COMMSENV-25-0117B_Olsen_et_al_2026_dataset

This dataset contains data from Leg 2 of The Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) expedition in 2019/2020 led by the Alfred Wegener Institute, Bremerhaven, Germany. In the following is a summary of measured variables and corresponding analysis methods. A more detailed description of the study and methods is given in the published article. The study described in the article Focus on how organic matter trapped in the sea ice in the polar night is released during sea ice deformation
Samples for identification and quantification of bacteria and protists were taken from sea ice and water column by using KOVACS Mark II ice corer, Niskin water sampling bottles, horizontal plankton net tow by net attached to a remotely operated vehicle (ROV) and suction pump on the ROV. Samples for light microscopy was fixed with 25% glutaraldehyde and 20% hexamethylenetetramine-buffered formaldehyde solution to a final concentration of 0.1% and 1% (vol/vol), respectively. Protist cells were settled in Utermöhl sedimentation chambers for 48 h before identification and quantification in an inverted light microscope.
Samples for flow cytometry (FCM) were fixed with glutaraldehyde, frozen in liquid nitrogen and stored at -80 °C. Bacteria stained with the nucleic acid dye SYBR Green I were quantified in a FACS Calibur (Becton Dickinson, San Jose, Calif. USA) flow cytometer. Heterotrophic nanoflagellates stained with SYBR Green I (HNF) were quantified in an Attune® NxT, Acoustic Focusing Cytometer (Thermo Fisher Scientific). Biomass was calculated from equivalent spherical diameter (ESD) and a carbon conversion factor. Phytoplankton were quantified from autofluorescence in chlorophyll a.
Chlorophyll a samples from sea ice and water was collected on GF/F filters before extraction in 90% acetone and measurement in a Turner 10AU fluorometer, before and after acidification for Chla and phaeopigments, respectively (Holm-Hansen and Riemann 1978).
Bacterial production was measured by incorporation of tritium labeled leucine according to the method of Smith and Azam (1992).
Samples for particulate organic carbon (POC) from sea ice was collected on preignited Whatman GF/F filters, packed in tin cups and POC was measured in an elemental analyzer (Flash 2000, Thermo Scientific, Milan, Italy) at the University of La Rochelle, France (Littoral, Environment and Societies Joint Research Unit stable isotope facility).
Ridge temperature was monitored with deployed mass balance buoys and temperature of level sea ice was measured manually in ice cores. Bulk salinity was measured in melted ice cores with a salinometer, and data on temperature and salinity were used to calculate brine volume fraction (BVF) following the method in Cox and Weeks (1983).
References
Cox, G. F. N. & Weeks, W. F. Equations for Determining the Gas and Brine Volumes in Sea-Ice Samples. J. Glaciol. 29, 306–316 (1983).
Holm-Hansen, O. & Riemann, B. Chlorophyll a Determination: Improvements in Methodology. Oikos 30, 438 (1978).
Smith, D.C., F. Azam. A simple, economical method for measuring bacterial protein synthesis rates in seawater using 3H-leucine. Mar. Microb. Foodwebs 6, 107–114 (1992).