The Changing Shape of the Ocean

By about 2 billion years ago, the ocean probably had characteristics similar to our modern ocean, but the slow and steady geologic processes of plate tectonics continued to shift the locations of the continents and ocean basins, reconfiguring the shape of the ocean through time. This movement continues to this day.

Today’s continental arrangement is responsible for global ocean circulation patterns, which in turn impact our planet’s climate. Ocean currents act like a complicated conveyor belt, moving surface water around the globe and linking surface and deep currents. The overall result of global circulation is the transportation of warm surface water from the equator toward the poles and cold deep water from the poles back to the tropics. The formation of deep currents can sink carbon dioxide, removing a potent greenhouse gas from the atmosphere in a process called carbon sequestration. Thus, the speed, temperature, and location of ocean currents regulate the global climate, helping to counteract the uneven distribution of solar radiation at Earth’s surface. Without currents in the ocean, regional temperatures would be more extreme—super hot at the equator and frigid toward the poles—and much less of the planet would be habitable.

The Challenge of Exploration

The sheer size of the ocean is difficult to comprehend. It covers over 70% of our planet’s surface, and has an average depth of 3.7 km (2.3 mi), making it the largest livable space on the planet. Throughout these depths, from the surface of the ocean to the seafloor and everywhere in between, there is life. In fact, this space is home to 4/5ths of the world’s biodiversity, the majority of which has yet to be described.

Many of us might picture the ocean from a more familiar perspective: perhaps from the shores of a sandy coast, the shallow waters of a beach, the waves seen from shore or ship, or even from satellite imagery of the ocean’s surface. But the vast majority of ocean waters are beneath the surface.

Sunlight only penetrates the top 200 m (656 ft) of the ocean; below this is considered “the deep sea.” This remote realm is dark, cold, and under high pressure. These conditions make the deep sea very challenging to explore and study. Because of this, we know much more about shallow, coastal waters than we do about the rest of the ocean. In order to explore and study the full water column and the seafloor, we need new and specialized technologies.

Ocean Exploration Begins With Mapping

The first step in ocean exploration is mapping. Seafloor mapping provides a detailed guide and a sense of the features of an area. This information helps scientists make informed decisions about where to explore in greater detail. While the entire seafloor has been coarsely mapped using satellites, these maps provide only a general picture of what’s there. That’s because the resolution of these maps is 1.5 km (about one mile), meaning that only a seafloor feature 1.5 km or larger will be big enough to appear on a map of this resolution. Because detail is limited, features like seamounts, volcanic craters, coral mounds, or shipwrecks can remain hidden.

As of 2022, slightly less than 25% of the global seafloor has been mapped with modern, high-resolution sonar systems that can reveal the seafloor in much greater detail. Ocean mapping can also be used to detect features within the water column such as gas plumes that reveal the location of seeps, or even the ascent and descent of groups of marine organisms as they move through the water column. Many other forms of data are also collected at this initial stage using a wide range of technologies. Sub-bottom profilers penetrate through the seafloor surface and reflect off different layers of sediment, and conductivity, temperature, and depth sensors (known as CTDs) provide important information about the physical, chemical, and even biological properties of the water column.

Ocean Exploration: Onwards and Downwards

Once a detailed map of an area has been created, it can be used as a framework to guide the next steps in exploration. This often means exploring a small area of interest at a high level of detail with technologies such as human-occupied vehicles, remotely operated vehicles (ROVs), or autonomous (self-guided) underwater vehicles, all of which are essentially underwater robots. Scientists use high-resolution maps to carefully plan a path for the vehicle, which can be equipped with a range of sensors, lights, and cameras.

For example, an exploratory dive conducted by NOAA Ocean Exploration will usually use an ROV, which is controlled by pilots aboard a ship above, and might begin on the seafloor and proceed upslope towards a feature of interest, such as a seamount. Along the way, pilots maneuver the ROV and direct its lights and cameras to objects and organisms of interest, like rocks, coral groves, sponge communities, or any of the abundant animal life that may be found on the seafloor. Some ROVs can bring a limited number of physical samples and specimens back to the surface for further study. While space and time on ships is often limited and costly for scientists, some ships are equipped with telepresence technology, which allows for dives to be live streamed anywhere with an Internet connection—meaning that scientists around the globe can participate in the exploration in real time. This technology allows for a greater breadth of expertise to guide the mission and makes ocean exploration accessible to the public in real time.

The technology used to explore the full extent of our ocean has come a long way over the last century, and is improving rapidly. Meanwhile, the field of ocean exploration is constantly being broadened as more people from various disciplines bring their expertise to the table. An ocean explorer may be anyone, from a mechanical engineer to an oceanographer, a maritime archaeologist to a science communicator, a biologist, a geologist, a pilot, a filmmaker, and many others. Together, ocean explorers work to build a better understanding of the ocean and its importance, its current properties, and how it is changing—ensuring that decision-makers have the information they need to make sound policies for this life-sustaining asset: our ocean.