Abstracts 2009
Suzanne Carbotte
Science Community Lecture: Focusing in on mid-ocean ridge segmentation
It has long been known that the globe–encircling Mid–Ocean Ridge is segmented across a range of scales defined by transform and smaller non–transform offsets of the spreading ridge axis. Segmentation is observed in a diverse range of ridge properties and determines the primary heterogeneity of the oceanic lithosphere. Although this fundamental characteristic of the Mid–Ocean Ridge is well studied, the origin and significance of ridge segmentation remains poorly understood. Does it arise from lithospheric processes or is it controlled by convective flow patterns in the underlying asthenosphere? Are different scales of segmentation linked or do crustal processes decouple mantle segmentation from the smallest scale segmentation evident at the seafloor. Focused investigations of the East Pacific Rise 8 °–10°N conducted under the Ridge 2000 program have given rise to a suite of complementary multi–disciplinary datasets that provide a new perspective on segmentation across a range of scales. Mapping and near–bottom photographic studies constrain the surficial volcanic segmentation of the region and the distribution of hydrothermal mineral deposits and vent fauna at the seafloor. Studies of microseismicity and hydrothermal fluid geochemistry define segmentation in the ridge axis hydrothermal system within the upper crust. Seismic tomography and other geophysical studies constrain the distribution of melt below the crust within the shallow mantle. A recent three–dimensional seismic imaging study of crustal structure defines the fine–scale geometry of the molten lens of magma found within the mid–crust which is believed to be the source of the dike intrusions and volcanic eruptions that build the upper crust and possibly much of the lower crust as well. From integration of these high–resolution studies, a new view of the detailed architecture of the mid–ocean ridge is emerging which allows us to evaluate existing models of segmentation. The integrated view indicates linkages across scales with segmentation inherited from processes in the earth's interior intimately connected to the finest–scale variability on the seafloor above.
General Public Lecture: Peering beneath an erupting volcano on the bottom of the ocean
Most of the volcanic eruptions that occur on earth are located far from view, on the bottom of the ocean, where seafloor spreading occurs, along a vast mountain chain known as the Mid–Ocean Ridge. Due to the extreme difficulty of making observations in this remote environment, only a handful of volcanic eruptions have been directly observed. One of the few locations where an eruption has been detected is the fast–spreading East Pacific Rise at 9°50ÕN. Here, instruments deployed to monitor the region after an eruption in 1991, were fortuitously in place and continued to operate through a second eruption in 2005–2006. In addition to this documented history of volcanic eruptions, the region is also one of vigorous venting of hot water from the seafloor, abundant hydrothermal mineral deposits, and elaborate animal communities that thrive in the absence of sunlight through chemosynthesis. Focused investigations in this region over the past two decades have enabled us to document how the system evolved between the two eruptions and to construct views of the surface of this active seafloor volcano of unprecedented detail. In summer 2008, using modern techniques employed by the oil industry and now available to the scientific research community for the first time, we were able to image deep beneath this volcano to the magma reservoir that lies 1.5 km under the seafloor. The aims of our study were to better understand what triggers volcanic eruptions in this area and why hydrothermal deposits form and animal communities thrive here. The imaging technology (a multi–streamer seismic array) used in our study allows us to determine the distribution and amount of magma trapped within this magma reservoir in very fine detail and permits us to directly link the hydrothermal communities and volcanic eruptions on the seafloor with the underlying source of magma and heat deep within the earth's crust. This presentation will focus on the history of volcanic eruptions and hydrothermal activity at this site, and how modern seismic techniques are used to reveal the inner workings of this active volcano. .
Matt Schrenk
Science Community Lecture: Progress towards elucidating the roles of microbial biofilms in hydrothermal habitats
Submarine hydrothermal vents are some of the most favorable natural systems to study relationships between environmental conditions and the microbial communities they support. They contain highly compressed gradients between hot, highly reduced hydrothermal fluids and cold, oxygenated seawater– which results in copious amounts of energy for use in microbial metabolism. They also challenge microbial growth with high temperatures which degrade biomolecules, high concentrations of toxic heavy metals, and rapid and abrupt changes associated with tectonic and magmatic activity. A defining characteristic of microbial communities which grow in these ecosystems is their association with surfaces as in polymer–encased structures known as biofilms. In medical and industrial settings biofilms have been shown to have numerous functions including improving resistance to environmental stresses, playing roles in nutrient acquisition, and facilitating cell–cell interactions. Microbial biofilms have been observed in diverse hydrothermal settings including those at mid–ocean ridges, those away from the ridge axes, in shallow submarine habitats, and in terrestrial hot springs. They have been documented in both cold (2°C) deep–sea conditions near diffuse hydrothermal flow, and at and above temperatures known to support life (~ 121°C). However, despite their ubiquity in hydrothermal habitats, the role(s) that biofilms play in these systems remain to be elucidated
By carefully collecting, cataloguing, and comparing the biofilms in diverse types of hydrothermal habitats, we are beginning to gain a better appreciation of their many functions. High temperature habitats within "black smoker" sulfide chimneys provide just one endmember, but biofilms also inhabit high pH carbonate chimneys and shallow marine hydrothermal sediments. The study of these systems requires the integration of diverse methodologies to "peek" into the rocky nooks and crannies that microbes call home– and necessitates the development of new technologies. High–resolution microscopic techniques are being used to document where microbes occur and "who" they are in three–dimensions. Biochemical techniques are being used to extract, purify, and fractionate the organic compounds that microorganisms to glue themselves to surfaces. Geochemical studies of both dissolved compounds and minerals themselves are being used to design strategies for the enrichment of new organisms. New tools are also being developed to promote the in situ colonization of surfaces in hydrothermal environments with co–registered temperature and chemistry measurements. Each of these approaches provides a context for the vast array of genomic data being obtained from such systems. The focused study of the biofilm physiology is essential for a better understanding of microbial ecology in hydrothermal vent habitats, while also providing insights into the evolution and adaptations of life at high temperatures.
General Public Lecture: What can slimy rocks in the deep–sea tell us about microbial survival strategies at high temperatures?
Hydrothermal systems, like the 'black smoker' chimneys at mid–ocean ridges, are some of the most dynamic and extreme environments colonized by life and may have been inhabited since early in Earth's history. Biofilms, or 'microbial mats', attached to rocks were amongst the first forms of microbial life discovered at hydrothermal vents thirty years ago and have since been found in terrestrial hot springs and shallow submarine hydrothermal habitats. Studies of high temperature microbial ecosystems have been a rich source of genetic and functional diversity and novel enzymes for biotechnology. While biofilms have been extensively characterized in medical and industrial settings, their role(s) in natural ecosystems are only now beginning to be elucidated. Some of the roles that biofilms may play include improving microbial resilience to environmental stresses and thereby expanding the range of potentially habitable conditions. Biofilms also serve to 'tether' microorganisms in the otherwise dynamic and rapidly–changing habitats found at deep sea vents. Furthermore, biofilms may bind nutrients and facilitate cooperative relationships between organisms, or serve as food for higher trophic levels. The growth of microbial communities as biofilms has a number of properties and a level of complexity that would be hard to recognize if studied individually.
Comparative studies of biofilm structure and composition in hydrothermal environments are beginning to make headway into understanding high temperature microbial 'slimes'. The interactions between biofilms and mineral surfaces at hydrothermal vents play a prominent role in many scenarios speculated for the origins of life on Earth, and surface–associated biofilms may contain a record of these molecular interactions. Insights from biofilm studies also provide us with a better extent of the depths and potential extent of the deep subsurface biosphere. Finally, findings from modern–day hydrothermal systems on Earth may help to focus life detection efforts on volcanically active planets elsewhere in the universe.
Bill Seyfried
Science Community Lecture: Magmatic and tectonic effects on the chemical evolution of hydrothermal vent fluids at mid–ocean ridges
Tectonic and magmatic processes at mid–ocean ridges can have a profound influence on the style and intensity of heat and mass transfer between the ocean crust and seawater derived hydrothermal fluids. At fast–spreading ridges (e.g., EPR 9°N) the existence of relatively shallow subseafloor axial magma chambers limits the depth of fluid penetration, while the high thermal gradient enhances fluid phase separation into vapor and brine components with important implications for the evolution of the chemical composition of hydrothermal vent fluids, especially acidity and redox capacity. Episodic magmatic activity further enhances the flux of components (CH4, CO2) into hydrothermal fluids issuing from vents on the seafloor. In contrast, hydrothermal vent fluids on the tectonically active Mid–Atlantic Ridge (slow spreading) provide clues to a very different compositional evolution, in part due to interaction at relatively great depths of seawater with gabbroic and ultramafic crustal components exposed by low–angle detachment faults. The high dissolved H2, CH4, and more complex hydrocarbons, and moderately low dissolved Si, in vent fluids are consistent with this. Thus, the lecture will compare and contrast geochemical controls on hydrothermal alteration processes at fast and slow spreading ridges using results of recently completed field studies at 9°N (EPR) and Rainbow and Tag vent sites on the Mid–Atlantic Ridge. The field data will be augmented with results of laboratory experiments and theoretical models.
General Public Lecture: New technologies for in situ investigation of chemical and biological processes at deep–sea hydrothermal vents
Hydrothermal activity at Mid–ocean ridges has likely been active throughout Earth history. Fueled by heat associated with the formation of the ocean crust, hydrothermal fluids vent from spectacular chimney structures on the seafloor. These fluids can be strongly acidic, rich in dissolved sulfur compounds and metals, and reach temperatures in excess 400°C. The mixing of hydrothermal fluids with seawater creates chemical energy that supports thriving faunal communities. Recent advances in marine technology have facilitated the measurement and monitoring of vent fluid chemistry at extreme temperature and pressure conditions, directly in the vent environment (in situ). Thus, this lecture will focus on the application of in situ chemical sensors, first developed in the laboratory, but which now have been deployed at hydrothermal vent sites at mid–ocean ridges in the Pacific and Atlantic oceans using the submersibles, DSV Alvin and ROV Jason2. Time series changes in magmatic (volcanic) and tectonic (seismic) processes at mid–ocean ridges can affect hydrothermal activity, underscoring the need for in situ measurements of chemical, physical and biological systems.
Adam Soule
Science Community Lecture: With a bang, or a whimper– Can explosive volcanic eruptions occur in the deep ocean?
The bulk of volcanic activity on Earth occurs under more than a mile of water along the global mid–ocean ridge system. This 37,000 mile long chain of volcanoes circles the globe and passes through every ocean basin. Typical deep–ocean eruptions produce gently effusing lava flows that pile up at the eruptive vent or spread across the ocean floor and stack up to produce the upper oceanic crust. However, a growing body of evidence suggests that more violent explosive eruptions may be a common occurrence in the deep ocean. Although common at subaerial volcanoes, explosive eruptions have long been viewed as unlikely or impossible in the deep ocean. The significant pressure from the overlying water column was believed to inhibit the exsolution of dissolved volatiles and mitigate the interaction between seawater and erupting lava. In addition, mid–ocean ridge basalts commonly have low volatile concentrations further limiting the potential for explosivity. Recent evidence suggests that explosive eruptions are more common in the deep ocean than previously believed. Pyroclastic material of MORB composition, believed to have formed during energetic explosions, has been recovered at a variety of mid–ocean ridges throughout the ocean basins at depths as great as 4000 meters below the ocean surface. Active explosive eruptions have now been observed in arc environments and illustrate the physical processes of how erupting lava may fragment on the ocean floor. Models have been developed to investigate how pyroclastic material may be dispersed once an explosive eruption occurs. This talk will explore the evidence in support of explosive submarine eruptions, the implications of such eruptions for how we understand the generation and storage of magma beneath mid–ocean ridges, and the volatile budget of the largest magmatic system on the planet.
General Public Lecture: The 2005–06 eruption of the East Pacific Rise– Taking the pulse of a mid–ocean ridge.
More than two–thirds of our planets annual volcanic output occurs along the global mid–ocean ridge system where the earth's tectonic plates are separating. Voluminous lava flows produced in this deep–ocean environment result in the creation of much of the EarthÕs crust. Volcanic eruptions at the mid–ocean ridge axis tap a reservoir of magma stored deep below the surface. This 'magma lens' also drives vigorous hydrothermal circulation where cold seawater seeps into the crust, is heated at depth, and discharges from mineralized chimneys at the seafloor at temperatures over 300°C. These mid–ocean ridge hot springs support a unique and diverse ecosystem beneath the ocean waters. The linkages between volcanic eruptions, earthquakes, and hydrothermal fluid circulation, and biology at mid–ocean ridges are only beginning to be recognized. Studying the cause and consequences of volcanic eruptions, the 'heart beat' of the mid–ocean ridge, is vital to understanding the links between the unique processes that occur in this environment.
The East Pacific Rise (between 9°– and 10° north is a part of the mid–ocean ridge that has been intensively studied over the past two decades. In 1991, researchers using the submersible Alvin were fortunate to witness the first evidence of the impacts of a recent submarine volcanic eruption. In April 2006, researchers made another fortuitous discovery that an eruption on the EPR had occurred again, when seafloor instruments could not be recovered and were suspected to be trapped in a new lava flow. Over the next 18 months, several cruises to the site were able to verify that an eruption had recently occurred and collect the information necessary to understand what had happened. The wealth seafloor data collected over the decade prior to the eruption provided a baseline with which changes to the ridge crest as a result of the eruption could be evaluated. Through on–bottom observations, remote sensing data, and lava samples, a interdisciplinary group of scientists have been able to reconstruct the events of the 2005–06 eruption and evaluate our models of seafloor volcanic processes.This talk will describe how scientists explore the deep ocean environment using novel deep–submergence technology including manned submersibles and autonomous robots and summarize how a 'captured' eruption provides important clues to understanding how eruptions occur on the largest magmatic feature of the planet, the mid–oceanic ridge.
