UCSB Geological Sciences -Ken Macdonald- Research

General Research Interests

My research as a marine geophysicist has focused primarily on the mid-ocean ridge, the most active geologic feature on the planet, using whatever geophysical or geological tools I could employ to study the tectonics of this complex system. Some the areas I see as promising for future research include: the fundamental segmentation of mid-ocean ridges and the significance of ridge-axis discontinuities including overlapping spreading centers to the creation of oceanic crust, the processes responsible for the creation and deformation of oceanic crust particularly through the study of marine magnetic anomalies and quantitative geomorphology, and the importance of hydrothermal vent systems to the heat balance of the ridge. So much is still not known that I look forward to many more exciting discoveries and insights in the future as we continue to explore the mid-ocean ridge.
The mid-ocean ridge offers extraordinary opportunities for interdisciplinary research. The supply of magma to the ridge controls the geochemistry of erupted lavas, the magnetization of the crust and the location of seafloor hydrothermal systems; which in turn control the distribution of exotic benthic faunal communities. For example, if one plots the occurrence of hydrothermal vents versus axial depth, cross-sectional area or even crustal magnetization, there is an excellent correlation! These linkages provide rich opportunities for cross-disciplinary research.

	Current Projects
	I will be using ALVIN to dive on an area ~20 km west of the East Pacific Rise near 9° 30'N. An old ALVIN test dive in this area shows a near blizzard of presumably biological activity in the water, reminiscent of the bacterial snow storm during the 1991 eruption on the axis. We will dive in this area to investigate this finding and to study the structural control on hydrothermal activity in the off-axis environment. Significant hydrothermal activity off-axis on a fast spreading ridge has eluded detection so far, so this study should be exciting. We will also study aspects of normal faulting in young oceanic lithosphere.
	In January 2003, we go to sea to study the south San Clemente Basin in the southern California Borderlands. There is a fossil spreading center or pull apart basin here which may exhibit some persistent extensional activity. Post-Miocene rifting in the Borderland, contemporaneous with Gulf of California rifting, raises important questions regarding the coupling of Pacific lithosphere with North America, microplate tectonics, and the evolution of oblique-transform plate boundaries.
	The East Pacific Rise At its largest scale, the Integrated Studies Site centered near 10ºN spans the East Pacific Rise from just north of the Clipperton transform fault to the Siqueiros transform fault (8º-11ºN), encompassing 3 widely contrasting second-order segments. Only the central segment from the 9ºN OSC to Clipperton is mapped at a fine scale within a narrow swath along part of the axis (primarily DSL-120 side scan sonar). These observations have led to a widely- –debated conceptual model for the geological context of hydrothermal venting. This model has yet to be tested and verified by observations on the adjacent segments of the ridge. The segment north of Clipperton is a narrow razor-back ridge with small cross-sectional area; Clipperton-9ºN OSC is a broad segment with large cross-sectional area; 9ºN-Siquieros is horst-like in profile and has the greatest cross-sectional area. We propose to make the observations necessary to test the model at these contrasting yet adjoining ridge segments. We plan to address three questions: 1. Does the pattern seen at 9º08’-54’N, in which hydrothermal activity is enhanced along axial collapse troughs near 3rd order segment centers and diminished near segment ends where the volcanic morphology is dominantly lava mounds, hold for the adjacent segments in the ISS? 2. Can the fine scale segmentation of the ridge axis (3rd order and finer) be detected off-axis, giving us a better idea of how long these fine scale segments (and associated patterns of hydrothermal and volcanic activity) persist? 3. How have the hydrothermal plumes changed in location, intensity, and composition over the last decade from 9º-11ºN? A simultaneous DSL-120A/plume survey along the ridge axis from 8º-11ºN, combined with EM300 mapping and CTD casts would provide all the data needed for a detailed comparison of volcanic morphology and ridge segmentation to the composition and intensity of hydrothermal plumes. The DSL-120A will be used to provide fine-scale imaging of the individual volcanic vents and fissures in the ~1 km wide axial neovolcanic zone on the EPR, and host an array of hydrothermal plume sensors. An array of MAPRs spanning the lower 300 m of the water column will detect hydrothermal particle plumes. The Vents In-Situ Analyzer will provide a continuous record of dissolved hydrothermal tracers and volatiles. Additionally, two microCAT mini-CTDs will be deployed 60 m and 80 m above the seafloor to detect emissions from low-temperature, particle-poor vent fields. Mapping the active plate boundary zone within ISS using the new high-resolution EM300 multibeam system on the R/V Thompson investigates the hypothesis that small volcanic features may be used to trace the history of fine-scale ridge segments on the ridge flanks, and provides a regional examination of the connection between volcanic morphology and ridge segmentation. Our EM300 survey is supplemented by ~20 CTD casts to obtain a vertical distribution of samples of all tracers, especially trace metals, sulfur, and 3He, and calibrate the in-situ measurements against bottle samples. Broader impact: The ISS lacks a high-resolution, user-friendly grid of bathymetry easily used by biologists, chemists and others. DSL 120 is primarily a side scan sonar vehicle; its bathymetry has a nadir down the middle, troublesome smiles/frowns and noise at the edges and does not provide a map which is of use to non-specialists in seafloor geomorphology. Near-bottom side scan sonar also is of limited use to the non-specialist. At 30 KHz, EM300 provides a better than threefold increase in resolution while still collecting data at >10 knots over a swath ~3 km wide. A greater level of understanding of the geological setting of hydrothermal venting, and how segmentation of the ridge modulates the pattern of hydrothermal activity, will help us understand how hydrothermal activity varies spatially and temporally. Until we have predictive models for the distribution of hydrothermal activity along mid-ocean ridges, we will be unable to quantify the role of hydrothermal activity in global energy and ocean chemistry. This research will have implications for life on and within the deep seafloor and it will be used in the teaching of geology at the college and K-12 levels.
	The Galapagos Spreading Center A field experiment is proposed along the Galapagos Spreading Center (GSC) to investigate the response of the hydrothermal-geological-biological system along the ridge crest to large, hotspot-induced, along-strike gradients in magma supply and crustal thickness/structure. Unlike the East Pacific Rise (EPR) and other mid-ocean ridges (MOR’s) where variations in magma supply along strike are much debated, the GSC is known to exhibit increases in magma supply and crustal thickness toward the center of the Galapagos mantle plume (GMP) influence at 91.5ºW. The GSC is thus an ideal natural experiment, for which the observations have yet to be made, on how magma supply and crustal thickness affect the nature, abundance, and distribution of ridge crest hydrothermal activity, and interactions between hydrothermal, volcanic, tectonic, and biological processes. Sonar, water-column, and visual surveys along the GSC, 89.5ºW-94ºW, are proposed to establish the distribution and nature of hydrothermal activity, and to test the following competing models: 1. hotspot-enhanced magma supply produces abundant hydrothermal venting along eruptive fissures and volcanic collapse troughs, like a fast-spreading MOR, 2. hotspot-thickened crust suppresses venting altogether; or, 3. faulted, thickened crust causes most hydrothermal vents to focus along faults, like a slow-spreading MOR. We also will investigate if hydrothermal heat loss is a possible cause of the abrupt deepening of the axial magma chamber seismic reflector, and transition from non-rifted to rifted ridge morphology, that is observed near 92.7ºW. Comparisons between hydrothermal vent communities on either side of the GSC/GMP intersection area, across the 91ºW transform, and between communities on the GSC and EPR, will be made to better understand the effects of hotspots and transforms on ridge crest biota and on the biogeography of the eastern Pacific. The proposed studies will shed new light on how excess heat from mantle plumes is dissipated along hotspot-influenced MOR’s, and on consequences for biota and crustal accretion. The proposed survey area encompasses a smooth westward transition from a rifted ridge crest with normal ocean crust thickness at 94ºW (the western periphery of plume influence) to an unrifted ridge crest with thickened crust (at the center of mantle plume influence). The surveys will continue eastward past a major transform at 91ºW to a newly-discovered (May, 2002) biological community at 89º.5W. The field experiment requires a 2-leg interdisciplinary program of nested surveys and plume sampling (Leg 1: EM-300 sonar survey followed by DSL-120 sonar + autonomous plume sensor surveys, and CTD/rosette plume sampling; Leg 2: near-bottom Jason 2 visual surveys). Leg 1 provides a regional overview of ridge crest geology and a snapshot of current hydrothermal plume distribution; whereas Leg 2 provides a time-integrated view of past and present hydrothermal features, fine-scale photo-geology, and biological information. No on-bottom sampling is proposed on Leg 2; vent sampling will be proposed separately at a later time. Integration of the proposed survey results with those from recent (GPRIME) geophysical and petrologic studies in the same area, and with previous biological studies at 86ºW and 89.5ºW, will elucidate chemical, physical, and biological interactions between the mantle plume anomaly at depth upwards through the entire system to the deep-sea. Broader Impact: The proposed work will indicate how MOR/hotspot interaction affects global MOR hydrothermal chemical fluxes, and thermal energy sources that support life in the deep sea and form seafloor mineral deposits of potential economic value. The proposed research contributes directly to education and inspiration of young scientists and the public by incorporation of results, maps, and seafloor images into college courses taught by the PI’s, into encyclopedias and textbooks, and into science media for the general public. K-12 outreach will be facilitated via Internet using UCSB’s ScienceLine. Students will participate in data collection and course work at sea, and at least 3 graduate students will use the data in their theses. The proposed work fosters multi-institutional/interdisciplinary scientific collaboration, and supports the use and development of national deep submergence assets and UNOLS research vessels.

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UCSB Dept. Earth Science

General Research Interests

Current Projects