On the horizon: Climate change and the capacity of Antarctic benthos to store carbon

Kicking off our On the horizon series of posts about emerging issues in conservation and applied ecology, Nathalie Pettorelli explores how climate change and melting ice in the Antarctic could affect carbon storage on a global scale.

Just a few days ago, news outlets around the world were reporting on the findings from a study published in the Proceedings of the National Academy of Sciences and led by Eric Rignot on the melting of the Antarctic. The key message: the ice in Antarctica is melting six times faster than it did 40 years ago, having caused global sea levels to rise more than half an inch since 1979. This new publication only confirms previous assessments that an increasing amount of ice sheets are indeed being lost to climate change every year, leading to great freshwater outflows and rapid changes in nearshore salinity that may alter phytoplankton dynamics and put pressure on local biodiversity.

Yet continued melting of vast quantities of ice may not simply affect these highly distinctive ecological communities through changes in salt levels. Melting in Antarctica could also lead to increases in sedimentation – the process of deposition of particles in suspension. These increases could be more extensive than anything seen previously, suffocating benthic communities in bays and fjords around the continent.

Loss of sea ice could affect the rate at which icebergs are formed and cause iceberg-seabed collisions

Moreover, rapid loss of sea ice may affect the rates at which icebergs are formed, as well as the type of icebergs formed, ultimately heightening the potential for iceberg-seabed collisions (also known as ice scours). Such iceberg-seabed collisions are known to be associated with high levels of mortality in the zoobenthos, and could therefore significantly affect the functioning of seabed ecosystems.

If this was to happen on a large scale, then the consequences could be drastic for our climate system. The seabed on the polar continental shelves is indeed among the largest sinks of oceanic, or blue, carbon on Earth. Changes in the functioning of seabed ecosystems could therefore substantially alter the global carbon cycle and ultimately impact the rate of change in climatic conditions.

Admittedly, there is a lot of uncertainty about the impact of climate change on carbon storage capacity in Antarctica. This is because the current warming may be favourable to multiple organisms, while also potentially leading to changes in seabed ecosystem functioning. If phytoplankton bloom increases are sustained, sea temperatures remain only marginally elevated and iceberg scour declines, then benthos growth rates and benthos carbon storage could drastically increase. Under this scenario, the region could double its annual carbon storage budget and thus its importance as a negative feedback on climate change. However, things might turn out to be much less favourable for our planet if the current melting leads to diminished capacity for carbon sequestration in regions of frequent giant iceberg grounding.

The lack of certainty regarding the short-term and long-term impacts of the rapid melting of the Antarctic on the global carbon cycle clearly emphasizes the complexity of the relationships between the chemical-physical environment and biota in the region. Given the unicity of the ecological communities found in Antarctica and the importance of the region for the global climate system, there is however a pressing need to maintain strong research efforts in the area, while making sure that other pressures to the local biodiversity are kept to a minimum.

A Horizon Scan of Emerging Issues for Global Conservation in 2019 is available to read in Trends in Ecology and Evolution.

Read more from our ‘On the horizon’ series here:

Introduction  by Bill Sutherland and Nancy Ockendon

Deforestation expansion of plantations and infrastructure threaten Indo-Malay island species by Nafeesa Esmail and Alice Hughes

Options for cultivating rice as climate changes and salinity increases by Erica Fleishman

Plastic alternatives – the ecological impact is not always clear by Becky LeAnstey

Mercury rising by Colleen Seymour

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