Longer term storage: peat. https://en.wikipedia.org/wiki/Peat https://en.wikipedia.org/wiki/Peat " Peat forms when plant material does not fully decay in acid

Longer term storage: peat. https://en.wikipedia.org/wiki/Peat https://en.wikipedia.org/wiki/Peat " Peat forms when plant material does not fully decay in acidic and anaerobic conditions. It is composed mainly of wetland vegetation: principally bog plants including mosses, sedges, and shrubs.... " "Across the world, peat covers just 3% of the land’s surface, but stores one-third of the Earth’s soil carbon...." "In natural peatlands, the 'annual rate of biomass production is greater than the rate of decomposition', but it takes 'thousands of years for peatlands to develop the deposits of 1.5 to 2.3 m [4.9 to 7.5 ft], which is the average depth of the boreal [northern] peatlands', which store around 415 gigatonnes ... of carbon...." Now and then a well-preserved body thousands of years old has been found in a bog.