‘Sharp decline in Antarctic sea ice due to negative IOD’

Namrata Devikar
Thursday, 7 February 2019

ANTARCTIC ICE EXTENT
Antarctic sea ice is the sea ice of the Southern Ocean. It extends far north in winter and retreats almost to the coastline each summer. This frozen area that expands between the coastline and the end of the ice in winter is the sea ice extent. It is frozen seawater that is usually less than a few metres thick.

PUNE: Long term warming contributed to record negative Indian Ocean Dipole (IOD) in 2016 was the major reason behind the decline of Antarctic Sea ice in 2016. This was revealed in a recent paper published by Dr Harry Hendon, Senior Principal Research Scientist and Climate Processes, Team Leader, Bureau of Meteorology, Melbourne, Australia.

Speaking about his paper during the ‘PR Pisharoty Distinguish Lectures at Indian Institute of Tropical Meteorology (IITM), Hendon said that there were a lot of factors that influenced the event in the Antarctic of 2016. The lecture series was organised by Indian Meteorological Society, Pune chapter on Wednesday. Antarctic Sea ice is frozen seawater and is usually less than a few metres thick.

However, it is very important to the global climate and marine ecosystems. Climate experts mentioned that in contrast to the Arctic, sea ice around Antarctica had been slowly expanding. 

“The sharp decline in Antarctic sea-ice extent in September to October 2016 promoted by record negative IOD event. This negative IOD affected Antarctica sea-ice during September to October 2016. La Nina conditions played a secondary role for promoting anomalous circulation to the south of south Antarctica,” said Hendon.

ROLE OF STRONGEST NEGATIVE IOD
Speaking about the negative IOD from June to September 2016, Dr Hendon said that typically the IOD peaks from September to November.

“Negative IOD of 2016 developed from May, peaked in July and September and decayed rapidly in November. This event was the strongest negative IOD since 1960,” said Dr Hendon. 

He further added that reason why IOD was strongly negative because of strong El Nino in 2015-16.

“The effect of El Nino of 2015-2016 remained which was a primary reason for the negative IOD. Followed by the long term warming trend,” said Hendon.

ROLE OF GLOBAL WARMING
Speaking during the lecture, Dr Hendon said that the Indian Ocean is getting warmer since the 1960s.

“In 2016, we experienced biggest El Nino. But La Nina of 2015 ended up to be a weak event. Also, with the early development of strong negative IOD in July,” said Dr Hendon.

ACCORDING TO NATIONAL SNOW AND ICE DATA CENTER
- As of January 1, 2019, Antarctic Sea ice extent had experienced several days of record lows.
- On January 1, 2019, Antarctic sea ice extent stood at 5.47 million square kilometres, the lowest extent on this date in the 40-year satellite record.
- This years value of 5.47 million square kilometres, is 30,000 square kilometres below the previous record low for January 1, 2017.

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