Arctic fjords losing ability to capture and store carbon, study finds

As temperatures rise at an accelerated rate in the Arctic, fueling rapid sea ice decline and irreversible glacial ice loss, researchers led by Jochen Knies at the iC3 Polar Research Hub, sought to identify the impact of the melting in the cryosphere – the region comprising all frozen parts of the Earth, including snow, ice and frozen ground – on Arctic marine carbon cycles and ecosystems. 

In a study published April 25th in Communications Earth & Environment, the researchers found that the rapid environmental changes are reshaping dynamic fjord ecosystems, causing not only a shift in phytoplankton communities but also a growing inability of fjords to capture and store carbon. The Hub is funded by the Research Council of Norway.

“The Arctic cryosphere is the epicentre of acute global change impact, with abrupt warming and amplification driving rapid sea ice decline and irreversible glacial ice loss,” the report states, underscoring the urgency for researchers to address the pressing challenge of understanding how this cryospheric meltdown will influence Arctic marine carbon cycles and ecosystems

Key Findings:

• Over the past 14,000 years, major shifts in sea ice cover and glacial retreat have repeatedly restructured phytoplankton communities in the dynamic fjord ecosystem of Kongsfjorden in Svalbard, Norway
• Ecosystem shifts were closely linked to significant climate warming events such as the Holocene Thermal Maximum 
• Using organic geochemical biomarkers, the study tracked contributions from different plankton groups and found that during ice-free, warm periods, there was a dominance of pelagic phytoplankton, but reduced carbon transfer to sediments
• Phytoplankton communities, which form the base of the food web in these ecosystems, shifted depending on how much sea ice or glacial meltwater was present
• As glaciers melted, nutrients were dispersed into the ocean, fueling plant growth and helping to trap carbon in ocean sediments
• However, after the ice fully melted and in a warm, ice-free period, surface waters became more stable and nutrient production decreased. Plant growth increased, but lower levels of carbon sank to the seafloor for storage

As the Arctic continues to warm and glaciers continue to melt, researchers predict that in a future warmer climate state, the enhanced stratification of ocean surface waters and depleted nutrient supply from ice-free terrestrial terrain will lead to the reduced transfer of carbon to the seafloor in Arctic fjords. Without a steady flow of nutrients, the ecological balance in these fjords may be disrupted, threatening productivity and the overall food web. 

The full research article can be viewed at this link.

Mary McAuliffe, formerly a Jerusalem-based correspondent for an international news channel, is a freelance journalist, photographer and filmmaker, covering the most pressing issues facing society for television, digital, and radio.