New paper: Polar blue carbon: bringing the Arctic and Antarctic into the picture

When we talk about blue carbon, the same ecosystems usually come to mind: mangroves, salt marshes and seagrass meadows. These habitats capture carbon through biological processes and can store some of it for decades, centuries or longer.

But what about the polar oceans?

Together, the Arctic and Antarctic make up around 20% of the global ocean. They contain highly productive ecosystems and enormous stores of carbon, yet they have received surprisingly little attention in discussions about blue carbon. At the same time, these regions are undergoing some of the fastest environmental changes on Earth, including declining sea ice, warming waters and major changes to coastal habitats.

In a new paper published in Global Change Biology, led by Nadescha Zwerschke and involving colleagues from across the POMP project, we ask a fairly simple question: should polar marine ecosystems play a larger role in how we think about blue carbon?

Blue carbon at the poles looks different

One reason the polar regions have been overlooked is that their carbon pathways do not fit neatly into the traditional blue-carbon model.

Some systems are relatively familiar. Arctic salt marshes and seagrass meadows, for example, already have fairly strong evidence supporting their ability to accumulate and store carbon.

Others are much harder to classify.

Kelp forests and other macroalgae can capture large amounts of carbon, but much of that material may be transported away from where it was produced before eventually being buried elsewhere. That makes the entire pathway from carbon capture to long-term storage much more difficult to trace.

Then there are systems that have barely entered the blue-carbon conversation at all: phytoplankton, ice algae, microphytobenthos, fjord sediments, continental shelves and the deep seafloor.

Microphytobenthos is particularly interesting from my own research perspective. These microscopic algae growing on the seafloor can photosynthesise across surprisingly large areas of the shallow Arctic. In the review, we estimate an Arctic habitat extent of roughly 931,000 km², with annual production on the order of 11–16 Tg of carbon. But how much of that production ultimately contributes to long-term carbon storage remains uncertain.

That distinction is important. Capturing carbon is not the same thing as storing it for climatically meaningful periods.

Climate change does not point in only one direction

There is another complication: climate change could increase some forms of polar carbon uptake while decreasing others.

Less sea ice and snow can allow more light into the ocean, potentially stimulating photosynthesis by phytoplankton, macroalgae and organisms living on the seafloor. But the same rapidly changing Arctic can experience increased coastal erosion, river runoff and sediment entering the ocean. That can make coastal waters more turbid and actually reduce the light available for photosynthesis.

The result is not a simple story of “less ice equals more productivity”. The direction and magnitude of change will differ greatly between regions and ecosystems.

Understanding those interactions is one of the major scientific challenges ahead.

The science and the policy are not quite there yet

Our review also asks what would have to happen before polar blue carbon could be incorporated more systematically into marine and climate policy.

There are several obstacles.

The terminology and accounting systems used for blue carbon were largely developed around tropical and temperate coastal wetlands. Measurements of carbon capture, transport, storage and sequestration are still difficult to compare among polar ecosystems. And governance is complicated: the Arctic encompasses several national jurisdictions as well as international waters, while Antarctica operates under a very different international governance system.

There are also some very basic scientific gaps. For many polar habitats, we still lack robust estimates of their extent, carbon stocks, sequestration rates and vulnerability to disturbance. Remote sensing helps, but clouds, sea ice and the unusual optical properties of polar waters mean that some of the most important processes remain difficult to observe from space.

For these reasons, the paper does not argue that polar blue carbon is ready to become a conventional carbon-offset mechanism. Questions surrounding measurement, additionality and permanence are still too substantial.

Protect first, understand better

Instead, the paper sets out a more cautious approach.

We call for greater investment in understanding polar carbon pathways, better and more standardised ways of measuring them, and management approaches that consider carbon storage alongside biodiversity and other ecosystem functions. We also argue that known carbon-rich and relatively undisturbed habitats deserve attention now, rather than waiting until every uncertainty has been resolved.

This is particularly relevant because only around 10% of the global ocean is currently protected, with polar regions among the least protected. The central idea is therefore not to put a price on every tonne of polar carbon, but to recognise carbon storage as one of the important services these ecosystems already provide.

The paper's broader message is that protecting polar biodiversity and protecting natural carbon stores do not need to be treated as separate objectives. In many places, they are different reasons for looking after the same ecosystem.

As the Arctic and Antarctic continue to change, understanding where carbon is captured, where it goes, how long it remains there and how human activities might disturb it will become increasingly important.

Polar blue carbon is not yet a fully formed management tool. But it is increasingly difficult to leave the polar oceans out of the blue-carbon conversation.

Read the paper:
Zwerschke, N., Krause-Jensen, D., Barnes, D. K. A., Renaud, P. E., Austin, W. E. N., Ardyna, M., Attard, K., Bluhm, B. A., Comeau, S., Gattuso, J.-P., Hauck, J., Leu, E., Maar, M., Oziel, L., Poste, A. E., Schourup-Kristensen, V., Svensen, C., Thyrring, J., & Sejr, M. (2026). Status of Polar Blue Carbon: Toward Recognition and Integration in Marine Policy. Global Change Biology, 32(9), e71098. https://doi.org/10.1111/gcb.71098