Origin of δ13C minimum events in thermocline and intermediate waters of the western South Atlantic
Résumé
Stable carbon isotopic (δ13C) minimum events have been widely described in marine archives recording the properties of thermocline and intermediate waters during glacial terminations. However, the mechanisms associated with these events remain ambiguous. Here we present three high temporal resolution deep-dwelling planktonic foraminifera δ13C records from the main thermocline and one benthic δ13C record from the modern core of Antarctic Intermediate Water (AAIW). Our sediment cores are distributed along the western South Atlantic from the equator to the subtropics, with the longest record spanning the last ∼300 kyr. The results show that δ13C minimum events were pervasive features of the last three glacial terminations and Marine Isotope Stage 4/3 transition in the western South Atlantic. Two distinct mechanisms were responsible for the δ13C minima at the thermocline and intermediate depths of the Atlantic, respectively. We suggest that the δ13C minimum events at the thermocline were mostly driven by the thermodynamic ocean-atmosphere isotopic equilibration, which is supported by calculated δ13C of dissolved inorganic carbon in the subtropical western South Atlantic as well as by previously published model simulations. On the other hand, intermediate depths δ13C minimum events in the tropics were likely caused by the slowdown of the Atlantic meridional overturning circulation and the associated accumulation of isotopically light carbon at mid and intermediate depths of the Atlantic Ocean.
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