Shikinejima Island belongs to Niijima Village in Tokyo, Japan. It is located 160 km south of central Tokyo and accessible by public vessel.
Surrounded by the Kuroshio Current, the waters of Shikinejima forms unique diving spots. The transparency reaches 30 meters and varieties of life can be seen as well as the complex and dynamic topography created by the volcanic activities. Above all, the most distinctive feature is the underwater hot springs. Such diving spots are not far off shore and can be reached by a boat trip of 5 minutes. No wonder why many divers have been visiting this island for decades.
CO2 seeps in the undersea hot springs of Shikinejima
CO2 seeps are areas where carbon dioxide gas is released from the seafloor into the surrounding seawater. The CO2 seeps on Shikinejima island are associated with the vents of hot springs that gush up from the seafloor due to volcanic activities in the surrounding area. It is difficult to find CO2 seeps that gush out of the vast seafloor. At the time, this was the fourth example of such a discovery in the world and the first in the temperate zone of the Pacific Ocean.
*Since then, CO2 seeps have been found in many other locations.
Since that time, Shikinejima has attracted worldwide attention as a convenient research and experimental site of CO2 Seep for its easy accessibility.
What will the ocean be like in 100 years from now?
While it is not uncommon for volcanic gases containing carbon dioxide to dissolve into groundwater to form acidic hot springs (such as so-called carbonated springs), it is valuable to have an environment where one can closely observe such a sea that gases erupting from the sea floor continue to dissolve into, causing localized acidification.
Nowadays, environmental problems caused by human CO2 emissions have long been a concern. Relatedly, there are three problems in the oceans: ocean warming, acidification, and deoxygenation. This combination has been known as “Deadly Trio” for marine environmental issues.
What happens when seawater becomes acidic?
A clue lies in the sea of Shikinejima island, which is locally acidified by the same CO2 but for a different cause.
Originally, the seawater is slightly alkaline with a pH of about 8.1, but near this underwater hot springs releasing CO2, the water is neutral with a pH of 7.8. This may seem like a small difference, but large seaweeds do not grow, and shellfish, corals, and other calcifying organisms that produce calcium carbonate shells and skeletons cannot live here. Instead, microscopic algae that take to carbon dioxide spread out in mat-like forms. The sight of sea turtles leisurely bathing in the hot springs is lovely, but the number of benthic organisms and fish species that live in an environment where coral and large seaweed grow has decreased, and the sea has lost its diversity.
The research team estimates that this is what the ocean will look like in 100 years if the acidification continues at its current rate.
What if this colorless figure is the “ocean of the future” related to the CO2 emission problem?
Based on an awareness of the major issues, various studies are being conducted around the world.
On the other hand, if you move away from the underwater hot springs area, the concentration of carbon dioxide in the sea gradually decreases, creating a wonderful scene unique to Shikinejima full of colorful tropical fish dancing, large migratory fish swimming at their leisure and corals shimmering on the white sand of rhyolite.
From “the sea of the future” to “the sea of today.”
Even the general public can see and compare the contrast between these two types of sea through easy diving, which is an attraction of Shikinejima but unusual anywhere else in the world.
Now don’t miss your opportunity to visit the diving services and tours of Shikinejima and dive into the waters of Shikinejima. The “sea of the future” is awaiting you.
