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Redefining 'Depth Perception' For Scientific Diving Standards
Four-Phased Approach to Scientific Diving Allows Team Working in the Bahamas to Break 90-Meter Benchmark

By Michael Lombardi
Diving Safety Officer
University of Rhode Island
Narragansett, Rhode Island

To date, the vast majority of deep dives (deeper than 90 meters seawater) using scuba are undertaken within the private and recreational communities. The complexity of such dives is often prohibitive of being productive during the working phase (the observational and data-gathering tasks of the scientific diver). Despite the difficulties of working in this environment, there is a growing need to systematically investigate this region of ocean space while taking advantage of the dexterity of the human hand.

An international science priority, according to a NOAA-sponsored workshop in 2008, is studying mesophotic coral ecosystems (MCEs), which encompass depths between 60 and 150 meters and are believed to account for a vastly overlooked region of ocean space. Scientific diving to these depths is highly feasible but generally disregarded as the best tool for the job, given the presumed liabilities associated with this activity under institutional auspices and the perceived inefficiencies of humans working at these depths. Many argue that ROVs or other robotic platforms are a more appropriate research tool, but the human element of reaction, surprise and real-time decision making or interaction is largely lost.

Despite more than 60 years of benthic marine science using scuba diving as a commodity research tool, no long-term, institutionally driven, ongoing series of academic fieldwork has found its roots in this alien environment. With human accessibility in this depth range at its infancy, opportunities exist across all disciplines of science, as well as within the technology sector, though much debate exists over the most appropriate means to place humans at these depths.

Recent developments in this area came to a head in 2006, when that year's Smithsonian-hosted Advanced Scientific Diving Work'shop addressed the considerations for pursuing scientific diving to 90 meters seawater. The proceedings include varied opinions on the most appropriate and 'safe' techniques to pursue scientific diving at this depth. The workshop proved to be controversial, as opinions varied on acceptable methodologies, from large surface-supplied spreads commonplace in commercial diving to highly maneuverable small teams using rebreather technologies.

Sample of scaled image acquired for quantitative analysis. The MCE is abundant with encrusting organisms. The scale bar is 25 centimeters long, with 5-centimeter bands. The gauge measures depth to archive imagery across depth gradient. (Photo by Michael Lombardi)
Unarguably, the cost and complexity of all proposed solutions pose problems for academic dives. Working to these depths and beyond requires a commitment to training and proficiency that is nearly impossible for an end-user group to maintain without ongoing and routine in-water experience. This field time is costly and does not fit the present fieldwork paradigm of spending only weeks in the field during any calendar year. An apparent need is to focus on the diving as the vehicle to accomplish scientific tasks, though, of course, the science is needed to justify the means.

In spite of these barriers, the author's team has proven the possibility of working beyond this 90-meter benchmark in its recent investigations in the Bahamas, which was chosen for its ease of access to vertical wall habitats and the intrinsic value of the rich maritime history of the region stemming from the Age of Exploration. The core exploration team, comprised of the author and University of Connecticut diving safety officer Jeff Godfrey, performed research at depths up to 136 meters seawater. As a result, the team has made incremental advancements in performing such dives with limited resources, working to advance depth and duration in systematic exploration by scientific divers.

Origins of the 90-Meter Benchmark
The air diving limit of 58 meters seawater imposed by the American Academy of Underwater Sciences is the result of limiting oxygen partial pressure exposure at the maximum depth. At this depth, oxygen partial pressure is 1.4 bar. This meets the NOAA single-exposure limit that is more popularly recognized when diving with nitrox, a breathing gas composed of oxygen and nitrogen. At 90 meters seawater, limiting oxygen partial pressure to 1.4 bar would permit a breathing gas with 14 percent oxygen content. This is the lower limit of normoxic breathing gas, or being able to breathe the gas at the surface with no ill effects. Much less than 14 percent is considered hypoxic—unable to sustain life at the surface.

Among the many complications in deep scientific diving stem from this use of hypoxic breathing gas and not necessarily the depth itself. Incorporating hypoxic breathing gasses into the dive plan requires special equipment and increased discipline by the diver to avoid breathing an improper gas (with possible fatal consequences) at or near the surface.

Recent Fieldwork and Results
While working in the Bahamas through Small Hope Bay Lodge in 2010 and the John H. Perry Jr. Caribbean Research Center in 2011, the author's team focused on investigating the deep vertical wall environments that span from the shallows, through the full MCE, to the abyss. This type of environment lends itself well to the concept of working vertically rather than in the conventional horizontal fashion, a method that is generally defined by a descent time, working horizontally along the bottom and an ascent.

After observing dive profile data from 2010, the team found that the vertical habitat influenced the actions its divers were taking during portions of the dive. On descent, for example, in addition to a 6-meter safety drill (a common diving practice), the team would pause at the reef crest at a depth of about 30 to 40 meters to conduct another safety check and also make an intentional gas switch to hypoxic breathing gas along with its verification on our computers. Likewise, while working vertically rather than horizontally, this phase of the dive lent itself to varied types of working ascents (multilevel, consistent, varied ascent rates), which were keyed to the specific objectives. To continue this article please click here.

Michael Lombardi, a contract scientific and commercial diver for 15 years, is the diving safety officer at the American Museum of Natural History and at the University of Rhode Island. He is the leading force behind scientific exploration of deep vertical wall environments in the Bahamas.

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