Effects of Fluorescence Self Absorption of Algae in Sea Water Candy Barbaran Annie Becerra Mentors: Prof. Fred Moshary Dr. Alex Gilerson NYCRI C N p

Background Satellite imagery of ocean color provides important information about water quality and composition. Abundance of phytoplankton (algae) in the ocean can be traced by Chlorophyll A concentration which exists in all types of algae and has distinct spectral features. Part of the light energy absorbed by algae in blue- green emits in the red as chlorophyll fluorescence. Chlorophyll fluorescence is a vital parameter which can be considered as an indicator of chlorophyll concentration and photosynthetic activity in the ocean.

Analyze the spectral shape of chlorophyll fluorescence and absorption in order to detect patterns in the fluorescence spectral shift - detecting patterns in the spectral shift will allow us to eliminate all other factors and measure pure fluorescence. Goal Improve algorithms for instruments aboard satellites in order to make fluorescence measurements of algae more accurate. Purpose of the experiment

Water Composition for Open Ocean and Coastal Waters Algae Colored Dissolved Organic Matter (CDOM) Minerals Open oceanCoastal waters

Challenges of Using Chlorophyll Fluorescence Methods For Algae Detection Fluorescence overlaps with the other spectral features. Special algorithms are needed to separate fluorescence from self absorption and elastic reflectance. Sea surface Algae Depth

Fluorescence Magnitude and Peak over Baseline Reflectance of the sun Reflectance of the sun with fluorescence Reflectance= Eu/Ed~b b /a

WET Labs AC-S Instrument The AC-S instrument measures absorption and attenuation at 82 wavelengths from 400 to 750 nm

Algae absorption measured by WET Labs ACS instrument There is strong algae absorption in the fluorescence zone which causes change of fluorescence spectra

Changes of the fluorescence spectral shape due to algae absorption Fl(λ)~(1/r2)*Fl0(λ)*exp(-a(λ)*h) Spectrometer FP Laser light from argon laser λ = 488 nm h r

Experimental Setup for the Measurements of Fluorescence Spectral Shape Objects tested: algae Isochrysis sp., Tetraselmis striata, concentrations up to 4x10 6 cells/mL with necessary dilutions Algae are illuminated by the laser light at different depths. Emitted fluorescence is partially absorbed during propagation through algae. Spectral shape of fluorescence is measured by fiber optic sensor connected to the Ocean Optics spectrometer Spectrometer FP Laser light from argon laser λ = 488 nm

Shift of fluorescence of Algae Isochrysis as a function of depth under 488nm excitation Fluorescence spectra for different excitation depths Shift of fluorescence maximum for various excitation depths Algae absorption peak

Shift of Fluorescence of Tetraselmis striata as a function of Depth under 488 nm excitation Fluorescence spectra for different excitation depths. Shift of fluorescence maximum for various excitation depths

Conclusions Both types of algae in the original concentration have strong absorption and cause spectral shift of fluorescence This spectral shift should be taken into account in the analysis of fluorescence and reflectance data for the waters with high chlorophyll (algae) concentrations

Further Work After accounting for absorption and attenuation we can graph pure fluorescence. Compare pure fluorescence results from the experiment to the calculated ones using Matlab software

Acknowledgements Dr. Alex Gilerson Professor Fred Moshary NASA-NYCRI