Abstract

Anoxic zones, regions of the water column completely devoid of dissolved oxygen, occur in open oceans and coastal zones worldwide. The Baltic Sea is characterized by strong salinity-driven stratification, maintained by occasional water inflows from the Danish Straights and freshwater input from rivers. Between inflow events, the stratification interface between surface and deep waters hinders mixing and ventilation of deep water; consequently, the bottom waters of large regions of the Baltic are anoxic. The onset of the anoxic zone is closely coincident with the depth of the halocline and, as a result, the interface between oxic and anoxic waters corresponds to a strong impedance contrast. Here, we track acoustic scattering from the impedance contrast utilizing a broadband split-beam echosounder in the Western Gotland Basin and link it to a dissolved oxygen level of 2 ml/l using ground truth stations. The broadband acoustic dataset provides the means to remotely observe the spatiotemporal variations in the oxic–anoxic interface, map out the extent of the anoxic zone with high resolution, and identify several mechanisms influencing the vertical distribution of oxygen in the water column. The method described here can be used to study other systems with applications in ongoing oceanographic monitoring programs.

中文翻译：

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利用宽带声学跟踪波罗的海含氧-缺氧界面的时空变化

摘要

缺氧区是水柱中完全不含溶解氧的区域，发生在全世界的大洋和沿海地区。波罗的海的特征是强烈的盐分驱动分层，丹麦直管偶尔会流入水，河流会输入淡水。在流入事件之间，地表水和深水之间的分层界面阻碍了深水的混合和通风；因此，波罗的海大片区域的底水是缺氧的。缺氧区域的开始与盐卤的深度非常一致，因此，有氧和缺氧水之间的界面对应于强的阻抗对比。这里，我们使用哥得兰岛西部盆地的宽带分束式回声测深仪从阻抗对比中跟踪声散射，并使用地面真站将其链接到2 ml / l的溶解氧水平。宽带声学数据集提供了一种手段，可以远程观察有氧-缺氧界面中的时空变化，以高分辨率绘制出缺氧区域的范围，并确定影响水柱中氧气垂直分布的几种机制。此处描述的方法可用于研究其他系统，并将其应用于正在进行的海洋监测程序中。绘制出高分辨率的缺氧区范围，并确定几种影响水柱中氧气垂直分布的机制。此处描述的方法可用于研究其他系统，并将其应用于正在进行的海洋监测程序中。绘制出高分辨率的缺氧区范围，并确定几种影响水柱中氧气垂直分布的机制。此处描述的方法可用于研究其他系统，并将其应用于正在进行的海洋监测程序中。