Group 2i Isochrysidales (Haptophyta) microalgae were recently suggested to be the main producer of the C37:4 alkenone in high latitude oceans with seasonal sea ice, enabling potential quantitative sea ice reconstructions using C37:4%. However, the conditions favoring the growth of Group 2i are currently unclear. Phylogenetically based on small subunit 18S rDNA sequence data, Group 2i is indistinguishable from OTU8 and Hap-A previously reported in numerous saline lakes around the world, and has been found to bloom in the early spring season in Lake George, North Dakota. These observations suggest Group 2i may have a preference for low growth temperatures and may grow within or underneath seasonal ice. Here we performed systematic culture experiments of Group 2i RCC5486 (isolated from sea ice of Baffin Bay) at exceedingly low temperatures (0, 3, 6, 9 °C at 31 ppt) and different salinities (15, 21, 26, 31, 38 ppt at 3 °C). We found Group 2i RCC5486 displays unusually fast growth from 0 to 6 °C, but failed to grow at 10.5 and 12 °C. These data confirm that Group 2i is explicitly adapted to low temperatures in both saline lakes and high latitude ocean regions (i.e., it is a psychrophile). Salinity, on the other hand, does not significantly influence the growth rates of Group 2i RCC5486. In addition, both growth temperature and salinity show minimal influence on C37:4%, which supports the use of C37:4% as a proxy for sea ice, rather than temperature or salinity in high latitude oceans.