In this work, It was found that in addition to radiance differences between summer and winter, there are differences in the quality and quantity of available light energy to photosynthesis. Those differences are related to the changes in phytoplankton biomass and of phytoplankton pigments. Our goals in this work were: To follow seasonal changes in abiotic factors and in phytoplankton quality and composition. To examine the relationships among optical properties of the Gulf of Eilat, algal concentrations, and the composition of photosynthetic pigments. To determine the annual course and bathymetric distribution of primary production. Link between phytoplankton taxa and their photosynthetic activity and to understand the connections between underwater spectral irradiance, phytoplankton pigments and photosynthesis over the depth profile.
Kd (PAR) values are low in comparison to other waters (0.03-0.06 m-1), and show a high dependence on pigment concentrations and depth. 1% of UV penetrates to 69m depth, and more than 90% of red light are absorbed in the first 10m.
In the Gulf of Elat we can see both latitudinal and longtitudial gradients in light field, phytoplankton characteristics composition, and pigment concentration. Integrated primary production values per water column till 100m depth were: 19-36 mgC m-2 h-1 , with the high values measured in winter, In summer Pmax is found deeper, 40-60m (18.6.96) while in winter it is close to the surface. Primary production values in yearly average are 103 gC m-2 y-1, this result locates the Gulf of Eilat among moderate oligotrophic waters. Quantum yields (max) were measured increased with depth, from 0.00025 at the surface to 0.110 in 80m depth. In addition, we find seasonal changes in max,; in summer low values as a result of low nutrient levels, and high values as the water is mixed and nutrients abound. photoacclimation to light intensity in the environment can be seen in all phytoplankton groups in their distributions in the water column.
From reflectance ratios, at the same wavelengths used in remote sensing, we can estimate chlorophyll concentration quite precisely. Best fit function for 1995-96 observation (1994 was quite different) is:
Chl = 0.644* (R440/R550)-1.199
the correlation was r2=0.69 with coeff. var.= 0.03 mg chl m-3.
Therefore, reflectance as we calculated in this work, Kd values from field work, a* data, and the measured photosynthesis parameters; Pmax, Ik and max are very important, because they complement the satellite data alow the development of improved algorithms for more precise estimation of global primary production.