45°
51.8' N, 130° 00.2' W
Air temperature 62° F, 1600 PST
Map of
Axial caldera with pressure sensor benchmark locations and 1998 lava
flow boundaries.
The
first ROPOS dive at Axial began yesterday at 1300 PST. Two traverses from
the Southern Pillow Mound to the center of the caldera are near completion.
On each traverse pressure sensor readings at the 5 benchmarks have been
completed. On the first traverse (south to north) the Ocean Bottom Hydrophone
that was deployed before the dive was sighted near the Marker-33 benchmark.
During the second traverse (north to south) one transponder was cut loose
and recovered, a second could not be located. The third and final traverse
(south to north) will begin shortly, to complete the pressure sensor readings
at all benchmarks. Additional tasks on the third traverse include recovery
and deployment of several temperature probes, as well as biological sampling
in the Marker-33 Vent area. The dive is scheduled to end tomorrow morning.
In the mean time, the PMEL engineers are preparing the NeMO Net buoy for
deployment after the dive ends.
Scientists were surprised to see this healthy
tubeworm bush NE of Marker-33 vent, in the area of the pressure sensor
benchmark. Noone recollects seeing this lush clump of tubeworms here
last year, which indicates that the hydrothermal system is evolving.
Teacher's Report
Bill Hanshumaker, Educator at Sea
It's
another beautiful day at sea. Because of my late watch last night, I woke
up too late for the scheduled time of breakfast, but the Thompson is well
prepared for 24 hour shifts. I grabbed some fruit and yogurt and ate on
the foredeck, enjoying the calm seas and sunshine, while an albatross
briefly kept me company.
Yesterday
it took over an hour for ROPOS to descend over 1700 meters to its dive
location at South Pillow Mound on benchmark 66. After spending about 60
minutes to locate the benchmark and taking bottom pressure measurements,
the cage (a garage of sorts for ROPOS) was raised to a depth of 1500 meters
to prepare for ROPOS underwater transit to the next location, called "Bag
City", near the southeastern edge of the caldera. The Thompson tows
the empty cage with ROPOS traveling under its own power, connected to
the cage by a tether. It takes less time to tow the cage underwater at
1.5 knots, than to raise and secure ROPOS and proceed at full steam to
the next location. Even so, it took 4 hours to transit to Bag City, one
of the previously identified vent sites of Axial.
Pressure sensor reading
at benchmark 66, the Southern Pillow Anomaly. The ROPOS arm is placing
the sensor on the benchmark, where it will sit for 30 minutes gathering
data.
Benchmarks
were placed on the seafloor three years ago, at five different locations
for a time-series experiment. By comparing measurements and observations
over subsequent years, long-term changes can be documented. For example,
bottom pressure measurements can determine whether the caldera floor is
inflating or deflating. If magma moves in from below, then the caldera
floor would rise slightly. This might mean that volcanic activity may
increase in this area. Digital still frames and video records are utilized
to record changes in biological activity at know vent sites. Increased
biological activity is often associated with the increased venting of
bacteria-enriched hot water. Near Benchmark 5 at Marker 33 Vent we recorded
a vigorous colony of tubeworms that hadn't previously been observed. The
shimmering water around the colony was thick with bacterial floc.
The bright yellow ball contains glass floats
and the transponder used for underwater navigation. One of the ROPOS
arms is visible on the left. ROPOS cut the transponder loose and it
was retrieved at the surface by the Thompson's small boat.
Using
the digital camera, we were able to capture stunning close-ups of the
tubeworms, and a myriad of smaller associated vent creatures as well.
The plume (or gill) of the worm is bright red and complexly structured,
comprised of tightly stacked sheets of divided filaments. The plume structure
facilitates rapid and efficient exchange of dissolved molecules from the
surrounding seawater.
Locating
the scattered benchmarks requires a combination of space age and deep
sea technologies. The Thompson uses the GPS (Global Positioning Satellite)
system to determine its exact longitude and latitude location. Transponders
are placed on the seafloor at known locations to generate an acoustic
signal that ROPOS can use for precise underwater orientation. However,
transponders are powered by a series of D-cell batteries that need to
be replaced periodically. Another mission accomplished today was to recover
a transponder and replace its batteries for later deployment.