[O-08] Poster presentations by senior high school students

[O08-P70] Research on upwelling of deep ocean currents -Quantitative analysis using diffusion coefficient-

*Shoyo Taguchi¹, *Hiroto Kondo¹, *Haruki Miyagawa¹, *Ryu Mantani¹, Kazumi Igawa¹ (1.Zushi Kaisei Senior High School in Kanagawa)

Keywords:Sea, Environment

In recent discussions on global warming, the interconnectedness of all natural phenomena has been pointed out. Among these, ocean phenomena are natural phenomena that are interrelated with mid- to long-term global environmental changes. Humans have been trying to understand ocean-related phenomena, to utilize them in our daily lives, and to elucidate their mechanisms. The best example of this is the phenomenon of ocean currents. Needless to say, analyzing the flow of seawater from a macroscopic viewpoint provides insight into the causal relationship with factors such as topography, wind currents, and temperature that lie behind it. In this study, we focus on the “Deep Ocean Currents”, which are the general circulation of seawater around the entire ocean, and discuss the factors that cause them. Deep Ocean Currents are a type of thermohaline circulation, an action that attempts to balance the energy and salinity of the entire globe. It is a millennia-long advection that extends from the North Atlantic offshore to Antarctica and then to the North Pacific. It is known that the mechanism that drives the deep ocean current is the settling of densely populated seawater due to the freezing of surface water off the North Atlantic coast. On the other hand, the factors that cause upwelling, which doesn’t correspond to the amount of deposited seawater, have been considered a mystery (named “Missing Mixing”) in physical oceanography, but recent studies have revealed that tidal forces are the key to solving this problem. Tidal force is a force resulting from the non-uniformity of the mass distribution of the earth, as shown by the circular motion of the earth and the moon in their rotation system. It has been proposed that the flow of water caused by this force is a tidal current, and that turbulence is generated when the flow collides with seamounts, resulting in the upwelling of deep-ocean currents. However, the amount of upwelling calculated based on this theory is not as large as the actual upwelling, and the mystery has not been solved. In this study, we focused on turbulence caused by tidal currents and seamounts, and conducted an experiment to examine whether the degree of turbulence depends on the slope of seamounts. On this basis, as an experimental model, we incorporated a method in which tidal currents impinging on a seamount are created relative to the seamount by moving the seamount in a tank. The ink layer was then placed at a certain height from the seamount, and the diffusion of the ink layer after the seamount moved was measured as the turbulent diffusion coefficient. Next, I would like to describe in detail the method used to calculate the turbulent diffusion in this experiment. The diffusion coefficient is a proportional coefficient in the diffusion equation expressed in partial differential form. This coefficient has a unit of [m^2/s] in the SI unit system, and is expressed as the volume of material passing through the water in a unit time. By calculating this coefficient in the experiment, we can compare the volume of material diffused by the movement of the seamount, i.e., the degree of turbulence generation. In the experiments of this study, the vertical displacement of a layer colored with blue ink of 1 cm at the beginning was examined and quantified using the image analysis software “ImageJ” to determine how much the layer was displaced vertically per unit time after the seamount was moved. These experiments were conducted for each simulated seamount with fixed height and inclination angles of 30, 45, 60 degrees, etc., respectively, for each ink-colored layer.
Through this study of deep ocean currents, I was able to not only gain knowledge, but also experience an approach to a question for which there is no clear answer, which I hope to apply to my studies after entering university. We hope for the further development of ocean physics in the future.