Seasonal formation of ikaite in slime flux jelly on an infected tree (Populus fremontii) wound from the Sonoran Desert

Ikaite is the calcium carbonate hexahydrate (CaCO₃·6H₂O), which precipitates below ~ 7 °C, first identified from Ikka Fjord in southwest Greenland and subsequently more widely reported. Here is described the serendipitous discovery of ikaite on a tree (Populus fremontii) wound from the hot Sonoran Desert, which precipitates during short cold periods in the winter, whereas monohydrocalcite forms through most of the year. The tree wound consists of infected wood, called wetwood that exudes a nutrient-rich water on which a jelly-like slime flux forms. Ikaite, along with alpha sulfur, precipitates in and on the bacterial slime flux jelly. Each tree wound occurs as an island of mineralization: all the elements for the mineral formation are supplied through the xylem sap expressed from the wetwood infection. The P. fremontii wetwood is capped and surrounded by a hard mineralized zone dominated by ikaite/monohydrocalcite, alpha sulfur, and a range of carbonates and sulfates, on which the slime flux jelly occurs. Water oozing from the wetwood is modestly alkaline (pH = 8.34), with elevated concentrations of K⁺ (5554.7 ppm) and S as SO₄²⁻ (1662.9 ppm), with Ca²⁺ (151.9 ppm) and Mg²⁺ (270.3 ppm). This water chemistry favors the precipitation of ikaite/monohydrocalcite, both within and below the jelly. The ikaite is temperature sensitive, though the laboratory results show that it can persist for several days at room temperature in the sulfur-rich jelly. The ikaite, and associated mineralization within and around the slime flux jelly, illustrates a new, and likely, global form of bio-mediated mineralization.