650-Years of Climate Change Recorded in Arctic Algae Similar to Tree Rings

The calcite crust that grows among layers of seafloor algae helps in reconstructing climate change and will also aid in forming models of  future climate change, according to a latest study.

According to a latest study conducted by researchers at the University of Toronto Mississauga, the coralline algae offer strong clues to decipher 650 years of annual change in sea-ice cover. This is the first time that researchers have used coralline algae to track the changes taking place in the Arctic sea ice. Analysis revealed that for the last 150 years there has been a dramatic decline in the ice cover.

The study was based on the sample of a coralline alga called Clathromorphum compactum that was collected during the research cruise that was led by Walter Adey from Smithsonian. Widely spread across the Arctic and sub-Arctic Oceans, this plant species is known for its formation of thick rock like calcite crusts on the seafloor of shallow waters (15-17 meters deep).

The growth rate of the algae heavily depends on the availability of light as well as the temperature of the water. The plant's growth is limited when water over the algae is covered with sea ice. The algae resumes it growth in the calcified crusts during the warmer periods when sea ice melts. Such repeated cycles of dormancy and growth result in noticeable layers that help to determine the time frame when the algae could thrive each year during the warm period.

"It's the same principle as using rings to determine a tree's age and the levels of precipitation," said Jochen Halfar, an associate professor in UTM's department of chemical and physical sciences. "In addition to ring counting, we used radiocarbon dating to confirm the age of the algal layers."

On retrieving the algae sample the researchers polished and cut it and then using specialized microscope they captured over thousand images of each sample. Then they merged all the pictures to produce an overview of the algae.

The researchers determined the length of the algal bloom period by looking at the levels of magnesium preserved in each growth layer, as this mineral is dependent on both light and temperature of the sea water. Higher amount of algal magnesium indicated there were longer periods of open and warm water.

The researchers also noticed that the algae's annual growth increments were narrow during the 'Little Ice Age' mostly due to the widespread sea ice cover. Little Ice Age- a global cooling period that stretched from the mid 1500-mid1800.

This coralline alga not just presents a new technique for reconstructing a climate model but also provides useful insight into the climate records of ancient years.

"In the north, there is nothing in the shallow oceans that tells us about climate, water temperature or sea ice coverage on an annual basis," said Halfar. "These algae, which live over a thousand years, can now provide us with that information."

The findings were documented in the journal Proceedings of National Academy of Sciences.