Germination

January 3, 2010, 7:42 am • Tags: , ,

icon_121Watermelon snow, also called snow algae, is snow that is reddish or pink in color, with the slight scent of a fresh watermelon. Compressing the snow by stepping on it or making snowballs leaves it looking red. Walking on watermelon snow often results in bright red soles and pinkish pant cuffs.

This type of snow is common during the summer in alpine and coastal polar regions worldwide, such as the Sierra Nevada of California. The snow is caused by the presence of Chlamydomonas nivalis, a species of green algae containing a secondary red carotenoid pigment. Unlike most species of fresh-water algae, it is cold-loving and thrives in freezing water. At altitudes of 10,000 to 12,000 feet, the temperature is cold throughout the year, and the snow has lingered from winter storms.

Chlamydomonas nivalis owes its red color to a bright red pigment which protects the chloroplasts from intense visible and ultraviolet radiation. They also absorb heat, which provides the algae with liquid water as the snow melts around it. Algal blooms may extend to a depth of 10 inches. It has been calculated that a teaspoon of melted snow contains a million or more of these cells.

The algae sometimes accumulate in “sun cups”, which are shallow depressions in the snow. The carotenoid pigment absorbs heat and as a result it deepens the sun cups and accelerates the melting rate of snowbanks. During the winter months when snow covers them, the algae become dormant. In spring, increased levels of light and melting water stimulate germination.

The first accounts of watermelon snow are in the writings of Aristotle. Watermelon snow has puzzled mountain climbers, explorers, and naturalists for thousands of years, some speculating that it was caused by mineral deposits or oxidation products that were leached from rocks.