New study refines our understanding of biogenic indicators to reconstruct past sea-ice conditions

Published 17-12-2018

A collaborative study led by GEUS researchers from the Glaciology and Climate Department provides important new information for reconstructing past ice cover conditions in Arctic fjords.


Arctic sea ice is one of the most sensitive indicators of climate change. During the satellite era, the Arctic region has lost nearly half of its seasonal sea ice, and it continues to warm at a rate 2-3 times faster than the global average. Extrapolations of recent observed data suggest a seasonally ice-free Arctic Ocean by the late 2030s, earlier than projected by most climate models.

For improved future predictions, it is necessary to place recent antropogenic change in a broader context and document sea ice variability on historical and geological timescales, as the natural dynamics of the climate system are poorly understood.

Paleo-records such as marine sediment cores can help extend time-series of sea-ice cover to the pre-instrumental era, and scientists have been working on developing new proxies or indicators that can trace past sea ice evolution.

Sea ice is the habitat of highly specialised microalgae (mainly diatoms). Some sea ice diatoms produce a unique compound (IP25 – ice proxy with 25 carbon atoms) that can remain stable in the sediments for millions of years. This has proven to be a useful indicator in marine settings, but its applicability in Arctic fjord sediments has been questioned.


Scanning electron image (2600x magnification) of a sea ice diatom (Haslea crucigeroides) found in ice core samples from the Young Sound, Northeast Greenland. Cell length ca. 100µm.

Important findings

During a project lead by GEUS, diatoms and the sea-ice biomarker IP25 were analysed in a series of first-year sea-ice cores, sediment trap and surface sediment samples collected in the Young Sound fjord, Northeast Greenland.

This study involved researchers from Denmark, Canada and Finland, and the results have just been published in the journal Frontiers in Earth Sciences.

The paper reports on the seasonal diatom growth succession and production of IP25 in the fjord, and vertical export of diatom valves and sea-ice biomarkers to the underlying seafloor sediments.

“The work refines our understanding of the paleo-ecological significance of the diatoms that preserve in the seafloor sediment and notably confirms the identification of those diatom species that produce IP25. These new findings are important to infer information about past climate fluctuations and their impacts on marine ecosystems,” says Sofia Ribeiro, Senior Researcher at the Geological Survey of Denmark and Greenland.