Guest post: An Antarctic voyage in search of blue carbon

A guest article from Dr David Barnes, a marine benthic ecologist at the British Antarctic Survey, and colleagues Chester Sands, Narissa Bax, Rachel Downey, Christoph Held, Oliver Hogg, Kirill Minin, Camille Moreau, Bernabé Moreno and Maria Lund Paulsen from the Antarctic Seabed Carbon Capture Change project.

As global temperatures rise, the response from different parts of the climate system can amplify or dampen the pace of warming. These are known as feedback loops.

Melting sea ice, for example, tends to cause a positive feedback loop. The loss of sea ice means that energy from the sun that would have been reflected away by the bright white ice is instead absorbed by the darker ocean. This causes further warming, which in turn causes more sea ice loss, and so on.

Negative feedback loops, on the other hand, work to reduce further warming. Blue carbon is one such example.

Blue carbon is the term given to carbon stored in coastal or marine ecosystems. It typically refers to salt marshes, mangroves, and seagrass beds, which capture CO2 from the atmosphere and store it in their leaves, stems and in the soil.

A less well-known – but no less important – contribution to blue carbon comes from tiny organisms that live on the seabed.

These creatures, known as zoobenthos, take up carbon from the plankton they eat and the CO2 in seawater they use to build their skeletons. When the zoobenthos die, their bodies are eventually buried in the sediment of the seabed, sequestering carbon in the process.

Our initial research suggests that coastal areas of the Arctic and Antarctic are absorbing and storing more blue carbon as the climate warms. This boost to carbon storage could form one of the biggest negative feedback loops against climate change on Earth.

And it’s blue carbon that’s taking us to Antarctica in November for a five-month research voyage. The trip will carry scientists from our Antarctic Seabed Carbon Capture Change (ASCCC) project, with the aim to investigate how life on Antarctic seabeds is responding to human-caused climate change.

But more on that later.

Life on a seabed

So, first off, why are polar regions so important for blue carbon?

The answer lies in their continental shelves. These are the areas of seabed immediately surrounding a land mass, where the sea is relatively shallow compared to the open ocean beyond it.

Global land and undersea elevation. Continental shelves are shown in bright blue. Credit: NOAA

The waters above continental shelves tends to be very “productive”. This means conditions are ideal for tiny marine plants called phytoplankton to bloom. A lot of plankton attracts a lot of tiny creatures that come to feed on them.

These creatures include zoobenthos, such as sea mosses, sea urchins, corals and sponges, Sea mosses are the y-shaped creatures in photo c in the figure below. Photo b shows an Antarctic shelf playing host to multiple zoobenthos, while photo d shows the skeletons of dead zoobenthos collecting on the seabed, a precursor to their carbon being buried in the sediment.

a) Satellite image showing fast disintegration of sea ice over a polar continental shelf; b) Zoobenthos on an Antarctic continental shelf; c) Examples of sea mosses (specimens on the left are from an open-water location and hence have had more plankton to feed on); and d) Dead bryozoan and other benthic skeletons covering the seabed, most likely to be buried, sequestering their blue carbon in the seabed. Credit: BAS

Continental shelves in the Earth’s polar regions are among the widest and deepest on the planet. In the Weddell and Ross seas in the Antarctic, for example, the continental shelf extends beyond 1,000km out from the coast. At 200-800m deep, polar continental shelves are as much as five times deeper than anywhere else.

And when it comes to storing carbon, size matters. The zoobenthos that inhabit the shelves may be tiny, but multiplied across such a large area, the amount of carbon they can store is considerable.

Recent research cruises of the RRS James Clark Ross, funded by the Department of Environment Food and Rural Affairs (Defra), the Darwin Initiative, and the Natural Environment Research Council (NERC), have found that life on Antarctic shelf zoobenthos is accumulating millions of tonnes of carbon per year.  

The evidence to back this up is still in its infancy, but we have identified several pieces of the puzzle, including estimates at multiple locations of how much carbon the seabed stores.

Rapid change

The continental shelves around the Arctic and Antarctic are changing rapidly as global temperatures rise. This is having a significant impact on life on the seabed.

Collapsing ice shelves and melting sea ice leaves more open water in the Earth’s polar regions (photo a in earlier figure). Without a covering of ice, sunlight floods the ocean, triggering plankton blooms.

This abundant source of food has led to new communities of zoobenthos establishing themselves on the continental shelf. More zoobenthos means more carbon being taken from the air and sequestered in seabed sediments.

In Antarctica, even though as a whole it’s slightly gaining in sea ice cover, most of these gains are over unproductive, deep-lying seabeds, whereas the newly ice-free areas are mostly located over highly productive continental shelves in the West Antarctic.

Our fieldwork has recorded the changes in zoobenthos by collecting samples from the seabed and taking underwater photos. And the results suggest that blue carbon capture and storage in these regions has doubled over the last two decades. Capturing more carbon means less ends up in the atmosphere to warm the planet – this is the negative feedback loop.

Antarctic voyage

Despite the recent advances, we’re still lacking a complete picture of how much carbon is being sequestered around Antarctica and how it is changing.

This is important because the potential to capture our carbon emissions is huge. We could even enhance this feedback loop by creating artificial reefs and by reducing fishing trawling along the seabed in polar regions.

Enter the new Swiss Polar Institute and their first major programme – the Antarctic Circumnavigation Expedition (ACE).  

In November this year, the Russian polar research vessel Akademik Treshnikov will sail to Cape Town, South Africa from St. Petersburg. At Cape Town, the ship will collect scientists representing 22 funded projects from 30 nations.  

From December to March it will circumnavigate Antarctica, visiting the major archipelagos around Antarctica, acting as a platform for an unparalleled multi-disciplinary attempt to investigate southern polar maritime science.  

You can see the expected route in the figure below.

Aboard this expedition at various points will be eight scientists from the ASCCC project. Our scientists will sample all the major sub-Antarctic shelves, compiling data for the first assessment of carbon storage and annual accumulation in this key region.  

Proposals are already in place with NERC to do similar work on Arctic continental shelves over 2017-2019.

The planned route of the Antarctic Circumnavigation Expedition. Credit: ACE

Global oceans provide many vital “silent services” besides being a source of food, and carbon sequestration is one of its most important.

Tiny creatures on polar seabeds may be uniquely positioned to increase this service, and we are set to explore this new and exciting area of research to understand the role they have in slowing global climate change.

Main image: The RRS James Clark Ross, a marine research vessel, in South Georgia. Photo: Jonathan Ashburner, British Antarctic Survey.