Over the course of Earth’s long history, glaciers have repeatedly risen and fallen in 100,000-year intervals known as Milankovitch cycles. Despite a clear consensus that they exist, scientists still debate the forces behind these ice age cycles. A new study by Tolstoy finds a potential answer in an unlikely place.
It’s tough to track what happens in the deep waters of the East Pacific Rise, where hydrothermal seafloor ridges like Juan de Fuca can spew out a variety of elements ranging from solid lead to methane and carbon dioxide. The eruptions happen far from land, with seismic signatures too low to be measured by global networks.
New hydroacoustic techniques allowed the author to record 10 eruptions and unveil a surprising cycle. Most events initiated during neap tide—a situation in which the Moon, Earth, and Sun form a right angle and the difference between high tide and low tide is smallest. Additionally, Earth’s not quite circular orbit appears to contribute to the cycle: All the eruptions occurred during the first 6 months of the year, at a time when Earth is moving farther away from the Sun and thus the Sun’s grip on Earth is slightly reduced. This slightly reduced long-term tidal tug seems to favor eruptions.
The author suspects these mid-ocean ridge cycles might pack an even bigger punch over the longer 100,000-year period, when Earth’s elliptical orbit becomes even more pronounced. Previous studies have struggled to tie this eccentricity to climate shifts, but her research has uncovered evidence that lava builds on the mid-ocean ridges over the same period of time. Also, tying up Earth’s seawater in massive glaciers would reduce the amount of seawater available to push down on the volcanoes, possibly helping to fuel more eruptions.
If the author’s hypothesis is true, the ridges might serve as a feedback into long-term climate shifts, contribute to glacial cycles, bring an abrupt end to ice ages, and help finally explain the 100,000-year Milankovitch cycles.
Of course, these eruptions would have a tiny impact on Earth’s current climate woes; their contribution pales in comparison to the amount of climate-altering carbon dioxide released by humans. (Geophysical Research Letters, doi:10.1002/2014GL063015, 2015)
—Eric Betz, Freelance Writer
Citation: Betz, E. (2015), Earth’s climate cycles might have an eccentric explanation, Eos, 96, doi:10.1029/2015EO038361. Published on 30 October 2015.