Monitoring the Environment in the Northwestern Mediterranean Sea

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The Mediterranean basin is considered a "hot spot" of climate change. A continuous trend toward drier conditions over the past several years is expected to continue and possibly increase in the coming decades. At the same time, extreme weather events continue to cause human and economic losses. These events also cause serious damage to marine ecosystems in intermediate and deep waters and in all marine habitats.
To meet this challenge, a Mediterranean Ocean Observing System for the Environment (MOOSE (http://www.moose-network.fr/)) network was put in place in the northwestern Mediterranean basin in 2010, and it has been in operation ever since. MOOSE integrates multiple platforms and collects data on multiple variables to detect and identify long-term environmental anomalies and to define effective health indicators.

A Dynamic Region
The northwestern Mediterranean basin is a very dynamic region: It concentrates many physical processes that are of great importance to the global-scale functioning of the oceans.
In this region, intense deep open-sea convection and shelf water cascading occur every winter. These processes renew and ventilate deep ocean water, and they are crucial to transporting heat, salt, oxygen, and carbon [Testor et al.  Cold, dry, intense mistral and tramontane winds drive these processes over a cyclonic gyre circulation. The intense vertical mixing that results is essential to replenishing nutrient stocks and for the development of phytoplankton, which forms the basis of the marine food chain and play a key role in the carbon biological pump.

The MOOSE Network Strategy
The MOOSE network aims to observe the variability over space and time of processes interacting between the land, coast, and open ocean and between the ocean and the atmosphere. It was built as an in situ observing system, capable of capturing variability at many scales. MOOSE was designed to monitor seasonal or interannual variabilities, as well as the impact of extreme events that control physical and biogeochemical fluxes and marine biodiversity. Water Column Observatory (http://emso.eu/) (EMSO)), meteorological buoys, glider endurance lines, annual basin-scale and monthly fixed-site ship surveys, high-frequency radars, river and atmospheric observatories, and Biogeochemical-Argo (https://eos.org /project-updates/bringing-biogeochemistry-into-the-argo-age) profiling floats that can make observations on seasonal to decadal scales.
An observing system simulation experiment (https://cires.colorado.edu/research/research-groups /project/climate-observing-system-simulation-experiments) approach was used to validate the MOOSE network strategy and its capacity to respond to key scientific issues. This Monitoring the Environment in the Northweste... https://eos.org/science-updates/monitoring-the-... approach has confirmed the performance of the network to capture the newly dense water volume (https://eos.org/editors-vox/observing-winter-mixing-and-spring-bloom-in-the-mediterranean) and its dispersion into the northwestern basin [Waldman et al. (

Scientific Issues and Advancements
The observation strategy of MOOSE is based on four topics that are relevant to the northwestern Mediterranean basin: water mass properties and regional circulation, climate and anthropogenic impacts from river inputs and atmospheric depositions, marine biogeochemical cycles and acidification, and biological communities and biodiversity. Since 2010, the MOOSE network has provided essential data to the scientific community, enabling progress on these key scientific issues.
Deepwater convection processes and their interaction with dense shelf water cascading  Regular and long-term monitoring (https://eos.org/features/monitoring-ocean-change-in-the-21stcentury) has provided significant results to interpret the temporal variability of nutrients and the zooplankton community, which are sensitive to deep vertical mixing events.
Coastal observations showed that the long-term evolution of nutrient inputs here is driven by Rhône River water discharges, which respond differently depending on whether it is a climatic or an anthropogenic forcing (Figure 4).

Data Management and European Integration
MOOSE oceanic data are validated using international protocols and best practices [Pearlman et al. (https://doi.org/10.3389/fmars.2019.00277), 2019]. This validation covers everything from sensor preparation to the systematic control of data at national data centers before these data are archived and released to the public.
The network was therefore designed to be based on proven techniques and procedures to ensure that these techniques and procedures are applied consistently across all measurements and by all partners with common collection and analysis protocols. The network is also designed to promote shared data to the end users. Once the data are qualified, they are archived on the Sea Scientific Open Data Edition (SEANOE (https://www.seanoe.org/)) repository, where a digital object identifier (DOI) is assigned. Real-time MOOSE data are transmitted to public databases for use with operational We also have a greater ability to correct model biases and to produce some virtual variables (high-value biogeochemical variables based on temperature, salinity, and oxygen data sets) with the introduction of new deep learning techniques [Sauzède et al. (https://doi.org/10.3389/fmars.2017.00128), 2017]. The next challenge will be to adapt these deep learning techniques to regional basins through downscaling processes and specific training, which is largely based on the quality of in situ data provided by observing networks such as MOOSE.