The principle aim of the PIPERS project is to observe how sea ice and dense water are produced in coastal polynyas. The word “polynya” is Russian for “hole in the ice”. It refers to a region of persistent open water that is surrounded by sea ice. Coastal polynyas are kept open by strong offshore or “katabatic” winds. These winds pick up sporadically, and blow as fast as 60 km/hr, typically for 18-48 hours. These katabatic wind events push the ice out of the polynya, even as new ice is made from the extreme wind and cold air temperatures (well below -20 C in the winter). This process of incessant sea ice production concentrates salt in the polynya producing the densest water in the global ocean. Sinking dense water produces deep convection down to the ocean bottom, releasing ocean heat to the air and producing a deep column of seawater that exchanges gas, aerosols and other chemical species with the air. This deep column will pick up some of the anthropgenic carbon dioxide (CO2) that we produce and convey that CO2 into the deep sea. Deep convection over the ocean floor may also release methane, another greenhouse gas, from the sediments.
The water made in the coastal polynyas of Antarctica eventually sinks along the ocean floor to become part of Antarctic Bottom Water – the largest and densest water mass in the ocean. In this way, a polynya is like chimney or a stove pipe between the deep ocean and the atmosphere.
There is evidence that the rate of sinking and Bottom Water production is decreasing, but we will save that for another post.