place a series of wooden panels into the bottom at a depth of 1,830 m. After 104 days of exposure, several were recovered (Turner, 1973):
The wood was so weakened as a result of the activity of wood-boring bivalve mollusks, that it began to fall apart while being picked up by the mechanical arm of Alvin. The minute openings of their burrows covered the surface, averaging about 150 per square centimeter ....
High population densities, high reproductive rates, early maturity, rapid growth, apparent ease of dispersal, and the ability to utilize a transient habitat make these wood borers classic examples of opportunistic species, the first recorded for the deep sea.
The site at which Dr. Turner carried out her initial wood borers experiments was known as DOS #1 for Deep Ocean Station number one, the first long-term bottom station established in the deep sea. Although others have subsequently been established, scientists continue to return to this site even today. The site was selected in 1971 as the first permanent bottom station because it lay along a line between Woods Hole and Bermuda, where benthic biologists had conducted deep-sea dredging operations for more than six years.
In fact, the first dive Alvin made for science took place in 1,785 m of water off Bermuda on July 17, 1966 with biologist Robert Hessler aboard. Hessler wanted to learn more about the benthic world he had been studying for years using deep-sea dredge hauls (Ballard, in press):
I was awed by the tremendous vertical precepts, and I finally understood why we had so much difficulty ever taking any samples from that area ....
That dive really taught me something. From then on whenever I lowered a dredge into the ocean, I could close my eyes and picture what the bottom of the deep sea looked like.
Hessler and benthic biologist Howard Sanders were impressed by the diversity of life in the deep ocean sediments. A student of Sanders, Fred Grassle, began to use Alvin to quantify these early observations. Returning to DOS #1, Grassle disturbed small patches of occupied seafloor with No. 2 fuel oil and fertilizer and left trays of sterilized, uninhabited mud to measure its colonization. Others put down small instrumented jars to measure respiration and found that deep-sea animals needed ten to a hundred times less oxygen than their shallow-water counterparts. Microbiologists, like Holger Jannasch, injected organic material into the seafloor as the field of benthic biology moved into a more quantitative phase in its history.
In 1971, manned submersibles entered a new phase in their application that would eventually dominate their use. Prior to this time, submersibles were used primarily by biologists and geologists in sedimentary settings,; ranging from soft mud bottoms to calcium carbonate terrains,,. But in 1971, Alvin began a comprehensive mapping program in the Gulf of Maine. Unlike most continental margin settings, which consist of thick sedimentary wedges, the Gulf of Maine is a seaward continuation of the Appalachian Mountain range. Instead of soft sediments, it consists of crystalline igneous and metamorphic rock dating back hundreds of millions of years.
To carefully map this area required the submersible to implement traditional field mapping techniques used by geologists on land. The creation of such maps requires the collection of geologic information in three dimensions, including not only surface exposure but subsurface structure and composition. First and foremost was the need for detailed bathymetric maps of a region measuring more than 100,000 km2 at a contour interval of at least 20 m or better. Fortunately, extensive bathymetric data existed for this area.
Such bathymetric data provided a picture of the regional morphology but not its internal structure and composition. To provide this information required extensive surveying using seismic profiling techniques. The database used in this study included tens of thousands of kilometers of seismic survey lines collected over a period of more than eight years prior to and during the actual diving program. This coverage led to the creation of a three-dimensional picture of not only the regional bedrock geology but also the sedimentary basins contained within it and equally important where the bedrock geology was exposed as outcrops.
Once such outcrops were pinpointed samples had to be collected to determine the bedrock composition. Unfortunately, the entire Gulf of Maine had undergone extensive glaciation during the Ice Age and the retreating glaciers covered the area with glacial deposits of varying thickness, deposits that bear no relationship to the underlying rock formations. As a result, traditional dredging operations could not be carried out since they almost always resulted in the collection of glacial erratics instead of the more difficult to sample bedrock outcrops. Here, careful coordination was required between surface seismic profiling activities needed to pinpoint bedrock outcrops and subsequent ,:lives by Alvin to sample them. This mapping program in the Gulf of Maine set the stage for a new phase in the use of Alvin.
Although research programs carried out by scientists around the world began in the 1950s and continue to this day using manned submersibles, the 1970s marked a fundamental change in their use. This shift in focus came as technological improvements in deep submergence engineering made it possible for manned submersibles to go much deeper than before. Principal among these improvements was the fabrication of higher-strength steel and titanium pressure spheres. Two vehicle programs led the way, one in the United States and the other in France. America's Alvin was modified to carry a titanium pressure hull with an initial operating depth of 3,050 m, while France's CNEXO (Centre