Seas Bordering Indonesia: The World's Largest Archipelagic State

Indonesia—17,000+ islands spanning 5,100 km east-west—is uniquely positioned at the convergence of the Pacific and Indian Oceans, bordered by multiple marginal seas.

Northern Seas (Pacific Marginal Seas)

• South China Sea: West of Natuna, Anambas; major EEZ disputes (Nine-Dash Line)
• Sulu Sea: North of Sulawesi; Tubbataha Reefs (Philippines/UNESCO); pirate history
• Celebes Sea: Northeast of Sulawesi; deep basin (>6,000 m); tuna fisheries
• Molucca Sea: Between Sulawesi and Halmahera; volcanic arcs
• Banda Sea: South of Maluku; Weber Deep (7,351 m — deepest non-trench point)
• Seram Sea: East of Seram; high endemism
• Halmaheira Sea: Northeast Maluku; coral triangle core

Southern Waters (Indian Ocean)

• Indian Ocean proper: South of Java, Sumatra, Lesser Sundas
• Timor Sea: South of Timor; oil/gas fields (Bayu-Undan)
• Arafura Sea: Southeast of Papua; shallow, biologically rich

Internal Seas (Archipelagic Waters)

• Java Sea: Between Borneo, Java, Sumatra; shallow (<50 m); Sunda Shelf
• Flores Sea: North of Flores; volcanic arc
• Savu Sea: Between Timor, Sumba, Flores; deep channels
• Bali Sea: North of Bali; Lombok Strait connection

Strategic Straits

• Malacca Strait (west) — 25% global trade
• Sunda Strait (Krakatoa)
• Lombok Strait (Wallace Line)
• Makassar Strait (Borneo-Sulawesi)
• Ombai-Wetar Straits (Timor-Leste)

Geopolitical Significance

Indonesia's archipelagic baselines (UNCLOS) enclose 3.2M km² of internal waters. Managing this maritime domain—security, resources, environment, sovereignty—is the central strategic challenge of the world's largest archipelagic state.