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University of Bergen

Ocean microstructure measurements using an MSS profiler during the Nansen Legacy cruise, KH2021702, February 2021.

Recommended citation:
Fer, Ilker; Baumann, Till M.; Kalhagen, Kjersti; Koenig, Z; Kolås, Eivind H. (2023) Ocean microstructure measurements using an MSS profiler during the Nansen Legacy cruise, KH2021702, February 2021. https://doi.org/10.21335/NMDC-1939445412
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Abstract
As a part of the Nansen Legacy project, ocean microstructure data were collected using an MSS (Microstructure Sensor Profiler, Sea&Sun Technology, Germany) profiler during the Nansen Legacy cruise, KH2021702 in February 2021. The goal was to conduct ocean mixing and water transformation process studies in the Barents Sea Polar Front region east of Svalbard, in the northern Barents Sea. During the cruise, we obtained 181 microstructure profiles (23 of which were obtained from a drifting ice floe). Nine casts were aborted and not processed. Out of the processed 172 files, 181 sections were extracted and supplied in the grouped NC files (i.e., one profile cast can have multiple sections of profiles interrupted, for example, by a gap when the instrument did not fall freely; it is a coincidence that the number of sections matches the number of attempted casts). Here we provide 172 NetCDF (NC) files (one NC file per instrument's native file) compressed in one folder, as well as 2 NC files, one for profiles of CTD and a second one for profiles of dissipation rates, collated for the entire cruise. The converted data are prepared following the SCOR Working Group 160, ATOMIX guidelines and convention (https://wiki.uib.no/atomix). Files per cast: CAST0001.nc to CAST0181.nc (except casts 3, 35, 39, 125, 138 and 140) The NC files per instrument's native file include five groups. 4 levels of microstructure data in ATOMIX format and a CTD group, derived from the MSS’s CTD sensors. L1_converted: full resolution 1024 Hz sampled data converted to physical units L2_cleaned: data at full resolution from the shear probes and the vibration sensor that are filtered and despiked before spectral analysis. Time stamp and length of the signals are same as L1. L3_spectra: wavenumber spectra from shear probes and vibration sensors L4_dissipation: dissipation estimates together with quality control parameters CTD: 0.1dbar vertically averaged CTD profiles obtained from the precision sensors Detailed attributes and metadata are given at the global level as well as at the group level, including choices of processing parameters. For detailed information on the parameter names, description, and processing choices, the user is referred to https://wiki.uib.no/atomix. CTD profiles are 0.1 dbar vertically averaged. Dissipation estimates are from half-overlapping 6 s segments, using 2-s spectral calculations. The practical salinity obtained from the MSS is corrected against the shipboard SBE-911plus CTD system (calibrated against salinity water samples), using an offset correction of Scorrected = Smeasured - 0.018. The motivation for providing the full-resolution data is that the user can reprocess the data with their own routines if needed (either from the time series level or from spectra level). A user interested in CTD and dissipation rate profiles may find the collated two NC files more practical and easily accessible. Data quality flags are provided for dissipation estimates (L4) and for the CTD profiles. A final dissipation estimate failing the data quality control is reported as not-a-number (NaN); however, the individual dissipation estimates from each probe are accessible in the L4 data. Data quality flags in the CTD profile are not applied, except for the data transmission errors when there is no data. We also suspect unreliable data in the upper water column in some profiles, which we did not flag but left for the user's discretion. Collated files: Because each file includes full-resolution data at two levels and full-resolution spectra in the third group, the grouped NC files are large in size and may be unpractical to download and merge. Furthermore, the grouped NC structure is non-standard for some users. For users only interested in the dissipation and CTD profiles, we also provide two separate NC files with all sections from the L4_dissipation and CTD groups collated into one file each. Out of a total of 172 NC files, there are 181 sections. A section is a more general term for a profile and is a continuous segment of the time series with dissipation estimates. One profile cast can have multiple sections if, for example, the profile is interrupted by a gap when the instrument did not fall freely. MERGED_CTD.nc: collated from the CTD group MERGED_EPSI.n: collated from the L4_dissipation group Data quality flags from the groups are applied to the collated profiles. We also suspect unreliable data in the upper water column in some profiles, which we did not flag but left for the user's discretion. Parameters in the MERGED files are filled with NaNs to a common maximum depth or section duration, hence are in uniform dimension size, to allow easy handling of the data. Note, however, the data are not gridded in time or pressure. Each data point has its own time stamp and pressure value.
Scientific keywords:
EARTH SCIENCE> OCEANS> MARINE GEOPHYSICS
Key words:
Arctic Ocean, mixing, turbulence, dissipation rate, microstructure, shear probes
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