Aragonite preservation in late Quaternary sediment cores on the Brazilian Continental Slope: implications for intermediate water circulation

We present late Quaternary records of aragonite preservation determined for sediment cores recovered on the Brazilian Continental Slope (1790-2585 m w ater depth) where North Atlantic Deep Water (NADW) dominates at present. We have used various indirect dissolution proxies (carbonate content, aragoni te/calcite contents, and sand percentages) as well as gastropodal abundance s and fragmentation of Limacina inflata to determine the state of aragonite preservation. In addition, microscopic investigations of the dissolution s usceptibility of three Limacina species yielded the Limacina Dissolution In dex which correlates well with most of the other proxies. Excellent preserv ation of aragonite was found in the Holocene section, whereas aragonite dis solution gradually increases downcore. This general pattern is attributed t o an overall increase in aragonite corrosiveness of pore waters. Overprinte d on this early diagenetic trend are high-frequency fluctuations of aragoni te preservation, which may be related to climatically induced variations of intermediate water masses.