In­flu­ence of car­bon di­ox­ide leak­age on the seabed

Storing carbon dioxide (CO2) deep below the seabed is one way to counteract the increasing concentration of CO2 in the atmosphere. But what happens if such storage sites begin to leak and CO2 escapes through the seafloor? Answers to this question have now been provided by a study dealing with the effects of CO2 emissions on the inhabitants of sandy seabed areas.

Day-in, day-out, we re­lease nearly 100 mil­lion tons of car­bon di­ox­ide (CO2) into the at­mo­sphere. One pos­sible meas­ure against stead­ily in­creas­ing green­house gases is known as CCS (car­bon cap­ture and stor­age): Here, the car­bon di­ox­ide is cap­tured, prefer­ably dir­ectly at the power plant, and sub­sequently stored deep in the ground or be­neath the seabed. However, this method poses the risk of reser­voirs leak­ing and al­low­ing car­bon di­ox­ide to es­cape from the ground into the en­vir­on­ment. The European research project ECO2, co­ordin­ated at GEO­MAR Helm­holtz Centre for Ocean Re­search Kiel, ad­dresses the ques­tion of how mar­ine eco­sys­tems re­act to such CO2-leaks. The field study of an in­ter­na­tional group of re­search­ers headed by Massimili­ano Mol­ari from the Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy in Bre­men and Katja Guilini from the Uni­versity of Ghent in Bel­gium, now pub­lished in Science Advances, re­veals how leak­ing CO2 af­fects the seabed hab­itat and its in­hab­it­ants.

Substantial changes to algae, animals and microorganisms

For their study, the re­search­ers vis­ited nat­ural leaks of COin the sandy seabed off the coast of Si­cily. They com­pared the local eco­sys­tem with loc­a­tions without CO2-vent­ing. In ad­di­tion, they ex­changed sand between sites with and without CO2-vent­ing in or­der to study how the bot­tom-dwell­ers re­spond and if they can ad­apt. Their con­clu­sion: In­creased CO2 levels drastic­ally al­ter the eco­sys­tem. “Most of the an­im­als in­hab­it­ing the site dis­ap­peared due to the ef­fect of the leak­ing CO2”, Massimili­ano Mol­ari re­ports. “The func­tion­ing of the eco­sys­tem was also dis­rup­ted – and what’s more, long-term. Even a year after the CO2-ven­ted sed­i­ment had been trans­por­ted to un­dis­turbed sites, its typ­ical sandy sed­i­ment com­munity had not es­tab­lished.”

The re­search­ers re­port the fol­low­ing de­tails:

  • Together with the ascending gas bubbles, nutrients were transported to the surface. As a result, tiny algae in the sand grew much better.
  • The small and larger animals (invertebrate meio- to marofauna) inhabiting the sand were affected particularly badly by a CO2 leak: their numbers and diversity fell considerably with increasing carbon dioxide levels. The biomass of the animals dropped to a fifth, although more food was actually available due to the numerous small algae
  • The numbers of seabed-dwelling microorganisms did not drop as CO2 increased, but their composition changed substantially.
  • The modified community of organisms led to a change in the entire ecosystem. Most inhabitants cannot adapt to the altered environmental conditions in the long term. Instead, few species, which can cope better with the increased CO2levels, populate the sand.

“A leak in a car­bon stor­age sys­tem be­neath the sea fun­da­ment­ally al­ters the chem­istry of sandy seabeds and sub­sequently the func­tion of the en­tire eco­sys­tem”, Mol­ari sum­mar­izes. “That is, there is a con­sid­er­able risk that a car­bon di­ox­ide leak will harm the local eco­sys­tem. These car­bon di­ox­ide stor­age sys­tems can nev­er­the­less glob­ally re­duce the im­pact of cli­mate change.”

A first holistic overview

For the first time, this cur­rent study de­liv­ers a “hol­istic” view of the ef­fects of in­creas­ing COcon­cen­tra­tions on the sea­floor. It con­siders both bio­lo­gical and biogeo­chem­ical pro­cesses and dif­fer­ent levels of the food chain, from mi­crobes to large in­ver­teb­rate an­im­als.

CCS fa­cil­it­ies are already in op­er­a­tion, for ex­ample off the Nor­we­gian coast. Within the European Union, CCS is con­sidered a key tech­no­logy for re­du­cing green­house gas emis­sions. “Our res­ults clearly re­veal that the site se­lec­tion and plan­ning of car­bon stor­age sys­tems be­neath the seabed also de­mand a de­tailed study of the in­hab­it­ants and their eco­sys­tem in or­der to min­im­ize harm”, em­phas­izes prin­cipal in­vest­ig­ator Antje Boe­t­ius. „Hav­ing said that, global mar­ine pro­tec­tion also in­cludes tak­ing meas­ures against the still high CO2-emis­sions.“