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IODA6000, the ANTARES' jedi spirit

Production and remineralisation of organic matter by microorganisms along water column is a key point of carbon cycle. If the euphotic zone has been much studied by all scientific community, activities in deep water are still not well known. One of reasons is the lack of techniques. Since last decades, new instruments have been developed (Bianchi 1999) to sample and incubate under in situ conditions (i.e. temperature and hydrostatic pressure).

A method for quantifying remineralisation rates of organic matter is to measure the respiration rate of microorganisms but until now, there is no direct method to reach it.

This is why a new tool has been developed through a tight collaboration between the LMGEM (Laboratoire de Microbiologie Géochimie et Ecologie Marine) and the CPPM (Centre de Physique des Particules de Marseille). The In situ Oxygen Dynamics Auto-sampler (IODA6000) is an autonomous and programmable equipment made of a 5 litre incubation chamber auto sampling water at its depth of immersion. At high frequency, temperature and oxygen concentration are measured in and out the chamber by two optodes Aanderaaô. The combination of these measured parameters enables to derive the respiration rates in the dark ocean and to observe the evolution of water masses oxygen contents.

Description : IODAv3_ANTARES_novembre2009  
IODA6000 V3.0 deployed on ANTARES line 12 (L12)  

Design

IODA6000 is composed of an incubation chamber, two oxygen optode sensors (one in the chamber, one in situ), an electronic compartment and a power supply.

Since may 2008, several versions of the IODA6000 have been developed:

- v2.0 was used to test at sea the different components of the instrument  (mechanical, electronical and power supply).

- v3.0 was developed to be deployed on the ANTARES site (L12) collecting real-time data.
The IODA
6000 is remotely controlled via the ANTARES optical cable.

- v4.0 has been developed to be autonomous on drifting or fixed mooring lines.*

 Both IODA6000 v3.0 and v4.0 have an internal and external O2 optode.

 

- Power supply : the ANTARES power supply is completed with equipressured rechargeable batteries which allows 4 weeks of autonomy in case the ANTARES power supply would be down. For deployments on other autonomous mooring lines, another type of battery has been tested with autonomy longer than 3 months.
- Electro-mechanics : Electromechanical parts are equipressured: this is the "brain" of the IODA6000 system holding the motors for opening in and out the incubation chamber. The MSP computer holds the program and the acquired data from both external and internal O2 optodes. The incubation chamber (5 dm3) made of polycarbonate and Versilicô with the internal O2 optode sensor for the IODA6000v3.0.Another version of IODA6000 with chamber in glass is already in test at laboratory to replace all plastic components which can disturb oxygen dynamics measurement. A complete version has been deployed at ANTARES site in July 2010 on line 12 at 2000 m depth.

 
Bientôt, en français.

 Data

IODA6000ôs data on ANTARES site at 2000 m depth from May 2008 to September 2010 are presented on the figure on the right. Each cycle is 5 days long, with an opening time of 3 hours in order to remove completely the water sample.

 

Since 2008, in situ oxygen concentration fluctuates a lot with a delta of 2 to 3 ôM, even at short time scale. This first result is surprising compared to discrete measurements by CTD profiles. In parallel, mean respiration rates measured in the incubation chamber is around 0.3 ôM O2 d-1. This result is 2 order of magnitude higher than predicted by indirect measurements (Del Giorgio and Williams 2004). So this is another surprising result, but concomitant with previous study (Tamburini 2002) which has shown that activities of samples incubated under in situ conditions are higher than those incubated under atmospheric pressure.

Contact persons: D. Lefèvre & C. Tamburini (dominique.lefevre@univmed.fr tamburini@univmed.fr)

Oxygen concentration measured by the IODA6000 on the ANTARES site from May 31th 2008 to September 2010.
- Green line is the bulk in situ O2 concentration (external O2 optode sensor);
- Blue line is the concentration within the IODA6000 chamber;
- Red line is the temperature measured by the internal optode sensor.
Two ruptures of the optical-cable stopped the real-time acquisition between June 24th and September 6th 2008, and between September and November 2009. NB: data are not validated. Data provided by the ANTARES collaboration.

 

Author : Thierry Stolarczyk