Slide 1

A close look at optode performance in the test basin at Ifremer Hypox 2nd annual meeting Horw, Switzerland Mai 2011 N. Lo Bue*; L. Delauney A.Khripounoff ; A.Vangreisheim L. N. Gayet; L. Le Douaron *INGV, Rome- nadia.lobue@ingv.it IFREMER, Brest laurent.delauney@ifremer.fr Slide 2 Recent analysis of datasets collected at bottom depths showed unexpected O 2 variations. These seem to be inversely correlated to current velocity and in some cases well correlated with abrupt current direction changes ( Lo Bue et al. Anomalies of Oxygen measurements performed with Aanderaa Optodes, submitted to Journal of Operational Oceanography ) One step behind...: 1904 m 1866 m Mid-Atlantic Hydrothermal sources Lion Gulf 2113 m 2260 m Var Canyon MEDITERRANEAN SEA Aanderaa RCM8 or 11 Current meter + OPTODE 3830 Sediment traps 15 m Bottom 1700 m Slide 3 Mid-Atlantic Hydrothermal sources Mean Oxygen value ~ 307.5 mol/l. Abrupt oxygen drops (minor value~ 213 mol/l) T decrease Speed decrease Correlation between all parameters acquired by RCM11 shows that Oxygen drops occurred in correspondence of: T increases are associated to fluid emission episodes highlighting the normal behavior of hydrothermal sources A. Vangriesheim, 2007. Mesure d'oxygne par optode installe sur un courantomtre Aanderaa Rcm11. Cas des donnes des campagnes Exomar 2005 et Envar 4 et 5 (2006, 2007). Rapport.Interne. DEEP/LEP 07-14 Deviation from mean values is too big to reflect natural event Slide 4 Mid-Atlantic Hydrothermal sources Oxygen drops are well correlated with low speed values. Correlation with low temperature values should be a consequence of vent inactivity (NO fluid emissions NO T peaks) lower velocity = lower [O 2 ] Oxygen drops seems mostly oriented towards direction >250 Scatter O 2 /Speed allows to define the speed limit (~ 5 cm/s) where oxygen drops occurred Slide 5 Mediterranean data lower velocity = lower [O 2 ] No evident correspondence between O2 and direction No correspondence with temperature Correspondence with current regime Slide 6 Why testing the Optode and what did we expect to find? The aim of the test was to check the sensor performance in controlled current speed conditions, in order to know the dependence of the Aanderaa Optode from the water motion in front of the sensing foil Creating low hydrodynamic conditions in an artificial tank, the O 2 drops should have appeared, as already observed in natural environment. This should allow to better explain strange data recorded in several dataset. Slide 7 Test site characteristics Length : 50 m Width : 4 m Depth : 3 m Towing carriage of sensors: adjustable speed from 0 to 4,5 m/s (relative uncertainty: 10-) Control cabin Mechanical arm to fix and move sensors 100% theoretical [O2]: [O 2 ]= 240-250 M at 35 PSU and 16-17C Chlorination effect on Winkler analysis =+3.5 M Slide 8 2 Optodes 3830 were tested through independent sensor cable both synchronized through a PC acquisition system (news sensors) Tested sensors 1 Optode 3830 was tested through a current meter RCM8 (the same that acquired anomalous data in natural environment) in order to check the whole acquisition system MANUAL SYNCHRONISATION between the optode mounted on the RCM8 and the stand alone Optodes Slide 9 Data acquired Sensor stabilization time (~ 2 hours) Motion at 1 cm/s The sensors immersed in the channel were left to stabilize for more than two hours in completely calm water, then the truck was started up to speed of 1 cm/s. Sampling rate: 1 sample/s Increased O 2 values recorded during truck motion: hydrodynamic on sensing foil effect or O 2 mixing??? Motion at 1 cm/s Min value recorded 228.4 M During the stabilization time the optode mounted on the RCM8 appeared rather instable (values floating between 243 and 228.4 M). Slide 10 Data acquired Sensor stabilization time (17 hours) Motion at 3 cm/s During stabilization time, all sensors showed a different variability. In calm water condition the sensor 350 reached a minimum value of about 227.9 M (drop of about 34 M). Sampling rate: 1 sample/s The O 2 recorded by the three sensors at the start up of the truck was between 12 and 16 M Motion at 3 cm/s Stand alone Optodes Optode on RCM8 Inconsistency in the sensor records during the stabilization time Slide 11 Data acquired Motion at 5 cm/s stabilization time (2 hours) stabilization time O 2 23 M O 2 8.3 M O 2 10 M O 2 6.2 M O 2 8 M O 2 9 M O 2 10.5 M O 2 7.5 M O 2 3.5 M Sensor out of the water Motion at 5 cm/s An inconsistency in the sensor record during the stabilization time: a drop of about 10 M was recorded by Optode 500. O2 recorded during trucks start up are all positive shifts but different absolute values Sampling rate: 1 sample/s Stand alone Optodes Optode on RCM8 Slide 12 Data acquired Motion at 10 cm/s Sensor stabilization time (16 hours) Motion at 10 cm/s Sampling rate: 1 sample/s During stabilization time the O 2 values recorded by the Optode on RCM8 gradually decrease of about 27 M Min value recorded 201.5 M During trucks start up the O 2 recorded was between 13 and 21 M Stand alone Optodes Optode on RCM8 Slide 13 Data acquired 4 days of measurement in stationary water Sampling rate: 6 samples/ hour Sampling rate: 1 sample/s O 2 of about 100 M Stand alone Optodes Optode on RCM8 Consistency of signals Slide 14 Data acquired Motion at 1 m/s Sampling rate : 10 sample/min Sampling rate : 1 sample/s O2 of about 25M O 2 < 10 M for both sensors recorded during trucks start up Autonomous Optodes Optodes on RCM8 Slide 15 Statistical summary SensorO 2 at 1 cm/s O 2 at 3cm/s O 2 at 5 cm/s O 2 at 10 cm/s O 2 at 1 m/s Optode 3830 s/n 500 ****14.5 M During stabilization Min= 242.3 M Mean= 248.6 M 9M During stabilization Min= 234.2 M Mean= 244.8 M 18 M During stabilization Min= 240.4 M Mean= 259.2 M 10 M During stabilization Min= 222.6 M Mean= 228 M Optode 3830 s/n 350 ****14.3 M During stabilization Min= 227.9 M Mean= 262.2 M 10.5 M During stabilization Min= 258 M Mean= 261.9 M 13.7 M During stabilization Min= 240.4 M Mean= 259.2 M 9.9 M During stabilization Min= 264.9 M Mean= 269.7 M Optode 3830 (s/n 625) on RCM8 6 M16.4 M During stabilization Min= 228.4 M Mean= 240 M 23 M During stabilization Min= 217.2 M Mean= 240.6 M 21 M During stabilization Min= 201.5 M Mean= 228.9 M 26.7 M During stabilization Min= 216.7 M Mean= 224 M Slide 16 Remarks In stationary water conditions sensors showed different trends. Up to now no explanations about that!! The O 2 increases observed during the startup of the trolley are not directly proportional to the increases of speed. The optode mounted on RCM8 seems more affected by hydrodynamism (low hydrodynamism O2 =6 uM, high hydrodynamism O2 =26 uM). Could the anode effect be responsible of recorded drop? If so, decrease [O 2 ] should have affected all (RCM8) measurements collected during the stabilization time in calm water. Also, can oscillation of the order of 30-40 M be really related to anode corrosion? Slide 17 In consideration of the performed test, optode sensors seem to be affected by current speed variations (26.7uM). The frequent drops (100uM) observed during the test in stationary condition confirmed that the anomalous data recorded in the past in natural environment can be referred to the sensor instability in stationary waters, explaining the occurrence of unexpected O 2 drops. Could a pump improve the efficiency of the sensor ensuring a constant flow in low hydrodynamic environments ? Conclusions Thank you for your attention!!!