Enlarge / If these walls could talk… they’d complain about the weather, too. (credit: Patty Ho)

Sometimes, Earth’s climate system seems a lot like a Rube Goldberg machine—those zany marbles-and-mouse-traps sequences that circuitously complete some simple action. The ocean can interact with the atmosphere, which can interact with ecosystems on land, which can turn back and affect the atmosphere, and end up interacting with the ocean again. It can seem too complex to keep track of at first, but scientists have become quite familiar with many well-worn tracks in this climate contraption.

Records of climate during the last “ice age” show us a number of these crazy connections. When the planet was around 5°C colder and ice sheets covered large areas of the Northern Hemisphere, the climate featured some impressive fluctuations that aren’t possible in today’s warmer world. One of those was a periodic cycle of colder periods called “stadials” that each lasted for hundreds of years.

When the cold periods caused ice sheets in North America and Europe to expand sufficiently, they sometimes spawned sudden and massive outpourings of Atlantic icebergs called “Heinrich events.” These events are known from seafloor sediment cores, where you can find layers of pebbles and rocks that can only travel the open ocean by being trapped in icebergs.