In the world of archeology there are no digs more difficult than those lying beneath watery depths. With land sites archaeologists are sometimes faced with extremely difficult challenges such as such as the environment in Ozette Washington where they found themselves digging through sticky mud and trying to preserve spongy artifacts. Or the Inca site of Machu Picchu where the air is so thin that it’s difficult to breathe, and the sun so intense that it burns the skin almost immediately. No matter how difficult the dry land dig, however, some basic human needs exist in this environment that are simply not there underwater. The most obvious is air and gravity, but there are literally a myriad of other logistical challenges that become apparent when a team goes to plan an underwater dig.
Digging underwater has in fact, proven so difficult that most archaeologists find more reasons to avoid these sites than to dig them. When an underwater site is taken on the team will sometimes resort to extremely complex and costly ends to make it a dry site. They may, for instance, attempt to divert or drain the water from a shallow site, effectively making it a dry land dig, avoiding the challenges involved with a submerged site. Techniques like these are not cheap, and require massive amounts of time and planning so the fact that they are done in the first place tells us that if at all possible any archaeological project is best dug on on dry land. This gives us a hint as to how complex and challenging an underwater dig must be.
Why is it so difficult? Shouldn’t a team just be able to put on some scuba gear and head on down to the site? After all, the bottom of the ocean is silty and soft; shouldn’t that make it even easier to dig? In this study, I will talk about some of the less obvious problems involved in underwater archeology; the ones that people might not think of right away like physiological and mobility issues. I will start by talking about shallow water digging which is usually the simplest, then more on the more complex problems with digging deeper sites in the 100 to 500 feet deep range. I’ll then move on to the most complex challenges with underwater digs that lye in very deep water like the Titanic or the Yorktown. These sites are tens of thousands of feet deep and if it’s not amazing enough that they’ve been found in the first place, the obstacles involved in actually digging them are mind boggling. Finally, I’ll conclude by talking a little about some of the political and moral issues involved in underwater archeology and explain why it is important that these sites are responsibly dug.
In almost all cases, projects that involve digging in shallow water (15-50 feet) are the simplest. They render only slight physiological complexities and divers are usually able to stay down much longer than on deeper dives. This is, however, not to say that they aren’t without their challenges. How for instance, does an archeologist remove the silt covering the artifacts without causing the water around him to become so clouded with sediment that he can’t even see? One might think that you could just brush the silt aside and the water would carry it away but it doesn’t. Once the visibility has been ruined it can take several hours for it to settle again. Underwater archaeologists have had to invent techniques and tools that literally suck up silt, leaving behind the covered artifacts. These giant underwater vacuum cleaners are usually powered by the thrust generated by the boat’s propeller, and the silt is forced by the engine away from the site, while the artifacts are filtered out by a screen on the front of the vacuum hose. (Martin)
Of course if the site is at the bottom of a river or in an area of the ocean where there is a current, the silt is simply washed away by the moving water, but how does the team keep themselves and the artifacts from being washed away as well? I can say from my own experience that fighting against a strong current gets to be exhausting and frustrating after only a few minuets. It is important also to remember that in a current the simple action of the water moving over the sediment will kick it up and ruin the visibility without any help from the divers. When we take this into account, it is no surprise that the sites with the least visibility tend to be the ones with the most current. Archaeologists have gone so far as to build structures around a shallow site that divert the current. This technique does not actually emerge the site, but rather acts as a shield against the current much as a car’s windshield diverts the strong wind from the driver’s face. This allows for a calm area over the site where the visibility will be improved and the archaeologists won’t have to tether themselves to a solid object or swim against the current. (Martin)
Finally there is the concern of air consumption. If the water is extremely cold, a diver must plan for his dive taking in to account that his bottom time will be shorter because his body has to work harder to keep warm, thus needs more oxygen. However, even under ideal conditions, using divers with the most developed breath control, a team can’t really expect a diver to get more than about an hour out of a single 80 cubic foot tank. More tanks can be added to increase bottom time, but it is important to remember that the more tanks a diver must carry, the more difficult it is for him to move around and the more quickly he will grow tired. It is exhausting enough to work in an underwater environment where every movement is met with the resistance of water; the effect is only compounded when more gear is strapped on. It has to be expected then that a diver can only work four or five hours as day and not the eight or ten he would be able to in a dry land environment, thus the project either has to employ many more people, or it will take much longer than a conventional dig.
When it comes to SCUBA (Self Contained Underwater Breathing Apparatus) some unique problems begin to pop up when the diver gets to depths of much more than thirty feet and they become the primary concern at depths in excess of one hundred feet. Since very few shipwrecks lie in shallow water and the cost of diving on an extremely deep wreck is often too great, most underwater archeology in done in water in water ranging in depth from 100 to 500 feet. As any experienced scuba diver will attest to, these are the depths where the danger in scuba becomes most apparent, but they are also the depths where you will find the most interesting things, especially if you are into wrecks. So why is it more dangerous to dive on sites at these depths than those in the fifteen to thirty foot range? One might think that it would be because of the risk of equipment failure or the diver running out of air, but in reality, these are of very little concern. The real danger at these depths come from the way a diver’s body reacts to the pressure from the water above him.
The most notorious of these physiological complications is the bends or DCI (decompression illness). Most people have heard of this, but many who don’t dive don’t understand exactly what it is. Whenever a diver goes underwater, he is under the pressure of the water above him. This is why your ears hurt when you dive to the bottom of a swimming pool. At around thirty feet, the pressure is twice what it is at sea level and it grows greater as the diver descends. As the depth increases and the pressure increases each breath the diver takes consists of air that is denser because of the outside pressure. This means that at thirty feet, the diver is breathing twice as much air as he is breathing at sea level. As we know, our bodies absorb the gasses from the air we breathe into our bloodstream and since normal air is almost all nitrogen, our blood is absorbing more nitrogen than anything else. (McCallum)
Take for instance a diver at sixty feet. With each breath he is absorbing roughly three times the nitrogen of a person on the beach. This doesn’t become a problem however until there is a change in pressure. After all, everyone has a good deal of dissolved nitrogen in their blood at any given point, but we need not worry about it because we know the pressure around us is not likely to change much. With the diver, however, this is not the case. If he has been working at a site lying in 200 feet of water four twenty minuets, he’s been absorbing outrageous amounts of nitrogen into his bloodstream and if he were to suddenly decide to come to the surface, the dissolved nitrogen, like any gas in its liquid form under pressure, would turn back into its gaseous state as the pressure diminished.
As we know, having gas bubbles in our bloodstream is extremely dangerous, and in some cases it can even lead to death, so those planning underwater excavations at these depths must take great care and planning to avoid this dangerous problem. Many divers use, for instance, dive computers which will calculate how much time a diver spent at a given depth with his rate of air consumption to determine the nitrogen levels in his blood and tell him when he must come up and at what depths he must make timed decompression stops to outgas nitrogen. These computers allow divers maximum flexibility in their work because they can dive right up to their physiological limits, yielding the best bottom time. (TDI)
If the site is under water ranging in depth from sixty to one hundred feet, the team may chose to use a special gas mixture called NITROX to yield even more bottom time than can be achieved with normal air. Historically, this gas has been used by the navy and research teams, but in recent years, it has fallen into the mainstream of casual scuba. NITROX doesn’t actually introduce any unfamiliar gasses into the compressed air, but rather increases the oxygen level, replacing some of the nitrogen. This means that if a diver is breathing a 40/60 (40% oxygen and 60% nitrogen) blend, he is dissolving roughly twenty five percent less nitrogen into his bloodstream, allowing him to stay on the site longer. (C.N.P Program)
Why then don’t underwater archaeologists simply breathe pure oxygen and eliminate the nitrogen completely from the equation? The answer is that under pressure, oxygen levels in a divers blood can become too high causing the diver to convulse. As I mentioned above, the deeper a diver goes, the more actual gas he breaths, and at even a very shallow depth pure oxygen will cause blood-oxygen levels to become so great that they are toxic to the diver. NITROX, then is a very customizable gas and a team will choose the best mix for the depth of the site. If, for instance, the site is in eighty feet of water, the team might use a NITROX blend of 40% which would become toxic if the diver was to descend to eighty five, but yields the best bottom times at eighty because of the reduced nitrogen levels. The trouble with NITROX is that it is only beneficial for relatively shallow dives because you quickly reach a point of diminishing return as you go deeper. If a team needs to reach a depth below two hundred feet, even the air we are breathing now has oxygen levels that are too high and would become toxic. (C.N.P Program) How then do teams carry on projects at say three hundred feet?
The answer: use a gas called TRIMIX by partially replacing both the nitrogen and oxygen with helium. This type of diving is highly theoretical and is usually reserved only for the Navy, research teams and highly trained technical divers. However, if the financial and technical resources are available, archeological teams may sometimes use it to conduct their excavations. Since these dives usually involve very long decompression stops on the way back up, and since the gas mixtures consumed at the bottom are often so thin in oxygen that they wouldn’t even support life at sea level, it is not uncommon for as many as eight individual tanks to be used by each diver on a single dive. (TDI) This is extremely expensive and the diver’s bottom time is usually limited to only a few minuets, so the work must be conducted quickly and sometimes with haste, since a high element of danger hangs over each diver’s head. The team usually needs to have a recompression, or hyperbaric chamber on location to deal with any instances of DCI, as well as many diving teams since a single diver may only be able to make one or two.
Again, diving with TRIMIX is extremely expensive. Depending on the blend a single tank of TRIMIX can cost as much as $80, and each diver needs a separate regulator for each blend of gas he breathes. (TDI) Hyperbaric chambers often have to be leased from the government or hospitals and the staff that runs them costs in the realm of two hundred dollars per hour. Each diver is highly trained and faces a strong element of danger, so they don’t come cheap, and the team usually needs a full fledged research vessel just to carry all the gear. These dives are also extremely dangerous. DCI is not an uncommon occurrence, and since the depths they are dealing with are so great, any slight error in planning leads to disastrous consequences. It is not surprising then that only the most glamorous projects at these depths are taken on.
Even TRIMIX reaches a point of diminishing return at about six hundred feet (although at least one person has made it past one thousand breathing it). Thus, for very deep wrecks like the Yorktown, another solution must be found. Without a tremendous budget, raw determination and the latest sonar technology, Pieces of history like the Yorktown and the Titanic can’t even be found, let alone dug. Bob Ballard, above all others, has pioneered this technology, and exemplified the strong will it takes to discover wrecks at these astronomical depths. On his deepest discovery, the Yorktown, he combined a vast array of technological innovations and sheer luck to discover and make the three mile trip down to the ship’s decks. (National Geographic)
So where does an archaeologists begin to take on a project of this magnitude? Well, as it would logically follow, the first challenge is actually finding the wreck. On his search for the Yorktown, Ballard used mostly eyewitness accounts and charts from World War II to outline a one hundred square mile section of midway which he searched by using a massive research vessel to pull a navy sonar module in a criss-cross pattern. As he covered the ocean floor, he took note of anything unusual that came up on the sonar screen and charted them as possible sites of the ship. Once he had the possibilities narrowed down, he attempted to send an unmanned Navy probe into the depths to try and get a first hand look at what he thought was sure to be the Yorktown. He didn’t get his chance this time, however, since four hundred feet from the ocean floor, the probe imploded and needed serious repair. Navy technicians spent days repairing the crippled probe and it was only after the second dive that Ballard was able to confirm that what he had found was indeed the Yorktown. (National Geographic)
Needless to say, not every archeologist has access to a research vessel and cutting edge Navy sonar and submarine technology, so clearly this type of research is left to those like Ballard with the highest budgets. But the cost of a project like this only begins with finding the site. Once the wreck is found, deep diving research subs and costly camera equipment must be obtained to properly map and chart the site. If the decision is made to bring artifacts to the surface it can take years and costly chemicals to properly preserve them. For these reasons, most sites at these depths will never be explored. Tragically, there are simply not enough institutions willing to foot the bill for such expensive research.
Since we can’t have a shipwreck to explore without a wrecked ship, and since the action of a ship wrecking tends to kill people, archaeologists, have to be sensitive to the idea that in most cases these sites should be treated as graveyards. Some archaeologists like Ballard take great care not to disturb the wrecks he finds. He refuses to bring any artifacts at all to the surface and focuses instead on mapping and charting the sites. This “take only pictures, leave only bubbles” mentality shows great respect for those who have perished and their families. The archeologist is still able to discover and learn key facts about the history of the ship or the way it went down but the wreck is left intact.
All too often, however, another team will come in after the serious archaeologists have left and pillage the site. The most notorious of these cases is the Titanic where Ballard, as usual, went to great effort not to disturb the anything, only to have a French team come in later and recover artifacts so they could sell them for a profit. This kind of treasure hunting really is a tragedy, not only because it shows no respect for the people who have died, but because it causes governments to be cautious about letting anyone conduct research in their waters. Countries have had so many artifacts stolen from them in this way that they often assume any archeologist is a treasure hunter and refuse to give research permits to anyone at all.
If our base of knowledge is to continue to grow with respect to maritime history and ship construction, it is absolutely essential that archaeologists are allowed to continue exploring both the very shallow and the very deep wrecks alike. For this to happen, universities and research institutions must be willing to finance these projects, and there must be some world wide provisions put in place to eliminate the trend of treasure hunting so that countries will be able to trust this delicate research to those most qualified. Bob Ballard stands out as a shining example of a good scientist with his priorities firmly in place. He has respect for both the memories of those who died in the wreck as well as the countries who’s waters hold these fascinating sites. Anyone planning an underwater dig would do well to follow his lead.
Photos from some of my TRIMIX wreck dives >
Photos from various other TRIMIX and NITROX dives >
Martin, Dean (1995).
Archaeology underwater: The NAS guide to principles and practices
McCallum, Paul (1970).
The Scuba Diving Handbook
Pearson, Cliff (1998).
Cliff’s NITROX Project (computer program)
Publishing Staff (1999).
National Geographic Explorer: The search for the Yorktown
Film Archive: National Geographic
Publishing Staff (1999). TDI Website.