Press release: Arctic algae: witnesses of sea-ice decline

Nr. 229/2013 - 18.11.2013

Göttingen scientists document changes since medieval times – sea-ice decline ongoing since 1850

(pug) Scientists from the University of Göttingen have succeeded in tracing the changes and decline of Arctic sea-ice back to medieval times. Thus, they discovered that Arctic sea-ice has been melting continuously since the mid-19th century. Satellite observations of summer Arctic sea-ice cover extend back only a few decades, hampering climate modelers‘ attempts to simulate centuries of climate variation. On the shallow sea floor, a team of German, US-American and Canadian scientists now discovered 650 year old algae that grow successive layers of calcite each year. Similar to trees preserving precipitation history within their annual rings, these algal layers act as sea-ice cover records. The study was published in PNAS this week.

„Clathromorphum compactum is one of the oldest marine organisms that we know,“ explains Dr. Andreas Kronz from Göttingen University’s Geoscience Centre. The algae grow successive layers of calcite each year while sunlight reaches the shallow sea floor. When winter sea-ice covers the ocean and blocks the sun, photosynthetic growth slows and ultimately stops. Seawater temperature is also preserved in the algae’s mineral layers as the ratio of magnesium to calcium, which is only archived during photosynthetic growth periods. Together with Prof. Dr. Jochen Halfar from the University of Toronto, Dr. Kronz analysed the algae’s growth layers using an electron microprobe at Göttingen University. Its micrometer resolution allows for precisely establishing the relationship between algal chemistry and light and water temperature.

The combination of algal growth and chemical composition enabled the researchers to reconstruct a record of changes in summer sea-ice cover dating back to around 1400 AD. „During the Little Ice Age, which lasted from the early 16th to the mid-19th century, Arctic sea-ice cover displayed year-to-year variability but overall stability,“ says Dr. Kronz. „However, since the end of the Little Ice Age around 1850, variability in sea-ice cover has not been confined to annual scales, but has extended across decades, forming a trend of declining sea-ice cover up to the present day. This decline is more pronounced than any other observable trend in the past 650 years.“

Original publication: Jochen Halfar et al. Arctic sea-ice decline archived by multicentury annual-resolution record from crustose coralline algal proxy. Proceedings of the National Academy of Sciences of the USA (PNAS). Doi: 10/1073/pnas.1313775110.

Contact:
Dr. Andreas Kronz
Georg-August University Göttingen
Faculty of Geosciences and Geography
Geoscience Centre
Goldschmidtstr. 1, 37077 Göttingen
Phone +49 551 39-9336 / -33975
Email: akronz@gwdg.de
Internet: ems-laboratory.uni-goettingen.de