Lake persisted where ice was expected in Arctic oasis

“We thought this part of the Arctic was hidden under kilometers of ice during the last glacial maximum, the coldest phase of the Last Ice Age, between 20,000 and 29,000 years ago. But then we stumbled upon sediments deposited during this time in a small lake that existed on Svalbard”, says Willem van der Bilt. 

The sediments were collected in 2012, and the discovery of this unique deposit was first published in 2019. But already at that point, van der Bilt was mostly interested in understanding why this environment existed, and what lived there.  

Optimizing lab techniques

Now, the Research Professor at the University of Bergen and the Bjerknes Centre has a new paper out in Nature Communications Earth & Environment that tells this story, and shows that life survived in water under, and along, permanent lake ice that trapped solar heat. 

It took a few years to put this study together, as there was so little to analyze in sediment from this extreme environment that lab techniques had to be optimized. 

“We wanted to squeeze every drop of measurable material from this mud” van der Bilt says. 

"Greenhouse effect"

What van der Bilt, and his co-authors found, turned the traditional interpretation of the methods that they used upside-down.  

“We used fats from fossil algae to find out what water temperatures were and found that they were way too warm. In addition, the distribution of leaf wax molecules indicated big shifts in water availability, while the presence of ions that make up salt, elements like Bromide or Chloride, was very high”.  

All the above interpretations pointed the authors in one direction: a permanently ice-covered lake that trapped the heat from sunlight, warming the water and allowing photosynthesis to occur, so that life could survive during very brief summers. 

“You could say it was like a greenhouse effect under the lake ice”, van der Bilt explains. 

Survive extreme environments

He explains that every time the lake thaws a little and then freezes again, salts are left behind. They're not part of the refreezing process. Over thousands and thousands of years, these salts, which are heavy, sink to the bottom. As a result, the bottom waters of these lakes became very salty. And a few weeks a year, you get a tiny moat of liquid water around the edge of the lake, allowing some plants to grow. 

Fill the gaps 

These findings offer new insight into how life can survive and maybe even thrive in extreme environments. Also, the existence of a lake ecosystem in the Arctic during the coldest phase of the last ice age highlights potential gaps in our understanding of what makes ice sheets grow.   
 
“It was definitely cold enough, at least eight degrees colder than today, and this place remains a polar desert, but it was likely too dry at the time, so little snow fell to help build up big glaciers and ice sheets”, van der Bilt says.  

“While more research is needed to draw definitive conclusions, we should not consider ice age Svalbard as an island like today, as it was surrounded by permanent sea ice that did not allow any moisture to move from ocean to atmosphere”, he concludes.