Field investigations using high temperature chemical sensor with DSV Alvin conducted in 1999 (AT 03-39) shortly after a subseafloor seismic/magmatic event. Subsequent measurements in the same area (2005, AT 11-31) with a modified array of chemical sensors, confirmed substantive changes in redox state and acidity of the hydrothermal vent fluids. The results will help us better understand temporal variability in subseafloor reaction zones at depth as well as the linkage between high temperature hydrothermal fluids and their more biologically active diffuse flow fluids in the in vent/chimney environment. Image courtesy of K. Ding and W. E. Seyfried, Jr.

3. PLAN FOR THE NEXT PHASE OF R2K RESEARCH

The overall vision for the next phase of R2K is one where true integration of spreading center research results takes precedence and moves the community forward to whole system understanding. The emphasis on obtaining multi-disciplinary data that entailed major effort during the first phase will now be balanced by efforts to enhance the cross-disciplinary analyses that can illuminate linked processes. To that end, the Steering Committee has developed a plan for ramping up a new ISS, where key physical controls differ from the initial three ISS, and transitioning some of the latter to a phase that emphasizes science integration and inter-site comparison. TCS will adjust its scope to take advantage of new observatory assets that are expected to become operational in the near future.

3.1 Examples of Integrations for which the R2K Community is excellently poised

• Co-located microseismicity, fluid temperature and chemistry, and at least some biological data are in hand at both EPR and Endeavour; some initial analyses having been presented but in-depth integration is truly getting underway as of late 2006/early2007. These local integrations are now taking place in the context of segment scale structure (and any variability thereof), drawing from the significant base of geophysical and petrological understandings obtained during R2K (and RIDGE).
• Lau and Endeavour sites both exhibit variation in source rock composition, which appears to influence diversity of vent fluid chemistry and distributions of organisms. Aspects of Lau substrate variation and ecosystem impacts were mentioned in prior sections. At Endeavour ISS, fine-scale sampling of basalt, fluid and sulfide is allowing a diverse group of scientists to rule out a major role for sediments (using Pb isotopes) as the cause of variability. These data will also be used to model the scale of hydrothermal circulation relative to the scale of basalt heterogeneity: i.e., the degree to which the hydrothermal system "averages" the diversity seen in basalts.
• Ecological and genetic barriers to dispersal have been demonstrated to exist for many vent species (including microbes and invertebrates presumed to be highly dispersive). The extent to which topographically-influenced hydrodynamic mechanisms may help retain larvae near natal sites is now ripe for documentation.

3.2 Integrated Studies Sites: Plan for a New Site and Transitioning Initial ISS

The R2K program was designed to enable comparison of detailed results from a small number of Integrated Studies Sites, each representing a different set of controlling parameters of the system. This approach was considered the optimal way to tease out how differing rates of energy (heat, mass transfer) and chemical flow/exchange (crustal composition, fluid-rock reactions, biological intermediaries) affect ecosystem development and evolution along Earth's oceanic spreading centers. In addition to illuminating the biological consequences, these studies document the extent of interplay between various geological processes that constitute plate rifting and crustal accretion/evolution.

At the April 2007 Steering Committee (StCom) meeting and in subsequent email exchanges, the strategy for taking on a new ISS and transitioning initial ISS was developed. StCom consensus is that both the East Pacific Rise and Endeavour ISS have obtained sufficient multi- and inter-disciplinary data that they are ready to transition to a phase where science integration takes priority within R2K. This will allow a new ISS to be ramped up so that comparisons available at site(s) other than the current Pacific ISSs can be made, while the science integration at the heart of program continues with existing data.

R2K will fund seagoing investigations at 'active' ISS only; proposals for seagoing investigations at 'legacy' sites must be submitted to core OCE programs after the ISS transitions from active status within R2K.

R2K will continue to support science integration proposals for both active and legacy ISS. Highest priority will be given to proposals that advance understanding of links between various components of the geo-hydro-bio-chemical systems at ISS(s). For ISS that have transitioned from active to legacy status, this will entail use of existing data and ongoing modeling. Such analyses are encouraged, where relevant, to include inter-ISS comparison.

EPR will transition from active status in 2008. Endeavour will transition in 2009. Acceptance of Endeavour proposals by R2K through Jan 2008 is intended to encourage efforts that link to, supplement, or add value to data that will begin streaming from NEPTUNE Canada.

A new ISS on the Mid-Atlantic Ridge is planned for the ~35-37.5°N area, where ongoing InterRidge efforts and prior US consensus have embraced the site for integrated studies (Providence Meeting Report (http://www.ridge2000.org/science/meetings/index.php)). Since the early planning stages of R2K, there has been very strong interest in the Mid-Atlantic Ridge. Its slow-spreading rate is thought to control axial characteristics that differ notably from the faster-spreading Pacific ridges. However, only with comparable data at both types of spreading centers can hypotheses on factors such as melt supply, time scale for eruptive activity, and corresponding effects of such temporal forcing differences on ecosystem development and evolution be tested. In addition to the Lucky Strike hydrothermal field, exposures of serpentinized peridotite in the axial valley in the next segment south host the Rainbow hydrothermal system, which can provide crucial tests of the relationship between host-rock chemistry and microbial processes, and abiotic mechanisms for hydrocarbon formation.

3.3 Modeling/Experimental Opportunities

At the 2006 Theoretical Institute "Modeling Mid-Ocean Ridge Hydrothermal Processes: Magma to Microbe", there was general consensus that quantitative models are essential for developing and verifying conceptual models of axial biological, chemical, and physical interactions because key regions of the crust are not directly accessible for study. While numerical experiments have been used for several years to constrain physical and chemical processes, such approaches have not been extensively utilized as biologists investigate life in hydrothermal environments. The R2K community is now in a position to develop models that quantitatively relate biological activity and community structure to distribution and metabolic activity to fluid flow and chemical composition. The hydrothermal system models will need to encompass a wide range of spatial scales, including the millimeter to centimeter scale of microbial processes, meter scale of biological communities, vent field scale of kilometers, and the crustal scale. The models must also address a wide range of temporal scales, ranging from minutes to millions of years. Short time scales reflect times on which microbial, geochemical, and hydrological processes may act, while the largest time scales reflect processes of ridge reorganization due to tectonic events or changes in magma supply. The R2K community is in a strong position to lay the most appropriate groundwork that can eventually lead to full realization of these goals.

Three-dimensional, time-dependent models are now realizable for some systems; significant insights are expected with such approaches in, for example, vent-proximal hydrodynamics. The influence of larval behavior on dispersal and retention in flow is being addressed by recent modeling and this relates to the question of whether vent populations are open or closed. Modeling of population dynamics and of metapopulations, such as employed in other areas of biology, has recently been applied to vent species.

Regional geodynamic modeling will continue to be important for maximizing the return on R2K field work that targets ridge segmentation, mantle structure, and geochemical source variability. Numerical experiments can provide crucial tests of conceptual models as well as determining the range of physical or chemical parameters that could produce observed signals. First-phase R2K experiments at each of the current ISS lend themselves to associated modeling of mantle and crustal generation processes. Two R2K postdocs target this type of modeling and a funded experimental study will contribute constraints (Table 4). Members of some seagoing teams are also tackling site-specific modeling that in some cases pushes the forefront of coupled (for example, mantle flow/anisotropy or mantle flow/geochemistry) geodynamic modeling currently being undertaken throughout the Geoscience community.

3.4 Time Critical Studies- vision for the next phase

The pursuits of the rapid response program in terms of its first-phase goals and primary geographic focus continue to be appropriate. There is potential for expanding efforts to incorporate TCS capability in the Atlantic with InterRidge partners, if current European Union plans to deploy a real-time observatory capability come to fruition. This will be a topic of discussion at the Mid Atlantic Ridge ISS Implementation Plan workshop in March 2008.

The current TCS group recommends continuing to target 4 main ridge processes:

Mega-plume formation. This was the basis of the currently-funded TCS proposal, but mega-plumes are difficult to intercept. Rapid response teams have not encountered one during any cruises since R2K began. Because they provide a critical link to the subseafloor biosphere (microbial), mega-plumes are still considered a high priority target.

Heat and Chemical flux. Magmatic volatiles are controlling components of hydrothermal chemistry. Obtaining samples during or immediately following a diking event or an eruption is the only way to document the magmatic-hydrothermal evolutionary cycle of volatiles.

Modes of crustal accretion. Catching a seafloor eruption in process can shed new light on how flows are emplaced and on what time scales. The location of eruptive vents and their relation to overall volcanic structure and seismic activity can be assessed. There is some documentation of the relationships between seismicity, dike injection, and eruption but the datasets in hand are limited.

Mega-faunal community dynamics. Catching the biological response to an eruption has always been a dominant driver for rapid response efforts. Parts of the system are thought to evolve on time scales of hours to days when an axial event (cracking, magma injection/eruption) occurs. How do the fauna react and how do the communities evolve with time? What is the relation between eruptions, microbial community succession, and megafaunal community dynamics? Early observations are critical due to chemical evolution and faunal recruitment.

Geographic areas that are high priority for future rapid response efforts are those where basic mapping is sufficient and, preferably, where instruments have been in place to provide correlative measurements.

As the Program gets underway in the second phase, the Time Critical Studies component should be assessed. The potential for adding to the scope by including rapid responses in the Atlantic, if a collaborative approach with InterRidge partners is feasible, has already been mentioned. Collaboration with the NOAA Vents program is expected to continue but the current agreement for cost sharing should be revisited soon. NOAA Vents priorities have evolved over the years, so a new balance in personnel/ship sharing may be warranted. An advantage is that as the plan is updated, new researchers will have the opportunity to join the TCS team as a new proposal is funded.

3.5 Need for a fluid chemistry database.

The need for a mechanism for sharing ISS fluid chemistry data, similar to what exists for rock data, has become crucial. Awareness of this developing need existed in 2005. After discussion at the Vancouver Community Meeting and subsequent AGU meeting, members of the community put together an initial proposal for a fully-searchable, referenced hydrothermal vent fluid chemistry database (that would have included much more than R2K data), but it was not successful. The lack of a working data sharing mechanism needs to be addressed so that, for example, biologists can access the available data and relate observed changes in microbial or macro faunal behavior to evolution (or constancy) in fluid chemistry. At the same time, biochemical reactions that are documented in an area need to be made available to fluid chemists so they can factor that process into their model of the system. And geochemists may need access to the fluid chemistry data in order to understand alteration of their samples. Following the Oct. 2007 StCom meeting, the discussion of what is required for workable fluid chemistry data sharing is being revisited. It is crucial that this be resolved soon since the hydrothermal fluids are a key link to understanding exchange between the crust, biological communities, and the oceans.

3.6 Challenges and Decisions for the Next Phase.

Budget and Infrastructure Availability Limitations. The original vision for R2K was to have comparable datasets and analyses for half a dozen different types of spreading centers (slow- and fast-spreading, hot spot influenced, sedimented, back-arc) and this appeared viable based on NSF budget projections in 2000. Cuts in OCE budget growth rate, increased ship costs, delays in infrastructure availability (specialized ships and instrumentation), and the usual challenge of getting desired topics funded through a competitive proposal process, all contribute to the need to reduce the range of system types that the Program tackles over the envisioned 10-yr span. Some of the field projects outlined in the EPR and Endeavour Implementation Plans have not been possible thus far for one or more of the above reasons.

At the mid-term of the Program, it appears likely that some aspect(s) of the mantle-to-microbe system at each of the ISS will not be able to be addressed directly within the R2K program. Interpreting a given ISS as a whole will require having sufficient understanding of first principles, obtained from one or two sites, and being able to use that to bridge a current gap in measurements the site. Updates to ISS implementation plans (and development of any new ones) will need to focus strongly on what measurements can only be made at a particular site or, for example, what exact comparisons between sites are crucial for documenting the control of a given physical, chemical, biological, or oceanographic factor on system evolution.

StCom determination of which sites should be transitioned to 'legacy' status included assessment of the strength of framework that existing data provides, such that strong proposals to core programs could be developed in the future, as warranted. The idea is that inter-disciplinary scientific goals at legacy sites would be attainable as future core-funded projects document additional (or more fully) components of the system. Interest in multi-disciplinary research at both EPR and Endeavour sites remains very strong.

Next R2K Focus(es). The StCom plan to begin ISS work on the Mid-Atlantic Ridge (MAR) was based on the strong interest in understanding how slow-spreading systems compare to faster-spreading systems. The reason for moving ahead with the decision, without re-opening full-community discussions about other possible ISS, was both pragmatic and a result of prior recommendations. A specific section of the spreading center had already been selected, some members of the community were already involved in ongoing InterRidge studies there, significant progress can be achieved during the remainder of the Program, and the level of interest in Atlantic work was documented to be strong (number of MAR ISS proposals submitted at the start of R2K, amount of ongoing US research on the MAR). At the same time, StCom clearly saw the need for renewed discussion of what other exciting opportunities the Program is ideally suited to tackle, particularly in light of findings of the past 5-7 years.

There may be opportunity to make inroads on an additional focus during the second phase of R2K. In late 2008, there will be a call for white papers outlining a potential final R2K focus 'area' that could follow ramp-up at the MAR ISS. The community will be encouraged to consider a range of possibilities. A new ISS at a different type of spreading center will almost certainly be proposed as community interest in such is strong. In light of the limited time and budget that will be available near the end of the program, other ways of enhancing understanding of the linkages within the spreading/hydrothermal system will be seriously considered (a series of focused laboratory experiments? an intensive suite of linked numerical models?). The full community will have access to all white papers and a forum for comments/discussion will be maintained for a set period. The selection process for the final focus area will be designed based on the forum feedback, with possibilities including a community workshop for consensus development, a community vote to guide a StCom decision, which again would be followed by a community feedback period. If there is a consensus workshop held in early 2009, the selection and comment period could be complete by Summer, and an Implementation Plan meeting would be held in early Fall 2009. First proposals for this topic would be invited Jan 15, 2010, and funds could be in hand for such work throughout most of the 2010-2012 period.

Next Chair of the Steering Committee. The ~3-year rotation period for the Chair of the Steering Committee is expected to be retained, with the term of the current Chair finishing near the end of 2008. A call for nominations/applications for the next Chair was made to the community in August, 2007, and an Eos ad was run the first half of September. By late October just a single applicant was in hand, although a general expression of interest from a second potential candidate was known. StCom and NSF agreed that having 2 or more candidates was important so the effort to solicit applicants was renewed. At this time there are 2 strong candidates who have applied. StCom will complete the selection of the next Chair when the recommendations of the Program Review Panel are known. If there are particular strengths that could help in addressing Panel suggestions, these will be factored into the selection.