Evidence of atmosphere–sea ice–ocean coupling in the Terra Nova Bay polynya (Ross Sea—Antarctica)

Abstract

A rare long time series of hydrographic profiles and moored current meter data, collected from 1995 to 2008 in Terra Nova Bay polynya, are used in combination with meteorological data, acquired by an Automatic Weather Station, and remote sensing data from a Special Sensor Microwave/Imager. The behaviour of Terra Nova Bay coastal polynya in terms of air–ice–sea interactions and the consequent High Salinity Shelf Water production are detailed. The katabatic regime that characterizes Terra Nova Bay polynya is investigated and different types of events are distinguished on the bases of their duration and intensity. The more frequent katabatic events take place during the winter season from April to October, blowing on average 1–7h, with speed between 25 and 56ms−1 and they abruptly end in just a few hours. The link between the persistence of the wind and the opening of the polynya is showed. In particular, an increase of the open water percentage in correspondence with each katabatic event of long duration is detected. Terra Nova Bay polynya appears characterized by two different periods of activity during the winter season. A period characterized by a considerable sea-ice free area and by an increase in salinity along the water column (from July to November), which is preceded (from March to June) and followed (from December to February) by a period in which the polynya is still open but the salinity of the water column decreases. While the period between July and November appears related to a maximum efficiency of Terra Nova Bay polynya in the sea-ice production, the period from March to June marks a “partial” functioning of the polynya. During March–June, the polynya is partially free of ice and consequently the brine is released but, at this time of year, it is merely increasing the salinity of the upper layer of the ocean, reducing the stratification, but not causing High Salinity Shelf Water to be formed.