Since the last ice age, a rise in carbon dioxide (CO2) levels stalled for about 2,000 years that resulted in warming, puzzling scientists. But a recent discovery of marine life in ancient Antarctic ice sheet has helped in providing insights to this puzzle.
A study published in Nature geoscience journal led by Chris J. Fogwell reveals that there was a huge increase in productivity of marine life at the surface of the Southern Ocean thousands of years ago. This discovery has huge implications for future climate studies, as this ancient marine life once played a significant role in climate regulation.
Antarctic exploration and marine life discovery
The team took a 4 hour flight traveling from Chile to the Weddell Sea, at the extreme southern end of the Atlantic Ocean, to land on an ice runway at a frigid latitude of 79° south. The Weddell Sea is frequently jammed with sea ice and has been dangerous to ships since the earliest explorers voyaged to the Antarctic region.
Ernest Shackleton, an Irish, Antarctic explorer in 1914 along with his crew became stuck in Antarctic region for two years, 1,000 kilometres from civilization. The crew was starved, faced isolation, freezing cold temperatures, gangrene, as they wandered the icebergs, along with the threat of cannibalism.
“Surviving here is tough, as is undertaking science,” said Dr. Fogwell. We spent 3 weeks in the nearby Patriot Hills, drilling through ice to collect samples.
Usually when scientists collect ice samples, they drill a deep vertical core through ice and snow, but the team led by Dr. Fogwell did something quite the opposite, they pursued a series of shorter cores across the icy landscape by the help of horizontal drilling. Patriot Hills is a fiercely wild place strafed by Weddell Sea cyclones dumping large snowfalls, followed by strong winds (called katabatic winds) pouring off the polar plateau, which is why the team had to try an alternate method for core drilling.
Winds blowing in the region throughout the year result in the removal of surface ice via process known as “sublimation“. Due to sublimation, older deeper ice is drawn up to the surface, as the team walked across the blue ice towards Patriot Hills they were essentially travelling back in geologic time. This exposed Antarctic ice revealed what happened during the transition from the last ice age around 20,000 years to our current world (Holocene). As the Earth warmed, CO2 levels in the atmosphere increased rapidly from 190 to 280 ppm (parts per million).
This warming trend wasn’t constant, it started around 14,600 years ago, then there was a 2,000 year long period of cooling in the Southern Hemisphere (known as Antarctic Cold Reversal). During the Antarctic cold reversal the CO2 levels stalled at about 240 ppm. Why this event happened was the geologic puzzle and understanding it could be significant for improving current and future climate change projections.
For 3 weeks the research team battled strong weather conditions, both winds and snow while collecting the ice samples. The team was surprised to know that they found organic molecules (remains of ancient marine life). The Weddell Sea cyclones brought these organic molecules from the ocean surface and deposited them onshore to eventually be preserved in the ice.
“Antarctic ice which is created due to snowfall tells us about the climate,” says the lead author of the study. “It is exciting to discover evidence of ancient life for the first time in the Antarctic ice because we can reconstruct what happened in the Southern Ocean thousands of years ago,” he added further to the statement. The researchers found high concentrations and diverse range of marine microplankton which correlated with Antarctic cold reversal in terms of increased ocean productivity. Climate modelling showed that Antarctic cold reversal was indeed a time where massive changes in the amount of sea ice occurred across the Southern Ocean.
While the world was coming out of the last ice age, warming of climate led to melting of large amount of sea ice that formed during winter. As the sea ice melted, it released valuable nutrients in the Southern Ocean, that helped with marine productivity at that time. This increased marine life helped in acquiring more CO2 from the atmosphere due to photosynthesis. Later on when the marine life died they sunk to the ocean floor, as they locked away the carbon, the CO2 absorbed by these organisms was large enough to register around the world.
Marine life in the Southern Ocean still plats a significant role in the cycling of atmospheric CO2. As of today, the Southern Ocean consumes 40% of all carbon put in the atmosphere by anthropogenic activity therefore, it is necessary to have a better comprehension for the driving factors involved in carbon cycle and its impact on climatic conditions. As the world is getting warmer due to climate change, less ice is expected to form in polar regions. The carbon sink of marine life will weaken, leading to an increase in global temperatures.
Marine life found in ancient Antarctica ice helps solve a carbon dioxide puzzle from the ice age
Chris Turnery, Chris Fogwill | July 7, 2020 | The University of New South Wales, Australia