Poster Session 2, Tuesday,  October  4, 10:40–12:40

Poster 6

Diel Variability in Phytoplankton Backscattering and Cell Composition

Photons scattered by particles in the backwards direction (bbp) have the potential to leave the ocean surface and be detected by remote sensing. To first order, bbp is a proxy for particle abundance, but it is also dependent on particle refractive index (i.e., morphology and composition). Global bbp has been reported to vary over diel timescales, decreasing from day to night. Phytoplankton contribute to these diel variations of bbpas they increase their size and organic carbon content during the day and then divide and respire at night. However, the ability to constrain the contribution of phytoplankton to diel variability in bbp is complicated by the uncertainty in the backscattering efficiency of individual cells and how that efficiency varies by species, cell morphology, and composition. Here we report results from laboratory culture experiments that provide the first characterization of phytoplankton bbp over complete diel cycles for two different species, Thalassiosira pseudonana and Synechococcus spp., grown under three different photoperiods. To describe how bbp is influenced by changes in phytoplankton cell composition over the day-night cycle, we synthesized particulate absorption, attenuation, and scattering measurements collected using a WET Labs AC-S and ECO-BB3, along with measurements of cell stoichiometry (i.e., C:N), cell composition (i.e., lipids: proteins: carbohydrates), and photophysiology. This work helps to strengthen interpretations of diel patterns in bbp observed from remote sensing.

Nicholas Baetge, Oregon State University, [email protected], 0000-0002-3868-9857

Kimberly Halsey, Oregon State University, [email protected]

Amanda Appel, Oregon State University, [email protected]

Charlotte Begouen Demeaux, University of Maine, [email protected]

Emmanuel Boss, University of Maine, [email protected]

Guillaume Bourdin, University of Maine, [email protected]

Jason Graff, Oregon State University, [email protected]

Amelia Noall, Oregon State University, [email protected]

Toby Westberry, Oregon State University, [email protected]

Brian VerWey, Oregon State University, verweyb[email protected]

Michael Behrenfeld, Oregon State University, [email protected]

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