| title: | CTD data (temperature, conductivity, salinity, chlorophyll, uncalibrated oxygen) from Troll Transect cruise 2020/21 to Dronning Maud Land, Antarctica |
| summary: | CTD data collected off the coast of Dronning Maud Land, Antarctica during the Troll Transect Cruise 2020/21. This dataset contains pressure-gridded (1 dbar) CTD data (temperature, conductivity, salinity, chlorophyll, uncalibrated oxygen) from 14 profiles collected between 28.12.2020 and 07.01.2021. Data were collected using an SBE911+ unit (other CTD data were collected during the cruise - they are not included here).
Stations from 010_01 constitute a meridional (offshore) transect along approximately 6.1°E.
Data from an SBE 43 oxygen sensor are included (both as dissolved oxygen and raw sensor voltage) - please note that these data have not been calibrated or quality-controlled, and are provided as-is.
CTD Chlorophyll data were calibrated based on a linear fit of CTD fluorometer against bottle fluorescence measurements:
1. First, the median value of dark counts at depth was determined based on measurements from 100 to 500 m depth.
2. A visual inspection confirmed that there were no offsets between profiles.
3. To calibrate the bottle Chl-a data to the bottle fluorescence measurements, we first only considered the bottle Chl-a value when the standard deviation of the bottle value divided by the fluorescence measurement was < 0.15, to avoid highly noisy parts of the fluorescence profile. Then we subtracted the offset value (1.0495) from the bottle fluorescence measurement, then we fit a linear regression with the bottle Chl-a measurement.
Salinity values have been compared with salinometer measurements from bottle samples from >1000 dbar (n=16). The average offset (CTD minus salinometer) was -0.0038. This was considered within the total margin of error, except for one notable outlier at station sta010_01, where a salinity difference of -0.0164 was found. Removing this offset from the profile brings the bottom temperature-salinity properties closer to the deep water masses further offshore along the same transect. Sta010_01 was also the first profile taken after the unloading operations, during which the CTD package was unsupervised inside a shipping container for several days, where e.g. accretion of salt crystals in the conductivity cell may have led to a time-depended bias when measurements were resumed. However, at this point, we cannot conclude whether the difference at this station is related to a sensor offset or an inaccurate salinometer sample, and no correction was applied to any of the profiles in this file, and with a greater uncertainty to be accounted for at sta010_01. |
| history: | 2020-12-28 to 2021-01-07: Data collection.
2021-01-13 to 2021-01-21: Processed to .cnv using SBE software (details in "SBE_processing").
2023-12-29: Post-processing.
2024-01-22: Creation of this netcdf file. |
| id: | TrollTransectCTD_2020_2021_v1 |
| version: | 1.0 |
| doi: | 10.21334/npolar.2023.b1504a66 |
| date_created: | 2024-01-22T14:16:27Z |
| comment: | Chlorophyll-a profiles calculated based on best fit against in-situ water sample measurements (see CHLA attributes for details). Oxygen NOT calibrated against water sample measurements. |
| source: | CTD profiles from SBE911+ |
| instrument: | In Situ/Laboratory Instruments>Profilers/Sounders>CTD |
| platform: | Water-based Platforms>Vessels |
| institution: | Norwegian Polar Institute (NPI) |
| cruise_name: | TrollTransect Cruise 2020/2021 |
| project: | Norwegian Polar Institute 2020/21 TrollTransect pilot project cruise; Ocean-ice shelf interaction and channelized Melting in Dronning Maud Land project, Research Council of Norway grant no. 295075 |
| area: | Southern Ocean |
| location: | Kong Håkon VII Hav / Dronning Maud Land (DML) |
| license: | CC-BY 4.0 |
| time_coverage_start: | 2020-12-28T09:19:47Z |
| time_coverage_end: | 2021-01-07T10:59:14Z |
| time_coverage_resolution: | variable |
| time_coverage_duration: | P0000-00-10T01:39:27 |
| geospatial_lat_max: | -67.01620000000000 |
| geospatial_lon_max: | 10.62470000000000 |
| geospatial_lat_min: | -70.01220000000001 |
| geospatial_lon_min: | 5.514700000000000 |
| geospatial_bounds: | POLYGON ((5.51 -70.02, 5.51 -67.01, 10.63 -67.01, 10.63 -70.02, 5.51 -70.02)) |
| geospatial_bounds_crs: | EPSG:4326 |
| geospatial_vertical_min: | 2.000000000000000 |
| geospatial_vertical_max: | 3403.000000000000 |
| geospatial_vertical_positive: | down |
| geospatial_vertical_units: | dbar |
| geospatial_bounds_vertical_crs: | EPSG:5831 |
| data_set_language: | eng |
| data_assembly_center: | NO/NPI |
| creator_name: | Norwegian Polar Institute (NPI) |
| creator_email: | post@npolar.no |
| creator_type: | institution |
| creator_institution: | Norwegian Polar Institute (NPI) |
| creator_url: | www.npolar.no |
| publisher_name: | Norwegian Polar Institute (NPI) |
| publisher_url: | www.npolar.no |
| publisher_email: | post@npolar.no |
| publisher_institution: | Norwegian Polar Institute (NPI) |
| keywords: | OCEANS>OCEAN TEMPERATURE>OCEAN TEMPERATURE PROFILES,OCEANS>OCEAN CHEMISTRY>OXYGEN,OCEANS>SALINITY/DENSITY>OCEAN SALINITY>OCEAN SALINITY PROFILES,OCEANS>SALINITY/DENSITY>CONDUCTIVITY>CONDUCTIVITY PROFILES,OCEANS>OCEAN OPTICS>CHLOROPHYLL>CHLOROPHYLL CONCENTRATION |
| binned: | 1 decibars (SBE software) |
| SBE_processing: | SBE SOFTWARE PROCESSING STEPS (extracted from .cnv file header):
1. Raw data read from e.g. STA018_01.HEX, STA018_01.XMLCON.
2. Oxygen hysteresis correction applied.
3. Wild editing applied.
> Parameters: n_std (first pass): 2.0, n_std (second pass): 20.0, min_delta: 0.0,
> # points per test: 100.0.
> Applied to variables: prDM t090C c0S/m.
4. Cell thermal mass correction applied to conductivity from sensors: [primary, ].
> Parameters ALPHA: [0.0300, 0.0000], TAU: [7.0000, 0.0000].
5. Low-pass filter with time constant 0.03 seconds applied to: t090C c0S/m sbeox0V flECO-AFL altM.
6. Low-pass filter with time constant 0.15 seconds applied to: prDM.
7. Loop editing applied.
> Parameters: Minimum velocity (ms-1): 0.250, Soak depth range (m): 5.0 to 20,
> Bad scans excluded. Deck pressure offset: Yes.
8. Derived EOS-8 salinity and other variables.
9. Bin averaged (1 decibars).
> Bad scans not excluded, skipped over 0 initial scans.
> (No surface bin). |
| source_files: | E.g. STA018_01.HEX, STA018_01.XMLCON -> STA018_01.CNV |
| featureType: | profile |
| standard_name_vocabulary: | CF Standard Name Table v83 |
| instrument_vocabulary: | NASA/GCMD Instrument Keywords Version 17.2 |
| keywords_vocabulary: | NASA/GCMD Science Keywords 9.1.5 |
| iso_topic_category: | oceans |
| Conventions: | ACDD-1.3, CF-1.8 |
| naming_authority: | npolar.no |
| ship: | Malik Arctica |
| program: | Norwegian Polar Institute Antarctic Porgram, Research Council of Norway POLARPROG |
| acknowledgement: | Data collection and processing was a part of the Norwegian Polar Institute 2020/21 TrollTransect pilot project cruise and supported by the Ocean-ice shelf interaction and channelized Melting in Dronning Maud Land project, Research Council of Norway grant no. 295075 |
| data_set_progress: | complete |
| PRES: | Array of 64 bit Reals [PRES = 0..3401] _FillValue: NaN units: dbar sensor_serial_number: 0972 sensor_calibration_date: 20-Feb-14 coverage_content_type: coordinate standard_name: sea_water_pressure long_name: Pressure due to seawater positive: down valid_min: -1.000000000000000 valid_max: 12000.00000000000 axis: Z sensor_mount: mounted_on_shipborne_profiler |
||||||
| TIME: | Array of 64 bit Reals [TIME = 0..13] _FillValue: NaN units: Days since 1970-01-01 00:00:00 standard_name: time long_name: Average time of measurements SBE_source_variable: timeS axis: T coverage_content_type: coordinate |
||||||
| TEMP: | Grid _FillValue: NaN units: degree_Celsius standard_name: sea_water_temperature long_name: Sea water temperature processing_level: Data manually reviewed QC_indicator: good data sensor_serial_number: 5299 sensor_calibration_date: 08-Sep-20 valid_min: -3.000000000000000 valid_max: 40.00000000000000 sensor_mount: mounted_on_shipborne_profiler reference_scale: ITS-90 coverage_content_type: physicalMeasurement
| ||||||
| CNDC: | Grid _FillValue: NaN units: S m-1 standard_name: sea_water_electrical_conductivity long_name: Seawater electrical conductivity processing_level: Instrument data that have been converted to geophysical values QC_indicator: unknown sensor_serial_number: 3742 sensor_calibration_date: 10-Sep-20 valid_min: 0.000000000000000 valid_max: 50.00000000000000 sensor_mount: mounted_on_shipborne_profiler coverage_content_type: physicalMeasurement
| ||||||
| OXYV: | Grid _FillValue: NaN units: volt long_name: Raw signal (voltage) of instrument output by oxygen sensor processing_level: Instrument data that have been converted to geophysical values QC_indicator: unknown sensor_serial_number: 1740 sensor_calibration_date: 17-Oct-20 valid_min: 0.000000000000000 valid_max: 1000.000000000000 sensor_mount: mounted_on_shipborne_profiler coverage_content_type: physicalMeasurement
| ||||||
| PSAL: | Grid _FillValue: NaN units: 1 standard_name: sea_water_practical_salinity long_name: Practical salinity comment: Salinity values have been compared with salinometer measurements from bottle samples from >1000 dbar (n=16). The average offset (CTD minus salinometer) was -0.0038. This was considered within the total margin of error, except for one notable outlier at station sta010_01, where a salinity difference of -0.0164 was found. Removing this offset from the profile brings the bottom temperature-salinity properties closer to the deep water masses further offshore along the same transect. Sta010_01 was also the first profile taken after the unloading operations, during which the CTD package was unsupervised inside a shipping container for several days, where e.g. accretion of salt crystals in the conductivity cell may have led to a time-depended bias when measurements were resumed. However, at this point, we cannot conclude whether the difference at this station is related to a sensor offset or an inaccurate salinometer sample, and no correction was applied to any of the profiles in this file, and with a greater uncertainty to be accounted for at sta010_01. processing_level: Data manually reviewed QC_indicator: good data sensor_serial_number: 5299, 3742 sensor_calibration_date: 08-Sep-20, 10-Sep-20 valid_min: 2.000000000000000 valid_max: 41.00000000000000 sensor_mount: mounted_on_shipborne_profiler reference_scale: PSS-78 coverage_content_type: physicalMeasurement manual_editing: 14 data points have been removed from this variable based on visual inspection.
| ||||||
| DOXY_instr: | Grid _FillValue: NaN units: mL l-1 standard_name: volume_fraction_of_oxygen_in_sea_water long_name: Dissolved oxygen from sensor. Not calibrated against water samples. comment: Not compared with water sample oxygen measurements. Quality unknown! processing_level: Instrument data that has been converted to physical values QC_indicator: unknown sensor_serial_number: 1740 sensor_calibration_date: 17-Oct-20 valid_min: 0.000000000000000 valid_max: 1000.000000000000 sensor_mount: mounted_on_shipborne_profiler coverage_content_type: physicalMeasurement
| ||||||
| STATION: | Grid long_name: CTD station ID sensor_mount: mounted_on_shipborne_profiler coverage_content_type: physicalMeasurement cf_role: profile_id
| ||||||
| LATITUDE: | Grid _FillValue: NaN units: degree_north standard_name: latitude long_name: latitude sensor_mount: mounted_on_shipborne_profiler coverage_content_type: physicalMeasurement axis: Y
| ||||||
| LONGITUDE: | Grid _FillValue: NaN units: degree_east standard_name: longitude long_name: longitude sensor_mount: mounted_on_shipborne_profiler coverage_content_type: physicalMeasurement axis: X
| ||||||
| CRUISE: | String long_name: Cruise ID sensor_mount: mounted_on_shipborne_profiler coverage_content_type: physicalMeasurement |
||||||
| CHLA: | Grid _FillValue: NaN units: mg m-3 standard_name: chlorophyll_concentration_in_sea_water long_name: Chlorophyll-A concentration calibrated against water sample measurements comment: No correction for near-surface fluorescence quenching (see e.g. https://doi.org/10.4319/lom.2012.10.483) has been applied. processing_level: Post-recovery calibrations have been applied QC_indicator: good data calibration_formula: chla_calibrated = A * chla_from_ctd + B coefficient_A: 0.08950000000000000 coefficient_B: -0.09393025000000001 sensor_serial_number: FLRTD-1547 sensor_calibration_date: 4-Jan-16 valid_min: -1.900000000000000 valid_max: 100.0000000000000 sensor_mount: mounted_on_shipborne_profiler coverage_content_type: physicalMeasurement manual_editing: Profile *sta013_01* removed from the dataset due to issues with the sensors causing unrealistic values
|