AWIPEV-CO2 Time Series Data

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Information on the AWIPEV-CO2 project

Summary

The AWIPEV-CO2 project aims at starting the first time series for the carbonate chemistry in the Arctic Ocean as part of the AWIPEV Underwater Observatory. It comprises two components: (1) continuous real-time measurements and (2) discrete measurements. The rationale is that discrete measurements are absolutely needed to calibrate and validate the sensors.

AWIPEV Underwater Observatory

The AWIPEV Underwater Observatory (UWO) has been deployed at Ny-Alesund (Spitsbergen) in June 2012. It is part of the German Project COSYNA (Coastal Observation Systems of the Northern- and Arctic Seas), which aims at increasing the availability of continuous real-time data from remote but climatically-sensitive ecosystems. The AWIPEV underwater observatory comprises a fully remote controlled FerryBox system with sensors for temperature, salinity, pressure, turbidity, oxygen, chl-a fluorescence. Furthermore, an additional remote controlled underwater sensor unit able to profile from 12 m to the surface at any frequency carries additional sensors for salinity, pressure, turbidity, oxygen chl-a fluorescence and PAR. The system also comprises an ADCP for continuous measurements of currents and waves. Besides these standard sensors, the underwater unit is equipped with a webcam and stereo-optical device to remotely assess fish and jellyfish populations. The AWIPEV observatory is specifically designed for polar experimental work under extreme conditions including ice coverage and the inaccessibility for about 7 months during polar winter. During this time, the system is remotely controlled and maintained from Germany. All data sampled by the sensors are continuously sent to a central server system at Helgoland Island where the data are stored and processed. The processed data are open access and available at http://codm.hzg.de/codm.

Continuous and semi-continuous measurements

The Arctic version of the Contros-Kongsberg pCO2 sensor (HydroC CO2 FT sensor) has been installed in July 2015. Molecules of dissolved CO2 diffuse through a thin composite membrane into the internal gas circuit leading to a detector chamber, where the partial pressure of CO2 is determined by means of infra-red absorption spectrometry. Concentration-dependent IR light is converted into the output signal from calibration coefficients stored in firmware and data from additional sensors within the gas circuit. The measuring range is 200-1000 uatm, resolution is < 1 uatm and accuracy is +- 1% reading. The sensor is the first instrument in the measuring loop; data are logged every minute. This instrument requires yearly factory calibration; two sensors ara available to allow a continuous time series.

Since February 2016, total alkalinity (AT) is measured every 90 min with a Contros-Kongsberg HydroFIA TA instrument. Fifty ml of seawater is filtered (0.2 um) using a Contros-Kongsberg cross-flow filter and then acidified using dilute hydrochloric acid (0.1 N). CO2 is then flushed out (open-cell titration) and the final pH measured by means of an indicator dye (bromocresol green) and visible absorption spectrometry. Together with salinity and temperature at the time of measurement, the pH reading is used to calculate AT. According to the manufacturer, the measuring range is 400 umol/kg dynamic range, resolution 0.1 umol/kg, accuracy 25 umol/kg (+- 1%) and precision 5 umol/kg (+- 0.2%).

In August 2017, a seaFET Ocean pH sensor (Sea-Bird Scientific) has been added to the UWO. This new sensor continuously measures pH at 11 m using an ISFET (Ion Sensitive Field Effect Transistor). According to the manufacturer, the measuring range is between 6.5 and 9 pH units, initial accuracy is 0.02 pH units and precision is 0.004 pH units. Operating salinity and temperature range are 20 to 40 PSU and 0 to 50°C respectively.

In August 2017, a Durafet III pH electrode connected to a UDA2128 Analyser (Honeywell) was also implemented to the Ferrybox flow-through system. This electrode continuously measures pH, in the Ferrybox, through an ISFET. According to the manufacturer, the measuring range is between 0 and 14 pH units. The operating temperature range is -10 to 110°C.

Discrete measurements

Seawater samples are collected weekly. They are poisoned with HgCl2 and stored as recommended by (Dickson et al., 2007). The Service National Analyse des Paramètres Oceaniques du CO2 of Université Pierre et Marie Curie (Paris6) will determine CT and AT potentiometrically (Edmond, 1970). Samples will be shipped from Ny-Alesund to Paris every 6 months.

Variable informations

  • Salinity_filtered: Salinity measured by a SBE45 sensor in the FerryBox and filtered from any non-natural spikes (cleaning, …).
  • Temperature_filtered: Temperature measured by a SBE45 sensor in the FerryBox and filtered from any non-natural spikes (cleaning, …).
  • TempSBE38_filtered: Temperature measured _in situ (11 m depth) by a SBE38 sensor and filtered from any non-natural spikes (cleaning, …).

  • PCO2_Corr_filtered: Raw pCO2 data measured by a Contros sensor and filtered from any non-natural spikes (cleaning, …). Only pressure- and temperature-corrected.

  • PCO2_corr_contros: Calculated pCO2 corrected for the sensor span drift and sensor baseline drift.

  • PCO2_corr_contros_filtered: PCO2_corr_contros_filtered filtered from any non-natural spikes (cleaning, …). These are the final pCO2 data.

  • PCO2_Corr_Zero2: pCO2 during the zeroing phase (used to correct the pCO2 data).

  • AT: Total Alkalinity, non-filtered.

  • AT_filtered: Total Alkalinity data filtered from any spikes. These are the final AT data.

  • pH_AT: pH of the AT sample after acidification (used for checking the proper functioning of the instrument).

  • Tsample: Temperature of the AT sample (used for checking the proper functioning of the instrument).

  • Tbox: Internal temperature of the AT analyser box (used for checking the proper functioning of the instrument).

  • Vcorrfact: Correction factor volume (used for checking the proper functioning of the instrument).

  • A509: Absorbance at 509 nm (used for checking the proper functioning of the instrument).

  • InvSal: Salinity flag (used for checking the proper functioning of the instrument).

  • InvpH: pH flag (used for checking the proper functioning of the instrument).

  • HW_pH1_filtered: pH measured by the Durafet sensor in the Ferrybox and filtered from any non-natural spikes (cleaning, …).

  • HW_Temperature1_filtered: Temperature measured by the Durafet sensor in the Ferrybox and filtered from any non-natural spikes (cleaning, …).

  • T_seaF: Temperature measured by the seaFET sensor in situ.

  • phINT_filtered: Internal pH measured by the seaFET sensor.

  • phEXT_filtered: External pH measured by the seaFET sensor.

  • Humidity: Humidity inside the seaFET sensor.

  • V_MainBatt: Voltage of the main seaFET sensor battery set.

Data processing and availability

The data shown on this web site are raw data coming out from the sensors which have not been subject to quality control. The AT data are not post-processed while the pCO2 data are filtered as follows.

  • data collected during the zeroing and flushing of the sensor are eliminated by removing data with the flags state_zero or state_flush set to 1.
  • Data collected during the acid cleaning and freshwater flushes of the FerryBox. They are removed using functions written by B.Gentilli. First, peak values above a given threshold (600 uatm) are located. Second, all data during the stabilisation period are removed by looking at the maximum difference between 2 consecutive values (0.5 uatm) during a given time (5 min). If the difference is larger than 0.5 uatm, the instrument is still in a stabilisation period and the value set to NA.

The frequency of data displayed depends on the date range: every minute for plots dispalying less than 7 days of data or hourly averages for longer time intervals. These data will eventually be made publicly available via the World Data Center Pangaea.

Acknowledgments

This AWIPEV-CO2 project is jointly supported by the Alfred Wegener Institute for Polar and Marine Research (AWI) and the French Polar Institute (IPEV). The assistance of 4H-Jena Engineering is essential to the project.

Further information