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Glacial cycles drive variations in the production of oceanic crust

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Science  13 Mar 2015:
Vol. 347, Issue 6227, pp. 1237-1240
DOI: 10.1126/science.1261508

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Connecting orbit to the ocean floor

The amount of magma erupted at mid-ocean ridges can be modified by periodic ice ages that alter sea level. Crowley et al. analyzed high-resolution ocean depth data across the Australian-Antarctic ocean ridge (see the Perspective by Conrad). The results revealed 23-, 41-, and 100-thousand-year periodicity. These periods are similar to the well-known Milankovitch cycles associated with ice ages that are triggered by changes in Earth's orbit. Decreasing sea levels decrease the overlying pressure, thereby increasing the amount of erupted magma. The cyclic nature of glaciations and sea level creates a series of spaced topographic highs along the sea floor. Thus, Earth's atmosphere and mantle are coupled on a glacial time scale.

Science, this issue p. 1237; see also p. 1204

Abstract

Glacial cycles redistribute water between oceans and continents, causing pressure changes in the upper mantle, with consequences for the melting of Earth’s interior. Using Plio-Pleistocene sea-level variations as a forcing function, theoretical models of mid-ocean ridge dynamics that include melt transport predict temporal variations in crustal thickness of hundreds of meters. New bathymetry from the Australian-Antarctic ridge shows statistically significant spectral energy near the Milankovitch periods of 23, 41, and 100 thousand years, which is consistent with model predictions. These results suggest that abyssal hills, one of the most common bathymetric features on Earth, record the magmatic response to changes in sea level. The models and data support a link between glacial cycles at the surface and mantle melting at depth, recorded in the bathymetric fabric of the sea floor.

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