Relationships between picophytoplankton and optical properties in the Azores Front region in the Atlantic Ocean |
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| Institution: | 1. Department of Hydrobiology, Inland Fisheries Institute, Oczapowskiego 10, 10-719 Olsztyn, Poland;2. Department of Water Protection Engineering, University of Warmia and Mazury in Olsztyn, Prawocheńskiego 1, 10-719 Olsztyn, Poland;3. Department of International Public Law, University of Warmia and Mazury in Olsztyn, Warszawska 98, 10-702 Olsztyn, Poland;1. Faculty of Sciences and Technology, University of the Azores, 9501-801, Ponta Delgada, Portugal;3. CE3C – cE3c, Centre for Ecology, Evolution and Environmental Changes /Azorean Biodiversity Group, University of the Azores, 9501-801, Ponta Delgada, Azores, Portugal;4. University of Albany – Department of Environmental Health Sciences, University at Albany School of Public Health One University Place, Rm 153, Rensselaer, NY, 12144-3456, USA |
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| Abstract: | The picophytoplankton evolved to become extremely effective harvesters of light and, thus, dominating productivity in the open ocean. In this study, their distribution in relation to the underwater light field was examined in the Azores Front region of the North Atlantic. In this region, attenuation coefficients of downward irradiance varied between 0.038 and 0.065 m? 1. Maximum absorptions were at the red and green parts of the light spectrum, typical of the oligotrophic ocean. The euphotic zone ranged from 70 to 120 m. The deep chlorophyll maximum (DCM) was found at depths where subsurface light ranged between 0.1 and 1% of its surface values. Prochlorococcus was the dominant phytoplankton group while Synechococcus (cyanobacteria) and picoeukaryotes were much less abundant. The ability of chlorophyll to absorb light, i.e., the absorption coefficient of chlorophyll (a?), was found to be dependent on the photoacclimation of the cells and was lower at low-light intensities. Due to a packaging effect and probable pigment changes, a? at the DCM was the lowest while the chlorophyll per Prochlorococcus cell was the highest. This is a major adaptation of the picophytoplankton to low light (less than 1% surface light), which allows them to bloom at the DCM. This study indicates that the Atlantic Ocean models for the estimation of phytoplankton concentration and/or primary production should not use a constant carbon biomass-to-chlorophyll ratio for phytoplankton based on phytoplankton size, and should take into account the variation in chlorophyll-absorption ability. |
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