Fish otoliths in sediment samples from expedition SAS, Arctic Ocean, 2021

Pauline Snoeijs Leijonmalm, Claudia Morys, Julek Chawarski, Flor Vermassen, Hauke Flores, Kim Vane

This dataset contains metadata and 296 files with photographs of 325 fish otoliths (calcium carbonate structures in the heads of bony fishes) sampled from the Arctic Ocean.

The otoliths were sampled from the upper 15 cm sediment layer during the Synoptic Arctic Survey (SAS) 2021 expedition with the Swedish icebreaker Oden serving as the research platform. The sediments were collected at 713⁠ – ⁠1537 m of water depth from eight 50 x 50 cm box-cores taken at six sampling stations.

These otoliths can be used for reconstructing fish occurrence in the Central Arctic Ocean and above the Morris Jesup Rise and Yermak Plateau during the last 50,000 years. Radiocarbon dating of 90 otoliths showed that the otoliths were deposited in the sediments during the Holocene (ca. 11.7⁠ – ⁠0 ka BP), the Last Glacial Maximum (ca. 29⁠ – ⁠11.7 ka BP) and the final stage of the Last Glacial Period (ca. 29⁠ – ⁠57 ka BP).

Citation

Pauline Snoeijs Leijonmalm, Claudia Morys, Julek Chawarski, Flor Vermassen, Hauke Flores, Kim Vane (2024) Fish otoliths in sediment samples from expedition SAS, Arctic Ocean, 2021. Dataset version 1. Bolin Centre Database. https://doi.org/10.17043/oden-sas-2021-fish-otoliths-1

References

Snoeijs-Leijonmalm Pauline, the SAS-Oden Scientific Party (2022) Expedition Report SWEDARCTIC: Synoptic Arctic Survey 2021 with icebreaker Oden. Swedish Polar Research Secretariat, 300 pp, ISBN 978-91-519-3672-7

Snoeijs-Leijonmalm P, Flores H, Sakinan S, Thorvaldsson B, Hildebrandt N, Chawarski J, Menger F, Leroy P, Pérez-Martínez C, Morys C, Vargas-Calle J, Muchowski J (2022) Ecosystem mapping in the Central Arctic Ocean (CAO) during the SAS-Oden expedition. Final Report. European Commission. 102 pp.

Snoeijs-Leijonmalm P, Sakinan S, Stranne C, Nilsson H, Hentati-Sundberg J, Niehoff B, Hildebrandt N, Flores H, Schaafsma F, Vane K, Vortkamp M, Volckaert F, Maes S, Verheye M, Chawarski J, Vermassen F, Bertilsson S, Buck M, Leroy P, Churcher A, Sundh J, Kierczak M (2023) Sample elaborations, data analyses, results and conclusions from the seagoing MOSAiC and SAS expeditions in the Central Arctic Ocean – Final report, Publications Office of the European Union. https://doi.org/10.2926/137293

Data description

This dataset is provided in one zip file with two directories:

• metadata, containing one xlsx and two csv files with metadata
• photographs, containing 294 tifand two pdf files with photographs of 325 fish otoliths.

Total file size: 694 MB (compressed 383 MB).

Metadata

The file SO21-fish-otoliths-241024.xlsx has three data sheets:

• 1. Explanations Detailed explanations of all variables in Sheets 2 and 3.
• 2. Box-core sampling data Overview of sampling dates, sampling times, water depth and geographical positions for the eight box-core samples taken during the SAS expedition with icebreaker Oden in 2021.
• 3. Otolith data Overview of the 325 fish otoliths sampled, each with reference to the photographs, including sampling details, morphometrics, species identification and fish age at death.

The data in sheets 2 and 3 are also provided as two separate csv files (encoding: UTF-8):

• SO21-box-core-sampling-data-241024.csv
• SO21-fish-otolith-data-241024.csv

The content in sheets 2 and 3 of the xlsxfile is provided below for each column_header:

2. Box-core sampling data

This sheet has 8 columns and 9 rows, with the following column headers:

1. Device_operation A code consisting of the expedition abbreviation (SO21 = SAS-Oden 2021), the station number (1-60) and the cast number (a running number for each device operation performed at one station), providing a unique code for each scientific sampling operation carried out during the SAS-Oden expedition. A device operation is either a winch operation from the ship or an ice station. In the Logbook, the device operation is coupled to date, time, geographical position and ocean depth. Ice stations next to the ship are in the Logbook classified as sampling operations at the ship station while ice stations reached by helicopter each have their own station number. Single sampling activities within the ice stations (e.g., ice coring, long-line deployment) were not recorded in the Logbook; their sampling details are recorded in the respective metadata files. With the help of the time of each device operation, the ship's exact position, speed and wind conditions can be extracted from the ship data. During the SAS-Oden expedition, 260 successful device operations were carried out, 9 failed and 2 were short test CTD casts. The latter 11 operations are also included in the Logbook, which in total contains 271 device operations.
2. Sampling_station Number of the sampling station.
3. Box_core_ID Eight box-core samples were taken during the expedition. They are numbered in chronological order.
4. Sampling_date Sampling date.
5. Time_bottom(UTC) Time when the box-core sample was taken at the seafloor. UTC = Coordinated Universal Time, or UTC, is the primary time standard by which the world regulates clocks and time. It is within about 1 second of mean solar time at 0° longitude and is not adjusted for daylight saving time. It is effectively a successor to Greenwich Mean Time (GMT).
6. Depth_bottom(m) Water depth at which the box-core sample was taken in meters.
7. Longitude_bottom(DM) Longitudal geographical coordinate at which the box-core sample was taken. DM = Degrees Minutes.
8. Latitude_bottom(DM) Latitudinal geographical coordinate at which the box-core sample was taken. DM = Degrees Minutes.

3. Otolith data

This sheet has 21 columns and 326 rows, with the following column headers:

1. Otolith_ID Identification number of the otolith sampled.
2. Box_core_ID Eight box-core samples were taken during the expedition. They are numbered in chronological order.
3. Stratum(cm) Sediment depth from which the otolith were sampled. The otoliths were collected from two types of samples: 1. Stratified samples with the upper 10 cm analyzed per 1-cm layer and the layer 10-15 cm combined, the layers from 11 or 12 pushcores of 8 cm in diameter were merged. 2. BULK samples include a non-stratified bulk sample of the upper 0-15 cm of the sediment taken in-between the pushcores for taking the stratified samples.
4. Photograph_file_name Name of the file that contains a photograph of the otolith.
5. Species_name Name of the species (Arctogadus glacialis, Boreogadus saida, Paraliparis bathybius). Otoliths that were too small or too damaged to be identified are denoted as "unidentified".
6. Otolith_status Whole otoliths are denoted as "whole", otoliths with missing parts are denoted as "chipped".
7. Diagenesis Physical and chemical changes of the otoliths since the time of deposition.
8. Boreholes Boreholes made by bottom fauna since the time of deposition.
9. Coated Coating of the otoliths by (often dark-coloured) external materials since the time of deposition.
10. Mass(mg) Weight of the otolith in milligrams.
11. Area(mm2) Area of the otolith in square mm.
12. Perimeter The length of the outside boundary of the otolith.
13. Major_axis(mm) The primary axis of the best fitting ellipse ("length").
14. Minor_axis(mm) The secondary axis of the best fitting ellipse ("width").
15. Aspect_ratio Ratio between the major and the minor axis ("length/width")
16. Feret(mm) The longest distance between any two points along the object boundary ("maximum caliper diameter")
17. MinFeret(mm) The shortest distance between any two points along the object boundary ("minimum caliper diameter").
18. Circularity (4π*area)/)perimeter^2). A value of 1 indicates a circle. As the value approaches 0, it indicates an increasingly elongated shape.
19. Roundness (4area)/(πmajor_axis^2). A value of 1 indicates a circle. A value greater than 1 indicates an increasingly non-circular shape with increasing difference from 1.
20. Solidity Area of the otolith divided by its convex area. The convex area is the area when every segment of a line, which has its ends within the area, has all its points within the area.
21. Age_at_death Age of the fish at death analyzed visually by counting otolith increments.

Photographs of fish otoliths

For each photograph the tif file name is composed of the expedition ID (SO21), the box core ID (BC1⁠ – ⁠BC8), the sediment stratum (in cm) or BULK sample (see metadata file), and the otolith ID.

For two otoliths (OTObc228, OTObc451) photographs are missing.

Two pdf files contain photographs of otoliths in the bulk samples from box cores BC7 and BC8 that have not been analyzed. They belong to the reference collection at AWI.

Comments

The data were collected in summer 2021 from Swedish icebreaker Oden during the Synoptic Arctic Survey (SAS) 2021 expedition organized by the Swedish Polar Research Secretariat.

The otolith material remaining after this study (for ¹⁴C analyses otoliths were destroyed) is kept at the Alfred Wegener Institute (AWI), Bremerhaven, Germany. Contact person: [javascript protected email address].