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title:
CTD data (temperature, conductivity, salinity, chlorophyll, uncalibrated oxygen) from Troll Transect cruise 2020/21 to Dronning Maud Land, Antarctica
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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\302\260E.
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.
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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.
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id:
TrollTransectCTD_2020_2021_v1
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version:
1.0
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doi:
10.21334/npolar.2023.b1504a66
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date_created:
2024-01-22T14:16:27Z
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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.
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source:
CTD profiles from SBE911+
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instrument:
In Situ/Laboratory Instruments>Profilers/Sounders>CTD
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platform:
Water-based Platforms>Vessels
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institution:
Norwegian Polar Institute (NPI)
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cruise_name:
TrollTransect Cruise 2020/2021
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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
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area:
Southern Ocean
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location:
Kong H\303\245kon VII Hav / Dronning Maud Land (DML)
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license:
CC-BY 4.0
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time_coverage_start:
2020-12-28T09:19:47Z
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time_coverage_end:
2021-01-07T10:59:14Z
(Type is String)
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time_coverage_resolution:
variable
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time_coverage_duration:
P0000-00-10T01:39:27
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geospatial_lat_max:
-67.01620000000000
(Type is Float64)
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geospatial_lon_max:
10.62470000000000
(Type is Float64)
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geospatial_lat_min:
-70.01220000000001
(Type is Float64)
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geospatial_lon_min:
5.514700000000000
(Type is Float64)
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geospatial_bounds:
POLYGON ((5.51 -70.02, 5.51 -67.01, 10.63 -67.01, 10.63 -70.02, 5.51 -70.02))
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geospatial_bounds_crs:
EPSG:4326
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geospatial_vertical_min:
2.000000000000000
(Type is Float64)
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geospatial_vertical_max:
3403.000000000000
(Type is Float64)
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geospatial_vertical_positive:
down
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geospatial_vertical_units:
dbar
(Type is String)
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geospatial_bounds_vertical_crs:
EPSG:5831
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data_set_language:
eng
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data_assembly_center:
NO/NPI
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creator_name:
Norwegian Polar Institute (NPI)
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creator_email:
post@npolar.no
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creator_type:
institution
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creator_institution:
Norwegian Polar Institute (NPI)
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creator_url:
www.npolar.no
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publisher_name:
Norwegian Polar Institute (NPI)
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publisher_url:
www.npolar.no
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publisher_email:
post@npolar.no
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publisher_institution:
Norwegian Polar Institute (NPI)
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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
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binned:
1 decibars (SBE software)
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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).
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source_files:
E.g. STA018_01.HEX, STA018_01.XMLCON -> STA018_01.CNV
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featureType:
profile
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standard_name_vocabulary:
CF Standard Name Table v83
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instrument_vocabulary:
NASA/GCMD Instrument Keywords Version 17.2
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keywords_vocabulary:
NASA/GCMD Science Keywords 9.1.5
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iso_topic_category:
oceans
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Conventions:
ACDD-1.3, CF-1.8
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naming_authority:
npolar.no
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ship:
Malik Arctica
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program:
Norwegian Polar Institute Antarctic Porgram, Research Council of Norway POLARPROG
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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
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data_set_progress:
complete
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