Planktonic foraminifera in the sediment of a western boundary upwelling system off Cabo Frio

The distribution of planktonic foraminifera in box-core tops under the influence of a western boundary upwelling system along the southeastern Brazilian continental margin was examined to evaluate the similarity percentage (SIMPER) and to create a biofacies model for paleoenvironmental applications. Species associated with warm and oligotrophic water were distributed in the Rio de Janeiro sector of the Campos Basin, while productive water species were most abundant in the Rio de Janeiro sector of the Santos Basin, and cold-water species were most abundant in the Cabo Frio Upwelling System (CFUS). Four major biofacies are associated with the oceanographic setting of the CFUS: one from the Campos Basin (A - Brazil Current front), one from the Santos Basin (B - mixture of coastal and oceanic waters), and two associated with the Cabo Frio High in the northern biofacies (C) and southern biofacies (D). The distribution of biofacies C and D was associated with temperature differences. Biofacies C represents a mixture of upwelling and tropical waters, while biofacies D represents a mixture of cold, nutrient-rich and Santos Basin waters. These biofacies were also defined in core CF10-01B, in which six main paleoceanographic phases were characterized during the last 9 cal kyr, predominantly showing alternating dominance between biofacies C and D. From 9.0 to 5.0 cal kyr before the present (BP), the system was dominated by biofacies C. Between 4.0 and 3.5 cal kyr BP, biofacies D was dominant. Between 3.5 and 2.5 cal kyr BP, a strong influence of coastal waters and weakened upwelling activity were indicated by the dominance of biofacies B + C + D. The last 2.5 cal kyr was dominated by biofacies D. The SST in this core was reconstructed using the Modern Analog Technique (MAT), which revealed 0.35 °C of variability, indicating no SST changes during the Holocene. The weak sensitivity of the MAT was due to the interplay among different oceanographic features.

本研究针对巴西东南部大陆边缘西边界上升流系统影响下的箱式岩心顶部浮游有孔虫（planktonic foraminifera）分布特征展开分析，旨在评估相似性百分比（SIMPER）并构建适用于古环境研究的生物相模型。与温暖贫营养水体共生的物种分布于坎波斯盆地里约热内卢段，而适应高生产力水体的物种在桑托斯盆地里约热内卢段最为富集，冷水物种则集中分布于卡波弗里奥上升流系统（CFUS）内。四大典型生物相与CFUS的海洋学背景密切相关：其一源自坎波斯盆地（A——巴西洋流锋面），其二源自桑托斯盆地（B——沿岸水与外海水的混合水团），另外两类分别对应卡波弗里洛海脊的北部生物相（C）与南部生物相（D）。生物相C与D的分布与海水温度差异密切相关：生物相C代表上升流与热带水团的混合，生物相D则代表寒冷富营养水与桑托斯盆地水团的混合。上述生物相在岩心CF10-01B中同样被识别，该岩心记录了过去9个校准千年（cal kyr）以来的6个主要古海洋学阶段，整体呈现生物相C与D的交替主导特征。在距今9.0至5.0个校准千年（Before Present, BP）期间，该区域以生物相C为主导；在4.0至3.5个校准千年BP期间，生物相D占据主导地位；3.5至2.5个校准千年BP期间，生物相B+C+D占据主导，指示沿岸水团影响增强且上升流活动减弱；过去2.5个校准千年BP以来，则以生物相D为主导。本研究采用现代类比法（MAT）重建了该岩心的海表温度（Sea Surface Temperature, SST），结果显示其温度变化幅度为0.35℃，表明全新世期间海表温度未出现显著变化。现代类比法的敏感性较弱，这源于不同海洋学特征之间的相互作用。