南海东北部陆坡铁锰沉积记录对环境变化的指示意义

通过对南海东北陆坡沉积柱的研究,建立了高分辨率铁、锰、CaCO₃,Fe/Mn的值和醋酸溶性镁的变化序列.研究表明,铁和锰含量之间呈正相关关系,两者在垂直方向上总的变化趋势基本一致,锰的氧化还原界面的深度要比铁的浅.经过成岩作用,铁基本上可以保存它原始的沉积含量,间冰期沉积物中铁含量要比冰期的高,铁含量波动幅度和频率可以表示短期的气候剧烈波动的强度和频率,同时也表明了陆源供给的相对稳定性.锰保存的含量比它原始的沉积含量明显减少,锰含量的变化主要受海洋沉积环境的控制,在冰期锰含量得到相对富集,锰含量的较大波动多出现在碳酸盐含量发生较大变化的时候,锰含量的变化反映了曾经发生的海洋生产力、沉积速率和温度的巨大波动.在沉积柱中Fe/Mn的值的变化与碳酸钙的变化在总体上表现出相反的变化趋势,冰期Fe/Mn的值小,而在间冰期时其比值较大,Fe/Mn的值可以作为一个表征碳酸盐旋回的灵敏的替代性指标,同时Fe/Mn的值的变化可以表征大气二氧化碳的波动和海洋沉积速率的变化.

Deposit record of iron and manganese in northeast continental slope of the South China Sea and its indication to environmental changes

The high-resolution content sequences about iron,manganese,ratios of iron to manganese,CaCO_3 and acetic acid-soluble magnesium in the SZ2 column from the northeast continental slope of the South China Sea have been set up.There are remarkable positive correlations among iron, manganese and CaCO_3 and negative correlations between CaCO_3 and the ratios of iron to manganese. The positive correlations between iron and manganese show that their content changes on the vertical are identical.The depth of redox boundary of iron is deeper than that of manganese. In the process of diagenesis, the original content of iron has been kept in the deposit column, and the content of manganese kept in the column is much less than its original content, however, the content of manganese in the column is enriched during glacial era. It is concluded that the changes of manganese content reveal the strong fluctuation of sea productivity, deposit rate and temperature, and the fluctuation of the concentration of iron reveals the fluctuation strength and frequency of global climate and supply of iron from the continent. The changes of concentration of manganese in the column are abrupt, which often happen in the depth where there are the turning points of content changes of CaCO_3.The ratios of iron to manganese in the glacial era are less than those of interglacial. The ratios of iron to manganese are an important and sensitive proxy indicators for the deposit rate, and for the changes of CaCO_3 in the column, and for the changes of CO_2 in the atmosphere.