Toshio SUGA Toshio SUGA Toshio SUGA

The reason I started research was the encounter with the “unknown”.


Toshio SUGA

1.What kind of the research are you doing?

My research topics are summarized as ventilation of the ocean. The ocean ventilation means that the water below the sea surface is replaced by the water in contact with the atmosphere at the sea surface. In spite of original meaning of “ventilation,” the ocean ventilation means not only the provision of oxygen and other gases to the ocean below the surface but also the provision of heat and other substances to the subsurface layer. That is, anomalies of temperature, salinity and other water properties generated at the sea surface as a result of their ocean-atmosphere exchanges are carried into the ocean below the surface by the ocean ventilation processes. The ocean ventilation connects the sea surface and the ocean interior and maintains distribution of temperature and other water properties in the ocean.

According to firm scientific assessment, enormous amount of heat has been accumulated on the earth over the past 40 years due to global warming, which is equivalent to more than 200,000 times the annual power generation of one nuclear power plant per year; more than 90% of this heat has been stored in the ocean. Understanding of the ocean ventilation is essential to elucidate the mechanism of heat accumulation in the ocean and is indispensable for reliable future projections of global warming. The ocean ventilation also needs to be well understood in order to elucidate and predict ocean changes that have major impacts on marine ecosystems, such as the ocean acidification and deoxygenation associated with global warming.

Under this background, we are conducting research concerning the ocean ventilation and its variability. Our main targets are ventilation processes in the upper ocean down to several hundred meters deep and on time scales from intra-season to several decades. We analyze both in-situ and satellite observation data and outputs of ocean general circulation models that reproduce the ocean circulation/environment using computers. A major features of our research is full use of the data from Argo. Argo is an epoch-making international ocean observing network that covers the global ocean with nearly 4,000 profiling floats (autonomous observing robots), and acquires temperature and salinity data from the sea surface to 2000 m in near real time. All the Argo data are freely available through the Internet. In addition to temperature and salinity, we are planning to extend the measurement to biogeochemical properties such as oxygen, nutrients and acidity, and to extend the observation depth to the ocean bottom. I have been participating in the international Argo program from the beginning and actively using its data. However, since information contained in the Argo data is enormous, it is not still fully utilized for elucidating how the ocean properties are maintained and how they change. In order to bring a breakthrough, new ideas are indispensable. We are looking forward to active participation of young people including graduate students in this field.

2.What is the reason for starting your study?

When I was a 3rd year undergraduate student, I first learned about seasonal changes in temperature and salinity under the sea surface, through diagrams on the blackboard drawn by my professor during his lecture “Physical Oceanography.” I somehow became very interested in these phenomena. At that time, I was aspiring for meteorology, but in the 4th year I entered Physical Oceanography Laboratory because I was attracted by its exploratory atmosphere associated with research cruises. I went to graduate school and experienced ship observations. I became enthralled with the charm of the ocean, even though I was troubled by seasickness.

My master's thesis theme was the subtropical mode water, which is a vertically uniform water mass formed by wintertime deep convection reaching a depth of nearly 300 m. The deep convection is due to cooling caused by cold air outbreak over the Kuroshio Extension region east of Honshu. I was excited to reveal how this water expanded thousands of kilometers under the sea surface, keeping the “memory” of being cooled by cold air in the form of temperature changes. This phenomenon is just part of the ocean ventilation, and the same kind of ventilation process is involved in the seasonal changes in temperature and salinity inside the ocean mentioned above. It was a little later that those parts were connected within the concept of the ocean ventilation in my head. But when I looked back, I realized that the reason I started research on the ocean ventilation was the encounter with the “unknown” during the undergraduate lecture.

3.Message for prospective students

I was not such a child who loves summer science project in elementary school, or a student who immerses himself in research by joining a science club in middle/high school. I may have had enough of science knowledge in textbooks. After entering university, I realized that the world around us is filled with what human beings still don’t understand, or thing that are not even known, owing to encounter with the scene of knowledge creation regardless of science or humanities through classes and exchanges with professors, seniors and friends. A few months after birth, babies begin to understand the relationship between causes and consequences, and research has shown that they begin to eagerly explore events around them. As we grow up in early childhood, school age and adolescence, more or less we will become more and more likely to lose our curiosity about the world. It seems that the above mentioned awareness in university was the second birth for me in terms of intellectual activity. I can't help thanking the good luck that I met that opportunity in the middle of my youth. University has an environment where you can experience intellectual encounters that enable you to rediscover the world and enrich your life. I look forward to seeing you in our Aobayama Campus!