In situ absolute salinity and sea water density

In situ absolute salinity and sea water density measurement: NOSS, Nke Optical Salinity Sensor Y. Dégrés, Managing Director D. Malardé, Ph. D Optic and Oceanography

Key Physical Variables « Since 1978, Oceanographers have used a calculated value formally (PSS-78) called the Practical Salinity (denoted SP) as a proxy for true salinity. Practical Salinity is defined as a function of temperature, pressure and conductivity. In 2009, Absolute salinity was introduced. However, oceanographers use the word salinity they often mean Practical salinity, although it is better to use the full name to prevent ambiguity. » * *T. J. Mc. Dougall et al. , The international thermodynamic equation of seawater – 2010 calculation and use of thermodynamic properties, Intergovernmental Oceanographic Commission, Manuals and Guides. , 20, 196, 2009 27/02/2021 2

Key Physical Variables Until 2009, EOS-80 was the reference. Absolute salinity has allowed to introduce the Thermodynamic Equation of Seawater TEOS-10. Ø An important milestone towards the implementation of a global thermodynamic ocean model. Why use the variable “absolute salinity”? Ø Essential for physical oceanographic applications to take into account density and salinity anomalies. Ø First step to get accurate density measurements. 27/02/2021 3

Density: Definition of TEOS-10 17/03/17 4

Chemical composition of seawater Salinity anomaly δSA Open Ocean q Relative chemical composition of seawater is in fact slightly different in different geographic locations. Spatial distribution of absolute Salinity Anomaly δSA (at p=2000 dbar) around the world q Anomaly salinities can vary from 0 to 0. 025 g/kg. Coastal waters q The difference between Absolute salinity and Reference salinity can be large as 0. 1 g/kg. 27/02/2021 T. J. Mc. Dougall et al. , The international thermodynamic equation of seawater – 2010 calculation and use of thermodynamic properties, Intergovernmental Oceanographic Commission, Manuals and Guides. , 20, 196, 2009 5

How to make a direct measurement of density variable ? 27/02/2021 6

NOSS in situ density sensor US Patent: US 7821622 B 2 European Patent: EP 1910805 B 1 q Optical sensor: Measurement of refractive index of seawater with high accuracy q Measurement of Temperature and Pressure q NOSS delivers absolute salinity and density q Partners involved in development : v Funded by FUI, BMO, Territorial Authority, Brittany Regional Council, Cap l’Orient Agglomeration v Approved by Pole Mer Bretagne v Supported by the EQUIPEX NAOS Project 27/02/2021 7

Links between : Refractive Index and absolute salinity Refractive index and density Refractive index Uncertainty < 10 -6 Laboratory Calibration NOSS Sensor Seaver&Millard Accuracy ± 0, 003 kg/m 3 Estimation of Accuracy ± 0, 005 g/kg Density TEOS-10 Standard error: 0, 0036 kg/m 3 27/02/2021 Absolute Salinity SA (g/kg) 8

Laboratory calibration (1/2) NOSS is calibrated at multiple refractive index points q Calibration method for salinity: o Thermostated bath: Range: -2°C to 40°C, stability: 0. 001°C o Pressure balance (D&H n° 5183) o Salinometer (Autosal & Portasal Guildline): Range: 2 – 40 psu, Accuracy: ± 0. 002 psu 27/02/2021 9

Laboratory Calibration (2/2) q Calibration system in density: o Thermostated bath: Range: -2°C to 40°C, stability: 0. 001°C o Densitometer (An Paar 5000 M) Range: 900 to 1030 kg/m 3, Linearity Error : ± 0. 0013 kg/m 3, Stability: 0. 002 kg/m 3 27/02/2021 10

NOSS Sensor: Design&Performances Multiple outputs: o Refractive index o Temperature, Pressure o Absolute salinity, Density Communication: o RS 232 Serial output, Data Format ASCII Mechanical features: o Dimensions: diam. 100 mm height 185 mm o Weight: 2. 4 kg (in air) 1. 7 kg (in water) NOSS 2 -2 DESIGNATION Refractive Index Temperature Operational Depth Absolute Salinity Density* Range Initial accuracy Response time (at 63%) Range Initial Accuracy Range Initial accuracy** 1. 3353 to 1. 3458 <1. 10 -6 -2 +35°C < ± 0. 006°C < 150 msec 0 to 2100 dbar ± 1 dbar 15 to 42 g/kg ± 0. 005 g/kg 1020 to 1030 kg/m 3 0. 003 kg/m 3 *Calibration interval depends on use and deployment environments **Theoretical value and depending on laboratory conditions 27/02/2021 11

NOSS Sensor: Design&Performances Temperature sensor q Cell detection is located between 2 prims, open q On board temperature and pressure measured near sensing window q Design for fast and slow profiling applications (floats, bathysond …) q Others applications available: buoy, deep observatory… Cell detection Pressure sensor Protective guard q Antifouling solution (chlorination method) has been identified and tested 27/02/2021 12

Laboratory result: Analysis of chemical composition of seawater 36 35. 5 δS(NOSS – TEOS-10)=0. 067 g/kg δS(Sp– TEOS-10)=-0. 158 g/kg 35 34. 5 δS(Sp– TEOS-10)=1. 69 g/kg δS(Sp– TEOS-10)=1. 65 g/kg 34 Practical Salinity (Portasal salinometer) Salinity (NOSS V 2. 2) 33. 5 δS(NOSS – TEOS-10)=0. 02 g/kg δS(NOSS – TEOS-10)=0. 04 g/kg Absolute Salinity (TEOS-10) 33 32. 5 32 Reconstituted Seawater (Rade de Brest, sea water composition N° 1 sea water composition N° 2 1024, 96 kg/m 3)** (1023, 31 kg/m 3)** (1023, 44 kg/m 3)** 27/02/2021 13

Validation in seawater trials: 2010, 2012 o Refractive index, temperature and salinity profiles at 2000 m (deepwater) and at a lower depth (coastal area) o Radial profiles completed. o Sensor drift characteristics o Easy to adjust calibration slope in field validation © SHOM 27/02/2021 14

Design for various integration o Integration on a profiling float CTS-4 and CTD probe o Contribute to improve the knowledge of in situ density and absolute salinity of seawater across TEOS -10 in parallel of current measurement instrument. o Promise tool to estimate the composition anomalies of seawater and for accurate evaluation of the ocean’s role in heat transport and in climate changes 27/02/2021 15

Deployment of PROVOR NOSS in the Mediterranean Sea o Moose mission in the Dyfamed/Boussole zone (Mediterranean sea) - 2015 27/02/2021 16

Deployment of PROVOR NOSS in the Mediterranean Sea SBE 41 NOSS Sensor Reference salinity q Good quality profiles of absolute salinity and in situ density obtained between 1000 m and 2000 m during the Moose mission in the Dyfamed/Boussole zone (Mediterranean sea). q Salinty differences are observed between NOSS and Salinity Reference ( <0. 02 g/kg below 300 m). 27/02/2021 17

As a conclusion of the NOSS presentation o New tool for monitoring absolute salinity SA and in situ density ρ of seawater across TEOS-10 in parallel of current measurement instrument. o Improve the accuracy of algorithm Seaver&Millard in pressure and temperature o The absolute salinity will replace in the future the conductivity measurement, nke wishes to contribute to the tasks to the "sea water density measurement" community. 27/02/2021 18

Thank you for your attention CONTACT Damien MALARDE Ph. D Optic and Oeanography, R&D Engineer dmalarde@nke. fr www. nke-instrumentation. com 6 Rue Gutenberg - ZI de Kerandré - +33 (0)2 97 36 10 12