TINY OR­GAN­ISMS HAVE A BIG IM­PACT ON THE EARTH’S CAR­BON CY­CLE

Scuba Diver Australasia + Ocean Planet - - Briefing -

Re­searchers from Florida State Univer­sity have dis­cov­ered that sin­gle-celled or­gan­isms called phaeo­dar­i­ans, which in­habit the the area 100 to 1,000 me­tres be­low the ocean’s sur­face, con­sume sink­ing car­bon-rich par­ti­cles be­fore they set­tle on the seabed. Th­ese par­ti­cles would oth­er­wise be stored and se­questered from the at­mos­phere for mil­len­nia.

This is sig­nif­i­cant as it sug­gests that micro­organ­isms around the world could be play­ing a much big­ger role in the car­bon cy­cle than sci­en­tists pre­vi­ously be­lieved.

Car­bon diox­ide is con­stantly dif­fused into the ocean from the at­mos­phere and back into the at­mos­phere from the ocean. In the sur­face ocean, dur­ing the pho­to­syn­the­sis process of phy­to­plank­ton, car­bon diox­ide is ab­sorbed. How­ever, phy­to­plank­ton have short life­spans, be­tween days and weeks, and are con­sumed by small or­gan­isms like krill. Krill in turn re­lease car­bon diox­ide when they breathe, even­tu­ally adding to the car­bon diox­ide in the at­mos­phere. In this sense, the car­bon diox­ide in the sur­face ocean and at­mos­phere re­mains bal­anced at a near equi­lib­rium. Thus, the only way the ocean sees an up­take in car­bon diox­ide from the at­mos­phere is when or­ganic car­bon from the sur­face is trans­ported to the deep ocean in the form of sink­ing par­ti­cles.

Th­ese sink­ing par­ti­cles con­sist of any­thing from dead or­gan­isms to fae­cal mat­ter. In ad­di­tion, di­atoms, which are an abun­dant type of phy­to­plank­ton, pro­duce glass-like sil­ica shells that also sink. If all of th­ese par­ti­cles sink un­ob­structed, the car­bon can be kept out of the at­mos­phere for mil­len­nia. How­ever, the study re­vealed that as much as 20 per­cent of the par­ti­cles are be­ing con­sumed, mean­ing that a lot less car­bon reaches the seabed. In ad­di­tion, the pres­ence of the phaeo­dar­i­ans vary from place to place, from be­ing abun­dant enough to con­sume

30 per­cent of sink­ing par­ti­cles to barely be­ing present at all. Given this, sci­en­tists have yet to de­ter­mine the im­pact of phaeo­dar­i­ans on the global car­bon cy­cle, but be­lieve that the dis­cov­ery has sig­nif­i­cant im­pli­ca­tions.

ABOVE Phy­to­plank­ton are mi­cro­scopic ma­rine al­gae that re­quire sun­light to live and grow

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