A novel probe to sample dissolved and particulate matter in sea ice at high vertical resolution

Sea ice can be interspersed vertically with both permeable and impermeable layers. These features can be smaller than a few centimetres but are important for understanding biogeochemical cycles in sea ice. Traditionally, sea-ice samples are collected by drilling into the ice with a rotating core barrel with a cutting head. Ice cores are extracted and then cut into sections that are melted to collect the variable of interest. Drawbacks to this method include difficulty cutting sections smaller than a few centimetres thick and contamination of samples. Brines may also drain from their in-situ locations and be lost, meaning that important micro-environments in sea ice may be overlooked or misrepresented. To address these drawbacks, we developed a sea-ice melt probe that bores into sea ice and collects high-resolution samples. The capability of the melt probe to delineate a layer of dye in artificial sea ice was tested during cold laboratory-based experiments. Complementary field experiments were carried out in first-year landfast sea ice during February–March 2023 at Saroma-ko Lagoon, Japan. Experiments consisted of testing the high-vertical-resolution capability of the melt probe as well as its ability to be deployed on snow-covered sea ice. The melt probe was able to delineate a layer of dye at a finer resolution (20 mm) than traditional ice coring (approximately 50–100 mm) and could sample sea-ice brine in the field at a high vertical resolution. Melt-probe samples were also used to measure iron in sea ice without contamination. This proof-of-concept study provides an alternative method of sampling sea ice with the ability to support new research on fine-scale structures, with applications for sampling dissolved and particulate sea-ice constituents including trace metals, macro-nutrients, microplastics and gases.