In the summer of 2004, NURP sponsored
a pioneering scientific expedition to the waters surrounding a U.
S. chain of islands that teem with marine life yet remain largely
uninvestigated. The Aleutian Islands, most of which are part of
Alaska, are located 2200 km (1200 nautical miles) west of the tip
of the Alaska Peninsula. Their waters are home to some of the most
productive fisheries in the world; and Dutch Harbor, on Unalaska
Island, is currently the largest fishing port in the U.S. The Aleutians'
waters also harbor cold-water corals, more commonly referred to
as deep-sea corals.
The Aleutian Islands are home
to the largest fishing port in the United States, Dutch Harbor,
which for the past 15 years has held the top slot for fish
and shellfish landings.
The Aleutians' remote and dramatic location
has significantly challenged scientific investigation of its waters.
The islands sit on top of a continuous submarine ridge that divides
the North Pacific Ocean and the Bering Sea. The Aleutians are part
of the Pacific Ring of Fire, with approximately twenty-four active
volcanoes and frequent earthquakes, caused by the collision of two
of the tectonic plates that form the Earth's crust. Although a few
good harbors can be found in the archipelago, numerous reefs and
almost perpetual fog can prove dangerous to even the most skilled
Jason II allows scientists to collect samples
at depths to 6500 m. Photo: Gene Yogodzinski,
University of South Carolina.
In July and August 2004, NOAA's Undersea
Research Program (NURP) Center for the West
Coast and Polar Regions organized and funded a research cruise
to the central Aleutians on the R/V Roger Revelle. Expedition
goals were to collect biological and substrate samples, map the
sea floor, and capture video of areas never before documented.
The main tool in this research was the Jason II,
a deep-diving remotely operated vehicle (ROV) operated by Woods
Hole Oceanographic Institution, capable of diving to 6500 m (21,320
f). This was the first operation of a civilian deep-diving vehicle
in the North Pacific Ocean or Bering Sea. Other research equipment
included a towed deep-sea camera system (TowCam) and a 12 kHz multibeam
sonar system on the ship's hull for mapping the seafloor.
Four research teams took part in the
expedition. The first two groups departed Dutch Harbor for Leg 1
of the research cruise (July 10 - 24) to study an area south of
Study sites: Site (1): Ugamak Slide - Team
1 Lead: Tony Rathburn; (2) Derikson and Sirius Seamounts -
Team 1 Lead: Randy Keller; (3) Deep water coral distribution
- Team 1 Lead: Robert Stone; (4) Adak Canyon geology - Team
1 Lead: Gene Yogodzinski. (Larger
Team 1, headed by Tony Rathburn of Indiana State University,
focused on the Ugamak Slide (1), thought
to be the site of a massive submarine landslide that may have caused
the destructive, Pacific-wide 1946 tsunami. The objectives were
to confirm whether the landslide occurred in 1946, as well as to
study the recovery of the seafloor ecosystem on the landslide slope.
Multibeam mapping revealed a highly eroded, and therefore,
mature seafloor that showed no evidence of a recent landslide. These
unexpected findings leave the cause of the 1946 tsunami a mystery
and indicate that a great deal more investigation is needed to pinpoint
the cause of the tsunami.
(Top left) Bubble gum coral (Paragorgia
sp.) shown covered with brittle stars was collected southwest
of Amlia Island at 844m. Photo: Sonya
Senkowsky, Alaska Science Outreach Reporter.
(Top right) Manipulator arm of Jason II
closes in on a black coral and deepwater king crab, at a depth
of 2160m, just south of Amlia Island. This may be the first
documentation of a king crab resting on a black coral colony,
which is thought to be an important habitat. Photo:
(Bottom left) A gorgonian coral (Muriceides
sp.) retrieved by Jason II at a depth of 490 m. Photo:
Sonya Senkowsky, Alaska Science Outreach Reporter.
(Bottom right) Samples of rock and associated
invertebrates, retrieved by Jason II near Amlia Island. On
the left: igneous dropstone, a rock of volcanic origin transported
by a glacier and dropped at that site as floating ice melted.
On the right: slab of siltstone, from an outcrop on the seafloor.
Photo: Jennifer Reynolds, University of
At the same location, biologists collected
depth transects that will yield some of the first information about
the mosaic of benthic communities on the Alaskan margin. Additionally,
they identified both disturbed and undisturbed areas to help assess
the biological impact of small-scale disturbance. They also discovered
cold methane seeps at a water depth of 3000 m and documented a new
type of deep-sea coral habitat that may be associated with methane
Team 2, headed by Randy Keller from Oregon
State University, mapped and explored Derikson and Sirius Seamounts
(2), two 50-60 million year old undersea
volcanic mountains that are riding on the Pacific Plate as it approaches
the Aleutian Trench. They found that the seamounts are being cut
by deep, active faults as the plate bends downward into the trench.
These faults may act as pathways for water circulation and the venting
of warm, chemically altered fluids, which in turn have the potential
to support vent-related ecosystems at the seafloor and in the rock
fractures. Additionally, new species of deep-sea corals were retrieved
with Jason II at this site.
Coral distribution was systematically
studied down to a depth of 3000 m. An apparent change in density,
diversity, and species composition was observed at a depth
of approximately 1400 m.
Deep-sea coral and sponge ecosystems found
in the Aleutian Islands. Photo: Alberto
Lindner, NOAA Fisheries.
After two weeks, the R/V Revelle returned
to Dutch Harbor and exchanged science teams for Leg 2 of the research
cruise (July 24 – August 8). NOAA Fisheries biologist, Dr.
Robert Stone from the Auke
Bay Laboratory in Juneau, Alaska, headed Team 3, which studied
deep-sea coral and sponge distributions (3),
habitat associations, and species diversity, along a 500-km region
between Amlia and Semisopochnoi Islands.
Jason II dives documented a
great variety of habitats down to a water depth of 3000 meters,
from soft silt ponds to current-swept sandy banks, canyon walls,
young volcanic cones, and glacially scoured rock outcrops. Deep-sea
corals and sponges were widely distributed at the study sites with
an apparent change in density, diversity, and species composition
at a depth of approximately 1400 m. The ultimate goal is to construct
a model that predicts the distribution and density of coral habitat
throughout the Aleutian Islands; this model may be used to directly
assist managers in developing methods to minimize fishing interactions
with coral habitat.
(Left) Adak Island. Photo:
Tom Bolmer, Woods Hole Oceanographic Institution
(Right) Gene Yogodzinski, of the University
of South Carolina, peruses seafloor maps during the cruise.
For several days of the Aleutian research cruise, he led the
use of Jason II to find and sample some of Adak canyon's oldest
volcanic rocks. Photo: Sonya Senkowsky,
Alaska Science Outreach Reporter.
Team 4, led by geologist Gene Yogodzinski from the
University of South Carolina, devoted several days to investigating
Adak Canyon (4), located immediately southwest
of Adak Island. Adak Canyon is a steep-walled, tectonically active
rift that appears to form a window into the inner structure of the
Aleutian Ridge. New multibeam sonar maps of the seafloor were used
to select dive targets, and the ROV dives successfully recovered
plutonic rocks, the magmas related to earlier generations of Aleutian
volcanoes. Geochemical studies of these rocks will provide information
about how the crust of the Aleutian volcanic arc has grown over
its 50 million year history, and possibly how magma from this kind
of volcanism may have influenced the growth of continents throughout
geologic time. Biologists utilized the ROV dives to investigate
the distinct ecology of the canyon walls and floor.
For more information on the Aleutian Islands Research
Cruise (Leg 1 and 2):