BIO-OPTICS AND BIOGEOCHEMISTRY I

THE GSM BIO-OPTICAL MODEL: ACHIEVEMENTS AND RECENT DEVELOPMENTS

Maritorena, Stéphane¹; Siegel, David¹; Babin, Marcel²; Hembise Fanton d'Andon, Odile³; Huot, Yannick²; Mangin, Antoine<sup>3

1</sup>ICESS/UCSB ICESS - University of California Santa Barbara, Santa Barbara, CA, 93108, United States; ²Laboratoire d'Océanographie de Villefranche, B.P. 8, Villefranche-sur-Mer, Cedex, 06238 , France; ³ACRI-ST, 260 route du Pin Montard, B.P. 234, Sophia Antipolis, Cedex, 06904 , France

The GSM (Garver-Siegel-Maritorena) model is a semi-analytical bio-optical model that allows the retrieval of oceanic inherent optical properties (IOP) and of the sub-surface chlorophyll concentration from spectral measurements of the water-leaving radiance in bands similar to those of the current ocean color satellite sensors. In recent years, the model and its derived products have been used successfully to address various aspects of ocean color or ocean biogeochemistry using both in situ and satellite data. Two of these applications are presented here: the merging of ocean color data originating from different satellites sensors and the use of the model outputs in ocean biogeochemistry. The recent availability of new, high quality, in situ measurements and improved computational power allow for several improvements of, or new developments to, the GSM model. This includes improved parameterization, the use of red bands in coastal waters, the addition of a fluorescence module and the retrieval of additional variables. Results and examples of these recent developments using in situ and satellite data are also presented.

GLOBAL ANALYSIS OF PHYTOPLANKTON PHYSIOLOGY USING SATELLITE CHLOROPHYLL FLUORESCENCE

behrenfeld, michael¹; Westberry, Toby¹; Boss, Emmanuel²; O'Malley, Robert¹; Wiggert, Jerry³; Siegel, David⁴; Franz, Bryan⁵; McClain, Chuck⁵; Feldman, Gene⁵; Dall'Olmo, Giorgio¹; Milligan, Allen¹; Doney, Scott⁶; Moore, Kieth⁷; Lima, Ivan⁶; Mahowald, Natalie<sup>8

1</sup>Oregon State University Cordley Hall 2082, Corvallis, OR, 97331, United States; ²University of Main, Orono, Maine, 04469, United States; ³University of Mississippi, Stennis , Mississippi, 39529, United States; ⁴University of California, Santa Barbara, Santa Barbara, California, 93106, United States; ⁵NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771, United States; ⁶Woods Hole Oceanographic Institute, Woods Hole, Massachusetts, 02543, United States; ⁷University of California, Irvine, Irvine, California, 92697, United States; ⁸Cornell University, Cornell, New York, 14850, United States

Chlorophyll fluorescence from surface ocean phytoplankton has been monitored from space since 2002. Here we provide a global analysis of these data and show that the three primary factors influencing fluorescence distributions are phytoplankton pigment concentrations, pigment-packaging effects on light absorption efficiencies, and a globally-expressed physiological response aimed at protecting photosynthesis from high-light damage. Adjusting satellite fluorescencedata for these three factors, we derive global distributions of fluorescence quantum yields that reveal additional information on phytoplankton physiology and appear particularly sensitive to iron-stress conditions. Our resultsidentify satellite fluorescence observations as an important new global tool for resolving climate-phytoplankton interactions, testing nutrient-stress predictions of ocean ecosystem models, detecting phytoplankton responses to iron enrichments, and improving estimates of ocean photosynthesis

SEASONALITY OF SURFACE CHLOROPHYLL CONCENTRATION: A PROXY TO CHARACTERIZE PHYTOPLANKTON TROPHIC REGIMES

D'Ortenzio, Fabrizio¹; Antoine, David¹; Martinez, Elodie ¹; Ribera d'Alcala, Maurizio<sup>2

1</sup>CNRS Quai de la Darse, Villefranche sur mer, --, 06230, France; ²Stazione Zoologica Napoli “A. Dohrn”, Villa Comunale, Naples, NA, 80121, Italy

A primary goal of biological oceanography is the determination of the relative importance of the environmental (i.e. physical, chemical) and biological (i.e. species composition, grazing, nutrients uptake) forcing factors on the phytoplankton evolution. The separation of the impact of the different forcing factors is however not trivial, as they act on the biomass at different temporal and spatial scales. The main consequence is that the seasonal evolution of the phytoplankton shows a large spectrum of trends. In this sense, it could be interpreted as an indicator of a specific trophic regime.

Ocean color satellites offer more than 10 years of continuous and high-resolution observations of the surface oceanic chlorophyll concentration. In addition, CZCS data, recently reprocessed to be coherent with more modern sensors, allow estimating chlorophyll concentration for the period 1979-1983. We used these data to determine oceanic regions showing similar seasonal trends in the surface chlorophyll concentration. The main hypothesis here is that similarity in the seasonal trend indicates similarity in the forcing factors.

To generalize the approach, we produced a climatological weekly data set from ocean color data, we normalized, on a pixel-by pixel basis, each curve with his absolute maximum, and finally we applied a K-means cluster analysis. Each pixel was then classified on the basis of his seasonal courses of chlorophyll concentration and pixels exhibiting similar characteristics have been grouped together.

The method has been applied to the Mediterranean Sea ocean color observations from both the SeaWiFS and the CZCS sensors (using the Antoine et al., JGR, 2005, coherent data set). A first attempt at global scale and on an interannual scale has been also performed.

COVARIABILITY OF CHLOROPHYLL AND SEA SURFACE TEMPERATURE AT GLOBAL AND DECADAL SCALES

Martinez, Elodie¹; Antoine, David¹; D'Ortenzio, Fabrizio<sup>1

1</sup>CNRS LOV, Villefranche sur mer, --, 06230, France

A comprehensive and consistent reprocessing of the CZCS and SeaWiFS data sets was previously performed (Antoine et al., JGR, 2005), in order to investigate the decadal changes in the global ocean chlorophyll (Chl). This global reanalysis showed an average increase of Chl by ~20%, with a high spatial heterogeneity (regions of increase and decrease of Chl) and significant changes of the Chl seasonal cycles in many areas.

We now analyze these decadal changes in the global ocean phytoplankton in parallel to their forcing variables. In a first step, the SST variability was investigated for the same time period, using the Reynolds reanalyses. Then, we performed Multivariate EOF (MEOF) analyses on both the seasonal and non seasonal signal components, in order to study the spatial and temporal covariability between Chl and SST, and to identify the origin of the Chl changes.

Our results show that, at global scale, the Chl decadal changes are largely explained by the first mode of the non-seasonal components. The principal component (PC) of this first mode exhibits a similar time evolution than the Multivariate ENSO Index (MEI). Anti-correlation of Chl and SST is frequently observed.

When the MEI and the PC are analyzed at global scale, the similarity of their temporal signals is, however, essentially driven by the signal from the Pacific Ocean, due to its large area and to the strong signal of the Pacific Decadal Oscillation. Therefore, we did additional MEOF analyses separately for each ocean. They show that the Chl changes observed in our 20-year ocean color record essentially result from basin-scale low-frequency natural oscillations.

Other parameters which are likely to have played a role in the evolution of the total phytoplankton biomass (irradiation, wind…) over the last two decades will have to be investigated in parallel to SST.