Analysis of Radiative Forcing Effects by Oceanic Phytoplankton and Spatiotemporal Variation during 2001–10

Phytoplankton may affect the radiation budget in the atmosphere-ocean coupled system by altering the ocean surface albedo (OSA) caused fundamentally by the variation of the inherent optical properties of seawater. This study aims to assess the radiative forcing effect caused by phytoplankton and to analyze long-term radiative forcing changes from reconstructed OSA scheme data sets for a period of 2001 — 2010, on a global scale. Using a GCM version of high accuracy, rapid radiative transfer model (RRTMG) and chlorophyll concentration images from NASA’s Ocean Color Web, we compute the radiative forcing by phytoplankton and discuss its magnitude and variability, as well as consequences on climate. Results show that phytoplankton leads to a negative radiative forcing values, which is lower over the high latitude oceans and the coastal regions as OSA values are higher in those areas. Spatial and temporal variability of the forcing is affected by phytoplankton concentration, and seasonal variations of radiative forcing in those regions are found to be larger in spring, which may associate with the OSA fluctuations resulted from the biomass level (e.g., phytoplankton bloom). By analyzing the time series of radiative forcing in 16 years, the present analyses reveal that interannual to decadal phytoplankton radiative forcing fluctuations decrease on long-term trends linking to phytoplankton concentration variations, which generally related to climatic and oceanographic variability over the past years. Essentially, the radiative forcing from phytoplankton should be taken into account explicitly in climate studies for a better estimation of radiation budget in the atmosphere-ocean coupled system.