CE04 - Innovations scientifiques et technologiques pour accompagner la transition écologique

Subsea Water Isotope Sensors: A novel tool for continuous and in-situ analysis – SWIS

Subsea Water Isotope Sensors: A novel tool for continuous and in-situ analysis

The isotopic composition of seawater represents an important fingerprint of water masses, containing information about conditions during their formation and evolution. Following at high resolution its spatial and temporal variability in the ocean would allow to discriminate between different water sources. This project proposes to design and construct a new instrument relying on our recent patent able to provide water isotope mapping at very fine spatial and temporal resolution in the ocean.

Main issues raised & general objectives

Main Objectives: Developping a novel instrument for in situ continous measurements of dD and d18O of water. An novel dedicated optical spectrometer will be developped and coupled to a membrane based extraction system. <br />Main issues araised: <br />1) The alignment of the optical cavity was not as easy as expected, and required longer time.<br />2) We changed our plans on the two membranes (one sampling external water and the other producing the standard gas), and after different test, we decided to go for the same type of membrane which will both be stabilized in temperature. <br />3) We decided to not develop the high-pressure system for testing the sensor, but rather to go to an existing infrastructure for those type of tests. The test will be performed once the instrument will be fully constructed, and are planned for the summer 2021.<br />4) The choice of the battery technology required to consider size, weight and regulation for shipping it by air. Li-ion were finally selected.<br />5) The M1 internshipwhich was supposed to take place from Feb 13 to Mai 22 2020 was canceled because of the sanitary restrictions. But the same candidate is starting an M2 internship on Feb 1st 2021. He will work on the characterization of the performance of sensor on the water isotopic measurements. <br />6) Because of the delay on the project (due to some technical issues explained above as well as the sanitary restrictions) the contract of the engineer was extended by 9 months, allowing him to finalize the development of the instrument. <br />Despite the delays accumulated, we should therefore be able to finalize the project within the 42 months as expected (includes the 6 extra months because of pandemic).

The optical spectrometer works in the infrared region and si based on the OFCEAS technique (Optical feedback cavity enhanced absorption spectroscopy). The extration systeme works as an evaporator, allowing to collect water vapour that is continously flushed to the optical cavity. The instrument will be integrated in an high pressure casing (up to 600 m) of in situ measurements. It will be designed to be deployed in a borehole (diam of the instrument 19 cm) and to be integrated in an AUV (50 cm long).

Up to now the work was on the design and consumption of the entire sensor. We are now ready to test its precision which will be an important point that would tell us if the current performance of the sensor would allow precise in-situ measurements in the ocean.
A further milestone will be the finalization of the entire sensor followed by the first test in real conditions.

We are now reaching the phase of the test of the performances of the optical spectrometer as well as laboraty test chaing water temperature and salinity. In parallel we are finalised the entire design of the sensor, which should be ready by the end of the summer, where high pressure tests will be conducted. A test campaign will then be conducted in the Mediterranean sea where samples from niskin bottles will be collected and analysed in the laboratory by standard technique for comparison and validation.

1. hal.archives-ouvertes.fr/hal-03042596
2. Grilli et al. Under review in Biogeoscience (Frontires in Earth Science).

The isotopic composition of seawater represents an important fingerprint of water masses, containing information about conditions during their formation and evolution. Following at high resolution its 3D spatial and temporal variability in the ocean would provide a direct link to the freshwater cycle, allowing to discriminate between different water sources, such as the one coming from glacier and sea ice melting, riverine freshwater and precipitations. Current knowledge of water isotopes in the ocean remains very poor due to scarcity of measurements obtained from discrete sampling. This project proposes to design and construct a new instrument relying on our recent patent able to provide water isotope mapping at very fine spatial and temporal resolution in the ocean. After validation, the instrument will further be employed for, e.g., field campaigns in the Austral Ocean, helping to better constrain ocean/ice-shelf interactions and ice melting processes, both so far poorly constrain.

Project coordination

Roberto GRILLI (Institut des Géosciences de l'Environnement)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

IGE Institut des Géosciences de l'Environnement

Help of the ANR 275,598 euros
Beginning and duration of the scientific project: January 2019 - 36 Months

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