Seafloor grooves record the beat of the ice ages

Abstract

Sea level changes influence the underwater eruptions that build abyssal hills.In addition to carving up the continents, the ice ages also tattoo the sea floor with rhythmic patterns, according to two studies published this week. At seafloor spreading centers, plates of ocean crust diverge and magma erupts in the gap, building new crust onto the plates' trailing edges. Parallel to these spreading centers are "abyssal hills": long, 100-meter-high ridges on the diverging plates, separated by valleys. It turns out that these periodic grooves reflect the timing of the ice ages. Ice ages are driven mainly by periodic variations in Earth's orbit and spin that alter sunlight in the Northern Hemisphere. During these periods, ice sheets trap so much frozen water that sea levels can drop a hundred meters or more. This reduces the pressure on the ocean floor and, in turn, speeds up the eruptions at the spreading centers—thickening the ocean plates and creating the abyssal hills, researchers say. The periodic strength of the eruptions helps explain the long-debated origin of the abyssal hills. Also intriguing is the question of whether emissions from seafloor volcanoes could be a feedback that helps bring about the end of ice ages.