Sediment and pore water chemistry and physical oceanography of samples obtained during Baltic Sea research cruises

Sediment samples from approximately 40 stations in the Western, middle and eastern Baltic Sea were investigated for manganese and iron content. In a series of interstitial water samples and numerous deep and surface water samples, the manganese content was likewise determined. A strong enrichment of these elements in the basin sediments was shown. In many instances, several percent manganese were present. As a maximum value, 13% was found in a 1 mm thick layer. Furthermore, a distinct decrease in manganese content with increasing sediment depth was shown in the upper 10 to 20 cm of the Sediment at almost all stations. Both phenomena may be explained by the release of manganese from the Sediment through diffusion. In the flat parts of the Baltic and those parts having good bottom water circulation, this diffusion progresses especially vigorously as a result of a steep gradient of the Mn++ concentration in the interstitial water-deep water interface. The manganese which hereby passes into the water overlying the bottom (manganese contents between 10 and 100 y Mn/l were determined in numerous deep water samples) is partly reprecipitated on the Sediment surface, and partly carried by currents into the deeper basins where it is finallv deposited. It is bound there as a manganese-rich mixed carbonate, the composition of which can be proved chemically and by x-ray methods. Iron is likewise of higher content in the basinal sediments, however, the extent of its enrichment is far less since it is less soluble than manganese under the reducing conditions in the sediments. The fine bands of manganese- and iron-rich layers in the basin sediments may likewise be explained as a result of diffusion.

对波罗的海西部、中部及东部海域约40个站位采集的沉积物样品开展了锰与铁含量分析。同时对一系列孔隙水（interstitial water）样品以及大量深水、表层水样品进行了锰含量测定。研究表明，波罗的海盆地沉积物中这两种元素存在显著富集：多数情况下锰含量可达数百分点，其中一处厚度1mm的层位中测得最高值13%。此外，几乎所有站位的沉积物表层10~20cm范围内，锰含量均随沉积深度增加呈现明显下降趋势。上述两种现象均可通过沉积物中的锰通过扩散作用释放得以解释。在波罗的海地势平缓且底层水循环良好的区域，由于孔隙水-深水界面处Mn++浓度存在陡峭梯度，该扩散过程尤为剧烈。由此进入底层覆水的锰（大量深水样品测得锰含量介于10~100 μg Mn/L），一部分在沉积物表面再沉淀，另一部分则随洋流被搬运至更深的盆地并最终沉积于此。这些锰以富锰混合碳酸盐的形式被固定于此，其组分可通过化学方法及X射线（x-ray）方法得以验证。铁在盆地沉积物中同样含量偏高，但其富集程度远低于锰，这是因为在沉积物的还原环境下，铁的溶解度远低于锰。盆地沉积物中富锰、富铁层的细密条带同样可通过扩散作用得到解释。