Spatiotemporal patterns of carbonate sedimentation in the South Atlantic: Implications for carbon cycling during the Paleocene–Eocene thermal maximum

Abstract

Rapid carbon input into the ocean–atmosphere system caused a dramatic shoaling of the lysocline during the Paleocene–Eocene thermal maximum (PETM), a transient (∼ 170 kyr) global warming event that occurred roughly 55 Ma. Carbon cycle models invoking an accelerated carbonate–silicate feedback mechanism to neutralize ocean acidification predict that the lysocline would subsequently deepen to depths below its original position as the marine carbonate system recovered from such a perturbation. To test this hypothesis, records of carbonate sedimentation and preservation for PETM sections in the Weddell Sea (ODP Site 690) and along the Walvis Ridge depth transect (ODP Sites 1262, 1263, and 1266) were assembled within the context of a unified chronostratigraphy. The meridional gradient of undersaturation delimited by these records shows that dissolution was more severe in the subtropical South Atlantic than in the Weddell Sea during the PETM, a spatiotemporal pattern inconsistent with the view that Atlantic overturning circulation underwent a transient reversal. Deepening of the lysocline following its initial ascent is signaled by increases in %CaCO 3 and coarse-fraction content at all sites. Carbonate preservation during the recovery period is appreciably better than that seen prior to carbon input with carbonate sedimentation becoming remarkably uniform over a broad spectrum of geographic and bathymetric settings. These congruent patterns of carbonate sedimentation confirm that the lysocline was suppressed below the depth it occupied prior to carbon input, and are consistent with the view that an accelerated carbonate–silicate geochemical cycle played an important role in arresting PETM conditions.