Methodology:

The bottom 10 cm of sea ice cores were collected on May 23 from 14 locations along a 240-m transect spanning both first-year ice (FYI) and multi-year ice (MYI) floes, using a 9-cm diameter Mark II ice coring system from Kovacs Enterprise LLC. These cores were melted without dilution and processed within 24h for the variables defined.

Variables were processed according to the following references:

Chlorophyll a (Parsons et al., 1984); 0.7 µm GF/F (Whatmann)

Exopolymeric substances (Dubois et al., 1956); 0.4 µm polycarbonate filters (Millipore)

Sea ice algal taxonomy (Campbell et al., 2018); Lugol preservation

Net community production (Campbell et al., 2016)

Inorganic nutrients (Strickland and Parsons, 1972); 0.7 µm GF/F (Whatmann) pre-filtered

Data collected on 23 May were taken from 14 locations (10 first-year ice; 4 multi-year ice). Data from single point locations in the study region were also taken for first-year ice on 4, 11, 15, 19, and 23 May, and for multi-year ice on 7, 11, 19, 23 May.

Data collection:

Chlorophyll a (Turner Designs 10AU fluorometer)

Exopolymeric substances (Agilent Cary 60 spectrophotometer)

Sea ice algal taxonomy (Nikon inverted microscope)

Net community production (Firesting oxygen optodes; modelling with Matlab R2019b software)

Inorganic nutrients (LaChat QuikChem 8500 series 2 flow injection analyser (QuikChem Method 31-114-27-1-D))

Data quality:

Instrument calibration was done prior to measurements of fluorescence (chlorophyll a), net community production (two-point calibration), and inorganic nutrients. The concentration of exopolymeric substances was determined with reference to glucose.