Data were collected as part of the DiatomARCTIC project during the Multidisciplinary Arctic Program - Last Ice sampling campaign (82.576 N 62.471 W), 7-23 May, 2018. The bottom 10 cm of ice samples were collected during this time from neighbouring first-year and multi-year sea ice floes, from which the following parameters were determined: chlorophyll a, exopolymeric substances, ice algal taxonomic composition, oxygen-based net community production and bulk-ice nitrate, nitrite and phosphate concentrations. All samples were melted without dilution and were processed by K Campbell. This work is a contribution to the Diatom ARCTIC project (NE/R012849/1; 03F0810A), part of the Changing Arctic Ocean program, jointly funded by the UKRI Natural Environment Research Council and the German Federal Ministry of Education (BMBF) and Fisheries and Oceans Canada (DFO) Science and the Marine Productivity Laboratory Program. The Multidisciplinary Arctic Program (MAP) - Last Ice is funded by Fisheries and Oceans Canada (DFO) Science in support of Tuvaijuittuq Marine Protected Area (MPA). Additional support was provided by Polar Continental Shelf Program (PCSP, Project 10718) and the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Funds to CM and CHSR.

The long term monitoring of water chemistry in Signy Island lakes is unique in polar limnology, in its duration (30+ years), detail, and range of sites. It details seasonal patterns of snow and ice cover, inorganic nutrient status and chlorophyll-a and includes vertical profiles of various physical chemical parameters. There are detailed data for several study lakes and twice/thrice yearly analyses for all the Signy Island lakes. Temperature and light climate has been studied in certain lakes using automatic data loggers. Micrometeorological monitoring with additional data loggers provided data on solar radiation (PAR, UVR), air temperature, humidity and wind conditions. Data are collected by chemical analysis, use of temperature, pH light probes and observation. The ''grand prix'' was the sampling of 16 lakes in a short period (approx. one week), this was carried out perhaps two or three times a year. Approximately three to five lakes were sampled monthly or fortnightly in more detail, these were representative of the 16 lakes. Comparative studies were also undertaken in the Arctic. The long-term programme was established in 1971, although some observations were made in 1963/1964 and 1969/1970. The programme finished in 2004. As the exact months of the data collection were not provided, and the metadata standard requires a YYYY-MM-DD format, this dataset has been dated as 1st January for start date, and 31st December for stop date.