Submarine turbidity currents are one of the most important sediment transfer processes on earth. Yet the fundamental nature of turbidity currents is still debated; especially whether they are entirely dilute and turbulent, or a thin and dense basal layer drives the flow. This major knowledge gap is mainly due to a near-complete lack of direct measurements of sediment concentration within active submarine flows. Here we present the most detailed near-bed sediment concentrations measurements from a powerful turbidity current in Monterey Canyon, offshore California. We employ a novel approach using correlations between conductivity and sediment concentration, which unlike previous methods can measure very high concentrations and not sensitive to grain size. We find that sediment concentrations close to the canyon floor gradually increased after the arrival of the turbidity current, until reaching a maximum value of 12%, the highest concentration ever inferred from direct measurements in turbidity currents. We also show a two-layer flow head, with a fast (up to 4 m/s), thin and dense basal layer overlain by a thicker (~50 m) dilute flow. At the interface of these two layers, there seems to be a sharp steep concentration gradient. Such quantitative measurements of sediment concentration can produce a key step forward in understanding the basic character and dynamics of these powerful submarine flows.

海底浊流是地球上最重要的沉积物转移过程之一。然而，浊流的基本性质仍在争论中。尤其是它们是完全稀薄且湍流的，还是薄而致密的基底层驱动流动。这种主要的知识差距主要是由于几乎完全缺乏对活跃海底流中沉积物浓度的直接测量。在这里，我们介绍了加利福尼亚海上蒙特利峡谷的强浑浊流中最详细的近床沉积物浓度测量值。我们采用一种新颖的方法，利用电导率和沉积物浓度之间的相关性，与以前的方法不同，该方法可以测量非常高的浓度并且对晶粒尺寸不敏感。我们发现，在浊流到达后，靠近峡谷底部的沉积物浓度逐渐增加，直到达到最大值12％，这是直接从浊流测量得出的最高浓度。我们还显示了一个两层流头，具有快速（高达4 m / s），薄而致密的基底层，被较厚的（约50 m）稀流覆盖。在这两层的界面处，似乎有一个陡峭的陡峭浓度梯度。对沉积物浓度的这种定量测量可以在理解这些强大的海底流动的基本特征和动力学方面迈出关键的一步。快速（高达4 m / s），薄而致密的基底层被较厚的（约50 m）稀流覆盖。在这两层的界面处，似乎有一个陡峭的陡峭浓度梯度。对沉积物浓度的这种定量测量可以在理解这些强大的海底流动的基本特征和动力学方面迈出关键的一步。快速（高达4 m / s），薄而致密的基底层被较厚的（约50 m）稀流覆盖。在这两层的界面处，似乎有一个陡峭的陡峭浓度梯度。对沉积物浓度的这种定量测量可以在理解这些强大的海底流动的基本特征和动力学方面迈出关键的一步。