PRIMARY PRODUCTIVITY II

LIGHT-DRIVEN CARBON FLUXES IN THE ARCTIC OCEAN: THE BALANCE BETWEEN PHOTO-OXIDATION AND PHOTOSYNTHESIS IN THE CONTEXT OF CLIMATE CHANGE

Simon, Bélanger¹; Babin, Marcel<sup>2

1</sup>Département de biologie, chimie et géographie, Université du Québec à Rimouski, Rimouski, Québec, G5L 3A1, Canada; ²CNRS - Villefranche LOV, BP 8, Villefranche-sur-Mer Cedex, --, 06238, France

Primary production and CDOM photo-oxidation have opposing impacts on carbon fluxes in the ocean. The balance between the two processes may be significantly affected in the near future by climate change. This is especially true for the Arctic Ocean, which is increasingly exposed to light as perennial ice recedes, and which receives increasing amounts of terrigenous dissolved organic matter (tDOM) as the permafrost thaws and river discharges increase. In this study, we used remote sensing data to estimate the pan-Arctic distributions of primary production and CDOM photo-oxidation, and how they evolved from 1998 to now. Ocean color (merged data from SeaWiFS, MERIS and MODIS), ozone, cloud (ISCCP) and ice (SSMI) data are combined to run a UV-visible atmospheric radiative transfer code, and primary production and photo-oxidation models. We used state-of-the-art optical models for Case 2 waters, some being specific to the Arctic Ocean. A sensitivity analysis is conducted to assess the impact of chosen ocean color algorithms and of various model parameters on results. Our results provide the first pan-Arctic combined estimates of primary production and CDOM photo-oxidation based on remote sensing, and allow determining how these two processes compare. They indicate that CDOM photo-oxidation accounts for a major fraction of allochthonous organic carbon mineralization in the Arctic Ocean, and is comparable in magnitude to the fraction of gross primary production that ends up sequestered within the ocean bottom sediments. The ratio between photo-oxidation and primary production turns out being highly variable, which indicates significant competition for light between CDOM and phytoplankton. As a response to sea ice decline, both photo-oxidation and primary production showed increasing trends from 1998 to 2007. We speculate that the increasing photomineralization of tDOM is boosting the productivity of whole microbial communities and the food-web dynamics of the Arctic Ocean coastal.

VARIATIONS OF PHOTOACCLIMATION RELATED TO ENVIRONMENTAL CONDITIONS

Comeau, Adam Joseph¹; Craig, Susanne¹; Babin, Marcel²; Lewis, Marlon¹; Bruyant, Flavienne¹; Cullen, John<sup>1

1</sup>Dalhousie University 1355 Oxford street, Department of Oceanography, Dalhousie University, Halifax, NS, B3H4J1, Canada; ²Laboratoire d’Océanographie de Villefranche, Villefranche-sur-Mer, France, 06238, France

By understanding factors that influence parameters related to photosynthesis, better estimates of primary productivity and particle dynamics can be obtained. We describe a new method to estimate photoacclimation, a physiological process that influences both photosynthesis vs. irradiance (P vs. E) parameters and chemical composition of phytoplankton, based on profiles of in situ fluorescence and irradiance and apply it to a variety of datasets collected all over the world, to examine its variability in relation to environmental variables. Profiles of in situ chlorophyll fluorescence have been routinely measured during oceanographic surveys for several decades. Near surface decreases of fluorescence yield, chlorophyll fluorescence normalized to some measure of phytoplankton biomass, are commonly observed during daytime profiles. This decrease in fluorescence is due to physiological processes, activated in high irradiance, which act to dissipate light energy absorbed by phytoplankton. Lab studies show that the irradiance at which this quenching of fluorescence yield begins is related to the light saturation parameter, of P vs E curves. With the simple requirements of irradiance and fluorescence yield profiles, this method can be applied to many existing datasets. Examining variations of the light level where fluorescence quenching begins in response to environmental variables such as average light in the mixed layer, will provide new information on how phytoplankton acclimate to their environment.

VARIABILITY IN THE DISTRIBUTION OF CHLOROPHYLL-A AND PRIMARY PRODUCTION IN THE ARGENTINE SEA USING FIELD AND SATELLITE ESTIMATIONS

Lutz, Vivian¹; Segura, Valeria¹; Dogliotti, Ana Ines²; Gagliardini, Domingo Antonio²; Bianchi, Alejandro³; Balestrini, Carlos<sup>3

1</sup>INIDEP Paseo Victoria Ocampo Nº 1, Mar del Plata, --, B7602HSA, Argentina; ²Instituto de Astronomía y Física del Espacio (IAFE-CONICET), Pabellón IAFE-Ciudad Universitaria , C.C. 67- Suc. 28, Buenos Aires , Buenos Aires, 1428, Argentina; ³Departamento Oceanografía, Servicio de Hidrografía Naval, Av. Montes de Oca 2124, Buenos Aires, Buenos Aires, 1271, Argentina

The Argentine Sea, specially its extended shelf-break, appears as one of the most brightly colored areas in satellite images of chlorophyll-a (chla). This is indeed an area rich in marine resources, such as commercial fish, marine mammals, and seabirds. Scarce field programs have been performed to study in more detail the productivity of this region. A project to study chla distribution, optical properties, and primary production involving three cruises (during spring, summer, and winter) in an extensive area of the Argentine Sea was carried out in the period 2005-2006. We show here the wide spatial and temporal variability found in the chla distribution during these cruises. We focus then in the spatial variability observed during spring 2005 in the chla concentration, the [chla/in vivo-fluorescence] ratio, and the primary production. At this period strong phytoplankton blooms had developed in some areas, with surface chla concentrations and integrated production that ranged from ~ 0.40 to 28.00 mg m^-3 and from ~ 275 to 5477 mg C m^-2 d^-1, respectively. The [chla/in vivo-fluorescence] ratio at the surface showed also a variation of two orders of magnitude. These results indicate the extreme variations in environments and phytoplankton diversity of this region of the South West Atlantic. As a first approach we compare and discuss differences encountered between field and satellite (using a standard algorithm with fixed parameters) estimations of primary production.