Can our oceans save us? The role of seaweed in large scale carbon capture

With‌ ‌governments‌ ‌such‌ ‌as‌ ‌the‌ ‌UK’s‌ ‌looking‌ ‌to‌ ‌rapidly‌ ‌accelerate‌ ‌investment‌ ‌into‌ ‌large-scale‌ ‌carbon‌ ‌capture‌ ‌and‌ ‌storage‌ ‌(CCS)‌ ‌technologies‌ ‌that‌ ‌will‌ ‌target‌ ‌excessive‌ ‌carbon‌ ‌dioxide‌ ‌emitted‌ ‌found‌ ‌in‌ ‌the‌ ‌air,‌ ‌should‌ ‌policy-makers‌ ‌and‌ ‌ministers‌ ‌set‌ ‌their‌ ‌sights‌ ‌on‌ ‌the‌ ‌sea‌ ‌instead‌ ‌to‌ ‌find‌ ‌an‌ ‌effective‌ ‌solution‌ ‌to‌ ‌the‌ ‌mounting‌ ‌carbon‌ ‌emissions?‌ ‌Sami Cheqrouni-Espinar investigates.

Seaweed piled up on a beach. Image credit: nir_design via Pixabay

‌‌A‌ ‌study‌‌ ‌carried‌ ‌out‌ ‌by‌ ‌researchers‌ ‌from‌ ‌the‌ ‌King‌ ‌Abdullah‌ ‌University‌ ‌of‌ ‌Science‌ ‌and‌ ‌Technology‌ ‌(KAUST)‌ ‌has‌ ‌shown‌ ‌that‌ ‌seaweed‌ ‌in‌ ‌the‌ ‌oceans‌ ‌plays‌ ‌an‌ ‌important‌ ‌role‌ ‌in‌ ‌the‌ ‌sequestering‌ ‌and‌ ‌burying‌ ‌of‌ ‌carbon‌ ‌dioxide‌ ‌from‌ ‌the‌ ‌atmosphere.‌ ‌They‌ ‌used‌ ‌metagenomic‌ ‌data‌ ‌(genetic‌ ‌material‌ ‌recovered‌ ‌from‌ ‌organic‌ ‌samples,‌ ‌in‌ ‌this‌ ‌case‌ ‌taken‌ ‌from‌ ‌the‌ ‌sea bed)‌ ‌obtained‌ ‌through‌ ‌previous‌ ‌ocean‌ ‌expeditions‌ ‌such‌ ‌as‌ ‌the‌ ‌‌Malaspina‌ ‌Circumnavigation‌ ‌Expedition,‌ ‌a‌ ‌large-scale‌ ‌research‌ ‌project‌ ‌funded‌ ‌by‌ ‌the‌ ‌Spanish‌ ‌government,‌ ‌to‌‌ ‌assess‌ ‌microalgae‌ ‌movement‌ ‌through‌ ‌the‌ ‌oceans‌ ‌-‌ ‌how‌ ‌far‌ ‌it‌ ‌drifts‌ ‌from‌ ‌the‌ ‌shore,‌ ‌and‌ ‌how‌ ‌deep‌ ‌it‌ ‌sinks.‌ ‌The‌ ‌research,‌ ‌which‌ ‌was‌ ‌published‌ ‌in‌ ‌the‌ ‌August‌ ‌2019‌ ‌edition‌ ‌of‌ ‌‌Nature‌ ‌Geoscience,‌ ‌identified‌ ‌seaweed‌ ‌DNA‌ ‌in‌ ‌the‌ ‌waste‌ ‌at‌ ‌the‌ ‌seabed,‌ ‌allowing‌ ‌them‌ ‌to‌ ‌conclude‌ ‌that‌ ‌70‌ ‌per‌ ‌cent‌ ‌of‌ ‌the‌ ‌sampled‌ ‌seaweed‌ ‌had‌ ‌sunk‌ ‌to‌ ‌a‌ ‌depth‌ ‌of‌ ‌1000‌ ‌meters.‌ ‌This‌ ‌finding‌ ‌is‌ ‌significant‌ ‌for‌ ‌CSS‌ ‌because‌ ‌it‌ ‌means‌ ‌that‌ ‌any‌ ‌carbon‌ ‌captured‌ ‌by‌ ‌seaweed‌ ‌is‌ ‌permanently‌ ‌removed‌ ‌from‌ ‌the‌ ‌atmosphere‌ ‌and‌ ‌tied‌ ‌to‌ ‌the‌ ‌sea‌ ‌floor‌.‌ ‌ ‌

Research‌ ‌into‌ ‌blue carbon‌ ‌storage‌ ‌began‌ ‌at‌ ‌the‌ ‌turn‌ ‌of‌ ‌the‌ ‌century.‌ ‌Tim‌ ‌Flannery,‌ ‌former‌ ‌environmental‌ ‌commissioner‌ ‌of‌ ‌Australia,‌ ‌shed‌ ‌light‌ ‌on‌ ‌the‌ ‌potential‌ ‌of‌ ‌seaweed‌ ‌as‌ ‌a‌ ‌carbon‌ ‌store‌ ‌in‌ ‌his‌ ‌widely‌ ‌acclaimed‌ ‌book,‌ ‌‌Atmosphere‌ ‌of‌ ‌Hope.‌‌ ‌Flannery‌ ‌asserted‌ ‌that‌ ‌afforested‌ ‌macroalgae‌ ‌could‌ ‌eventually‌ ‌be‌ ‌harvested‌ ‌as‌ ‌a‌ ‌carbon-neutral‌ ‌fuel‌ ‌source,‌ ‌in‌ ‌the‌ ‌form‌ ‌of‌ ‌bio-methane,‌ ‌lessening‌ ‌dependence‌ ‌on‌ ‌fossil‌ ‌fuels.‌ ‌A‌ ‌study‌ ‌by‌ ‌the‌ ‌University‌ ‌of‌ ‌the‌ ‌South‌ ‌Pacific‌ ‌in‌ ‌2012,‌ ‌which‌ ‌analysed‌ ‌ocean‌ ‌afforestation‌ ‌and‌ ‌has‌ ‌been‌ ‌cited‌ ‌by‌ ‌Flannery‌ ‌as‌ ‌testament‌ ‌to‌ ‌seaweed’s‌ ‌potential,‌ ‌showed‌ ‌that‌ ‌macroalgae‌ ‌covering‌ ‌9‌ ‌per‌ ‌cent‌ ‌of‌ ‌the‌ ‌Earth’s‌ ‌surface‌ ‌could‌ ‌store‌ ‌53‌ ‌giga-tons‌ ‌of‌ ‌carbon‌ ‌dioxide,‌ ‌exceeding‌ ‌our‌ ‌annual‌ ‌CO‌2‌‌ ‌output‌ ‌which‌ ‌is‌ ‌currently‌ ‌at‌ ‌39‌ ‌giga-tons.‌ ‌ ‌

Despite‌ ‌the‌ ‌confidence‌ ‌of‌ ‌seaweed‌ ‌advocates‌ ‌such‌ ‌as‌ ‌Flannery,‌ ‌seaweed‌ ‌is‌ ‌far‌ ‌from‌ ‌the‌ ‌spotlight‌ ‌when‌ ‌it‌ ‌comes‌ ‌to‌ ‌carbon‌ ‌capture‌ ‌research.‌ ‌‌Dr‌ ‌Alejandra‌ ‌Ortega,‌ ‌a‌ ‌lead‌ ‌author‌ ‌of‌ ‌the‌ ‌KAUST‌ ‌study‌ ‌whose‌ ‌research‌ ‌is‌ ‌focused‌ ‌on‌ ‌blue‌ ‌carbon‌ ‌sequestration‌ ‌said,‌ ‌‌“‌When‌ ‌scientists‌ ‌discuss‌ ‌blue‌ ‌carbon‌ ‌strategies,‌ ‌which‌ ‌are‌ ‌key‌ ‌for‌ ‌climate‌ ‌change‌ ‌mitigation,‌ ‌they‌ ‌often‌ ‌refer‌ ‌to‌ ‌mangroves,‌ ‌seagrass‌ ‌or‌ ‌saltmarsh‌ ‌habitats.‌ ‌Very‌ ‌few‌ ‌scientists‌ ‌consider‌ ‌macroalgae‌ ‌(or‌ ‌seaweed)‌ ‌in‌ ‌the‌ ‌blue‌ ‌carbon‌ ‌framework,‌ ‌despite‌ ‌the‌ ‌fact‌ ‌they‌ ‌contribute‌ ‌2-4‌ ‌per‌ ‌cent‌ ‌to‌ ‌marine‌ ‌primary‌ ‌production.”‌ ‌Carbon‌ ‌in‌ ‌macroalgae,‌ a type of‌ ‘blue‌ ‌carbon’,‌ ‌sinks‌ ‌to‌ ‌the‌ ‌seabed.‌ ‌Once‌ ‌it‌ ‌is‌ ‌trapped,‌ ‌it‌ ‌is‌ ‌permanently‌ ‌stored‌ ‌there.‌ ‌One‌ ‌reason‌ ‌for‌ ‌seaweed‌ ‌being‌ ‌overlooked‌ ‌in‌ ‌blue‌ ‌carbon‌ ‌research‌ ‌could‌ ‌be‌ ‌its‌ ‌relative‌ ‌inaccessibility:‌ ‌the‌ ‌KAUST‌ ‌study‌ ‌found‌ ‌that‌ ‌seaweed‌ ‌often‌ ‌drifts‌ ‌from‌ ‌coastal‌ ‌to‌ ‌oceanic‌ ‌waters‌ ‌by‌ ‌as‌ ‌much‌ ‌as‌ ‌5000km,‌ ‌making‌ ‌its‌ ‌study‌ ‌difficult.‌ ‌ ‌

Should more scientists be casting their thoughts to the sea, then? A study conducted by the Plymouth Marine Laboratory calculated the average annual carbon sequestration rate of a sample of seaweed as 8.75 grams Cm-2y-1  (the amount of carbon captured by a centimeter squared of sea-weed per year). Deciduous trees found in UK woodlands in comparison capture on average 120 grams Cm-2y-1 of carbon dioxide, which on the surface makes the seaweed figure appear insignificant, but the huge volume of seaweed across the oceans brings the total capture to an impressive sum.

Seaweed is showing great promise as a large-scale carbon store to tackle global warming. The World Bank has refined estimates about the storage potential of carbon dioxide in seaweed, stating that 135 mega-tonnes of carbon added annually to sea waters as a result of greenhouse gas emissions could be captured through the production of 500 mega-tonnes of seaweed – this means harvesting over a quarter of its own mass in carbon.

Algal blooms, like this one off the South coast of England in 1999, occur when algae undergo sudden, rapid growth. This can disrupt entire ecosystems for many reasons, including the blocking of sunlight, toxin production and mechanical damage. Image credit: Public domain, via Wikimedia Commons

Reservations and criticisms have, however, been raised about the potential implementation of farmed seaweed. In 2018, an uncontrollable, self-reproducing body of Sargassum seaweed in the Caribbean claimed the lives of baby turtles and dolphins, and entered Barbados into a state of national emergency. As a result, such algal blooms have been likened to natural disasters.

The power of seaweed and macroalgae can clearly be devastating as well as beneficial, raising many challenging questions for blue-carbon researchers going forward. It is still early in this emerging but promising field of research, as Dr Ortega confessed. “Work is still needed to be able to translate a specific amount of DNA into a specific amount of organic carbon in a specific taxonomy but finding macroalgal DNA is the first step”.

Written by Sami Cheqrouni-Espinar and edited by Ailie McWhinnie.

Interested in reading more about climate and the environment? Sami recommends these books to get you started: There Is No Planet B, by Mike Berners-Lee; This Changes Everything, by Naomi Klein; Don’t Even Think About It: Why Our Brains Are Wired To Ignore Climate Change, by George Marshall; and The Winning Of The Carbon War, by Jeremy Leggett.

Sami’s thoughts… Carbon capture storage is a small part of a very complicated picture in dealing with global warming. Carbon capture is a costly technology for dealing with climate change and largely addresses a symptom of it, not a cause. As much as governments like the UK’s want to accelerate investment in technologies like ‘direct air capture’, significant work needs to go into to make sure aspects of society like public services, business practice and transport align with wider environmental goals.

Sami is a final year Mechanical Engineering student interested in the energy industry, policy and politics.

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