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Despite its immense size and critical role in global carbon cycling and climate regulation, the vast expanse of the deep sea, often referred to as the Earth's largest biome, has long eluded thorough scientific exploration.

New research led by USGS and its partners offers unprecedented insights into the complex dynamics of deep-sea ecosystems, particularly within submarine canyons.

Deep-sea organisms, dwelling in complete darkness, rely predominantly on particulate organic matter from the surface as their primary source of energy. These creatures, often overlooked yet crucial to the functioning of marine ecosystems, play pivotal roles in the transport, transformation, storage, and sequestration of carbon—a process vital for regulating Earth's climate.

Among the most dynamic and complex environments within the deep sea are submarine canyons. These canyons, characterized by varied morphology, powerful currents, and fluctuating nutrient conditions, serve as hotspots of biodiversity and activity. Understanding the distribution of species and the transport of organic material within these ecosystems has long been a challenge for researchers.

Mapping resource use across seafloor canyons and slopes

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In an effort to shed light on deep-sea food webs and nutrient cycling, the research team turned to stable carbon and nitrogen isotopes. Stable isotopes are non-radioactive forms of atoms that do not decay into other elements. They persist in the environment and can be tracked from where they are produced to where they are consumed. These transfers of nutrients—as well as isotopes—are known as trophic interactions, and they are represented as food webs.

By collecting animals, particulate organic matter, and sediment samples from submarine canyons and adjacent slope environments along the U.S. Mid-Atlantic margin and analyzing their stable isotopes, researchers tracked the sources of organic matter and the trophic levels within these deep-sea communities. This innovative approach enabled them to create "isoscapes" of the deep sea, mapping the spatial variability of resource use across seafloor canyon and slope environments.

"Deep-sea isoscapes provide us with a powerful tool to untangle complex relationships between organisms and their environment in these remote and poorly understood sites,” said Amanda Demopoulos, USGS Research Ecologist and lead author of the study. “By identifying and tracking these isotopic signals, we can gain insights into how energy and nutrients flow within dynamic deep-sea ecosystems such as submarine canyons."

By tracking the spatial variation in resource use and trophic interactions, scientists can better characterize potential impacts of environmental changes on deep-sea ecosystems. As climate change continues to alter oceanic conditions, understanding how these shifts affect deep-sea biodiversity and carbon cycling becomes increasingly crucial.

"Deep-sea isoscapes not only provide a snapshot of current conditions but also offer a means to monitor shifting baselines as the climate changes," said Demopoulos. "This knowledge is essential for informing conservation efforts and mitigating the potential impacts of environmental disturbances on these fragile and poorly understood ecosystems."

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