Quantifying the Effects of Phytoplankton Self-shading on Ocean Heating and Circulation with BGC Argo

Rosalind Echols, University of Washington Seattle, School of Oceanography, Seattle, WA, United States and Stephen Riser, University of Washington, School of Oceanography, Seattle, WA, United States
Abstract:
It has been well-established that the presence of upper-ocean phytoplankton affects heating of the ocean by solar radiation, and that the choice of parameterization for the absorption of solar radiation by phytoplankton in models therefore has implications for sea surface temperature and mixed layer depth. Studies have also shown that secondary effects on ocean circulation and sea ice cover may also result from the choice of parameterization. However, accounting for self-shading by phytoplankton in coupled physical-biogeochemical models requires more computational power than simple exponential parameterizations, and may not be necessary everywhere in the ocean. Here we use simple one-dimensional models and Argo biogeochemical floats equipped with sensors measuring chlorophyll fluorescence and optical backscatter to quantify the impact of phytoplankton self-shading on water column absorption of solar radiation and the resulting changes to the physical system. We identify the regions where this is most likely to be an important effect and explore seasonal variability within those regions. We examine the temporal and spatial scales of variability associated with changes to the vertical phytoplankton distribution and discuss the applications both to mixed layer heat budgets as well as parameterization of solar radiation in modeling studies.