Imma Perfetto
Cosmos science journalist
Despite covering 66% of the Earth’s surface, the deep ocean remains one of Earth’s great mysteries, and a new report has brought to light just how little we know about these vast regions.
For example, it’s been determined that only 0.001% of the deep seafloor has been visually observed by humans.
The estimated area, 2130km2, is only roughly the size of the US state of Rhode Island (2678 km2) or the Australian Capital Territory (2,358 km2). More than 65% of these visual observations have been carried within just 370km of 3 countries: the US, Japan, and New Zealand.
The authors of the new study, which appears in the journal Science Advances, are calling for “a fundamental change in how we explore and study the global deep ocean”.
“As we face accelerated threats to the deep ocean – from climate change to potential mining and resource exploitation – this limited exploration of such a vast region becomes a critical problem for both science and policy,” says lead author of the study Dr Katy Croff Bell, president of Ocean Discovery League and National Geographic Explorer.
“We need a much better understanding of the deep ocean’s ecosystems and processes to make informed decisions about resource management and conservation.”
Visual observations are a critical method for studying the seafloor. According to the researchers, they “provide situational context to collected samples, observe behaviours and interactions of marine life, conduct more accurate biodiversity and abundance surveys” and simultaneously gather biological and geological data.
To determine just how much of the deep seafloor has been studied in this way, the team aggregated data from about 44,000 deep-sea dives conducted since 1958.
“We present the most comprehensive global estimate of deep-sea benthic observation coverage to date,” the authors write.
“Our goal is to provide all stakeholders with baseline data they can use to strategically plan future expeditions and dive locations.”
Their findings reveal stark biases in the areas of the seafloor sampled, with dives increasingly being undertaken at shallower depths, in rarer deep-sea habitats, and within the Economic Exclusion Zones (EEZs) of a few counties.
“In 67 years of deep sea dives, only 19.1% of all dives occurred on the high seas, the area beyond national jurisdiction that encompasses 58% of the ocean,” the authors write.
“In the 1960s and 1970s, before the formation of EEZs through the adoption of the 1982 United Nations Convention on the Law of the Sea, 46.0% of all dives were conducted on what is now the high seas.
“Since the 1980s, there has been a global shift toward working within EEZs, with only 14.7% of all dives from the 1980s to the present taking place on the high seas.”
Just 5 countries – the US, Japan, New Zealand, France, and Germany – are responsible for 97% of all deep-sea submergence observations.
Despite 3 quarters of the ocean lying 2,000-6,000m below sea level, the proportion of dives conducted deeper than 2,000m decreased from 58.4% in the 1960s to 25.9% in the 2010s.
Dives also disproportionately focused on less common seafloor features, including canyons, escarpments, and slopes, while neglecting more abundant features such as shelves, rises, and abyssal plains.
“If the scientific community were to make all assumptions about terrestrial ecosystems from observations of 0.001% of that total area, it would equate to an assessment area of 1489 km2, smaller than the land area of Houston, Texas, at 1669 km2,” the authors write.
According to the researchers, the deep ocean is the largest ecosystem on our planet and “provides critical services and resources to humankind … ranging from oxygen generation and climate regulation to food and pharmaceuticals.”
Despite this, they say that humans continue to negatively impact the deep ocean through “disposal of litter and chemical pollution, exploitation of biological and geological resources, and climate change and ocean acidification.”
This includes deep seabed mining to harvest polymetallic nodules. These nodules are “inextricably connected” to deep-sea ecosystems, and the potential impacts of their large-scale mining are poorly understood.
“With the continued anthropogenic pressures on this ecosystem and the slow pace of deep ocean exploration and observations, we do not have the thousands of years it would take to visually characterise the entire deep seafloor once,” they write.
Instead, the findings underscore an urgent need for a more comprehensive and global effort to explore the deep ocean in a way that will more accurately reflect it.
“As technology advances and deep-sea tools become smaller, more affordable, easier to use, and more autonomous, we anticipate a proliferation of technology worldwide and a broadening of the deep-sea community, resulting in a more equitable collection of global deep-sea data,” the researchers write.
This is already happening. Since the 2000s, their analysis shows there has been a notable increase in the number of dives conducted worldwide and the number of countries and institutions carrying out deep-sea exploration and research.
“In addition to accelerating visual data collection, the deep-sea community needs to identify a targeted set of locations that, when explored, will fill in the gaps and create the first unbiased and statistically representative biogeographical characterisation of the entire deep seafloor.”
The Ultramarine project – focussing on research and innovation in our marine environments – is supported by Minderoo Foundation.