Calcium carbonate dissolution triggered by high productivity during the
last glacial-interglacial interval at the deep western South Atlantic
Abstract
Studies reconstructing surface paleoproductivity and benthic conditions
allow us to measure the effectiveness of the biological pump, an
important mechanism in the global climate system. In order to assess
surface productivity changes and their effect on the seafloor, we
studied the core SAT-048A, recovered from the continental slope of the
southernmost Brazilian continental margin, in the western South
Atlantic. We assessed the sea surface productivity, the organic matter
flux to the seafloor and the dissolution effects, based on
micropaleontological (benthic and planktonic foraminifers, ostracods),
geochemical (benthic and planktonic δ13C isotopes) and sedimentological
data (carbonate and bulk sand content). Superimposed on the
climate-induced changes related to the last glacial-interglacial
transition, the reconstruction indicates paleoproductivity changes
synchronized with the precessional cycle. From the reconstructed data,
it was possible to identify high (low) surface productivity, high (low)
organic matter flux to the seafloor, and high (low) dissolution rates of
planktonic Foraminifera tests during the glacial (postglacial).
Furthermore, within the glacial, enhanced productivity was associated
with higher insolation values, explained by increased NE summer winds
that promoted meandering and upwelling of the nutrient-rich South
Atlantic Central Water. Changes in the Atlantic Meridional Overturning
Circulation and the reorganization of bottom water masses could also
have changed the CO3 2- saturation levels and have influenced the
carbonate preservation. However, changes in the Uvigerina spp. δ13C
values are very likely linked to the organic matter flux and not to the
sea bottom dissolved inorganic matter δ13C values.