Time Critical Studies

TCS overview

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Introduction to TCS

The Time-Critical Studies (TCS) Theme of Ridge 2000 focuses on observations of the immediate geochemical and geobiological consequences of magmatic and tectonic events along the global mid-ocean ridge system.

To date funding has centered on the Juan de Fuca and Gorda Ridges (Figure 1) which are within the range of the U.S. Navy’s Northeast Pacific Sound Surveillance System (SOSUS). NOAA’s T-Phase Monitoring Program has accessed SOSUS in real-time since 1993, providing the TCS community with detection of seismicity associated with eruptive or tectonic activity along these two ridges (Figure 2). This remote detection of earthquake swarms along the N.E. Pacific mid-ocean ridge coupled to NSF funding for pre-event staging of equipment and supplies has allowed directed and increasingly well-organized field responses to the event site. Major rapid and follow-up response cruises have been successfully mounted to 1993 CoAxial, 1996 and 2001 Gorda Ridge, the 1998 Axial Volcano, and 2001 Middle Valley magmatic episodes. The logistical approach required to study these events has been greatly facilitated by the RIDGE/Ridge 2000 programs and collaboration between university, NOAA and Canadian investigators. Not only have our studies of these events significantly impacted our ideas on the nature of crustal accretion, but they also have led to the discovery and preliminary documentation of a previously unrecognized biomass reservoir that lives below the seafloor and is swept out during these cataclysmic events, and to increased appreciation of the formation and thermal, chemical and biogeochemical implications of the “Event Plumes” commonly associated with seafloor magmatic events.

Insights from TCS

Some examples of new insights into the causes and implications of MOR magmatic (and tectonic) events that have been derived from TCS efforts include:

  • SOSUS system is an effective means of remotely detecting MOR seismic events (Figure 2);
  • SOSUS detected seismic events can be associated with episodes of significant magmatic activity within the crust and seafloor eruptions;
  • Events occur along the MOR with high frequency (>0.5 year within Northeast Pacific SOSUS system in 1993–2003);
  • Event plumes are commonly associated with seismic events; multiple event plumes can be released during a seismic event (Figure 3 and Figure 4). (At least 7 event plumes have been encountered in the Northeast Pacific MOR);
  • Thermochemical fluxes of event plumes have a distinct signature, differing qualitatively from those of chronic plumes;
  • Total thermochemical fluxes associated with events change rapidly with time following the event (Figure 5);
  • Subseafloor populations of extremophiles are released in association with events (Figure 6);
  • Lagrangian drifter floats (e.g., RAFOS) are an effective means of tracking event plumes for time series observations of physical and biogeochemical processes that ultimately link event thermochemical fluxes to the global ocean (Figure 4).
  • 210Po-210Pb and 210Pb-226Ra dating of young-appearing lavas allow determination of high-resolution eruption ages, eruption durations, and age offset with antecedent topography. They can also provide event “verification” in cases where no seismic data is available at suspected eruption locales (Figure 10 and Ridge 2000 Events 3, Spring 2005, 28-30).

New proposals sought

The Ridge 2000 Program is seeking proposals for innovative ways of augmenting and extending existing Time Critical Studies. Proposals are encouraged for all aspects of TCS, including event detection, rapid response efforts and instrument development. Even the most rapid shore-to-event site response will not be fast enough to record the earliest subsurface and water column expressions of magmatic events. The development of alternate ultra-rapid response methods are needed to extend the ship response efforts. These might range from air-droppable monitoring devices (e.g., vertical profilers, moorings, AUVs) to in situ sensors. The latter include continuous recording instruments, as well as more sophisticated autonomous instruments/vehicles that are pre-programmed to respond to signals detected by an array of physical, chemical and biological sensors. In this regard, Time Critical Studies should get a helping hand from the increasing instrument deployments at R2K’s Integrated Studies Sites. If a future event occurs at an established Integrated Studies Site, it is likely that the earliest perturbations will be captured by in situ monitoring instruments, providing data that could be acquired in no other way.

Presently, NSF will fund primarily Time Critical Studies supported by real-time detection capabilities through the Ridge 2000 program. Nevertheless, the usefulness of autonomous monitoring systems is clearly recognized. While unable to provide from the Ridge 2000 program, Ridge 2000 may assist such efforts with communication and other logistical support. Non-real-time detection uses autonomous hydrophone arrays (e.g. see PMEL VENTS Program seismicity page) to monitor activity along large sections of the mid-ocean ridge system that are not accessible to real-time monitoring (e.g. equatorial East Pacific Rise; Galapagos Spreading Center; northern Mid-Atlantic Ridge). The principal scientific purpose of such monitoring is to determine the size, distribution and frequency of events in different, complementary parts of the global mid-ocean ridge system. Such events, although interesting in their own right, may be important triggers, precursors or complements to activity recorded in more detail at the Integrated Studies Site. For instance, the recovery of data from the EPR autonomous hydrophone arrays indicated a significant seismic event near 8° 37' N EPR, that led to a “ship-of-opportunity” delayed response to this site (Bohnenstiehl et al. 2003). Similarly a delayed response was mounted to investigate possible magmatic effects from a significant earthquake swarm at the hydrothermally active Lucky Strike segment in 2001 that was identified from recovered MAR autonomous hydrophone arrays.

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