Research voyage yields solid data on Arctic sea ice loss
By Summit Voice
SUMMIT COUNTY — Old, thick sea ice that helps sustain a long-term ice cover in the Arctic is disappearing, according to researchers with the Alfred Wegener Institute who recently sailed more than 12,000 miles through Arctic seas aboard the Polarstern to investigate ice loss and related issues. In the central Arctic, the ice cover now largely consists of thin, one-year-old floes.
As part of their research, the team of 130 scientists aboard the research ship wanted to determine whether the Arctic sea ice melted to a greater or lesser extent than in previous years.
“The ice has not recovered. This summer it appears to have melted to exactly the same degree as in 2007 … it is exactly as thin as in the record year,” said Stefan Hendricks.
Measuring the extent of the sea ice is relatively simple using satellite images, but gaining a clear picture of ice thickness and total mass is more challenging. During this summer’s research, the scientists used a helicopter to deploy a probe that measured ice thickness by electromagnetic induction.
The sea ice physicists concluded that, at sites where the sea ice was mainly composed of old, thicker ice floes in the past decades, there is now primarily one-year-old ice with an average thickness of just 90 centimeters. The scientists found old, thick ice in only two areas: The Canadian Basin and near the Severnaya Zemlya island group in northern Siberia. As a rule, the old ice is between two and five meters thick.
The researchers detected significant differences in places where ice was lacking this summer – in the Laptev Sea, for example.
“On our expedition in 2007 we encountered thin, newly formed ice in the Laptev Sea in September. This time, however, there was no sign of ice formation anywhere. The water temperature at a depth of ten meters was three degrees Celsius — that is how much the sun had heated the ice-free water surface,” said Prof. Dr. Ursula Schauer, scientific head of the leg through the central Arctic. However, this warming is restricted only to the top layers. In the depths of the Arctic Ocean colder water from the Atlantic currently provides for falling water temperatures.
The sea ice physicists also made big strides in answering questions about how much sunlight penetrates the Arctic ice. Changes in sea ice thickness and extent also have direct consequences for the ecosystem of the Arctic Ocean. The reason is that the edge of the ice sheets create a biological hotspot, where algae thrives. It’s not clear yet whether the Arctic Ocean will become more productive because of the decline in ice and the related increase in light.
Scientists like Dr. Ilka Peeken therefore investigated the biology of the algae not only in the sea ice, but also in the melt ponds and in the water column under the ice. The initial results point to regional differences: in the Atlantic part of the central Arctic the algae biomass and carbon intake, both in the ice and in the melt ponds and water column, were significantly higher than in the Pacific section.
This also applies similarly to the climate-relevant trace gas methane, which may form during algal bloom. Measurements by the biogeochemists headed by Dr. Ellen Damm showed that the formation and release of the greenhouse gas are influenced by which region of the Arctic Ocean is seasonally ice-free. In addition, the researchers succeeded for the first time in verifying how much methane is oxidized to carbon dioxide in the ice.