A study of the causes of the heavy sea ice conditions in the Antarctic when Shackleton’s Endurance Expedition was heading south has been published just as the same phenomena (called ‘El Nino’) is causing record sea ice levels in the area today
The study’s authors, Robert Burton and John C King, debunk the myth that it was the whalers at South Georgia that warned Shackleton of it being ‘a bad ice year’ in the Weddell Sea. Shackleton actually knew the ice was likely to be an obstacle because the effects of what is now known as ‘El Nino’ were beginning to be understood by meteorologist Robert Mossman. Today El Nino is defined as an anomalous, yet periodic, warming of the central and eastern equatorial Pacific Ocean which occurs every 2-7 years for a period of 6-18 months.
Mossman was interested in links between weather and ice in the Antarctic and weather in South America and he realised that rainfall in South America could be an indicator of ice extent further south, and vice versa.
Mossman’s theory was recognised when, whilst Endurance was in Buenos Aires, the expedition geologist James Wordie wrote in his diary: ‘…it looks as if the pack would be very heavy this season; this is following Mossman’s theory of heavy rains in the Argentine in Spring (just what we are having) being due to the ice in the Weddell Sea not having broken out early’.
Despite Shackleton’s expedition waiting a month at South Georgia because of the ice threat, their ship Endurance was still trapped in the ice and ultimately sunk.
One hundred years later record breaking sea ice is being recorded in Antarctica, and once again the large ice extent is associated with an El Nino event. Sea ice levels are nearly 45% higher than the 1981-2010 average. This is 570 000 square kilometers more than the previous sea ice record set in 2008. Vessels trying to reach science bases in the Antarctic have been struggling to get through the ice to deliver vital stores. The greater extent of sea ice also affected tourist ships trying to visit the continent last summer, preventing some of them from reaching their regular landing sites. The current El Nino is expected to persist and may be one of the strongest ones in two decades according to U.S. and Australian government meteorologists.
Why does El Nino affect the Antarctic sea ice? During El Nino years the waters of the Eastern Pacific heat up and warm the air which rises and starts to move toward the South Pole. The effect of the earth's rotation is to turn the winds eastward where it strengthens the subtropical jet stream. This stronger jet stream diverts storms away from the Pacific side of the South Pole so there is less wind to blow sea ice farther out into the ocean, so the ice stays close to shore.
Source: South Georgia News