The Aptian evaporites of the South Atlantic: a climatic paradox?

Abstract

Abstract. For a long time, evaporitic sequences have been interpreted as indicative of an arid climate. Such systematic interpretations led to the suggestion that the Central segment of the South Atlantic (20-0 • ) was characterized by an arid climate during the upper Aptian. Indeed, synchronous to this period that corresponds to the rifting and to the opening of this part of the South Atlantic, a large evaporitic sequence spreads out from the equator to 20 • S. Using the fully ocean atmosphere coupled model FOAM, we test the potential for the Aptian geography to produce an arid area over the Central segment. Sensitivity to the altitude of the rift shoulders separating the Africa and the South America cratons, to the water depth of the Central segment and to the drainage pattern have been performed. Using seawater salinity as a diagnostic, our simulations show that the southern part of the Central segment is characterized by very high salinity in the case of catchment areas draining the water out of the Central segment. Conversely, whatever the boundary conditions used, the northern part of the Central segment remains humid and salinities are very low. Hence, we conclude that the evaporites deposited in the southern part of the Central segment may have been controlled by the climate favouring aridity and high saline waters. In contrast, the evaporites of the northern part can hardly be reconciled with the climatic conditions occurring there and may be due to hydrothermal sources. Our interpretations are in agreement with the gradient found in the mineralogical compositions of the evaporites from the North to the South, i.e. the northern evaporites are at least 4 times more concentrated than the southern one.

The role of eastern Tethys seaway closure in the Middle Miocene Climatic Transition (ca. 14 Ma)

“…The atmospheric and oceanic components are linked by a coupler, which calculates and interpolates fluxes between the two components (Tobis et al, 1997). FOAMv1.5 compares well with other generalised climate models for present-day climate (Jacob, 1997) and has also proven to be useful in the study of past climates (Poulsen et al, 2001;Donnadieu et al, 2006;Zhang et al, 2011;Chaboureau et al, 2012;Hamon et al, 2012;Lefebvre et al, 2012). Moreover, a recent study showed that FOAMv1.5 simulates a modern ACC which is in good agreement with observations and with coupled models from the IPCC AR4 (Lefebvre et al, 2012).…”

Links between CO<sub>2</sub>, glaciation and water flow: reconciling the Cenozoic history of the Antarctic Circumpolar Current

“…It runs on a 1.4 • by 2.8 • grid with 12 of the 24 vertical levels in the upper 1000 m. The sea ice model uses the thermodynamics of NCAR's CSIM (Community Sea Ice Model) 2.2.6. FOAM has been used to successfully simulate presentday climate (e.g., Zhang et al, 2005) as well as paleoclimates (Chaboureau et al, 2012;Dera and Donnadieu, 2012;Poulsen et al, 2003).…”

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“…The atmospheric and oceanic components are linked by a coupler, which calculates and interpolates fluxes between the two components (Tobis et al, 1997). FOAMv1.5 compares well with other generalised climate models for present-day climate (Jacob, 1997) and has also proven to be useful in the study of past climates (Poulsen et al, 2001;Donnadieu et al, 2006;Zhang et al, 2011;Chaboureau et al, 2012;Hamon et al, 2012;Lefebvre et al, 2012). Moreover, a recent study showed that FOAMv1.5 simulates a modern ACC which is in good agreement with observations and with coupled models from the IPCC AR4 (Lefebvre et al, 2012).…”