Indian Ocean

The floor of the Indian Ocean has deep valleys.

The deepest one is called the Java Trench. Scientists used sound to find its deepest spot.

The bottom of the ocean is too dark and deep to see, so scientists map it with sound. A ship sends sound pulses down and times the echoes that bounce back from the seafloor.

For a long time people were not sure where the deepest place in the Indian Ocean was. Some thought it was the Dordrecht Deep, in an area of the seafloor called the Diamantina Fracture Zone. The Five Deeps Expedition (2018–2019) mapped both places and found that the Java Trench is deeper, at 7,187 meters, while the Dordrecht Deep is 7,019 meters.

Bongiovanni and colleagues (2021) report that before the Five Deeps Expedition the exact location and depth of each ocean's deepest point were uncertain. The expedition used a full-ocean-depth Kongsberg EM 124 multibeam echosounder and corrected the depths with CTD (conductivity, temperature, depth) data from the surface to the seafloor.

In the Indian Ocean two candidates were surveyed: the Java Trench and the Dordrecht Deep in the Diamantina Fracture Zone. The Java Trench deep, at 7,187 ± 13 m, proved deeper than the Dordrecht Deep, at 7,019 ± 17 m, settling which is the deepest point of the Indian Ocean; the Java Trench deep had no name at the time of the report.

Off the coast of Africa, the sea flows one way for part of the year.

Then it turns around and flows the other way!

The Somali Current, off the northeast coast of Africa, is unusual: it reverses with the seasons, flowing north for part of the year and south for the rest.

Scientists long linked the change to the monsoon winds, which also change direction with the seasons. Observations showed that the current can turn north before the southwest monsoon winds arrive, and scientists now also use computer models to study why.

The US Department of Energy's research summary describes the Somali Current as an atypical western boundary current that reverses seasonally off the northeast coast of Africa. Its reversal was first associated with the Indian Monsoon winds, but observations showed northward flow beginning between 5°S and 10°N before the southwest monsoon set in.

A momentum-budget study using a global 0.1° ocean model for 2005–2009 found that the timing depends on location: from 2° to 5°N the flow follows the monsoon wind reversal directly, while from 5° to 10°N an annual Rossby wave and the life cycle of the Great Whirl extend northward flow. The current matters for regional climate and ecology through summer upwelling and may affect Indian Monsoon rainfall.

Whale sharks are a kind of shark.

Every year many whale sharks visit a reef in Australia, on the Indian Ocean. Lots of sea turtles live there too.

The Ningaloo Coast in Western Australia is a World Heritage Site on the eastern Indian Ocean. Its coastal waters hold one of the longest near-shore reefs in the world.

Every year an estimated 300 to 500 whale sharks gather there, at the same time as corals release their eggs in mass spawning and the water becomes richer in food. Ningaloo is also home to many sea turtles and to a great variety of other ocean animals, from the lagoon and reef to the open ocean.

UNESCO describes the Ningaloo Coast (604,500 ha) on Western Australia's coast along the East Indian Ocean as combining a major near-shore reef system with an adjacent limestone karst system on an arid coast. It holds high marine species diversity and abundance, and habitats ranging from lagoon and reef to open ocean, continental slope and shelf, with rocky shores, sandy beaches, estuaries and mangroves.

An estimated 300 to 500 whale sharks aggregate there each year, coinciding with mass coral spawning and seasonal local increases in productivity, and the coast supports a wealth of sea turtles. On land, the karst holds caves and groundwater streams with rare species.

Beaches on the Indian Ocean are lovely to visit.

Swim only where there are lifeguards, with a grown-up. Never turn your back on the waves.

Waves and currents can be strong at any ocean beach. Weather services give simple advice: check the beach forecast, talk to the lifeguards and swim only at beaches with lifeguards.

Rip currents are powerful, narrow channels of fast-moving water, and they can form even on calm, sunny days. If one pulls you, don't fight it. Swim parallel to the shore, then come back to land at an angle.

General beach-safety advice from the US National Weather Service applies on any coast: check the local beach forecast, talk to lifeguards, swim only at beaches with lifeguards, and never turn your back on the ocean, because rip currents often form on calm, sunny days.

NOAA's National Ocean Service describes rip currents as powerful, narrow channels of fast-moving water that can move at up to 8 feet (about 2.4 m) per second, faster than an Olympic swimmer. Swimmers who try to swim straight back against them tire; the advice is to swim parallel to the shore and return at an angle.