South Atlantic paleobathymetry since early Cretaceous

We present early Cretaceous to present paleobathymetric reconstructions and quantitative uncertainty estimates for the South Atlantic, offering a strong basis for studies of paleocirculation, paleoclimate and paleobiogeography. Circulation in an initially salty and anoxic ocean, restricted by the topography of the Falkland Plateau, Rio Grande Ridge and Walvis Rise, favoured deposition of thick evaporites in shallow water of the Brazilian-Angolan margins. This ceased as sea oor spreading propagated northwards, opening an equatorial gateway to shallow and intermediate circulation. This gateway, together with subsiding volcano-tectonic barriers would have played a key role in Late Cretaceous climate changes. Later deepening and widening of the South Atlantic, together with gateway opening at Drake Passage would lead, by mid-Miocene (∼15 Ma) to the establishment of modern-style thermohaline circulation

Heat-flow anomaly and residual topography in the Mascarene hotspot swell (Indian Ocean)

We review the sea-bottom heat-flow determinations and present a new heat-flow observation on the Mauritius island, which is part of the long-lived Reunion hotspot track. The marine heat flow is on average 66 \ub1 11 mW m 122 and is consistent with the on-land value of 61 \ub1 18 mW m 122 found in Mauritius. Since these values do not significantly deviate from the reference cooling-plate model, lithosphere erosion does not seem a likely mechanism for the swell formation. The lack of significant reheating due to a mantle plume impacting the lithosphere base is confirmed by thermal modelling. Moreover, the coherency between on-land and marine data is argument against advective redistribution of heat near the axis of the swell. We also analyse the large-scale features of the ocean lithosphere, which are not simply a function of the plate cooling and can reflect variations in mantle dynamic topography. The predicted topography variation along the swell shows amplitude and wavelength comparable to other hotspots. Both the topographic swell magnitude and the wavelength increase northwards with the increase of the age of volcanism. The estimated flux of material from the mantle follows the same trend, being larger in the northern part of the swell. The result that residual topography and the buoyancy flux are smaller at the active volcano of Reunion could be evidence that the activity of the plume has decreased with time