Monterey Bay Aquarium Research Institute

Cruise History and Purpose

Keck Expedition 2004

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A series of primers and essays by the cruise participants

Cruise Information (Back to Top)

Cruise Dates: July 30, 2004 - August 12, 2004
Cruise Location: Endeavour Segment
Chief Scientists: Will Wilcock and Paul McGill

The purpose of Leg 2 of this Expedition is to install and/or service seismometers for the Keck Experiment. This project is collaborative with the University of Washington and the University of Oregon. The results of the seismic study will be integrated with chemical and biological studies to understand the linkages between deformation (earthquakes), changes in fluid flow (both hydrothermal and diffusive), and microbial blooms. The seismometers used in this study have been designed by MBARI's Ridge Observatory effort, the Margin Seismology program and the ongoing MOBB project. Eight seismometers will be recovered and redeployed on the Endeavour Segment. Two new broadband sites will be established--one on the Explorer plate and a second near the Nootka fault zone. Another three seismonuments will be deployed on Nootka. WHOI will also be deploying a mooring-based seismometer this summer to support the same experiment. Elevators will be at the Broadband sites. 

Equipment:
We will require three elevators--one to shuttle the broadband electonics package at the Endeavour broadband site. The two others will need additional ballast to carry the broadband beads and funnel along with the electronics package at the new broadband installations. The seismometer deployments will all be marked with Homers provided by project funds. All installation will require 3 serial lines  for communications. We will need two manipulators on vehicle. Need water lifter, new suction pump and bead  hopper rigged for elevator deployment. Need cable run to have GPS in control room.

Participants:
Paul McGill (CoChief scientist); Will Willcock (UW CoChief  Scientist); Debra Stakes, Tony Ramirez, Ben Potter, Mike Conway, Andrew Barclay (UW), Doug Toomey (U OR), Troy Durant (U OR), Taimi Mulder (PGC, Victoria), John Rostau (PGC, Victoria).
 
Region Desc:    (Click on map for larger image of the expedition area.)                 
Planned Track Desc:
Seven Endeavour short period sites need to have instruments recovered and redeployed:
KEMO 47.9N 129.1W 2285m C3 Mothra corehole    
KEMF  47.9N 129.1W 2202m C2 Main Field corehole
KESQ  48.N 129.1W 2164m C1 Sasquatch corehole
KENW 48.0N 129.1W 2160m C6 NW flank corehole
KENE  48.1N 129.1W 2340m C5 NE flank corehole
KESW 47.9N 129.1W 2381m C7 SW flank seismonument    
KESE  47.9N 129.1W 2342m C4 SE flank seismonument
One Endeavour broadband site needs to have electronics/battery package replaced: 
KEBB  47.9N 129.1W 2376m B11 SW flank broadband
New broadband on Explorer plate at approximately 49.5N and 129 W
New broadband site and three new seismonuments on Nootka "Worm Hovel" Seep:
Nootka Broadband--49:31:00N; 127:42:00
Three seismonuments
49:18:00N; 127:34:00W
49:24:00N; 127:42:00W
49:19:00N; 127:50:00W

Cruise History and Background (Back to Top)

The five-year collaborative Keck Research Program  is a proto-type NEPTUNE Experiment in that achievement of the overarching objectives will require the full capabilities of a regional cabled observatory and many years to reach fruition.  The ultimate principal objective is to test the hypothesis that plate tectonically modulated microbial productivity at the bottom of the ocean may be a significant fraction of the photosynthetically generated productivity near the top of the ocean. At present there is no data on the seafloor sources.  Our near-term approach is to develop and deploy sensors that allow simultaneous detection of deformation, fluid/chemical fluxes, and microbial output associated with three types of plate boundaries adjacent to one another. The northern boundaries of the Juan de Fuca plate are the focus of the effort for three reasons: 1) they are spatially condensed, well-defined examples of a ridge, a transform fault, and a subduction complex, 2) they are close to major ports, and, 3) the entire experiment will be central to the Phase I installation by Canada of NEPTUNE.
In close collaboration, scientists and engineers from MBARI and the UW will have placed on all three plate margin types a suite of short period and broad band seismometers. In addition, UW and Scripps scientists will expand deployment of a variety of fluid flow sensors and chemical monitors in co-located coordination with the seismometer arrays by the end of 2004 field season. It is intended that these networks will continue to operate in an autonomous, annual servicing mode until they can be connected to the regional cabled observatory in 2007-8.  
As the final, and key element in the program, Keck funds are also supporting development of the “Deep Environmental Sampling Processor” (D-ESP), an adaptation of Chris Scholin’s original instrument (link to esp pages).  The D-ESP will be 4000m-rated ESP that will be crucial to allow real-time microbial investigations of microbial populations in real, or near-real-time when connected to the cabled network. Testing and deployment of this system is scheduled for late 2005 or mid summer 2006.  With completion of the D-ESP deployments in the NE Pacific, all components of the entire experiment will be ready for use on the submarine network, and several years of experience with the experimental approaches will have been digested by the time NEPTUNE is operational.

This project is collaborative with the University of Washington and the University of Oregon. The results of the seismic study will be integrated with chemical and biological studies to understand the linkages between deformation (earthquakes), changes in fluid flow (both hydrothermal and diffusive), and microbial blooms. The seismometers used in this study have been designed by MBARI's Ridge Observatory effort, the Margin Seismology program and the ongoing MOBB project. Eight seismometers will be recovered and redeployed on the Endeavour Segment. Two new broadband sites will be established--one on the Explorer plate and a second near the Nootka fault zone. Another three seismonuments will be deployed on Nootka. WHOI will also be deploying a mooring-based seismometer this summer to support the same experiment. Elevators will be at the Broadband sites. 

Primer on Earthquakes by Doug Toomey (Back to Top)

Earthquakes :

The Endeavour region is both tectonically and magmatically active. Magma delivered to seafloor volcanoes provides the heat source for profound hydrothermal activity. Each of these processes -- tectonism, magmatism and hydrothermal heating/cooling -- give rise to stresses within the newly formed oceanic crust. Thus we expect to see a wide variety of earthquakes, roughly categorized as follows:

  • Tectonic earthquakes are the result of slip on faults or cracks within solid rock. Local events will have high frequency content (>1Hz) and will have sharp compressional (P) and shear (S) arrivals.
  • Volcanic earthquakes tend to be more difficult to classify. Given the inflation and deflation of volcanoes, they also cause stresses within the surrounding rock, which results in slip on faults and cracks. Visually, these events look like tectonic earthquakes, but they are called volcano-tectonic earthquakes. The reason being that the cause of the stress is volcanic in nature. Volcano-tectonic earthquakes can also be caused by the rapidly varying thermal structure that surrounds volcanoes.
  • Volcanic or Harmonic Tremor. The movement of fluids -- either hydrothermal or magmatic in origin -- can give rise to harmonic signals with frequencies of 1-10 Hz. These events can last from seconds to many tens of minutes, even hours in some cases. It would be very exciting to record a sequence of harmonic tremor, as that would be a clear indication of active fluids movement.

  • Long Period or Very Long Period Signals.In recent years seismologists and volcanologists began to record broadband seismic data near volcanically active regions. A broadband seismometer is capable of recording ground motion between 0.01-50 Hz (100 seconds to 1/50th of a second). A unique aspect of our experiment is the deployment of a broadband seismometer near the ridge crest. We hope that this instrument will record signals related to magma movement. Typical signals will be around periods of 10 to 30 s, with unknown durations. Broadband seismometers also provide good recordings of regional and teleseismic (distant, large) events.

Historic perspective on seismic observatory development (Back to Top)

by Taimi Mulder on the Western Flyer

Remote seismic observatories have always been detailed setups. The year I ran the geophysical observatory at Alert, Northwest Territory, Canada, (that's 82 degrees north for you southern dwellers) there was an entire small building devoted to the geophysical equipment and maintenance equipment. The shed outside held several snow shovels, a broom, a wheelbarrow, and other assorted shed-type tools. Inside was a mini electronics workshop consisting of a soldering iron, several drawers full of solder, wire, tools, and miscellaneous bits. To the left of that was a rack of electronics and other mysterious items. This included a portable clock that had to be taken to the HAM radio booth to set the time (which depended on actually being able to receive a good enough signal to use - this was NOT a daily occurrence). The remaining two rooms housed the geomagnetic instruments and the seismic vault. The seismic vault was dug into the permafrost on the back of a hillside. It contained 3 concrete piers (approx 5 ft wide x 6 ft long x 3 ft high) and 7 seismometers: 3 short period, 3 long period, and 1 very long period seismometer, occupying each of the 3 concrete piers. It was dark and heated to -5 degrees Celsius. The data was recorded on photographic paper that I had to develop, hang to dry, and interpret every day. This required a darkroom (heated to something substantially warmer than -5 Celsius!), and a computer. I was very fortunate in that I was able to send data south via microwave link during a one-half-hour time slot each day. Often I was not able to send all the data each day when the communication link was poor. The station operators before me had to send the data out via telex that involved specific formatting of the message. This was a well planned and well built observatory with high quality instrumentation that was run by a succession of intrepid individuals hired by the Geological Survey of Canada to maintain the site and send the data out in as timely a fashion as possible given the constraints of technology.

As I sit here at the computer, floating in the middle of the ocean, it occurs to me that remote observatories, either in the high arctic, on a distant mountain top, or on the ocean bottom are not all that dissimilar. I am struck by the similarities, especially, between the quality of seismic observatory installation in Alert, in the high Arctic, and the installation we are building on the ocean bottom. Technology has changed but the challenges of operating in a difficult environment remain. Communications is still the biggest obstacle. The science party gathered onboard this ship have a beautiful blend of engineering and science all in one small space. There's an electronics lab on board that puts my bench at Alert to shame. There is daily feedback, modification, and correction of problems with equipment and methods of deployment. As in the high arctic, your work and life may depend on attention to detail. Costs are high and the work needs to last. Timing of the seismic data resides with a clock in the sensor/datalogger assembly, which drifts slowly over the year either running a bit fast or a bit slow. As in the Arctic, the seismic data needs to be corrected for drift between clock corrections. The seismometers are dug into the seafloor for good coupling with the earth, just as the seismic vault at Alert was dug into the permafrost. The attached figure KXBB_install.jpg (18498 bytes) shows the Explorer plate broadband seismometer being lowered into a caisson dug into the seafloor. Data recording abilities have improved a thousand-fold. Analog data requiring a lot of preparation by the station operator before the earthquakes could even be seen has morphed into gigabytes of digital data stored on hard disks on the ocean floor, no human operator in sight. I was astounded when the first seismometer and data logger came aboard after a year at the bottom of the ocean. Not only did the instruments look almost as pristine as the ones we were preparing to deploy, when the data was downloaded the background noise level was the same as many of our stations in western Canada, and much better than the remote mountaintop stations being hammered by wind and waves on the western coast of Vancouver Island. There are earthquakes galore on the data we are pulling up. And we recovered a year's worth of data from every site. The quality of the work being done out here impresses me: high site installation standards resulting in low noise sites, robust instrumentation and data collection. The site installation itself can take less time than installing a comparable seismic observatory vault on land. The remaining challenge: communication...in real time. Neptune cable, here we come!

Biogeochemical Linkages Cruise (Aug 15-25) (Back to Top)

Chief Scientist: Peter Girguis

Purpose:

This is a multidisciplinary effort to examine the biogeochemical linkages at hydrothermal vent systems along the Endeavour segment of the Juan de Fuca ridge and possibly off the coast of Vancouver Island in the vicinity of the Nootka fault. There are three main goals of this biogeochemical linkages program. The first goal includes collecting an extensive series of water samples to examine the linkages between hydrothermal vent fluid chemistry and the concomitant distribution and abundance of microbial communities in the Endeavour main field. These samples will be used to assess the distribution and abundance of microbial communities at the Endeavour segment, as well as provide a diversity of samples for development of the ESP. The second goal is to survey the Endeavour main vent field for any qualitative changes in sulfide structure features, as well as flow rates, and to document these changes via video and still frame digital photography. The third goal is to recover two prototype instruments that were deployed in the walls of diffusely venting sulfide chimneys in the Endeavour vent Field in 2003. We may choose to redeploy one of these instruments into the same coreholes, and recover these instruments will on a follow-on Thompson-Ropos cruise in September 2004. The ultimate goal of this experiment is to explore the geochemical constraints on the distribution and abudance of microbial assemblages. Should time weather and time permit, we hope to further explore the middle valley sedimented vent field or the Nootka fracture zone, near the Maquinna mud volcano and at the junction of the Nootka Transform Fault and accretionary margin in ~ 2500 m water, for signs of hydrocarbon seepage and methane venting.

ExpdChiefScientist: Peter Girguis

ExpdPrincipalInvestigator: Ed DeLong

ScheduledStartDtg: 2004-08-16 0600 Local Moss Landing time

ScheduledEndDtg: 2004-08-26 2000 Local Moss Landing time

The details of our dives are currently being worked out. In general, the first five dives will be along the Endeavour segment (approx. 47.40-48.20N by 129.20-128.50W). The first two dives will be at the main Endeavour field, collecting water and rock samples, as well as temperature data and recovering one sulfide insert. Next, we will head north along the segment and visit the mothra vent fields and two other lesser visited sites (for a total of five dives along this segment). At each site, we intend to collect water and rock samples, as well as temperature data. At lesser visited sites, we intend to take extensive video and still images in order to photomosaic the structures. Should there be any remaining dives, we hope to visit the middle valley sedimented vent fields, and possibly continue north towards Nootka fault, off the coast of Vancouver. Details of LAT and LONG for each site will be provided shortly.

Aug 30-Sept 8                   (Back to Top)

The Juan de Fuca Ridge is the intermediate-spreading rate example chosen for intensive study by the RIDGE2000 program of the US National Science Foundation. At a Fall 2003 meeting of that program, high priority was given to improving geological mapping and igneous petrological and geochemical studies of basalts from this ridge. This cruise helps meet that need by continuing work at the Cleft and Endeavour segments. At both sites, this cruise will be dedicated to collecting basalt lavas based on high-resolution bathymetric maps that enable the relationships between magma composition and tectonic setting to be understood. 
The last five dives of Leg 4 are a NURP-funded project to Jim Gill that focuses on the Endeavor Segment. Although the Endeavour segment is less active volcanically than Cleft, its entire edifice is less than 50,000 years old based on the spreading rate, and 226Ra excesses in samples of uncertain location suggest that basalts have been erupted on both the axial valley floor and adjacent ridge flanks within the past 8000 years. We will collect samples and document lava morphologies and relative ages across a 5 km long E-W transect perpendicular to the ridge between the Salty Dawg and High Rise vent fields. Special attention will be given to the valley floor and west wall. These basalts will be analyzed for major and trace elements, volatiles, Sr-Nd-Pb-Hf isotopes, and U-series disequilibria. We will use this information to: characterize the "FOZO-type" mantle source anomaly which results in the atypical chemical composition of the basalts (a variety of "E-MORB"); determine the melting processes involved (depth, volatile content, nature of the magmatic plumbing systems, time scale of melting); evaluate the roles of the sub-axial magma chamber (spatial patterns of differentiation and mixing); and compare on-axis with off-axis magma compositions and processes. Integrating this information with tectonics will be done through collaboration with scientists at the University of Washington. 

The purpose of the first two dives of Leg 4 of the expedition are to complete sampling basalts from off-axis sites on the south Cleft region of the Juan de Fuca Ridge. Our previous work has suggested that the lavas erupted either off-axis or very near the Blanco Fracture Zone are derived from the cooler fringes of an axial magma chamber. These results are counter to the broadly-held "split volcano" model for intermediate rate ridges such as the Juan de Fuca Ridge. We will specifically look for geological evidence of off-axis volcanism thickening the crust such as suggested by recent multichannel seismic surveys. The potential of significant volumes of off-axis volcanism impacts the range of lava chemistry, impacts models of the distribution of megnetism and greatly expands the potential for microbial habitat.