METEOR 2017

Name: METEOR 2017
Start: 2017-03-08
End: 2017-12-04
Location: Bay of Biscay

Type	Oceanographic cruise
Ship	Côtes De La Manche
Ship owner	CNRS until 2019 - IFREMER since 2020
Dates	08/03/2017 - 04/12/2017
Chief scientist(s)	GRASSO Florent
	DYNECO/DHYSED - LABORATOIRE DYNAMIQUE HYDRO-SÉDIMENTAIRE IFREMER Centre de Bretagne ZI Pointe du diable CS 10070 29280 PLOUZANE 33 (0)2 98 22 47 60 https://dyneco.ifremer.fr/Qui-sommes-nous/Dynamique-hydro-sedimentaire-DHYSED
DOI	10.17600/17010200
Objective	The METEOR cruises are aimed at measuring the environmental parameters between the mouth of the Gironde Estuary and the West Gironde Mud Patch (WGMP), in order: 1) to calibrate and to validate the simulated fluxes of Suspended Particulate Matters (SPM) coming from the estuary and potentially deposited in the WGMP (ANR AMORAD project); 2) to validate the satellite image products (e.g., SPM, Chl-a) developed for the Gironde Estuary and the Gironde plume (FP7 HIGHROC project). In addition, METEOR has the ambition to measure the environmental parameters at time scales of months (continuous measurements and quarterly cruises). Four legs have been carried out in 2017: March 8-12, May 21-25, September 1-5, November 30-December 4. The related project are ANR AMORAD, FP7 HIGHROC.

Sea/Ocean

Bay of Biscay

(Mouth of the Gironde Estuary)

Ports

Port of departure : La Rochelle (France)

Port of return : La Rochelle (France)

Scientific Authority

DYNECO/DHYSED - LABORATOIRE DYNAMIQUE HYDRO-SÉDIMENTAIRE

IFREMER Centre de Bretagne

ZI Pointe du diable

29280 PLOUZANE

33 (0)2 98 22 47 60

https://dyneco.ifremer.fr/Qui-sommes-nous/Dynamique-hydro-sedimentaire-DHYSED

Participating bodie(s)

CNRS

Discipline(s)

CHEMICAL OCEANOGRAPHY
ENVIRONMENT
PHYSICAL OCEANOGRAPHY

Code	Label	Quantity	PI
B71	Particulate organic matter (inc POC Bottom/surface organic matter content measured by loss of ignition	200 samples	GRASSO Florent
D71	Current profiler (eg ADCP)	-	GRASSO Florent
H09	Water bottle stations	-	GRASSO Florent
H10	CTD stations Vertical profiles	100 stations	GRASSO Florent
H11	Subsurface meas. underway (T,S) GEMMES 20 and 40 buoy stations	2 deployments	GRASSO Florent
H17	Optics (eg underwater light levels)	-	GRASSO Florent
P01	Suspended matter Bottom/surface SPM concentration measured by filtration	200 samples	GRASSO Florent

Summary of measurements

-Vertical profiles of salinity, temperature, turbidity and fluoresence. Bootom and surface water samples for filtration.
-Deployement and maintenance of benthic survey stations and instrumented buoys.

Location map

Scientific context

Context

Coastal environments are strongly influenced by terrigenous supplies from rivers. Determining the quantity of nutrient, pollutant, and contaminant supplies is essential for marine resource protection. Interfaces between fresh and salt waters, as for instance estuaries, are dynamic areas experiencing strong gradients of temperature, salinity, turbidity, and biogeochemical processes, with an important filtration role. Such areas can impact dissolved and particulate fluxes from rivers to seas, as for instance metallic contaminants in the Gironde Estuary (Dabrin, 2009; Lanceleur, 2010). Evaluating net fluxes between rivers and seas is therefore a major issue to quantify the influence of continental supplies on marine systems (Eyrolle et al., 2011).

Two main questions are related to river-sea particulate transfers. On the first hand, intra-estuary processes are influenced by the presence of turbidity maximum and intertidal flats. And on the other hand, particulate matters exported from the estuary are likely deposited in less energetic areas along the continental shelf, and potentially trapped on subtidal mudflats or resuspended and advected to coastal areas (e.g., Sottolichio et al., 2000; Le Hir et al., 2001). Concerning such dynamics, The Gironde Estuary is specifically relevant, having one of the most developed estuarine turbidity maximum in Europe (with suspended sediment concentrations reaching few g/l at the surface), and two subtidal mudflats on the Bay of Biscay continental shelf close to the estuary mouth (Figure 1). Such mudflats (e.g., the West Gironde Mud Patch) represent temporary or permanent receptacles for fines particles coming from the Gironde Estuary (Lesueur et al., 2002).

In this context, the METEOR campaigns aimed at carrying out multi-parameter measurements between the Gironde Estuary mouth and the West Gironde Mud Patch:

to calibrate and validate simulated sediment fluxes between the estuary and the continental shelf (project AMORAD, see below).;
to validate satellite products based on water color images (e.g., suspended sediment concentration, Chl-a) dedicated to the Gironde Estuary and its turbid plume (project HIGHROC, see below).

In addition, these campaigns aimed at measuring the seasonal sediment dynamics (continuous measurements + campaigns every trimester).

Figure 1. Map of surficial sedimet distribution on the Bay of Biscay continental shelf and at the mouth of the Gironde Estuary (from Castaing, 1981 and Doxaran, 2002).

Associated programmes

The ANR AMORAD project (2013-2022) aimed at ¿Improving radionuclides dispersion and impact assessment modelling in the environment¿ within marine, continental and atmospheric compartments. In this framework, the objective of the ¿Sediment Task¿ in the ¿Marine Axe¿ was to improve the understanding and modelling of particulate matter fluxes. More specifically, a doctoral project was dedicated to the modelling of sediment transfers between the Gironde Estuary and the adjacent continental shelf in the Bay of Biscay (Diaz, 2019), in order: (i) to evaluate the influence of hydrometeorological events on particulate fluxes, and (ii) to determine the dispersion and accumulation areas of estuarine particles on the continental shelf.

To answer these questions, it was necessary to assess the turbidity at the mouth of the Gironde Estuary, which has not been done before. Such a lack of data has motivated the METEOR campaigns and the deployment of new instrumented stations.

The FP7 HIGHROC European project (HIGH spatial and temporal Resolution Ocean Colour products and services) develops products and services for European coasts based on water colour satellite images. Improving spatial and temporal resolutions opens new application fields for teledetections (e.g., Oyster farming, dredging), as well as providing information for the European Marine Strategy Framework Directive. In this context, the METEOR campaigns enabled to carry out match-ups between in-situ measurements and satellite images to validate satellite products developed for the Gironde Estuary and its turbid plume (e.g., turbidity, suspended sediment concentration, Chl-a, optical depth, reflectance).

References

Castaing P. 1981. Le transfert à l'océan des suspensions estuariennes : cas de la Gironde. Thèse de l'U. Bordeaux 1, 530.

Dabrin A., 2009. Mécanismes de transfert des éléments traces métalliques (ETM) et réactivité estuarienne ¿ Cas des systèmes Gironde, Charente, Seudre et Baie de Marennes Oléron. Thèse de l'Université Bordeaux I.

Doxaran D., 2002. Télédétection et modélisation numérique des flux sédimentaires dans l'estuaire de la Gironde. Thèse de l'U. Bordeaux 1, 278p. + annexes.

Eyrolle F., et al., 2011. EXTREMA contrat ANR-06-VULN-005, Episodes météo climatiques extrêmes et redistribution des masses sédimentaires et des polluants associés au sein d'un système côtier. Colloque de restitution finale, Compilation des actes du colloque, Rapport DEI/SESURE 2011-24.

Lanceleur L., 2010. L'argent, sources, transfert et bioaccumulation ¿ Cas du système fluvio-estuarien girondin. Thèse de l'Université Bordeaux I.

Le Hir, P., A. Ficht, R. Silva Jacinto, P. Lesueur, J.-P. Dupont, R. Lafite, I. Brennon, B. Thouvenin, P. Cugier, 2001. Fine Sediment Transport and Accumulations at the Mouth of the Seine Estuary (France). Estuaries, 24(6B), 950-963.

Sottolichio A., P. Le Hir, P. Castaing, 2000. Modeling mechanisms for the turbidity maximum stability in the Gironde estuary, France, In: W.H. McAnally, A.J. Mehta (Eds.), Coastal and Estuarine Fine Sediment Processes, Elsevier, Amst, 373-386.

Main results

Measurement stations deployed in the framework of the METEOR campaigns enabled the suspended sediment concentration to be quantified at the mouth of the Gironde Estuary mouth and on the proximal part of the West Gironde Mud Patch. These data were used to validate a hydrodynamics and sediment dynamics model (MARS + WAVE WATCH III® + MUSTANG) stretching from the fluvial estuary (Garonne + Dordogne) toward the Bay of Biscay continental shelf (Figure 3).

Figure 4. Illustration of the CurviGironde numerical model domain (1 every 5 cells plotted), and the locations of GEMMES 20 (G20) and GEMMES 40 (G40) stations deployed in the framework of METEOR campaigns.

This work was carried out in the framework of Mélanie Diaz' PhD thesis (Diaz, 2019), highlighting the model capacity to satisfactory simulating turbidity levels at the estuarine mouth surface (GEMMES 20, Figure 4a) and at the bottom of the West Gironde Mud Patch (GEMMES 40, Figure 4b). The waves, correctly simulated by the WAVE WATCH III® model (Figure 4c), had a significant impact on sediment dynamics as they represent the main driver of sediment resuspension at the estuarine mouth and on the continental shelf (Figure 5).

The model validation represented a crucial step before analyzing the variability of sediment fluxes between the Gironde Estuary and the adjacent continental shelf, and especially on the West Gironde Mud Patch (Diaz et al., 2019a; Diaz et al., 2019b; Diaz et al., 2021).

Figure 5. Time series comparison between measurements (red) and simulations (blue) from November 2016 to September 2017 of suspended sediment concentration SSC at (a) GEMMES 20 surface and (b) GEMMES 40 bottom, and (c) significant wave height Hs at GEMMES 40.

Figure 6. Comparison of the measured (black) and simulated (red) suspended sediment concentration SSC versus the significant wave height Hs, from November 2016 to September 2017, at (a) GEMMES 20 surface and (b) GEMMES 40 bottom.

Moreover, current velocities and turbidity measurements collected at the GEMMES 40 station were used to investigate the influence of hydro-meteorological forcing (i.e., waves, tides, and internal waves) on sediment resuspension (Grasso et al., 2018). The sediment at the mooring location was mainly muddy, consistent with the WGMP sediment characteristics. During the six-month survey, many storms were registered with significant wave heights reaching 12 m at the measurement location (by 40-m water depth). These severe storms induced large sediment resuspension over the entire water column. However, tidal currents reaching approximately 30 cm/s during spring tides did not induce significant resuspension.

Figure 7. Characterization of internal waves in April 2017 from ADCP measurements at the GEMMES 40 station. Vertical profiles of horizontal current Uxy (a) intensity and (b) direction, and (c) backscatter index BI.

Intriguingly, strong signatures of internal waves were observed in Spring 2017 (Figure 6), whereas the summer stratification was not yet developed and the measurement location was far from the continental shelf edge that classically generates tide-topography interactions. These observations are likely to result from the Gironde River plume acting as a gravity current and generating large-amplitude internal waves. Substantial sediment resuspensions were observed during low energetic periods of gravity waves that may be related to internal wave actions (Figure 7). These results provide knowledge on continental shelf sediment dynamics under estuarine influence and can be used to test numerical models simulating sediment transfers from estuaries to coastal areas.

Figure 8. Concentration des matières en suspension SPM en fonction de l'intensité du courant horizontal Uxy et de la variation l'isopycne Dz (couleur), lors de conditions de vagues calmes.

In addition, the turbidity data recorded between November 2016 and March 2017 at the mouth of the estuary (GEMMES 20) allowed re-analyzing and reconfirming the relationship between water turbidity and tidal conditions for satellite image analysis (Figure 8; Constantin et al., 2018). During spring tides and high river discharge conditions, the correlation between the two parameters is evident (Figure 8d; maximum values of SPM are reached during such periods: up to 80-90 g/m³, in this particular case). It is less obvious during neap tides (Figure 8b and c). During medium tidal range and high river discharge (Figure 8c), although the fluvial discharge is higher than in case (a), the SPM variations are similar. This is due to the fact that tides play a more important role in SPM dynamics compared to river outputs. Also, patterns of sediment sinking are well visible during the minimum water levels, when the tidal current is at its minimum. Such local observations were then spatially analyzed based on water color satellite images (Figure 9).

Figure 9. In-situ variations of SPM concentrations plotted against tidal water level fluctuations, for different scenarios: a) high tidal range and low river discharge; b) low tidal range and low river discharge; c) medium tidal range and high river discharge; d) high tidal range and high river discharge.

Figure 10. SPM maps obtained from SEVIRI satellite information for March 10, 2017.

Data acquired and analyses carried out at sea and on shore

The METEOR cruises aimed at deploying the "Gironde Estuary Mouth MEasurement Stations" (GEMMES) to measure hydrodynamics and sediment dynamics at the mouth of the Gironde Estuary and on the West Gironde Mud Patch (SW France, Bay of Biscay, see Figure 1a). Measurements were carried out between November 2016 and December 2017: i) from a buoy station around 20-m water depth (GEMMES-20), collecting sub-surface data of temperature, salinity and turbidity; and ii) a benthic station around 40-m water depth (GEMMES-40), collecting data of current velocity and turbidity (Figure 1b).

In addition, bottom and surface water samples were collected during METEOR cruises (every trimester) to calibrate turbidity measurements (Turb in NTU) to suspended particulate matter concentrations (C_SPM in g/l). The obtained calibration coefficient was: C_SPM (g/l) = 0,0015(± 0,0003) x Turb (NTU).

Figure 2. (a) Locations of stations GEMMES 20 and 40, and (b) schematic of the instrumented benthic station and buoy.

The GEMMES dataset (https://doi.org/10.17882/78968) includes measurements collected at two locations (GEMMES-20 and GEMMES-40).

1/ GEMMES-20 (N 45.6375; W 1.3917), in front of the Gironde Estuary Mouth:

Surface measurements from a buoy station moored around 20-m water depth (CTD Sea-Bird SBE19+, turbidimeter Wetlab FLNTU, 1-m below mean sea level, every 15 minutes), data file `GEMMES-20_hydrosed.txt' with Time, Temperature (°C), Salinity (PSU), Turbidity (NTU) and SPM concentration (g/l).
Water samples at the sea surface (1-m below mean sea level) and at the bottom (1-m above bed level), data file `Samples_NISKIN_GEMMES-20.txt' with Time, Water depth (Bottom/Surface) and SPM concentration (g/l).

2/ GEMMES-40 (N 45.7167; W 1.5750), on the West Gironde Mud Patch offshore of the Gironde Estuary Mouth:

Bottom measurements from a benthic station at around 40-m water depth:
- data file `GEMMES-40_hydrosed.txt' (turbidimeter Wetlab FLNTU, 1-m above bed level, every 15 minutes) with Time, Turbidity (NTU) and SPM concentration (g/l);
- data folder `GEMMES-40_ADCP' (ADCP 600 WORKHORSE, 1-m above bed level, every 10 minutes) with vertical profiles (50-cm cells) of Time, 3D current velocities (u, v, w), Water Depth, Backscatter Index, Significant wave height, Wave peak period.
Water samples at the sea surface (1-m below mean sea level) and at the bottom (1-m above bed level), data file `Samples_NISKIN_GEMMES-40.txt' with Time, Water depth (Bottom/Surface) and SPM concentration (g/l).

Figure 3. Illustration of data collected at stations GEMMES 20 (a-b) and GEMMES 40 (c-e) from November 2016 to September 2017. (a) Salinity (blue) and temperature (orange), (b) suspended sediment concentration SSC from instruments FNLTU (blue) and BBFL2 (orange), (c) water surface elevation (blue) and significant wave height Hs (orange), (d) suspended sediment concentration SSC from instrument FNLTU, and (e) vertical profile of suspended sediment concentration SSC from the ADCP backscatter index.

Published data

Grasso Florent, Bocher Alan, Jacquet Matthias, Le Berre David, Lecornu Fabrice (2021). Gironde Estuary Mouth MEasurement Stations (GEMMES). https://doi.org/10.17882/78968

Data managed by SISMER

Bibliography

Publications

Constantin Sorin, Doxaran David, Derkacheva Anna, Novoa Stefani, Lavigne Heloise (2018). Multi-temporal dynamics of suspended particulate matter in a macro tidal river Plume (the Gironde) as observed by satellite data. Estuarine Coastal And Shelf Science, 202, 172-184. https://doi.org/10.1016/j.ecss.2018.01.004

References of International Seminar Communications

Diaz Melanie, Grasso Florent, Sottolichio Aldo, Le Hir Pierre, Caillaud Matthieu (2021). Investigating sediment budgets on a continental shelf sub-tidal mud patch under estuarine influence: a numerical modelling analysis. ISOBAY 17 - XVII International Symposium on Oceanography of the Bay of Biscay. 1-4 June 2021, virtual event.

Diaz Melanie, Grasso Florent, Le Hir Pierre, Caillaud Matthieu, Thouvenin Benedicte (2019). Accumulation and dispersion dynamics of mud and sand particles in a continental shelf under estuarine influence: a numerical modelling analysis (Gironde, France). Advances in Coastal and Estuarine Physics from Nearshore to Continental-Margin Scales - Coastal Ocean Dynamics, Gordon Research Conference. 16-21 June 2019, Manchester, NH, USA.

Diaz Melanie, Grasso Florent, Le Hir Pierre, Thouvenin Benedicte, Caillaud Matthieu (2019). Numerical modeling of sediment budgets in intertidal and subtidal mud flats of a macrotidal estuary and its adjacent coast: influence of hydro-meteorological and estuarine forcing. INTERCOH 2019 - 15th International Conference on Cohesive Sediment Transport Processes. 13-17 October 2019, Istanbul, Turkey.

Grasso Florent, Bocher Alan, Jacquet Matthias, Le Berre David, Lecornu Fabrice (2018). Observations of sediment suspension induced by waves, tides and internal waves in a shallow continental shelf under estuarine influence. PECS 2018 - Physics of Estuaries and Coastal Seas meeting 2018. October 15-19, 2018, Galveston, TX, USA.

Thesis using campaign data

Diaz Melanie (2019). Modélisation numérique des transferts sédimentaires de l'estuaire de la Gironde au plateau continental / Numerical modelling of sediment exchanges from the Gironde estuary to the continental shelf. PhD Thesis, Université de Bretagne Occidentale.

File	Mission	Processing level	Size	Format
Open access FI35201701020_0G20S_H11.txt		DATA CONTROLLED WITH SCOOP	1 MB	MEDATLAS, ODV or NC
Open access FI35201701020_0G40B_H11.txt		DATA CONTROLLED WITH SCOOP	1 MB	MEDATLAS, ODV or NC