Ocean observation methods

This course is an option of the course “Observations and physical modeling in the atmosphere and the ocean”.

The objective of the course is to learn about methods for observing the ocean, its physical and biogeochemical properties, in the context of dynamic constraints. The focus is on the general circulation and its variability and the processes that contribute to it. From the implementation of instruments, including observation networks, to interpretation techniques, the course shows how these properties and constraints can be observed by taking different laws and theories of general and mesoscale circulation into account. This course is mainly organized in the context of practical work with first analyses of in situ (and satellite) data, to produce an oral presentation and a poster, as a basis for evaluation.

This course takes place partly during a cruise at sea which is the occasion of a first familiarization with some oceanographic techniques (positioning, meteorological, hydrological and current measurements), including the implementation of the instruments, the exploitation of a processing chain for formatting data.

The MOOSE-GE 2024 cruise (22 Jun to 17 Jul) on the R/V Atalante, divided into 2 legs of about 12 days, is dedicated to the hydrological network of the North-West Mediterranean basin and the maintenance of the mooring lines which are deployed by the laboratories. This is the fourteenth “Grande Echelle” (GE) cruise of the MOOSE national observation network. The practical work of the course continues during this cruise.

• Medical certificate for boarding
• Confidential health information

Conduct of the course and evaluation.

The course begins with a general presentation in common (ppt P. Testor, 89 M) and is followed by practical work. This year's practical work on data analysis will take place on Thursdays 01/02, 08/02, 15/02, 22/02, and 29/02 at 14:00-17:30.

The evaluation of the course is done by binome or trinome. The notation is based on

1. the oral presentation on 07/03/2024 of a scientific topic based on scientific articles that are provided, the analysis of the data done in practical work (see topics and articles to download below) and perspectives;
2. when possible, the poster/oral presentation of the work done on the data, more in-depth, to be returned at the end of the campaign (if before end of June)

The data and sample code for analyzing them with matlab are available here:

• examples of code (25 Mb) and some information on data format and coast_fix
• Satellite altimetry data 2010-2020 (0.9 Gb) more available at CMEMS see below.
• Ocean Color images 2020 (1.3 Gb) and Ocean Color images 2019 (1.0 Gb) more available at CMEMS see below.
• Basin-scale scientific cruises (MOOSE-GE and others) data (95 Mb) updated on 09/02/2022
• MOOSE monthly stations data (12 Mb)
• MOOSE moorings data (150 Mb) updated on 09/02/2022
• Mediterranean historical (1960-2018) in situ data (3 Gb)

Additional data (SST, Ocean Color, model outputs …) are available on the CMEMS website (Copernicus Marine Environment Monitoring Services):

• register at: http://marine.copernicus.eu/services-portfolio/access-to-products/ (<1 day for activation)
• get data at: ftp://my.cmems-du.eu/Core/ with your credentials. More specifically for Ocean Color here and for altimetry here.

Seven topics are available, for seven different groups:

Characterize the different water masses found in the NW Mediterranean Sea in terms of thickness, depth, density and T/S characteristics. This should include surface Atlantic Water (AW), Western and Levantine Intermediate Waters (WIW and LIW) and Western Mediterranean Deep Waters (WMDW). Describe their spatial distribution and temporal evolution from 2010 up to now.

The CTD profiles collected during all the MOOSE-GE cruises since 2010.

First, read general papers about the study area (see section “Downloadable items below”). Prepare a short overview of the following publications as an introduction to your topic to be included in your oral presentation:

• Fuda et al., 2000. XBT monitoring of a meridian section across the Western Mediterranean Sea
• Juza et al., 2019. Characterization of changes in Western Intermediate Water properties enabled by an innovative geometry-based detection approach
• Schroeder et al., 2008. An extensive western Mediterranean deep water renewal between 2004 and 2006

Practical work :

(This is a tentative work plan leading to the described objectives. Students are encouraged to take initiatives by completing different and/or complementary analysis.)

Draw and comment vertical sections of potential temperature, salinity, density (Oxygen, Chl-a, turbidity if you like…) from a cross-basin section of your choice sampled during the last MOOSE-GE 2019 campaign. Focus on the different layers (surface, intermediate, deep) and make a first identification the different water masses. Give particular attention to the scale of the colorbar.

Draw Theta-S diagrams and identify the minimum (resp. maximum) in salinity that characterizes surface AW (resp. LIW) and the local temperature minimum associated with WIW and WMDW. Define the ranges of potential density of the different water masses, examine the distribution of temperature and salinity (min, max, mean and std) for each layer, as well as the distribution of depth and thickness.

For the last MOOSE-GE cruise, map the T-S characteristics of the water masses across the basin. Pay attention to gradients along the continental slope. Repeat the exercise with the first cruise in 2010 and comment. Finally, combining the data from all the MOOSE-GE cruises, characterize of the evolution trend of the different water masses. Restrict the analysis to an area of interest (e.g, the Gulf of Lion, Ligurian Sea, …).

Characterize the thermic and haline content of the water column of the NW Mediterrean Sea. Compare the trends in surface, intermediate and deep layers. Observed and describe the long-term trends from historical data. Evaluate the role of these trends on sea-level rise.

• The CTD profiles collected during all the MOOSE-GE cruises since 2010.
• Database of historical T-S profiles in the Mediterranean Sea since 1960.

First, read general papers about the study area (see section “Downloadable items below”). Prepare a short overview of the following publications as an introduction to your topic to be included in your oral presentation:

• Schroeder et al., 2017. Rapid response to climate change in a marginal sea
• Jorda et al., 2017. The Mediterranean Sea Heat and Mass Budgets : Estimates, Uncertainties and Perspectives
• Carillo et al., 2012. Steric sea level rise over the Mediterranean Sea: Present climate and scenario simulations

Practical work :

(This is a tentative work plan leading to the described objectives. Students are encouraged to take initiatives by completing different and/or complementary analysis.)

Draw and comment vertical sections of potential temperature, salinity, density from a cross-basin section of your choice sampled during the last MOOSE-GE 2019 campaign. Identify different layers containing the different surface, intermediate and deep water masses. Give particular attention to the scale of the colorbar.

Compute the heat (HC) and salt (SC) contents from CTD profiles of the MOOSE-GE cruises using temperature and salinity reference adapted to the Mediterranean Sea. Describe HC and SC within the different depth layers and assess its evolution over the period of 10 years since the first MOOSE-GE cruise.

Explore the historical data base of CTD profiles in a region of interest characterized by a good data coverage (e.g, the Gulf of Lion or the Ligurian Sea) and evaluate the heat and salt content evolution over several decades. Link these changes with the thermosteric and halosteric components of sea-level change, compare with literature and tide gauge records (for instance the historical Maregraph in operation Marseille since 1885, https://www.psmsl.org/data/obtaining/stations/61.php)

Characterize the mean cyclonic circulation of the NW Mediterranean Sea. Compare the flow associated with the Northern Current with different data sets and characterize it in terms of intensity and transport along different sections. Identify the position of the North-Balearic Front, the southern recirculation branch of the gyre, and its T-S signature.

• The ship-, lowered-ADCP and CTD profiles collected during the MOOSE-GE cruises.
• Gridded altimetric products.

First, read general papers about the study area (see section “Downloadable items below”). Prepare a short overview of the following publications as an introduction to your topic to be included in your oral presentation:

• Sammari et al., 1995. Some aspects of the seasonal and mesoscale variabilities of the Northern Current
• Carret et al., 2019. Synergy between in situ and altimetry data to observe and study Northern Current variations (NW Mediterranean Sea)
• Garcia et al., 1994. Surface circulation variability in the Balearic Basin

Practical work :

(This is a tentative work plan leading to the described objectives. Students are encouraged to take initiatives by completing different and/or complementary analysis.)

Draw and comment maps of horizontal currents in the upper 100-m measured by ship-ADCP along the ship track during the available MOOSE-GE cruises. Add lowered-ADCP and check the coherence of the two data sets. Choose a cross-basin section and observed the distribution of the currents with depth from ship- and lowered-ADCP. Characterize the Northern Current (width, intensity, volume transport integrated to a chosen depth level). For the same section, draw T-S and density sections in order to broadly identify the water masses concerned by the strongest currents. Pay attention to the regions of sloping isopycnals and interpret in term of geostrophic currents, in particular in the slope region where the Northern Current is found.

Use altimetry data to reconstruct the surface horizontal geotrophic currents during the cruise period. Compare the obtained currents with the ones measured during the cruise. Comment on the discrepancies. Get the mean surface circulation by averaging over a sufficiently long period of time.

Identify the mean eastward circulation associated with the North-Balearic Front from altimetry data and from currents measurements performed during MOOSE-GE cruises. This area being known to be dominated by mesoscale structures, it might not always be possible to identify a clear signature. Try to identify the T-S signature of the front from a north-south section crossing the basin.

Characterize the depth of vertical mixing during the winter using the data from LION mooring line from 2010 up to now. Determine the geographical extension of the deep convection area by examining chlorophyll-a images from satellite.

• The LION mooring data (timeseries of T-S and currents)
• Chl-a images observed by satellite (Globoclor merged 8-day product)

First, read general papers about the study area (see section “Downloadable items below”). Prepare a short overview of the following publications as an introduction to your topic to be included in your oral presentation:

• MEDOC group, 1970. Observation of Formation of Deep Water in the Mediterranean Sea
• Houpert et al., 2016. Observations of open‐ocean deep convection in the northwestern Mediterranean Sea: Seasonal and interannual variability of mixing and deep water masses for the 2007‐2013 Period
• Macias et al., 2018. Deep winter convection and phytoplankton dynamics in the NW Mediterranean Sea under present climate and future (horizon 2030) scenarios
• Margirier et al. 2020. Abrupt warming and salinification of intermediate waters interplays with decline of deep convection in the northwestern mediterranean sea

Practical work :

(This is a tentative work plan leading to the described objectives. Students are encouraged to take initiatives by completing different and/or complementary analysis.)

Observe the evolution of temperature and salinity from the last mooring deployment. Expand the analysis to previous year and comment on the seasonal and interranual variability. Define a criterion to evaluate the mixed layer depth (see Houpert et al, 2016) and report the maximum depth reached by vertical mixing during each winter. Inspect and comment the variability of ocean horizontal and vertical currents on a seasonal and interrannual timescale.

To evaluate the horizontal extension of the mixing zone, map the surface chlorophyll-a seen from satellite. Observe the evolution of the surface chlorophyll-a concentration from the winter to the spring. Comment on the role of ocean mixing for the primary production and the ecosystem, and its evolution in the context of climate change.

Identify and characterize Submesoscale Coherent Vortices (SCVs) from the cruise data.

• The ship-, lowered-ADCP and CTD profiles collected during the MOOSE-GE cruises.

First, read general papers about the study area (see section “Downloadable items below”). Prepare a short overview of the following publications as an introduction to your topic to be included in your oral presentation:

• McWilliams, 1985. Submesoscale, Coherent Vortices in the Ocean
• Testor and Gascard, 2006. Post-convection spreading phase in the Northwestern Mediterranean Sea
• Bosse et al., 2016. Scales and dynamics of Submesoscale Coherent Vortices formed by deep convection in the northwestern Mediterranean Sea

Practical work :

(This is a tentative work plan leading to the described objectives. Students are encouraged to take initiatives by completing different and/or complementary analysis.)

Draw and comment maps of horizontal currents at depth of >500m measured by ship-ADCP (when resolved by the instrument after 2016, look at shallower depth otherwise) along the ship track during the available MOOSE-GE cruises. Identify potential eddies by looking at the rotation of currents with a CTD station close to the center of rotation (hint : leg 1, station 47 during MOOSE-GE 2019). Add lowered-ADCP and check the coherence of the two data sets. Choose a cross-basin section including the eddy and comment on the heterogeneity (if any) sampled the eddy center in the basin-scale context.

SCV are small-scale non-linear eddies in cyclogeostrophic balance (pressure gradient balanced by Coriolis and centrifugal forces). First, identify the eddy center from ship-ADCP data, then make a radial section of velocity across it. Comment on the depth and radial position of peak velocities. Characterize the Rossby and Burger number of the eddy and compare to the literature. Make a rough estimate of the non-linearity of the SCV.

SCVs can more largely impact biogeochemical tracers and ecosystem. Extent the analysis to other variable measured during the cruises (oxygen, chlorophyll-a fluorescence, turbidity, …). Observe the oxygen signature of the SCV and draw hypothesis about its formation mechanism.

Follow the same procedure and try to identify other SCVs in the cruises data set.

Characterize and locate double-diffusive staircases in the Western Mediterranean Sea.

• The CTD profiles collected during all the MOOSE-GE cruises since 2010.
• Database of historical T-S profiles in the Mediterranean Sea since 1960.

First, read general papers about the study area (see section “Downloadable items below”). Prepare a short overview of the following publications as an introduction to your topic to be included in your oral presentation:

• Kunze 2003. A review of oceanic salt-fingering theory
• Zodiatis and Gasparini 1996. Thermohaline staicase formations in the Tyrrhenian Sea
• Durante et al., 2019. Permanent Thermohaline Staircases in the Tyrrhenian Sea

Practical work :

(This is a tentative work plan leading to the described objectives. Students are encouraged to take initiatives by completing different and/or complementary analysis.)

Identify staircases in temperature and salinity profiles collected during the MOOSE-GE cruises between the warm and salty Levantine Intermediate Waters and the colder and less saline Deep Waters. Describe the favorable conditions to the developpment of salt-fingering and explain the mechanisms leading to the instability. Evaluate the Turner angle on profiles showing staircases.

A Turner angle favorable to salt-fingering does necessarily imply the formation of thermohaline staircases. Explore the larger data set of historical profiles collected in the Western Mediterranean to find the areas prone to the development of double-diffusion in the Western Mediterranean Sea.

Characterize the mean distribution of inorganic carbon in the North Western Mediterranean Sea. Evaluate multi yearly changes in the Inorganic carbon content. During the year 2021, compare different methods to assess inorganic carbon content

CTD profiles collected during the MOOSE-GE cruises. Bottles parameters collected during the MOOSE-GE cruises available at SISMER : https://doi.org/10.18142/235 or dowload this file: Water samples data

Tools and information for carbonate chemistry calculation are available here : https://www.ncei.noaa.gov/products/ocean-carbon-acidification-data-system

CANYON-MED tools can be downloaded here : https://github.com/MarineFou/CANYON-MED/

First, read general papers about the study area (see section “Downloadable items below”). Prepare a short overview of the following publications as an introduction to your topic to be included in your oral presentation:

• Álvarez, M., Sanleón-Bartolomé, H., Tanhua, T., Mintrop, L., Luchetta, A., Cantoni, C., Schroeder, K., and Civitarese, G.: The CO2 system in the Mediterranean Sea: a basin wide perspective, Ocean Sci., 10, 69–92, https://doi.org/10.5194/os-10-69-2014, 2014
• Coppola, L., Boutin, J., Gattuso, J.P., et al. (2020). The carbonate system in the Ligurian Sea. The Mediterranean Sea in the Era of Global Change 1: 30 Years of Multidisciplinary Study of the Ligurian Sea, 79-103. https://hal.science/hal-02541817/file/Carbonate_Coppola_06052019_final_version.pdf
• Fourrier M, Coppola L, Claustre H, D’Ortenzio F, Sauzède R and Gattuso J-P (2020) A Regional Neural Network Approach to Estimate Water-Column Nutrient Concentrations and Carbonate System Variables in the Mediterranean Sea: CANYON-MED. Front. Mar. Sci. 7:620. doi: https://doi.org/10.3389/fmars.2020.00620

Practical work :

(This is a tentative work plan leading to the described objectives. Students are encouraged to take initiatives by completing different and/or complementary analysis.)

Draw and comment North-South sections (Marseille-Menorca and Nice-Calvi) of inorganic carbon data available from the MOOSE-GE cruises (Sections are available since 2016). Please note that some strong uncertainties can be associated to DIC measurements, pay attention to strong outliers that you can eventually filter out. The quality control flags will first guide you to only keep good data. Outliers might still be present and evaluating the DIC concentration with CANYON MED at the same location is a way to detect them. Based on different average values (Deep waters, intermediate waters, surface water) evaluate if the trends in inorganic carbon are significantly different for the different water masses. The same analysis can be done for each section and/or at different latitudes in the basin. For the year 2021, inorganic carbon content along the two sections can be (1) estimated from direct measurements of DIC, (2) derived from pHT and AT by solving the carbonate chemistry equations (use CO2SYS under Matlab for example) and (3) derived from the neural network CANYON-MED method. Compare the three estimates and evaluate if the difference between these three estimates is significantly different from the trend observed between 2016 to 2021.

to read quickly whatever the subject chosen:

• Millot (1999). Circulation in the Western Mediterranean Sea
• The MERMEX group: Marine Ecosystems Responses to climatic and anthropogenic forces in the Mediterranean (Intro, parts 4.3 and 4.4 only)
• Testor et al., 2017. Multi-scale observations of deep convection during winter 2012-2013 using multiple platforms

Objectives, student Groups, presentations, posters and code 2022

Objectives, student Groups, presentations, posters and code 2021

Objectives, student Groups, presentations, posters and code 2020

Objectives, student Groups, presentations, posters and code 2019

Objectives, student Groups, presentations, posters and code 2018

Objectives, student Groups, presentations and posters made by students of OE course from previous years

• Ayoub et al. (1997). A description of the variable surface circulationfrom combined ERS-1 and TOPEXrPOSEIDON altimetric data
• Begovic et al. (2001). Mediterranean Sea (Dyfamed site)
• Marty et al. (2002). Seasonal and interannual variations in phytoplankton production at DYFAMED time-series station, northwestern Mediterranean Sea
• Marty et al. (2002b). Seasonal and Interannual Dynamics of Nutrients and Phytoplankton pigments in the Mediterranean Sea at the DYFAMED time-series station (1991-1999)
• Moutin el al. (2002). Primary production, carbon export and nutrients availability in western and eastern Mediterranean Sea in early summer 1996 (MINOS cruise)
• Schneider et al. (2007). Alkalinity of the Mediterranean Sea

on the law of the sea:

• United Nations Convention on the Law of the Sea (UNCLOS) (print part 13 only, ~ 200 pages if not)
• Marine Research Act
• Draft decree relating to the Marine Research Act (NOT TO BE DISTRIBUTED)
• Various documents UNCLOS-ZONEX