For the past week, we have been diving near the McMurdo Jetty. Our dive hole and hut are located very close to shores of Ross Island, and during our 15ft, 3 min safety stop – we enjoy playing underneath the sea ice close to shore in amongst the wonderous anchor ice.
Achor ice forms in the spring/early summer here in Antarctica. Supercooled water flows out from underneath the ice shelves and moves North. Although this “supercooled” water is only 0.1-0.2°C [or 32°F] colder than the surrounding seawater (the annual mean water temperature in McMurdo Sound is -1.87°C or 28.6°F) the temperature difference is enough to stimulate ice crystal growth.
Beautiful, shimmering crystals form in the water column and larger crystals start to grow on the seafloor. Eventually, a giant blanket of thick interlocking crystals known as “anchor ice” forms on the shallow seafloor, growing up to 2 feet thick in some areas.
Swimming next to this anchor ice is a phenomenal experience. As you gently graze the anchor ice, the crystals break off and float up into the water column. With light reflected in all directions, you feel like you are inside a magical kaleidoscope or surrounded by fairy dust.
The experience of being beneath sea ice is almost indescribable. The colors of blue that pass through the cracks in the snow and ice are so beautiful – it almost reminds me of the milky way!