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QC procedures for Oxygen - Performance of float Oxygen measurements and “Shore-based adjustment”-

QC procedures for Oxygen - Performance of float Oxygen measurements and “Shore-based adjustment”-. Taiyo Kobayashi IORGC/JAMSTEC, Japan now visiting at NOCS, UK. This presentation has 2 issues: The performance of observations of Japanese floats in the North Pacific.

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QC procedures for Oxygen - Performance of float Oxygen measurements and “Shore-based adjustment”-

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  1. QC procedures for Oxygen- Performance of float Oxygen measurements and “Shore-based adjustment”- Taiyo Kobayashi IORGC/JAMSTEC, Japannow visiting at NOCS, UK. • This presentation has 2 issues: • The performance of observations of Japanese floats in the North Pacific. • Suggestion: To install “Shore-based adjustment” for DO data consistency.

  2. DO sensors installed on Argo floats SBE43 (now IDO)（SBE, USA） Oxygen Optode 3830(AANDERAA, Norway) Based on the electro-chemical method: (Clark 1959) Lifetime-based optode(Kautsky 1939, Holst et al. 1995) Note: including T sensor

  3. 4 APEXs in Jun. 2005by R/V Ryofu-maru (JMA) 9 floats (JAMSTEC 6, Tohoku U. 3) were deployed in the N. Pacific by 5 cruises sinceFeb. 2005. Area of DO float deployments by Japan Red： Optode, 6 floatsGreen: SBE43, 3 floats Light-blue: Bottle sampling DO stations selected from WOD2001 At all stations of float deployments, bottle sampling measurements are conducted to evaluate the performance of Argo float DO measurements. Float DO data shown here have been adjusted with the methods of the official (with T, S, P) and the T adjustment for Optode (with T of CTD).

  4. Surface layer: 10-25 micro-mol/kgMiddle layer: 2-5 micro-mol/kg Annual consumption rate of DO Comparison of first profiles of DO floats with shipboard bottle sampling data Deployed by Ryofu-maru (JMA) in Jun. 2005 Circle: shipboardStars: float Green: SBE43Other: Optode Circle: float deployedObs. Station by R/V Star: Location of the first float measurement To compare the same colored data T-S diagram: The water in deep layer (<4C) is very similar. Larger variations are found in upper layer except for the cyan float. The negative bias is greater than the error range of the maker’s announcement (gray region for Optode). P-DO/T-DO diagram： Below the DO minimum, float measurements have negative bias. => The bias is also caused by some other reasons than the longer settling time of DO sensor (e.g., initial bias, …). T-DO diagram: Even in deep layer, all float DO data have negative bias (about 0-10 micro-mol/kg)。 Cyan float shows the negative bias of 25-40 micro-mol/kg in the upper layer. Both of SBE and Optode have the similar negative bias with almost the same degree. Other DO floats (deployed at 165W) show similar features.

  5. Response time: about 30 sec (Specification: 10sec) Temperature difference between Optode and SBE41 and Enhancement of Optode-DO data by T data improvement TOptode – TSBE41 Deep: -0.03C Thermocline: beyond -0.5C DOcorrected – DOraw Up to 3u-mol/kg in thermocline

  6. SBE 100sec 300sec 600sec SBE Slower response of DO sensor (after T adjusted) • Response time • (official specification) • - SBE43: 12-48 sec (with SBE41) • - Optode: < 25sec for 63% response • If all biases of float DO measurements are caused by the slower response of sensor… Here, λ is time for 63% (e-1) response, dp/dt is upward float velocity (0.09dbar/sec) DO sensor response seems 100 sec or much longer, especially in colder layer….

  7. Performance: Summary and issues to be solved • DO measurements by Japanese Argo floats show negative bias compared to the shipboard bottle sampling data. • Deep layer; 0-10 micro-mol/kgSurface layer; more than 40 micro-mol/kg in maximum • This bias is greater than the official range for accuracy, and it is comparable to (or exceeds) the annual consumption of DO. • Note: The similar negative biases are found in the Canadian floats deployed in the N. Pacific. (Dr. D. Gilbert, Canada) • Drift of DO sensor is hardly found from our 9 floats for up to 17 months. Note: A long-term drift is found clearly in a float of Washington Univ. • Causes of the negative DO bias are unclear. • From the problem in calibration at sensor manufacture? • From mismatch of sensor and float hardware? • Much longer settling time than advertised? • Others …? • Need a certain method to post-calibrate float DO data (like salinity). Note: this is different from “Shore-based adjustment” to be mentioned later. • DO measurements by floats should be as accurate as possible to detect climatological change by Argo (at least, just after deployments):Float measurements will be allowed to have some uncertainness, but no-bias.

  8. Suggestion: Introduction of“Shore-based adjustment” for consistency of DO data Why… • We use 2 types of DO sensors (Optode and IDO) for floats. • Optode DO data need “Shore-based adjustment” of pressure/salinity influenceon the measurement (clarified in their operational manual). • Degree of the adjustment is up to 10% of the raw measurements. • N. Atlantic: ~ 25 micro-mol/kg • N. Pacific: ~ 5 micro-mol/kg • No information about this adjustment is provided in the data. • Shore-based adjustment (from direct contacts with PIs):Done (in RT) by MEDS Not done (in RT) by JMA, CSIRO Unknown by Others (probably not done)

  9. Inconsistency of DO data obtained by SBE43 and Optode Data transition **** Unit: Hz DO Unit: ml/L DO Unit:umol/kg Unit change SBESBE43 Need sensor parameters Data conversion in the sensor Phase shift Unit: degree AANDERAAOptode 3830 JMA, CSIRO DO (1) Unit:umol/kg Unit change DO Unit:umol/L Salinity: up to 2% (S=33~37), assuming a Salinity setting of 35. Depth: 4% every 1000m (or 1000dbar) diff. is up to 0.4 micro-M at 2000dbar Correction: S & depth (or P) of CTD DO (2) Unit:umol/kg MEDS Easy conversion Need sensor parameters and inverse calculation Correction:replace TDO to TCTD DO (3) Unit:umol/kg ΔT in thermoclines: ~0.5C => up to ~ 3 micro-mol/kg Some recent APEXs don’t report TEMP_DOXY (Dr. Gilbert, Canada) Float Measuring Argo data to GDAC Conversion on Land DO (2) Unit:umol/kg Optode DO (2) data are comparable with SBE DO data. DO (1) data are the raw measurements, so it is better that they are recorded in the data.

  10. Suggestion: Introduction of “Shore-based adjustment” of consistency of DO data • “Shore-based adjustment” should be installed into the DOXY data-stream to be in consistency among the float DO data.The data conversion is easy. • Besides the adjustment we need a sort of “delayed-mode QC” for DO data to check/correct the values in the future. • The following data (in META data) should be filled: SENSOR_MAKER ="AANDERAA" or “SBE”; SENSOR_MODEL ="Oxygen Optode 3830" or “IDO (SBE43)”; They are essential to distinguish DO sensor type, which is also important for users. • The recent APEX with Optode has no TEMP_DOXY transmission (to reduce the amount of profile data, probably), so these are the only clue to distinguish DO sensor.

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