How global warming is changing the ecology of the Arctic Ocean

The warming of the Arctic Ocean due to climate change means sea ice cover is becoming increasingly seasonal, with larger areas of open water and marginal ice zones during the spring and summer months.

In the coming decades it is predicted that ice cover will completely disappear every year during the warmer months. The knock-on effect of this environmental change means organic matter which was previously contained within the ice is now being released into the surface water of the Arctic Ocean as the ice melts.

New research by the University of Essex, with partners in Canada and Germany, gives a greater insight into how this could change the microbial balance in this remote area of the planet and the impact on the food chain.

Climate change has resulted in the continuing loss of thicker multi-year ice, and, instead, thinner first-year ice – which freezes and melts each year – becoming the dominant type of ice in the Arctic Ocean.

Essex marine biologist Professor Graham Underwood teamed up with Dr Christine Michel, a Canadian expert in sea ice ecology from the Fisheries and Oceans Canada Freshwater Institute in Winnipeg, to study the impact of sea ice melt on microbial processes in the Arctic Ocean. Through experiments carried out in the High Canadian Arctic, they demonstrated that different organic carbon compounds released from the sea ice modify the abundance, activity, and composition of surface water microbial communities.

Published in the high-profile Nature Climate Change journal, this significant research project shows the impact of this on the microbial communities in the Arctic and the impact on the food chain and water column carbon cycling in areas where seasonal ice is replacing permanent ice cover.

The research involved collecting surface water and first-year ice cores in an area about 2km offshore in Resolute Passage in the Canadian Arctic Archipelago – an area typically covered with ice from late November to the beginning of July.

The project is the latest study in ongoing research by Professor Underwood into microbial ecology and carbon turnover in sea ice. This latest research is the most exciting development as it lifts the lid on the impact of the melting ice on the Arctic water column’s microbial communities.

“From above, sea ice looks pretty inhospitable to life, but within and underneath the sea ice there are whole cities of microbes, made up of hundreds of different species, photosynthesising and producing a wide range of organic compounds. When the ice melts, there is this strong seasonal pulse of organic matter flowing into the surface water,” explained Professor Underwood. “This creates a frenzy of microbial activity which has the knock-on effect of changing what the bacteria feeds on, which in turn feeds seals, fish and other species in the Arctic.

“We know the whole environment of the Arctic is changing but what we have found is a greater understanding of the effect on the biological make-up of the changing Arctic region.

“For example, we now know how some bacteria prefer different types of matter, which will change the microbial community food chain in ways we didn’t know before.”

Dr Michel added: “Our study reveals that different organic carbon fractions released from Arctic sea ice modify the abundance, activity, and composition of surface water microbial communities. These results point to wide-ranging consequences of the transition from multi-year to first-year ice as the Arctic Ocean continues to warm.”

Further research is now needed to establish how large areas previously covered by multi-year ice will respond to changes in the sea ice biochemistry and seasonal dynamics.

“We need to define the new biogeochemical cycles in the ‘new’ Arctic which melts and freezes every year,” added Professor Underwood.