DYFAMED Service Activities

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SA Number: 8.1

Name of the SA: DYFAMED – LIGURIAN SEA WATER COLUMN PHYSICAL AND BIOGEOCHEMICAL PROPERTIES INCLUDING PRODUCTIVITY AND pCO2-PH ESTIMATES

Institute:

Centre National de la Recherche Scientifique et l’Institut National des Sciences de l’Univers (CNRS/INSU), France

Institut français de recherche pour l’exploitation de la mer / IFREMER, France

Name: DYFAMED (“Dynamique des Flux Atmospheriques en MEDiterranee”)

Contact: coppola@obs-vlfr.fr

SA Description:

In the framework of the French MOOSE program (Mediterranean Ocean Observing System for the Environment), an eulerian time series so-called DYFAMED (Ligurian Sea) performs since 1991 a monthly multidisciplinary monitoring to observe: 1) the evolution of the water mass properties (LIW and WMDW), 2) the carbon export change and 3) the variability of the biological species relative to climate forcing (temperature, acidification). In addition to monthly CTD profiles, a fixed standalone mooring is located in the DYFAMED site for T-S-O2 and currents continuous measurements since 2009 and two sediment traps since 1988 for collecting large sinking particles and zooplankton swimmers. Since 1999, an ODAS buoy from Meteo France (ODAS Cote d’Azur) provides real-time meteorological survey and surface oceanic measurements.

The DYFAMED observatory provides oceanic and meteorological data freely accessible through CORIOLIS GDAC (OceanSites data policy). The oceanic data regroup physical (temperature, salinity, currents), biogeochemical (oxygen, nutrients, inorganic carbon and alkalinity) and sediment trap data (mass flux, organic carbon and nitrogen fluxes). The frequency at which data are provided and the delay between data production and dissemination depends on data type and range from annually (sediment trap) to near real-time (meteorology data).

The service provided here can be used for atmospheric research dedicated to air-sea interactions (e.g. heat budget) and oceanography (e.g. water mass properties, carbon cycle, acidification, biomass production). It contribute to the international programs as HyMEX (Hydrological cycle in the Mediterranean EXperiment), MERMEX (Marine Ecosystems Response in the Mediterranean Experiment), ICOS (Integrated Carbon Observation System), GMES (Global Monitoring for Environment and Security), EMSO (European Multidisciplinary Seafloor and water column Observatory) and CIESM (Mediterranean Science Commission).

Visualisations:

Fig.1: Mixed layer depth (meter) estimated from CTD monthly profiles

Fig.1: Mixed layer depth (meter) estimated from CTD monthly profiles

To estimate the strength of the mixing process on oxygen content, we use the mixed layer depth (MLD) indicating the depth reached by turbulent mixing in a recent past. The MLD was calculated as the depth where the difference of density from the surface reference, fixed at 10 m depth, is 0.03 kg m-3 (de Boyer Montegut et al., 2004; D’Ortenzio et al., 2005). Density profiles were calculated from temperature and salinity profiles and linearly interpolated at 1 m depth interval. If no observation was available at 10 m, the shallowest measurement was used as the surface reference.

Fig.2: In situ temperature time series 2009-2015 at 6 depth levels (200 to 2000m) from DYFAMED mooring

Fig.2: In situ temperature time series 2009-2015 at 6 depth levels (200 to 2000m) from DYFAMED mooring

Temperature variability at DYFAMED provide information on MLD deepening and vertical mixing occurring in the Ligurian Sea. Since 2009, the winter mixing affected only the upper 200 m except in February-March 2013 where a stronger mixing has been observed. During this period, the first 1000m layer has been mixed due to colder winter and stronger winds.

Fig.3: Dissolved oxygen time series (µmol/kg) from 2014-2015 at 350 and 2000 m depth from mooring (blue lines) and from Winkler analysis (red dots)

Fig.3: Dissolved oxygen time series (µmol/kg) from 2014-2015 at 350 and 2000 m depth from mooring (blue lines) and from Winkler analysis (red dots)

Since summer 2014, new optical O2 sensors have been deployed on DYFAMED mooring in LIW and WMDW levels (385 and 2100 dbar respectively), the two major water masses in the Ligurian Sea. Oxygen concentrations near the LIW correspond to the Oxygen Minimum Layer (OML), sensitive to MLD deepening and O2 ventilation from upper layer. Oxygen in WMDW show a slow decrease suggesting an effect of bacteria respiration and no O2 supply from vertical mixing or from a newly formed dense water spreading.

Fig.4: Total Chlorophyll-a content from 0 to 200 m (mg/m2)

Fig.4: Total Chlorophyll-a content from 0 to 200 m (mg/m2)

Chlorophyll-a is measured during monthly cruises and analyzed by HPLC technique since 1990. The integrated content from 0-200m provide information on phytoplantonic biomass production which is very variable over the last 25 years and shows a strong seasonality (bloom vs stratification period).

Fig.5: Dry mass (blue line) and total organic carbon (green line) fluxes collected from DYFAMED sediment traps from 2009 to 2013

Fig.5: Dry mass (blue line) and total organic carbon (green line) fluxes collected from DYFAMED sediment traps from 2009 to 2013

Sediment traps are deployed in DYFAMED since 1988. Recent results show a consistency between mass and total carbon fluxes at 200m. The strong seasonality indicates the impact of winter mixing (January-March) and bloom production (April-May) which affect exported flux. An interannual variability is also observed from the 2009-2013 depending on physical forcing (mixing) and bloom history.

One click links to your SA:

The DYFAMED observatory data can be downloaded here:

http://doi.org/10.17882/43749

These data are associated to a DOI:

Coppola Laurent, Diamond Riquier Emilie, Carval Thierry (2016). Dyfamed observatory data. SEANOE. http://doi.org/10.17882/43749

More information about national program MOOSE can be found here:

http://www.moose-network.fr