Sensitivity of a 3D-model biogeochemistry to ocean physics forcing frequency 

<p>The frequency of ocean dynamics model output forcing transport-biogeochemical models in off-line coupling configuration can be a critical aspect when mesoscale and high variability dynamics are simulated. In the present work, the sensitivity of ocean dynamics frequency on biogeochemistry is evaluated for the Copernicus Mediterranean Sea forecasting system.</p> <p>The current off-line coupling strategy between Med-BIO and Med-PHY (respectively, biogeochemical and physical components of the Mediterranean Sea operational system embedded in the Copernicus Marine Service) is based on the forcing of daily mean fields (3-D potential temperature, salinity, current velocity, vertical eddy viscosity, and 2-D wind stress, sea surface height) produced by the hydrodynamic component based on the coupled NEMO-WW3 modeling system including the OceanVar 3DVAR data assimilation model. The daily means are then linearly interpolated to extract data at higher temporal frequency (30 minutes), which are then used by the MedBFM system, through the OGSTM model, to transport (via advection and diffusion) the biogeochemical tracers (e.g. nutrients). The biogeochemical reactions are then computed by the Biogeochemical Flux Model (BFM).</p> <p>In the present work the outputs of 1-year long runs (year 2019) produced by the OGSTM-BFM off-line coupled with NEMO-OceanVar using physical forcing at different temporal frequencies, 6-hr, 4-hr, 2-hr averages, are evaluated comparing them with a run forced by the conventional 24-hr average. The sensitivity of the high frequency forcing, which is basically related to a finer temporal resolution of the physical processes acting on the vertical dimension, indeed reduces the approximation related to the daily averaging and is investigated and discussed measuring the impact on the biogeochemical product quality. Improvements in the western Mediterranean area and Ionian Sea, especially during the winter season, are observed: this corroborates the fact that induced higher variability of dynamical processes is important for the quality of biogeochemical variables.</p>