The effect of melting treatments on the assessment of biomass and nutrients in sea ice (Saroma-ko lagoon, Hokkaido, Japan)

Abstract

Melting of sea-ice samples is an inevitable step in obtaining reliable and representative measurements for biogeochemical parameters such as inorganic nutrients and particulate matter. The impact of the sea-ice melting procedure has been previously evaluated for biological parameters such as chlorophyll a and cell abundance. For nutrient and biomass concentrations in sea ice, it is generally considered to be best practice to melt samples fast; however, no systematic evaluation exists in literature. The impact of melting temperature and buffer addition to avoid osmotic shock was tested on ice samples in Saroma-ko Lagoon on the northeastern coast of Hokkaido, Japan. The focus was on inorganic nutrient concentrations (NO3−, NO2−, PO4−, NH4+, Si(OH)4) and particulate organic carbon and nitrogen concentrations and their isotope ratios. Coherent small changes have been observed for the parameter related to nitrogen, suggesting marginal cell lysis of a specific part of the microbial community. When differences are statistically significant, they are close to the uncertainty of the measurements and small in regard to the expected natural variation in sea ice. Our study suggest a minimal effect between melting treatments on biomass (POC, PN, and Chl a) and nutrient measurements in diatom-dominated sea ice and should be repeated where the sympagic community is dominated by flagellates.