Ocean Turbidity Feedback in a Coupled Ocean-Atmosphere Model for the
Mediterranean and Black Seas
Abstract
Ocean water turbidity, influenced by marine chlorophyll concentration,
significantly alters the distribution of shortwave radiation in the
water column. This work aims to assess the effects of turbidity on the
upper-ocean physical properties and their subsequent impact on the
atmosphere, using a coupled ocean-atmosphere regional model for the
Mediterranean and Black Seas. We performed 11-year (2011-2021)
twin-simulation experiments, based on different chlorophyll
concentrations to estimate turbidity and the penetration of solar
radiation in the ocean. The first simulation used a monthly climatology
field of chlorophyll concentrations derived from satellite observations,
whilst in the second experiment, the chlorophyll concentration was kept
constant at 0.05 mg m−3, representing clear water turbidity conditions.
Results show that radiative heating driven by ocean turbidity amplifies
the seasonal cycle of temperature in the upper layers, leading to
increased surface warming in summer and surface cooling in winter. Also,
higher turbidity contributes to cooling in subsurface layers throughout
the year due to its shading effect. The temperature response to
turbidity in the water column is controlled by the mixed layer depth and
a balance between (1) direct near-surface radiative heating due to
chlorophyll solar absorption, and (2) indirect cooling resulting from
vertical turbulent mixing processes with subsurface waters. The
atmosphere moderates the seasonal sea surface temperature (SST) response
to turbidity, primarily through changes in latent heat flux. Ultimately,
our simulations suggest that increased turbidity enhances the
Mediterranean overturning circulation, highlighting the necessity of
incorporating realistic turbidity forcing into regional climate modeling
studies.