Geochemical and physical sediment properties of sediment cores from the Portuguese shelf

Marine sediments from the Portuguese shelf are influenced by environmental changes in the surrounding continental and marine environment. These are largely controlled by the North Atlantic Oscillation, but additional impacts may arise from episodic tsunamis. In order to investigate these influences, a high resolution multi-proxy study has been carried out on a 5.4 m long gravity core and five box cores from the Tagus prodelta on the western Portuguese margin, incorporating geochemical (Corg/Ntotal ratios, d13Corg, d15N, d18O, Corg and CaCO3 content) and physical sediment properties (magnetic susceptibility, grain-size). Subsurface data of the five box cores indicate no major effect of early postdepositional alteration. Surface data show a higher fraction of terrigenous organic material close to the river mouth and in the southern prodelta. Gravity core GeoB 8903 covers the last 3.2 kyrs with a temporal resolution of at least 0.1 cm/yr. Very high sedimentation rates between 69 and 140 cm core depth indicate a possible disturbance of the record by the AD1755 tsunami, although no evidence for a disturbance is observed in the data. Sea surface temperature and salinity on the prodelta, the local budget of marine NO3- as well as the provenance of organic matter remained virtually constant during the past 3.2 kyrs. […]

葡萄牙大陆架的海洋沉积物受到周边大陆及海洋环境变化的显著影响。此类变化主要受北大西洋涛动所调控，而周期性的海啸也可能带来额外的冲击。为了探究这些影响，研究人员在葡萄牙西部边缘的塔古斯三角洲处，对一长度为5.4米的重力柱状样和五个箱式柱状样进行了高分辨率的多代数研究，涉及地球化学参数（如Corg/Ntotal比值、d13Corg、d15N、d18O、Corg及CaCO3含量）及物理沉积特性（如磁化率、粒度）。五个箱式柱状样的地下数据表明，早期沉积后变化对记录并无重大影响。地表数据则显示，在河口附近及南部三角洲地区，陆源有机物质的含量相对较高。重力柱状样GeoB 8903覆盖了过去3200年，时间分辨率为至少每年0.1厘米。在柱状样深度69至140厘米之间，非常高的沉积速率暗示了公元1755年海啸可能对记录造成了干扰，尽管在数据中并未观察到明显的干扰证据。在过去3200年间，三角洲地区的海表温度、盐度、海洋NO3-的局部收支平衡以及有机物质的来源均保持相对稳定。