accessory pigment concentration Vertical distribution Remote sensing

KEYWORDS

Roman Majchrowski1 Joanna Ston-Egiert2 Miroslawa Ostrowska2 Bogdan Wozniak1'2 Dariusz Ficek1 Barbara Lednicka2 Jerzy Dera2

1 Institute of Physics, Pomeranian Academy,

Arciszewskiego 22B, PL-76-200 Slupsk, Poland; e-mail: majchrowski@apsl.edu.pl

2 Institute of Oceanology, Polish Academy of Sciences,

Powstancow Warszawy 55, PL-81-712 Sopot, Poland; e-mail: aston@iopan.gda.pl

Received 10 September 2007, revised 22 November 2007, accepted 27 November 2007.

This is the second in a series of articles, the aim of which is to derive math­ematical expressions describing the vertical distributions of the concentrations of different groups of phytoplankton pigments; these expressions are necessary in the algorithms for the remote sensing of the marine ecosystem. It presents

Abstract

formulas for the vertical profiles of the following groups of accessory phytoplankton pigments: chlorophylls b, chlorophylls c, phycobilins, photosynthetic carotenoids and photoprotecting carotenoids, all for the uppermost layer of water in the Baltic Sea with an optical depth of т « 5. The mathematical expressions for the first four of these five groups of pigments, classified as photosynthetic pigments, enable their concentrations to be estimated at different optical depths in the sea from known surface concentrations of chlorophyll a. The precision of these estimates is characterised by the following relative statistical errors according to logarithmic statistics a-: approximately 44% for chlorophyll b, approx. 39% for chlorophyll c, approx. 43% for phycobilins and approx. 45% for photosynthetic carotenoids. On the other hand, the mathematical expressions describing the vertical distributions of photoprotecting carotenoid concentrations enable these to be estimated at different depths in the sea also from known surface concentrations of chlorophyll a, but additionally from known values of the irradiance in the PAR spectral range at the sea surface, with a statistical error a- of approximately 42%.

1. Introduction

This article is the second in a series of three, whose objective was to find mathematical formulas to describe the vertical distributions of phytoplankton pigments in the Baltic Sea, formulas that would be useful in algorithms applied in the remote monitoring (mostly by satellite) of the Baltic ecosystem. The first article in this series (see Ostrowska et al. (2007), this volume) presented a mathematical description of the vertical distribution of the total chlorophyll a concentration in the Baltic. The model formula given there enables the chlorophyll a concentration at different depths in the Baltic Sea Ca(z)[2] to be estimated from known surface concentrations of this pigment Ca(0), which can be defined by remote-sensing techniques (e.g., Ruddick et al. 2000, Sathyendranath 2001, Darecki et al. 2003). In the present article the focus is on equivalent mathematical descriptions of the resources and spatial distributions of the accessory pigments in Baltic phytoplankton.

The compositions and concentrations of phytoplankton pigments at different depths in seawaters of different trophic index[3] vary widely (see

E2 Ca(0) =2-5 (3.5); E3 Ca(0) = 5-10 (7.5); E4 Ca(0) = 10-20 (15); E5 Ca(0) =20-50 (35); E6 Ca(0) =50-100 (70).а

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0 0.2 0.4 0.6 pigment ratio CPPC / Ca

0  0.1 0.2 0.3 0.4

pigment ratio Cb / Ca

0 0.2 0.4 0.6 0.8 1.0 pigment ratio CPSC / Ca

0 0.1 0.2

pigment ratio Cc / Ca

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pigment ratio CPPC / Ca

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0 0.2 0.4 0.6 0.8 1.0 pigment ratio CPSC / Ca

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pigment ratio Cc / Ca

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0 10 20 30 40 pigment ratio Cphyc / Ca

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Figure 1. Vertical distributions of measured concentrations of pigments relative to chlorophyll a, in different trophic types of waters in seas and oceans containing waters approximating to Case 1 waters (a, c, e, g) and in the Baltic Sea (b, d, f, h, i). The separate figures refer to: photoprotecting carotenoids PPC (a, b), chlorophylls b (c, d), photosynthetic carotenoids PSC (e, f), chlorophylls c (g, h) and phycobilins (i). The symbols on the figure denote the various trophic types of water in accordance with the classification in footnote 2

Figure 1). The absolute concentrations of these pigments are known to de­pend in large measure on the trophic index of the waters in question, which

is the principal factor regulating the magnitude of phytoplankton resources in the sea (Steemann Nielsen 1975, Babin et al. 1996, Wozniak & Dera 2007). On the other hand, the composition of these various phytoplankton pigments, i.e., the mutual relations between their concentrations, is governed largely by the irradiance conditions in the water. It is these that determine the light adaptation processes taking place in phytoplankton cells, and the light acclimation occurring at the phytocoenosis level that leads to changes in the species composition of the phytoplankton. These processes of light acclimation and adaptation lead to the earlier-mentioned differentiation in pigment compositions observed at different depths in different types of seas (Babin et al. 1996, Majchrowski 2001).

The processes by which single organisms (as a result of internal changes) or entire phytocoenoses (as a result of changes in the species composition) adapt to light factors may be of two kinds:

1) photoacclimation (or photo-adaptation), which gives rise to changes in the relative concentrations of photoprotecting pigments Cppc/Ca, i.e., relative to the concentration of chlorophyll a, Ca,atgiven depths and in given types of waters. These photoprotecting pigments are primarily the following carotenoid pigments: diadinoxanthin, alloxanthin, zeaxanthin, lutein, neoxanthin, violaxanthin, diatox-anthin, myxoxanthophyll, antheraxanthin,-carotene. The role of these photoprotecting pigment molecules is mainly to capture part of the excitation energy of chlorophyll a; this prevents its photo-oxidation. The mechanisms of these processes have been described in, e.g., Grodzinski (1978), Majchrowski (2001) and Wozniak & Dera

(2007);

2) chromatic acclimation (or chromatic adaptation), which gives rise to changes in the concentrations of accessory antenna pigments (photosynthetic pigments) relative to the concentration of chloro­phyll a, Ca, i.e., the relative concentrations of chlorophyll b (Cb/Ca), chlorophyll c (Cc/Ca), photosynthetic carotenoids like fucoxanthin, peridinin, a-carotene, prasinoxanthin, 19'butanoyloxyfucoxanthin and 19'hexanoyloxyfucoxanthin (CPSC/Ca), phycobilins (Cphyc/Ca)and others. It is the role of these accessory photosynthetic pigments to obtain light energy for photosynthesis mainly from those spectral intervals in which chlorophyll a is a poor absorber. This follows from the absorption of light quanta by molecules of these pigments and the transfer of this absorbed energy to chlorophyll a molecules. This question is discussed at length, e.g., in Govindjee (1975), Majchrowski

(2001), and Wozniak & Dera (2007).

In our earlier publications (Wozniak et al. 1997a,b, 2003, Majchrowski et al. 1998, Majchrowski & Ostrowska 1999, 2000) a mathematical de­scription was presented of the effects of both these kinds of adapta­tion of phytoplankton to the irradiance conditions prevailing in ocean basins. In particular, mathematical expressions were derived describing the dependence of the relative concentrations of photoprotecting pigments Cppp/Ca and photosynthetic pigments Cpsp/Ca on various irradiance characteristics in the sea. In the case of photo-adaptation, we found that the factor governing this process quantitatively was the Potentially Destructive Radiation (PDR), defined as follows:

480 nm

PDR* =   a*a(X) (£o(A))day d\, (1) 400 nm

where

PDR* - the potentially destructive radiation per unit mass of chloro­phyll a (the asterisk indicates that this is the PDR per unit mass of chlorophyll a)[/iEin (mg chl a)-1 s-1];

aa(A) - the specific coefficient of light absorption by chlorophyll a [m2 (mg tot. chl a)-1 ];

(E0(A)) - the scalar irradiance in the medium - <E0(A) >day stands for the mean daily value of this irradiance typical of a given season, region and depth in the sea [//Ein m-2 s-1 nm-1].

The magnitude of PDR* is equal to the energy from the blue spectral region (400-480 nm) which can be absorbed by chlorophyll a and which could cause this pigment to photo-oxidise. It turns out that this magnitude of PDR* correlates well with the relative concentration of photoprotecting carotenoids in phytoplankton, if its mean value is taken for a water layer Az from 30 m to 60 m thick (see explanation in eq. (3)) in order to allow for the vertical migration of phytoplankton as a result of water mixing. This interrelationship is expressed by the following formula (Majchrowski 2001,

Wozniak et al. 2003):

Cppc/Ca = 0.1758 x <PDR* >Az +0.176, (2)

where

< PDR* >Az= —-— f PDR*{z)dz. (3)

zi

The thicknesses of the water layers are defined as follows: Az = z2 z1, where z2 = z + 30 mand z1 = 0 if z< 30 m, or z1 = z30 mif z > 30 m.

Now, our studies of chromatic adaptation processes have shown that magnitudes well correlated with the relative concentrations of the various groups of photosynthetic pigments are the so-called spectral fitting functions Fj (dimensionless) for the jth pigment, known as chromatic adaptation factors. They have been defined as follows:

-forchlorophylla:

700 nm

Fa = -1—   І  /(A) a*(A)dA, (4a)

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R Majchrowski - Remote sensing of vertical phytoplankton pigment distributions in the baltic new mathematical expressions