Paleo-oceanographers have analysed two marine sediment cores from the northernmost Barents Sea at about 80°N to evaluate if sea-ice persisted in the region during a geological warm-than-present period. Photo: Vårin T. Eilertsen/ The Nansen Legacy
An ice-free Barents Sea by the end of the century?
Since the start of satellite observations in 1979, Arctic sea-ice cover has retreated on average with 13 percent per decade. Averages like this hide, however, the vast differences in sea-ice loss between Arctic regions.
To investigate regional differences in the evolution of Arctic sea-ice loss until the end of this century, researcher Marius Årthun and colleagues from the University of Bergen have analysed projections from the latest generation of global climate models.
The analysis shows that when and where sea-ice is lost will change. Until now, the largest loss of sea-ice occurred during summer and in areas tiddly connected to the North Atlantic or North Pacific. Unlike today, future sea-ice loss will take place in all Arctic regions and all seasons including the dark and cold Arctic winter.
This will result in that all Arctic shelf seas will become ice-free in summer before the end of the century even under low CO2 emissions. According to the models, the Barents Sea will even turn ice-free during winter, and hence become the first year round ice-free region in the Arctic before the end of the century.
Investigating the past to understand the future
While model simulations offer insight into potential future sea-ice states in the Arctic, geological archives provide information on how sea-ice has responded to climatic warming in the past, especially during periods characterized by warmer-than-present conditions.
One of such periods took place after the last glaciation. At that time, the northern hemisphere warmed due to changes in the Earth’s orbit that led to increased absorption of solar heat. This resulted in air temperatures above present day some 10 to 6 thousand years ago.
Paleo-oceanographers at the Norwegian Polar Institute have now analysed two marine sediment cores from the northernmost Barents Sea at about 80°N to evaluate if sea-ice persisted in the region during that geological warm period.
For that, the scientists took advantage of that the seafloor conserves chemical remains of microalgae and other single celled organisms over thousands of years. The remains of these organisms lie stacked in layers, which allow dating the layers back in time similar to when dating trees by their rings.
Sea ice persisted during a geological warm period
Analysis of 11.7 to 9.1 thousand years old marine sediment layers from the northernmost Barents Sea clearly showed chemical traces of sea-ice algae, which means algae that only occur in marine regions where sea ice is present.
Based on the amount of these ice algae traces, the researchers calculated that sea-ice concentrations must have been about 55% in the region during spring even under warmer-than-present conditions.
The scientists also found remains of single celled organisms, which only occur in relatively warm Atlantic water. This suggests that the hydrographic situation in the northern Barents Sea 11.7 to 9.1 thousand years ago was similar to what we see today, where relatively warm Atlantic water has an increasing influence on the northernmost Barents Sea, and is the main driver of sea ice decline in the region.
Hence, the historical data are in keeping with model predictions placing the sea-ice edge around the northern Barents Sea shelf break from the 2070s onwards.
Årthun M, Onarheim IH, Dörr J, Eldevik T (2021) The seasonal and regional transition to an ice-free Arctic. Geophysical Research Letters 48: e2020GL090825. doi.org/10.1029/2020GL090825
Pieńkowski AJ, Husum K, Belt ST, Ninnemann U, Köseoğlu D, Divine DV, Smik L, Knies J, Hogan K, Noormets R (2021) Seasonal sea ice persisted through the Holocene Thermal Maximum at 80°N. Communications Earth & Environment 2: 124. doi.org/10.1038/s43247-021-00191-x
Anna Pienkowski is a researcher at the Norwegian Polar Institute is one of the authors behind the paleo-geological study. She explains that ‘While model simulations offer insight into potential future sea-ice states, geological archives provide information on how sea-ice responded to substantial climatic warming in the past’. Photo: private
Marius Årthun is a researcher at the University of Bergen and lead-author behind the model study on future sea-ice loss. Photo: UiB