POSTER SESSION 2
10:30–12:30, Tuesday, September 15
Poster Session | 1 | 2 | 3 | 4 | Schedule at a Glance
ABSTRACT 1204 | POSTER 94
RECONCILING MODELED AND OBSERVED WATER-COLUMN PAR BEHAVIOR
The vertical distribution of water-column light regulates biological productivity and shapes marine ecosystems. Photosynthetically available radiation (PAR), or the light supporting photosynthesis, penetrates to depth depending on the quantity and direction of solar flux transmitted through the air-water interface, as well as the attenuation profile of the water and its constituents. The Beer-Lambert equation, which describes the log-linear extinction of monochromatic flux passing through a homogeneous medium, is theoretically ill-suited for describing PAR attenuation in aquatic environments: biogeochemistry is vertically heterogeneous, PAR integrates a polychromatic flux, and scattering modifies the isotropy and spectral quality of the flux with depth. Radiative transfer modeling of water columns with idealized or empirical (e.g., chlorophyll-based) profiles produces nonlinear PAR attenuation: as the spectral centroid of downwelling flux shifts with depth towards less-attenuated wavelengths (e.g., deeper oligotrophic waters become bluer), PAR penetration systematically deepens relative to that predicted by PAR attenuation nearer the surface. We reexamine these model predictions using five independent radiometric datasets and find that, although PAR attenuation profiles exhibit variable structure, Beer-Lambert approximates observed relationships between the diffuse attenuation coefficient of PAR and the positioning of decadic light-level depths, e.g., the euphotic depth. Biogeochemical mechanisms—including phytoplankton distribution and photoacclimation, which can increase blue absorption—modify water-column light attenuation toward log-linear behavior relative to idealized or empirical model water columns. These findings suggest an emergent simplicity in aquatic light environments analogous to the Monsi–Saeki theory in terrestrial plant canopies, wherein log-linear extinction approximates observations despite inherent complexity in the organization of photosynthetic and non-photosynthetic tissues.
Henry Houskeeper, Woods Hole Oceanographic Institution, [email protected], https://orcid.org/0000-0001-5848-5440
Stanford Hooker, Independent Researcher, [email protected]
Raphael Kudela, University of California Santa Cruz, [email protected]
Koji Suzuki, Hokkaido University, [email protected]
Charlotte Begouen Demeaux, University of Maine, [email protected]
Poster Session | 1 | 2 | 3 | 4 | Schedule at a Glance
