The Indian Ocean, spanning one-fifth of the world’s ocean area, is the smallest, youngest, and most intricate of the major oceanic divisions. Stretching over 6,200 miles between Africa and Australia, it covers approximately 27,243,000 square miles, excluding its marginal seas. With an average depth of 12,274 feet, its deepest point plunges to 24,442 feet in the Sunda Deep off Java, Indonesia. This ocean is a realm of geological complexity, influencing climates and ecosystems across continents.
Geographical Boundaries and Confluences
The Indian Ocean is bordered by diverse landmasses: Iran, Pakistan, India, and Bangladesh to the north; the Malay Peninsula, Indonesia, and Australia to the east; the Southern Ocean to the south; and Africa and the Arabian Peninsula to the west. It merges with the Atlantic Ocean southwest of Africa and intermingles with the Pacific Ocean to the east and southeast. Defining its oceanic limits remains a complex task, particularly its northeastern border, which weaves from Cape Londonderry in Australia across the Timor Sea, along the Lesser Sunda Islands and Java, and through the Singapore Strait.
Cape Agulhas and Oceanic Division
The boundary between the Indian and Atlantic Oceans is clearly defined, running south from Cape Agulhas along the 20° E meridian. The border with the Pacific Ocean is generally set from South East Cape on Tasmania along the 147° E meridian. The inclusion of Bass Strait, between Tasmania and Australia, as part of either the Indian or Pacific Ocean remains a point of debate. These delineations highlight the ongoing challenges in mapping and understanding the Earth’s oceanic systems
Continental vs. Oceanic Islands: A Tale of Two Terrains
Continental islands, located southwest of the Andesite Line, are characterized by their mountainous, folded structures. These islands are typically larger and higher than those to the east, boasting fertile soils capable of supporting diverse vegetation. Examples include the Marianas, New Guinea, and New Zealand. In contrast, oceanic islands are primarily composed of basaltic lava. They are classified as either high volcanic islands, like Hawaii, or low coral islands and atolls, such as the Marshalls. The majority of Pacific islands are coral formations built upon volcanic or other substrates.
Coral Reefs and Island Submergence
Both continental and oceanic islands in tropical waters foster coral growth, forming fringing reefs—partially submerged limestone platforms where coral organisms thrive on nutrients brought by waves and currents. Over time, many islands have gradually submerged due to geological sinking and ice cap melting. As islands flood, coral growth extends outward, creating barrier reefs separated from the shorelines by lagoons.