Chemical Sensors on Profiling Floats

Transcription

1 Chemical Sensors on Profiling Floats Todd Martz Scripps Institution of Oceanography Ken Johnson MBARI AST March 2010

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3 Seven years of O 2 data near HOT from floats. Biggest challenge make data from each float consistent climateresearch quality. Oxygen at 75 m

4 Six Apex/ISUS floats deployed, 30+ funded and in production. These are Argo equivalents and data stream is public. Data available at

5 Upper 40 meters

6 Annual average profile December to December Net Comm. Prod. = 2.2 mol C/m 2 /y

7 Status of ph sensor technology ph sensors now operate continuously in the surface ocean on moorings for months. On a mooring, performance of ph and O 2 sensors is similar both operate satisfactorily for several months and are ultimately limited by biofouling. The same oxygen sensors that operate for months on surface moorings operate for years on floats. Next step put ph sensors on floats and operate them for years.

8 ph sensors

9 MBARI test tank 1,420,000 L (375,000 gal) sterilized seawater. 10 meters deep. Emptied and refilled in Dec. 2008, and PCO 2 was out of equilibrium with atmosphere.

10 8 months Durafet ph data in MBARI test tank after refill.

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12 Baby Steps First: Autonomous sensors on moorings

13 ph on Del Mar Mooring;

14 ph and pco 2 on CCE-1 Mooring from

15 Two Durafets deployed for two months on M0 mooring. Very little drift relative to pco 2 or relative to each other.

16 expanded view of an upwelling event (~2 week window) Durafet captures the same variability as the MapCO2 sensor

17 Eight months on the M0 mooring. Multiple sensors used here, all calibrated in the MBARI test tank

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19 Moorings are easy. How do we transition the Durafet ph sensor into a profiling float? already low power already small The big challenge: Increasing pressure tolerance requires addressing chip encapsulation at the Fab level. The other big challenge:

20 Development of an Integrated ISFET ph Sensor for High Pressure Applications in the Deepsea NOPP FY09 funded collaboration between K. Johnson (MBARI), T. Martz (SIO), S. Riser (UW), A. Gu (Honeywell). MBARI: Devise novel mechanical support for ISFET sensor die. SIO: T/P characterization of sensors in Tris, seawater, dilute HCl; develop calibration protocol UW: Integrate sensor prototypes into four Apex floats and deploy on multi-year missions. Honeywell: Re-engineer MBARI design for high volume production.

21 Chip Encapsulation

22 Advances in chip encapsulation: EPDM seals used by Honeywell Media Seal A mechanically sealed chip was a major step in prolonging sensor lifetime because packaging integrity of resins can be unreliable and H 2 O penetration is problematic at the Chip/seal interface. ISFET DIE Conductive elastomer PCB & James G. Connery, Maple Glen, PA

23 High pressure ISFET Temperature-Pressure controlled chamber can go to 6000 psi over the seawater temperature range on programmed intervals. We are now routinely cycling ISFETs with mechanical seals from psi.

24 Commercial Durafet rated to 69 dbar (100 psi). Now running custom Durafets to 3000 dbar with decent performance. This plot shows 3 cycles from 20 dbar to 2100 dbar and back. The pattern is reproducible.

25 Enhancing these activities and expanding the global time-series network with new carbon and ph sensors will provide important information on the changing conditions in open-ocean and coastal environments that are presently undersampled. At this point, most of the current moored carbon observatories only accommodate measurement of pco 2, which is insufficient to fully constrain the carbon system necessary for effective monitoring and forecasting ocean acidification and the concomitant biological effects.additional sensors for dissolved inorganic carbon and total alkalinity would also be beneficial.. Consequently, there is an immediate need to improve upon existing technologies and for the development of autonomous sensors for DIC and TA for moorings and floats.