[ 1 ] The present study examines the potential of using the near-surface chlorophyll a concentration ([Chla ] surf ), as it can be derived from ocean color observation, to infer the column-integrated phytoplankton biomass, its vertical distribution, and ultimately the community composition. Within this context, al arge High-Performance Liquid Chromatography (HPLC) pigment database was analyzed. It includes 2419 vertical pigment profiles, sampled in case 1w aters with various trophic states (0.03-6 mg Chla m À 3 ). The relationships between [Chla ] surf and the chlorophyll a vertical distribution, as previously derived by Morel and Berthon (1989), are fully confirmed. This agreement makes it possible to go further and to examine if similar relationships between [Chla ] surf and the phytoplankton assemblage composition along the vertical can be derived. Thanks to the detailed pigment composition, and use of specific pigment biomarkers, the contribution to the local chlorophyll a concentration of three phytoplankton groups can be assessed. With some cautions, these groups coincide with three size classes, i.e., microplankton, nanoplankton and picoplankton. Corroborating previous regional findings (e.g., large species dominate in eutrophic environments, whereas tiny phytoplankton prevail in oligotrophic zones), the present results lead to an empirical parameterization applicable to most oceanic waters. The predictive skill of this parameterization is satisfactorily tested on aseparate data set. With such atool, the vertical chlorophyll a profiles of each group can be inferred solely from the knowledge of [Chla ] surf .B yc ombining this tool with satellite ocean color data, it becomes possible to quantify on ag lobal scale the phytoplankton biomass associated with each of the three algal assemblages.

Variability in the chlorophyll (chl) a-specific absorption coefficients of living phytoplankton a•h(A) was analyzed using a data set including 815 spectra determined with the wet filter technique in different regions of the world ocean (covering the chlorophyll concentration range 0.02-25 mg m-3). The a* ph values were observed to decrease rather regularly from oligotrophic to eutrophic waters, spanning over more than 1 order of magnitude (0.18 to 0.01 m 2 mg -1) at the blue absorption maximum. The observed covariation between a•h(A) and the field chl a concentration (chl} can be explained considering (1) the level of pigment packaging and (2) the contribution of accessory pigments to absorption. Empirical relationships between a•h(A ) andwere derived by least squares fitting to power functions. These relationships can be used to produce a ph spectra as a function of (chl}. Such a simple parameterization, if confirmed with further data, can be used, e.g., for refining estimates of the carbon fixation rate at global or regional scales, such as those obtained by combining satellite pigment concentration maps with primary production models based on physiological parameters among which a* , ph is an important one. R(A) = Fbb(A)/a(A ) where a and bb are, respectively, the absorption and backscattering coefficients of the water body, and the dimensionless number F depends, in particular, on the volume scattering function within water [Prieur and Morel, 1975] and on the geometrical structure of the incident light field [Kirk, 1984; Gordon, 1989; Morel and Gentili, 1991]. Analytical models of the phytoplankton growth and primary production also basically rely on the in vivo absorption capacity of living algal cells [Kiefer and Mitchell, 1983; Platt and Sathyendranath, 1988; Morel, 1991; Anderson, 1993], namely, on the absorption coefficients of phytoplankton per unit of chlorophyll (chl) a concentration ("chl a-specific" coefficients or, equivalently, absorption cross sections of algae per mass unit of chl a hereafter denoted a* , ph ('•) and expressed as m 2 mg chl a-•). Such models, combined with satellite data, have been recently used to convert maps of surface pigment concentration into maps of the carbon fixation rate at global or regional scales [e.g., Morel and Andre, 1991]. Up until now, in the application of these models (with the exception of that of Platt and Sathyen-Paper number 95JC00463. 0148-0227/95/95JC-00463 $05.00 dranath [1988]) a* (A) coefficients have been assumed as , ph constant, whatever the water type, and values considered as "typical" have been introduced. These coefficients, however, are now widely recognized as varying, not only for individual species grown in culture, but also for natural phytoplanktonic assemblages [e.g., Mitchell and Kiefer, 1988b; Bricaud and Stramski, 1990]. These variations result from the combined influences of the pigment composition [Bidigare et al., 1990; Hoepffner and Sathyendranath, 1992] and the so-called "package effect" [Kirk, 1975]. The latter, as predicted by...

The aim of the present study is to review and tentatively to interpret the optical behavior of oceanic case I waters, those waters for which phytoplankton and their derivative play a predominant role in determining their optical properties. Chlorophyll‐like pigment concentration is used as the index to quantify the algal material (living and detrital), and statistical relationships between this index and the depth of the euphotic layer, the spectral values of the attenuation coefficient for downwelling irradiance, or the scattering coefficient are investigated. On the basis of these statistical relationships a pigment‐dependent optical model is developed. It allows the propagation of the visible radiant energy within the ocean or the backscattered radiation from the upper layer to be predicted as a function of the local phytoplanktonic content. Other geophysical or geochemical applications are derived which concern the heating rate due to penetrating visible radiations or the rate of energy storage due to photosynthesis. The nonlinear trends observed in the algal biomass‐attenuation relationships are analyzed by (1) considering the rather regular change of the living‐to‐detrital organic carbon ratio which seems to occur in oceanic waters ranging from oligotrophic to eutrophic, and (2) accounting for the respective contributions of absorption (by pigmented cells) and of scattering (by all kind of particulates) in the attenuation process of radiant energy.

Abstract. The apparent optical properties (AOPs) of oceanic case 1 waters were previously analyzed [Morel, 1988] and statistically related to the chlorophyll concentration ([Chl]) used as a global index describing the trophic conditions of water bodies. From these empirical relationships a bio-optical model of the upper layer was developed. With objectives and structure similar to those of the previous study the present reappraisal utilizes AOPs determined during recent Joint Global Ocean Flux Study cruises, namely, spectral attenuation for downward irradiance Kd(X) and irradiance reflectance R(X). This revision also benefits from improved knowledge of inherent optical properties (lOPs), namely, pure water absorption coefficients and particle scattering and absorption coefficients, and from better pigment quantification (via a systematic use of highperformance liquid chromatography). Nonlinear trends, already observed between optical properties and algal biomass, are fully confirmed, yet with numerical differences