Calcareous and agglutinated benthic foraminifera data from the Tagus prodelta (Portugal)

A high resolution sedimentary sequence recovered in the Tagus Prodelta has been studied in order to reconstruct paleoenvironmental conditions on the western Iberian Margin, Portugal, through the last ca. 2000 years, including the historical time when anthropogenic influence became significant. Benthic foraminiferal assemblages as well as stable isotopic composition of the benthic foraminifera Uvigerina sp. were investigated. Considerable environmental fluctuations are indicated by all these proxies. Between AD 400 and 1400 (1550-550 cal year BP), during a period including the Medieval Warm Period, bottom water temperatures, as reconstructed from Uvigerina sp., were high, 13.3°C. In this time interval, species typical for shelf environments (Cassidulina laevigata, Nonion asterizans and Hyalinea balthica) maintained a high abundance along with opportunistic species like Bolivina dilatata and Bolivina pacifica, the most abundant species in the record. A faunal change occurred at around AD 1300-1400 (650-550 cal year BP), at the beginning of the Little Ice Age. After this, the environment became more variable in the Tagus Prodelta, as reflected by a decrease in faunal diversity and benthic foraminiferal composition and flux values. After about AD 1800 (150 cal year BP), bottom water temperatures rose to maximum values of the record. The disappearance of certain benthic taxa and the appearance of the species Saidovina karreriana indicate a change in bottom water conditions during the last 100 years, possibly induced by anthropogenic pollution.

本研究对葡萄牙特茹河前三角洲（Tagus Prodelta）获取的高分辨率沉积序列展开分析，旨在重建过去约2000年以来伊比利亚西部陆缘的古环境演化历史，其中涵盖了人类活动影响显著的历史时期。研究同时分析了底栖有孔虫（benthic foraminifera）组合特征，以及底栖有孔虫Uvigerina属（Uvigerina sp.）的稳定同位素组成。上述两类代用指标均揭示了研究区存在显著的环境波动。在公元400年至1400年（对应校正年代为1550~550 cal BP）的中世纪暖期时段内，基于Uvigerina属壳体重建的底层海水温度较高，均值达13.3℃。此阶段内，陆架环境典型种（Cassidulina laevigata、Nonion asterizans及Hyalinea balthica）与机会种（opportunistic species）如Bolivina dilatata和Bolivina pacifica（本记录中丰度最高的物种）均保持较高的丰度。在公元1300~1400年（对应校正年代为650~550 cal BP），即小冰期起始阶段，底栖有孔虫动物群发生了更替。在此之后，特茹河前三角洲的环境波动愈发剧烈，具体表现为动物群多样性下降、底栖有孔虫组合组成及通量数值出现变化。约公元1800年（对应校正年代为150 cal BP）之后，底层海水温度升至本记录中的最高值。近百年来，部分底栖有孔虫类群消失，同时出现Saidovina karreriana物种，这一现象指示底层海水环境发生了改变，其诱因可能为人类活动造成的污染。