What are your goals?

Example of ocean mesoscale eddies (colors: ocean surface elevation in the center of eddies) Research in 2009 showed that an ocean mesoscale eddy forms south of the Alaska Peninsula (Alaskan stream eddy), travels west along the south side of the Aleutian Islands, and later diffuses in the open ocean of the subarctic Northern Pacific.

The ocean is changing greatly, both temporally and spatially. The sea surface temperature is high near the equator and low near the poles, and in the past hundred years, its average global temperature has risen about 0.5 ºC. Such large-scale long-term change is well-known, but other changes on a variety of temporal and spatial scales take place in the ocean. For example, in the same way that day-to-day weather is affected by the movement of high pressure and low pressure, the water temperature and salinity of the ocean fluctuates on a scale of about hundred kilometers over a few months under the effects of the high and low pressure of the ocean. These fluctuations are called ocean mesoscale eddies. Our goal is to clarify these varied temporal and spatial scale changes to gain an understanding of their mechanisms.
Various temporal and spatial changes of the ocean have severe impacts on marine ecosystems that consist of zooplankton and phytoplankton, fish, marine mammals, and so on. For example, ocean mesoscale eddies transport the sea water horizontally and vertically, varying the production of phytoplankton and having a major effect on the overall ecosystem.

Example of the impact on marine ecosystems of ocean mesoscale eddies.
(colors: net primary production (red: high), lines: ocean surface elevation)

We know that there is little phytoplankton in the open seas of the subarctic North Pacific, even though the water is rich in nutrients such as nitrogen and phosphorus, and it has been noted that there a shortage of iron, a tiny amount of which is indispensable for the propagation of phytoplankton. It is thought that ocean mesoscale eddies transport iron-rich coastal water and mesopelagic water to the off-shore surface, supporting the production of phytoplankton in the off-shore waters of the subarctic North Pacific. We also conduct research for one more goal, which is to understand the impact of such temporal and spatial changes of the ocean on marine ecosystems.

 

How do you conduct your research? 

A large quantity of basic data such as ocean water temperature and salinity obtained by ships in past has been published, and anyone can use it free of charge for research purposes. And in recent years, we have been able to obtain real time ocean data from the worldwide floating observation network of the Argo program, as well as from observation satellites. We are analyzing these data to investigate the North Pacific and worldwide ocean changes, and the relationships between these changes and the changes in ocean ecosystems.

In order to clarify relatively small-scale ocean changes and the relationship between such ocean changes and living organisms in greater detail, we must not only analyze existing data; we must also actually go out to sea to make our own observations. Our laboratory, mainly using Training Ship Oshoro-maru of the School of Fisheries Science, Hokkaido University, conducts observations ranging from the subarctic North Pacific to the Arctic Ocean, investigating the properties of the ocean mesoscale eddies and their impact on marine ecosystems. My specialty is physical oceanography, so I study ecosystems in cooperation with researchers inside and outside Hokkaido University.

Left: View of entrance to a port on Kodiak Island, State of Alaska (2012, Oshoro-maru)
Right: View of ocean observation (2013, Oshoro-maru cruising in the Arctic)
Note: The Oshoro-maru in the photo is the former ship (Oshoro-maru IV) Since August 2014,
a new ship (Oshoro-maru V) has been used for training and surveying.

 

What do you plan to do next?

I wish to continue my research in order to clarify global scale ocean changes based on data analysis, perform observations to clarify ocean changes in the subarctic North Pacific and the Arctic Ocean, and to clarify the relationship of these changes with ecosystem changes. During my student days, I was undecided whether to major in meteorology or oceanography. I clearly remember talking this over with an associate professor, who gave me the following advice: "There are far more mysteries about the ocean than the weather. In this sense, the ocean is more interesting," Progress in observation technologies and in computers have helped bring great advances in oceanography, but there are still many aspects of the ocean that remain unknown. I hope that all students interested in this will study the ocean with me to help clarify these unknown topics.

 

References

(1) Y. Fujita, M. Yuasa, editors, Floating School, Hokkaido University's Ocean Campus, Oshoro-maru (Gakusen Hokkaido daigaku yojo-no-campus Oshoro-maru) Nakanishi Shuppan (2014).