Project title and acronym    

Fixed-­‐point    Open Ocean   Observatories    (FIXO3)

Host facility


Modality of Access

MoA2 – Partially remote (the presence of the user is required at some stage, e.g. for installing and uninstalling an instrument)


The proposed project is intended to test sensors and instruments measuring partial pressure of carbon dioxide (pCO2) and pH at deep sea conditions (2500 m) during a (minimum) of one year deployment at the TNA observatory ANTARES. The experiment requires real-time data communication, which will be provided through secondary junction box (BJS), a part of the ANTARES infrastructure. This TNA action is a follow-up of the recently conducted shallow water (4.5 m) intercomparison exercise of pCO2 and pH instruments (project FixO3, WP12, RT1 and RT2).The two months deployment at the Koljo Fjord Cabled Observatory (, which was performed in spring 2014 on the Swedish west coast in collaboration with partners from Europe, Japan and the USA, was overall successful and showed how feasible different pCO2 and pH sensors are for autonomous unattended measurements in dynamic coastal environments.

A total of 15 instruments/sensors were tested: 4 different technologies from 5 different manufacturers for pCO2 and 4 different technologies from 5 different manufacturers for pH measurements. For deployment at the Koljo Fjord Observatory a special module, which multiplexed the mentioned instruments into one unit (one power and communication line), was designed and set up (see the Methodology section for further description). Only depth-rated instruments from those tested during the coastal deployment will be used. The main aim of the proposed TNA action is to assess the performance of various pCO2 and pH instruments at high pressure and relatively stagnant conditions, to test long term stability of the technologies and feasibility for measurements of the carbonate system parameters in the deep sea.

Quality of the measured sensor value will be assessed through comparing with water samples data collected with CTD rosette and Niskin bottles. Another objective of the proposed study is to record a long-term multiparameter time-series (pCO2, pH, O2, salinity, T, currents, turbidity, etc.) and to use the measurements for observations of deep-water formation and related processes in the NW Mediterranean Sea (Diurrieu de Madron et al., 2013; Tamburini et al., 2013).