Executive Summary:

The Shikoku Basin region is of significant geopolitical and strategic importance located in the Pacific Ocean part of the Philippine Sea. It is surrounded by critical East Asian economies, including Japan, South Korea, China, and Taiwan, thereby increasing the significance of maritime and geopolitical dynamics in regional energy security and international maritime strategies. This strategically significant region has its pursuant tensions with its demarcation as part of Japan’s EEZ which is not accepted by China and South Korea. This report explains the strategic importance of the Shikoku basin, geopolitical dynamics and China’s intentions over this region.

Overview:

The Shikoku Basin region is a part of Japan’s EEZ and covers an area almost equivalent to half the size of Japan, which is 378,000 square kilometres. Okinotorishima Island is a coral atoll that Japan considers as its Southernmost point. However, this is differed by China claiming it as a rock rather than an island under UNCLOS Article 121. This distinction has critical legal implications for maritime jurisdiction and resource rights.

The basin serves as a strategic chokepoint and an essential area for Japan’s maritime dominance. It also plays a pivotal role in Japan’s energy security, as key sea lanes transporting resources from Australia to Japan traverse the region. Given its proximity to the Senkaku Islands and other contested territories in the region, the basin is increasingly a focal point of regional maritime disputes.

Okinotorishima Island (Contiguous zone):

• Okinotorishima (distant bird island) is a remote, storm-wracked coral atoll in the Philippine Sea.
• Japan regards the atoll as its southernmost point. While China says it is no island, merely a rock.
• This reef is now dying because of climate change and the rising sea level. Japan is therefore on a desperate quest to regrow the reef.
• The island is also of Strategic significance as it is between the two island chains separating China from the Pacific: the first running through the main Japanese islands, to Okinawa and Taiwan; the second through Japan’s Ogasawara Islands to the Marianas and the US submarine base at Guam.

China’s Activities in the Shikoku Basin:

• Buoy Deployment: In June 2024, a Chinese research vessel (Xiangyanghong 22) installed a buoy on Japan’s continental shelf in the Shikoku Basin. Beijing claimed the buoy was for tsunami observation, but its placement raises concerns about surveillance and strategic intentions.
• Repeated Intrusions: This deployment follows earlier instances of Chinese activities in Japan’s territorial waters, including near the Senkaku Islands in July 2023. These actions highlight China’s strategy of incremental assertions of presence and control.
• Maritime Surveys: China’s persistent oceanographic surveys and military exercises near Okinotorishima underscore its intent to challenge Japan’s sovereignty and expand its maritime influence in the Pacific.

Strategic Importance

1. Geopolitical dynamics:

• US-China Rivalry: The Shikoku Basin is located within the first and second island chains, which makes it an important theatre for US-China power competition. Okinotorishima Island is one of the potential flashpoints in any future conflict.
• Regional Alliances: The security of Japan’s maritime security is supplemented by the US military presence in Okinawa and joint patrols with allies. This cooperation shows the basin’s role in regional stability.
• Territorial Disputes: While the basin itself is not contested, adjacent areas like the Senkaku Islands influence its strategic calculus. China’s policies heighten already present tensions.

1. Strategic Routes:

• The Okinotorishima Island is an important waypoint for China’s nuclear submarines attempting to reach the Pacific. It will allow China to project power while disrupting Japan’s maritime supply chains.
• The closeness of the basin to critical sea lanes assures that the basin will continue to be significant regarding global trade and energy flow.

Analysis:

• China had repeatedly conducted oceanographic surveys and military exercises close to Okinotorishima island.
• This indicates that China enjoys provoking states, particularly the US allies.
• If there was a future conflict between the US and China, their navies would collide in the ocean between the two island chains. Okinotorishima is the only spot of land in those waters.
• Since China could install buoys in Japan’s EEZ on the Pacific Ocean side in the future, just like in the East China Sea, the Japanese government needs to be vigilant about China’s surveillance activities.
• Japan’s plan of growing coral reefs over the atoll is more applaudable than mirroring China by filling up sand and concrete to make artificial islands as it satisfies the norm of Article 121 of UNCLOS.

Conclusion:

With the rise in regional powers to play in the Indo-Pacific, geopolitical significance to the Shikoku Basin will continue. For Japan, this basin remains a crucial factor for sovereignty and security, management of resources, and strategic positioning. It will be a future with a balance of active defence with multilateral engagement.