MIT researchers have discovered that bacteria hitchhiking on marine snow particles dissolve calcium carbonate, the mineral ballast that helps particles sink to the deep ocean. Using microfluidic experiments simulating sinking particles, the team found bacteria excrete acidic waste that erodes calcium carbonate, slowing the descent of marine snow. Crucially, dissolution peaks at intermediate sinking speeds where bacteria are well-oxygenated and waste products accumulate. This microscale process explains why dissolved calcium carbonate appears in shallow ocean layers where thermodynamics predict it should remain intact, and suggests the ocean's biological carbon pump may be less effective than previously assumed. The findings have direct implications for climate engineering proposals that aim to enhance ocean carbon sequestration.
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