Artemia cysts at subzero temperatures studied by differential scanning calorimetry

Abstract Artemia cysts, with various contents of water, were studied by differential scanning calorimetry during cooling to −65 °C and subsequent heating to +20 °C. Several exothermic transitions were observed during cooling. One of them, at a temperature around −20 °C, was associated with separation of ice from subcooled “bulk” water. The enthalpy of this transition, and of the broad melting endotherm observed during heating, was used as a basis of estimates of the amount of water freezing and ice melting. The data support the view that water above a content of 0.55 g H 2 O g dry wt behaves as “bulk” water; 0.55 g H 2 O g dry wt appears as “vicinal” water, i.e., as water adjacent to components of the cysts. About 0.3 g H 2 O g dry wt is so closely bound to components of the cysts that it is precluded from any thermal transitions during cooling to −65 °C. The viability of the cysts, after a cooling-heating cycle, was estimated by hatching. The data indicate that the death of the cysts is associated with the occurrence of “vicinal” ice.