A River Runs Through ItThe Fraser River in western Canada picks up chemical signatures from the environment it flows through. Scientists can analyze samples from the river to track a geochemical journey that starts in the atmosphere, moves through rocks and plants, and sinks to the seafloor.

Chemical WeatheringRaindrops soak up carbon dioxide in air and convert it into carbonic acid (H2CO3). Carbonic acid in rain reacts with minerals in rocks (with occasional rogue strontium atoms embedded). The reaction releases calcium (Ca), strontium (Sr), and bicarbonate (HCO3) ions that dissolve in water. This process extracts heat-trapping carbon dioxide from the air.

Strontium clocksStrontium-87 (Sr-87) is produced by the constant radioactive decay of rubidium-87 in rocks. It takes millions of years for detectable amounts of strontium-87 to build up in minerals. The Sr-87 signature in the Fraser River reveals how much material came from older rocks in the Rocky Mountains, which have accumulated more Sr-87, or from younger rocks in the Coast Range.

Adding organic carbonOrganic carbon, the residue of dead plants, bacteria, and algae, also enters the river. Some of this carbon is consumed by organisms along the way and removed from the river, but some continues downstream into the sea.

Burying carbonMarine organisms use calcium (Ca) and bicarbonate (HCO3) ions to build hard shells. When they die, their shells, and the carbon in them, sink to the seafloor. This carbon—which started out in the atmosphere as CO2—along with the organic carbon from plants, bacteria, and algae, stays locked away in sediments for millions of years.