Response
cruise summary map:
white stars = CTD casts
white lines & stars = CTD tows
blue lines & dots = camera tow
red dots = earthquake epicenters
Bathymetry is NOAA multibeam. |
Back
to main event page: Endeavour,
March 2005
Visit:
Endeavour Science Update site
News
from sea, Jim Cowen (Chief Scientist)
Cruise TN-177B, R/V Thompson
March 2005 Endeavour Rapid Response Cruise:
March
9:
~0044 hr: End V05B-02.
~0144 hr: Start third off-axis vertical cast VO5B-03: 47o
58.4’ N; 129o 18.5’ W
~0311 hr: End cast V05B-03. None of the last three casts (all
verticals) showed any real-time (CTD-optical) evidence of
a particle or thermal plume, which would be indicative of
hydrothermal plumes that had been carried off-axis by prevailing
ocean currents. Chemical analyses of the water samples collected
during these casts will take some time.
We
then moved operations back to the main Endeavour axial valley,
with intention of performing a series of vertical casts over
most of the known active vent fields.
~0500 hr: Started vertical cast V05B-04: 47o 56.866’
N; 129o 05.962’ W, over the Main Endeavour field.
~0630 hr: End V05B-04. A vigorous thermal and particle plume
was found, typical of this site. Further analyses are needed
to determine whether the recent earthquake swarm caused a
change in the subseafloor’s hydrothermal plumbing, in
terms of heat flux and chemical composition.
~0936 hr: Start V05B-05. Vertical cast over the Mothra vent
field, about 2.5 km south of the MEF (47o 55.4140’ N,
129o 06.5310’ W).
~1115 hr: End V05B-05. Again, like the MEF, this cast over
Mothra found a vigorous hydrothermal plume. The plume was
less intense than at MEF in terms of the particle anomaly,
but from the strong presence of hydrogen sulfide (that rotten
egg smell) in some of the water samples collected, it appears
that we were able to obtain samples of the buoyant phase or
very young neutrally buoyant phase of the plume. This should
facilitate comparisons of values for current hydrothermal
fluid compositional ratios with historic values. However,
ship-board analysis of methane and hydrogen indicate that
vent fluid chemistry at MEF and Mothra do not significantly
differ from “normal”.
 |
 |
| Images
from camera tow.
Camera photos show moderate to heavily sedimented pillows
and talus throughout the whole traverse. Lots of sessile
biota (sponges, corals) and even viewed a small octopus
in one photo. No evidence of recent lavas or venting in
the area we traversed. (click images for full view) |
~1630
hrs: Deep-sea camera is launched. CTD-rosette casts have been
temporarily halted in order to stage and launch the deep-sea
camera. While the ‘water column’ crew repeatedly
launched, recovered, and processed CTD-rosette casts through
the night and morning hours, the camera crew troubleshooted
the problem with the camera system. After much work and creative
solutions, the deep-sea camera was launched for an 8 hour
tow along the seafloor from 48o 05.628’ N, 129o 01.596’
W toward 48o 01.7, 129o 03.5’ W. This path is north
of the known Endeavour vent fields and directly over a suspected
magma chamber. Oops, back up for a little more problem solving.
~1930 hrs: Camera back in the water. This time everything
was working, including the CTD. During this tow several small
thermal anomalies may have been picked up by the camera system’s
CTD. All indications are that the digital camera and strobes
themselves are functioning properly.
Camera
system aboard the response cruise. |
~0430
hrs: Camera system back on deck after successful 8 hour tow.
The data collected during the camera tow are consistent with
the other cruise results. Camera images of the seafloor along
its single tow path showed only sediment covered seafloor,
no fresh basalts. Neither the camera sled’s CTD data
nor data from the Miniature Autonomous Plume Recorder (MAPR)
attached to the camera sled showed any significant thermal
or optical anomalies (the MAPR was mounted on the sled in
case the CTD malfunctioned during the tow).
Following the recovery of the camera system, the vertical
CTD-rosette casts were continued over the northern known Endeavour
vent fields:
~0530
to ~0700 hrs: Vertical cast V05B-06 (High Rise vent field
at 47° 58.1259 N, 129° 05.2027).
~0910 to ~1100 hrs: Vertical cast V05B-07 (Salty Dawg vent
field at 47° 58.922 N, 129° 04.569).
Both
of these casts intercepted buoyant hydrothermal plumes, thus
supplying concentrated plume samples for chemical analyses.
Bottom
line as we head for shore:
1. It appears unlikely that this February/March 2005 earthquake
swarm induced corresponding expression at the seafloor (e.g.,
eruptive flow) or in the water column (e.g., hydrothermal
chronic or event plume). The in situ and ship-board physical
and chemical data from the 3 long tow-yo casts and 7 vertical
casts revealed no water column signal that can be clearly
associated with the recent earthquake swarm, whether magmatic
or tectonic. Initial calculation of methane to hydrogen ratios
from MEF and Mothra are comparable to historic values from
vent fluids. On the other hand, methane to hydrogen ratios
from CTD-bottle casts at High Rise and Salty Dawg may differ
from pre-event vent fluid ratios, which could imply a connection
to the seismic event, especially since these vent fields are
farther north than MEF and Mothra (and thus closer to the
event earthquake epicenters). No evidence of any temperature
or optical anomalies were seen in the near-bottom camera tow
data (CTD or MAPR). Camera images of the seafloor revealed
no fresh basalt; rather, the entire camera tow track was sediment
covered. Finally, we searched for evidence of new lava flows
in the earthquake area by comparing high-resolution multibeam
bathymetry data with the historic Seabeam data. No bathymetric
anomalies were detected.
Time-series records from in situ sensors currently deployed
at various vents along the Endeavour segment may have recorded
event-related fluctuations in temperature (or other parameters);
all investigators with sensors deployed at Endeavour should
check these records carefully once they are recovered.
2.
Extensive shore-based chemical analyses of samples collected
during this short but intense cruise, as well as further scrutiny
of CTD, optical, and ship-board chemical analyses, are needed
before the possibility of event-related venting can be finally
confirmed or eliminated.
3.
Possible explanations for failure to discover significant
event-related hydrothermal discharge include:
• The earthquake swarm was likely an intrusive, magmatic
event that may not have 1) reached sufficiently shallow crustal
depths to lead to extrusion (eruptive flows), 2) caused changes
in hydrothermal circulation at the seafloor and/or 3) did
not stimulate new venting or changes to existing venting as
discernable via surface ship sampling.
• Hydrothermal changes associated with this event were
focused at the 5 known Endeavour Vent fields. Detailed sampling
of the plumes overlying the known Endeavour vent fields was
performed following an earthquake swarm west of Endeavour
in 1999 demonstrating clear changes in the fluid chemistry
of several of these vents following that 1999 swarm. It may
be that even subtle changes in the ratios of key hydrothermal
species following the earthquakes will be detectable in these
plume samples since there exists an extensive history of the
chemistry of these fluids and plumes. However, our preliminary
ship-board analyses clearly do not support this hypothesis.
• Inadequate sampling. Our rapid response was not fast
enough and event-related venting had stopped in the week between
the start of the earthquake swarm and our on-site arrival,
so that any event plume was swept away out of reach of our
time-limited search net. This option seems unlikely since
the pattern of our tow-yos should have detected any sustained
significant venting occurring within the region defined by
the earthquake swarm, given the most likely current patterns
and regional geology/bathymetry. Furthermore, event-related
hydrothermal discharge has been sustained for months to years
following the original seismic event for all of the few seafloor
eruption events that have so far been documented.
4.
This episode of event remote detection and rapid response
demonstrated a remarkable degree of cooperation and dedication
among university and government scientists and their respective
infrastructures, funding agencies and their program managers,
UNOLS and university ship operators, and a host of other important
contributors to this effort. The Ridge2000 community was informed
of the seismic swarm on Monday, February 28. Animated discussion
concerning the nature and implications of this event started
immediately. Response personnel were enroute by Thursday,
loading the ship on Friday, and sailed from the University
of Washington dock at 0900 hr Saturday morning. We were on
station by Sunday morning, just 6 days after notification
of the seismic swarm, a task that usually requires a lead-time
of over a year. The detection and response team gratefully
acknowledges the assistance of the very many who got us on
our way. We want to especially thank Dave Epp of the NSF-Ridge2000
Program and Steve Hammond of NOAA-Ocean Exploration for
R/V Thompson at the dock. |
funding
the response cruise, Daniel Schwartz and the UW marine facility
for logistical help of all kinds, the US State Department
and the Canadian Ministry of Fisheries and Ocean for expediting
the permit process (operation in foreign waters), UW’s
and SIO’s Radiation Safety Offices, and of course Captain
Phil Smith and the entire crew of the RV Thomas T Thompson
for incredible hospitality and skilled assistance throughout
this cruise even though we had so suddenly upended their home
port time. Most of all we want to thank our families and close
friends for their support during the temporary loss of normal
life. Finally, the shipboard PIs would like to thank each
and every one of the shipboard scientists who upended their
own lives to enthusiastically join the cruise; you have all
been lively and professional.
March
8
~1430 hrs: Ended cast T05B-03. Then deployed the deep-sea
camera (beautiful deployment), but had to abort because of
a problem with its CTD. Camera crew immediately set to work
to troubleshoot problem.
~1930 hrs: It was subsequently determined
that camera testing could take several additional hours. Decision
was made to switch back to CTD-bottle casts while camera crew
remains hard at troubleshooting, and hopefully repairs. A
series of vertical casts will be made further to the Southwest
of the second tow at:
V05B-01: 48o 7.9’ N; 129o 13.0’ W
V05B-02: 48o 3.0’ N; 129o 15.6’ W
VO5B-03: 47o 58.4’ N; 129o 18.5’ W
The motivation behind these vertical casts to expand the search
net for any potential event plumes. These vertical casts will
be followed by a series of casts or a tow along the main axis
of the Endeavour over the known vent fields in order to test
the hypothesis that the intense seismic activity north of
these fields could have induced changes in the intensity and
chemical character of the hydrothermal discharge here, as
observed following the 1999 Endeavour seismic swarm.
Spirits
and motivation remain high. Science crew has meshed very well
and has become quite an efficient team. Ship’s crew
is fantastic, demonstrating great cooperation and excellent
skill—a can-do captain and crew. Weather has also improved,
for the moment at least. Wonderful pumpkin pie last night!
March
7 continued
~1710 hr: Cast T05B-02 on deck. Full sampling started immediately
as above, but also included analyses for radon, extremophile
cultures, dissolved organic carbon, and scanning electron
microscopy, as well as manganese-54 tracer experiments. The
instrument for in situ particle size distributions appeared
to work well during the cast. Again no clear hydrothermal
signal. The bottom nephaloid layer intensified over the southern
third of the tow. Ship-board analyses showed above background
values for methane (4-14 nM) along the tow tract and at variable
depths above bottom ((<50 to ~300 m), both with and without
corresponding particle plumes. No clear nearby source for
this plume is yet evident, although temperature-salinity plots,
the spatial pattern of light scattering plumes, and the nature
of the suspended particles suggest that at least some of the
particle plumes (at ~ 2400 m) and elevated methane may derive
from resuspension of sediments (and associated reduced gases—i.e.,
methane) on the broad shallow sill to the east of the earthquake
swarm area.
~1720-1930
hrs: Ran a EM300 multibeam (high resolution bathymetry) track
from .
~2000
hrs: Started a new tow-yo cast, T05B-03. Cast start position:
48o 12.50 N; 129o 3.47’ W, heading in a southerly direction
to 48o 5.8’ N, 129o 4.6’ W then on to 47o 5.3’
N, 129o 9.3’ W. This tow bisects region between the
first two, and then continues much further south. Following
this tow, we anticipate a series of vertical tows both expanding
our initial survey of the region as well as further investigating
certain areas closer to the seafloor. Weather permitting we
also anticipate performing a camera tow starting this afternoon.
Currently the winds are out of the SSE at about 30 knots.
March
7
Cast T05B-01 was recovered and immediately subsampled for
He, CH4/H2, CH4 stable isotopes, ammonia, CO2, pH, voltammetric
electrochemistry, Total, dissolved, and particulate metals,
microbial biomass and molecular biology, transmission electron
microscopy. Initial ship-board analyses do not reveal any
dramatic hydrothermal signals, but preliminary results suggest
that one or more samples from (the 2400 m particle plume and
the Eh spike) may have elevated methane and soluble FeS, elemental
S. More calibrations need to be performed before such preliminary
results are confirmed. EM300 bathymetry data is great.
~0300
to ~0430 hr: An EM300 (bathymetry) line was run from 48 05.00
N, 129 05.0700 north to 48 15.000 N, 129 00.4200 W, during
cast turn around and transitting to new cast start postion.
~0502
hr: Cast T05B-02 started. Start point: 48 12.990 N, 129 07.487
W; End point: . This is a tow from start WP due south. A small,
but significant above-bottom particle plume signal appeared
about half way through this tow; no other electronic signals
appeared to correspond to this particle plume, but several
Niskin bottles were tripped for on-board sample analyses.
This tow is still underway. Strong winds (gusts to ~50 knots)
and rising seas (20-30 ft) are expected later this afternoon/evening;
we will likely be restricted to vertical casts at that time.
A lessening in the wind and sea conditions is expected in
morning or early afternoon of following day.
Late
March 6 2350 hrs: Arrived on station after some working
through some first cast issues, we started the first cast
(T05B-01). EM300 multibeam (high resolution bathymetry) data
was collected during this and all tows. Once fish was near
seafloor, we started the tow-yo, tripping 3 bottles per each
ascent cycle. During this cast Marshall Schwartz (WHOI) was
our early cruise hero; he was tireless and instrumental in
troubleshooting and repairing an in situ electronic instrument
of the Hawaii group, with the sustained help of UH?s Yves
Plancherel and Brian Glazer, All sample (Niskin) bottles were
tripped. A significant nephaloid layer was observed near bottom
throughout cast. A secondary vertically narrow particle plume
was also observed for about the first half of the tow at ~2400
m. There was also sharp change in Eh at one location (descent
only)?may have been instrument problem because the baseline
appeared to have readjusted itself at this time.
March
6: Continuing toward Endeavour Segment (Way Point
1: 48o 12’N, 128o 58.9’W). Estimated time of arrival
is 1400 hrs (two hours from now). It is overcast, 9 degrees
C, with ~12 ft seas and ~22 knot winds.
Weather permitting we will do a tow-yo
(CTD-rosette) cast immediately upon arrival on station,
towing from WP 1 toward the SSW, essentially over the ridge
axis. I sea and wind conditions preclude a tow, we will commence
a series of vertical CTD-rosette casts. Watches are set and
all hands ready to go. Stay tuned.
March
5: Departed from UW dock at 0900 hr. Proceeded through
locks to Straights of Juan de Fuca.
The
following scientists are participating on the event response
cruise:
Back
to main event page: Endeavour,
March 2005
Note
there was another swarm of earthquakes in this same area in
October 2004.
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