Arctic researchers measure climate change impact on oceans

A research team led by University of Galway is investigating whether climate change is reducing the impact that some of tiniest organisms in the oceans have on CO2 levels in the atmosphere.

The researchers spent several weeks at sea on board the Marine Institute's Celtic Explorer in the Labrador Sea between Canada and Greenland, to record levels of phytoplankton.

The expedition team are assessing the role of these tiny plants in carbon absorption from the atmosphere in the context of the threat from climate change on the seas from freshwater and meltwater in the Arctic regions.

Water samples and atmospheric measurements gathered by the researchers will help to assess how phytoplankton living on the sunlit ocean surface absorbs CO2 and nutrients, and in turn produces organic carbon, some of which sinks into the deep ocean, locking in the greenhouse gas for centuries.

The outstanding question is to quantify how much carbon is exported to the deep ocean.

This process of carbon transfer is known as the Biological Carbon Pump (BCP)and it plays a critical role in global climate regulation.

Professor Brian Ward, Professor of Oceanography at University of Galway, said:"The interplay between the physics and biology of phytoplankton and their role in the carbon cycle, and how climate change is affecting this, is not well understood. Our current ability to predict changes in the Biological Carbon Pump in the face of ongoing and future climate change is weak at best."

The research expedition was funded by the Marine Institute, and led by Professor Brian Ward, School of Natural Sciences, University of Galway and involved researchers from Dalhousie University, Nova Scotia, Canada and the Ocean Frontier Institute; Memorial University Newfoundland; and the Science Foundation Ireland research centre for applied geosciences -iCRAG.

The Labrador Sea in the North Atlantic is home to the largest sustained phytoplankton bloom annually, but it is believed that rapid changes are occurring in this region, and there are very few assessments of the Biological Carbon Pump. Current estimates suggest that the BCP removes 5-12 gigatonnes of carbon from the atmosphere per year, roughly equal to anthropogenic CO2 emissions - the environmental change caused or influenced by people, either directly or indirectly.

The research project - Biological Carbon Export in the Labrador Sea (BELAS) - used a 10m mast on the bow of the Marine Institute research vessel Celtic Explorer to directly measure how much CO2 is being transferred from the atmosphere to the ocean.

Preliminary analysis indicates that an enormous flux of CO2 transfer occurred during the research expedition, driven by the abundance of phytoplankton photosynthesising in the surface waters.

The University of Galway team also measured the turbulence in the ocean down to 100m with their unique profiling instrument, as turbulence is a critical process for controlling phytoplankton behaviour, which is just gaining recognition within the international community. This places UGAL at the cutting edge of the interaction between ocean physics and biology.

The Canadian scientists involved in the research project took water samples during the two weekexpedition, with the aim that their analysis will bridge the knowledge gap over the role of phytoplantkonin the carbon cycle.

Professor Ward said:"Building on the successful international research expedition in 2022, our aim is to assess the functioning of the biological carbon pump in the Labrador Sea and improve our understanding of the mechanisms behind it so that we can make better predictions about its impact in the face of climate change.

"By transferring carbon into the deeper ocean, the BCP effectively removes CO2 from the atmosphere for centuries, slowing global warming. However, there is mounting evidence that climate warming is affecting the BCP, especially in higher latitudes, via increasing freshwater inputs, altered nutrient dynamics, and declines in phytoplankton growth."

This research is very timely given the deepening interest in carbon dioxide removal (CDR), where one of the controversial methods proposed is to "fertilise" the ocean to stimulate phytoplankton with the aim of removing CO2 from the atmosphere. CDR is rapidly gaining momentum and several companies are already deploying methods to remove CO2 from the atmosphere.

According to Professor Ward:"There remains fundamental research to be carried out before we can scale up the removal of CO2 using the proposed fertilisation methods. There is no doubt the concentration of CO2 in the atmosphere needs to be reduced by the end of this century, but CDR methods are unlikely to offset anthropogenic CO2 emissions, which is where the main focusneeds to be."

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