Iceland, the Farallon Slab, and dynamic topography of the North Atlantic

Upwelling or downwelling flow in Earth's mantle is thought to elevate or depress Earth's surface on a continental scale. Direct observation of this "dynamic topography" on the seafloor, however, has remained elusive because it is obscured by isostatically supported topography cau...

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Bibliographic Details
Published in:Geology (Boulder) 2004-03, Vol.32 (3), p.177-180
Main Authors: Conrad, Clinton P, Lithgow-Bertelloni, Carolina, Louden, Keith E
Format: Article
Language:English
Subjects:
Atlantic Ocean
Atlantic Ocean Islands
Azores
bottom features
Cartography
downwelling
dynamics
Europe
Farallon Plate
Geophysics
Iceland
mantle
Mid-Atlantic Ridge
mid-ocean ridges
North Atlantic
ocean floors
Oceanography
Scotian Basin
slabs
solid Earth (tectonophysics)
upwelling
Western Europe
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Summary:Upwelling or downwelling flow in Earth's mantle is thought to elevate or depress Earth's surface on a continental scale. Direct observation of this "dynamic topography" on the seafloor, however, has remained elusive because it is obscured by isostatically supported topography caused by near-surface density variations. We calculate the nonisostatic topography of the North Atlantic by correcting seafloor depths for lithospheric cooling and sediment loading, and find that seafloor west of the Mid-Atlantic Ridge is an average of 0.5 km deeper than it is to the east. We are able to reproduce this basic observation in a model of mantle flow driven by tomographically inferred mantle densities. This model shows that the Farallon slab, currently in the lower mantle beneath the east coast of North America, induces downwelling flow that deepens the western North Atlantic relative to the east. Our model also predicts dynamic support of observed topographic highs near Iceland and the Azores, but suggests that the Icelandic high is due to local upper-mantle upwelling, while the Azores high is part of a plate-scale lower-mantle upwelling to the south. An anomalously deep area off the coast of Nova Scotia may be associated with the downwelling component of edge-driven convection at the continental boundary. Thus, several of the seafloor's topographic features can only be understood in terms of dynamic support from flow in Earth's mantle.
ISSN:0091-7613
1943-2682
DOI:10.1130/G20137.1