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<DIV id=cite minmax_bound="true"><I minmax_bound="true">Nature</I> <B
minmax_bound="true">456</B>, 938-941 (18 December 2008)</DIV>
<DIV minmax_bound="true"><SPAN class=doi minmax_bound="true"><ABBR
title="Digital Object Identifier" minmax_bound="true">doi</ABBR
minmax_bound="true">:10.1038/nature07573</SPAN></DIV>
<DIV>
<P id=errorcor minmax_bound="true"></P>
<H2 id=atl minmax_bound="true"><FONT size=4>How supercontinents and superoceans
affect seafloor roughness</FONT></H2>
<P id=aug minmax_bound="true">Joanne M. Whittaker<A title="affiliated with "
href="http://www.nature.com/nature/journal/v456/n7224/abs/nature07573.html?lang=en#a1"
minmax_bound="true"><SUP>1</SUP></A><SUP>,</SUP><A title="affiliated with "
href="http://www.nature.com/nature/journal/v456/n7224/abs/nature07573.html?lang=en#a5"
minmax_bound="true"><SUP>5</SUP></A><SUP> </SUP><A
href="mailto:jw@getech.com" minmax_bound="true">jw@getech.com</A>, R. Dietmar
Müller<SUP minmax_bound="true"><A title="affiliated with "
href="http://www.nature.com/nature/journal/v456/n7224/abs/nature07573.html?lang=en#a1"
minmax_bound="true">1</A></SUP>, Walter R. Roest<SUP minmax_bound="true"><A
title="affiliated with "
href="http://www.nature.com/nature/journal/v456/n7224/abs/nature07573.html?lang=en#a2"
minmax_bound="true">2</A></SUP>, Paul Wessel<SUP minmax_bound="true"><A
title="affiliated with "
href="http://www.nature.com/nature/journal/v456/n7224/abs/nature07573.html?lang=en#a3"
minmax_bound="true">3</A></SUP> & Walter H. F. Smith<SUP
minmax_bound="true"><A title="affiliated with "
href="http://www.nature.com/nature/journal/v456/n7224/abs/nature07573.html?lang=en#a4"
minmax_bound="true">4</A></SUP></P>
<DIV id=affiliations-notes minmax_bound="true">
<OL class=decimal minmax_bound="true">
<LI id=a1 minmax_bound="true">Earthbyte Group, School of Geosciences, Building
F09, The University of Sydney, Sydney, New South Wales 2006, Australia
<LI id=a2 minmax_bound="true">Ifremer, Centre de Brest, Département des
Géosciences Marines, BP 70, 29280 Plouzané, France
<LI id=a3 minmax_bound="true">Department of Geology and Geophysics, SOEST,
University of Hawaii at M<IMG
style="BORDER-TOP-WIDTH: 0px; BORDER-LEFT-WIDTH: 0px; BORDER-BOTTOM-WIDTH: 0px; VERTICAL-ALIGN: baseline; BORDER-RIGHT-WIDTH: 0px"
alt="a macr"
src="http://www.nature.com/__chars/a/special/macr/black/med/base/glyph.gif"
minmax_bound="true">noa, Honolulu, Hawaii 96822, USA
<LI id=a4 minmax_bound="true">National Oceanic and Atmospheric Administration,
Silver Spring, Maryland 20910, USA
<LI id=a5 minmax_bound="true">Present address: GETECH, Kitson House, Elmete
Hall, Elmete Lane, Leeds LS8 2LJ, UK.</LI></OL>
<P class=caff minmax_bound="true">Seafloor roughness varies considerably across
the world's ocean basins and is fundamental to controlling the circulation and
mixing of heat in the ocean<SUP minmax_bound="true"><A
href="http://www.nature.com/nature/journal/v456/n7224/full/nature07573.html#B1"
minmax_bound="true">1</A></SUP> and dissipating eddy kinetic energy<SUP
minmax_bound="true"><A
href="http://www.nature.com/nature/journal/v456/n7224/full/nature07573.html#B2"
minmax_bound="true">2</A></SUP>. Models derived from analyses of active
mid-ocean ridges suggest that ocean floor roughness depends on seafloor
spreading rates<SUP minmax_bound="true"><A
href="http://www.nature.com/nature/journal/v456/n7224/full/nature07573.html#B3"
minmax_bound="true">3</A></SUP>, with rougher basement forming below a
half-spreading rate threshold of 30–35 mm yr<SUP
minmax_bound="true">-1</SUP> (refs <A
href="http://www.nature.com/nature/journal/v456/n7224/full/nature07573.html#B4"
minmax_bound="true">4</A>, <A
href="http://www.nature.com/nature/journal/v456/n7224/full/nature07573.html#B5"
minmax_bound="true">5</A>), as well as on the local interaction of mid-ocean
ridges with mantle plumes or cold-spots<SUP minmax_bound="true"><A
href="http://www.nature.com/nature/journal/v456/n7224/full/nature07573.html#B6"
minmax_bound="true">6</A></SUP>. </P>
<P class=caff minmax_bound="true">Here we present a global analysis of marine
gravity-derived roughness, sediment thickness, seafloor isochrons and
palaeo-spreading rates<SUP minmax_bound="true"><A
href="http://www.nature.com/nature/journal/v456/n7224/full/nature07573.html#B7"
minmax_bound="true">7</A></SUP> of Cretaceous to Cenozoic ridge flanks. Our
analysis reveals that, after eliminating effects related to spreading rate and
sediment thickness, residual roughness anomalies of 5–20 mGal remain over
large swaths of ocean floor. We found that the roughness as a function of
palaeo-spreading directions and isochron orientations<SUP minmax_bound="true"><A
href="http://www.nature.com/nature/journal/v456/n7224/full/nature07573.html#B7"
minmax_bound="true">7</A></SUP> indicates that most of the observed excess
roughness is not related to spreading obliquity, as this effect is restricted to
relatively rare occurrences of very high obliquity angles (>45°). </P>
<P class=caff minmax_bound="true">Cretaceous Atlantic ocean floor, formed over
mantle previously overlain by the Pangaea supercontinent, displays anomalously
low roughness away from mantle plumes and is independent of spreading rates. We
attribute this observation to a sub-Pangaean supercontinental mantle temperature
anomaly<SUP minmax_bound="true"><A
href="http://www.nature.com/nature/journal/v456/n7224/full/nature07573.html#B8"
minmax_bound="true">8</A></SUP> leading to slightly thicker than normal Late
Jurassic and Cretaceous Atlantic crust<SUP minmax_bound="true"><A
href="http://www.nature.com/nature/journal/v456/n7224/full/nature07573.html#B9"
minmax_bound="true">9</A></SUP>, reduced brittle fracturing and smoother
basement relief. </P>
<P class=caff minmax_bound="true">In contrast, ocean crust formed above Pacific
superswells<SUP minmax_bound="true"><A
href="http://www.nature.com/nature/journal/v456/n7224/full/nature07573.html#B10"
minmax_bound="true">10</A></SUP>, probably reflecting metasomatized lithosphere
underlain by mantle at only slightly elevated temperatures<SUP
minmax_bound="true"><A
href="http://www.nature.com/nature/journal/v456/n7224/full/nature07573.html#B11"
minmax_bound="true">11</A></SUP>, is not associated with basement roughness
anomalies. These results highlight a fundamental difference in the nature of
large-scale mantle upwellings below supercontinents and superoceans, and their
impact on oceanic crustal accretion.</P></DIV>
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