Stephanie Lim

On a research cruise to the Alaskan Arctic, we measured the sinking speeds of individual algal cells and colonies. This behavior control the delivery of food to marine animals.

The seasonally ice-covered Chukchi Sea is a region of high primary productivity, with three main pulses of production by sea ice algae, under-ice phytoplankton, and open water phytoplankton. The fate of organic carbon from these blooms on the shallow Chukchi Sea shelf is not well understood, despite its importance in feeding both the benthic and pelagic food webs. Microalgal behavior and physiology partially determine carbon export, but these small-scale factors are difficult to study in field conditions; traditional measurements of export flux integrate across the bulk biological community. On a research cruise in June-July 2024, we used a scale-free vertical tracking microscope, the Gravity Machine, to measure the sinking speeds of single microalgal cells and colonies from all three algal groups. Preliminary results suggest that a significantly greater proportion of phytoplankton exhibited positive buoyancy than ice algae, perhaps related to the fact that ice algae grow in/on sea ice and do not need to actively regulate their position in the water column.