When sea ice forms during the polar winter it is often possible to observe the growth of frost flowers, intricate structures that are composed from frozen atmospheric moisture and from brine wicked from the sea ice surface. The transport of brine into these structures means that they are unusually salty, up to 5 times the salinity of the ocean. By this same mechanism other things in seawater concentrate in frost flowers, including bacteria. For the last two years we’ve been traveling to Barrow, Alaska to collect frost flowers in an effort to understand which bacteria are concentrated at the sea ice surface. Several important processes at the ice surface, including the production of aerosols and reactive organohalogens, are likely to be influenced by these bacterial. In addition since the surface of sea ice is very cold this is a great place to study how bacteria adapt to extreme conditions.
Although frost flowers are very abundant in the Arctic and Antarctic getting to them isn’t easy. The ice underneath them is often too thin to walk across and prone to drifting with the wind. The basic sampling strategy is to find a place where the water is kept open by winds or currents (called a lead if smaller and short lived, polynya if larger and more permanent), stand on the thick ice at the edge, and hope the wind drifts the newly forming ice and frost flowers within reach. This is not ideal! Our new project in Antarctica is a continuation of this effort to characterize the microbes at the sea ice surface. With luck we will find a range of better options for accessing these regions of new sea ice growth within McMurdo Sound.