Abstract
Abstract. Data assimilation has led to advancements in biogeochemical modelling and scientific understanding of the ocean. The recent operational availability of data from BGC-Argo (biogeochemical Argo) floats, which provide valuable insights into key vertical biogeochemical processes, stands to further improve biogeochemical modelling through assimilation schemes that include float observations in addition to traditionally assimilated satellite data. In the present work, we demonstrate the feasibility of joint multi-platform assimilation in realistic biogeochemical applications by presenting the results of 1-year simulations of Mediterranean Sea biogeochemistry. Different combinations of satellite chlorophyll data and BGC-Argo nitrate and chlorophyll data have been tested, and validation with respect to available independent non-assimilated and assimilated (before the assimilation) observations showed that assimilation of both satellite and float observations outperformed the assimilation of platforms considered individually. Moreover, the assimilation of BGC-Argo data impacted the vertical structure of nutrients and phytoplankton in terms of deep chlorophyll maximum depth, intensity, and nutricline depth. The outcomes of the model simulation assimilating both satellite data and BGC-Argo data provide a consistent picture of the basin-wide differences in vertical features associated with summer stratified conditions, describing a relatively high variability between the western and eastern Mediterranean, with thinner and shallower but intense deep chlorophyll maxima associated with steeper and narrower nutriclines in the western Mediterranean.
Highlights
In recent years, biogeochemical modelling has significantly contributed to the knowledge of key aspects of marine ecosystem processes at both local and global scales (Fennel et al, 2019)
We demonstrate the feasibility of joint multi-platform assimilation in realistic biogeochemical applications by presenting the results of 1-year simulations of Mediterranean Sea biogeochemistry using the MedBFM (Mediterranean biogeochemical flux model) system that includes the OGSTM-BFM is designed with a transport model (OGSTM) and the low-trophic-level BFM (Salon et al, 2019) offline coupled with the NEMO-OceanVar
The Mediterranean Sea biogeochemistry was simulated for 1 year (2015) with four different assimilation set-ups and a reference run without assimilation using the MedBFM model system that is operationally implemented in the Copernicus Marine Environment Monitoring Service (CMEMS) and provides nominal biogeochemical products for the Mediterranean Sea (Bolzon et al, 2020; Salon et al, 2019)
Summary
Biogeochemical modelling has significantly contributed to the knowledge of key aspects of marine ecosystem processes at both local and global scales (Fennel et al, 2019). Observations can be sparse and unevenly distributed in time and space (in situ), limited to the ocean surface (satellite remote sensing) and generally affected by calibration and measurement errors (Bittig et al, 2019; Xing et al, 2020). The assimilation of satellite ocean-colour observations has been successfully applied in research and operational applications at both global and regional scales (Fennel et al, 2019; Groom et al, 2019).
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