Abstracts 2009

• Breea Govenar
• Rob Reves-Sohn
• Dana Yoerger

Breea Govenar

Science Community Lecture: Patterns and processes of species diversity in hydrothermal vent communities

In the absence of sunlight, dense assemblages of animals thrive at deep–sea hydrothermal vents, where they are exposed to steep environmental gradients and rapid changes in temperature and environmental chemistry. Mixing of hydrothermal fluids with seawater provides the chemical energy used by chemoautotrophic microbes to fix inorganic carbon into simple sugars, forming the base of the food web in hydrothermal vent communities. Abiotic factors associated with the composition or flux of hydrothermal fluids have been shown to regulate the distribution and abundance of some vent species and to modify biological interactions in vent communities. In addition, the physical structure of large or spatially–dominant foundation species, such as tubeworms and mussels, may facilitate species coexistence and the maintenance of species diversity at hydrothermal vents by providing additional area for colonization, increasing access to food sources, and serving as refuge from mobile predators.

The composition and diversity of hydrothermal vent communities differ among mid–ocean ridges around the globe. On the Juan de Fuca Ridge (NE Pacific Ocean), tubeworms are the dominant foundation species and mussels do not form dense beds; unlike the Mid–Atlantic Ridge, where mussels are the dominant foundation species and tubeworms have never been reported. On the East Pacific Rise, tubeworms are the first colonists to settle new vent habitats after large–scale disturbances, including seafloor eruptions, and mussels colonize within a few years to eventually overgrow the tubeworms at most sites. There is little overlap among the communities associated with tubeworms and mussels on different mid–ocean ridges, and species diversity is highest at the East Pacific Rise, where tubeworms and mussels coexist. In this talk, the patterns and processes of local and regional species diversity at hydrothermal vents will be presented for the Juan de Fuca Ridge, the Mid–Atlantic Ridge, and the East Pacific Rise.

General Public Lecture: Diving deep into life at hydrothermal vents on mid–ocean ridges

Hydrothermal vents are some of the most productive habitats on earth, where tube–dwelling worms can grow to lengths greater than one meter and pea–sized snails can reach densities of several thousands per square meter in less than a year. This highly productive deep–sea ecosystem is driven by chemical energy, generated by the mixing of hot hydrothermal fluids with cold seawater and converted into food by microbes, in a process called chemoautotrophy. At hydrothermal vents, some animals have highly–specialized relationships with internal chemoautotrophic microbes that directly supply the bulk of their nutrition, but the majority of animals eat free–living microbes, their products, or other organisms.

The distribution and abundance of organisms at hydrothermal vents depends on both abiotic factors, such as temperature, dissolved metals, and concentrations of reduced chemicals, and biological interactions among species, including facilitation, competition, and predation. Spatial and temporal variation in the composition or flux of hydrothermal fluids can influence species interactions and can lead to changes in the diversity of hydrothermal vent communities. To unlock the mysteries of who is there, what they are doing, and how they interact with each other and their environment, special collection devices, in situ sensors, laboratory experiments and field manipulations have been used to study life at hydrothermal vents on mid–ocean ridges around the globe. This talk will compare and contrast the dominant species, physiological adaptations, biological interactions, and patterns of species diversity in hydrothermal vent communities on three different mid–ocean ridges, the East Pacific Rise, the Juan de Fuca Ridge, and the Mid–Atlantic Ridge.

Rob Reves–Sohn

Science Community Lecture: The Importance of Being Detached: Towards A New Paradigm for Hydrothermal Circulation on Oceanic Detachment Faults

It has long been assumed that, because of the fundamental role of volcanic heat in driving hydrothermal convection, there ought to be a first–order correlation between plate tectonic spreading rate and the distribution of hydrothermal fields along the global mid–ocean ridge (MOR) system. As a result (of this belief and other miscellaneous, though interesting, factors), hydrothermal research has historically been focused on volcanically active MOR segments, where high–temperature (>300°C) fluids circulate above a crustal magma chamber. The complex interactions between hydrothermal fluids and active magmatic systems provides fertile ground for interdisciplinary research, but the myopic focus on volcanically–hosted hydrothermal systems created a blind spot in the scientific trajectory of the research. We didn't bother to search for hydrothermal fields in places where we thought it unlikely to find them, such as (cold, exhumed) detachment terrains. Over time the lack of observations was mistaken for corroborating evidence, and eventually the tenet that tectonized, slow–spreading, ridge segments are uninteresting from the standpoint of hydrothermal research crept into the unofficial canon.

The serendipitous discovery of the Lost City hydrothermal field in 2000 on an exhumed mantle outcrop just north of the Atlantis Fracture Zone on the Mid–Atlantic Ridge (MAR) therefore came as a major shock. Here we had hydrothermal circulation occurring in a way and place that was previously not thought to be possible. Not only were hydrothermal fluids vigorously circulating in a cold chunk of exhumed mantle, the fluids turned out to have a unique chemistry that fostered previously undiscovered kinds of biological organisms. The deep seafloor demonstrated its never–ending capacity to amaze and astonish us who have seen so little of it, but who all too easily believe, subconsciously or otherwise, that we have seen it all.

Since Lost City, the new discoveries have been coming fast. We have recently learned that detachment faulting and mantle exhumation is not an anomalous process, but rather accommodates extension along a surprisingly large fraction of slow–spreading ridges. A fresh look at the MAR through new lenses has shown that more than half of the known active hydrothermal sites in the North Atlantic are located on detachment faults or mantle outcrops, as opposed to volcanic systems. And it has become clear that detachment faults provide a unique hydrological setting where hydrothermal discharge is focused in discrete locations for long–periods of time (10s–100s kyr), leading to the generation of massive mineral deposits. We now realize there is an incredible abundance and diversity of hydrothermal circulation on oceanic detachment faults – places that only a few short years ago were thought to be uninteresting. Which begs the question, "What else have we got so terribly wrong?" Plenty, I'm sure!

General Public Lecture: The Arctic Gakkel Vents (AGAVE) Expedition: A High–Stakes Technology Gamble Pays Big Dividends Beneath the Arctic Ice Cap

The Gakkel Ridge, stretching for thousands of kilometers across the Eastern Arctic Basin, represents one of the most inaccessible domains on the surface of the Solid Earth. Extreme environmental conditions limit the field season to a few short months each year, and along most of its length the ridge is covered not only by more than two miles of water, but also a permanent layer of ice. These logistical challenges have precluded the use of standard deep–submergence technologies on the Gakkel Ridge, and as a result the scientific community has been unable to determine what kind of life forms, if any, populate the hot spring 'oases' that are presumed to be generated by volcanic activity in this remote region at the top of the Earth. In this regard the Gakkel Ridge is analogous to Europa, the Jovian moon that is believed to host volcanic eruptions into an ice–covered ocean. Clearly we cannot expect to search for exotic life forms on Europa if we do not have the technology to search for them beneath ice–covered oceans on our own planet.

These considerations motivate a concerted effort to develop new technologies, and underwater robotics instrumentation, in particular, to allow scientific access to the Gakkel Ridge – both as an important scientific pursuit in its own right, and also as a testing ground and springboard for future astrobiology missions to Europa. During the International Polar Year in 2007, an international team of scientists and engineers, led by the Woods Hole Oceanographic Institution, deployed novel deep–submergence technologies from the Swedish icebreaker Oden to search for volcanoes, hydrothermal vents, and biological organisms on the Gakkel Ridge. The research included the use of free–swimming robots that dove to depths of more than 4000 m to search for evidence of hydrothermal vents, and a fiber–optically controlled camera platform that acquired high–definition video and samples of this hidden domain.

The AGAVE expedition made startling discoveries in both the Life and Earth sciences, including the observation of explosive volcanic deposits at the bottom of the Arctic Ocean where they were supposed to be impossible, and bizarre 'mats' of microbial communities containing a half dozen or more new species on a previously unknown chain of volcanoes. Although we still have a long way to go to develop instrumentation capable of exploring under the ice of Europa, the AGAVE expedition demonstrated many of the fundamental technologies needed to accomplish this important objective, and showed that life is full of all kinds of surprises when you deploy new robotic instrumentation under the Arctic ice cap.

Dana Yoerger

Science Community Lecture: Autonomous Discovery, Mapping, and Sampling of Deep Sea Hydrothermal Vents

This talk will begin by presenting a future concept for hydrothermal vent discovery, exploration, and sampling. Imagine if we could we go to an unexplored ridge segment, launch one or more autonomous underwater vehicles, and locate, survey, and sample life from all the vents on that segment. How much of this problem is presently solved, and how much remains?

Recently, we have succeeded in locating undiscovered hydrothermal vent sites using our autonomous underwater vehicle ABE. These discoveries include vent sites in the Lau Basin and the first vents found on the Southern Mid Atlantic and Southwest Indian Ridges. During this process, ABE makes maps of the water column, creates detailed bathymetric maps, and takes bottom photos of the vent sites. While the vehicle runs autonomously, we execute at least three dives with substantial data interpretation and planning by the science party between each dive. In this presentation, these results will be reviewed, the underlying engineering presented, and the role of human decision–makers explained.

Based on these experiences, we believe these results can be extended to enable fully autonomous vent discovery, mapping, and even sampling. The capabilities of autonomous underwater vehicles are improving in many aspects, including range, navigational capability, and ini–situ sensing. In this talk, our initial attempts to improve efficiency through autonomous decision making will be reviewed, and candidate paradigms that can enable fully autonomous search will be presented. Plans for autonomous sampling will also be discussed.

General Public Lecture: Exploring the Deep Sea with Robots

In the past two decades, robots have been used in the deep ocean to discover ancient and modern shipwrecks and to study basic processes at sites of scientific interest, such as the Mid Ocean Ridge. In this talk, the basic types of robotic vehicle systems we have used will be reviewed, including towed vehicles, remotely operated vehicles, and autonomous vehicles. Their underlying technologies will also be reviewed, including navigation and control systems, mapping sensors, and in–situ sensors. The talk will include my personal remembrances from the Titanic discovery, our mapping of ancient shipwrecks in the Mediterranean, the first autonomous vehicle surveys of the Mid–Ocean Ridge, and our use of autonomous vehicles to make the first discoveries of hydrothermal vents on the Southern Mid-Atlantic and Southwest Indian Ridges. The role of international cooperation and the use of complementary technologies will also be presented. Finally, our Nereus vehicle, which will have the capability to explore the deepest parts of the seafloor both as an autonomous robot and as a remotely–operated vehicle, will be discussed. The talk will conclude with speculation about how these systems will evolve in the future.