We’ve mapped stars billions of light years away. But what lies just hundreds of feet below the surface of our own water has been unfathomable.
A scorpion fish in a deep sea coral reef. (Credit: U.S. National Oceanic and Atmospheric Administration)
This article was produced exclusively for News Decoder’s global news service. It is through articles like this that News Decoder strives to provide context to complex global events and issues and teach global awareness through the lens of journalism. Learn how you can incorporate our resources and services into your classroom or educational program.
Back in 2022, scientists mapping the ocean floor off Tahiti discovered a coral reef they called the “Twilight Zone” because of its depth: 30–60 meters below the surface (roughly 100-200 feet).
It took a decade for scientists to map one even deeper. At 600 meters, “Million Mounds” off the U.S. state of Florida is the world’s largest deep sea coral reef. The reef is entirely in the dark and is fed by nutrients from the Gulf Stream, the warm Atlantic Ocean current.
This year marks the halfway point of the United Nation’s Decade of the Ocean. In June, leaders of governments, NGOs and research groups will gather at the UN Ocean Conference in Nice, France on the shores of the Mediterranean where once ancient Greeks and Roman sailors used sounding leads to improve their knowledge of the seas.
“Seafloor mapping is critical to pretty much everything, from national security to blue economy sustainable ocean initiatives,” said Caitlin Adams, the operations coordinator of ocean exploration and research at the U.S. National Oceanic and Atmospheric Administration or NOAA.
Mapping the ocean seabed is key to monitoring and predicting how the ocean works. The changes in the seafloor affect currents and mapping is vital to understand how heat moves through the oceans.
The need to understand our oceans
As climate change affects the oceans, coastal communities around the world need to be safeguarded from erosion and storms. Detailed maps of the seafloor locating coral reefs can boost resilience measures from rising sea levels.
NOAA deploys one ship, the Okeanos Explorer, to comb the seafloor with multi-beam sonar. It has mapped two million square kilometres, still, what you might call a drop in the ocean.
Fun facts about our ocean:
- The Puerto Rico Trench in the Atlantic at 8,378 meters is deeper than Mount Everest is tall (8,234 meters).
- Jellyfish have been spotted at the deepest point in the ocean — the Mariana Trench in the western Pacific at 10,924 meters deep.
It is part of an ambitious international programme to meet the urgent need for new data. Called Seabed 2030, the project aims to provide high-resolution maps of the entire seafloor within the next five years.
But while the sea may be where life first evolved on earth, we know more about the surface of the moon than the sea floor of our oceans. They cover 70% of our planet but we have only mapped a mere 23% of the seabed.
Since prehistoric times, when people first set out in boats to seek food and travel, the sea waters below were a mystery. Were there unexpected hazards? Where could the riches of sea life be found?
Connecting continents across the sea
For centuries the only way to find out about the hidden seafloor was to measure the water’s depth, a method known as sounding. Sailors lowered a weighted rope with a lead and measured it in fathoms — originally the span of a man’s outstretched arms — about six feet or two meters.
It wasn’t enough to know the depth of a harbour or coastline. Warships and commercial vessels needed charts which could help them safely navigate treacherous reefs and rocks.
The invention of the telegraph and telephone presented even bigger challenges. To connect continents for communication required a route for underwater telegraph cables across the Atlantic.
Victorian hydrographers — surveyors who measured underwater features — searched for a safe, relatively shallow route. They believed their soundings found one they named the Telegraph Plateau. It stretched from England to the United States.
But it was wishful thinking. Their widely spaced soundings taken from dozens of Atlantic voyages had somehow missed a dramatic feature, the longest underwater mountain range on the earth, the Mid-Atlantic Ridge. Despite this oversight and after many false starts, telegraph cables were successfully laid in 1866.
Technology reveals the ocean floor.
Only when sonar was developed in the early 20th century was the full extent of the Mid-Atlantic Ridge revealed.
Sonar, which stands for ‘sound navigation and ranging’, measures underwater topography by sending out sound pulses and then recording the time it takes to bounce back. Now we use multi-beam sonar which provides high-resolution data to create maps that provide the kind of detail of the seafloor that Victorian surveyors could have never imagined.
Underwater cables are still needed for digital communications and pipelines. But the expense and logistics needed to map the enormous expanse of the oceans means there are huge gaps of information about the seabed.
That lack of high-resolution data nearly resulted in the loss of an American submarine in 2005 when the USS San Francisco collided with an underwater mountain in the Pacific. Even nuclear submarines operate with imperfect knowledge of the oceans.
The need for high-resolution seafloor data goes far beyond keeping ships safe. Only by mapping the ocean’s underwater topography, known as bathymetric data, can we locate, recognise and manage the resources in our seas. Fisheries management and conservation activities need accurate information to monitor biodiversity and ocean currents.
For ancient mariners to return home safely, they needed to know what lay below the surface of the sea. For all of us now, we need this knowledge to keep everyone safe, both the creatures that live in the water and those of us who live on land.
Questions to consider:
1. Why do we need to map the ocean floor?
2. How did ancient mariners learn what was beneath their boats?
3. Would you like to dive to great depths in the ocean? Why?
Tira Shubart is a freelance journalist and media trainer based in London. She has produced television news and trained journalists across four continents for international broadcasters, including BBC News, Canadian Broadcasting Corporation and Al Jazeera, over several decades.