TLDR
The Coral Sea holds the title, with a deepest point near 9,140 meters (30,003 feet) at the South Solomon Trench. The Caribbean Sea comes in second at 7,686 meters (25,220 feet), thanks to the Cayman Trough — home to the deepest hydrothermal vents ever found. Below that, the Banda Sea, Sulu Sea, South China Sea, Mediterranean, Bering Sea, Sea of Japan, and Gulf of Mexico round out the list, each shaped by a different geological accident.
Table of Contents
- Sea vs. Ocean vs. Trench
- 1. Coral Sea
- 2. Caribbean Sea
- 3. Banda Sea
- 4. Sulu Sea
- 5. South China Sea
- 6. Mediterranean Sea
- 7. Bering Sea
- 8. Sea of Japan (East Sea)
- 9. Gulf of Mexico
- Depth Comparison Table
- FAQ
Sea vs. Ocean vs. Trench
People use these three words like they’re interchangeable. They aren’t, and mixing them up is why half the “deepest sea” lists online are actually ranking oceans or trenches by mistake.
An ocean is one of the five major bodies of water that cover most of the planet — Pacific, Atlantic, Indian, Southern, Arctic. A sea is smaller and partially enclosed by land, but still connected to an ocean. The Caribbean is a sea because the Antilles wrap around it; the Mediterranean is a sea because Europe, Africa, and Asia box it in on three sides.
A trench is neither. It’s a narrow, canyon-like scar on the ocean floor formed where one tectonic plate slides beneath another — a subduction zone. Trenches can sit inside a sea’s boundaries or out in open ocean, and they’re almost always the deepest feature nearby, which is exactly why sea depth rankings tend to hinge on which trench happens to cut through them.
That distinction matters for this list, because the deepest point connected to a sea and the deepest sea aren’t always found in headline-grabbing places. The Mariana Trench, for instance, isn’t a sea at all — more on that below.
1. Coral Sea
Max depth: 9,140 m (30,003 ft) | Location: Between Australia’s Great Barrier Reef and the Solomon Islands | Responsible feature: South Solomon Trench
The Coral Sea earns the top spot largely because its southeastern edge butts up against the South Solomon Trench, a subduction zone where the Solomon Sea plate dives beneath the Pacific plate. That’s a genuinely brutal drop for a body of water most people associate with the shallow, sunlit reefs of Queensland.
It’s also the site of the Battle of the Coral Sea in 1942, the first naval engagement fought entirely by aircraft without the opposing ships ever sighting each other. The wrecks from that battle — including the USS Lexington, found in 3,000 meters of water in 2018 — sit well above the sea’s deepest trench.
2. Caribbean Sea
Max depth: 7,686 m (25,220 ft) | Location: Between Central America, the Antilles, and South America | Responsible feature: Cayman Trough, at the Milwaukee Deep
The Caribbean is the one most people guess first, and it’s not a bad guess — it’s the deepest sea in the Atlantic basin. The Cayman Trough runs along a fault where the North American and Caribbean plates grind past each other, and its Milwaukee Deep hits nearly 7.7 kilometers down.
The trough is also home to the Beebe Vent Field, the deepest known hydrothermal vents on Earth, sitting roughly 5,000 meters below the surface. According to Woods Hole Oceanographic Institution, the superheated water there erupts at temperatures over 400°C — hot enough that it stays liquid only because of the crushing pressure.
3. Banda Sea
Max depth: 7,440 m (24,410 ft) | Location: Eastern Indonesia | Responsible feature: Weber Deep
The Weber Deep is the single deepest point of any forearc basin on the planet — a basin that forms in front of, rather than at, a subduction zone. That’s an unusual way to get this deep, and it puts the Banda Sea in a geological category of its own.
The Banda Islands at its center were once the only source of nutmeg and mace on Earth, which made this stretch of water one of the most fought-over pieces of ocean in colonial history. The surrounding waters also sit inside the Coral Triangle, the epicenter of global marine biodiversity — more coral and reef fish species pass through here than anywhere else on the map.
4. Sulu Sea
Max depth: 5,576 m (18,300 ft) | Location: Between the Philippines and Malaysian Borneo | Responsible feature: Sulu Trench, at the Cape Melville Deep
The Sulu Sea is nearly landlocked, ringed by the Philippine archipelago, Borneo, and the Sulu Archipelago, yet it still manages a depth that rivals seas twice its size. Tubbataha Reef, a UNESCO World Heritage site, sits near its eastern edge — a limestone atoll rising straight out of that deep basin with almost no shallow shelf to soften the transition.
5. South China Sea
Max depth: 5,559 m (18,238 ft) | Location: Between mainland Southeast Asia, the Philippines, and Borneo | Responsible feature: Central basin trough
This is the sea everyone’s heard of for reasons that have nothing to do with depth — roughly a third of global shipping trade passes through it, and the Spratly and Paracel Islands make it one of the most contested patches of water on the planet. Geologically, though, its deepest point sits in a spreading center in the central basin, not a subduction trench, which is a quieter and less dramatic origin than most entries on this list.
6. Mediterranean Sea
Max depth: 5,267 m (17,280 ft) | Location: Between Europe, North Africa, and the Middle East | Responsible feature: Hellenic Trench, at the Calypso Deep
The Calypso Deep sits in the Ionian Sea, the Mediterranean’s southeastern arm, and takes its name from Jacques Cousteau’s research vessel, the Calypso, which surveyed it in 1961. The Hellenic Trench that produces this depth is also seismically active — it’s the same subduction zone responsible for much of Greece’s earthquake activity, since the African plate is sliding beneath the Aegean here at roughly the pace fingernails grow.
7. Bering Sea
Max depth: 4,151 m (13,442 ft) | Location: Between Alaska and Russia’s Far East | Responsible feature: Bowers Basin
The Bering Sea separates Asia from North America and is better known for what happens on its surface than what’s underneath it — this is the setting for the king crab fisheries made famous by “Deadliest Catch,” where boats work through some of the roughest, most unpredictable weather on Earth. Its depth comes from the Bowers Basin, a back-arc basin tied to the volcanic Aleutian Island chain that curls along its southern edge.
8. Sea of Japan (East Sea)
Max depth: 3,742 m (12,276 ft) | Location: Between Japan, Russia, North Korea, and South Korea | Responsible feature: Japan Basin
The name itself is a live political dispute — South Korea calls it the East Sea, and international bodies increasingly list both names side by side, a compromise the BBC has covered as one of the more persistent naming conflicts in modern geography. Depth-wise, the Japan Basin formed as the sea floor spread during the opening of the back-arc basin behind the Japanese island arc, a process that’s still active today.
9. Gulf of Mexico
Max depth: 4,384 m (14,383 ft) | Location: Bounded by the U.S. Gulf Coast, Mexico, and Cuba | Responsible feature: Sigsbee Deep
Technically a gulf, but hydrographers classify it alongside marginal seas because of how it’s enclosed and connected to the Atlantic through the Florida Straits. The Sigsbee Deep sits in a basin shaped by ancient salt tectonics — thick underground salt layers that have been slowly deforming the seafloor for tens of millions of years. It’s also the depth zone where the Deepwater Horizon wellhead sat in 2010, a fact NOAA has documented extensively in its ongoing Gulf restoration monitoring.
Depth Comparison Table
| Rank | Sea | Max Depth (m) | Max Depth (ft) | Deepest Feature |
|---|---|---|---|---|
| 1 | Coral Sea | 9,140 | 30,003 | South Solomon Trench |
| 2 | Caribbean Sea | 7,686 | 25,220 | Cayman Trough (Milwaukee Deep) |
| 3 | Banda Sea | 7,440 | 24,410 | Weber Deep |
| 4 | Sulu Sea | 5,576 | 18,300 | Sulu Trench (Cape Melville Deep) |
| 5 | South China Sea | 5,559 | 18,238 | Central basin trough |
| 6 | Mediterranean Sea | 5,267 | 17,280 | Hellenic Trench (Calypso Deep) |
| 7 | Bering Sea | 4,151 | 13,442 | Bowers Basin |
| 8 | Gulf of Mexico | 4,384 | 14,383 | Sigsbee Deep |
| 9 | Sea of Japan | 3,742 | 12,276 | Japan Basin |
For reference, the Mariana Trench — the deepest point on Earth at roughly 10,935 meters (35,876 feet) — would sit above even the Coral Sea if it counted as a sea. It doesn’t.
FAQ
Is the Mariana Trench a sea? No. It’s a trench in the open Pacific Ocean, not a sea — there’s no landmass partially enclosing it the way there is with the Caribbean or Mediterranean. It’s the deepest point in any ocean, but it doesn’t belong to this list by definition.
What’s the deepest sea in the world? The Coral Sea, at approximately 9,140 meters (30,003 feet), measured at the South Solomon Trench.
Is the Caribbean Sea deeper than the Mariana Trench? No. The Caribbean’s deepest point, the Milwaukee Deep, reaches about 7,686 meters. The Mariana Trench goes down another 3.2 kilometers beyond that.
Why are some deep points called trenches and others called basins or deeps? “Trench” specifically means a subduction zone feature. “Basin” describes a broader depression in the crust, which can form from subduction, spreading, or other tectonic processes. “Deep” is just the name given to the single deepest point within either — the Milwaukee Deep is the deepest point of the Cayman Trough, for example.
Do any land animals or fish live at these depths? Fish, yes — some species of snailfish and cusk eels have been recorded below 7,000 meters. But conditions get extreme fast: near-freezing temperatures, crushing pressure, and total darkness limit what survives much past a few thousand meters, except around hydrothermal vents like the Beebe Vent Field, where chemosynthetic bacteria support entire ecosystems that never see sunlight.
