SCIENTISTS in Goa have discovered that a massive open-water gap in the frozen Antarctic Ocean has recurred several times over 250 years, suggesting that the phenomenon is not a rare one-time event. Reconstructing environmental data from a 122-metre ice core, the researchers at the Goa-based National Centre for Polar and Ocean Research (NCPOR) identified 25 potential opening events of the Maud Rise Polynya - a large area of open water surrounded by sea ice. The study, recently published in “The Cryosphere” journal, uses a multi-proxy analysis of an ice core from coastal Dronning Maud Land in East Antarctica to reconstruct Maud Rise Polynya (MRP), also known as the Weddell Polynya, from 1774 to 2016.

 

The study was conducted by Rahul Dey, Chavarukonam M Laluraj, Kenichi Matsuoka, Ashish Paiguinkar, Bhikaji L Redkar, and Thamban Meloth. The study identified distinct clusters of polynya activity, which they said may correspond to particular combinations of atmospheric circulation patterns and oceanographic preconditioning that favour the formation of the phenomenon. A polynya is an area of open water that forms within sea ice. Open-ocean polynyas are considered important features of the Southern Ocean because they facilitate exchanges of heat and gases between the ocean and atmosphere and can influence deep-ocean convection, carbon cycling and ocean circulation. The Maud Rise Polynya, located over the Maud Rise seamount in the eastern Weddell Sea, is one of the most significant open-ocean polynyas in the Southern Ocean.

 

During 1974-1976, it reached an extent of more than 300,000 sq km at its peak and triggered intense ocean convection to depths of more than 3,000 metres, the study showed. It reappeared on a smaller scale during the winters of 2016 and 2017, when the opening exceeded 40,000 sq km, renewing scientific interest in the phenomenon. Researchers stated that understanding the phenomenon before the satellite era has been difficult, and to overcome this limitation, the team analysed a 122-metre ice core drilled at Djupranen Ice Rise in coastal Dronning Maud Land. The core was transported to NCPOR, where it was stored and processed in the institute’s ice-core laboratory - one of its kind in India. The chronology of the core was established through annual layer counting and dated markers, extending the record back to 1774. The scientists developed a polynya index by combining four ice-core indicators - sea-salt sodium flux, oxygen isotope ratios, deuterium excess and annual snow accumulation.

 

The multi-proxy approach was designed to identify signals that occur together during polynya formation and reduce the limitations associated with relying on a single indicator. The study recorded clusters of activity in the late 18th and 19th centuries, notable events in the early 20th century and a relatively suppressed period between about 1920 and 1950. Moderate polynya activity was also identified in several years after 1980. The reconstruction also captured the lesser-known 1964 polynya event, although its likelihood was lower than that of the 1974-1976 event, said Dr Laluraj, Scientist F and co-author of the study. Air-mass trajectory analysis further showed a consistent atmospheric connection between the Maud Rise region and the ice-core site. The researchers found that a significant proportion of air masses reaching the study site had travelled over the polynya-prone region, providing a basis for detecting polynya-related signatures in the ice core.

 

The study said that the recurring nature of polynya activity suggests that favourable atmospheric and oceanic conditions may persist for periods of years or decades, making the region more susceptible to repeated openings. The findings could also help scientists understand how such events may respond to climate change. The researchers noted that future changes in Southern Ocean winds, sea-ice extent and surface freshening could alter the conditions required for deep convection and potentially affect the frequency and persistence of Maud Rise Polynya events. Dr Thamban Meloth, Director, NCPOR and co-author of the study, said, “Integrating the ice-core-based climate reconstruction with modern observations and coupled ocean-atmosphere models could improve understanding of the factors governing openings in the sea ice and its implications for global ocean circulation, carbon exchange and climate variability.”