Nitrate and ph sensors for deployment in a global ocean observing array: simple sensors that operate for years without recalibration

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1 Nitrate and ph sensors for deployment in a global ocean observing array: simple sensors that operate for years without recalibration Ken Johnson Monterey Bay Aquarium Research Institute Moss Landing, CA MBARI Chemical Sensor Lab

2 1. Why develop chemical sensors for multi-year deployments (with no chance for direct human intervention after deployment). a. Global problems demand global observing with seasonal resolution only possible with large scale, sensor networks. Frequent service not possible 2. Examples Nitrate/pH 3. Efforts in other labs focused on sensors for profiling floats MBARI Chemical Sensor Lab

106 CO 2 + 16 HNO 3 + H 3 PO 4 + 122 H 2 O

3 106 CO HNO 3 + H 3 PO H 2 O (CH 2 O) 106 (NH 3 ) 16 H 3 PO O 2

4 All sensor data I ll show today is available online at FloatViz

5 Ship based science cannot address these problems at a global scale!

7 Argo array monitors ocean T 1,000,000 profiles to date 20 min on sea surface 1000 m 1 to 10 days drifting Collect T/S profile on ascent UW/MBARI Chem Sensor array 2000 m Five year life. Ascent driven by a volume change of ~250 ml

8 Optical nitrate sensors Absorbance µm Br µm NO Nitrate has a moderate UV absorption band π π* ε ~ 4000 L mol -1 cm -1 at 217 nm Wavelength (nm) MBARI Chemical Sensor Lab

9 MBARI Chemical Sensor Lab In situ ultraviolet spectrophotometer (ISUS)

5 year life at 5 day cycle time 44 joule/measurement = 20% of battery 800 grams (we were

10 MBARI ISUS nitrate sensor integrated into modified Apex profiling float. 60 NO 3 - meas./profile to 1000 m Precision <±0.2 µm (1 SD) Float endurance 320 profiles to 1000 m. ~4.5 year life at 5 day cycle time 44 joule/measurement = 20% of battery 800 grams (we were allowed 1 kg) Johnson et al. (2013) J. Atm. Ocean. Technol. Optical probe Electronics and sensor

11 MBARI Chemical Sensor Lab

12 North Pacific/Gulf of Alaska MBARI Chemical Sensor Lab

13 Surface T and NO 3 - for float 5143 at 50 N in the North Pacific. Station sampled 3x per year A B Temperature (C) Nitrate ( mol L -1 ) /08 07/09 07/10 07/11 Date 4 07/08 07/09 07/10 07/11 Date MBARI Chemical Sensor Lab

14 1000 m T and NO 3 - for float 5143 at 50 N in the North Pacific. Station sampled 3x per year C 50 D Temperature (C) Nitrate ( mol L -1 ) /08 07/09 07/10 07/11 Date 40 07/08 07/09 07/10 07/11 Date MBARI Chemical Sensor Lab

15 Acidification signal = ph/year Production/Respiration signal = 0.03 ph/year

16 Ion Sensitive Field Effect Transistor (ISFET) Nadine Le Bris Kiminori Shitashima

17 ISFET: Potentiometric ph Sensor Amphoteric Metal Oxide insulator on FET gate MeOOH - MeO MeOH + Honeywell DuraFET

18 ISFET Packaging Deep-Sea DuraFET Low pressure DuraFET ISFET Media seal (gasket) ISFET die Cl-ISE Conductive Elastomer PCB

19 Deep-Sea DuraFET responds to the activity of HCl in seawater V RS = [k 0 + k 2 * t + f(p, T) ] - RT/F ln (a H+ a Cl- ) = [k 0 + k 2 * t + f(p, T) ] - RT/F ln (γ ±HCl2 ) - RT/F ln (m H+ m Cl- ) Calibrate k 0, k 2 and f(p, T) in lab, Know γ ±HCl and m Cl- from literature (and salinity, T, P), Measure V RS (Voltage between reference and source), Calculate m H+ ±0.001 ph is equivalent to a 0.2% error in m H+

21 Alkalinity can be predicted using regional regressions of TAlk on Temp/Salinity/Depth and Dissolved Inorganic Carbon can be determined. ph (total) 25 C DIC ( mol kg -1 ) Depth (m) Float HOT 2009/

22 Other chemical sensors available Fluorescence lifetime O 2 optode Otto Wolfbeis Ingo Klimant Ocean community

Reagentless and Silicate interference free electrochemical

MoO 2-4 + 27 H + H 3 PMo 12 O 40 + 12 H 2 O Silicate

23 Reagentless and Silicate interference free electrochemical method for Phosphate detection in seawater Jońca et al., Electrochim. Acta, 2012 Mo + 4 H 2 O MoO H + + 6e - PO MoO H + H 3 PMo 12 O H 2 O Silicate Phosphate ph = 1 ; H + /MoO 4 2- = 70 Detection limit: 0.11 µm Precision: 5.7 % (1.60 µm) Measurement time: 15 min Amperometry at rotating gold electrode (0.29 V, 2000 rpm): Standard addition of phosphate µm and silicate µm in artificial sea water J. Jonca, C. Barus, W. Giraud, M. Comtat, M. Armengaud, N. Striebig, V. Garçon

25 J. Bishop UC Berkeley, PIC sensor now operating on float

ph Anode ISFET alkalinity titration Todd Martz, SIO/UCSD The on-chip titration concept was invented in 1989 and developed in the Netherlands (Olthuis & Bergveld, 1995).

Concept: coulometrically generated protons diffuse across the ph sensitive gate at a rate determined by the total alkalinity.

26 ph Anode ISFET alkalinity titration Todd Martz, SIO/UCSD The on-chip titration concept was invented in 1989 and developed in the Netherlands (Olthuis & Bergveld, 1995). NSF OTIC funded UCSD/SIO to modify the Honeywell Durafet chip to measure seawater total alkalinity (Award ). Concept: coulometrically generated protons diffuse across the ph sensitive gate at a rate determined by the total alkalinity. A titration curve is recorded in the time domain where longer endpoints correspond to higher alkalinity. ISFET chips are currently being modified in the nano3 facility at UCSD. SIO will carry out tests using prototype chips in H + diffusion from anode 2H 2 O 4H + + 4e - + O Cathode H + Anode I titr time (sec)

27 Ocean chemistry will change from a ship board science to an autonomous sensor based science to address the global challenge.

In the future, vessels will be support, not monitoring platforms Mel Briscoe, 2010. Which means the next generation of global ships can be small to control costs. E.g., 28 meter R/V Kaharoa.

28 In the future, vessels will be support, not monitoring platforms Mel Briscoe, Which means the next generation of global ships can be small to control costs. E.g., 28 meter R/V Kaharoa. Works globally supporting the Argo system. Astronomers no longer go to the observatory. Data comes to them on the Internet - think Hubble Space Telescope.

29 The train is leaving the station!!

- Acid-base equilibria - ph concept and scales - ph measurements - ph sensors, types - glass electrodes - Spectrophotometric sensors - Solid

- Acid-base equilibria - ph concept and scales - ph measurements - ph sensors, types - glass electrodes - Spectrophotometric sensors - Solid electrodes Melchor Gonzalez-Dávila. ULPGC Workshop, Trieste