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Ridge-Crest Processes
and Mechanisms of Global Change:
Synthesis of Oceanographic and
Satellite Observations

Updated: 4/5/95

Progress Reports: 1996 | 1997


Research towards a Ph.D. in Marine Geology and Geophysics within the School of Oceanography at the University of Washington is proposed involving the synthesis of oceanographic and satellite observations to better characterize global ridge-crest processes, including their potential role in affecting global change.

Recent ridge-crest research suggests that further investigation of submarine spreading centers will provide multi-disciplinary insights in the Earth system sciences, elucidating mechanisms of past and present global change. Researchers working in the Northeast Pacific are developing the capability to observe moderate (100 km) to fine (1 m) scale ridge-crest phenomena; the suite of measurements from such endeavors will be crucial to understanding the complex, interdisciplinary nature of the ridge-crest systems. But even with relatively fine-scale observation and mapping improving, a recent scientific re-evaluation concludes that the dynamics and distribution of ridge-crest systems remain poorly constrained, especially on global scales.

Satellite data may provide a convenient way to extend local, high-resolution oceanographic understanding to a global assessment of submarine ridge-crest activity. If ridge-crest processes result in sea surface expressions, there is a constellation of satellites aloft with the potential to survey the global distribution, dynamics, and net impact of Earth's ridge-crest systems.


While the scientific community has recognized and begun to study the impact of subaerial volcanic eruptions on climate, the global impact of submarine volcanic systems remains largely unexplored. Given the identification of volcanism as a key issue in understanding global climate change and the belief (based on geophysical extrapolation) that submarine eruptions are the most common on the planet, it is surprising that no one has ever observed an active, submarine eruption anywhere along the Earth's 75,000 km of mid-ocean ridge (Reynolds, 1994). Direct observation of activity at seafloor spreading centers is clearly problematic; most of the Earth's ocean ridges are submerged in thousands of meters of seawater. Nevertheless, hydrothermal vent systems were discovered in 1977, and since then multi-disciplinary research has begun to illuminate the general nature of submarine ridge-crest processes. Recent assessments, however, emphasize that thorough investigation of the systems' complexity, diversity, and potential global impact is warranted and only beginning.

Several recent, direct observations and fortuitous encounters at sea have spurred renewed interest in ridge research. Remotely-operated vehicles, submersibles piloted by humans, and traditional oceanographic instruments have provided photographic and in situ observations of apparently recent -- and sometimes catastrophic -- volcanism along submarine ridges; sonar has generated bathymetric maps which reveal annual and decadal changes in geologic features on the seafloor; and data from the Navy's SOund SUrveillance System (SOSUS) have supplemented ship-board seismic detection of earthquake activity along some of the oceans' ridges.

Opportunities for the use of satellite remote sensing in ridge-crest research are already emerging from basic oceanographic observations. Mechanisms like "megaplumes" may translate ridge-crest activity into a detectable surface expression. In fact, significant information may already be contained in the archives of the TOPEX/POSEIDON radar altimeter, as well as a host of other satellite sensors.

Global Impact of Ridge Processes:

In a recent workshop entitled "The Global Impact of Submarine Hydrothermal Systems," (Kadko et al, 1994), a multi-disciplinary group of scientists discussed the latest discoveries (see Table 1) and defined priorities for future research (see Table 2) in the search for possible links between ridge processes and the rest of the globe. The tables reveal a new scientific consensus that hydrothermal venting is a complex mechanism by which ridge-crest processes influence the Earth system in unexpected ways. Indeed, illustrations of the mid-ocean ridge are becoming increasingly complicated (see Figure 1); further characterization of sea-floor heat, mass, and energy fluxes will reveal additional, novel interactions between Earth systems previously-presumed disconnected.

Importantly, the workshop group (Kadko et al, 1994) considering the "Variations of Hydrothermal Activity in Space and Time" concluded that variability of hydrothermal systems on societal to orbital time scales is "possible, [and] potentially of great importance to questions of global change." Additionally, the group stated that on geologic time scales global variation is probable (in response to changing crustal generation rates) and regional variation is observed (in response to lithospheric rifting events).

Solid earth processes literally underlie the Earth's hydrothermal vent systems. Consequently, I propose to study the global impact of submarine ridge processes through participation in oceanographic observation and geological exploration. Simultaneously, I will consider the utility of satellite measurements in extending local and regional groundtruth to quantification of global impacts.

Oceanographic Research: Interests and Opportunities

The intense oceanographic research conducted on the Juan de Fuca Ridge by (JdFR) researchers concentrated in the Pacific Northwest (particularly at the University of Washington and the NOAA Pacific Marine Environmental Laboratory) affords an excellent opportunity to further scientific understanding of the ridge-crest system through conventional in situ techniques. As a graduate student at the University of Washington's School of Oceanography, I will strive to contribute to the geological and geophysical characterization of active spreading centers and hydrothermal vent systems primarily through conventional oceanographic observations. In the spring of 1995, in preparation for participation in a research cruise to the Endeavor Segment of the JdFR, I will be trained in the assimilation and processing of data from both the Alvin submersible and multi-beam and side-scan sonar: two technologies that produce the high-resolution maps integral to studies of seafloor geology. Also during the spring and summer, I will be employed by the Volcano Systems Center to ascertain current research and promote future collaborations in subaerial and submarine volcanology. With such skills and resources readied, I plan to make myself available throughout my graduate career for ship-board and laboratory research within the interdisciplinary community studying ridge and vent phenomena (primarily in the Northeast and East Pacific Ocean); I am most eager to participate in "field" work, helping to gain more detailed and comprehensive observations of ridge processes at sea.

During the observational process, I will remain engaged in the search for mechanisms -- both theoretical and observed -- integrating ridge processes within the operation of the Earth system as a whole. I believe there are many connections to be made, for the scientific literature contains surprisingly few hypotheses linking submarine volcanic systems to other systems, and consequently, to global change. In search of a historical analog to contemporary greenhouse gas increases, Owen and Rea (1985) argue that past CO2-induced climate changes. . . were caused by pulsations in the intensity of sea-floor hydrothermal activity induced by tectonic rearrangements of sea-floor spreading centers, and that the most obvious example of this process occurred in the early Eocene. Subsequently, Shaw and Moore (1988) discover that mid-ocean ridge magma production was coincident with El Niño events, and Daniel Walker (1988) correlates seismicity on the East Pacific Rise with the Southern Oscillation Index. Most recently (1995), Walker reinforces his hypothesis with further data.

However, each of the correlations made thus far have suffered from a lack of observed, causative mechanisms. While conventional oceanographic research has revealed some mechanisms (see Table 1) and will inevitably reveal more, the development of sea-floor observatories and the capability to detect and quickly respond to transient ridge-crest phenomena will inevitably improve our ability to study a notoriously inaccessible site, thereby increasing the likelihood of observing mechanisms linking ridge systems with the rest of the Earth.

Potential Contribution of Satellite Observations:

At the same time, the expense of ship-based oceanographic research provides an incentive to discern which small-scale, in situ observations might be extended globally through relatively cost-effective remote sensing technology. Hydrothermal vents occur on topographic highs along ridge-crests (Francheteau, 1983) and the cross-sectional area of the ridge reflects the underlying magmatic conditions (Macdonald, 1988; Scheirer, 1993). Since 99% of the variation in the Earth's mean sea surface is caused by the shape of the Earth's geoid (Koblinsky, 1993), which is predominantly influenced by density inhomogeneities in the mantle, a map of global hydrothermal activity could be inferred from steady state, mesoscale features in the geoid (and therefore the mean sea surface topography (Tsaoussi, 1994)). If the sea surface mimics (detectably) changes in the geoid due to bathymetric variations, areal extent of the submarine ridge network, and fluctuations in magmatic intensity (see Figure 1), then TOPEX/POSEIDON (and perhaps past or future satellite altimetry) data could be used to generate a global magmatic budget for the ridge systems.

Additionally, transient surface expressions (topographic or temperature anomalies) of megaplumes may be detectable from space. Preliminary investigation (Veirs, 1994 ) of TOPEX/POSEIDON data did not reveal (the only) event plumes observed in situ since the satellite's launch (Baker et al, 1993); however, an event of larger magnitude has been observed (Baker et al, 1986) and might be within the temporal coverage and resolving ability of past satellites. Additionally, in the high latitudes (above 60 degrees N or S latitude), the physical structure of the oceans may allow megaplumes to reach the surface (Lavelle, 1994), resulting in a thermal expression detectable by a host of heat-sensitive satellite instruments. Whether space-borne sensors have the sensitivity and spatio-temporal resolution to detect surface expressions of submarine volcanic activity from orbit awaits further exploration; the potential scientific benefit remains tremendous.

Part of the remote sensing scientists' predicament is the paucity of fine-scale (traditional oceanographic) observations of events which might be recorded by satellite sensors. In addition to assessment of the geological underpinnings of ridge systems, the lack of groundtruth motivates my fundamental interest in pursuing observational research via high-resolution multi-beam bathymetric and side-scan sonar surveys, and acquiring general in situ measurements (heat flux, biological, chemical, light attenuation, and salinity anomalies) and observations (from submersible, remotely operated vehicle, automated underwater vehicle, seismometers, and hydrophone arrays (SOund SUrveillance System).

With an enriched base of ridge observations in hand and an assessment of whether or not extant remote sensors have shed light on global ridge-crest studies, we will be much better equipped to specify the scientific objectives pertinent to the study of ridge-crest processes and mechanisms of global change. Simultaneously, the design of future EOS components, Earth Probes, Geostationary Earth Observation platforms, and other space-borne instruments will be better informed.


Baker, E.T., Massoth, G.J., and Feely, R.A. Cataclysmic hydrothermal venting on the Juan de Fuca Ridge. Nature, Vol. 329, 149-151, 10 Sept. 1987.

Baker, E.T., Massoth, G.J., Feeley, R.A., Embley, R.W., Thompson, R.E., and Burd, B.J. Hydrothermal Event Plumes from the CoAxial Seafloor Eruption Site, Juan de Fuca Ridge. June, 1994, Geophysical Research Letters.

Francheteau, J., and R.D. Ballard. The East Pacific Rise near 21oN, 13oN and 20oS: inferences for along-strike variability of axial processes of the Mid-Ocean Ridge. Earth and Planetary Science Letters 64:93-116, 1983.

Kadko, D., E. Baker, J. Alt, and J.Baross. RIDGE/VENTS Workshop: Global Impact of Submarine Hydrothermal Processes. Sept. 11-13, 1994.

Koblinsky, C. "Ocean Surface Topography and Circulation" reprinted from Atlas of Satellite Observations Related to Global Change (Gurney, R.J, Foster, J.L., and Parkinson, C.L., eds.), Cambridge University Press, 1993.

Lavelle, W. Personal communication, NOAA/PMEL, Sep.29, 1994.

Macdonald, K.C., and J.P. Fox. The axial summit graben and cross-sectional shape of the East Pacific Rise as indicators of axial magma chambers and recent volcanic eruptions. Earth and Planetary Science Letters, 88:119-131, 1988.

Owen, R.M., and D.K. Rea. Sea-Floor Hydrothermal Activity Links Climate to Tectonics: The Eocene Carbon Dioxide Greenhouse. Science, V. 227, 166-169, Jan. 11, 1985.

Reynolds, J. Aftermath of a sea-floor eruption. Nature, Vol. 367, p.115, 13 January, 1994.

Scheirer, D.S., and K.C. Macdonald. Variation in Cross-Sectional Area of the Axial Ridge Along the East Pacific Rise: Evidence for the Magmatic Budget of a Fast Spreading Center. Journal of Geophysical Research 98, 7871-7885, 1993.

Shaw, H.R., and J.G. Moore. Magmatic Heat and the El Nio Cycle. Eos, Vol. 69, Nov. 8, 1988.

Tsaoussi, L.S., and Koblinsky, C.J. An Error Covariance Model for Sea Surface Topography and Velocity Derived From TOPEX/POSEIDON Altimetry. Journal of Geophysical Research, June 29, 1994.

Veirs, S. Megaplume Meanderings: Searching for a Signal in the Sea. 1994.

Walker, D.A. Seismicity of the East Pacific Rise: Correlations With the Southern Oscillation Index? Eos, Vol. 69, Sep. 20, 1988.

Walker, D.A. More Evidence Indicates Link Between El Nios and Seismicity. Eos, Vol. 76, Jan. 24, 1995.


Preferred start date: September 1, 1995


spring-summer '95
Continued training and course work
fall '95-spring '96
Course requirements and active research begin

spring-summer '96
Research intensifies, opportunities at sea sought
fall '96-spring '97
thesis topic stated, research highly specified

spring-summer '97
Ship-board research continued
fall '97-spring '99
***Subsequent support sought from the National Science Foundation and other sources judged applicable***

June, 1999
Ph.D. dissertation completed

Return to first reference to Table 1 in text
Table 1:
Recent discoveries pertinent to assessment of the global impact of submarine hydrothermal systems.
Hypothetical Inter-System Links

Physical oceanographic implications
It has been postulated that the heat flux generated by ridge venting can have an impact upon local and basin-scale circulation.

Hydrothermal plumes
These are the "conveyor belts" that carry the products of seawater/basalt interactions, and vent larvae and nutrients, away from the ridge to the world ocean. It has been demonstrated that chemical scavenging and microbial activity within plumes have significance for the global geochemical cycle of some elements.

Entrainment of seawater by hydrothermal plumes
The entire ocean volume is entrained by this mechanism on the order of only 1000 years. This is comparable to the deep ocean residence time arising from the thermohaline circulation.

Occurrence of megaplumes
These release large quantities of heat and chemicals in single events as opposed to the "steady state" emissions usually observed at vent locations.

Off axis, lower temperature venting
Although the axial ridge systems are the focus of most hydrothermal studies, approximately 75% of the advective heat loss from cooling occurs on the ridge flanks. The implication for a large seawater flux on the flanks is clear; however, the chemical and biological significance of this flux is not known.

Hydrothermal input of iron
The role of iron as a potential limiting nutrient in the ocean productivity is considered significant in areas that are nitrate-rich but chlorophyll-depleted. the hydrothermal input of Fe may be the major global input of this element, implying that variability in hydrothermal output may be linked to variations in ocean productivity.

Return to first reference to Table 2 in text
Table 2:
Future research directions in assessing the global impact of submarine hydrothermal processes.

Figure 1:
The increasingly complex picture of a submarine ridge-crest system with an illustration of the possibility of detecting surface expressions of ridge processes with satellite sensors, like the TOPEX/POSEIDON radar altimeter.