Sea ice helped control atmospheric carbon around 14,500 yrs ago: Study

Sea ice across Antarctic Ocean — a fundamental player in global carbon cycle and climate — may have had a vital role in controlling atmospheric carbon dioxide levels, according to a new research published in Nature Geoscience.

The Antarctic Ocean is a substantial marine carbon sink — it has captured around half of human-related carbon that entered it. It was this knowledge that researchers used to understand the modulation in past and future air-sea carbon flux.

The research

The team of researchers led by Chris Fogwill, honorary professor at University of New South Wales, Australia, showed that growth and destruction of sea ice due to warming enhanced the amount of marine life present in the sea around Antarctica. This enhanced carbon dioxide sequestration and created a regional marine carbon sink, which eventually contributed to a dip in atmospheric carbon dioxide.

Fogwill and other researchers studied data related to the end of last Ice Age — around 7,000 years ago — when carbon dioxide rose from around 190 parts per million (ppm) to 280 ppm. 

The other period studied was over 14, 600 years ago, when CO2 levels plateaued at a nearly constant level of 240 ppm. This period lasted for about 1,900 years.

To understand what happened during this period, the team of researchers travelled to the Patriot Hills Blue Ice Area of Antarctica to capture evidence of marine life in ice cores.

“Organic biomarkers and DNA from the Southern Ocean are blown onto Antarctica and preserved in the ice, providing a unique record in a region where we have few scientific observations,” co-author and UNSW professor Chris Turney said.

How did the researchers sample ice for the analysis?

“Instead of drilling kilometres into the ice, we could simply walk across a blue ice area and travel back,” UNSW quoted Turney as saying.

“Blue ice areas have a unique topography. The top layer of snow is effectively eroded, exposing the ice below. This provides access to ancient ice below,” he added.

Results

The team discovered that the number and diversity of marine organisms present across the 1,900-year period increased significantly. At the same time, carbon dioxide levels plateaued.

This coincided with one of the greatest seasonal changes at that time — when sea ice grew extensively across the Southern Ocean. However, each summer the sea ice would be rapidly destroyed due to warming.

These developments together led to marine life enhancement and therefore, enhanced carbon sequestration.