Back to Expeditions & Projects

A variety of deep-sea corals (and other marine life) observed during the 2025 Aleutian Arc expedition.

AT50-38

The Aleutian Arc: Integrated Exploration of Biodiversity at Priority Benthic Habitats

Past Expedition

Primary Goal

Explore and provide initial characterization of high-priority sites in the central and western Aleutian Islands

Dates

June 15-July 2, 2025

Location

Pacific Ocean: Central and western Aleutian Arc; Arctic

Vessel

Research Vessel Atlantis

Primary Technology

Human occupied vehicle Alvin, multibeam sonar, CTD (conductivity, temperature, depth instrument)

Expedition Summary

*The U.S. Navy’s human occupied vehicle (HOV) Alvin being launched from the Office of Naval Research’s Research Vessel Atlantis. — The U.S. Navy’s human occupied vehicle (HOV) *Alvin* being launched from the Office of Naval Research’s Research Vessel *Atlantis*. *Alvin* can reach depths of 6,500 meters (approximately 4 miles), carrying two scientists and one pilot for about eight hours per dive. Owned by the U.S. Navy, *Alvin* has been in operation since 1964 through Woods Hole Oceanographic Institution. *Image courtesy of The Aleutian Arc: Integrated Exploration of Biodiversity at Priority Benthic Habitats (USGS/BOEM/NOAA/ONR). Photographer: Art Howard.*
Download largest version (jpg, 2.75 MB)

From June 15–July 2, 2025, federal and academic scientists explored the deep waters of the Aleutian Arc off Alaska. This ship- and submersible-based expedition gathered vital data about the region’s natural resources and seafloor hazards. Using advanced ocean exploration technologies, the team aimed to enhance understanding of the area and inform natural resource management and hazard-related policymaking, ultimately benefitting Alaskan and national economies and human health and safety.

Why Explore the Aleutian Arc?

The Aleutian Arc is a volcanic arc and island chain extending west from the Alaska Peninsula. The biological and geological resources within its vast waters are ecologically and economically important. Yet, much of the deep Aleutian Arc — including the hazard potential — is largely unknown. Scientists, resource managers, policymakers, industry, and the public can all benefit from greater knowledge about what lies within the deep waters of the Aleutian Arc and how they interact.

Map showing *R/V Atlantis* ship track and HOV *Alvin* dive locations along the Aleutian Arc. — Ship track and dive locations for The Aleutian Arc: Integrated Exploration of Biodiversity at Priority Benthic Habitats expedition. The National Ocean Mapping, Exploration, and Characterization Council has identified the Aleutian Arc as a priority area for exploration. *Image courtesy of Brian Andrews, U.S. Geological Survey.*
Download largest version (jpg, 1.85 MB)

Expedition Plan

This expedition built on data collected during expeditions on NOAA Ship Okeanos Explorer and by the uncrewed surface vehicle Saildrone Surveyor.

Aboard the Office of Naval Research’s Research Vessel Atlantis, a team of ecologists, biologists, oceanographers, geologists, geochemists, and geophysicists sought answers to questions about the region’s:

Ecologically and economically important seafloor habitats, such as coral and sponge gardens that may serve as essential fish habitats.
Other geological and biological resources, like critical minerals and natural products.
Seafloor hazards, including volcanoes, earthquakes, and landslides, particularly those capable of producing tsunamis.

To do so, they:

Used human occupied vehicle (HOV) Alvin to:
- Collect biological samples, rocks, sediment cores, water samples, and video.
- Examine seafloor environments.
- Ground truth recently mapped features.
Deployed a CTD (conductivity, temperature, depth instrument) with sensors and Niskin bottles to collect environmental data and water samples.
Collected multibeam and split-beam sonar data to fill mapping gaps, refine dive-site selection, and learn more about life in the water column.

HOV *Alvin* push cores being placed into seafloor sediment near Bogoslof Island. — Push cores inserted into the seafloor using human occupied vehicle *Alvin* offshore of Bogoslof Island during the 2025 Aleutian Arc expedition. The expedition team is using the resulting sediment cores to describe these sediments and the animals that live within them, many of which are likely new to science. *Image courtesy of Amanda Demopoulos, USGS; NOAA Ocean Exploration, ONR, NOPP, BOEM, NOAA IOCM, USGS; © Woods Hole Oceanographic Institution.*
Download largest version (jpg, 2.03 MB)

Researchers ready Niskin bottles on a CTD rosette for water sampling. — Aaron Aunins and Katlin Adamczyk with the U.S. Geological Survey and Florida State University’s Lauren Rice (left to right) preparing the Niskin bottles on the CTD (conductivity, temperature, and depth) rosette to collect water samples. The CTD is an essential oceanographic tool used during the 2025 Aleutian Arc expedition to detect hydrothermal vents and collect water for analysis of environmental DNA (eDNA), the genetic material animals shed into the water. *Image courtesy of The Aleutian Arc: Integrated Exploration of Biodiversity at Priority Benthic Habitats (USGS/BOEM/NOAA/ONR). Photographer: Art Howard.*
Download largest version (jpg, 1.63 MB)

Expedition Results and Discoveries

While data analysis is ongoing, some results are already in. During the expedition, the team:

Explored 3,631 kilometers (2,256 miles) of the Aleutian margin.
Conducted 11 dives in HOV Alvin ranging in depth from 697–3,353 meters (0.4–2.1 miles).
Collected 884 samples — 444 biological, 29 geological, and hundreds of liters of seawater.
Mapped more than 6,475 square kilometers (2,500 square miles) of previously unmapped seafloor.

Life was abundant on the seafloor. Preliminary biological observations include:

A high diversity of corals and sponges that was more widespread than previously observed.
A high apparent diversity and abundance of coral- and sponge-associated species, highlighting the importance of coral and sponge habitats for benthic biodiversity and ocean health.
Extended ranges for many corals and sponges and their associates.
Potentially new species in the region and/or possible species new to science.

HOV *Alvin* sampling a bubblegum coral amid diverse deep-sea habitat. — Human occupied vehicle *Alvin* collecting a sample from a bubblegum coral (*Paragorgia* sp.) surrounded by other corals and marine life during the 2025 Aleutian Arc expedition. *Image courtesy of Amanda Demopoulos, USGS; NOAA Ocean Exploration, ONR, NOPP, BOEM, NOAA IOCM, USGS; © Woods Hole Oceanographic Institution.*
Download largest version (jpg, 1.39 MB)

One significant discovery was a massive submarine landslide near the epicenter of the 1957 Andreanof Islands earthquake, which caused a Pacific-wide tsunami that devastated parts of Alaska and Hawaiʻi. This suggests the landslide may have contributed to the power of the tsunami and the damage it caused, but further study is needed to confirm.

The team didn’t find any hydrothermal vents — deep-sea hydrothermal activity has yet to be discovered along the Aleutian Arc — but they did find potential hydrothermal minerals. Other geological collections included basalts, altered volcanic rocks, volcaniclastics, rocks, and mudstones.

Bathymetric map of the southern Aleutian shelf showing the newly identified submarine landslide area. — Map of the seafloor on the southern Aleutian shelf showing the area of the massive submarine landslide discovered during the 2025 Aleutian Arc expedition. Colors show depth ranging from 500 meters (0.3 miles) below sea level in red to 4,000 meters (2.5 miles) below sea level in purple. The data were collected using the multibeam sonar on the Office of Naval Research’s Research Vessel *Atlantis*. *Image courtesy of The Aleutian Arc: Integrated Exploration of Biodiversity at Priority Benthic Habitats (USGS/BOEM/NOAA/ONR).*
Download largest version (jpg, 536 KB)

Next Steps

The scientists are now busy analyzing collected samples and data. Multiple data requests already received show the value of their work — work made possible by extensive and effective partnerships between the participating federal agencies and their academic colleagues. Despite all the data collected, the team returned to shore with more questions than answers, underscoring the need for more exploration and research in the region. Nevertheless, their achievements are significant and will advance scientific discovery and aid resource and hazard management in the Aleutian Islands region.

Scientist Alexis Weinnig exits HOV *Alvin* after a dive. — Alexis Weinnig climbs out of human occupied vehicle (HOV) *Alvin* following a dive during the 2025 Aleutian Arc expedition. During an *Alvin* dive, a pilot and two science observers juggle responsibilities and work through a list of research objectives. The observers guide the dive, telling the pilot where to go and what to sample. *Image courtesy of The Aleutian Arc: Integrated Exploration of Biodiversity at Priority Benthic Habitats (USGS/BOEM/NOAA/ONR). Photographer: Art Howard.*
Download largest version (jpg, 2.62 MB)

Corals and eels seen on the Aleutian seafloor

Fisheries of the Aleutian Arc and Alaska: Their Importance, Challenges, and the Role of Exploration

The Aleutian Arc, a remote chain of volcanic islands stretching from the Alaska Peninsula to international waters, harbors some of the ocean’s most diverse yet largely unknown marine ecosystems. This complex underwater landscape supports fish species with remarkable adaptations that allow them to survive in extreme environments.

September 3, 2025

Human occupied vehicle (HOV) Alvin with the Office of Naval Research’s Research Vessel Atlantis in the background during the 2025 Aleutian Arc expedition.

Volcano Watch — Discovery of a Massive Submarine Landslide Near the 1957 Aleutian Earthquake Epicenter

As part of a growing national effort to understand seafloor hazards, scientists from the U.S. Geological Survey’s Volcano Science Center are working across agencies to investigate how submarine earthquakes, landslides, and volcanic activity shape tsunami risk — not just in Hawaiʻi, but across the broader Pacific.

August 7, 2025

Recovering human occupied vehicle (HOV) Alvin from the deck of the Office of Naval Research’s Research Vessel Atlantis

Into the Unknown: BOEM Dives Deep to Explore Offshore Mineral Frontiers

The ocean floor holds more than just mystery. It could hold the keys to America’s energy future. That’s why we are making big moves to better understand the hidden mineral resources of the U.S. Outer Continental Shelf.

July 22, 2025

View More View Less

Schoolchildren examining marine algae with Christina Bonsel

Diving Deep Along the Aleutian Arc: Inside a Rare Mission to Explore Alaska’s Mysterious Seafloor

West of the Alaska Peninsula lies the Aleutian Arc. This volcanic island chain stretches deep into the North Pacific. Above the water, it’s known for its windswept cliffs and active geology. But beneath the surface? It’s practically a blank map.

July 15, 2025

Maria Figueroa, a research geologist with the U.S. Geological Survey holds two splits from a mudstone

Exploring Critical Minerals and Volcanic Processes in Aleutian Rocks

One of the motivations of this expedition along the Aleutian Arc is centered on collecting and characterizing submarine volcanic and seafloor rocks to support two complementary objectives: improving assessments of volcanic hazards and identifying environments favorable for critical mineral formation.

July 3, 2025

Seamus Jameson, a scientist with the U.S. Geological Survey, prepares the Niskin bottles on the CTD (conductivity,

Detecting Hydrothermal Vents and Collecting Environmental DNA: Investigating the Water Column in the Aleutian Arc

Exploring the deep ocean along the Aleutian Arc requires a suite of advanced tools to investigate the intricate connections between marine ecosystems and their dynamic environment. One of the most valuable instruments aboard any deep-sea exploration expedition is the CTD (conductivity, temperature, and depth instrument).

July 3, 2025

Life Cycles Below: Corals and Sponges in the Offshore Aleutian Habitats

As we explore more communities of animals that live in the deep sea, one question almost always arises: How did they get there? One important way we can begin to answer this question is by studying reproduction.

July 1, 2025

Christina Kellogg, a researcher with the U.S. Geological Survey, about to have lunch inside HOV Alvin

Life in the Sphere: Exploring the Aleutian Arc

The deep seafloor of Alaska’s Aleutian Islands features unique geology and a huge variety of animals. Using human occupied vehicle Alvin allows us to explore new places, untethered to a ship, and personally visit the seafloor to make detailed observations with a stronger sense of context, which can be lost when only using cameras.

July 1, 2025

Into the Deep: Exploring the Hidden Slopes of Bogoslof Volcano

Far out in Alaska’s Bering Sea, Bogoslof Volcano rises from the ocean floor. Although it looks small from the surface, the volcano is massive beneath the sea, and it plays an important role in helping scientists understand how underwater volcanoes grow, erupt, and sometimes collapse.

June 30, 2025

Katlin Adamczyk, a marine geochemist with the U.S. Geological Survey, holds up rock samples

Investigating Potential Seabed Minerals in the Aleutian Arc

Seabed minerals form when dissolved metals in seawater or hydrothermal fluids precipitate over timescales of thousands to millions of years. Mineral types found in deep-sea environments include seafloor massive sulfides, phosphorites, ferromanganese crust, and manganese nodules.

June 26, 2025

Celebrating an Aleutian Anniversary

Twenty-one years after she found herself in the Aleutian Arc for her first cold-water coral expedition and her first submersible dive, a U.S. Geological Survey scientist celebrates her return to the Aleutians with a dive in human occupied vehicle Alvin.

June 25, 2025

Deep Mud Diaries: Exploring Seafloor Biodiversity on the Aleutian Arc Expedition

Most of the deep seafloor is covered by large expanses of soft sediments. These sediments are home to communities of tiny animals that provide an important link in transferring energy between the marine snow that rains down from surface waters to larger animals feeding at the seafloor and in the water column.

June 24, 2025

A Laysan albatross observed flying near the Islands of Four Mountains during the 2025 Aleutian Arc expedition.

Alaskan Wildlife: Observations from the Aleutian Arc Expedition

Though this expedition focused on natural resources below the waves, the science team marveled at Alaska's abundant wildlife above the them, finding joy in watching marine birds and northern fur seals.

June 23, 2025

The Office of Naval Research’s Research Vessel (R/V) Atlantis in Dutch Harbor, Unalaska, before the 2025 Aleutian Arc expedition.

Connecting Communities to Ocean Exploration: Outreach From the Aleutian Arc Expedition

Alaska’s rich and dynamic ecosystems draw scientists from around the world. But for the people who live here — many of whom have deep cultural, historical, and personal connections to the land and sea — it’s especially important that scientific research feels local, accessible, and relevant.

June 18, 2025