Aragonite distribution and preservation of sediment cores from the Brazilian Continental Slope

We present late Quaternary records of aragonite preservation determined for sediment cores recovered on the Brazilian Continental Slope (1790-2585 m water depth) where North Atlantic Deep Water (NADW) dominates at present. We have used various indirect dissolution proxies (carbonate content, aragonite/calcite contents, and sand percentages) as well as gastropodal abundances and fragmentation of Limacina inflata to determine the state of aragonite preservation. In addition, microscopic investigations of the dissolution susceptibility of three Limacina species yielded the Limacina Dissolution Index which correlates well with most of the other proxies. Excellent preservation of aragonite was found in the Holocene section, whereas aragonite dissolution gradually increases downcore. This general pattern is attributed to an overall increase in aragonite corrosiveness of pore waters. Overprinted on this early diagenetic trend are high-frequency fluctuations of aragonite preservation, which may be related to climatically induced variations of intermediate water masses.本研究报道了采自巴西大陆坡（水深1790~2585米，现今受北大西洋深层水（North Atlantic Deep Water, NADW）主导）的沉积物岩芯的晚第四纪文石保存记录。本研究采用多种间接溶蚀替代指标（碳酸盐含量、文石/方解石含量及砂粒百分含量），结合腹足类丰度与膨胀海若螺（Limacina inflata）的破碎程度，以研判文石的保存状态。此外，通过对3种海若螺属（Limacina）物种的溶蚀敏感性开展显微观测，我们构建了海若螺溶蚀指数（Limacina Dissolution Index），该指数与多数其他替代指标具有良好的相关性。全新统地层中可见极佳的文石保存状况，而随岩芯深度增加，文石溶蚀程度逐渐加剧。这一整体趋势被归因于孔隙水对文石的溶蚀性整体增强。该早期成岩趋势之上叠加了文石保存状况的高频波动，这一波动或与气候驱动的中层水团变化相关。